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Immortal Interstellar Probes

Ronald Bracewell’s name doesn’t come up as often in these pages as I might like, but today James Jason Wentworth remedies the lack. Bracewell (1921-2007), active in radio astronomy, mathematics and physics for many years at Stanford University, developed the concept of autonomous interstellar probes. Such a craft would be capable not only of taking numerous scientific readings but of communicating with any civilizations it encounters. His original paper on these matters dates back to 1960 and relies on artificial intelligence, long-life electronics and propulsion methods that don’t necessarily involve high percentages of c. Jason considers these factors from the perspective of 2018 and explains what a program sending such probes to numerous stars might look like. If you’re recalling Arthur C. Clarke’s ‘Starglider’ from The Fountains of Paradise, you’re not alone, but as the author notes, there are quite a few directions in which to take these ideas.

by J. Jason Wentworth

The writer wishes to extend his special thanks to Ellen N. Bouton, Archivist, at the National Radio Astronomy Observatory, for locating and providing a scan of Dr. Ronald N. Bracewell’s June 1, 1974 Stanford University Alumni Conference lecture, “Studies of Extraterrestrial Life” (Reference 25), and to Jim Hassel, Library Technician at the Rasmuson Library, University of Alaska Fairbanks, for providing scans of the Nature and American Journal of Physics articles (References 21, 22, and 23).

Starflight and the Matter of Time

The problems of interstellar spaceflight, more than any other type of travel, whether on Earth or in space, are inextricably bound up with time. This is true of starprobes as well as starships. Everything about starflight—from the choice of onboard power systems to the desires of the mission personnel (and those who fund the missions) to see the final mission results, and everything in between—is determined, or at least heavily influenced, by the lengths of the journeys. Insisting on rapid trips compounds the difficulties and costs of the missions, while being content to accept longer transit times eases their engineering (and financial) challenges, including those posed by cosmic rays and physical erosion. Lower interstellar cruise velocities also make stellar rendezvous missions less difficult. However, settling for slower interstellar passages introduces another possible cause for partial or total mission failure—the breakdown of components and systems due to aging and wear. The planners of interstellar missions must arrive at acceptable compromises between these and other competing, and sometimes diametrically opposed, factors. Longer missions also exacerbate another, all-too-human problem, which would be present even for the fastest possible missions: the long intervals between departure and arrival at distant stellar systems. Fortunately, there are countervailing factors which may—of necessity, in some cases—make slower interstellar missions acceptable, and even desirable.

Just as the Galileo and Cassini spacecraft examined asteroids and/or Venus while in flight to their destination outer planets, there are other, closer interstellar worlds that starprobes may be able to investigate while en route to other stars. If interstellar asteroids like 1I/2017 U1 (‘Oumuamua) are as common as some astronomers suspect, interstellar probes may have more to do while in transit than collecting fields and particles data and making VLBI (Very Long Baseline Interferometry) radio astrometric observations. Indeed, it would be prudent, in the interests of the probes’ safety—and to collect population statistics of use to future starship missions—for them to keep a constant watch for such objects, as well as for ejected comets, rogue planets, and even brown dwarfs, all of which (even if observed from afar) would be scientifically rewarding targets of opportunity. [1]

But before such interstellar probe missions can come to fruition, it will be necessary to develop electronics and power systems that can operate reliably in interstellar space for decades, centuries, or even longer. We will have to create machines which are, for practical purposes, immortal. While no such devices have been developed for consumer use (where “planned obsolescence” appears to often be a design factor), it is not uncommon for electronic devices—including solid-state ones—to remain perfectly functional for decades. As Dr. Ronald N. Bracewell (the electrical engineer and radio astronomer who developed the interstellar exploration/messenger probe concept that bears his name) pointed out in his 1974 book The Galactic Club: Intelligent Life in Outer Space, the lifetimes of electronic components and systems could already, at that time, be accurately predicted (an engineering capability that had existed long before he wrote the book).

He gave an extreme example, to demonstrate how even the lifetimes of large, distributed electronic systems operating in hostile environments can be known. A transatlantic submarine telephone cable contains many amplifiers built into the cable along its length, with each amplifier containing many vacuum tubes (not transistors, he found interesting to note). The entire cable is required to operate as a functional whole for twenty years under water (and hopefully longer). But even though none of these cables’ components had been subjected to a twenty-year test, engineers were able to simulate such tests for entire cables with confidence. The service lifetimes of transistors, he noted, could also be determined, because their deterioration depends in a calculable way on their temperature. If they were maintained at very low temperatures, which is easily done between the stars (and even, with known techniques, closer to a star), electronic devices could easily have indefinite lifetimes. Bracewell also suggested that if it proved necessary, some components could even—in a manner foreshadowing today’s 3D printing—be produced aboard interstellar probes as they neared their destination stars. [2]

Another enemy of such probes (and their electronics) is radiation and particle impact erosion, but these obstacles also appeared to be straightforwardly solvable to him. Referencing an article by I. R. Cameron in the July, 1973 issue of Scientific American (“Meteorites and Cosmic Radiation”), Bracewell noted in his book that the laboratory-measured rates of erosion on meteorites in space (between 0.2 to about 10 millimeters per 1 million years, depending on the meteorites’ compositions—and undoubtedly, where in interplanetary space they spent their lives after being exposed to space) indicated that a quite thin coating would suffice for protecting interstellar probes from erosion. [3] More recently, NASA and the Korea Advanced Institute of Science and Technology (KAIST) have been developing—and have working prototypes of—self-healing electronics for “spacecraft on a chip” vehicles. These devices can accept cosmic ray damage and then heal themselves (between 1,000 and 10,000 times, so far). [4]

Image: Ronald Bracewell (left), with Stanford’s Von Eshleman, a key figure in early research into gravitational lensing. Here the two are examining the horn antennae that Bracewell used in 1969 to determine that the Sun is moving relative to the cosmic background radiation. Credit: Linda Cicero/Stanford University.

Examples of Long-Life Spacecraft

Even today, there are examples of unexpectedly long-lived spacecraft, and this bodes well for the prospects of developing essentially immortal interstellar probes. The Sun-orbiting Pioneer 6, 7, 8, and 9 spacecraft, which were launched between 1965 and 1968, lasted for decades past their six-month design lifetimes; indeed, all of them except Pioneer 9 (which failed in 1983) may still be functioning. These probes have seldom been listened to since the 1980s (the spacecraft were last monitored between 1995 and 2000). [5] The Pioneer 10 and 11 outer planet probes (launched in 1972 and 1973, respectively) operated until 2003 and 1995, respectively. The Pioneer Venus Orbiter functioned in the hostile thermal and radiation environment near Venus between 1978 and 1992 (when it burned up in Venus’ atmosphere), and Voyager 1 and 2 are in their 41st year of operation. Even older spacecraft continue to function, and two—despite decades of exposure to Van Allen belt radiation—came back to life after having fallen silent many years before.

Three of the U.S. Air Force’s LES (Lincoln Experimental Satellite) spacecraft have exhibited this unexpected longevity. LES 1, launched in 1965, was last heard from in 1967—until a British amateur radio operator heard its signal in 2013. [6] LES 8 and 9, launched together into geosynchronous orbit in 1976, are still operating 42 years later. [7 and 8]. In 1974, the AMSAT-OSCAR 7 (AO-7) ham radio satellite was launched into a near-polar, Sun-synchronous orbit as a “hitch-hiker” payload, from Vandenberg Air Force Base. It fell silent in 1981 when its battery shorted, and 21 years later it was heard again (after its short-circuited battery went open, allowing the satellite to operate on its solar cells when in sunlight). Despite its decades of passages through the Van Allen radiation belt, AO-7 remains fully functional, with all of its beacons and transponders operational when it is in sunlight, which is most of the time. [9]

Another long-lived spacecraft is ISEE-3 (the third International Sun-Earth Explorer, launched in 1978, which was re-named ICE—International Cometary Explorer—for the occasion of its 1985 encounter with Comet Giacobini-Zinner). After its many adventures (including multiple lunar flybys), it was re-contacted and operated by the private ISEE-3 Reboot Project in 2014. It may still be operable when it passes near the Earth again in 2031. [10]

Interstellar Probes that Can Learn and Make Decisions

While pre-programmed digital electronic computers would likely be sufficient for “fly-through” interstellar probes, stellar rendezvous probes would likely need to be able to learn and to make decisions for themselves (for seeking exoplanets around their destination stars, entering circum-stellar orbit in the proper plane and orbital direction, computing flyby trajectories to enable close examination of the system’s planets, etc.). This would especially be the case for Bracewell probes, which would also listen for any local, intelligently-produced radio and/or laser signals and attempt to contact any such civilizations, then learn their language(s) in order to act as local scientific and cultural emissaries of humanity. This would include informing the “local aliens” about how and where to contact the Earth directly, via interstellar radio and/or laser transmissions.

Analog computers, as the British biologist Rupert Sheldrake has pointed out, “enable complex, self-organizing patterns of activity to develop through sometimes chaotic, oscillating circuits.” He also noted that in 1952, William Ross Ashby, a British cybernetics researcher, published a book titled Design for a Brain, in which he showed how analog cybernetic circuits could model brain activity. More recently (as Sheldrake also noted), Mark Tilden developed insect-like robots that demonstrated self-organization—and even learning and memory—despite the fact that these devices contain fewer than ten transistors and have no computers in them. [11 and 12] BEAM (Biology Electronics Aesthetics Mechanics, or Biotechnology Ethology Analogy Morphology) robotics, a “reaction-based” type of machine building, was inspired by Tilden’s work. (In the nearer term, analog logic circuits-containing robots such as Tilden’s would be useful as rovers, “hopper” rovers, winged and aerostatic aerobots, instrumented boats, and submersibles for exploring planets, moons, asteroids, and comets in our own Solar System. In the future, stellar rendezvous starprobes could deposit similar robots on the worlds orbiting their target stars, and relay the robots’ findings to Earth.)

A network of such analog devices might also possibly (perhaps in combination with some digital subsystems—such devices are called hybrid computers) function together to form a type of STAR (Self-Testing And Repairing) computer, which could control interstellar spacecraft. Since about 1961, NASA’s Jet Propulsion Laboratory had conducted research on a digital STAR onboard computer, which later in that decade found favor for the planned four-spacecraft Grand Tour mission, for which a non-flight “study model” called TOPS (Thermoelectric Outer Planet Spacecraft) was built. [13, 14, and 15] Kenneth Gatland, and the Soviet engineer B. Volgin (as was mentioned on page 244 of the former’s book, Robot Explorers, see Reference 13), both discussed the need for interstellar spacecraft to have self-repairing computer systems that could also learn and make decisions for themselves. To ensure acceptable mission risks, the computer systems of interstellar probes (and of any robotic sub-probes that they might carry, in the case of some stellar rendezvous—or even “fly-through”—missions) would have to be able to repair themselves in some way, regardless of how rapidly or slowly the vehicles traveled. Fast starprobes would face more intense impact and erosion damage by high-velocity atoms and dust particles (and induced cosmic rays, at high relativistic speeds), while slow probes would be subjected to long-term bombardment by galactic cosmic rays during their decades-long or centuries-long journeys. Self-healing electronic components and STAR-type features appear to be promising solutions to ensure that the vehicles’ electronic brains would remain sharp during transit, and upon and after arrival.

Getting There—Practically and Affordably

Over the years, many interstellar probe concepts have been studied and advocated. Among the earliest ones were ion propulsion, which Soviet scientists discussed at the 1973 International Astronautical Congress in Baku, Azerbaijan. At that meeting, a paper written and endorsed by members of the USSR Academy of Sciences concluded that ion-drive starprobes using then-current technology were feasible. [16] They predicted a flight time of about four hundred years to Barnard’s Star (six light-years away), and a journey duration of six hundred years to stars approximately twelve light-years away. Elsewhere in the 1974 book that discusses the Soviet paper (Is Anyone Out There?, by Jack Stoneley with Anthony T. Lawton, see Reference 16), it is mentioned that ion-drive probe velocities of 5% of c, the speed of light, are possible. The researchers envisioned ion-drive probes about the size of a Saturn rocket, which would enter orbit around their target stars.

Nuclear pulse propulsion—using fission or fusion bombs, or laser- or electron beam-triggered fusion micro-explosions occurring at higher rates—has also been studied extensively. The designs of the Orion starship and the Project Daedalus starprobe (a 0.12 c stellar system fly-through probe) utilized both nuclear pulse methods. [17] While both the bomb-type (Orion) and the fusion micro-explosion-type (Daedalus) designs were enormous and extremely expensive, recent dramatic reductions in payload size and mass would make much smaller interstellar probes feasible. Dr. Mason Peck’s “Sprites”—chip-size spacecraft weighing just a few grams—could be accelerated to high interstellar transit velocities (and be decelerated for relatively slow flybys or circum-stellar orbit insertion) by much smaller propulsion systems. [18] In fact, a much smaller Daedalus-like starprobe could release dozens or even hundreds of Sprite probes, which could be targeted to fly by and examine all of the planets in the destination stellar system.

These tiny “spacecraft-on-a-chip” probes also make laser-pushed lightsails—and even solar sails—attractive as potential high-velocity propulsion systems. The Breakthrough Starshot lightsail starprobe project, and NASA’s notional 2069 0.1 c solar sail interstellar probe project (NASA is also considering other propulsion systems), have both become serious contenders thanks to Sprites. [19 and 20] Analyses of laser-pushed lightsails indicate that as the sail velocity approaches c, the beam’s effectiveness in imparting momentum to the sail falls sharply, because a visible light laser’s Doppler-shifted light descends to infrared frequencies (as the sail “sees” the beam’s light). [21, 22, and 23] For sail velocities of 0.1 – 0.2 c or so, these “wavelength-stretching” Doppler shift effects aren’t large enough to cause serious beam thrust drop-off.

G. Marx proposed a variation of the laser-pushed lightsail concept which could reduce the overall complexity and cost of such interstellar probes. [21] He pointed out that an X-ray laser located above the Earth’s atmosphere could emit a much more powerful collimated beam (for the same beam aperture) than an ultraviolet, visible light, or infrared laser. Since X-rays can only be reflected by grazing incidence (shallow-angle reflection) nickel reflectors (like those used in space-based X-ray imaging telescopes), an X-ray laser-pushed lightsail starprobe could be in the shape of a narrow cone of thin nickel foil, with the payload located in its rearward-facing tip. If spin stabilization proved necessary, the conical sail could have several spiral, ridged “flutes”—rather like the spirals depicted on a unicorn’s horn—running from its pointed tip to its base; the flutes would reflect some of the beam, imparting spin to the conical sail. Such X-ray lightsails could be quite small. A SETI “bonus,” for any aliens looking in our direction, would be that such an anomalous, directional X-ray laser beam emission coming from near our Sun should grab their attention (and vice-versa, if anyone out there launched X-ray laser-pushed lightsail starprobes—or starships—in our direction).

Sending slower probes would ease many of the challenges of designing such spacecraft, which would lower their unit cost and enable larger numbers of them to be launched. Cyril Ponnamperuma and A. G. W. Cameron pointed out that it would be extremely wasteful of economic and energy resources to design probes that would travel faster than 1 percent of the speed of light, advocating that technological resources should instead be devoted to ensuring that the probes would remain reliable for long periods. [24] At such a velocity, their propulsion requirements (including braking to enter circum-stellar orbits) and interstellar material (stray atoms and dust particles) erosion shielding requirements would be greatly reduced. Ronald Bracewell also supported this “longevity over speed” strategy, based on his conclusion that the closest spacing between civilizations was probably (except for rare, random close spacing) on the order of at least 100 light-years.

Such spacing would make radio and laser SETI searches problematic because we—and the nearest other technological civilization—would each have about 1,000 surrounding promising stars to check, yielding maximum odds of success of 1 in 1,000,000. The actual odds would be significantly lower than this due to both parties’ unavoidable complete ignorance of what frequencies to use, and when—and toward which star—each society was transmitting or listening at any time. These limitations led Bracewell to develop his interstellar messenger probe concept, which would avoid these problems (and would return data and images from all stellar systems visited—including those without resident intelligent life—making every probe mission scientifically worthwhile). He proposed that in order to examine their 1,000 closest stars, and to establish contact with intelligent beings found around any of them (or to at least inform the “seeking” planet of their existence), another technological civilization would dispatch 1,000 modest interstellar probes, launching at least one probe (and more, if finances permitted) per fiscal year. [25] Bracewell also suggested that humanity would one day engage in such interstellar exploration and SETI searches by means of starprobes. Frederick Ordway suggested that interstellar probes could also monitor for intelligent signals while in transit between the stars. [26]

The nanotechnology scientist Robert A. Freitas, Jr. also advocates the use of Bracewell probes, in a complementary fashion with traditional SETI searches. [27 and 28] Like Bracewell, he points out the relative insensitivity of a probe program’s effectiveness to interruptions in the probe launch rate (because probes already launched will continue with their missions). Freitas is also in favor of the development of self-replicating starprobes (Von Neumann probes), whose general principles were developed by the mathematician John Von Neumann. [29] While this is an economically and logistically attractive concept (because just a few probes, once launched, would multiply, at zero additional cost to the funding government), this approach has a potential ethical problem. Would an intelligent race—including our own—appreciate it if an alien spacecraft suddenly showed up and began harvesting the worlds of its stellar system to produce copies of itself? Its transmitted assurances that its purposes were entirely peaceful might ring very hollow. Also, the highly sophisticated technology that will be necessary for such self-replicating probes is nowhere near fruition. When we can build a device that—if set on the ground—can move around, find and process iron, and make tenpenny nails all by itself, there may be some hope for progress in this field; but even then, it must be remembered that even the simplest spacecraft are far more complex than carpentry nails.

Approach, Arrival, and Post-Arrival Activities

What terrestrial interstellar probes will do as they close in on their targets will depend not only on humanity’s technological capabilities, but also on economic and political considerations. These latter two factors are, of course, interdependent, and may be influenced by the probes’ transit times. (Modern-era governments are less enthusiastic about funding projects which will come to fruition long after the legislators involved are out of office, or even dead, and high-cost projects of this nature are even less popular among politicians.) Depending on the tradeoffs between these factors, interstellar probes may be either stellar system fly-through vehicles or stellar rendezvous (star-orbiting) spacecraft. While probes having cruise velocities of 10% – 20% of c would be more popular with the project scientists and enthusiasts, 1% of c probes would be considerably simpler and cheaper, and they would be less likely to meet premature ends due to in-transit debris impacts. From the point of view of the politicians who would appropriate the funding for the spacecraft, the difference between 0.1 c and 0.01 c probes would make little difference as far as their career durations were concerned, but the much lower price tag of each 0.01 c probe would be more attractive. Also, they could attract political merit by “investing in the future” and “voting to find new worlds for humanity to explore and, perhaps, discover other civilizations with whom we might one day communicate.”

Fly-through probes would be the least challenging in terms of size, complexity, propulsive capability requirements, and cost, while stellar rendezvous probes would be able to make more detailed observations of their target exoplanetary systems. Essentially immortal fly-through starprobes could also conduct “open-ended,” multi-target flyby missions, passing from star to star by utilizing stellar gravity assists to propel them. Such probes would be slow by human standards, as they moved in trajectories similar to those of comets that were ejected from stellar systems by encounters with gas giant planets. But in compensation, they would make leisurely passes through their destination stellar systems. This would give them time to examine the planets in some detail, and—if the probes were so equipped—to listen for intelligent electromagnetic signals and engage in communication with any “local aliens.” Ronald Bracewell initially advocated stellar rendezvous probes exclusively, but he later concluded that fly-through probes would also be sufficient for carrying out these functions. As David Darling wrote some years ago:

“More recently, Bracewell has suggested that it would be sufficient merely for a messenger probe to pass through a planetary system to achieve its goals (as in the case of Project Daedalus). Without the need for retrorockets, such a probe could be made smaller and at much lower cost. Our contribution to the success of attempts by alien races to establish contact in this way might be to construct a sophisticated space watch system, possibly an extension of one designed to search for Near-Earth Objects.” [30]

In his 1978 novel The Fountains of Paradise, Arthur C. Clarke described a stellar gravity assist-propelled, alien fly-through Bracewell probe called Starglider, which passed through the Solar System in 100 days after having been detected moving through the outer Solar System at six hundred kilometers per second. [31] Faster fly-through starprobes (particularly non-Bracewell ones intended only to examine stars and exoplanets) could make more rapid journeys, then slow down before arrival in order to conduct data-collecting and image-taking flybys.

A stellar rendezvous probe would require a greater delta-v capability, so that it could both accelerate to cruise velocity and later brake into orbit around its target star. Limiting such probes’ maximum velocity to 1% of the speed of light would reduce the amount of energy required for braking upon arrival. Ion or plasma propulsion could power the probes. Sail propulsion (using either a laser-pushed lightsail or a solar sail, with the latter utilizing a “Sun-diver” trajectory) could produce a departure velocity of 0.01 c, but braking into circum-stellar orbit upon arrival might limit the target list to multiple star systems (and only at certain times), where photo-gravitational braking could be used. An E-sail (Electric sail, which is pushed by solar wind or stellar wind ions) could also be employed for braking. One advantage of photon sails and E-sails for rendezvous starprobes is that after circum-stellar orbit capture, either type of sail would enable the spacecraft to change its orbit to visit interesting exoplanets in the system (especially in the star’s habitable zone), without expending any fuel.

The spin-rigidized E-sail could also potentially serve as a probe-to-Earth communications antenna and—in a Bracewell probe—as a signal-monitoring and (if local technological life was found) local communications antenna. An E-sail, which uses positively-charged wires to repel the positively-charged solar or stellar wind ions, can use any number of such wires, from one up to dozens (in a “wagon wheel” configuration). [32] The wires (which are typically kilometers in length) are many wavelengths long at the frequencies used by spacecraft radio systems. Extremely long—in terms of multiple wavelengths—wire antennas are highly directional. As the ARRL Antenna Book says (the American Radio Relay League is the governing body for amateur radio in the United States), “The longer the antenna, the sharper the lobe becomes, and since it is really a hollow cone of radiation about the wire in free space, it becomes sharper in all planes. Also, the greater the length, the smaller the angle with the wire at which the maximum radiation occurs.” [33]

In other words, as the antenna is made longer (increasing the frequency of the radio transmitter and/or receiver that is connected to the wire causes the same effect), the radio energy is concentrated and emitted more and more off the end of the antenna (and the receive pattern is identical to the transmit pattern, so that the antenna is most sensitive to signals arriving at its end). In Section 2.1 of his online article, “Small Smart Interstellar Probes,” Allen Tough suggested that a probe could trail a very thin antenna. [34] A spinning “wagon wheel” E-sail, if its spin axis was precessed so that the Earth was in or near the sail’s plane of rotation, could communicate with Earth by electronically selecting each wire in turn (in a multiplexed way), as its far end was pointed at the Earth at some point during each rotation (multiplexed antenna systems have long been in use). This same arrangement could be used in the destination stellar system, for radio science data collection and (if the vehicle was a Bracewell probe) to listen for and communicate with any intelligent inhabitants in the system. Used with a variable matching network, the E-sail’s long wires could serve as signal monitoring and transmitting antennas over very wide frequency ranges.

An often-expressed objection to non-relativistic interstellar spacecraft (as generally expressed, space vehicles that travel at 10% or less of the speed of light) is, “It wouldn’t be worthwhile to send such slow interstellar probes because no one a century or more from now would be interested in data from them.” The systematic collection of other, often far older data in science does not support this contention. Astronomers directly image Jovian-type exoplanets that are hundreds of light-years away, and have even measured their wind velocities via transits, and that is—by definition—*very* old data. (Old astronomical photographs, and even hand sketches in notebooks, are prized because they enable more precise orbits of celestial objects to be computed, and because they record changes in such objects’ brightness and/or physical characteristics over time.) Slow starprobes would tell us a lot while they were en route to their target stars, and after arrival they would have far more detailed instrument and imager views than what we could ever perceive from the distant Earth. Another example that runs counter to this assumption involves Pioneer 10 and 11 and Voyager 1 and 2; no space scientists ever suggested that they be turned off “because they’re too old and obsolete.” On the contrary, they were (Pioneer 10 & 11) and are (Voyager 1 & 2) treasured for reporting on conditions in remote regions of space, where no other on-site instruments are available (New Horizons will also be so valued, after its last encounter).

Stellar system fly-through and rendezvous probes would carry out planet and satellite observations similar to those of planetary flyby and orbiter probes in our Solar System, and they would also examine the stars (and any companion suns) in their target stellar systems. Fly-through probes would seek out and target (for close flybys) any planets orbiting in their destination stars’ habitable zones, as well as observe other planets as closely as possible. Slower fly-throughs would enable more opportunities to observe more planets at closer range. Stellar rendezvous probes could, after braking into orbit around their assigned stars, change orbits to investigate the various planets; sail-equipped probes could conduct such “extrasolar Grand Tour missions” (including comet-like outer planet flybys to return to the near-star regions) without using any propellant.

Seeking Neighbors and Making New Friends

Bracewell interstellar messenger probes (of either the fly-through or rendezvous type) would, in addition to exploring their target stellar systems, listen for any local artificially-produced electromagnetic (radio or laser) signals, then attempt contact if any such signals were detected. Ronald Bracewell developed a complete, language-independent contact and communication plan, which the probes could implement if they heard intelligently-produced signals. By merely receiving such signals, a probe would know that on that frequency, the planet’s atmosphere was transparent to the signals. It would also know that somewhere on the planet and/or in its vicinity, someone (and likely many someones) would be operating a receiver capable of receiving that frequency. Armed with this knowledge, the probe—an electronic ambassador of the human race—could get to work. [35]

Ronald Bracewell divided the problem of contact with technological life in the Milky Way into three categories—abundant, sparse, and rare life—in which our nearest neighbors would be less than 30, 30 to 300, or from 300 light-years to the edge of the galaxy away. (He also listed two special, extreme cases, in which humanity is alone in the galaxy, or alone in the universe). Being moderately pessimistic (or moderately optimistic, depending on one’s point of view), he surmised that the nearest technological society was probably no closer than 100 light-years (within his sparse life category), meaning that our search would be in a spherical volume of space containing 1,000 stars likely to possess habitable planets. With such a large number of possible stars for us—and for the nearest extraterrestrial civilization—to each search via radio and/or optical SETI methods (and they wouldn’t all be the same stars), the odds of both societies happening to cross electronic paths would be significantly less than one in a million. These unpromising odds led him to develop the interstellar messenger probe concept, which overcomes the geometrical (statistical), fiscal (the cost in time and money), and political (funding and operation interruptions due to wars, revolutions, or economic depressions) problems that could derail long-term SETI and METI programs. No matter what happened at home (short of extinction or “being bombed back to the Stone Age” events), the probes would be transmitting their findings and would, if necessary, be waiting to re-establish contact.

Before arrival at its destination star, each probe would locate the star’s equatorial plane, in (or near) which its planets orbit. (Imaging the star’s starspots and tracking their motion, or viewing the star’s zodiacal light dust plane with an occulting disc coronagraph, would enable the star’s equatorial plane to be found.) Upon entering the system, the probe would observe the planets and their moons, paying particular attention to any planets orbiting in the star’s habitable zone. (Once it was close enough to the star, the probe could supplement its onboard power with stellar power collected via photovoltaic cells, thermocouples, or perhaps Stirling cycle generators.) If any such planets were present, the probe would enter orbit around the star in the habitable zone (or if it was a fly-through probe, it would adjust its velocity and course to ensure a slow pass through the system). If its monitoring revealed any artificial radio (or perhaps laser) signals, the probe would announce its presence by retransmitting portions of the signals back to their source, at the same frequency on which it received them. Anyone listening to (or watching, if the signals were video) the original signals would detect what seemed to be a strong echo, whose delay (of seconds to minutes, depending on the probe’s distance from the planet) would be twice the time required for the signal to go out to the probe. Such an odd effect would attract the attention of whoever was receiving the original signals, and radio direction-finding techniques would immediately show that the echo was coming from a point out in space. Not long after that, its orbit should be roughly known.

If such beings were intelligent enough to have radio, they should also be clever enough to signal to the probe that they know it is there, by changing their transmission to short phrases separated by quiet intervals in order to remove any overlap of each phrase and its echo. The probe would then detect that the character of the transmission had changed radically to one that was periodic, with a period which would indicate that the probe itself was influencing the distant transmitter. By promptly ceasing to echo, the probe could signal to its new neighbors that it knew that they knew it was there. In other words, both parties would then be aware of each other, and that each party was aware that the other knew of its presence. Once this milestone was reached, events could unfold in multiple ways.

The operator of the transmitter might be under some pressure to persuade the probe to change its frequency, so that the transmitter’s normal function could resume. But desiring to avoid losing this first precarious contact, the probe—which would have the initiative, yet would know very little about the capabilities of the aliens’ radio technology—might begin to test the capabilities of their radio equipment. Without understanding a word (or its equivalent) of their language (and vice-versa), the probe could discover technical parameters such as how sensitive their equipment was, its bandwidth capability (how fast they could receive), and whether another frequency would be more convenient (for technical or political reasons that the locals would know about, but which the probe wouldn’t). The probe would also need to ensure that its message wouldn’t be lost because it would sooner or later—due to the planet’s rotation—set below the horizon of its first contact. It might also have to be prepared for local phenomena (afternoon thunderstorms, sandstorms, starspots, etc.) that could interrupt radio communication.

To test the sensitivity of the aliens’ equipment it could simply weaken its echo. Each time they responded, the probe would weaken its reply, until its signal level dropped low enough that clear reception was difficult, after which the aliens—who could no longer “read” the probe’s signal—would cease to repeat. Having gathered this information, the probe would bring its transmission power back up to its normal level. It would then shift its frequency slightly, which the aliens (if that particular set of radio gear could do it) would follow, and then—if they were able to follow—it would shift its frequency a little more. (Ronald Bracewell noted that if an alien probe happened to first make contact with a commercial radio or television station on Earth, its operators would have great difficulty following the probe’s frequency shifts, but that as soon as a variable-frequency transmitter was brought into action, we could take the lead in changing the frequency slightly, to lead the probe off to another frequency that would be more convenient to us.) By slowly shifting its frequency (both up and down), the probe could also determine the frequency “windows” of the planet’s atmosphere (that is, at what frequencies the atmosphere was transparent to radio waves).

Bracewell also considered the possible political implications of a probe making contact with an alien civilization, if the civilization of the planet in question had any degree of sociopolitical similarity to ours. Unless that world had global political, social, and/or cultural unity, any given “nation” (perhaps even of a different species or subspecies on the planet) might desire to enter into exclusive relations with a probe, for reasons of prestige or possible economic or military advantage (from using the probe’s knowledge and/or technology). The probe’s message (and its mere existence) would likely be disturbing to the planet’s inhabitants, so it would have to be resourceful in order to avoid being trapped into secrecy, to avoid exclusive relations with one power (which would invite an attack by a rival power), and to avoid having its signal jammed by a minor power. The very nature of the probe’s movements, however, would tend to encourage a degree of cooperation between even rival powers, because the probe would set below any station’s horizon within hours. Also, the probe could identify any planet-wide entity (if there was one), to which it could transmit its message. It could simply reduce its transmission power level until respondents lacking large antennas, sensitive receivers, and planet-wide interconnection dropped out; the probe would deal with any organization(s) (analogous to NASA and its Earth-wide communications capabilities) that remained. If some power insisted on communicating with the probe independently, the planet-wide entity would have to defer to that nation for part of each day, or invite jamming for refusing to defer.

Bracewell envisioned that the probe’s message would be in the form of a television broadcast, because TV is like sign language. Geometrical shapes provide a way for two people who don’t understand each other’s languages to learn them. If technological intelligent alien beings have sight similar to ours (this seems likely), they probably have some form of television, and it could be utilized to foster mutual understanding. He pointed out that the number of words in the dictionary that can be defined by drawings probably runs into the thousands, and that many more could be defined by animated drawings. Not only nouns, but many verbs, adjectives, and adverbs can be depicted via television. Other words are harder to define in this way, but given such a “vidioctionary” that defined a few thousand basic words using still and animated pictures, it would be possible to interpret at least some of the more difficult ones.

Until common linguistic understanding was established between the probe and its new neighbors, television would also enable them to learn the answers to basic questions of importance, such as where the probe came from. The probe would first reach a television format in common with that of the aliens. This could be done by repeating its message until they worked out the probe’s TV format and repeated it back to the probe, or the probe could simply adopt their format, transmitting images of simple mathematical shapes (circles, squares, etc.); they could repeat the signal back to tell the probe, “You’ve got our TV format right!” Once this was done, the probe’s message could be a “zoom movie” (using computer graphic imagery where necessary).

It could begin with a view of a constellation or a star field (calculated to appear as it would from their planet) that included our Sun, with the view quickly zooming in on the Sun. The view could then zoom in further until the Sun appeared as a substantial disc, with sunspots visible on it. From their motion (with other nearby—in the angular sense—stars visible in the frame), the Sun’s axis of rotation and the axis’ orientation in space would be shown. Closer zooming would show our Solar System, and at last the view would zoom in on the Earth. Supplementary animated plan views (which could come after a video tour of the Earth) could show the interrelationships between the rotational and orbital periods of the Earth, the Sun, the Moon, and the other planets. Such views would provide the relative rotational and orbital periods (but the aliens, once they knew which star the probe had come from, could determine the Sun’s “absolute” rotational period via spectroscopy, and—possibly—the Earth’s rotational period by monitoring terrestrial radio, TV, and radar emissions). A “zoom travelogue” of our home planet would show our newly-discovered neighbors our world, its natural beauty, its architecture, and views and voices of the beings—and their science, industry, and cultures—that created and launched the probe.

After this, the probe would have another, important piece of business to take care of—conveying the particulars (the frequency, listening schedule, etc.) of how the aliens could engage in direct radio (and/or laser) communication with the Earth. With multiple probes sent to as many stars, radio and/or laser communication telescopes on the Earth, the Moon, or in solar orbit would have to listen to the probes on a schedule, and blocks of time would also need to be allotted for receiving direct messages from any extrasolar civilizations discovered by the probes. (Any probe that found technological intelligent life could first send a report of the discovery to its Earthside controllers before attempting to contact the civilization—and probes that found no such life could also report their negative findings—as this would permit the most efficient use of the “listening time” blocks; such time periods need not be wastefully kept open for stars with no inhabited planets.) Bracewell believed—in the mid-1970s—that the direct interstellar communication information could be expressed by messenger probes using static and/or moving television images. With today’s vastly improved television and computer technologies, such information would likely be easier to convey effectively.

After this task was accomplished, the probe would be dispensable, although the aliens could learn much more about us (and vice-versa) through continued interaction with the probe, which could be packed with enormous quantities of information (even using today’s technology). If the probe met an untimely end, the aliens would have to transmit to the Earth a pictorial dictionary followed by their text or pictographs, and hope for the best. But assuming that the probe didn’t fail, it and they could learn each other’s languages, which would be most helpful for their direct transmissions to us. (The probe would have an “alien/Terran” language translation program, which the probe could send them a copy of on request.) The probe could readily learn their language in printed form, by utilizing an animated pictorial dictionary that they could transmit to it. Its first attempts to “talk” to them in their language might be quaint to them, but they could televise corrected versions back to it.

To be sure that it was properly understood, the probe could do what human beings do—say it again in different words. If they didn’t understand, they could question. (This is a huge advantage of real-time, quick-feedback loop communication with a local “resident” Bracewell probe; it facilitates rapid learning and understanding by both parties, as compared with very long-delay direct interstellar transmissions that take years, decades, or centuries each way). “Probe-mediated initial contact” would enable the direct interstellar transmissions between civilizations to be in mutually-understandable forms from the start. Knowledge of aliens’ languages would enable probes to exchange scientific (including medical and astronomical), philosophical, and cultural knowledge with them, and their races’ knowledge would, of course, immeasurably enrich our own civilization.

If we found even one other technological civilization, the messenger probe concept (which is tolerant of diversion of resources to urgent priorities, because interruption of the launching program does not affect in-flight probes’ chances of success) would enable our societies’ combined efforts to greatly enlarge the volume of galactic space in which more such societies could be sought out for contact. Our space program and theirs could, without wasteful overlap, dispatch messenger probes into large “bubbles” of unexplored space centered on our respective suns. But even if we are the only technological society for thousands—or tens of thousands—of light-years around, none of the Bracewell probes would be wasted, because they would return scientific data and images from the stellar systems they explored. (Even probes that failed to reach their destinations in functional condition would, if they operated well for several years, gather useful information on the interstellar medium, the galactic magnetic field, and cosmic rays in their regions of space.)

Launching interstellar messenger probes would be a “no-lose” (“win-win”) situation. Current and/or soon-to-be-in-hand technologies would likely be sufficient to produce and launch Bracewell probes, particularly ones designed to travel at 1% of the speed of light. (“Sun-diver” solar sails and large ion-drive spacecraft—Soviet scientists advocated the latter as starprobes in 1973, and wrote that they were feasible with then-current technology—could attain that velocity, given some engineering development work and flight testing; no new principles need to be discovered.) The “brains and senses” of Bracewell probes are probably already within our technological reach, at least in “breadboard” prototype form. Computers and software of the necessary sophistication to discriminate between natural radio noise and artificial signals—and to conduct the contact activities that Ronald Bracewell envisioned—already exist, as does the high-density information memory storage that such “electronic ambassadors” would require. The variable matching network-equipped, wideband-tunable longwire antenna and antenna multiplexing are both decades-old technology (which could be utilized if a braking E-sail’s wires were also used as probe-to-Earth, radio science, and alien signal-monitoring antennas; slowly rotating ion-drive starprobes could also use such antenna technology).

Sending realistically-realizable probes to other stars, even the nearest ones, will require patience. But even the fastest-possible (with foreseeable technology) ones, even if launched today, would not reach the Alpha Centauri system, let alone the considerably more distant potentially habitable stellar systems, within the lifetimes of most living adult interstellar spaceflight advocates. That is all the more reason to begin work on such ventures as soon as possible, so that—like trees planted by old men who knew they would never get to enjoy their shade—the first pictures and data from other stellar systems can inform and inspire the immediate descendants of our generation.


[1] 1I/2017 U1 (‘Oumuamua) interstellar asteroid information, NASA Solar System Exploration website: http://solarsystem.nasa.gov/planets/oumuamua/indepth

[2] The Galactic Club: Intelligent Life in Outer Space by Ronald N. Bracewell, page 83 (Published 1974 and 1975 by W. H. Freeman and Company, San Francisco, CA, ISBN: 0-7167-0353-X and 0-7167-0352-1 pbk.) Amazon.com link: www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Dstripbooks&field-keywords=The+Galactic+Club+by+Ronald+Bracewell

[3] “Meteorites and Cosmic Radiation” by I. R. Cameron (Scientific American, Vol. 229, No. 1, page 65, July 1973)

[4] “Self-Healing Transistors for Chip-Scale Starships” (IEEE Spectrum, January 30, 2017): http://spectrum.ieee.org/semiconductors/devices/selfhealing-transistors-for-chipscale-starships

[5] Pioneer 6, 7, 8, and 9, Wikipedia article: http://en.wikipedia.org/wiki/Pioneer_6,_7,_8,_and_9

[6] LES 1 satellite, Google website citations.

[7] LES 8, 9, Gunter’s Space Page article: http://space.skyrocket.de/doc_sdat/les-8.htm

[8] Lincoln Experimental Satellite Turns 40, MIT Lincoln Laboratory website article: www.ll.mit.edu/news/LES-9-turns-40.html

[9] AMSAT-OSCAR 7, Wikipedia article: http://en.wikipedia.org/wiki/AMSAT-OSCAR_7

[10] International Cometary Explorer, Wikipedia article: http://en.wikipedia.org/wiki/International_Cometary_Explorer

[11] Morphic Resonance: The Nature of Formative Causation by Rupert Sheldrake, page 247 (4th Revision, Published 2009 by Park Street Press, Rochester, VT, ISBN: 978-1594773174 and 1594773173) Amazon.com link: www.amazon.com/Morphic-Resonance-Nature-Formative-Causation/dp/1594773173/ref=sr_1_1?ie=UTF8&qid=1520811667&sr=8-1&keywords=morphic+resonance+rupert+sheldrake

[12] “Redefining Robots” by P. Trachtman (Smithsonian Magazine, February 2000, pages 97 – 112)

[13] Robot Explorers by Kenneth Gatland, pages 239 – 244 (Published 1972 by Blandford Press, London, ISBN: 0-7137-0573-6) Amazon link: www.amazon.com/Robot-Explorers-Colour-Kenneth-Gatland/dp/0713705736/ref=sr_1_fkmr0_1?ie=UTF8&qid=1520817457&sr=8-1-fkmr0&keywords=robot+explorers+by+kenneth+garland

[14] Planetary Exploration: Space in the Seventies by William R. Corliss (NASA Publication EP-82, June 1971): http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19750065009.pdf

[15] Computers in Spaceflight: The NASA Experience by James E. Tomayko, pages 149 – 153 (NASA Contractor Report 182505, March 1988): http://history.nasa.gov/computers/Ch5-5.html

[16] Is Anyone Out There? by Jack Stoneley with Anthony T. Lawton, pages 15, 17, and 174 (Published 1974 by Warner Paperback Library, New York, NY) Amazon link: www.amazon.com/Anyone-Out-There-Jack-STONELEY/dp/0446765740/ref=sr_1_1?s=books&ie=UTF8&qid=1522566430&sr=1-1&keywords=Is+Anyone+Out+There%3F+by+Jack+Stoneley

[17] Nuclear pulse propulsion, Wikipedia article: http://en.wikipedia.org/wiki/Nuclear_pulse_propulsion

[18] “Sprites: A Chip-Sized Spacecraft Solution” (Centauri Dreams, July 17, 2014): www.centauri-dreams.org/2014/07/17/sprites-a-chip-sized-spacecraft-solution/

[19] Breakthrough Starshot, Breakthrough Initiatives website: http://breakthroughinitiatives.org/initiative/3

[20] NASA 2069 Alpha Centauri solar sail probe, Google website citations.

[21] “Interstellar Vehicle Propelled by Terrestrial Laser Beam” by G. Marx (Nature, Vol. 211, July 1966, pages 22 – 24)

[22] “Interstellar Vehicle Propelled by Terrestrial Laser Beam” by J. L. Redding (Nature, Vol. 213, February 1967, pages 588 – 589)

[23] “Was Marx right? Or how efficient are laser driven interstellar spacecraft?” by J. F. L. Simmons and Colin R. McInnes (American Journal of Physics, Vol. 61 (1993), pages 205 – 207)

[24] Interstellar Communication: Scientific Perspectives by Cyril Ponnamperuma and A. G. W. Cameron, page 100 (Published 1974 by Houghton Mifflin Company, Boston, MA, Library of Congress Catalog Card Number: 73-11945, ISBN: 0-395-17809-6) Amazon link: www.amazon.com/Interstellar-Communication-Perspectives-Cyril-Ponnamperuma/dp/0395178096/ref=sr_1_1?s=books&ie=UTF8&qid=1522566770&sr=1-1&keywords=Interstellar+Communication%3A+Scientific+Perspectives+by+Cyril+Ponnamperuma

[25] “Transcription of the Lectures of Ronald Bracewell on the Studies of Extraterrestrial Life” (Stanford Alumni Conference Lecture, delivered on June 1, 1974, pages 16 and 17 [this transcript is available by e-mail from the author at: blackshire@alaska.net]).

[26] Life in Other Solar Systems by Frederick I. Ordway, III, pages 78 and 79 (Published 1965 by E. P. Dutton & Co., Inc., New York, NY, Library of Congress Catalog Card Number: 65-12184) AbeBooks link: http://www.abebooks.com/servlet/SearchResults?sts=t&cm_sp=SearchF-_-home-_-Results&an=Ordway%2C+Frederick&tn=Life+in+Other+Solar+Systems&kn=&isbn

[27] “Interstellar Probes: A New Approach to SETI” by Robert A. Freitas, Jr. (Journal of the British Interplanetary Society, Vol. 33, pp. 95-100, 1980): http://www.rfreitas.com/Astro/InterstellarProbesJBIS1980.htm

[28] “The Case for Interstellar Probes” by Robert A. Freitas, Jr. (Journal of the British Interplanetary Society 36:490-495, November, 1983): http://www.rfreitas.com/Astro/TheCaseForInterstellarProbes1983.htm

[29] Self-replicating spacecraft, Wikipedia article: http://en.wikipedia.org/wiki/Self-replicating_spacecraft

[30] Bracewell probes, The Worlds of David Darling website article: http://www.daviddarling.info/encyclopedia/B/Bracewellprobes.html

[31] The Fountains of Paradise by Arthur C. Clarke (Various hardcover, paperback, audio, and e-book editions, first published 1978) Amazon link: www.amazon.com/Fountains-Paradise-S-F-Masterworks/dp/1857987217/ref=sr_1_1?s=books&ie=UTF8&qid=1520817523&sr=1-1&keywords=the+fountains+of+paradise+by+arthur+c.+clarke

[32] Electric sail, Wikipedia article: http://en.wikipedia.org/wiki/Electric_sail

[33] ARRL Antenna Book, pages 13-1 and 13-2 in Chapter 13, “Long Wire and Traveling Wave Antennas” (Published at intervals by the American Radio Relay League, Newington, CT): http://www.qrz.ru/schemes/contribute/arrl/chap13.pdf

[34] Small Smart Interstellar Probes (Section 2.1), Professor Allen Tough’s website: http://ieti.org/tough/articles/8.htm

[35] The Galactic Club: Intelligent Life in Outer Space by Ronald N. Bracewell, pages 59 – 83 (Published 1974 and 1975 by W. H. Freeman and Company, San Francisco, CA, ISBN: 0-7167-0353-X and 0-7167-0352-1 pbk.) Amazon.com link: www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Dstripbooks&field-keywords=The+Galactic+Club+by+Ronald+Bracewell


Comments on this entry are closed.

  • David Evans May 18, 2018, 14:21

    One reason for not launching a probe with a travel time of centuries is that, because of technical progress, it would probably be overtaken by a faster and more capable probe which was launched later.

    • ljk May 18, 2018, 16:45

      We could have taken that attitude with Project Apollo, waiting for such things as the computer technology becoming more sophisticated than the 1600-bit version the spacecraft used. But then it would have become even more likely that we would still be talking about putting humans on the lunar surface some day, judging by all the non-technological factors that halted Apollo after 1972.

      If we can build and launch an interstellar probe, we should do it rather than wait until something better comes along. If a better model is built and overtakes the first one, so be it, no loss. Much will be learned by building those early probes anyway to assist in the later more advanced versions.

      • J. Jason Wentworth May 19, 2018, 1:58

        *Nods* There was even talk (as my 1969 Nelson Doubleday Science Service Science Program book series [the rival of the Vistas of Science book series] title “Rockets” mentioned) of plans to wait until 1975, to explore the Moon using nuclear thermal rockets. (In 1960, it was originally thought that atomic rockets could reach the Moon in ten years, but later it was determined that it would take until 1975.) Because of the political and economic circumstances, and the foreseeable state of the art of chemical rockets, the decision was made to go more quickly, using chemical rockets. Also:

        If a later, faster interstellar probe overtakes the first one (sent to any given star), it will be a “Win-Win-Win” situation all around, in the following ways:

        [1] If either the first, slower probe (or the later, faster probe) happened to fail in transit, each probe would serve as a back-up for the other;

        [2] If both probes succeeded, the faster probe could find features (or even entire, previously-unknown exoplanets, asteroids, or comets that the later-arriving probe could be targeted to examine closely), and:

        [3] Even for “just” exploring the worlds that the earlier-arriving probe visited first, the later-arriving spacecraft could (as Pioneer 11 did at Jupiter, and Voyager 2 did at Jupiter and Saturn) could look closely for changes that had occurred since their predecessor probes (Pioneer 10 and Voyager 1, respectively) had visited the same planets. In addition:

        [4] Even the time and effort spent by different probes (say, well-equipped outer planet orbiter/probe spacecraft such as Galileo and Cassini, which flew by–and conducted only limited observations of “targets of opportunity,” such as Venus and asteroids) is never wasted, because all such observations glean new scientific data. (Even Deep Space 1’s impaired flyby of the asteroid Braille collected new data.) As well:

        I’m with you–the more Bracewell probes we fly, the better we’ll get at designing and building them (even if we keep to a low launch rate; say, one per fiscal year, as Ronald Bracewell suggested), and the the smaller, cheaper, more capable, and more reliable they will become. If need be (to get started with such an enterprise, and to gain experience and confidence), this activity might be started with outer planet, ultraplanetary, and/or comet rendezvous missions in the outer solar system.

      • Brett Bellmore May 20, 2018, 8:31

        It wouldn’t have made sense to take that approach to Apollo, because we could reach the Moon in days, there was zero chance of a technological advance after the flight was launched that would result in somebody else getting there first. And with a three day trip, who cares anyway?

        The issue with interstellar travel is that if your probe is going to take 200 years getting there, the chance that there will be a technological advance allowing a later probe to beat it there is almost unity.

        But, again, if it’s only a probe, no big deal. Bigger issue with manned ships.

        • J. Jason Wentworth May 21, 2018, 2:44

          Sending interstellar probes, like the Apollo program, involves socio-politico-economic factors that can’t be relied upon to come together favorably–or remain so for very long, as the post-Apollo period has shown. If the money and enthusiasm for sending feasible starprobes come together, foregoing such opportunities until faster ones are possible would be opportunities wasted, particularly since applied research aimed at producing fast (greater than 1% of c) starprobes isn’t occurring.

        • ljk May 21, 2018, 10:42

          It isn’t the amount of time that it takes us to get to and from the Moon that I was concerned about. Because if that is all it was, we wouldn’t be lamenting the fact that the last manned mission there was in 1972. And it doesn’t look like we will be sending humans to Mars any time soon, either, unless Elon Musk has his way.

    • J. Jason Wentworth May 18, 2018, 17:59

      I used to think that, but no longer. Kids growing up in the 1960s who wanted to get involved in the space program feared that they would miss the exciting manned missions to Mars and Jupiter. For political, social, and economic reasons, we run hot and cold on space exploration, and the more expensive the missions are, the more “cold” society runs regarding them (like the SEI–Space Exploration Initiative–which never happened at all). If we keep putting off starprobes until we can launch faster ones (which will be far more expensive than 1% of c ones), we may never–ultimately–launch *any* interstellar probes.

    • Al Jackson May 22, 2018, 5:54

      As mentioned before , around here, that’s the plot of Far Centaurus by A. E. van Vogt , 1944.

    • ignatius May 23, 2018, 7:46

      > because of technical progress, it would probably be overtaken by a faster and more capable probe which was launched later.

      This might happen. But consider the alternative: There will be no significant technical progress in interstellar probes unless by and through building such probes.

      Consider what would happen, if the whole world would delay buying new computers because according to Moore’s Law, “we can get computers in 15 years that are 1000 times as capable for the same money”. Chances are that in fact you will not get any computers at all by then for any price because the industry simply will have disappeared and most of the process knowledge will have been forgotten by then.

      If we want to go there (either in person or by probes) we should try to go as soon as it seems possible. Otherwise we might as well give up right now once and for all.

  • Alex Tolley May 18, 2018, 15:18

    I wonder if we need some sort of long-lived institution to run such a probe program. Religious institutions like the Catholic Church have demonstrated great longevity and purpose. Or perhaps a Howard Foundation as envisaged by Heinlein. Such wealthy, long-lived organizations may be necessary to carry out such a program if it means launching a probe each year. Such institutions seem able to weather changes in nations and governments quite well.

    I agree that we need to consider such long-term programs as a viable approach. Should new technologies make that approach obsolete, the worst that will happen is that we will have acquired knowledge of interstellar space plus perhaps the nearer solar systems until that new technology arrives, if ever.

    The size of the bubble explored by these probes will remain limited unless they are self-replicators. Even assuming our civilization lives 1 million years, at 0.01c, the bubble will have a radius of just 10,000 light years. If civilization lasts just 1000 years, our interest in receiving information will end after the bubble radius is just 10 light years.

    While self-replicating probes are in our technological future, simpler probes could be replicated by moderately technological civilizations. Perhaps they should be made to be easily replicable and launched like a chain letter – if you receive a visit, make 10 more and send them on their way, adding your cultural information that you wish to share.

    Unless civilizations are common (Fermi Question) then perhaps we should assume that no probe will ever communicate with another civilization within the time frame worth sending information back to Earth. They might be designed primarily to acquire information on star systems as an altruistic project. Contact with any civilization in the distant future might, therefore, be quite safe as far as humans are concerned as we will be long gone. I wonder what the anti-METI folks think about this?

    • J. Jason Wentworth May 19, 2018, 3:47

      My apologies–I had misunderstood what you’d meant regarding self-replicating interstellar probes (that you meant they’re farther down the road; I was operating on very little sleep earlier! :-) ). Near-term starprobes could be equipped with something like the STAR (Self-Testing And Repairing) computer that JPL developed for the four planned Grand Tour mission spacecraft. (The two Voyager probes are simplified Grand Tour TOPS–Thermoelectric Outer Planet Spacecraft–which each have essentially a simplified version of STAR.) Also:

      Near-term interstellar probes could each have a “STAR-lite” computer, which would automatically connect spare circuit cards to replace cosmic ray-damaged ones. With the new NASA/KAIST-developed self-healing transistors, even damaged circuit cards could be repaired (and starlight-powered photovoltaic cells powering–or supplementing the internal “radio-voltaic” power of–Bracewell probes orbiting their assigned stars could likely also be made self-healing), giving the probes indefinitely-long lifetimes. In addition:

      Good–I’m glad I wasn’t the only one to think of “chain letter,” standardized-design Bracewell probes! Ronald Bracewell didn’t ^specifically^ mention in-contact civilizations using a standardized messenger probe design, but in his book, “The Galactic Club: Intelligent Life in Outer Space,” he did mention communicating civilizations “participating in the messenger probe program” at launch rates appropriate to their respective economic capabilities, exploring their respective surrounding regions of interstellar space without wasteful overlap, and sharing their findings with each other. It would make sense for a simple, reliable, easy-to-duplicate starprobe design to be developed, whose plans could easily (with a minimum of documentation) be included aboard a probe of its design, as well as be quickly transmit-able via interstellar radio and laser, and:

      Regarding METI–while Pioneer the 10 & 11 plaques, the Voyager 1 & 2 records, and whatever we manage to load into New Horizons’ memory aren’t likely to be found, these acts themselves constitute a statement to the universe: “WE ARE HERE!” Having decided to proclaim our presence to the Galaxy (including by means of the Arecibo message, other less-known METI transmissions [which have/will pass other, closer stars between the Earth and their targets], and planetary radar pulses), it’s a little late to change our minds about METI; it’s now a fait accompli, so we might as well start–judiciously–putting more attractive and interesting speech, music, and imagery–such as prime-number pictographs, as well as starprobes–out there.

      • Harold Shaw May 20, 2018, 13:08

        I consider myself a METI pragmatist. There are a range of risks and rewards and our approach to METI impacts those risks and rewards. I am also a critic of the risk analysis employed by METI enthusiasts. Forgive if this lands as uncivil, but you and Alex Tolley both offer what I consider immature approaches to risk analysis that are easily translated into the approaches of reckless young adults and the people who profit from their recklessness.
        “Contact with any civilization in the distant future might, therefore, be quite safe as far as humans are concerned as we will be long gone.” Alex Tolley

        I am sure we are all familiar with a reckless young adult modeling their current behavior on the assumption that they will be dead by 30. It is self defeating to assess risk with the assumption of an untimely death.

        J. Jason Wentworth, you employ the risk analysis fallacy where some potentially risky behavior warrants more risky behavior. It is the fallacy smokers employ, they could get hit by a bus tomorrow so why not smoke.

        I am genuinely a METI pragmatist, I think there are ways to employ METI that would increase our chance of survival even considering the existence of predatory ETIs. If people who support METI keep making reactionary arguments based on bad risk analysis we will never convince those who are anti METI.

        • Alex Tolley May 21, 2018, 0:01

          As a METI pragmatist, lay out the steps and some sort of timeframe when you would allow METI to proceed. What would satisfy you that humans were no longer recklessly shouting “hello out there!” into the void, potentially inviting advanced predators into our proximity.

          AFAICS, anti-METI arguments rely on the assumption that predators are a long way away, do not know we are here, yet can reach us if they wish. Yet our own technology is advancing so quickly that relatively soon we will have information on other world’s biospheres and possibly even artifacts indicative of ETI’s presence in the past. Our probes, as this post indicates, will be in other systems within 10,000 ly within 1 my, and probably a lot further out. Which means that advanced ETI is similarly capable of putting monitor probes in our system, invalidating the premise of distance. David Brin has made much of the fact that many of our broadcasts will be noise quite quickly and therefore do not represent unintentional messaging, justifying his “don’t shout in the jungle” meme. Yet his own SciFi works have posited alien probes on Earth, are this is hardly a new idea, as Clarke’s “Sentinel” story was published in 1951.

          Obviously, we cannot rely on logic alone to inform us how to make METI decisions, but conversely, I do want to know what empirical information will be enough for you to say the precautionary principle can be lifted.

          • Harold Shaw May 21, 2018, 11:29

            If lifting the precautionary principle on METI means allowing anyone and everyone to employ any or every messaging tactic then I don’t think we can ever lift the precautionary principle. Even in the scenario where we have made contact, we would have to take measures to insure that not everyone could message. Some of us are belligerent and irrational. If we could not control who messages, we would have to take measures to explain to the other civilization that some of us should not be listened to.

            Imo, it is likely that a sufficiently long lived ETI would fill the galaxy with sentinel probes. That does not invalidate the risk of shouting into the jungle unless those probes represent the only civilization present. If there is a sentinel probe watching us then there is also the risk of using METI tactics that prolong their silence. We have been messaging and they are not responding.

            I think the first step should be developing a process that prevents the over generalization of possible ETIs and METI tactics. Different METI tactics have different risks. For instance, embedding a message in our TV broadcast would be observable by sentinel probes but not by ETIs many light years away. Sending a probe to a system many light years away to broadcast is safer than broadcasting from Earth.

            I also think we need to develop better messages. Imo, our past messages are analogous to pick up lines and dick pics; at best they reveal us to be transactional. Imo, we need to develop ways to communicate that we have a robust theory of mind and understand non-zero game theory. If it is likely that ETIs know about us then there silence indicates there is likely something wrong with our message or how we message.

            As to time frame, I think we could employ the least risky METI tactics today. Assuming of course we have a message that is likely to prompt an observing ETI to become a communicating ETI. “We are here” won’t do that.

            • Alex Tolley May 21, 2018, 16:56

              Thank you for laying out your reasoning.

              I suspect that your argument about our METI messages prolonging non-contact is possible, but I think it doesn’t match our own experience with cultural contact. Sure, the idea that a tribe was warlike or cannibalistic might deter some explorers, but we did try to contact tribes wherever we met them. Perhaps the American experience with the natives during the westward expansion colors some views. ET is likely to have considerable experience with different cultures and is likely well aware that planets do not have monolithic cultures, any more than populations of social animals. I don’t see individual METI messages as being any more problematic than our own encounters with other individuals or groups. We make social exchanges with those we can engage with and avoid those whom we feel no worthwhile contact is possible. Why would ET be any different? Indeed, I could make the contrary argument. Any planet that has a monolithic culture that only emits certain types of messages might indicate a highly authoritarian, possibly militaristic culture and therefore best avoided. Conversely, a planet that emits a wide variety of messages indicates a greater freedom, more diversity of opinion, etc., and are therefore more likely to be open and engaging, when the most interesting messages are detected. Just as we might call in to a radio show, or comment on a blog that piques our interest while ignoring most of the other channels and ideas available.

              While Clarke’s “Sentinel”/monolith waited for an event indicating a technological presence, it seems to me that we would not build probes that way. We would have them make ongoing observations that might well include detecting signs of artifact construction. If one is going to send probes to other stars, why not include craft that can enter atmospheres and make ground observations, returning a wealth of information to pay back the costs? There must be myriad ways to communicate with pre-technological cultures, even if the craft cannot mimic a local lifeform. (Religious books have many examples.) Why wait until the culture has a radio or something so exotic we haven’t discovered it yet? If there are probes in our solar system, I would expect that they are for communications and that they are monitoring probes on Earth (and the other planets) to observe the planet and possibly even communicate with humans (and whales?) on some occasions.

              Worrying too much about aggressive aliens seems rather like worrying about gods. The ancient Greeks had a pantheon of gods they believed real, some you didn’t really want to tangle with, yet their literature includes heroes challenging those gods. I would hope that our descendants see us as bold (or reckless).

        • J. Jason Wentworth May 21, 2018, 3:19

          Being well beyond 30 myself, I have learned through experience–and I knew it well before then–“Nothing ventured, nothing gained.” While there might be malevolent beings out there waiting to pounce upon us, we hardly seem to be worth their efforts, given the likely distances–hundreds to thousands of light-years, or more–separating us from them. Also:

          If one accepts that aliens–as some doomsday scenarios postulate–intend to destroy us by sharing destructive information via radio (plans to build some deadly automaton or biological device, say), or even by simply overwhelming our culture by sharing knowledge far in advance of our ability to understand or use, then even SETI is too dangerous for us to engage in, and:

          If, having come this far, human beings (the Earth-dwellers who ask questions)–who now have the ability to obtain an answer to the question “Are we alone”–are too afraid to seek the answer, then all of human history, as far as this ultimate question is concerned, has been a waste of time.

        • ljk May 21, 2018, 10:44

          Reposting this quote:

          “Contact with any civilization in the distant future might, therefore, be quite safe as far as humans are concerned as we will be long gone.” – Alex Tolley

          METI may be conducted by a civilization that knows it is doomed for whatever reason, cannot escape its fate, and yet still wants to preserve something of itself so that it does not feel its time in this existence was for naught. So in this case they could reveal themselves without fear of a hostile response. James Gunn’s 1972 SF novel The Listeners is based on this premise.

          I do not advocate that we send just any ol’ messages into the galaxy. But guess what – others already have, including NASA and the ESA, plus we’ve got decades of electromagnetic leakage with no end in sight. And if the ETI are sophisticated enough, they won’t need any radio telescopes to determine there is life on Sol 3.

          Since I won’t be very surprised if real ETI do not have some form of Prime Directive ala Star Trek (the rule was broken half the time anyway in the series), we should spend more time preparing for a Cosmos that may appear on our doorstep at any moment in various forms rather than constantly fretting about (and threatening) anyone who may send a signal into space.

          • Harold Shaw May 21, 2018, 15:50

            A civilization that knows it is doomed may indeed let the universe know it existed. But unless you think humanity is doomed, I don’t see what this has to do with how humanity assesses the risks of different METI tactics. Taking Alex Tolley’s quote out of context is the type of over generalization and rhetorical slight of hand that I think keeps us from arriving at consensus or developing methodology to assess risk. If we keep listing possible risk scenarios and possible ETI scenarios then we will be in a place where either no one can message anything or anyone can message anything. We need to develop methodology to assess the risks of METI tactics and I do no understand why METI enthusiasts are so loathe to do so. I fear it is because they want to secure the ability for anyone to message anything, which Imo has more to do with human competitiveness and personal gain than a genuine desire do what is best for humanity.

            I am curious, do you believe that for any given technological civilization, discovery of another technological civilization immediately or quickly results in formal contact? Your comment regarding the likelihood of a type of Prime Directive makes me believe you do. I think it is more likely that the time it takes for discovery to lead to formal contact is proportional to the differences between the two civilizations. Given the likely rarity of technological civilizations and the age of the galaxy, that difference could be vast. I have yet to see a METI tactic that takes the likelihood that we are observed seriously. The only time I ever see the possibility offered is as an excuse to message however we like.

            • Alex Tolley May 21, 2018, 17:44

              Given the likely rarity of technological civilizations and the age of the galaxy, that difference could be vast. I have yet to see a METI tactic that takes the likelihood that we are observed seriously. The only time I ever see the possibility offered is as an excuse to message however we like.

              David Brin’s discussion of METI ends with:

              We are the youngest of all technological races in the cosmos, like an orphan child who suddenly finds herself wandering a strange jungle that’s quiet… too quiet. So quiet that the simplest, parsimonious explanations appear rather daunting. Almost as if the creatures and natives know something that we don’t know, and are keeping silent for a reason.

              Or else, something is keeping the number of creatures and natives low… too low. If you found yourself in such a situation, would you listen a while? Maybe talk things over with your fellow orphans? Especially when you are already learning at a rapid pace, and may have more of the clues you need soon, with a little more listening? And patience?

              Perhaps you have the kind of personality that says: “What the heck! I might as well shout and see what happens!”

              That’s all very well if the only one you are putting at risk is yourself. But when that risk is also imposed upon our children — all of humanity and our planet — is it too much to ask that we discuss it first? Think of it as an interstellar test of both IQ and common courtesy. A way to show that we’re the kind of responsible grownups who might actually be ready for First Contact with other adult minds.

              Firstly I find his characterization of the Fermi Question as wandering in a quiet jungle just plainl unscientific. Why not have one wandering around in a desert? Then the quiet has a very different reason.

              He dismisses METI as shouting into the dark. Yet he does not want to decry progress, and that progress will include probes to exoplanets. Yet his example is akin to a stone age tribe discussing whether they should use smoke or drums, or venture out of their valley, to meet another tribe if any exist, because it may be a dangerous enemy. Discussing it without empirical data gets you nowhere, and in the end, will be nothing more than whose rhetoric is most persuasive. There are risks, but there are opportunities. Brin wants Risk Analysis, but shouldn’t we really want Risk/Benefit analysis?

              • AlexT May 26, 2018, 2:32

                “We are the youngest of all technological races in the cosmos”
                Very strange supposition, that I frequently met in METI/ SETI related topics.
                Fermi Paradox, immediately stops to be paradox if we accept one simple thing – we are oldest technological race in the cosmos…

            • ljk May 21, 2018, 17:52

              No, I was not implying that I think humanity is doomed, I was just trying to give a scenario where a civilization might plausibly conduct METI without fear of reprisal. The other reasons they might do METI are religious and they feel they are invulnerable, or a combination of these scenarios. I was NOT trying to take Alex Tolley’s quote out of context, FYI.

              Quoting you:

              “I am curious, do you believe that for any given technological civilization, discovery of another technological civilization immediately or quickly results in formal contact? Your comment regarding the likelihood of a type of Prime Directive makes me believe you do.”

              Not necessarily nor did I actually imply that. And you misread my comment about a Prime Directive: I was saying that I doubt an ETI would have such a thing, though not impossible, so they could contact us whether we are ready or not. Could, not will.

              I have seen here and elsewhere people thinking because we are supposedly primitive that advanced ETI will leave us alone. I do not think that has to be the case. They could have very different views on how to handle less advanced cultures.

              If you are somehow bothered because I support METI in any way, what I have really been trying to say is there are 7.6 billion humans on this planet with access to communications technology easier than every before. They cannot all be regulated. Instead of hoping everyone will not signal the galaxy, we should be prepared for whatever may happen.

              • Alex Tolley May 22, 2018, 12:53

                I have seen here and elsewhere people thinking because we are supposedly primitive that advanced ETI will leave us alone. I do not think that has to be the case. They could have very different views on how to handle less advanced cultures.

                I agree. They might want to contact us out of [scientific] curiosity, much as we are now trying to communicate with the more intelligent mammals on Earth. [If we succeed, we might even gain some insight into the perceptions these mammals have of the world they live in, their thoughts and feelings. If a whale could express fear of death from human hunting, as well as other actions we do that upsets their ocean environment, I could well imagine humanity taking a very different collective attitude to our actions.]

                Wouldn’t it be bizarre if we discovered that whales only sing certain songs when humans are around because they enforce some messaging rules in that event? I suspect it is our hierarchical social evolution as plains apes that makes us ask: “Who speaks for humanity/Earth?” That may not be what ET wants.

                • ljk May 22, 2018, 16:56

                  Remember who the ETI showed up at Earth for in Star Trek 4: The Voyage Home and were not happen when the discovered that all (?) the cetaceans were extinct in the 23rd Century.

                  Thank goodness they included humpback whale songs on the Voyager Interstellar Record:


    • ignatius May 23, 2018, 9:11

      1. We know nothing about the lifetimes of technological civilizations in general and even less about our own. The only data point we have, the only thing we know is that right now, we are alive and there seems to be no immediate reason that this should not be the case tomorrow or in 100 years from now. And in 100 years, the outlook will most likely be exactly the same. What we know is, that in about 1 billion years, the Earth in its current orbit will be an uncomfortable environment but even that must not be the end. Bad things can happen but they cannot be predicted and our future ability to deal with them is even less predictable. What might be a catastrophe today (think a large inbound Meteor) might be a challenge in 100 years and a mere nuisance in 1000.

      2. Extinction is hard. Mankind is all over the place. It would take an apocalyptic event indeed to get all of them (a mere nuclear war would not cut it). And if there are some survivors, then it will take only a couple of centuries to repopulate and rebuild.

      3. Betting on your own death in is unreasonable. If you are right, it makes no difference, but if you are wrong you just created a self fulfilling prophecy. The bet has strictly negative expectation and should thus be avoided.

      4. From a practical point of view, existential or cultural pessimism is a destructive and dangerous mindset which is not conductive to any long term endeavor – and not much fun to live with either. The stars will not be conquered by pessimists.

      So I think the usual anti-METI arguments are alive and well. If the lifetime of technological civs is long, and this is IMHO the only reasonable working hypothesis, then our own civ is only in its early infancy and extremely vulnerable.

      But even if you insist on your pessimistic outlook and consider the probe merely as a glorified gravestone for humanity (good luck convincing your fellow pessimists to finance that), your reasoning only works when the civ lifetime happens to be about the same as the travel time of the probe. If it is much less, the probe will find nothing. If it is higher, see above.

  • Geoffrey Hillend May 18, 2018, 16:42

    I don’t think we will be long gone, but become an extremely technologically advanced civilization with interstellar travel. We will be able to go anywhere, yet still live here. It’s better to be positive and not assume that since we have not been contacted yet that there won’t be any anyone out there or there is not any one out there or vice versa.

    • J. Jason Wentworth May 19, 2018, 3:56

      I agree. Besides, if anyone really clever is out there, they’ve known there is life here (from bio-signatures of oceanic plant life, our forests, etc.) for a long time. Depending on their distances, they might not be aware of technological life here yet, in which case they might be presented with many potential choices.

  • J. Jason Wentworth May 18, 2018, 18:30

    While I won’t say it’s impossible, I discount spacecraft self-replication (now and for a long time to come), because it is *so* much easier to say than do. We haven’t even made machines that can find the ingredients for making concrete blocks and produce them all by themselves. When I see such machines for sale at building contractor supply stores, I will become a little sanguine about self-replicating probes (but only a little, considering the chasm of complexity between concrete blocks and even the simplest spacecraft), and:

    I am not a “parade rainer” here; I’m just sticking with in-hand and foreseeable-future technologies that are available now, or with engineering R & D (nothing that requires new theories). Ion drives, Hall Effect thrusters, Sun-diver solar sails, laser-pushed lightsails, self-healing electronics (including photovoltaic cells), “radio-voltaic” power sources of various kinds, and other existing technologies (and/or extensions of these [the Soviets concluded that Circa 1973 technologies were sufficient for interstellar probes]) appear sufficient to create interstellar probes (with our abilities becoming more polished as our experience increases). Also:

    I think your idea–of a supportive organization building and dispatching such probes, for philosophical or even religious reasons–should be looked into. A foundation of like-minded people (perhaps even a coalition of people with different but convergent–on this subject–goals) might be an ideal body to initiate and maintain such a program.

    • Curious May 18, 2018, 23:34

      Biological systems repair themselves quite well. Perhaps we should refocus our efforts to the very small scale and biological – possibly artificially biological with some non-biological systems built in. Don’t think of grams think of milli and micrograms. At such a small size you could then armor them and produce probes no bigger than a BB. Now accelerate those as fast as we can and perhaps as some form of propulsion that can use solar power to ionize collect space dust. Send them on courses that leverage gravitational boosts maybe even on a route that returns them to Earth vicinity in umpteen years. Nearly science fiction – but only just. I don’t believe anyone is actively working on this exact thing at all. NASA NIAC probably best candidate to fund such an idea. The beauty is it could be easily tested by say sending it around the moon to demonstrate, then Mars etc.

      • J. Jason Wentworth May 20, 2018, 2:46

        Curious, Ronald Bracewell described–to demonstrate how small autonomous interstellar probes could be made–the enormous quantity of information that can be stored in a human brain, then suggested that another race could, if they so chose, breed a subrace of interstellar messengers that would be, in effect, “brains in bottles.” He didn’t suggest that the interstellar messengers would be such actual living representatives of their race, but that they would be electronic versions of them. I’m not against “hybrid” biological/non-biological systems of the kind you mentioned, but some type of shielding would be necessary to prevent radiation-caused cellular mutations, which would damage the stored information.

        • ljk May 23, 2018, 9:24

          If AI can think and be aware/conscious, then it qualifies as a living being. I am not certain how many humans, professionals and otherwise, have really grasped the possibility that a starship with a “brain” might be a living being in itself, not just some vessel only good for carrying a “real” crew of organic beings.

          Recall in Star Trek: The Motion Picture the opposite attitude was taken by V’Ger, that the USS Enterprise was viewed by the vast Artilect as a living being while the organic crew were called “carbon units” and viewed by V’Ger as an infestation which needed to be eradicated like so much vermin.

  • Robin Datta May 18, 2018, 18:57

    That was good, J. J., and more so as it is based on the best of hard science and taking at the end the high moral ground. A rational and perhaps parsimonious way to look around our neighborhood beyond our Sun.

    Although biology knows little of where its replication imperative might wend its way, training the intellect to consider seven coming generations’ worth of implications, as in the Native Peoples’ traditions of the New World is a counterweight in morals and ethics to minimize the disruptions of science and technology.

    And a program as you outline might survive the disruptions of politics and economics.

    • J. Jason Wentworth May 19, 2018, 4:11

      Thank you, Robin. Other than a few details that I added, though, the ideas were all Ronald Bracewell’s; I merely “rescued his idea from its oblivion” (or more accurately, “lifted it out of its relative obscurity”).

  • Greg Matloff May 18, 2018, 19:01

    Dear Jason
    Excellent job! What your piece well demonstrates is the time factor. Any interstellar effort will require the originating society to be comfortable with the concept of “deep time”. Interstellar plans based on the political cycle of the US (or any other government) will be non-starters!

    Regards, Greg

    • J. Jason Wentworth May 19, 2018, 4:48

      Hello Greg,

      Thank you, Greg–I appreciate that! Indeed, Ronald Bracewell emphasized the deep time–as well as deep space–factors in “The Galactic Club: Intelligent Life in Outer Space,” and in his scientific papers on interstellar communication. Also:

      He pointed out that interstellar contact, whether via radio, laser, or messenger probe, will be an interaction between civilizations, not between individuals. He added, however, that even one-way communication with another civilization, even a long-dead one (such as between ancient Egypt or Babylon and today’s society) is exciting, enriching, and highly informative. Regarding government funding of such interstellar cultural research:

      While I wouldn’t want such work to have to depend *solely* on say, NASA or National Science Foundation funding (or the equivalent in Russia, the UK, France, China, etc.), the situation might not be quite as bad as that, because such one-way civilizational contact might reveal scientific and technological knowledge that could enable humanity to jump over years or even decades of scientific research. (That type and level of interest could result in plentiful DARPA and/or DIA research funding, but that would be quite a double-edged sword.)

      • hiro May 19, 2018, 19:45

        Giving some monkeys a nuke + a very shining red button will not have any happy ending (10/10). A truly advanced civilization would stay out of this because we are not mature enough to handle this “ET nuke”; yeah this is the doomsday machine argument but we can’t trust something we have no clue. The sad fact is that we’ll accept anything due to the competitions between “superpower nations”. There is also no free lunch in galactic scale, if an advanced civilization gives us lots of free stuff but asked for nothing in return then we should know something is very wrong here.

        • J. Jason Wentworth May 21, 2018, 3:52

          Ideas like these depend on another–that technological races (and races which have the potential to become technological) aren’t rare. They might be, but I’m not very optimistic (based on how many species–including clever ones–have arisen on Earth, versus the number of technological races on Earth [and how late humanity arrived on the Earth]), and:

          If technological life is rare, it wouldn’t be surprising if such a race, acting out of feeling of cosmic loneliness, was very generous, especially with radio and/or laser transmissions. (In his 1960 lecture “Radioastronomy and Communication Through Space,” Dr. Edward Purcell said that a 300′ radio dish could send a 10-word telegram to a similar dish 12 light-years away [with the receiver having a pre-MASER reactance amplifier] for 1$ of electrical energy.) The Arecibo radio message and the Pioneer- and Voyager-carried artifacts are examples of such human-sent “bottles in the cosmic ocean.”

          • Harold Shaw May 21, 2018, 10:02

            If technological species are rare then they are likely vastly separated in time. If a tech ETI civilization lasts long enough they will likely fully explore their galaxy, perhaps even placing probes in every system. They will witness the emergence of another technological civilization; they will know they are not alone without having to make contact and be able to observe that civilization, learn everything there is too know about that species except how that species will react to formal contact. They could even interact with that species without making formal contact. They could also uplift non-technological species, making the value of independently emergent tech civs even more dependent on limiting contact.
            I think your assumption about how a lonely civilization would act is based upon how this lonely civilization would act. I think it is more likely that an ancient people with a quantity and quality of cognitive functions beyond ours would agonize over when and how to make formal contact. Not just for ethical or moral reasons, but for selfish reasons. We would be a rare resource, creating artifacts never before seen in this galaxy or universe.

            • J. Jason Wentworth May 23, 2018, 6:28

              I didn’t assume anything; I only pointed out that acting out of loneliness is something they *might* do. I also don’t assume that even a highly advanced civilization would explore the galaxy. Freeman Dyson went even further when he wrote, “I make a sharp distinction between intelligence and technology. It is easy to imagine a highly intelligent society with no particular interest in technology.”

        • ljk May 21, 2018, 11:07

          Some humans like to think that our “primitiveness” will be obvious to ETI. Yet unless an alien culture happens to parallel ours, or they have plenty of examples, how would they know how unsophisticated we are? Especially if they are non-humanoid and evolved on a world very different from our own.

          We place a lot of emphasis on the possession of tools as an indicator. Star Trek makes a big deal out of a society having to have a warp drive before it lets them into the Federation.

          But what if some ETI are very smart and sophisticated and yet did not bother making tools, or at least tools as we would recognize them? And if they don’t look like us, the odds only increase that we won’t recognize them as intelligent beings. Just ask any cetacean or cephalopod about that one.

          • J. Jason Wentworth May 23, 2018, 6:51

            Amen. This difference (which Freeman Dyson spoke of, regarding a highly intelligent society with no particular interest in technology) even occurs among human beings. Most white people looked upon the Native Americans as being “primitive savages” who were of a lower order of humanity (the blacks, of course, were looked upon as being even lower), yet both had their own, different civilizations in which they were–until they were oppressed–happy and content for the most part, and:

            They may have seemed primitive in the whites’ admittedly biased view, but by their standards, the whites were technological barbarians who possessed amazing devices but acted in sub-human, sub-animal ways (the accounts by the Aztecs of the Conquistadors’ behavior were not flattering). If cetaceans think about human beings as a group, they can’t rate very high in their aquatic cousins’ minds (they do seem to take people at face value as individuals, though).

            • ljk May 23, 2018, 14:25

              Herman Melville’s classic novel Moby Dick was based on a real event of a whale that not only attacked and sunk a whaling vessel, the Essex, but pursued the survivors afterwards:


              Cetaceans, especially dolphins, are often not very nice. Yet another sign of high intelligence?


              And yes I know humpback whales go out of their way to protect other species from predators, usually sharks and orcas:


            • Michael May 23, 2018, 17:26


              “They may have seemed primitive in the whites’ admittedly biased view, but by their standards, the whites were technological barbarians who possessed amazing devices but acted in sub-human, sub-animal ways (the accounts by the Aztecs of the Conquistadors’ behavior were not flattering).”

              The Aztec were not nice at all and would commit mass murder of prisoners in the 10s of thousands! The native American Indians were not nice to each other either, raiding and killing each other! We should move away from blaming ‘groups’ for past despotic activities because we don’t have the insight to see what happened with any great detail at the time. Domination and destroying other cultures and peoples is not the reign of one ‘group’ but it is a human trait that is present in ALL cultures and races. Thankfully our social understanding of other cultures has improved and the best we can do is not repeat these actions again.

              • ljk May 24, 2018, 12:49

                Catholicism still has a ritual sacrifice of blood and flesh during its services, conducted by a priest on an altar: They have just been replaced with wine and bread. The progress of civilization.

                • Michael May 25, 2018, 16:43

                  The symbolic sacrifice was a willing one at that.

              • J. Jason Wentworth June 26, 2018, 4:58

                I’m sorry, Michael; I missed your message before (I just now came across it while looking for David Herne’s). Being part Native American (and English, Irish, Portuguese Jewish, and Caribbean black), I agree. I reject the “noble savage” idea about the various North, Central, and South American tribes. Many of them engaged in barbaric acts (the Aztecs and/or the Mayas cut the hearts out of living sacrificial victims to ensure that the world would continue, other tribes sacrificed young girls to Venus (which they didn’t think of in Roman terms, of course), and so on. Most if not all peoples can point to past atrocious activities.

  • Andrew Palfreyman May 18, 2018, 19:36

    I must say that the kind of contact scenarios envisioned by Bracewell border on the hilarious, simply due to the raw probabilities of the assumptions used. In order for his “visual TV” type scenarios to play out, the time of encounter would have to be so finely tuned such that the aliens possessed TV. and yet no means of coming and physically grabbing the probe in order to reverse engineer it! The probability of such a time window is vanishingly small set against the backdrop of a civilisation’s expected technical development timescales. A fine example of being unable to see the wood for the trees, due to chronological parochialism.

    • J. Jason Wentworth May 19, 2018, 6:08

      The aliens would not have to capture such a probe, or even see it, much less go anywhere near it, in order to engage in radio (including television or other video) communication with it. Dr. Bracewell’s carefully thought-out, language-independent method of establishing contact, via signal repetition with rapid feedback loops, would enable mutual understanding to be reached. Even today, human technology and software algorithms enable message formats to be determined, even via “brute-force” methods in which different combinations are tried. Also:

      The assumption that advanced technological civilizations would cease using radio is a curious one, because for deep sky astronomical observations, radio has the best penetration through galactic matter (neutral gas clouds, ionized gas clouds, and dark clouds of obscuring dust), enabling radio astronomers to see and map the entire Milky Way galaxy, other galaxies, and the intergalactic medium. A narrow-bandwidth interstellar radio signal, or a transmitting interstellar messenger probe in the stellar system of such a planet–would be a highly-conspicuous signal source that would attract much attention, and:

      Bracewell’s probe contact protocol–using video; digital video signals would be even more attention-attracting than the analog television signals he envisioned in the 1970s (the probe’s computer could produce and read either one, or any video format)–would not be implemented until after mutual understanding (to the point of a common video format) had been reached. In addition:

      Even if the inhabitants of the target stellar system no longer used radio for communication (a proposition that seems rather doubtful, since the production and reception of radio waves is simple and easy, requires little energy, and is very inexpensive), there are numerous quiet zones in the radio bands where the noise level is very low. Also, radio-receiving scientific instruments of theirs, such as radio telescopes, would easily pick up a probe’s radio signals. As well,

      The “Aliens don’t have X” game (and its close relative, the “Aliens no longer have [or no longer use] Y” game) both lead to a distressing result: “We stop looking for alien signals *and* alien interstellar probes,” because our assumptions lead us to stop searching. If we are ever going to find extraterrestrials, we’re going to have to accept one or more assumptions (even geometry requires us to accept a few axioms and postulates, without which even such a prosaic–yet very important–activity as carpentry wouldn’t be possible).

  • Michael Fidler May 19, 2018, 4:48

    Interesting, the problem with length of time and and amount of energy for high C velocity could be solved by a staged system. The possibility of using something like a neutron bomb to accelerate in stages or an X-ray laser that consumnes itself in the process of taking the sail to high C would solve that issue. Just like the stages of rockets of today but using self destructing light weight stages to counteract the loss of power due to redshift of EM waves.

    • J. Jason Wentworth May 20, 2018, 3:41

      This is where the trade-offs can drive one batty. Higher starprobe cruise velocities are achievable, but at two increased costs: financial and energetic, and these are inter-related. A faster probe is more expensive in terms of money, and the need to slow it down to enter circum-stellar orbit–or to achieve a slow enough stellar system fly-through to gather worthwhile data and images–makes it even larger, heavier, and more expensive (because not only does it reach a higher cruise velocity than 0.01 c, but its braking stage(s)–in addition to the probe itself–must also be accelerated to the > 0.01 c interstellar cruise velocity), but:

      There is a possible way out of this problem, but it involves two increased costs: expending much more energy, and employing highly-expensive engineering. The Breakthrough Starshot project is intended to utilize this method. By dumping prodigious quantities of laser energy into a large number of highly sophisticated, relatively low-unit cost (it is hoped) light-pushed sails, the sail probes would be accelerated up to approximately one-fifth of the speed of light. By sending many such ~0.2 c probes, their individual glimpses of the Alpha Centauri system would, it is hoped, be “knitted together” into a longer collective view by the probes’ instruments and imaging systems. Fundamental problems with the Starshot laser array and the lightsail probes are already beginning to appear, suggesting that the project may be a step too far.

    • Michael May 20, 2018, 9:36

      A free electron laser (they can be made to adjust wavelength over a few minutes) will give you your UV to X-rays to allow for the Doppler issue.

      • Michael Fidler May 20, 2018, 11:42

        I thought the problem was losing energy because of the wavelength becoming longer. If a miniature x-ray laser could be developed that used all its material structure to generate a focused beam after being released from the lightsail, like a nano Orion Nuclear pulse rocket. The military may have already developed such a device. Would this work on the physics side?

        • Michael May 20, 2018, 14:37

          It is very hard to reflect X-rays, they can be deflected by shallow angle reflection but you will lose a lot of energy transfer that way. With a free electron laser if you start at say UV and have a UV reflective sail you can keep the UV at the sail as you change from UV towards X-rays at the source (Doppler shift compensation). X-rays suffer less dispersion than longer wavelengths and so collimation will be better, getting them into an array configuration may be a challenge though.

          • Michael Fidler May 20, 2018, 21:54

            Ok, but a pellet UV laser that self destruct while laseing and is being expelled from the lightsail. A directed beam of high power UV radiation from the pellet laser. A nano Orion UV laser rocket that after the initial boost to 0.1 c from earth lasers uses nano fuel pellets expelled from the light as fuel to generate a UV beam from behind the sail to accelerate to higher c.

          • J. Jason Wentworth May 21, 2018, 7:03

            Simmons and McInnes (in their article that’s Reference 23 in my article) found that with relativistic treatment, laser-pushed lightsails suffer a serious loss of thrust (“momentum impartation”) from the propulsive laser beam as the sail’s velocity–with respect to the laser projector–increases. Because the sail “sees” the beam’s light as being of longer and longer wavelength at its velocity (away from the laser) gets closer to c, each photon, being of longer wavelength–and thus lower energy–than the previous one, imparts progressively less energy to the sail, but:

            For cruise velocities of up to 0.2 c or so, the thrust loss isn’t serious. Using an X-ray laser–and a suitably-designed X-ray sail–would also confer some advantages. An X-ray laser beam suffers less diffraction, enabling a physically smaller laser projector to be used (grazing-incidence nickel optics, like those used in sounding rocket and satellite imaging X-ray telescopes, could be used). A smaller sail (a rather narrow, nickel-foil cone might work) could also be used, to take advantage of the X-ray laser beam’s lower diffraction.

            • J. Jason Wentworth May 21, 2018, 7:35

              Such ~0.1 c – ~0.2 c laser-pushed lightsail probes (whether they employed visible light, ultraviolet, or X-ray lasers to push them) would still have the disadvantages of “eye-blink fast” planetary flybys (making “strings” of probes necessary to gather meaningful data and pictures). The high velocity would also result in probable high failure rates due to the probes’ impacts with interstellar atoms and dust particles while in transit (which would also make large numbers of probes–per target star–advisable), and:

              A “two-wave” probe program could employ both such fast probes and slower, stellar rendezvous (or months-long stellar system fly-through) probes. The fast, 0.1 – 0.2 c ones could–if huge numbers of them don’t prove to be necessary to gather the most basic habitability data, with their impact attrition rates–find potential abodes of carbon-based life. The slower, more capable Bracewell probes could be sent to the stars which the fast probes reported as having planets with habitable conditions. These probes could conduct comprehensive surveys of their planets (even if life isn’t present), and they could listen for and–if it’s there–contact technological life. They could also engage in scientific and cultural exchange (including sending these discoveries back here), and tell any “local aliens” how to contact the Earth directly.

            • Michael Fidler May 21, 2018, 9:42

              Ok, I think I see the problem – the mass of the sail becomes infinite the closer to c it becomes and time slows to a stop at c. The UV laser light will be shifted into long radio waves as the sail gets closer to c even if the pellet is laseing right behind the sail.

              • J. Jason Wentworth May 23, 2018, 7:01

                The mass increase definitely compounds the problem, but even if that one effect didn’t occur (so that the sail’s mass remained constant), the ever-weakening push from the laser (as its photons became of longer and longer wavelength, as “seen” by the sail) would continually reduce its rate of acceleration. By the time the laser beam became of radio wavelengths–especially longer than microwaves–the increase in the sail’s velocity would become negligible.

  • Alex Tolley May 19, 2018, 11:19

    I’d like to readdress the issue of the consequences of a slow probe (0.01 c). Assuming Earth is the target of returned information transmitted at c, then the radius of the bubble (light years) that the probes can reach R = L (1/((1/cp) + 1)). [ where cp is the probe velocity – 0.01 c, and L is a measure of Earth’s interest or ability to receive the signals. This may equate to Drake’s technological civilization’s lifetime.

    For L = 1,000,000 R = 9900. L=1000, R = 9.9. L = 10, R = 0.099 (~ 6300 AU).

    Therefore even if human civilization lasts 1 my, the radius is less than 10,000 ly. For a millennium, barely 10 ly – just 11 stars. For a short, political attention span of L=10, less than 1/10th ly.

    So even with just a political attention span, we reach about 6300 AU, which gets us to the Oort cloud and well past the gravitational focus of the sun. Both of these objectives, let alone the myriad others would be worth doing if the probe could make useful observations.

    At 1000 years, the probes could be delivering information for 11 star systems, although none will likely have ETI during that time frame, if ever.

    Assuming the probes can last 1 my, they are penetrating a fraction of the galaxy, but within the parallax measurements of Gaia (I think). Whether there are ETI within that bubble is anyone’s guess, although one could hope for many worlds with some form of life, hopefully, advanced life and even relatively intelligent life. ETI might be pretechnological, or at least early technological, but pre-industrial revolution capable. Possibly only their monuments and effects on their planet are observable. There are a lot of stars within 10,000 ly, so a once a year launch will mean sparse coverage even with multiple flybys by each probe unless the launch rate is increased. I would hope that if we have a solar system wide economy and a much larger economy, then launches will be far more frequent allowing full, possibly even multiple coverage of each star. Probes might well increase their launch velocity over this time too, expanding the bubble radius and their capabilities.

    What civilization will look like in a millennium is anyone’s guess, let alone after a million years. It wouldn’t surprise me if in a million years those probes (at least the later, most advanced ones), communicating with each other, is our civilization, with Earth as a distant memory.

    • hiro May 19, 2018, 19:56

      We will definitely have multiple interstellar civil wars among ourselves during the period of 1M years using relativistic rockets to erase each other out of existence for some (dumb) unknown reasons. Unless we have some very mean AI playing “dictators” minimizing our mistakes/misunderstandings.

    • J. Jason Wentworth May 20, 2018, 4:07

      That’s the way I look at Bracewell probes. They combine the functions and objectives of ultraplanetary probes, interstellar probes, and SETI & METI researchers. When Ronald Bracewell formulated the interstellar messenger probe concept, he accounted for Frank Drake’s technological civilization distances versus lifetimes (he devoted Chapter Seven [“Intelligent Neighbors: How Far, How Many?”] of his book, “The Galactic Club: Intelligent Life in Outer Space,” to this subject), and:

      He also figured that the probes’ capabilities would increase over time. He advocated sending the most modest interstellar probes that could fulfill the mission objectives, so that more probes could be launched with the given slice of the budgetary pie allocated to such space exploration activities. (What is “the most modest interstellar probe design” would, of course, become increasingly capable over time.)

    • Robin Datta May 20, 2018, 19:43

      From our hunter-gatherer forebears with the next “kill” and the next basket of fruit/vegetables to the agricultural and pastoral next harvest or next birthing season, the societal time-line focuses on a short-term. It may have been shortened from agrIculture & pastoralists towards the hunter-gatherer by the rise of the corporatocracy and quarterly reports.

      Until we are societally invested in an economy that provides its returns on much longer timescales, we will continue to prioritize short-term objectives.

  • Tom Mazanec May 19, 2018, 17:02

    Some maverick astronomers have speculated that Long Delayed Echos are from a Bracewell Probe.

    • J. Jason Wentworth May 20, 2018, 4:25

      Duncan Lunan speculated that the odd LDE (Long Delay Echo) radio signals that first became well known in the late 1920s might be from a Bracewell probe in the Solar System (in 1960, Bracewell himself suggested that other such signals should be sought), but this hypothesis isn’t now considered likely by most scientists. This doesn’t, however, mean that such interstellar probes aren’t present in our Solar System, and:

      An inactive (or any age) or active probe could be here, perhaps reporting back to its senders *without* attempting to contact us. There are immense volumes of space within our Solar System–not to mention the surfaces, caves, lava tubes, and subsurface areas of moons, comets, and asteroids–where derelict or silent probes, ancient extrasolar expedition sites, and/or artifacts could be awaiting our discovery one day.

    • ljk May 21, 2018, 11:11

      So what is the non-ETI answer to LDEs?

      • J. Jason Wentworth May 23, 2018, 7:16

        Particularly for the lower-frequency, HF LDEs (VHF ones also occur), one theory is that temporary “resonator cavities” made of plasma form in the ionosphere, and that these cause multiple internal reflections–with strengthening of the signals–before the signals escape and are heard after more than the 2.7-second moonbounce delay. Another theory is that temporary clouds of solar wind plasma collect at the Earth/Moon L4 and/or L5 Lagrangian points, and that these–in concert with our ionosphere–result in LDEs. Also:

        The VHF ones are puzzling because such short-wavelength signals travel by line of sight, which would make hoaxes very difficult (the towers are expensive, and hard to hide). John W. Macvey’s 1977 VHF LDE was odd in that his beam antenna, at the time, was pointed toward one of the Lagrangian points.

        • ljk May 23, 2018, 9:14

          Maybe we need to send some probes to scout around the LeGrange points. I know we have a few satellites at some of those places, but none of them so far as I know are designed to look for any “visitors”.

  • David Herne May 19, 2018, 23:07

    Jason, this essay could have been a chapter in an expensive textbook with a wider mandate but we get it for free, thank you, and the references… 👍

    Tom Mazanec, I guess this would be one link that shines light on this – http://www.setileague.org/editor/lde.htm

    • J. Jason Wentworth May 21, 2018, 6:36

      Thank you very much, David! It’s a less well-known SETI technique that is entirely complementary to Earth-based radio and laser SETI work, and one that we could engage in now. (It was only recently that I came across the advocacy–from Soviet scientists at the 1973 CETI conference–that such starprobes were already feasible with then-existing technologies, which means that even better, and smaller, ones could be built today.) Also:

      I see that you–like your countryman Ronald Bracewell (I nearly emigrated, with my parents, to Queensland in the early 1970s, but the plan fell through)–are also interested in LF and VLF (Low Frequency and Very Low Frequency, respectively) radio astronomy. One of the possible probe features (“wagon wheel” arrays of kilometers-long, spin-rigidized wires, which could serve as stellar wind sails and also [depending on the frequencies selected] as broadside or directional end-fire radio antennas [multiplexed, in the latter antenna case]) would make possible VLBI (Very Long Baseline Interferometry) at LF and VLF wavelengths while the probes were in transit (between two or more underway probes and/or such radio astronomy spacecraft in our Solar System). Regarding LDEs:

      There have been some more recent, intriguing ones (including at least one involving a television station, KLEE, a Texas TV station that was received–and whose Station Identification card was photographed–by viewers in the UK, three years after it went out of business in 1950). While a hoax can’t be ruled out for this incident, this and other such occurrences (such as the astronomy writer, amateur astronomer, and amateur radio operator John W. Macvey’s–and other hams’–reception in 1977 [on the 2-meter VHF band] of transmissions of the airship R-101, which crashed and burned in 1930) would have required expensive, large, and hard-to-conceal transmission towers in order to carry out such rather pointless–not to mention illegal, with severe punishment for violators–practical jokes, and:

      The lower-frequency LDEs may be accounted for by freak ionospheric “ducting” (theoretical models of such short-lived, natural “resonator cavities” comprised of ionospheric plasma have been developed), but these don’t account for VHF, UHF, and higher-frequency LDEs which have been reported (such signals simply punch right through the ionosphere into space). In addition:

      If two or more hams, picking up LDEs, used directional antennas to triangulate the LDEs’ source, and it proved to be a point out in space, that would be an exciting development! They could test Bracewell’s probe contact protocol that I reproduced in the article (they could do this even without first triangulating the LDEs’ point of origin).

  • Anthony Mugan May 20, 2018, 12:58

    What are people’s thoughts on the idea that the probe should more or less immediately make contact?
    In human societies contact between cultures at very different levels of development tend to end badly. We have no way of knowing how another civilisation would react to a ‘shock’ contact like that.
    Would it be advisable for the probe to stealthily study any civilisations found before deciding on the best way forward?

    The trickiest scenario might well be one around our level of development….much less advanced and you clearly leave them alone, much more and they’d know all about us anyway….I wonder if there are more subtle ways of ‘testing the water’ to see how a society might react….I may come back on this thought if it takes firmer form but any initial thoughts much appreciated.

    • Robin Datta May 20, 2018, 19:53

      Send them a “sub-probe” from the main probe and watch the response?

    • J. Jason Wentworth May 21, 2018, 4:24

      That’s a good question. If the aliens were at the same level we are at now (when a 0.01 c probe got there), we would–absent some worldwide calamity–be the more advanced party. The issue of culture shock, “from us toward them,” would be a possibility in such a case. Even if the other civilization was ahead of us, if technological civilizations are rare, they might still be very surprised (although not necessarily in a negative way) to have a terrestrial probe arrive in their planetary system.

      • hiro May 21, 2018, 19:21

        They would be more surprised if they see our nanobots coming into their system and converting dumb matter into more nanobots. This is the main reason why truly advanced civilizations don’t do colonizing the entire galaxy if they don’t know the # of other advanced ones existing somewhere in remote regions of our galaxy.

        • J. Jason Wentworth June 26, 2018, 5:37

          The starprobes that I wrote about in the article–and which Ronald Bracewell proposed–aren’t self-replicating von Neumann probes; that idea (which isn’t incompatible with Bracewell probes) was developed later. I am doubtful about whether von Neumann machines (and especially von Neumann probes) are feasible, or even possible. It’s one thing to express an idea and develop mathematical formulas describing it (I note that von Neumann was a mathematician–not an engineer, a technician, or a technologist), and quite another to realize it as actual hardware, and:

          I do agree with you regarding the emotional, legal, and political ramifications of a von Neumann probe (assuming that such devices can be created) suddenly showing up in a solar system and helping itself to raw materials to build a probe factory, planetary exploration sub-probes (to explore that system’s planets), and more von Neumann starprobes (to head out to explore other stars). We wouldn’t be too happy if such a probe arrived here and started taking material from asteroids, comets, and/or other bodies (even if it explained itself, it would be a rude first contact [by proxy] with the probe maker’s civilization). If von Neumann probes are possible, and if we ever dispatch any, it would be prudent to program them to seek and make contact ^first^, and then ask any local aliens if they could use a tiny bit of their systems’ material to replicate; such politeness would be “starting off on the right foot” in interstellar contact.

  • Harold Shaw May 20, 2018, 13:14

    Sending probes to the nearest systems is a lot safer than widely transmitting a signal. A probe is much less likely to be intercepted by nomadic pillager ETIs than a radio signal. With a probe we could also observe any ETI before making contact. If the most popular show on ETI TV is about cooking other people or the planet is engulfed in conflict, we have the chance to discreetly power down the probe or leave the system.

  • Anthony Mugan May 21, 2018, 8:16

    One of the most striking features of the contact strategy proposed by Bracewell is to directly transmit back radio or other EM signal back at a planet, leading inevitably to rapid and very public discovery of the probe. On reflection I think that would be a very risky approach, potentially leading to significant culture shock or a hostile response from a culture of which we have initially absolutely no knowledge or understanding. We also need to consider that there are some other perspectives on this other than a purely scientific one, including, but not limited to, political, military, intelligence, and legal perspectives, all of which tend to look at the world in very different ways. In the discussion below I am thinking more in a military / intelligence mindset than a scientific one (with overlaps), just to illustrate the way different stakeholders would look at this in very different ways.

    I think it would be essential to programme the probe to undertake a lengthy programme of studies of an inhabited world in a stealthy manner before progressing if that seems appropriate. It would also be an idea to enable it to locate and study pre-technological cultures and simpler life.

    For a pre-technological society, the probe or sub-probes could approach into a low orbit to undertake remote sensing. A real understanding of the society would need covert operations on the ground as there would be no other way to pick up language or to develop a deep understanding of the sociology / psychology involved. There are many scientific questions that would also need sampling operations or missions to establish ground truth for remote sensing etc. Such operations should begin in relatively uninhabited areas, focusing on purely scientific matters, to gain experience of operating in the environment, before progressing to the much higher risk operations to plant surveillance devices to gather intelligence on the species considered potentially capable of progressing to a technological civilisation.

    It seems to me that there are few benefits and many downsides to openly contacting a pre-technological culture.

    A really tricky question would be how to handle a civilisation that was undergoing technological take off, as began here on earth in the late 18th Century and is still progressing. This might be particularly tricky if they are anything like humanity in terms of behaviour (fractious, warlike, selfish and positively dangerous, at least in terms of the leaders, and with a population likely to react rather emotionally to crises). At some point this culture is likely to start moving out into space themselves and will eventually bump into us. They therefore represent a potential future threat.
    It would be desirable at this point (from a military and intelligence point of view) to undertake a more focused set of operations that combine what in military terminology are described as ‘ferret’ missions and ‘psyops’ missions. Ferret missions are deliberate intrusions close to sensitive installations to test technical capabilities and operating procedure. Recent developments in what is termed ‘ambiguous warfare’ (deniable ops for those of us of a certain age) may give useful guidance on the design of such operations to minimise the risk of precipitating culture shock prematurely. In that sort of scenario, it may be desirable to use these ferret operations as part of a pysops strategy to begin to create the impression that
    a) We might be there, but it’s not clear and fairly easily deniable if that is the policy decision they want to take and
    b) If we are there, then we are a long way ahead of them technologically, to reduce the risk of hostile action at such time as the culture begins to push out into space itself.
    c) Whilst our intent is not obvious to them, we do not appear to represent a threat. This could only become clear after a prolonged period – as initially such ferret operations would very definitely appear to signal a potential threat if recognised as possibly being such.

    In other words, we’d need to sustain a programme of infrequent and rather ambiguous intrusions over a prolonged period to achieve all three aims. If we got the early stages right it might actually be quite some time before the culture we are studying put two and two together and they could probably remain in denial for decades or even longer if that was better for them.
    If noticeably more advanced than us, again, study cautiously to assess the situation before deciding on initiating formal contact, in the unlikely event that they are not already fully aware of us and waiting for us to turn up in our own time.

    Current thinking on procedures and policies around extra-terrestrial contact are, understandably, focused on radio contact as part of SETI or someone else turning up here. An overview and references can be found at:


    There probably isn’t any great rush to develop these protocols to incorporate scenarios where we turn up there, but that may well need to be done at some stage.

    The above is just my initial thoughts on the matter – inevitably they will be at best incomplete and I may well be missing something very important here or got something completely wrong (it has been known!) A very interesting topic, as always, and any thoughts much appreciated.

    • J. Jason Wentworth May 23, 2018, 7:27

      Bracewell thought a lot about the political and even military implications of a probe making contact with a planet with multiple, rival powers (as I covered in the article; his book “The Galactic Club: Intelligent Life in Outer Space” goes into more detail), and those considerations led him to the “on-the-same-frequency-echoing” strategy, because it would encourage co-operation among the rival powers. He also suggested that method because it neatly avoids the “What frequency do we use?” problem; if the probe hears artificial signals on a given frequency, it knows that others are listening on that same frequency, which it can then use to make contact.

  • Harry R Ray May 21, 2018, 10:12

    Paul Gilster: I know that you are swamped, but you just HAVE to check this one out PRONTO!!! According to F. Namouni and M. H. M. Morais(Monthly Notices | Letters of the Royal Astronomical Society https://doi.org/10.1093/mnras/sly057. “An interstellar origin for Jupiter’s retrograde co-orbital asteroid”)(514107) 2015 BZ 509 joins `Oumuamua as a PROVEN object of an origin SOMEWHERE OTHER THAN our solar system. The reason I am postig this comment HERE is that despite being discovered in 2015, I have been UNABLE to locate ANY INFORMATION WHATSOEVER about its size, albedo, or chemical composition! Its discoverers designated it as an asteroid, but left open the possibility of it being a comet, or something else altogether. If it is of natural composition, it must be considerably larger than `Oumuamua, but if it is a ~100% reflective Bracewell probe, it may be considerably SMALLER! READERS OF THIS WEBSITE: Please help me out with ANY information regarding the size, albedo, and composition of this object by posting a comment about it on this blog. Thank you!

    • ljk May 21, 2018, 15:45

      This article confirms that 2015 BZ 509 is quite unusual, but there are still questions about it being interstellar in origin:


    • ljk May 21, 2018, 15:48

      Here is a working link to the paper:


      • Al Jackson May 22, 2018, 6:25

        You know this paper does bring up the question : Where does one store a ‘instrument’ in a planetary system in a long term observations (millions of years) an orbit that is stable?
        Burying it on the Moon , as in 2001, sure would work, but that one is not in an orbit.
        The Monolith around Jupiter is surely in an unstable orbit , but then the Monolith Makers would provide the magical tech mojo to keep it there (after all seems they have a traversable wormhole instrumentality).

        • Alex Tolley May 22, 2018, 12:38

          As you know, in the first novel, the monolith was on Saturn’s moon, Japetus (Iapetus).

          However, given the monolith’s eventual capabilities, maintaining an unstable orbit around Jupiter might be the least of its functions. ;)

          • Marshall Eubanks May 24, 2018, 11:37

            In the book for 2010, Clarke makes the point that, because the Monolith is still in orbit at a Io Lagrange point, it must still have active control, as that orbit is not stable over several million years.

            • ljk May 24, 2018, 14:30

              We know the Monoliths can last for at least four million years in working order and no doubt for much longer, as Earth certainly was not their first assignment by their makers.

      • Harry R Ray May 22, 2018, 9:53

        One thing that shocks me is that MAJOR(GROUND: Keck, VLT. SPACE: Hubble, Spitzer)telescopes were NOT pointed at such a strange object IMMEDIATELY after its discovery in 2015 to get at least some BASIC INFORMATION on its composition to compare it with that of Jupiter’s trojan asteroids. I am SURE that that is about to change, so even if it is later proven NOT to be of interstellar origin, we can get some sense of where it came from in our solar system. Until then, everyone should take the “3 kilometers wide” reported size with a VERY SERIOUS grain of salt! ALSO: I can’t wait to find out if there are any MAJOR variations in its light curve, like in `Oumuamua’s which could point to an unusual SHAPE for it(like `Oumuamua’s either cigar or Millennium Falcon-like shape).

  • James Stilwell May 21, 2018, 10:17

    “Curiosity killed the cat” is a proverb used to warn of the dangers of unnecessary investigation or experimentation. A less frequently-seen rejoinder to “curiosity killed the cat” is “but satisfaction brought it back”.

    The question should therefore be: Lets’s have a vote on this whole idea before we all get ourselves killed…

    • Alex Tolley May 21, 2018, 14:55

      The problem with using proverbs is that you can find one to suit any occasion.

      So let me counter with: “Fortune favors the bold”.

    • J. Jason Wentworth May 23, 2018, 7:32

      I’ve always liked the one (I forget who coined it, but it was a famous person–maybe Benjamin Franklin?) which says (in response to “Curiosity killed the cat”): “Ignorance killed the cat, sir. Curiosity was framed.”

      • Michael May 25, 2018, 9:35

        “I’ve always liked the one (I forget who coined it, but it was a famous person–maybe Benjamin Franklin?) which says (in response to “Curiosity killed the cat”): “Ignorance killed the cat, sir. Curiosity was framed.”

        From the cat’s perspective it could have been Schrödinger or Ignorance, both are equally catastrophic ;)

  • Harry R Ray May 21, 2018, 10:36

    UPDATE: According to an article in “scientific American”, (514107) 2015 BZ509 is three kilometers wide. ALSO: Scenarios ALTERNATIVE to the interstellar one have emerged, the ELEGANT one being that it IS of solar system origin but had a VERY CLOSE ENCOUNTER with planet nine BEFORE it encountered Jupiter, and the CONTRIVED(in my opinion)one being that it is a remains of a collision between two much larger asteroids which then had a very close encounter with Jupiter.

  • ljk May 21, 2018, 13:22

    Beam propulsion background and Breakthrough starshot update

    brian wang | May 18, 2018


  • Charley May 21, 2018, 14:13

    Many natural organisms have the ability to repair themselves. Now, manufactured machines will be able to mimic this property. In findings published this week in Nature Materials, researchers at Carnegie Mellon University have created a self-healing material that spontaneously repairs itself under extreme mechanical damage.

    This soft-matter composite material is composed of liquid metal droplets suspended in a soft elastomer. When damaged, the droplets rupture to form new connections with neighboring droplets and reroute electrical signals without interruption. Circuits produced with conductive traces of this material remain fully and continuously operational when severed, punctured, or had material removed.

    Applications for its use include bio-inspired robotics, human-machine interaction, and wearable computing. Because the material also exhibits high electrical conductivity that does not change when stretched, it is ideal for use in power and data transmission.

    “Other research in soft electronics has resulted in materials that are elastic and deformable, but still vulnerable to the mechanical damage that causes electrical failure,” said Carmel Majidi, an associate professor of mechanical engineering. “The unprecedented level of functionality of our self-healing material can enable soft-matter electronics and machines to exhibit the extraordinary resilience of soft biological tissue and organisms.”

    Read more at: https://phys.org/news/2018-05-self-healing-material-breakthrough-bio-inspired-robotics.html#jCp

  • DCM May 21, 2018, 17:09

    If the probe does encounter aliens capable at least of radio/tv communication it should be programmed to relay their messages, not tell them where we are — even if it’s so long from now our position is changed and so far away messages take 10,000 years to reach home.

    • J. Jason Wentworth May 23, 2018, 8:14

      In Bracewell’s concept, that would defeat the whole purpose of sending such probes, which is to facilitate direct planet-to-planet communication between other civilizations and ours. He wrote that other, older civilizations would likely send probes to us first, and he suggested that if decades went by with no contact, humanity should take the initiative and dispatch its own probes, because this would indicate that our nearest neighbor is more distant than had been thought, and:

      After the ability to detect biosignatures telescopically was developed, the number of target stars, while probably still large, could be greatly pared down by sending probes only to promising ones. Systems lacking such worlds could be explored via probe “as we got around to it” (some would be promising places to set up O’Neill-type colonies that could be built using local materials).

  • ljk May 22, 2018, 13:41

    Should We Stop Looking for Intelligent Life?

    What if it’s too intelligent?

    By Joelle Renstrom

    May 21, 2018

    As the first asteroid confirmed to have originated outside the Solar System whizzed by at roughly 85,000 mph, scientists scrambled unsuccessfully to figure out some way to catch up to it. Was it different from the asteroids in the belt between Mars and Jupiter? Was it even an asteroid? What if it was some kind of technology designed by an alien race?

    The Breakthrough Initiatives program observed and gathered data from the asteroid, but found no evidence of life or signals indicative of technology. For all we’ve learned about space, the more we realize we don’t know, especially when it comes to aliens.

    Full article here:


    To quote:

    The best option — at least, the best one the humans in Liu’s book come up with — is to make noise. It’s risky, as it reveals Earth’s location, but if it also reveals another civilization’s location, then the other inhabitants of the dark forest have a choice to make. Which race do they attack? And how do they know their coordinates won’t also be revealed? Is it worth the risk? Such questions underscore the deterrent possibilities of Dark Forest Theory, as well as the chance that nothing will deter an attacking race.

    In Shostak’s mind, we’re right where we’ve always been: Earthly members of a massive, intergalactic dark forest. The dark forest has, ostensibly, been populated for billions of years — that hasn’t changed. What has changed is our awareness of our relative smallness and vulnerability, as well as the precariousness of all life in the universal grand scheme of things. But such awareness doesn’t change reality or the odds of an alien civilization attacking.

    “Yes, anything’s possible. But that doesn’t mean that everything’s plausible,” says Shostak. “Sure, Martians could mount an attack on Earth in the near future. But that’s one worry that won’t keep me awake at night. Nor should it trouble you.”

    • ljk May 22, 2018, 13:45

      For more on the Dark Forest Rule, read here from Winchell Chung’s excellent site on aliens:


      • Alex Tolley May 22, 2018, 18:55

        Cixin’s logic fails as there are more options. Humans have managed to deal with different civilizations, and it works by preventing a single shot encounter with a “prisoner’s dilemma” result through multiple, iterative encounters so that mutual trust can build.

        There is no a priori reason to believe alien civs will not find the same value we do from cooperation rather than warfare.

        IOW, I find that argument bogus. Fine for a story premise, but not the real universe.

        • ljk May 23, 2018, 9:08

          That is the key problem when dealing with science fiction as guidelines for the various scenarios our encounters with ETI might take. Their stories need conflict and characters we either root for or hate as well as action.

          Some authors like Stanislaw Lem can turn encounters with ETI into fascinating philosophical discussions, but most do not or cannot. It gets even worse with film and television.

          I am not saying SF does not have its value when it comes to comprehending ETI, but we must keep in mind their first priority is to tell a story that people want to pay for and read. In most cases that means something they can chew and swallow. Even Winchell Chung’s great site on aliens and relevant technologies all come from the premise of RPG interstellar space battles and empires.

    • J. Jason Wentworth May 23, 2018, 8:01

      That was a trope of the original NBC miniseries “V,” starring Marc Singer and Jane Badler. The Visitors, from Sirius, were not here to help us, but to help themselves to our world and its resources, life, and water. Being unable to directly fight them, a scientist sneaked into a radio telescope facility and beamed a message to the Visitors’ enemies that said, in so many words, “Your enemies are here, where you can get them. By the way, please keep in mind who helped you find them.”

  • AlexT May 23, 2018, 8:35

    Some notes about listed propositons in this publication.
    1. Relatively to “Long wire” antenna design, this antenna has done gain and some reason for use on frequencies lower than 10MHz, on higher frequencies there it loose efficiency dramatically, and there is much better and smaller sized antenna’s designs with the better gain.
    Frequencies , where this antennas will work somehow, i.e. lower than 30MHz are bad choice for interstellar communication, because are blocked by atmosphere…
    For interstellar comunication usually used VHF/ SHF EM bands i.e. higher than 300MHZ – does to objective causes (less influence of earth’s atmosphere). On those frequencies long wire antenna design is almost equal to NO antenna at all, so it is huge nonsense to build any plans on “long wire” use, because you cannot use it.
    2. Relatively to Digital TV advantage for ETI communication.
    I am sure that our modern Digital TV implementations (and we do not know alternatives) – make probability to be decoded by ETI equal to zero, it is impossible to decode any digital data transmission without knowing multiple “hidden” parameters, for example ETI shold know in advance what is the next parameters:
    2.1 picture size (vertical and horizontal resolution)
    2.2 Which parameters are coded in data stream
    2.3 Signal modulation
    2.4 Data size (8, 16, 24 or 32 bits) bitstream and bytestream organization (bigendian or lowendian
    2.5 Error correction code algorythm, organization and principles.
    2.6 Image compression and coding algorythm
    2.7 etc., etc., etc.
    For Analog TV pargraphs 2.1/2.3 can be detected by simple analizing of received signal, all other data – is not existing and not needed for ATV decoding…
    So hope to use the DTV for the first contact with ETI – is nonsence, we how to send them the TV set for reception of our signals…
    3. The idea to tramsmit probe signals on the detected frequencies of broadcast stations , too not so good, because if will take as example our own radio / TV broadcast – it only transmitting service, and broadcasting stations have very high signal power (tens of kilowatts or megawatts) so to make probe’s signal somehow detectable , probe have to have comparable RF power…
    It is possible to interfere some dual side simplex or duplex sistems, but probe should have very developped intellect to make proper analyze..

    • J. Jason Wentworth May 24, 2018, 3:46

      I don’t know what “done gain” means. Also, I never mentioned–or even implied–specific signal modulation methods, including DTV–you inferred that (I only mentioned frequency bands to give terrestrial examples, such as our FM and TV bands). A probe would monitor for narrow-band signals, which would most likely be artificial (I know that other schemes such as frequency-hopping are now used on Earth, but the probe’s computer could analyze the patterns to emulate the local modulation method or methods), but:

      In the beginning, though, all it would have to do is echo what it heard, and it–and the aliens–could do quite a bit of communicating using this echoing method, even before they understood each other’s languages (I covered these in the article). As well:

      My purpose for mentioning the possible use of long wire antennas (they aren’t the only possibility for communication) is the severe payload mass limitation. Accelerating a probe up to even “just” 1 percent of the speed of light requires a lot of energy, and even more if the probe is to brake into orbit around the target star. For this reason, it is prudent to utilize onboard systems for multiple purposes wherever possible, to keep the probe’s mass as low as possible. In this connection:

      A Bracewell probe has to listen for local intelligent radio signals around its assigned target star. These signals could be on any frequency or frequencies (on Earth, for example, it’s between ~1 MHz and many gigahertz, for signals that can pass out through the ionosphere and into space), so the probe’s antenna system must be able to pick up signals over a very wide frequency range. This capability would also be very desirable for Voyager-type radio science observations of the star and its planets, and:

      A spin-deployed-and-rigidized electric sail (E-sail: http://en.wikipedia.org/wiki/Electric_sail ) could be used for braking the probe into orbit around its target star (or–depending on the mission’s scope and cost–it could brake the probe enough to allow a sufficiently-slow fly-through of the system). For both types of probe (rendezvous [stellar orbit] and fly-through), the E-sail would also enable in-system maneuvers (to conduct close flybys of promising planets, for example). An E-sail might also be able to function as an electrodynamic tether (see: http://en.wikipedia.org/wiki/Electrodynamic_tether ), producing a Lorentz force by interacting with the interstellar magnetic field, perhaps by selectively charging a few wires in the array, in turn. Also:

      Both of these groups of functions (radio monitoring/alien contact/radio science and braking/in-system maneuvers) could be catered to by *one* onboard system, a “wagon wheel” E-sail that would be suitably multiplexed to serve as both a stellar wind sail (and possibly also an electrodynamic tether array) and an antenna array.

      • AlexT May 25, 2018, 9:56

        >”what done gain means”
        My apologies, for multiple misprints (ipad’s autocorrection + plus virtual keyboard + my poor English together)…
        I meant Long wire antenna has SOME gain up to frequency approximately 10 MHz.
        In addition Homo Sapiens does not know, how to build efficient antenna for wide frequency range from 1MHz up to Gigaherz.
        We do not know the way. Most efective designs are based on some lenses or special form reflectors (like in light optics), but even in this case design is relatively narrow band. If you want to have good communication parameters you cannot save money on antenna design, in this case – no communication and no antenna will be more efficient way to save money. Long wire is mostly surrogate antenna design, worst case, and will not work anyhow on frequencies higher than 30MHz , on Gigaherz – it will be joke.
        In connection to digital TV (DTV) , I understood your text so , that you suppose DTV will be easier to decode by ETI than analog TV signal, may be I misunderstood your phrase about DTV, but in any way I suppose none can decide and extract usable information from any of multiple variants of DTV standard used on our planet without long and careful study of related technical documentation, it is not good for the «First Contact” with ETI, DTV usage on the first stage means – no contact at all.
        ATV and DTV in most countries around the globe uses same frequency , DTV broadcast is invented to replace ATV broadcast to use dedicated (same) frequency spectrum more efficiently, but it is in any way not easy to decode. In sddition ATV and DTV uses the same channel bandwidth, so I do not understand what the advantage you meant writing about DTV against ATV.

  • Roger May 23, 2018, 9:09

    A lot of these METI arguments assume one alien civilistion at a time. If a civilistion is long lived it will have come across potential many other civilistions in the Galaxy. It would have seen what happens when you make first contact vs observation only. I am thinking a civilisation will try harder, go further and make novel new science and technology if left alone to fourish. In the face of that evidence the long lived civilisation would prefer to generally leave uncontacted civilisations along, for the good of the Galaxy. If they expand and explore then you can roll out the welcome Mat, you have no choice, but until then live and let live. A civilisation that’s contacted will devote a larger and larger amount of resources trying to communicate and understand the older civilisation. It’s not useful compared to their natural development path and will lead to sub-optimal outcomes for both parties. If a new civilisation goes out and explores the Galaxy, they will naturally join the Galactic Club. Can’t do that by sitting at home and keeping quiet.
    It’s kind of like feeding the Dolphins at Monkey Mia here in Western Australia. The Dolphins have been comming for decades to be fed by people at the same spot at the sea shore, but the researchers found that the mothers who were hand fed stopped properly attending to their calfs. Here are five reasons why you should not feed dolphins in the wild:
    1.It Alters Dolphin Behavior
    2.It Can Lead to the Transfer of Zoonotic Diseases
    3.It can Lead to Injury (and Death)
    4.It Results in a Higher Dolphin Calf Mortality Rate
    5.It Gives out a Conflicting Conservation Message
    Is there an alien knowledge bank out there with similar advice, warning of contacting young civilisations?

    • Alex Tolley May 23, 2018, 11:43

      So the expansion of historic cultures, especially the global European expansion was a “bad thing” in the long run and all those stone age cultures were stopped from their natural development?

      There are both positive and negative impacts of cultural contact by more technologically advanced cultures. While we might lose something from contact with the galactic club, we will also gain benefits too.

      I would suggest that the Chinese self imposed isolation during the Ming dynasty is a salutary lesson about retreating from outward cultural contact.

      • AlexT May 23, 2018, 12:52

        We do not have any evidence of existence any ETI.
        There is radically opposite case with Chinese , they knew who live around their country and could study other (modern to them) civilizations and had pretty similar or more advanced cultural, technical and intellictual level , most time , “western” civilization was barbarian for Chinese, so your example is not correct in any way, radically different situation.
        I suppose if we could accept your arguments, we should conclude that ETI behaving exactly like Chinese in medieval ages :-)

        • Alex Tolley May 23, 2018, 15:05

          The Chinese did not have knowledge of the whole earth, just the explored bits. So they could not know whether an advanced culture was in existence. As it happened, European culture underwent rapid technological progress so that they did become advanced in a relatively short time horizon. The Japanese, similarly self-isolated were somewhat surprised by Perry’s ship when it arrived in 1853. Did the new engagement by Japan of the West not offer many benefits to Japan?

          The counter argument to yours is that an advanced culture would have contacted them, or at least one of the other cultures they did know about. But this is exactly the argument that anti-METI proponents ignore to make their case that advanced, predatory civs can be avoided by keeping quiet in the jungle.

          It is often joked that making false negative (type II) errors is far more deadly than making false positive (type I) ones. (Is that rustling in the grass a lion?) This seems to be the basic anti-METI argument. But civs are not individuals facing unknown dangers, but rather ones that can make many different approaches. Even where we think there is huge technological advantage (e.g. humans killing bugs with antibiotics) we know that evolution will eventually find ways to stymie that advantage. The US experience in Vietnam or Afghanistan is perhaps a more appropriate example.

          Then for laughs, I recommend Arthur C Clarke’s short story Superiority. It has relevance even today.

          • ljk May 23, 2018, 16:43

            Here is Clarke’s story online:


            I am also reminded of the “Star Wars” (SDI) program in the 1980s, which had plans for all sorts of fancy space weapons to stop incoming enemy nuclear missiles, including laser cannons and such.

            It was soon pointed out that a bucket of sand or pebbles released into Earth orbit moving at 18,000 MPH could do some pretty good damage to a satellite and for a lot less money.

            • AlexT May 24, 2018, 3:13

              This novel is another onr implementation of plot based on “good , old” aphorism – “Perfect is the enemy of good”.
              I cannot catch what connection this play of imagination play has to reality and our discussion, sorry.
              Present time it is very funny to read about supercomputer, that was built using thousand of vacuum tubes and requires 5000 of technical personall, to keep it in working state :-) Very actual, for modern reader , and explains well why Homo Sapeins will defeat every stupid ETI :-)

          • AlexT May 23, 2018, 17:16

            Sorry, I see that we have totally different point of view on the Chinese civilization, so this your argument, proves different things for you and me … Same about other your examples from human history.

            Wandering, what is the science facts that make you sure that ETI will bring us hapiness and prospers ?
            As well as I know, there is no facts at all.
            So I fully support METI pessimisitc arguments, and cannot accept your’s , even if some was writen by A.Clark , I like his science fiction books, but do not accept those books as the Bible :-)
            All live organisms on the Earth including Homo sapience are not good creature to met , so there is no chance that ETI could be better, meanwhile we have only our own example and it is bothering, but it is only real scientific fact.
            All other religious and philosophic Utopias, are not based on any real fact , only wishfull thinking.

            • Alex Tolley May 23, 2018, 23:11

              I think you are quite a pessimist.

              All live organisms on the Earth including Homo sapience are not good creature to met

              And yet we interact with both wild and domestic animals. There are even tours to get you acquainted with the non-dangerous ones in the wild.

              Humans are dangerous, yet here we are, with an integrated global community with the lowest per capita murder rate in history. All built on trust.

              Warfare is immensely destructive, not just to things and people, but economies and even the social fabric. Britain was the major global power in the 19th century, but was a shadow of its former self after 2 world wars. The Axis powers, Germany and Japan, are partly where they are today because of the huge amount of economic help the USA provided after WWII. The asymmetry of warfare approaches in Vietnam resulted in economic stress in the USA, as well as helping foment the civil unrest. Afghanistan is proving similarly unwinnable, racking up costs, although thankfully not US bodies.
              The irony of Vietnam is that while it is a Communist country, it is engaging with the world and growing rapidly as a low cost, manufacturing nation.

              The European Union, which Britain is now exiting was conceived as a way to prevent more bloody wars in Europe. Whatever the difficulties, that has been remarkably successful.

              If you cannot see that cooperation, even after conflict, is beneficial, then I can’t help you.

              what is the science facts that make you sure that ETI will bring us hapiness and prospers

              I didn’t say anything about happiness. One would have to be blind not to notice the unhappiness that has accompanied the economic growth that we have had.
              But let us consider this [Faustian] bargain with ET. Cooperation results in a hugely expanded solar system economy, but perhaps not a happy one, as depicted in the tv series of “The Expanse”. Humans are vastly richer, living as a multi-planet species, perhaps working with technologies that are also very dangerous, like the “proto-molecule”. I personally, would accept that bargain, rather than retreat from it. Is there a risk in trying to engage with a civilization that is highly dangerous? Yes, there is. We may be facing such a dangerous civilization right now with predatory, transnational corporations, some of which will soon be AI driven. Should we stick our heads in the sand and hope they leave us alone? No, I don’t think so.

              Earth’s history has shown us that species interaction and even clear cooperation has resulted in complex, highly rich ecosystems. The history of the human species has shown that cooperation, rather than aggression, has been hugely beneficial for the general welfare of the population, even if not evenly spread. Since we must assume that life elsewhere in the universe is based on Darwinian principles, I see no a priori reason to doubt that ET will have learned the same lessons. There might still be predatory civs out there, just as 13th century Europe faced destruction by Genghis Khan, and arguably Nazi Germany in the 20th century. I accept that maybe we are just experiencing “survivor bias”, but I think it is quite obvious that population welfare has benefitted from peaceful cooperation. For teh pessimist, let me say that even domesticated food animals and plants have benefitted from human control. The most abundant species are those that we have domesticated and those that have learned to adapt to our human manufactured environment. If we are but rats to ET, then I say bring on those interstellar ships to stow away on and let us spread throughout the galaxy. At least that ensures we no longer have to worry about an asteroid causing an extinction event!

              • ljk May 24, 2018, 11:34

                It is a sign of the times. Any optimism about an unknown like aliens is automatically considered naïve and dangerous.

                I worry about an alien invasion or attack about as much as I do an earthquake. It is not likely to happen where I live and if one does take place, there is darn little I can do about it anyway.

                And yes, if an advanced ETI wanted to take out humanity, they could do so with relative ease and there is blessed little to zip we could do about it. Forget all the SF alien invasion films you have seen. Most of them assume aliens would land in big ships with troops toting laser rifles.

                What I do know is this planet is infested with “carbon units” that are just learning how to be civilized but as still painfully tribal and on the edge of destroying themselves and much of an otherwise beautiful planet in the process every day.

                • J. Jason Wentworth May 24, 2018, 22:27

                  I’ve never accepted the self-derision toward humanity. Only human beings can prevent another impact like the one that wiped out the dinosaurs, and they have taken steps to detect potentially hazardous objects and formulate effective defenses against them. Also:

                  I wouldn’t agree that humanity is on the edge of destroying itself. In my lifetime, the numbers of nuclear weapons have gone down dramatically, and the would-be new nuclear powers (Iran and North Korea) aren’t anywhere near the same league as the U.S. and the former Soviet Union. May people could be killed, to be sure, but the specter of human extinction doesn’t loom over the threat they represent. Even India and Pakistan (who have fought three wars and are now nuclear powers) prefer to fight over conference tables now, and not even because they fear total mutual nuclear destruction; they both know that their growing prosperity, which took decades to achieve, would be instantly bombed back into abject poverty, misery, and famine if they fought even a limited nuclear war, and:

                  Regarding the Earth, it’s a problem of room–fewer human beings will open up more room for other, non-agricultural plants and animals. The human population is still growing, but the rate of growth is slowing, so much so that demographers are warning–as if it’s a bad thing!–of a coming fall of the world’s population. When I was born, the world population was about 3.39 billion, which was plenty. Increased education (including of girls), prosperity and improved health care (which make large families unnecessary, because children are more likely to survive), and the empowering of women are driving these positive trends. I have seen many (secular) apocalyptic predictions of doom from one thing or another come and go during my lifetime, and given their perfect (null) track record, I’m sure that the current “dooms du jour” will join them in the “Whatever happened to…?” articles of the future.

                  • ljk May 25, 2018, 9:20

                    We may have dropped considerably from a peak of about 55,000 nuclear weapons globally circa 1989, but that is still more than enough to destroy civilization and return us to a state of barbarism indefinitely.

                    Details here:


                    I do not want to be a doom-and-gloom guy. I too grew up during the Cold War assuming every day at any moment there could be a nuclear war. That we are still here is perhaps nothing short of a miracle, though people wanting to stay alive and keep all their stuff probably played a role in this, too.

                    • J. Jason Wentworth May 26, 2018, 8:49

                      We’ve already had one dark age, and overcame it. Civilization destruction is far less dire than human extinction (although I’d rather avoid both, of course). My only fear regarding nuclear weapons is terrorist-acquired ones, but that doesn’t keep me from sleeping, for the same reason the possibility of an unseen Tunguska-like comet (or asteroid) hitting us doesn’t–there’s nothing that I can do about either one, and I take solace in the statistics concerning both.

                  • hiro May 25, 2018, 18:14

                    Let’s discuss about this topic again on Dec 31st 2029, if I’m still alive.

                  • AlexT May 26, 2018, 2:43

                    I am sure that human extinction or self destruction is much more (orders) probable than any METI.

              • AlexT May 26, 2018, 2:24

                Yes, me too know well the hippie’s phrase: “make peace, no war!”
                I suppose that your note about “lowest per capite murders rate” cannot be proved by any science statistic, because we do not have this statistic, I am sure it is propaganda, but not science :-) There is no wars , no any criminality and drugs traffic in your ideal world, I am sure in this world ET should be imginated only like Budda or Jesus Christ and they go to sleep with K.Marx’s “the Communist Manifesto” laying near the bed :-)
                I agrre it is the good plot for fiction book, every one want to live in Paradise.

                • Alex Tolley May 26, 2018, 17:18
                  • AlextT May 29, 2018, 9:47

                    Sceintific statistic in 13 century, good to know.
                    By the way me too can suppose that number of people murder by inquisition is decreased dramatically in 20-th century.
                    Who cares about WW I and WWII , GULAG, Moaists, Pol Pot, Ruanda, Siria? Our statistic is perfect.

  • ljk May 23, 2018, 9:57
    • J. Jason Wentworth May 24, 2018, 12:02

      The MLT (Mach-Lorentz Thruster) wasn’t shown to not produce thrust, though (although they think it was probably “noise”). A sounding rocket flight would enable it to prove itself–or fall flat on its face. A payload with nitrogen jets could orient itself in different directions with respect to the Earth’s magnetic field, to ensure that the MLT isn’t acting like an anemic magsail (the Cannae Drive could also be tested in this way).

  • Geoffrey Hillend May 23, 2018, 16:27

    From what I recall from my electronic and CB radio buff brother, a lower frequency always corresponds to a longer wave length so the antenna must be longer for a lower frequency. 4 MHZ requires a 100 foot long antenna since the wavelength is really long to get the most efficiency of that frequency. CB and wakie talkie frequency is the 11 meter frequency or between 26 and 27 MHZ. Cell phone frequency is at 900 MHZ or 33 centimeters. Consequently, if we use a higher frequency, then it must be a shorter wavelength, so it needs only a small antenna like our cell phone. A radio signal still needs high energy to be sent from another star system which is why higher frequencies in the optical range of EMR have been considered.

    • AlexT May 24, 2018, 1:08

      You recall correctly, we also have to take in account that – as you have longer wire , you have higher electricsl losses and also losses in metall is increased with frequency, so using long wire antenna are limited to narrow frequency range laying in the area that is not used for space communication due to blocking by Earth atmosphere (so we can suppose will be blocked too on other planets ) .
      So summary using long wire as antenna for interstellar communication is technically wrong , we know to build much smalle and more effective antennas.

    • AlexT May 24, 2018, 1:19

      “higher frequency, then it must be a shorter wavelength, so it needs only a small antenna” – I forgot to mention, that this your phrase is correct , when you set one condition, when we talking about antennas with the sane gain!
      Because we can build on higher frequencies antennas that have very high gain (for example, using optical approach – i.e. parabolic mirror), but long wire is not used because it has high losses and also serious problems with effective energy transfer from amplifier to antenna (matching).

      • J. Jason Wentworth May 24, 2018, 11:06

        For decades, ham radio operators have used single end-fed long wire monopole antennas worked against RF ground (and also doublet antennas–these look like dipole antennas, but naturally resonate on multiple frequencies), and both end-fed and doublet antennas can be resonated on even more frequencies by using variable matching networks. Now:

        These antennas are used when hams only have room for *one* (usually outdoors) antenna. These antennas’ patterns change as they are used on different frequencies, but they are perfectly practical, and as higher frequencies are used, the signal increasingly is emitted in the direction of the end (or ends, for a doublet) of the antenna (likewise, they are increasingly sensitive to signals arriving at their ends, as the receiver is tuned to higher frequencies), and:

        A Bracewell probe is in a situation like that of the “real estate-deficient” hams–it must be able to receive and transmit over a wide frequency range, but it can’t spare the space–or the mass–for multiple antennas. The E-sail wires, being miles long but thin (and “self-healing” E-sail wires are under development, to deal with dust impacts), are lightweight, stow compactly, and they can receive and transmit over a very wide frequency range. At the highest frequencies, they are highly directional (and the USAF perfected electronically [via switching between multiple antennas on a spinning satellite] de-spun satellite antennas in the 1970s), so this single system could fulfill multiple functions, which is important on starprobes, where mass is at a premium.

        • AlexT May 24, 2018, 14:54

          Please read carefuly my notes about long wire antennas, it give you full information about when and how and long wire can be used and when it is working exactly like absolute absence of any antenna…
          By some occasion I am licansed Radio Amateur (HAM) since 1985 , so can suppose what explained about Long Wire antenna in ARRL book, and suppose it is not exacly what you write in your topic, sorry.
          Long wire antenna is not used on the frequencies that are used for the space communication is working present days , and this frequency range choice , that was maid by NASA and every other space agency on the Earth is natural, I am sure ETI will make the sane choice.
          So even if you have lot of long wires used for some other purposes, but if you want to have good RF communication with the probe, you must choose different antenna design, it will have much smaller size, in same time much higher gain and much better directivity.

    • J. Jason Wentworth May 24, 2018, 2:40

      Geoffrey, your brother is absolutely right, but there is more to it than that. Yes, the minimum resonant length of a monopole antenna, worked against an RF ground, is 1/4 wavelength (or 1/2 wavelength for a dipole, the two “legs” of which are each 1/4 wavelength long). BUT:

      As Reference 33 explains (ARRL Antenna Book, pages 13-1 and 13-2 in Chapter 13, “Long Wire and Traveling Wave Antennas” [see: http://www.qrz.ru/schemes/contribute/arrl/chap13.pdf ]), as an antenna is made longer and longer, the signal lobe increasingly “fires off” the end of the antenna (the receive pattern is identical), making it more and more directional. (The same effect occurs if the antenna length is held constant, and the transmitter and/or receiver is tuned to higher and higher frequencies.) Beverage antennas, which are wire antennas many wavelengths long, utilize this “end-fire” effect, and:

      This effect has been observed (sometimes accidentally, as Kirk Kleinschmidt related in his “Stealth Amateur Radio” book: http://www.amazon.com/Stealth-Amateur-Radio-Operate-Anywhere/dp/0872597571 ) with other antennas. After one ham, using a club’s station, had talked with another on the 2-meter band, he called the same distant ham on 2 meters, after accidentally connecting his transceiver to the club’s huge 160 meter band dipole. The distant ham asked if he was using a high-power linear amplifier, because his 2 meter signal was blasting in–but it was only the “bare” 2-meter rig’s signal being fired off the ends of the 160 meter dipole, one end of which pointed right at the distant ham’s location. As well:

      The spin-rigidized, “wagon wheel” E-sail’s wires on the probe would be *miles* long (see: http://www.google.com/search?ei=GV4GW4_ZGvy80PEPlM2h6Ao&q=solar+wind+sail&oq=e-sail&gs_l=psy-ab.1.1.0i71k1l8.….0…1..64.psy-ab..0.0.0….0.WIJFHCOKZAY ), making them excellent “end-fire” directional antennas over a very wide frequency range. They could be electronically de-spun (using solid-state switchers; the USAF’s DATS–De-spun Antenna Test Satellite, and several of their LESs–Lincoln Experimental Satellites–perfected this technology in the 1960s and 1970s [and some of these LES satellites are still functioning today!]). These long wire antennas can be either current-fed (as is usually done, because the feedpoint voltage is much lower) or voltage-fed; with the “wagon wheel” E-sail configuration, opposing pairs of wires could be current-fed, making them doublet antennas.

      • AlexT May 25, 2018, 10:24

        I suppose you are using only partial information from ARRL about antenna design…
        As you have Longer wire – you automatically higher active (and reactive too) losses in this wire, so after some small limit your gain will be totally compensated by losses.
        In addition there is one important problem with any antenna – it have to be matched with receivers/transmitter electronic circuit, and this is main problem when someone build communication system. Oversized antennas (i.e. those that have size that is integer multiple of 1/2 wave length) are used sometime as compromise or stealth antenna, but if I understand correctly we are talking about serious scientific mission.

      • Jose D. May 25, 2018, 10:42

        As you apply longer wire you automatically have higher active (Ohmic) losses in this wire, on some point increasing of wire length will not give any signal improvement, even opposite – will cause additional loses.
        In addition , every antenna should be perfectly matched with load (in our case receiver or transmitter), if it is not matched significant part of EM energy from this antenna will be radiated back to the space, part of this energy will be lost in matching circuit.
        This two facts explains why Long Wire antennas mostly used as surrogates in emergency situations or as stealth solution by partizans…
        It is not good solution for serious scientific project.

        • J. Jason Wentworth May 26, 2018, 0:48

          This is the last comment I will make regarding my proposed antenna/E-sail arrangement for spin-stabilized Bracewell probes, because this is Paul’s bandwidth that we’re using, and this is Centauri Dreams, not an antenna theory forum:

          If you read up on Beverage, long wire, and extended Zepp (Zeppelin) antennas, you will find that long wire antennas–Beverages are extremely long with respect to their highest operating wavelengths–are quite effective and directional. In the past, Beverage antennas were used for scientific purposes regarding signal propagation (and they are still used by some short wave hobbyists and ham operators). The Grasswire antenna is a portable, also directional, stealth version of the Beverage antenna; it’s often just a long length of enameled magnet wire, laid right on the ground, and worked against either a ground rod or counterpoise wires laid out on the ground. Also:

          Many hams and some short wave hobbyists, due to necessity (lack of space, homeowners’ association restrictions on towers, etc.), use random length, end-fed wire antennas, which they use on many different bands by employing an antenna tuner. These antennas aren’t the highest-performing ones (except on bands where they’re naturally resonant), *but they work well enough*, and in this connection:

          There are auto-couplers (which are often computer controlled, sensing and remembering the frequencies used by the transceiver) which will load up any length of wire (either a single wire, or a loop of wire, even a small, multi-turn, “scramble-wound” loop of wire) to function as a transmitting and receiving antenna, on any HF or VHF ham band. These are used by stealth-operating ham operators who can only put up a length of wire around a fence, around the edges of a ceiling, or wherever they can. Many of these autocoupler-matched antennas are of mediocre performance, but again, they work sufficiently well. In addition:

          I am also a long-time crystal set (xtal set) radio experimenter. Xtal sets don’t use batteries; these radio receivers are powered by the radio signal itself, and (usually) use piezoelectric earphones or magnetic headphones (or high impedance) to reproduce the audio. Because of this, they require long wire antennas–the longer, the better, in order to collect as much energy as they can from the radio signal. A well-designed xtal set can even–if the transmitting station isn’t too far away–power a speaker, via an audio transformer, using only the power of the radio signal, and:

          This same effect–of using the power of the incoming radio signal itself, collected by the long antenna wires and amplified if necessary aboard the probe–would work equally well for a Bracewell probe monitoring local alien radio signals. A computer-controlled autocoupler (used in concert with an electronic de-spin antenna multiplexer, a technology the USAF perfected in the 1960s and 1970s with their DATS and LES satellites) would enable the probe’s kilometers-long E-sail wires to be utilized as directional, electronically de-spun wide-band long wire antennas. On many frequencies, these antennas wouldn’t be the ultimate in performance, *but they would work well enough*, which is what matters. Plus, speaking of long wire antennas on spacecraft (which operated at wavelengths far shorter than the antennas’ lengths):

          The Canadian Alouette 1 and 2 satellites (see: http://en.wikipedia.org/wiki/Alouette_1 , http://en.wikipedia.org/wiki/Alouette_2 , and http://space.skyrocket.de/doc_sdat/alouette.htm ) had two very long dipole antennas (up to 73 meters long), which were used for both a sweep-frequency (1 MHz – 12 MHz) VHF “ionosphere topside sounder” transmitter and a VLF receiver. The wavelength differences between VLF and VHF band signals are very large, yet the long dipoles worked at both VLF and VHF, and:

          There is a lot of information about antennas–actual, working antennas–that was learned many years ago through experimentation, but isn’t included in modern antenna books because standardized designs have been developed since the early days, and because some of the obscure designs were quite large. Because smaller, effective antennas for the same frequencies were developed later, the older designs became obscure. But older books, and older ham radio operators and short wave hobbyists (particularly those who like to experiment with antennas), as well as xtal set experimenters, have and use the information on these obscure antennas. A Bracewell probe has unusual antenna requirements, which the older, directional, wide-band, multiple-wavelength long wire antenna design fulfills. No, it’s not an ideal antenna–but it is simple, lightweight, compact to stow, and *it works well enough* for the job it must do.

          • AlexT May 27, 2018, 4:46

            “Canadian Alouette 1 and 2 satellites” – again, you are using example of satellites that use different antenna (dipole) type to prove what?
            Dipole it is not “long wire” antenna.

            • J. Jason Wentworth May 27, 2018, 12:09

              Okay…*now* we’ve reached the nexus of this problem, whose persistence, no matter what I wrote, was puzzling to me. It’s a matter of rather old and specialized terminology, which your posting revealed that you don’t know (I am ^not^ saying this to be dismissive, because *I* didn’t know these terms either, until I read up on them some years ago). I mention this because it is relevant to many past and current satellites and space probes:

              If an antenna is much longer than the minimum natural resonant wavelength *for the frequency or frequencies at which it is operated*, it is a long wire (or a long rod, as the case may be) antenna, as it was in the Alouettes’ case. Many ionosphere “topside sounder” satellites had/have such long antennas, which work with LF and/or VLF receivers (to monitor magnetospheric radio emissions) and with VHF, HF, and/or UHF sweep-frequency transmitters in the satellites (some Sun-orbiting probes and planetary flyby and orbiter spacecraft have also had such equipment), utilizing switchable connections in order to use the same long antennas with both sets of radio equipment aboard the spacecraft, and:

              A long wire (which is a type of monopole antenna) is worked against RF ground, while a doublet (a dipole derivative, which is a common multi-band antenna)–is a ^pair^ of long wires, fed in the middle just like a dipole (using open wire line and an antenna tuning unit), which are worked against each other (they are each other’s RF grounds, just like with a dipole). Any long wire antenna–whether a monopole, or a dipole derivative such as a doublet (and there are other types of dipole derivative long wires)–can be electrically shortened using a series capacitor (with an inductor connected across the feedpoint) “L-match” antenna tuning unit (or a variation of this using two series inductors, for a dipole derivative long wire). These requirements result in a spacecraft design compromise:

              In the case of VLF frequencies–where a 1/4 wavelength can be half a mile or more!–even a huge dipole derivative long wire (or rod) antenna, while it’s definitely a long wire/rod at the VHF frequencies of the ionospheric “topside sounder” transmitter that broadcasts through it, is actually electrically ^short^ at VLF frequencies. So the spacecraft designer uses the largest stow-able antenna that the spacecraft can accommodate, and electrically “lengthens” it with a loading inductor in the antenna tuning unit (this doesn’t make the short antenna as efficient as a full-size one, but it makes it efficient enough to do its job at VLF wavelengths). As well:

              Many satellites and space probes, including CubeSats, use both (non-long wire/rod) monopole and dipole antennas, both of which are “cut” for the operating wavelength (or wavelength band, especially if it’s a narrow band) of the onboard radio equipment. (As you know, the lengths are 1/4 wavelength for a monopole [the spacecraft’s body serves as the RF ground for the monopole, of course], or 1/2 wavelength for a dipole [with each leg of the dipole being 1/4 wavelength long, and with each leg acting as the other’s RF ground]) Also:

              The Alouette satellites’ long rod antennas (and those of many ionospheric sounding satellites, and some planetary flyby and orbiter [and solar orbiting] space probes with such radio science experiments) were/are actually doublets (or other types of dipole derivative long wires), not dipoles; they were called “dipoles” because a lot of people aren’t familiar with doublets or other dipole derivative long wires (mostly ham operators use such antennas, and not all of them, either), and because of their physical resemblance to dipole antennas. (A doublet [or other dipole derivative long wire] can also ^be^ a dipole, *if* one of the multiple wavelengths at which it is used–usually the lowest frequency–is such that the antenna is 1/2 wavelength long at that particular wavelength. The same is the case for a long wire monopole, if one of the wavelengths that it’s used at is one at which the long wire is 1/4 wavelength long.) These are but two options that could be used in Bracewell probes (these happen to also double as E-sail wires for electrostatic braking), but other arrangements and probe configurations would also work in modest, assembly line-manufactured interstellar messenger probes.

              • AlexT May 29, 2018, 4:27

                I see now you invents your own rules for this “game” ( describing what real “long wire” is according your own definition …)
                Sorry I am out of this game.
                I’ve wrote already in this topic my arguments, that are related not only to the term “long wire”, but also to wide band frequency usage from VLF up to VHF etc…
                Summary, “long wire” (whatever you mean it is) it is the bad antenna for the purposes you are describing in this topic and in reality it is not working in the way that you describing.

  • Marshall Eubanks May 23, 2018, 19:55

    The image is an artist’s conception of the 1978 Pioneer Venus multiprobe bus after deployment of the 4 probes.


    • Paul Gilster May 23, 2018, 19:58

      Yes, Jason discovered that after I had posted the image, which I had found on the Net — it was mislabeled. I’m still looking for a good Bracewell probe image with which to replace it.

      • J. Jason Wentworth May 24, 2018, 1:59

        This (see: http://www.daviddarling.info/encyclopedia/B/Bracewellprobes.html ) is the only actual illustration of a Bracewell probe that I’ve found online, but Paul found that it wouldn’t display large enough to be used for that illustration in my article. (Entering “Bracewell probe” in Google will bring up additional images, but they are “place-holder” illustrations of other space probes, including a NASA interstellar precursor probe [see: http://en.wikipedia.org/wiki/Bracewell_probe ]) Actually, the drum shape–like that of the Pioneer Venus Multiprobe bus–is a plausible one for a Bracewell probe (an optionally-separable sail or ion-drive propulsion module would accelerate it [and decelerate it at arrival, if the mission’s objective is to orbit the target star]).

        • Paul Gilster May 24, 2018, 8:38

          Yes, and I think while I’m trying to locate a good Bracewell probe illustration, I’m going to remove the one that turned out to be the Venus probe.

          • J. Jason Wentworth May 24, 2018, 10:39

            The Pioneer Venus painting is in the public domain (it’s on the cover of the NASA Pioneer Venus book), and an actual Bracewell probe could even look like the Multiprobe bus, but the conical atmospheric probes are “out of place.” The NASA “Interstellar Probe” (actually an interstellar precursor probe, see: http://en.wikipedia.org/wiki/Bracewell_probe ) looks like Arthur C. Clarke’s description–in his novel “The Fountains of Paradise”–of the alien fly-through Bracewell probe called Starglider (only Starglider’s spin-rigidized dish was 500 kilometers wide! :-) ).

  • Marshall Eubanks May 24, 2018, 11:57

    It is a mistake to ignore the implications of deep time in SETI. Interactions cannot be treated as if both civilizations are equally ignorant of each other, as that seems unlikely, and I think it is very unlikely (albeit not impossible) that we would find or contact a civilization that was ignorant of us.

    Suppose that every stellar system eventually gives rise to a civilization such as ours, and that these last for 500 years* before they either grow up or go extinct. That implies that, if you come across a system such as ours at a random time in its history, you have a rough probability of 10^-7 (500/4.5 billion) of finding something like our civilization.

    Now, there are about 0.01 stars / lyr^3 around here**, and that implies that the nearest civilization like ours will be ~ 1000 light years away under these very optimistic assumptions. This also implies a total of order 20,000 civilizations “like ours” in the galaxy at any one time.

    In 500 years, a civilization capable of sending probes at 10^-2 c will only be able to reach out about 5 light years, so it will only be able to probe its nearest stars, and may well be ignorant of us.

    However, suppose that there is 1 chance in a billion that a civilization lasts for >> 500 years, let’s say for 1 billion years. That gives order 10 of these in the galaxy at any time, so the nearest such old civilization is about 10,000 light years away (assuming they haven’t expanded through the galaxy). Since in only 10 million years or so such a civilization could explore every planetary system within the galaxy, they should know about us, to the extent they care to. If they feel we are worthy of a Bracewell probe, there is presumably already one in our system, silently watching us.

    Note that all of this is robust of the central probabilistic assumption. If the chance a stellar system develops a civilization is lower, say 1 in 100 or 1 in 1000, it puts the nearest civilization further away, but as long as the probabilities are high enough to give total numbers > 1, we are still more likely to encounter an old civilization than an adolescent one such as ourselves.

    * That is 10 x the life of our civilization as an entity capable of deep space communication, and roughly the duration since the Renaissance. More fundamentally, civilizations with lifetimes < or ~ 500 years will not have had time to explore even every star system within a few hundred light years of their location, while significantly older civilizations could have done that if they want.

    **Stars like ours are in the galactic thin disk, which is not much thicker than 1000 light years. I am ignoring the 1/R^2 behavior in this case, but assuming it for the old civilization case.

    • J. Jason Wentworth May 25, 2018, 22:44

      I agree. Ronald Bracewell was inspired to develop the automated interstellar messenger probe concept (these spacecraft also carry out the same functions, on an interstellar scale, as our Sun-orbiting and planetary flyby–or orbiter–space probes today) partly due to deep time considerations. Bracewell, Carl Sagan, I. S. Shklovsky, Robert Freitas, and John Gertz (see: http://arxiv.org/ftp/arxiv/papers/1609/1609.04635.pdf ) saw/see no reason why such probes could not be functional indefinitely (for millennia or even longer; Bracewell even provided information about engineering lifetime tests for electronic systems [he used amplifier-equipped undersea telephone cables as an example] that can ensure any desired service lifetime), and:

      Slower probes, as they all pointed out, are desirable due to their long lifetimes and their much lower propulsive energy requirements and much-reduced erosion protection requirements as compared with those of higher-velocity probes (all of which reduce the probes’ complexity and cost, enabling many more of them to be launched, “spraying” [as Bracewell described it] the surrounding stars with such probes). Also:

      Because the probes are also repositories of huge quantities of scientific and cultural information about the launching civilization, they can–although this isn’t hoped for, of course–outlive the societies that built and launched them. In such cases, they can provide one-way inter-civilization contact, as Champollion’s deciphering of the Rosetta Stone enabled regarding ancient Egypt. In addition:

      It would be nice if faster probes were feasible, making missions to more distant stars in less time possible, but that will come in time. As our experience with these vehicles (as well as the general level of technological prowess of humanity) increases, the probes’ performance and operational capabilities will improve. But even currently-feasible ones would slowly diffuse outward through the Galaxy. While we can make reasonable conjectures about how far away our nearest neighbors, if any, may be found, the only way to really know is to look. As well:

      The interstellar probes that we can build now (and could have–although at great expense–even back in the 1970s, as the Soviets pointed out) can make a good start, and the sooner we can begin such a venture, the sooner we will (in terms of the generations to come) get probes out to the greater distances and make later ones capable of faster speeds. We have to start where we are, with what we’ve got, and with what we can do. Fortunately, there are plenty of phenomena, and even objects (interstellar asteroids, ejected comets and possible rogue planets, and possibly even undiscovered brown dwarfs), that the probes can examine and/or watch for while they’re en route to their target stars.

  • J. Jason Wentworth May 24, 2018, 23:36

    I read your comments several times (and I have built my own radio equipment, including antennas). Your knowledge is not wrong, but it is incomplete, and–most importantly–it is in improper context. You’re thinking in terms of the best antenna to use, but a Bracewell probe–like any spacecraft (or aircraft)–has to have the best aggregate efficiency and functionality, within its mass and size limits, *as a complete vehicle*, which is why design compromises are always necessary. Now:

    Other types of directional antennas (dishes, helicals, beams, etc.) are used on spacecraft and at ground stations not only because they are effective, but because [1] they don’t have to operate over very wide frequency ranges, and [2] they are physically smaller than equivalent long wire antennas would be (their smaller size also makes them more easily movable, which directional antennas must be). But:

    A Bracewell probe of practical size can’t accommodate a large number of antennas due to mass and space limitations, plus its need to cover a very wide swath of frequencies. Even the Voyager spacecraft each have two long wire antennas (the radio science experiment antennas), although they don’t have to cover as wide a frequency range as a Bracewell probe. Also:

    A long wire TV antenna many wavelengths long works perfectly well (and if it’s an odd number of 1/4 wavelengths long, its impedance is easy to match). It is also directional, being most sensitive to signals arriving from the direction of its far end (or both ends, if it’s built as a doublet). But with only one exception that I know of (my high school math teacher’s parents in Georgia’s Blue Ridge Mountains, who used a single outdoor long wire TV antenna to pick up Atlanta TV stations in the 1950s), no one uses such long wire TV antennas because a Yagi-Uda or a log-periodic TV antenna is much smaller (although some people in the bush here in Alaska use HF loop antennas to pick up TV stations), and:

    Yes, such antennas work better than *single* long wire antennas (longwire Vee [“half of a rhombic”] antennas are better), but a Bracewell probe’s antenna doesn’t have to be the ultimate in performance. It has to work well enough over a very wide frequency range, and it has to be lightweight and compact when stowed. Its ability to also be used as an E-sail makes it desirable, because all spacecraft engineering has the goal of maximizing utility of systems while minimizing their mass. As well:

    The RAE A and B (Radio Astronomy Explorer, see: http://space.skyrocket.de/doc_sdat/explorer_rae-a.htm and http://space.skyrocket.de/doc_sdat/explorer_rae-b.htm ) satellites used very long (up to 1,500 feet), wide-band extensible antennas (they were used for low frequency radio astronomy, because such signals are reflected off the top of the ionosphere and back into space). Wide-band, long antennas do work–and have already been used–aboard spacecraft, including deep space ones (RAE B was placed in lunar orbit).

  • AlexT May 26, 2018, 15:54

    I suppose some middle sized nail will work better for TV reception than “long wire” antenna.
    Accoriding iformation from your links about RAE satellites – there is used V and dipole antennas, do not understand why you provide this example and what it should prove? It prove only the fact that conductor wire can be used for antenna construction…
    By tha way RAE antennas have some predefined size and limited frequency range…

    • J. Jason Wentworth May 27, 2018, 1:53

      Please see the section on the Alouette 1 and 2 satellites, in posting May 26, 2018, 0:48 above. Also, very short, amplified antennas will also work well over very wide frequency ranges (especially for reception–look up the PA0RDT Mini-Whip, which receives from *10 kHz to 20 MHz* [many short wave, long wave, and Non-Directional Beacon DXers use them]). But such physically small antennas can’t brake a probe to enter stellar-centric orbit (or achieve a relatively slow stellar system fly-through), but an E-sail–which can also double as a wide-band antenna array–^can^, and:

      For reasons of cost, simplicity, and reliability, Ronald Bracewell (and also Robert Freitas and John Gertz, see: http://www.rfreitas.com/Astro/TheCaseForInterstellarProbes1983.htm and http://arxiv.org/ftp/arxiv/papers/1609/1609.04635.pdf , repectively) have advocated launching modest interstellar messenger probes, using the minimum equipment that can do the job. This enables more probes to be launched for the same financial outlay (enabling more stellar systems to be explored). It also–as Freitas and Gertz in particular point out–facilitates the production of the probes on an assembly line, which would further reduce their cost (with the probes being improved over time as technology advances). As well:

      All spacecraft, including current ones, are the products of design trade-offs and compromises. For civilian spacecraft in particular, cost is a major driver of their designers’ choices. Being able to utilize any spacecraft system (not just its antenna array) for multiple functions, as I have suggested here, would lower the cost, mass, and complexity of Bracewell probes, which are particularly mass-sensitive (because every extra kilogram of probe mass requires many extra joules of energy–and propellant mass, if the probe uses a propulsion stage rather than a sail to accelerate it to cruise velocity). Even if a solar sail was used to accelerate the probe up to cruise velocity, a heavier probe would make necessary either a bigger (and more expensive and unwieldy) sail, and/or a closer–and more stressful and risky–“Sun-diver” maneuver to get the vehicle up to the desired interstellar transit speed, and:

      We’ll have to respectfully agree to disagree regarding this particular probe/antenna combination. It certainly isn’t the only option for a modest interstellar messenger probe, but previous experience with long, wide-band spacecraft transmitting and receiving antennas (the Alouette 1 and 2 satellites used very long dipole antennas up to 73 meters long, which were used for both a sweep-frequency [1 MHz – 12 MHz] VHF “ionosphere topside sounder” transmitter and a VLF receiver) indicate that Bracewell probes could use braking E-sail wires as wide-band antennas, but:

      This isn’t the only possible configuration for a modest, assembly line-manufactured interstellar probe. Another design might be an ion-drive probe that could propulsively brake into orbit around its target star (or sufficiently to set up a relatively slow system fly-through; small sub-probes could be targeted to fly by the system’s planets). The probe proper–which could be quite small; say, a 6′ – 10′ diameter spin-stabilized drum (rather like the Pioneer Venus Orbiter or Bus spacecraft) containing the instruments and a “push broom” spin-scan camera (like Juno’s camera)–could separate from the propulsion stage after arrival braking. After braking, it could deploy either an E-sail or a solar sail (both types could be spin-deployed-and-rigidized) for maneuvering within the system without using any propellant. Its signal monitoring–and perhaps local communication transmission–antenna(s) could be amplified, active small whip or plate antennas, like the Mini-Whip (the probe could use a laser for communicating with Earth).

      • AlexT May 28, 2018, 3:26

        1. There is lot of possible antenna designs , I do not think there is any reason to discuss every possibility.
        My own negative notes was related to your proposition to use “long wire” antenna as wide band solution that will work from VLF up to SHF.
        In connection to “PA0RDT Mini-Whip ” I want to note that it is significantly worst solution, than “long wire”, it is bad antenna. And this variant usually used by people that have some problem with neighbors or neighborhood in their location, so have to use stealth antenna :-)
        As sequence your links to any existing satellite antenna like Alouette etc. are not related to the problem I discussing (long wire – bad choice).
        2. We can call the probe as Bracewell or “John Doe” probes, but I suppose the possibility of communication with Earth is one of the most important task that we cannot “save money” on it. I am sure there is no any reason to send any probe to the space and spend on it resources and money, if it cannot communicate with Earth. And antenna that will be used for this communication should be designed according last state of art, but not using principle of building stealth surrogates…
        3. If you mean antenna that we should put on the probe in addition to communication antenna , that will be used for measuring and SETI, even in this case antenna design should have well predictable parameters and stable (rigid?) shape.
        In any case “long wire” it is bad choice.
        There is one additional problem with “long wire” it is asymmetrical antenna, so it have to have conducting surface – Earth (our planet) as second electrode, as sequence antenna’s (directivity for example) parameters that you described are actual only in circumstance there is Earth near your “long wire” (i.e. huge conducting surface)… For sure, you can create “artificial earth” using “counterweight” wires, but it cannot simulate/compensate our planet size and it’s electrical property :-).
        Please pay attention, that in every your example about existing satellite with shortwave antennas – symmetrical antenna design is used (dipole, V-shape, spiral etc.).

        4. About E-sail (as I understood those sails are causing you to be so “hard” in connection to “long wire” choice). Meanwhile none know will this E-sail design work or not.
        I hope that arguments standing after E-sail choice , are not similar to argument that used for “long wire” antenna.

        • J. Jason Wentworth May 29, 2018, 22:24

          Because interstellar probes (including Bracewell probes–interstellar messenger probes that are capable of searching for and contacting “local” technological civilizations as well as exploring their target stars and their planets) must function for very long periods, spin-stabilization is preferable to three-axis stabilization for reliability and power consumption reasons:

          The spin-stabilized Pioneer 10 and 11 probes (whose RTGs’ electrical power output finally weakened to the point that their signal strength dropped below the detection threshold on Earth) kept their dishes pointed toward the Earth automatically. Only very occasionally (at intervals of years) did they have to perform small spin axis precession maneuvers to re-point their dishes. (New Horizons is three-axis stabilized only during encounters; while traveling between targets, it cruises in spin-stabilized “hibernation” mode, to save thruster propellant, and because no active pointing–which would require the probe to be “awake”–is necessary.)

          The three-axis stabilized Voyager 1 and 2 spacecraft have to actively keep their dish antennas pointed toward the Earth with occasional thruster firings, and they have to devote some RTG electrical power to running the guidance system and the thruster propellant line heaters (so that the hydrazine won’t freeze). These are two possible failure modes for the Voyagers, but even if neither the guidance system nor the propellant heaters fail, the need to reserve some RTG power for those systems reduces the amount of time that the RTGs will be able to power the entire spacecraft (their instruments, transmitters, and receivers), and:

          This is no criticism of the Voyagers’ design, as they were designed to explore Jupiter and Saturn, and their design was amply capable of doing that (Voyager 2’s Uranus and Neptune encounters were happy bonuses). But their three-axis stabilization–and the RTG power reserve that the guidance and heater systems need–is shortening the possible time that the Voyagers can devote to returning data from interstellar space; also:

          The Voyagers used three-axis stabilization partly because their TV cameras returned higher-resolution pictures than the Pioneers’ spin-scan IPPs (Imaging Photo-Polarimeters, which could also collect light polarization data). But since the Voyagers were launched, “push-broom” (also called “push-frame”) imagers have been developed. These produce a scan line (using a line of fixed optical sensors), and use the motion of the carrier vehicle–an airplane flying in a straight line, or a rotating spacecraft–to produce images as sharp as those of a regular TV camera (the JunoCam, aboard NASA’s Juno spacecraft orbiting Jupiter, is a “push-broom” imager).

          Spin-stabilized spacecraft are also advantageous for fields & particles instruments. A spin-stabilized interstellar probe could carry such instruments as well as a “push-broom” imager. The probe’s lack of needing a three-axis stabilization system (and heaters for thruster propellant lines–electromagnetic torque coils and/or charged tether wires could be used instead for attitude control) would make it simpler, more reliable, and cheaper. As well:

          A spin-stabilized starprobe could use spin-deployed-and rigidized antenna and E-sail wires (spin-stabilized solar orbit probes like ISEE-3/ICE http://en.wikipedia.org/wiki/International_Cometary_Explorer use them for radio science purposes). E-sails have been ground-tested (the DLR, the German national space agency, is particularly interested in E-Sails–one has flown aboard an Estonian CubeSat, called ESTCube-1 http://en.wikipedia.org/wiki/Electric_sail , but the sail wire failed to deploy). A replacement, ESTCube-2 https://en.wikipedia.org/wiki/ESTCube-2 , is scheduled to fly next year, and the next mission in the series, ESTCube-3, is a lunar mission. My only interest in this combination antenna/sail wires arrangement for modest interstellar messenger probes is its simplicity, low mass, and low cost, and its multiple uses (for braking, intra-system maneuvering, local artificial signal monitoring & communication, and radio science observations of stellar and planetary magnetospheres). Such a system might also–the ESTCube-2 mission results will provide data on this–be able to function as an electrodynamic tether system within a planet’s magnetosphere, for maneuvering relatively close to a planet without expending propellant, but:

          There are numerous effective designs for inexpensive, assembly line-produced interstellar probes that could be built using current and soon-to-be-in-hand technology. My main interest is in encouraging research and experimentation that will lead to such probes–regardless of their particular designs–being developed and launched. Even flight test prototypes of them could “earn their keep,” by exploring distant solar system objects (including ones we haven’t yet visited, such as Chiron, Pholus, Hidalgo, etc.).

  • J. Jason Wentworth May 27, 2018, 7:11

    One thing that Ronald Bracewell wrote–in his papers and in his book “The Galactic Club: Intelligent Life in Outer Space” (as reproduced below)–surprised me:

    Referring to Sir James Jeans’ 1941 suggestion that we could attract the attention of the Martians “if any such there be” by shining a group of searchlights toward Mars to “flash out” a sequence of prime numbers (a sequence which other authors, he noted, also later advocated using in order to contact extraterrestrials), he had a curious view of this method:

    “Personally, I think it would be rather anticlimactic for designers of some high-power radio transmitter in space to use their program time trying to prove to me that they could also *count*! At the least I would expect a little poetry or art. In any event, let’s give them credit for enough imagination to put on a program that would rivet our attention.” Now:

    I quite agree that having a prime number sequence comprise the ^entire^ message would be seemingly unimaginative, but as Carl Sagan suggested in “Cosmos” (at the 42:30 point here: http://www.youtube.com/watch?v=m-NIwzBFJ_Y ), a prime number sequence would be only the beacon message, a “calling card” to unambiguously mark the transmission as being of artificial, intelligent origin. The real message–containing the detailed cultural, historical, and scientific information that would shock, humble, awe, and delight us–would be elsewhere, perhaps at an adjacent frequency, or at some fraction or multiple of the beacon message’s frequency. Just off the top of my head, here are a couple of possibilities:

    If the actual message was on a nearby frequency, the prime number sequence beacon message could be sent at a frequency that, at intervals (perhaps every third repetition of the sequence), would be made to “drift” up or down to the frequency on which the actual message was being sent (this could be done by regularly varying the transmission frequency as the beacon message was sent; it could either “drift” back down [or up] to its normal frequency after each excursion, or it could instantly resume the prime number sequence on its normal frequency), and:

    The actual message could pause briefly each time the beacon signal’s frequency “drifted over onto” its frequency, or–perhaps better–it could ^not^ pause, being momentarily interfered with by the beacon message. This brief overlap of the two messages would tell us that there *is* another message at the other frequency. The brief portion of the actual message that the beacon message would “step on” for a few seconds at a time could be some frequently-repeating, low- or no-information content passage (rather like brief station identification notices on terrestrial radio and television. Or:

    If the frequency of the actual message was some distance away from the beacon message’s frequency, I can think of at least two ways that the beacon message might point to where the actual message could be heard. The frequency of the beacon message could slowly, in a step-wise fashion (as it would look on a graph), “drift” upward (or downward) in frequency to the frequency where the actual message could be heard. As the frequency went, say, upward in 1 kHz steps, each time the frequency moved up by 1 kHz, the beacon signal would be transmitted on that frequency for one-half, one-third, or one-quarter as long as it was on each previous 1 kHz step. This would make it easy for the recipients to predict where the frequency “drifting” would stop, and if they decided to check on that frequency before the beacon message “drifted” there and stopped “drifting,” they would hear the actual message. Also:

    Another possibility could involve the prime numbers themselves. At regular, relatively brief intervals (say, every sixth repetition of a sequence of, oh, maybe the first ten prime numbers), the prime number beacon message might repeat two or three of the prime numbers in the sequence. Or perhaps each sixth repetition would include only the first four prime numbers. In either case (or in other variations of this), the number of prime numbers could be chosen such that the product of those numbers–possibly also multiplied by the number 6 (since the unusual sequences occurred at every sixth repetition)–would yield the frequency at which the actual message could be received, or:

    Perhaps it could be that product, multiplied times the frequency of the beacon message’s signal, that would yield the frequency at which the recipients could pick up the actual message. (This particular method might be preferable, because it could avoid uncertainties in the actual frequency at which the message would arrive, due to the aggregate Doppler shift caused by the transmitting and receiving planets’ rotational and orbital motions, plus the relative motions of their stars with respect to each other.) The ratio of the beacon message’s frequency to the actual message’s frequency would, I think, remain the same, despite the Doppler shift of both. Plus, since their system of time-keeping would undoubtedly differ from ours, they wouldn’t need to know what our “cycle per second” (hertz) is in order to use the beacon message to find the actual message’s frequency–they would just have to be clever, and to experiment a bit to find it. All of my numbers are randomly chosen here; I’m just using them to show how a simple prime number beacon message could be used to point recipients to an actual (information-rich) interstellar message on another frequency.

  • Alex Tolley May 27, 2018, 12:35

    One advantage of visible light signaling is that organisms with eyes will likely see across a large spectrum simultaneously. A Martian on the street might detect Earth signaling with searchlights without any special equipment. If ET was modifying their star’s output with primes, telescopes like Kepler could detect that quite easily for many stars. If the light was modified so that red light indicated the primes, while the blue light was the high-density message, that would be detected very quickly. Gaia might be used for such a search in future.

    • AlexT May 29, 2018, 0:25

      Human eye has relatively bad sensitivity to get ETI light message directly, so to send us dome message using the method that you propose – modulate star light, ETi must own huge amount of energy (and know-how), I suppose that civilitation that will be able to modulate (operate with) star radiation, will be able to operate with star radiation in such way that it will move star in desired direction, so this will create ability to explore Universe using own star system (with sun and planets) as huge starship, so long space distances and travel time will not be a problem anymore, civilization must be patient.
      In this case there is not need to send any “Bracewell probes”… Whole star will arrive to desired direction someday.

      • Michael May 29, 2018, 13:55

        Moving the star with radiation is not practical, there is simply not enough momentum change to move the mass of the Sun to any real degree.

        • AlexT May 29, 2018, 15:12

          Have you maid some calculations? What is expected momentum and from which star radiation changes was used in this calculation?
          There are some people that sure that ETI civilization can easily apply Red/Blue shift to predefined direction of Star radiation :-) If we can accept that this is possible, so as sequence you can move this star to any direction you want (for example applying “red shift” to the side of the star).
          Some of them write that we should be open minded, don’t we?
          May be resulting moment will be small, but such advanced civilization will have unlimited amount of time for the interstellar travel with whole star system… need only patience and after 1 billion years of travel they will arrive to destination :-)

          • Michael May 29, 2018, 17:02

            If all the light pressure from the Sun was pointed in one direction I get an acceleration of the Sun of ~8 x 10^-13 (m/s^2).

            • AlexT May 30, 2018, 2:33

              Wandering how exactly this acceleration was calculated?
              What starting parameters was used for this calculation?
              Do you take whole electromagnetic spectrum radiated by the Sun or visible light only?
              Do you take in account alpha particle, etc., etc.

            • AlexT May 30, 2018, 9:37

              By the way, let accept that Sun acceleration ~8 x 10^-13 is correct number and can be constant and stable during tens million year.
              Assuming so , we can make very fun calculations:

              1. It will take to the Sun system ~3.5million years to travel 1 light-year distance with convenient speed 87m/s
              2. It will take ~7milion years to Sun to arrive to Proxima Centauri :-)
              3. If (as some commentators on this site supposed ) there was developed dinosaurs civilization 70 millions years ago, they could send our Sun to ~400 light years distance (during 70 million years after extinction), and today we could arrive to Paradise part of our Galaxy, where lot of angel-ETI living in peace :-)
              4. If we will compare this crazy idea to some other proposed on this site , for example – ETI will use artificially modified stars to build cosmic beacons or sentinels that will last billion years to send message to Earth :-)
              In this context the idea to move star to desired destination is more realistic.

              • Michael May 31, 2018, 1:58

                We can ignore alpha emission as it is very small in comparison to the light pressure.

                Rad Pressure = energy flux/c
                ~0.20 Pa

                Area of Sun ~ 6 x 10^18 m^2‎

                Force= rad pressure x area of Sun

                Acceleration of sun =F/m

                Acc ‘=’ not a lot !

                • AlexT June 1, 2018, 5:02

                  Ok, thanks, so you got ~8 x 10^-13 (m/s^2), it is the best case expected acceleration :-)
                  I accept your acceleration number.
                  In my previous comment, I applied this acceleration to time scale and on my opinion it seams that even this miniscule number can be very usable for advanced civilization to move the stars to desired destination, yes it will take tens million years to move it to tens light-year distance.
                  But if I compare this idea with idea to make beacon from some that will light Forever, I suppose to move star – is more practical :-)
                  At least the results can be used in the future by descendant of advanced civilizations (or by next coming civilisations)…

    • J. Jason Wentworth May 29, 2018, 22:46

      Bracewell was referring more to Jeans’ (and others’) idea of using prime numbers to indicate a signal’s artificial nature–rather than to using light to transmit them–but optical transmissions do have their advantages. Infrared laser beams would be less affected by interstellar matter than would visible light (to our eyes) lasers, and:

      One optical channel could carry the actual message, while another (or perhaps two, an equal “distance” away, on either side) channel could be a repeating prime-number beacon message, to attract attention. Probes could also carry laser beacon/message transmission systems to attract attention and convey messages (imagine a ground-, aircraft-, or satellite-based infrared astronomy survey picking up prime-number flashes from a point in the sky not corresponding to any natural celestial object…).

  • ljk May 29, 2018, 11:25

    OMG ET, we’re coming to kill you

    Physicist solves Fermi’s Paradox – but you won’t like the answer. Andrew Masterson reports.

    The human race is doomed never to find extraterrestrial life, because we are about to wipe it all out in a manner that is unintentional, yet horribly unavoidable.

    That’s the conclusion reached by physicist Alexander Berezin from the National Research University of Electronic Technology (MIET) in Russia, in a new and admirably parsimonious solution to Fermi’s Paradox.

    Full article here:


    To quote:

    Applied to the Fermi Paradox by Berezin, however, it becomes an instrument of cosmic damnation. There is, he concludes, only one reason why ET, in all the stellar multitude, has not so far been seen.

    “We are the first to arrive at the stage,” he says. “And, most likely, will be the last to leave.”

    In other words, we are the paradox resolution made manifest. It is us, our species, who will spread through the universe, demolishing anthills along the way. Avoiding this fate, suggests Berezin is impossible, because it will “require the existence of forces far stronger than the free will of individuals”.

    At the conclusion of his paper, the author adds that he hopes he is wrong in his prediction.

    “The only way to find out is to continue exploring the Universe and searching for alien life,” he adds – although many of his readers, perhaps, might conclude that this is not now the wisest course of action.

    The paper is available online here:


    This is certainly not the first time such a suggestion has been made. Here is one from 2011:


    Altruistic, peaceful aliens do not sell. Ravenous invading monsters playing to our primal fears do.

    • Alex Tolley May 30, 2018, 11:46

      The Berezin paper was almost embarrassing. Whatever possessed the author to write it, he will be subject to a lot of ridicule. He really offers nothing new, adding his own assumptions that undermines the logic of his approach. It might have been worth a blog post, but a paper?

      • ljk May 31, 2018, 9:21

        Worst of all, he did not really say anything knew that anyone following SETI/METI with even a casual interest has not read before. It’s the media that seems to be perpetually clueless when it comes to science.

  • J. Jason Wentworth May 29, 2018, 20:33

    Applied to civilizations, I guess Berezin’s idea could be called the Highlander Hypothesis (“There can be only one”). :-) I wouldn’t be surprised, though, if he turned out to be essentially correct, although there may be no anthills out there to bulldoze:

    Even some scientists, such as physicist Dr. James S. Trefil, who wrote (among other works) “Space, Time, Infinity: The Smithsonian Views the Universe,” think it’s quite possible that in all of the universe, life has arisen only once, and we’re it. I fully support searching for other life, but I won’t be shocked (although only a provable ^positive^ result could come in our lifetimes; demonstrating–with a high level of confidence–the non-existence of other life could take millennia) if it turns out that we’re alone. If so, everything out there is ours to explore, colonize, and use (although I’d rather have neighbors we can share cultures and ideas with).

    • ljk May 30, 2018, 13:58

      That reminds me of the famous Pogo comic strip from 1959 where two of the characters are wondering if there are “advanced brains” in the Universe more sophisticated than humanity’s intellects, or if we are the smartest beings in all of existence.

      Their conclusion:

      “Either way, it’s a mighty soberin’ thought.”

      • J. Jason Wentworth June 1, 2018, 13:53

        I was just reading Carl Sagan’s and I. S. Shklovsky’s 1966 book “Intelligent Life in the Universe,” and *that* very installment of the “Pogo” comic strip is reproduced right at the beginning of the book.

        • ljk June 4, 2018, 9:00

          I am well aware. :^)

  • J. Jason Wentworth June 2, 2018, 12:26

    A friend of mine in England sent me a link to a 2012 simulated documentary (with commentary by several well-known scientists) called “Alien Planet” (see: http://www.youtube.com/watch?v=mS3mbKvSVDI&feature=youtu.be ). It is about a faster (0.2 c) future terrestrial Bracewell probe mission to a fictional planet called Darwin IV, 6-1/2 light-years from the Earth, and:

    While the automated interstellar vehicle, called the Von Braun, is “over our current technological horizon” (being about the size of a nuclear attack submarine [yet having no propellant drop tanks], carrying a large planetary orbiter and three large, lifting body landers [Mars lander-type aeroshells would be smaller, lighter, and as accurate], each containing aerobot and walking robits, yet cruising at 37,000 miles per second [20% of the speed of light–such mass, size, and velocity would require fusion propulsion]), this will not always be the case. Also:

    Such a vehicle is not a modest interstellar probe. But with improved spectroscopy from the solar system (and/or with data from a previous survey by a large number of modest, assembly line-produced Bracewell probes), a smaller number of such promising worlds might be found. If so, this might make it unnecessary, after controlled nuclear fusion is developed, to produce a large number of such more-capable–and thus more expensive–starprobes.

    • Alex Tolley June 3, 2018, 21:57

      It was a creditable animation, although I prefer the book it was based on: Expedition by Wayne Barlowe. The atmosphere observation craft alone are Bracewell probe size. The starship is huge. We seem to be going in the reverse direction, with ever smaller devices, which would make physical detection difficult. They could be observing us now in intimate detail.

      • J. Jason Wentworth June 8, 2018, 5:49

        I found the book after a little online poking, after a friend of mine in England sent me the video’s URL: http://www.youtube.com/watch?v=mS3mbKvSVDI&feature=youtu.be . The book covers a speculative future *human expedition* to Darwin IV (see: http://waynebarlowe.wordpress.com/artwork/expedition/ ), for which he was the mission’s artist (his sketches and paintings are beautiful!). Three things about the interstellar probe Von Braun in the video “Alien Planet – Darwin IV” didn’t look plausible:

        [1] It had no propellant drop tanks, which would be jettisoned when empty, lightening the vehicle (the tanks could also be instrumented, to serve as starlight-powered flyby probes). For interstellar rocket vehicles, even nuclear-powered ones, reducing mass wherever–and whenever–possible would be the watchwords of the engineers who designed them. For rocket-propelled starprobes–whether they use ion drive, fusion rocket power, or some other type of rocket propulsion (and whether it be in a “pusher” or “tractor” arrangement, see: http://www.youtube.com/watch?v=pG-2Pvoq9Ck and http://www.youtube.com/watch?v=9KBSaam5Tkc )–drop tanks, like those in the design of the BIS’s Daedalus interstellar probe, would be used;

        [2] The Von Braun interstellar probe used “antimatter-catalyzed fusion” propulsion. That isn’t impossible (and it could enable the vehicle to use at least some protium–ordinary hydrogen–as propellant), but keeping the antimatter safely contained during the 42-year journey would involve engineering challenges and fail-safe systems that spacecraft designers would rather avoid, and:

        [3] The Von Braun’s three planetary exploration aerobots–“Leo” (Leonardo da Vinci), “Ike” (Isaac Newton), and “Bal?” (probe Vasco Núñez de Balboa was destroyed during entry, so its nickname was never given in the video)–were delivered to the surface of Darwin IV by Northrop HL-10-like lifting body entry vehicles. Winged and lifting body vehicles are larger and heavier than axisymmetric capsule or (Mars lander-type) aeroshells with the same payload and aerodynamic deceleration capabilities. Aeroshells and capsules can also land as accurately; with off-center centers of gravity (like the Gemini, Apollo, and Soyuz capsules, and the Viking and Curiosity aeroshells), they generate aerodynamic lift, which is vectored to achieve precision touchdown points. Aeroshell-packed surface probes are significantly lighter and more compact, and on planets with denser atmospheres, a parachute can lower such probes the final short distance to the ground, and:

        Yes indeed, because of the great amount of energy that must be imparted to an interstellar spacecraft, the smaller it can be made, the less difficult it is to accelerate it, even to “slow” transit velocities of “just” 1% – 5% of the speed of light. The lower starprobe mass (as well as a slower transit velocity) also makes it less difficult to brake the craft into orbit around its assigned star (and makes provision of shielding against erosion and velocity-induced [“speed-amplified”] cosmic rays less difficult). As well:

        For all we know, we could very well be being examined by one or more alien starprobes (they could have been here for millennia), which could be reporting back home via laser, without us having even an inkling of it happening; there are so many places in the solar system where such probes could be lurking. This needn’t cause fear; human anthropologists (and biologists) study pre-technological human societies (and other animals) with no nefarious purposes, staying unobserved–as much as they can–simply to avoid changing the behaviors and/or cultures of the subjects of their studies. In addition:

        If their makers’ purposes are–or were to become–negative (from our perspective, perhaps after observing us), there’s nothing we can do about it anyway. Destroying or otherwise silencing (say, by dismantling for study [although they might be programmed to self-destruct or destroy intruders, if tampered with]) any such alien probe(s) that we might find would only reinforce the aliens’ impression that we were dangerous and violent, and perhaps best left alone–or maybe exterminated… For this reason, John W. Macvey suggested that if we ever find active alien probes, instrument packages, or navigational beacons in our Solar System, we should be careful to not damage them or put them out of commission (and that even apparently-dead alien equipment might only be dormant, making only non-destructive scanning or examination of such equipment prudent).

    • J. Jason Wentworth June 4, 2018, 4:30

      Just in case the link to the “Alien Planet” video, posted above, won’t open, here is its URL’s original form: https://youtu.be/mS3mbKvSVDI . (Someone I sent the URL [in the comment above] to reported that it wouldn’t open; when the URL in ^this^ message is clicked on, it transforms–after it opens–to the form given in the comment above.)

  • ljk June 7, 2018, 9:19

    What if ET is an AI?

    After centuries searching for extraterrestrial life, we might find that first contact is not with organic creatures at all.

    Full article here:


    This idea is hardly new, but I guess whatever gets the SETI folks and the general populace to wake up to a new paradigm.

    • J. Jason Wentworth June 8, 2018, 8:41

      Thank you for posting that article link. The earliest space-related discussion of AI ETs (called “machine intelligence” back then) that I’ve seen is in “Flight Into Space,” a 1953 book (revised after Sputnik I; I have both editions) by Jonathan Norton Leonard, who was–among other things–“Time” magazine’s science editor. Interestingly, he also described possible physically-distributed artificial intelligence, as in the Aeon.com essay. I can think of a few reasons why such “savants” aren’t in evidence:

      [1] Such machines’ creators may have implemented the Von Neumann paradigm differently, for their and others’ safety (if we can conceive of the “gray goo” scenario [accidentally-triggered, cancer-like endless replication] so, it would seem, could they). Instead of making such machines self-replicating, they may instead have made them indefinitely self-repairing (or mutually-repairing, between individuals or perhaps between “savant modules”), maybe like this:

      Even our current current solid-state electronics can last for centuries or even millennia (see: http://www.rfreitas.com/Astro/TheCaseForInterstellarProbes1983.htm [“The Project Daedalus starship design study assumes a system reliability of 99.99% (the same as NASA’s Project Apollo) over a nominal 50-year mission lifetime. [37] This implies a survival probability of 99.8% after 1000 years and 81.9% after 100,000 years. To achieve this with foreseeable technology a ‘repair-by-repair strategy’ is required in which failed components are repaired and then returned to service.”]). Any automated replication of the probes–if any were done–could have been done on the probes’ home planet, or in its solar system (using different, specifically-programmed manufacturing robots, located right at home where they could be shut down if they started going crazy making probes upon probes);

      [2] We have discovered, with subjects in which the numbers of individual objects of study (or even just their categories) are enormous, even with the help of computers to catalog and organize them (as with comets, asteroids, and micro-organisms) that intimately examining each individual specimens is simply impractical. Instead, we organize such things into various categories, and then study representative samples from the various categories in detail (this is on its way to occurring with exoplanets, because there are so many). Likewise, alien races–and/or their AI “descendants”–may have done the same thing with regard to stars of various spectral types (and the various types of planets found orbiting them, and perhaps even the life found on some of them), and:

      Even if they’ve found some way around the “light barrier” (and especially–which seems more likely–that they haven’t), the Milky Way is vast, with hundreds of billions of stars in it. I wouldn’t be surprised if, after visiting and examining large samples of stars and planets, travel to other stars–especially if they’re a “fair piece” across the Galaxy, making communication of the data and images a very slow (and lower data rate) business–is done at a much lower level of activity, or maybe not at all. As well:

      [3] A point that Carl Sagan made in “Cosmos” in 1980 (in the book, and possibly also in the television mini-series) is still entirely valid. If the nearest other technological civilization is 200 light-years away, there is nothing special about our Sun and planets that they would see and hear if they pointed optical, ionizing radiation, and/or radio instruments in our direction. There hasn’t been enough time for our radio, radar, and atomic & hydrogen bombs’ emissions to reach them, because they “see” our Solar System as it was in 1818. Nothing yet stands out that would make our Sun of any more special interest to them than other F (cooler ones), G, and K (warmer ones) class stars of comparable distances from them. Our Sun, Epsilon Eridani, Tau Ceti, Epsilon Indi, and numerous other Sun-like ^single^ stars (not to mention the double- and multiple-star systems, some of which could–or do–host planets) in our local borough of the Milky Way would all be more or less equally interesting to such a civilization. Or:

      [4] Maybe there just aren’t any such intelligent machines, either because none were created (perhaps there’s no one out there to create them), or because such advanced, life form-emulating AIs might not be possible. A variation of this possibility could be that the closest other civilization (either biological or machine) is far away across the Galaxy, and fast (near-light speed) interstellar travel is so difficult–especially for vehicles of reasonable size–that they only employ slow (< 0.5 c, or maybe even 1 He + energy fusion reaction. While variations of the “classical” Bussard ramjet–the catalytic-fusion ramjet, the LINAC (Linear Accelerator Craft), and the RAIR (Ram-Augmented Interstellar Rocket)–appear feasible, and could make reasonably fast interstellar transits (although they would be quite large), they couldn’t reach near-c velocities at which time dilation would become significant.

  • J. Jason Wentworth June 8, 2018, 8:55

    Oops–my last posting was apparently long enough that the system “truncated” it (in part [4]). Not much was cut out of it, though. The missing portion referred to the extremely large mass ratios (fueled mass versus empty mass [with all propellant expended]) of self-contained (i.e., rockets of various kinds, even fusion or matter/antimatter ones, even if multi-staged or using drop tanks) vehicles that could reach nearly the speed of light. If decelerating from almost c into stellar orbit (or even just a relatively slow planetary system fly-through trajectory) was required, the mass ratio would be so high as to perhaps be impossible to achieve with real hardware.