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Closing Remarks at TVIW 2017

I know I said I wouldn’t post for a bit, but because I’ve just given my closing remarks at the Tennessee Valley Interstellar Workshop, they are ready to go for publication, and I thought I would go ahead and publish them here. I did much of the actual writing for this at the conference (where I still am), so there may be a few typos. I haven’t inserted the affiliations of the speakers, either, but I’d like to go ahead and get this up. My plan, once I’ve taken care of other obligations in the next ten days or so, is then to return to TVIW with greater focus and look at specific papers that caught my eye and the ways they fit in with the larger interstellar picture. For more background on the speakers here until then, check the TVIW 2017 Symposium page. I also didn’t mention the excellent workshop sessions in this talk because they had just been summarized immediately before my own talk. But more on them as well as other TVIW observations when I return to regular Centauri Dreams posts. This should be around mid-October.

I want to thank Les Johnson and the conference organizers at TVIW, Tau Zero and Starship Century for the opportunity to make this presentation, and for the huge outlay in time and energy they devoted to the event. That includes our workshop leaders and participants who carried the original workshop notion forward. What I now hope to do is give an overview of what we have done here and what it signifies.

Somewhere around the 6th Century BCE, a man named Lao Tzu, an almost legendary philosopher and writer, purportedly produced the book known as the Tao Te Ching, a fundamental text of Taoism and Chinese Buddhism. This year’s Tennessee Valley Interstellar Workshop arrived made to order for Taoist thought, with its theme “Step by Step: Building a Ladder to the Stars.” Because for years I’ve used as the line on my digital signature the Tao Te Ching’s aphorism: “You accomplish the great task by a series of small acts.” Confucius, who may have known Lao Tzu, would echo the same philosophy.

As anyone paying attention to this year’s sessions learned at the beginning, many of the acts we are trying to accomplish are anything but small. A 100 GW laser array is not small either in concept or in physical dimension. A sail five meters to the side is small by many earlier standards, but what we discuss doing with it, a mission to the nearest star, is not small, nor is the exploration of the outer Solar System — with precursors fueled by fusion or driven by plasma sail — a small accomplishment. But conceptualizing each of these things, one at a time, that is a series of small steps, and we need many such steps.

The emergence of Breakthrough Starshot clearly changes the game for everyone in the interstellar community. We have a congressional subcommittee report that ‘encourages NASA to study the feasibility and develop propulsion concepts that could enable an interstellar scientific probe with the capability of achieving a cruise velocity of 10 percent of the speed of light.” I doubt seriously that that phrasing would have emerged without the powerful incentive of the funding provided by Breakthrough, nor would the Tau Zero Foundation’s recent grant.

We’re on new terrain that is a long way from where we once were, in the days when there were few interstellar meetings as such and most discussions among those of an interstellar bent happened at occasional get-togethers in meetings on largely different subjects. Today we have a community and, if it is one with a pointing problem in terms of how often it meets and how well it stays focused, it is at least one with high energy levels and a steep drive to succeed.

TVIW 2017 gave us a range of focused sessions which I have chosen to group, trying to avoid being too arbitrary, into loose themes. Pete Klupar gave us the Breakthrough overview, which includes the welcome and related work of both Breakthrough Watch and Listen, a reminder that we must gain more information about the target of our mission, and indeed decide whether there may not be an even more attractive target near Centauri A or B. The welcome news that the RFP process has begun with work on the project’s laser array shows us a community with an actual interstellar project seriously defining the parameters of a mission.

Here we are in the larger realm of vision, as Andrew Siemion reminds us when he tells us that we search for ourselves as we venture to the stars. We also, whether or not we send Starshot sails on their journeys in 40 or 50 years, define the limits of our present technology and infuse the entire enterprise with an unprecedented prospect of well funded trade studies. The interstellar enterprise advances whether or not Starshot’s sails launch to Centauri, and who can say what spinoffs we won’t gain from the effort in the interplanetary arena with its tools.

On the matter of overview, let me mention Marc Millis’ discussion of the Tau Zero grant from NASA, which as I mentioned derived from the impetus of the Starshot initiative. Comparing propulsion approaches to take us through what Millis calls the era of precursors, the era of infrastructure and the non-extrapolatable future helps us identify the critical issues that need study, just as Starshot itself helps us locate, one by one, the major problems we need to solve for a specific mission concept. What we do need to be wary of is premature lock-in when competing methods for doing interstellar missions remain very much on the table.

In the realm of hard decisions and trade studies that illuminate them, Kevin Parkin showed us a system model that allows Starshot to study not only a Centauri mission at 20 percent of c, but also a precursor mission to a closer objective and a 70 km/sec ground vacuum tunnel test facility. It is heartening to realize that Parkin’s system has been used to conduct trade studies since March of 2016.

Meanwhile, the inputs from the broader community continue. Al Jackson showed us an analysis of trajectories for a Starshot probe, and we’re reminded by Benjamin Diedrich, who has been working with the NEA Scout mission, that we can learn much from a mission with a much different objective, and one with the ability to apply guidance and control forces that our Centauri-bound sail will be unable to muster. Congratulations to Diedrich and particularly Les Johnson for the recent successful deployment tests of the NEA Scout sail.

I want to also mention in the realm of trade studies and laboratory work the importance of the kind of measurements George Hathaway discussed for any work of this kind. Looking at problems in testing high voltages in high vacuum at cryogenic temperatures, Hathaway showed the measurement pitfalls that can ensnare experimenters, hard lessons to be kept in mind at all times by those who are evaluating propulsion technologies both understood and exotic.

Starshot’s mission components were a major factor in our deliberations. That 100 gigawatt laser array that Robert Fugate described can put something on the order of 30,000 g’s on the sail if we can get it to operate, despite the major issues of laser phase noise, optical path length differences, atmospheric fluctuation and pointing accuracy. We are considering a sail that goes from Earth orbit to 10 times the distance of the Moon in a matter of hundreds of seconds.

Can we make this happen? Starshot fails if it does not, and it fails if Jim Benford and those working with him cannot come up with a sail that can withstand the huge forces to be slammed into it. Here I want to pause to mention the rich sail background on display at the conference. The Benford brothers did the first work on sails in the laboratory — and as far as I know — the first actual tests of beamed sails, some 16 years ago. In the audience, we had Gregory Matloff, a distinguished figure in sail history who has been examining their prospects for decades.

Geoffrey Landis has published key papers on sail materials, and although his role in this TVIW was to discuss the Solar Gravity Lens, his contributions help us as we look toward possible sail materials and shapes within the Starshot envelope. The welcome presence of Giancarlo Genta reminds us of the tremendous contribution of the Italian sail effort through Project Aurora and other work in the 1990s. The need for the kind of sail test facility Jim Benford so carefully described is obvious and one hopes it will be the target of quick action, especially with the new wave of RFPs starting to translate the concept into reality.

Phil Lubin’s analysis of directed energy as the enabler for interstellar missions, beginning with a NIAC Phase 1 study under the name Starlight, led to Pete Worden’s making the connection with sails as a possible driver for a Centauri mission with a wafer scale payload. I was sorry that Mason Peck wasn’t here to participate in the discussion given his role in ‘spacecraft on a chip’ through his work at Cornell, but Lubin reminded us that an infrastructure like this can do much more than drive chip spacecraft. It can become a huge factor in planetary defense, in power beaming to Earth, in space debris removal and beamed transport within the Solar System.

Giancarlo Genta presented a preliminary analysis of inflated spherical sails of the kind recently proposed by Avi Loeb and Zac Manchester for Breakthrough Starshot. Working at far lower power levels for beam intensity, Genta found that an inflated sail essentially holds its shape under beam power, using a one meter diameter sail at 30 g’s acceleration. Further testing at increased power levels approximating Starshot are ahead. Key questions include whether hitting a sail with 30,000 g’s will not both deform and spin the sail, although as Genta pointed out, the sail can be abandoned for the duration of cruise if it can be brought safely up to speed.

I heard several people in the audience calling communications back to Earth the biggest challenge for Starshot, and although Dr. Fugate might disagree, I have to say that David Messerschmidt’s talk on data return was sobering. We have to make up 7 orders of magnitude of signal power when compared to our outer Solar System missions, perhaps a doable proposition if we allow decades for data return. We also deal with formidable issues of background radiation, pointing accuracy, atmospheric turbulence and scattering, and optical losses. All these factors push an increase in aperture area to 565 meters.

Our communications and imaging discussion, though, also takes in Slava Turyshev’s work on imaging an exo-Earth with the Solar Gravitational Lens. Clearly, getting a good idea of our target from a technology that could allow images of 1000 x 1000 pixels would be an outstanding precursor in its own right, and one that could be used at distances up to 30 parsecs if we can make it work. Geoff Landis’ reservations about the Gravity Lens don’t question its potential but do make us ask how likely we are to make it work and deliver genuinely useful information.

We got into these matters at the Sagan session on the 550 AU mission that Claudio Maccone has called FOCAL, where Landis, Turyshev, Greg Matloff and Pontus Brandt debated the issue. It should be kept in mind that some of Maccone’s recent work on the lens has shown the potential for communication, a feature that, if it could be realized, would suddenly turn many of the issues David Messerschmidt examined on their head. Thus, if it could be determined a lensing option is workable, an early Starshot mission to explore this region is a possibility.

Let me also mention the Sagan session on detecting life through biosignatures in planetary atmospheres in which I spoke along with Greg Benford and Angelle Tanner. This is by way of looking at what we can learn about nearby stars, the fact being that nearby red dwarfs are going to be under intense scrutiny by the James Webb Space Telescope, and we have the possibility of detecting gases like oxygen and methane which, if found together, offer us a strong indicator of some kind of metabolism. Tanner’s analysis of planet finding techniques in a later session took us through the range of methods available, ranging from radial velocity to direct imaging and transits, particularly in terms of distinguishing stellar noise from terrestrial mass planets.

We moved into the realm of other interstellar precursor missions with Pontus Brandt’s discussion of probe missions to 200 AU up to 1000 AU. This gets us into virgin territory, for going to this distance puts us into the relatively pristine interstellar medium. Quaoar lines up as an interesting target along the way because of what it may tell us about the KBO population, but we also would learn a great deal about dust distribution within the system, seeing the heliosphere from outside as we see similar astrospheres around other stars. Brandt’s comments on how we manage long-term missions ring true in the era of decadal data return from a Starshot mission and destinations that may require more than a single lifetime.

Gary Pajer’s take on precursors would use the Princeton Field Reversed Configuration machine to reach out to that magical 550 AU target, where the lens effects begin, with a mission time of 13 years, or 18 if we choose to stop. Using this technology, an Alpha Centauri flyby becomes feasible within 550 years, with both power and propulsion generated by a single engine.

Could we do this with a solar sail mission? Olga Starinova asked that question, noting a close solar flyby based on recent studies by Greg Matloff, Les Johnson, Claudio Maccone and Roman Kezerashvili to reach the inner Oort Cloud within 30 years. And Stacy Weinstein-Weiss discussed a key interstellar question: Why is science return from an interstellar mission better than local studies from Earth? Here, we learned about the unique science measurements that would be performed en route to the exoplanet, including the outer regions of our solar system, the Oort Cloud, the local interstellar medium, and the astrospheric environment around the host star. Perhaps trumping all of these is the search for life with in situ measurements.

Richard London and James Early helped us understand the dust impact hazard, which they believe will not threaten a sail, but of course our concern is likewise with the payload, which must be protected at all costs. London and Early used the HYDRA code for inertial confinement fusion in this work to study how we might reduce risks using optimal materials on a fast-moving craft’s leading side, with leading thin foil to atomize dust grains. Robert Freeland pointed out to me that one of Jeff Greason’s plasma magnet sails, discussed in a moment, could also serve as a useful shield.

On useful precursor technologies, Sandy Montgomery provided a way to avoid growth in the boom diameter and mass of sails as we move toward larger-scale missions by using what he calls a ‘space tow architecture,’ a train of gossamer sails integrated with a tension truss column. The advantages: We get much larger sails without growth in boom diameter and mass, using lightweight longeron filaments to connect a stack of smaller sails, much like a tandem kite.

I had mentioned to Pete Worden in a recent online exchange that I had seen several small sail analyses springing up and asked if they had any connection with Starshot. His answer was that they didn’t, but as he put it, the more the merrier given the magnitude of the problem. Thus it’s tremendously heartening to see the outgrowth of sail ideas that may eventually influence Starshot or, more likely, feed into designs outside of immediate interstellar goals that could play into our move toward the space-based infrastructure we need here in our system.

Thus Grover Swartzlander’s analysis of diffractive meta-sailcraft, which proposes that we look more carefully at diffractive sails, which absorb little light — a key issue for beamed sails — and have none of the re-radiation problems of reflective materials. Moreover, we might recycle photons to multiple sail layers if we can develop the right broadband space-qualified diffractive films.

TVIW 2017 was marked by its focus on sail technologies, due to all the factors I’ve already mentioned, but of course we have other options to consider. Jason Cassibry talked about the problems of solid state nozzles when dealing with pulsed fusion and fission/fusion hybrids for rapid precursor missions, the primary issues being erosion and wall heating. He showed us a 3D plasma simulation of a pulsed magnetic nozzle crafted for z-pinch propulsion.

Pauli Laine examined fission fragment possibilities, given the fact that uranium fission releases 81 percent of its energy in the form of kinetic energy. The escape of fission fragments rises when particle size decreases, so low density fissile material like americium or curium comes into play, with the escaping fission fragments being used as rocket propulsion. As Laine noted, fission fragment advocates also have to contend with fuel production — how to produce enough of the needed materials — as well as daunting issues of using such rockets safely.

Antimatter appeared in two sessions this year, with Gerald Jackson describing crowdfunded ongoing experimentation into antimatter production. Jackson would like to see antimatter emerge at a rate of at least 1 gram per year, a startling figure given that I can remember when NASA gave a figure of $62.5 trillion per gram of antihydrogen. Measure this against a Fermilab production rate of 2 nanograms per year. If we can do this in a way that is economically feasible we have the option of missions like the antimatter sail that Jackson and Steve Howe, also at Hbar, has developed through NIAC work. Jackson also examined antimatter storage possibilities through diamagnetic levitation.

Antimatter storage was the key of Marc Weber’s talk, which looks at the problem of controlling space charge, the repulsive force of all those stored charges in the fuel we would like to use. Weber is experimenting with storing electrons in a massively parallel micro-array of tubes in a 7-tesla magnetic field, seeking to discover the possible configurations in trap arrays. Everyone in the interstellar community from Les Shepherd and Robert Forward on has pondered the energetics of antimatter rockets, which still face the daunting storage and production issues Weber and Jackson have explored.

A bit less exotic but with exciting potential of its own is the plasma magnet sail described by Jeff Greason. Here we can imagine deploying magsails for braking against the interstellar medium as an interstellar probe enters a destination system, achieving orbit around the target star using the stellar wind. But Greason pointed out that such technologies are likewise ideal for precursor missions to 1000 AU, for example, and conceivably, using local beamers, within braking systems for a fast mission infrastructure inside the Solar System including cycling systems to Mars. Greason considered using particle beams and even fusion pellet delivery to the sail.

I should mention that a Sagan session also explored flyby vs. deceleration with the help of Jackson, Stacy Weinstein-Weiss and Gerald Jackson, along with David Messerschmidt. The deceleration problem looms large. If we do get Starshot probes to Proxima Centauri, the imagery we receive may well make clear the need for a sustained presence in that interesting system. The payoff, as Weinstein-Weiss made clear, would be in the search for extraterrestrial life, where we may need all the resources we can muster to verify a detection.

Talking about interstellar mission concepts reminds me inescapably of a loss we suffered this year in science fiction writer Jerry Pournelle. Familiar, I think, to most of us here, Jerry explored numerous interstellar schemes including beamed sails (early on), and in Footfall used Orion technology to save the species.

Because Larry Niven wrote Footfall with Pournelle, I want to mention how pleased I was to be able to shake his hand at long last. Larry brought a whole new dimension to my science fiction reading back in the early 1970s with short stories and the novel Ringworld. What a compliment to TVIW to have Larry along with writers Geoff Landis, James Cambias, Greg Benford and Alan Steele here for tonight’s writers’ panel, not to mention our host Les Johnson himself. About Steele, I want to say that I’ve read Arkwright twice, and if you don’t know the novel, you need to acquire a copy immediately, as it addresses the issues a small community of devoted advocates face when trying to do something as outlandish as build vehicles that can move between stars.

The valedictory theme continues: Let me also mention that this year we lost Jordin Kare, an innovative physicist who came up with ideas like SailBeam, a stream of micro-sails delivered to a receding starship as a form of propulsion, and the Bussard Buzz Bomb, as he called it, a starship that came up to speed through collision fusion with a string of pellets that had been laid out along a predetermined track. I never met Jordin, but he spent a lot of time on the phone with me when I wrote my Centauri Dreams book, and I think the field is diminished by his passing.

The infrastructure theme emerged several times at this year’s sessions, with Tracie Prater looking at NASA’s In-Space Manufacturing Project, under the theme Make It, Don’t Take it. And it only makes sense as we contemplate long-term manned missions that we look at manufacturing and recycling parts on demand, using the ISS while we can, before its 2024 deorbit, as a testbed. We learned about NASA’s plans for a multi-process fabrication laboratory called FabLab, with current experiments on the ISS pointing to a robust future for assembly of materials in space with 3-D printing technology.

Jon Barr told us about the United Launch Alliance’s robust work with ACES (Advanced Cryogenic Evolved Stage) and XEUS, a vertical-landing, vertical-takeoff lunar lander demonstrator. Can we use these refuelable, reusable technologies in company with the Vulcan booster to establish what will become trade routes to Cislunar space? The idea here is connecting Low Earth and Geostationary Orbits with Earth Moon L1 and the lunar surface. The goal: A robust Solar System economy, which will eventually translate our early interstellar precursors like Starshot into a longer-term framework of exploration and perhaps colonization.

Our leadership panel included Rep. John Culberson, whose language we’ve already discussed regarding a NASA inquiry into interstellar prospects to coincide with the anniversary of the Moon landing in 2069. Also Congressman Brooks of Alabama, Lt. General Kwast and Paul McConnaughey, who directs Marshall Space Flight Center. It was rousing to hear the energy in Rep. Culberson’s voice as he described missions like Europa Clipper and the possibilities of the Space Launch System. A takeaway was his belief that the discovery of life, either in our system at Europa or Enceladus, or in biosignatures in an exoplanet atmosphere, will be a civilization-changing discovery that ignites public support for future exploration.

But it was also sobering to consider the budgetary dilemmas of ever-rising deficits and accumulating national debt. Lt. Gen. Kwast emphasized that expansion into space demands we take our values with us even as we plan missions to ever more distant targets. The panelists’ responses to Pete Klupar’s concerns over installations like the Starshot 100 GW laser show that we still have many policy questions to answer as private initiatives like these go forward.

Can we get beyond bureaucracy and current cultural fatigue to expand the realm of values responsibly? Brent Ziarnick reminded us that interstellar technology presents us with the most daunting energies human beings have ever thought to develop. The analogy with nuclear energy is clear, and fortunately supported by deep scholarship. Our preoccupation with nuclear gloom, part of Sheldon Ungar’s ‘dynamic oscillation’, as Ziarnick described, ended Project Orion and threatens our development of nuclear power options as a positive tool for exploration.

Is METI likewise an ethical issue? Kelly Smith asks whether scientists are up to the challenge of dealing with broadcasting to the stars, given that this is a matter that potentially involves the entire species. METI may be low risk, but the risk is not zero, and that risk involves the survival of the entire species. Or what about the ethics of sending humans to the stars?

For we may discover that exoplanets are not empty, but filled with life. And given the fact that we use but 21 specific amino acids to build our proteins — and that there are some 300 naturally occurring amino acids — we cannot know what life may choose to use. Perhaps, as Ken Roy reminds us, we might look for lifeless worlds on purpose, seeking places we can terraform.

We’re now looking at issues of humans among the stars, a future that could involve vast worldships taking human populations to distant systems. Ore Koren discussed the vital question of how we reduce conflict in a closed environment in which causes of violence are numerous. Koren used large datasets to look at historical examples of violence, along with strategies by which we might reduce problems like lack of external ideas and migration. The result: Our worldship emerges as multicultural and semi-centralized, a hybrid of Sweden and Singapore.

James Schwartz worked similar turf but examined the ethics of worldship travel itself. Are colonists on dubious ground imposing a worldship future on their children? Perhaps not, but the real question becomes, should we put parents on worldships in the first place? Schwartz reminded us of the need for sufficiently large crews, and the fact that we will use extraterrestrial settlements much closer to home to learn valuable lessons before embarking starward.

And there we are, TVIW 2017. Thank you all for the opportunity to listen to and learn from your deliberations. If there is one thing that the interstellar community has taught me, it is that scientists working at the top of their form are willing to listen to questions and explain their work to writers like me, and to put breathtaking concepts out to a receptive and growing audience like those who gathered here. This is a mission that all of you make possible, and while it may seem less dazzling than a Starshot, it is vital in making our interstellar effort a planet-wide affair.

I close by returning to Lao Tzu: “To avoid disappointment,” says the Tao Te Ching, “know what is sufficient. To avoid trouble, know when to stop.”

I’m done.


Comments on this entry are closed.

  • Alex Tolley October 7, 2017, 10:59

    It was rousing to hear the energy in Rep. Culberson’s voice as he described ….. the possibilities of the Space Launch System.

    SLS is looking more like a white elephant every day. If SpaceX actually delivers on FH and the recently widely touted BFR, SLS will be obsolete before it even gets off the launchpad. Whether that BFR delivery is a BIG IF or not depends on your views of SpaceX’s ability to deliver. So far they seem to have shown their critics to be very wrong. The BFR will dramatically reduce the cost of access to space as well as making very large payloads possible and reduce the engineering costs of space hardware. At some point, it is going to be clear that Nasa’s pork barrel projects need to be curtailed and that they should focus on their strengths, like JPL’s robotic probes.

  • John walker October 7, 2017, 16:08

    For those interested the TVIW plans to upload videos of the presentations at this year’s workshop to their YouTube channel once the raw versions been edited. Last year’s talks can also be viewed there.

    • Douglas Loss October 8, 2017, 12:49

      In addition, we plan to have the videos of those presentations linked to on our website, from an interactive version of the symposium schedule, so you’ll be able to see the author and title of the presentation, then click on that to get to the video. Real soon now!

  • Cyril October 8, 2017, 1:55

    Great summary. One comment.

    “communications back to Earth the biggest challenge for Starshot”

    I have commented about this before on Centauri Dreams. Why assume only one probe, whose job will be to transmit its data all the way to Earth? Why not send many probes, one after another, to the same target? Each probe will only need to get its data to the next probe, which will relay the info to the third in line, and so on, all the way to Earth.

    The probes will be small and rather cheap, so we can afford to make and send them in the hundreds or even in the thousands, a few hours or days apart.

    There are many benefits. In my opinion, the major one will be the continuous science return we will get if we keep sending probes nonstop: there will always be another probe approaching the target. Another advantage is mission reliability: if one probe dies, we merely have to wait for the following one to reach the target, and the mission can resume.

    • Paul Gilster October 8, 2017, 11:28

      Thanks, Cyril. The Starshot people are looking at sending a ‘swarm’ of these probes, which would some multiplex communication and data return back to Earth. As David Messerschmidt’s talk made clear, the problems involved in setting this up are huge, but a lot of eyes are on the problem. The issue is still in the earliest stages of consideration.

    • Michael October 8, 2017, 12:35

      It may be a good idea to use the laser ‘lobes’ to drive slower relay probes to form a larger distributed transmitter/receiver system .

    • Douglas Loss October 8, 2017, 14:57

      One of the interesting thing about the presentations at this symposium was that along with the technological and scientific concerns mentioned the question of costs and how to factor the cost of mounting the mission along with all the other factors to determine the constraints on said mission. This happened in more than one presentation, and in presentations from various people unaffiliated with each other. This told me that we have probably turned the corner from intellectual design studies to seriously-considered efforts to actually fly interstellar missions. Ad astra!

    • Eniac October 9, 2017, 16:58

      If you double the number of probes, you get half the distance between them, which means their required transmission power is one fourth. Available power should scale linear with mass, so more, smaller probes have a better chance to get a signal relayed. So far, so good.

      However, smaller probes also means less gain. For radio, the gain is limited by the size of the antenna, for lasers by the aperture of the optics. This effect could completely negate the advantage provided by chaining probes, I am afraid.

      • Cyril October 10, 2017, 6:13

        A probe possessing a small antenna will have limited gain, agreed. And that is why sending data back through the light years in a single hop is such a daunting problem. Using many hops allows us to divide the problem into smaller, manageable pieces.

        For instance, a “probe” might actually be several devices, where each device would be a sail/antenna and a starchip. The combined antennas of the whole swarm may be sufficient to communicate with the following swarm. In this scenario, we would be sending hundreds or thousands of swarms at the same target.

        Other solutions could be imagined, such as using gossamer antennas that are tightly folded during launch and then unfurled. The main idea is to split the light years into many smaller sections.

    • ole burde October 9, 2017, 17:00

      In order for the probes to communicate efficiently , they have to know each others position relative to the theoretical center of the beam . This might be achieved by encoding information in the lacer-aray : each unit would have its signature , enabling the probes to navigate for the center of the beam ..and if the centering-proces is good enough , a small difference in the initial acceleration would make the probes pass each other at relatively short distances … IF they could join up , everything would become possible

    • David Messerschmitt October 20, 2017, 13:55

      Regarding the relay idea: We need all the ideas we can get — keep ’em coming!

      There are other problems with using intermediate relays that I should mention.

      1. I repeated the calculation from my talk, but assuming a 10 cm receive antenna that a 1 gram probe might carry. (That is probably very optimistic, but let’s flow with that.) The result is we need 5K probes as relays between here and Alpha Centauri, or 10K relay probes if we cover a distance up to 8 ly (yielding 20 years data transmission after encounter for the first prove). In this scenario, only the first probe can collect data, all the remaining 9999 are only relays.
      2. In my talk I assumed a photon efficiency of 10 bits per photon, but that presumes a lot of processing in the receiver. Although it helps that the bit rate is very low, I doubt this will be practical in a 1 gram probe. If we eliminate the error-correction coding processing, the number of probes increases to 22K and 44K.
      3. There will be 22K to 44K single points of failure in this system. The chances of any data return at all are slim to none.
      4. Each 1 gram probe requires on the order of 2 TJ of energy to launch, which is about a 500K kWh. If the cost of electricity is 10 cents per kWh, that comes to $50K per probe in energy cost. (I know, we are hoping for cheaper energy sources.) 10K probes = $500M or 22K probes = $1B to get the data back from the first probe, and a very large carbon footprint. If you compare that to the cost of a single really big aperture on Earth, and consider that the cost of the latter is amortized over decades of launches, a single really big aperture looks pretty attractive cost-wise.

  • Greg Matloff October 9, 2017, 9:41

    Dear Paul

    As always, you have produced a very comprehensive and inclusive review. I was very impressed by your speed and accuracy in preparing these comments and delivering them during the Workshop. It was great seeing you there!

    Regards, GREG

    • Paul Gilster October 9, 2017, 17:05

      Thank you, Greg, and the same to you. Always a pleasure to get to a conference and know we’ll get a chance to talk. Next time let’s do dinner as well.

  • Spaceman October 9, 2017, 11:37

    I like the idea of precursor missions since, even if the Starshot probes do not pan out, the technological quest to build them should leave us equipped with better technology to expore our own solar system more efficiently.

  • P October 9, 2017, 23:14

    Exactly. Whatever and wherever ‘Planet 9’ turns out to be, it will take decades or centuries to reach it with even quite advanced propulsion. A fast flyby of planet 9 should be a necessary precursor of anything heading further out.

    Luckily with all the searching going on, we are likely to know if the target exists and how interesting its likely to be within the next 5 years.


  • Ross Turner October 10, 2017, 0:52

    “Or what about the ethics of sending humans to the stars?

    For we may discover that exoplanets are not empty, but filled with life. And given the fact that we use but 21 specific amino acids to build our proteins — and that there are some 300 naturally occurring amino acids — we cannot know what life may choose to use. Perhaps, as Ken Roy reminds us, we might look for lifeless worlds on purpose, seeking places we can terraform”

    Alternatively, should we be looking to colonize other planets at all, lifeless or not, instead building true movable space colonies, starting closer to home and gradually moving out, avoiding the deep gravity wells of any other planets, rotating them for artificial gravity to produce worlds not tied to any specific planet? Perhaps O’neil’s vision using rotating O’Neill cylinders would be better, safer, less damaging, and less expensive option, than attempting to colonize other worlds? Perhaps leaving our own planet should be for becoming a truly space faring species, not one that skips and jumps to other planets, starting over in some cases, causing damage to existing life in others, each remaining subject to the same limitations we face on our planet now.

    • ljk October 10, 2017, 14:08

      Travelers who spend their lives in WorldShips as we currently envision them (very large – see the recent Orville episode on the subject with the Emerson quote for the title) may prefer to stay aboard rather than do anything more with a planet than visit it. Already we are seeing a youthful society that recreates indoors far more often than any previous generation, thanks to their fancy technological toys, if this is any indication.

      When they do require resources, and assume they do not want to interfere with or even have their presence known by any natives in the solar systems they visit for this purpose, they can mine for resources in those conveniently large chunks of free-floating raw minerals called planetoids and comets.

      While we are still not 100 percent certain, it is likely these bodies do not have any native life forms, at least not highly intelligent ones. Plus, unless the ETI of the particular solar system happen to be spacefaring and mining their own comet and planetoid belts, avoiding the natives may be fairly easy. That would certainly be the case for humanity at present. Even if astronomers did notice an increase in dust around a body in the Planetoid Belt or Kuiper Belt, it would naturally be assumed as a collision or eruption and left at that.

  • ljk October 10, 2017, 14:20

    Quoting from Paul’s excellent article:

    “Is METI likewise an ethical issue? Kelly Smith asks whether scientists are up to the challenge of dealing with broadcasting to the stars, given that this is a matter that potentially involves the entire species. METI may be low risk, but the risk is not zero, and that risk involves the survival of the entire species. Or what about the ethics of sending humans to the stars?”

    In addition to decades of unintentional broadcasts already over a century deep into the Milky Way galaxy by human civilization’s technological noise, there have been more than a few METI over the last few decades – including some from the European Space Agency (ESA) – where those in charge publicly stated having no worries about signaling deep space with superfluous messages, and as far as I can tell no one has even made a noise in their direction to question such acts. So how could a message carefully crafted by scientist be any worse? Note that among the items sent via electromagnetic waves in the galaxy are a Doritos advertisement and the full version of the terrible remake of The Day the Earth Stood Still (great choice, btw – not).

    Humans are always going to break the rules and knock down barriers, often just because someone told them they cannot do it. As I have stated in this blog before, what if China decides to do a METI with their new giant FAST radio telescope? Who is going to stop them outside of some strongly-worded letters of protest?

    Instead of trying to keep down and control our society, which is problematical at best, we need to prepare ourselves for what may be out there and deal with it as honestly and realistically as possible. Even if we were totally radio silent, there are other ways our planet Earth stands out as a world with life which someone with sufficient technology could detect even many light years away.

  • ljk October 12, 2017, 10:05

    Tennessee Valley Interstellar Workshop taking the long view to the stars

    by Bart Leahy

    October 12, 2017

    HUNTSVILLE, Ala. — While NASA and commercial operators plan to send human beings beyond low-Earth orbit, the participants of the Tennessee Valley Interstellar Workshop (TVIW) spent this past week contemplating something incomparably more ambitious: seeking practical ways to travel to the stars.

    Ahead of the curve

    The TVIW Chairman Les Johnson is a NASA physicist by day and a science fiction writer and interstellar visionary in his free time. Given that the exploration of the Solar System will be the work of generations, if not centuries, might TVIW not be getting a little ahead of themselves?

    Johnson told Spaceflight Insider: “Not at all. We’re providing the long-term vision… Can we do it today? No. Can we begin developing the technologies needed? Yes. Can we think about flying precursor missions today? Yes.”


    To quote:

    Humanity can solve many of the problems associated with interstellar travel while still within our own Solar System.

    However, TVIW Chairman Les Johnson feels that the interstellar quest is a natural human activity: “How can you look at the stars, think about all the exoplanets we’re finding, and not wonder how we’re going to get there someday?”

  • Ronald October 13, 2017, 4:44

    Off-topic, but there is always interesting astronomical news:
    – Some solar-type stars eat their own planets:
    – A debris disk may be a tell-tale sign of the presence of a giant planet in wider orbit:
    Slightly puzzling, because previously there were publications stating that a debris disk may be the sign of absence of a giant planet. Maybe this has to do with the orbital (AU) distance of the disk.
    – New telescope attachment allows ground-based observations of new worlds; Observations from telescopes on Earth rival those from telescopes in space:

  • Michael Fidler October 14, 2017, 0:06

    Kelly Smith remark, “For we may discover that exoplanets are not empty, but filled with life. And given the fact that we use but 21 specific amino acids to build our proteins — and that there are some 300 naturally occurring amino acids — we cannot know what life may choose to use.”
    Could we be looking at amino acid planets? The paper PLANETARY SYSTEMS AROUND LOW-MASS STARS UNVEILED BY K2.
    https://arxiv.org/pdf/1710.03239.pdf in the Discussion section, page 21, take a look at figure 17. Quote from page 22 about what is causing this dip at around 1.7 radius:
    “Although no completeness correction has
    been applied, it is interesting that Figure 17 shows
    that both types of stars have deficit of planets with
    Rp = 1.57 − 1.82R⊕, relative to somewhat smaller or
    larger planets. This is consistent with the findings of
    Fulton et al. (2017), based mainly on solar-type stars,
    that Kepler planets with sizes between 1.5-2 R⊕ are
    rarer than somewhat smaller or larger planets. This
    paucity has been interpreted as the outcome of photoevaporation
    on a population of planets with rocky cores
    (≈1.5 R⊕) with differing masses of gaseous envlopes and
    different levels of irradiation (Owen & Wu 2017). The
    same sort of deficit seen in Figure 17 suggests that the
    same processes are taking place around M dwarfs.”
    We are always assuming the worst when it comes to life on different types of exoplanets and their ability to have the necessary chemicals to spark life, but what if the change from rocky to large deep gaseous atmospheres is where life takes over. The depletion of exoplanets around 1.7 radius could be caused both by the levels of irradiation and reactions taking place that would make planets with basically amino acid oceans. This would eventually evolve into very deep layers of life beyond anything we could imagine. The exoplanets around 1.5 radius would then be the most probable place to find these paradise worlds for lifeforms. The collapse of the atmosphere thru chemical reactions would reduce the radius from the 1.57 to 1.82 to 1.5 or below.
    A new article on just what could be how this will play out in the next few years:
    SPECULOOS exoplanet search and its prototype on TRAPPIST.
    The regular pdf link is not working so use this one:

  • Michael Fidler October 14, 2017, 0:22

    Update: Look at figure 17, if you move the planets that have been added to the peaks at 1.3 to 1.5 to the peak a peak near 1.7 you get a much better looking bell curve!

  • Gregory Benford October 14, 2017, 17:49

    Indeed, a very comprehensive and inclusive review. Thanks, Paul!

  • Andrew Palfreyman October 16, 2017, 18:40

    After such an exciting and comprehensive review I can hardly wait for the TVIW videos.

    • Douglas Loss October 17, 2017, 9:01

      The TVIW 2017 presentation videos are currently being edited and should be available fairly soon. We hope to have easy-to-use archives of the videos from previous symposia available on the TVIW website in just a few days.

    • Douglas Loss October 18, 2017, 12:24

      The video archives of presentations from previous symposia are now available under the “Symposium Archive” section of the menu on the TVIW website (https://tviw.us).

      • Andrew Palfreyman November 5, 2017, 6:57

        Thank you Doug, This is just marvellous.

  • ljk October 17, 2017, 9:23

    The Man Who’s Bringing Us Closer Than Ever to Interstellar Travel

    Greg Matloff is one of humanity’s best hopes for traveling to unknown worlds.


  • ljk October 18, 2017, 16:24

    This Groundbreaking Astronaut and Star Trek Fan Is Now Working on Interstellar Travel

    Mae Jemison, the first African-American woman in space, wants us to look beyond Earth.


  • Harry R Ray October 20, 2017, 9:25

    In the extremely unlikely situation that the unusual goings on at Boyajian’s Star are finally PROVEN BEYOND A REASONABLE DOUBT to be an asteroid mining operation(and that is now the ONLY ETI solution standing) it would be a cautionary tale against EXCESSIVE AND WASTEFUL asteroid mining operations here. If we were able to COMPLETELY PULVERIZE Vesta, Juno, and Pallas SIMULTANEOUSLY, an equivalent amount of dust could be released as so to IMITATE the dips observed by KEPLER over the span of a few decades. The disastreous effects on astronomy ALONE means that we have to INSURE that this NEVER HAPPENS HERE!

  • ljk October 20, 2017, 12:00

    Why haven’t we had alien contact? Blame icy ocean worlds

    By Adam Mann Oct. 19, 2017 , 2:30 PM

    Might ET be buried under too much ice to phone Earth? That’s what planetary scientist Alan Stern of the Southwest Research Institute in Boulder, Colorado, has concluded may be delaying our contact with alien civilizations. Most extraterrestrial creatures are likely deep inside their home planets, in subsurface oceans crusted over in frozen water ice, according to a new proposal at this year’s American Astronomy Society Division for Planetary Sciences meeting in Provo, Utah.

    The hypothesis could explain the lack of signals from other technologically advanced civilizations, a conundrum known as the Fermi paradox.


    To quote:

    The idea is intriguing, says psychologist Douglas Vakoch, president of the San Francisco, California–based Messaging Extraterrestrial Intelligence, though he believes there’s no need to invoke the Fermi paradox. Biochemical indications of life are simply hard to detect remotely, he says, and it will likely take new telescopes and techniques to find them. If they don’t find us first, says Stern, it could be because they decide long-distance communication isn’t worthwhile, especially if they think everybody else is trapped in their own little icy bubbles.

  • Harry R Ray October 25, 2017, 9:49

    Paul Gilster: “Beaming Laser Power to Ion Drive is 300-400 Times more thrust than just Laser Photonic Sail.” Brian Wang: Next Big Future. Please check this out and respond ASAP. Aparrently NASA is ALREADY testing a PROTOTYPE, and that is WHY the Solar Lensing Telescope mission was proposed recently. Does this have ANY implications for Breakthrough Starshot in terms of possible design chances? Please try to have Brian do a guest post on this subject. Thanks.

    • Paul Gilster October 25, 2017, 11:20

      Harry, this is the subject of an upcoming post, which I should be able to run next week.

  • Harry R Ray October 25, 2017, 9:50

    Sorry, I meant “changes”, NOT “chances”.