by Paul Gilster | Jul 15, 2021 | Missions |
Near-Earth Asteroid Scout (NEA Scout) is a CubeSat mission designed and developed at NASA’s Marshall Space Flight Center in Huntsville and the Jet Propulsion Laboratory in Pasadena. I’m always interested in miniaturization, allowing us to get more out of a given payload mass, but this CubeSat also demands attention because it is a solar sail, the trajectory of whose development has been a constant theme on Centauri Dreams.
And while NASA has launched solar sails before (NanoSail-D was deployed in 2010), NEA Scout moves the ball forward by going beyond sail demonstrator stage to performing scientific investigations of an asteroid. As Japan did with its IKAROS sail, the technology goes interplanetary. Les Johnson (MSFC) is principal technology investigator for the mission:
“NEA Scout will be America’s first interplanetary mission using solar sail propulsion. There have been several sail tests in Earth orbit, and we are now ready to show we can use this new type of spacecraft propulsion to go new places and perform important science. This type of propulsion is especially useful for small, lightweight spacecraft that cannot carry large amounts of conventional rocket propellant.”
Image: Engineers prepare NEA Scout for integration and shipping at NASA’s Marshall Space Flight Center in Huntsville, Alabama. Credit: NASA.
The spacecraft, one of several secondary payloads, has been moved inside the Space Launch System (SLS) rocket that will take it into space on the Artemis 1 mission, an uncrewed test flight. Artemis 1 will be the first time the SLS and Orion spacecraft have flown together (the previous launch was via a Delta IV Heavy). NEA Scout, which will deploy after Orion separates, has been packaged and attached to an adapter ring connecting the SLS rocket and Orion.
Once separated from the launch vehicle, NEA Scout will deploy a thin aluminized polymer sail measuring 85 square meters (910 square feet). In terms of sail deployment, we can think of the mission as part of a continuum leading to Solar Cruiser, which will feature a sail 16 times larger when it launches in 2025. Deployment will be via stainless steel alloy booms. Near the Moon, the spacecraft will perform imaging instrument calibration and use cold gas thrusters to adjust its trajectory for a Near-Earth Asteroid. The solar sail will provide extended propulsion during the approximately two year cruise to destination. The final target asteroid has yet to be selected.
Image: NASA’s NEA Scout spacecraft in Gravity Off-load Fixture, System Test configuration at NASA’s Marshall Space Flight Center in Huntsville, AL. Credit: NASA.
The pace of innovation in miniaturization is heartening. I note this from a 2019 conference paper describing the final design and the challenges in perfecting the hardware (citation below):
The figurative explosion in CubeSat components for low earth orbital (LEO) missions proved that spacecraft components could be made small enough to accomplish missions with real and demanding science and engineering objectives. Unfortunately, these almost-off-the-shelf LEO components were not readily usable or extensible to the more demanding deep space environment. However, they served as an existence proof and allowed the NEA Scout spacecraft engineering team to innovate ways to reduce the size, mass, and cost of deep space spacecraft components and systems for use in a CubeSat form factor.
Image: Illustration of NEA Scout with the solar sail deployed as it flies by its asteroid destination. Credit: NASA.
At destination, NEA Scout is to perform a sail-enabled low-velocity flyby at less than 30 meters per second, with imaging down to less than 10 centimeters per pixel, which should enlarge our datasets on small asteroids, those measuring less than 100 meters across. Says principal science investigator Julie Castillo-Rogez (JPL):
“The images gathered by NEA Scout will provide critical information on the asteroid’s physical properties such as orbit, shape, volume, rotation, the dust and debris field surrounding it, plus its surface properties.”
The more we learn about small asteroids, the better, given our need to track trajectories and potentially change them if we ever find an object on course to a possible impact on Earth.
The presentation on NEA-Scout is Lockett et al., “Lessons Learned from the Flight Unit Testing of the Near Earth Asteroid Scout Flight System,” available here.
by Paul Gilster | Jul 14, 2021 | Outer Solar System |
Yesterday we looked at the behavior of ice on Enceladus, a key to making long range plans for a lander there. But as we saw with Kira Olsen and team’s work, learning about the nature of ice on worlds with interior oceans has implications for other ice giant moons. This morning we look at the hellish surface environment of Europa, as high-energy radiation sleets down inside Jupiter’s magnetic field.
Europa’s surface radiation will complicate operations there and demand extensive shielding for any lander. But below the ice, that interior ocean should be shielded and warm enough to offer the possibility of life. With Europa Clipper on pace for a 2024 launch, we need to ask how the surface ice has been shaped and where we might find biosignatures that could have been churned up from below.
Tidal stresses on the ice leading to fracture are one way to force material up, but small impacts from above — debris in the Jovian system — also roil the surface. If we’re looking for potential biosignatures, we have to consider this surface churn and the effects of radiation upon what it produces. This is the subject of new work from a team led by Emily Costello (University of Hawai?i at Manoa), which has been studying the effects of electron radiation accelerated by Jupiter on complex molecules.
Image: The University of Hawai?i at Manoa’s Costello. Credit: UH Manoa.
The operative term in this paper, just published in Nature Astronomy, is impact gardening. The authors estimate through their modeling that the surface of Europa has been affected up to an average depth of 30 centimeters (about 12 inches). Over millions of years, the impacts add up even as surface material mixes with the subsurface, all bathed by radiation.
“If we hope to find pristine, chemical biosignatures, we will have to look below the zone where impacts have been gardening,” says Costello. “Chemical biosignatures in areas shallower than that zone may have been exposed to destructive radiation.”
Image: In this zoomed-in area (Figure 2) of Europa’s surface, an inset to Figure 1, a cliff runs across the middle of the image, revealing the interiors of the ridges leading up to it. The thin, bright layer at the top of the cliff is at least 20 to 40 feet (6 to 12 meters) thick. This thin surface layer, and possibly layers like it elsewhere over Europa’s surface, is where a process called “impact gardening” is thought to occur. Impact gardening is the small-scale mixing of the surface by space debris, such as asteroids and comets. Scientists are studying the cumulative effects of small impacts on Europa’s surface as NASA prepares to explore the moon with the upcoming Europa Clipper mission. New research and modeling estimate that the surface of Europa has been churned by small impacts to an average depth of about 12 inches (30 centimeters), within the layer of the surface that is visible here. Credit: NASA/JPL-Caltech.
The study looks not only at surface impacts but goes on to consider secondary impacts when debris returns to the surface after the initial strike. We learn there is a case for a particular zone on Europa — the moon’s mid- to high-latitudes — that would be less affected by radiation. In any case, a robotic lander may need to probe at least 30 centimeters down to find material unaffected by the ongoing impact gardening.
Rebecca Ghent (Planetary Science Institute, Tucson) is a co-author on the study:
“The work in this paper could provide guidance for design of instruments or missions seeking biomolecules; it also provides a framework for future investigation using higher-resolution images from upcoming missions, which would help to generate more precise estimates on the depth of gardening in various specific regions. The key parameters in this study are the impact flux and cratering rates. With better estimates of these parameters, and higher-resolution imaging resulting from upcoming missions, it will be possible to better predict the depths to which gardening has affected the shallow ice in specific regions.”
As a side note, I found when looking through Costello’s other papers that she and Ghent have done work on impact gardening at Ceres as well as Mercury and our own Moon. The paper on Ceres argues that the phenomenon is orders of magnitude less intense on Ceres than on the Moon, involving a much thinner regolith and leaving surface ice to be affected primarily by sublimation rather than impacts. It seems clear that our work on icy gas giant moons will need to take impact gardening into consideration, just as we monitor the movement of crustal ice.
The paper is Costello et al., “Impact gardening on Europa and repercussions for possible biosignatures,” Nature Astronomy 12 July 2021 (abstract). The paper on Ceres is Costello et al., “Impact Gardening on Ceres,” Geophysical Research Letters 11 April 2021 (abstract).
by Paul Gilster | Jul 13, 2021 | Outer Solar System |
We could do with more information about how ice behaves on a gas giant’s moon. We’ll need this knowledge to understand the behavior of crustal ice on places like Europa and Enceladus, where oceans may provide sub-surface venues for life. One approach into the subject is to look at ice right here on Earth; specifically, the Antarctic ice shelves. A new study out of NASA’s Goddard Space Flight Center applies a model based on Antarctic data to the fractured south pole of Enceladus, probing tidally driven stress and seismic activity within an ice shell.
We assume that tidal stresses produced by the moon’s interactions with Saturn, as well as the planet’s larger moons, keep the interior of Enceladus warm, while at the same time producing cracks and accounting for the geysers of water vapor Cassini found erupting from the so-called ‘Tiger Stripes’ (fractures) at the southern pole. The tides of Enceladus must be massive, and learning about the seismic activity they induce offers a key to the movement of the ice.
Image: Dramatic plumes, both large and small, spray water ice and vapor from many locations along the famed “Tiger Stripes” near the south pole of Saturn’s moon Enceladus. The Tiger Stripes are four prominent, approximately 84-mile- (135-kilometer-) long fractures that cross the moon’s south polar terrain. Credit: NASA/JPL/Space Science Institute.
Future lander missions will benefit from knowing where and when icequakes occur on Enceladus. Led by Kira Olsen (NASA GSFC), the research effort described in the Journal of Geophysical Research: Planets focuses on data collected by seismometers deployed along Antarctica’s Ross Ice Shelf between 2014 and 2016, with an eye toward examining the tensile strength of the ice and the stresses on it. The researchers compared these data with satellite imagery of the same area.
They found that most icequakes on the Ross Ice Shelf happened as large rifts in the ice pulled apart, which occurs in conditions of falling tides. The team used the Antarctic data to produce models of seismic activity on Enceladus, having observed that “seismic activity at the Antarctic rifts is sensitive to both the amplitude and the rate of tensile stress across the rifts.”
Image: Ice shelves floating on Earth’s Southern Ocean rise and fall with tides, causing rifts, fractures. Icequakes occur most frequently when falling tides pull the rifts apart. Models suggest seismic activity on Enceladus likely corresponds to the tides inside the moon. From figure 1 of the new study. Credit: AGU/ JGR: Planets.
The paper makes the case that the similarities between Antarctica and Enceladus are strong, homing in on a pair of interior, parallel fractures in the central part of the Ross Ice Shelf:
These internal rifts, named WR4 and WR6 (for Western Ross rifts 4 and 6; e.g., Walker et al., 2013), exist within a geophysical environment closely analogous to the TSF(Tiger Stripe Fractures) within the Enceladean icy shell. Physical similarities include (1) the Antarctic rifts are concentrated regions of deformation within the ice shelf, as are the TSF within Enceladus’ ice shell, (2) the Antarctic rifts undergo daily cycles of tidal deformation, similar in time scale to the tidal cycle that the TSF undergo throughout an Enceladean orbit (?33 h), (3) the Antarctic rifts share similar geometries with the TSF (Table 1), and (4) fracture mechanics and seismicity generation is expected to be similar between the Antarctic and Enceladean environments.
The authors combined the Antarctic data with calculated stress values along Enceladus’ Tiger Stripes to predict seismic-activity levels along the ice-shell fractures. The result: Seismic activity on Enceladus should peak when the moon is 90°–120° past the closest approach in its orbit around Saturn, with seismic activity levels decreasing by about 50 percent during the last 180° of the orbit. The activity along the cracks, according to the model, should not be massive, but rather a series of small movements and fractures producing sustained stress on the ice, consistent with our observations of plume eruptions at the Tiger Stripes, which tend to be discrete rather than simultaneous ‘curtain eruptions’ along an extended fracture segment.
Image: A satellite image of the research study site on the Ross Ice Shelf in Antarctica (top) shows two rifts in the ice from rising and falling tides. Similarly sized “Tiger Stripe fractures” crease the ice in Enceladus’ South Polar Terrain, in an image captured by the Cassini Imaging Team. Also from figure 1 of the new study. Credit: AGU/ JGR: Planets.
A useful approach, according to the authors, would be for any future mission to Enceladus to place seismometers within 10 kilometers of these fractures. For now, while Europa is in our thinking with the upcoming Europa Clipper and JUICE missions, no Enceladus missions are in the works. But the scientists see their model offering insights into other icy moons:
Though we focus this study on Enceladean rifts, the relationship that we observed at the Ross Ice Shelf rifts between tensile stress, stretching rate, and seismic activity could be applicable to tidally forced seismicity in other planetary settings. The key input needed would be robust models of stress evolution through an orbital cycle at the fracture locations of interest. Future work applied to Titan would be especially insightful, given the collection of on-ice seismic data planned as part of the Dragonfly mission. Observation and study of the energy generated by icequakes will be one of the primary ways such missions to icy worlds advance our understanding of a range of scientific goals, from better understanding tidal tectonics, surface deformation, cryovolcanism, and material properties, to seismically probing the structure of the ice and sub-ice interior. Our study demonstrates the utility of even a single seismograph for these future missions.
The paper is Olsen et al., “Projected seismic activity at the tiger stripe fractures on Enceladus, Saturn, from an analog study of tidally modulated icequakes within the Ross Ice Shelf, Antarctica,” JGR: Planets 21 May 2021 (full text).
by Paul Gilster | Jul 9, 2021 | Advanced Rocketry, Uncategorized |
Building a Bussard ramjet isn’t easy, but the idea has a life of its own and continues to be discussed in the technical literature, in addition to its long history in science fiction. Peter Schattschneider, who explored the concept in Crafting the Bussard Ramjet last February, has just published an SF novel of his own called The EXODUS Incident (Springer, 2021), where the Bussard concept plays a key role. But given the huge technical problems of such a craft, can one ever be engineered? In this second part of his analysis, Dr. Schattschneider digs into the question of hydrogen harvesting and the magnetic fields the ramjet would demand. The little known work of John Ford Fishback offers a unique approach, one that the author has recently explored with Centauri Dreams regular A. A. Jackson in a paper for Acta Astronautica. The essay below explains Fishback’s ideas and the options they offer in the analysis of this extraordinary propulsion concept. The author is professor emeritus in solid state physics at Technische Universität Wien, but he has also worked for a private engineering company as well as the French CNRS, and has been director of the Vienna University Service Center for Electron Microscopy.
by Peter Schattschneider
As I mentioned in a recent contribution to Centauri Dreams, the BLC1 signal that flooded the press in January motivated me to check the science of a novel that I was finishing at the time – an interstellar expedition to Proxima Centauri on board a Bussard ramjet. Robert W. Bussard’s ingenious interstellar ramjet concept [1], published in 1960, inspired a generation of science fiction authors; the most celebrated is probably Poul Anderson with the novel Tau Zero [2]. The plot is supposedly based on an article by Carl Sagan [3] who references an early publication of Eugen Sänger where it is stated that due to time dilation and constant acceleration at 1 g „[…] the human lifespan would be sufficient to circumnavigate an entire static universe“ [4].
Bussard suggested using magnetic fields to scoop interstellar hydrogen as a fuel for a fusion reactor, but he did not discuss a particular field configuration. He left the supposedly simple problem to others as Newton did with the 3-body problem, or Fermat with his celebrated theorem. Humankind had to wait 225 years for an analytic solution of Newton‘s problem, and 350 years for Fermat’s. It took only 9 years for John Ford Fishback to propose a physically sound solution for the magnetic ramjet [5].
The paper is elusive and demanding. This might explain why adepts of interstellar flight are still discussing ramjets with who-knows-how-working superconducting coils that generate magnetic scoop fields reaching hundreds or thousands of kilometres out into space. Alas, it is much more technically complicated.
Fishback’s solution is amazingly simple. He starts from the well known fact that charged particles spiral along magnetic field lines. So, the task is to design a field the lines of which come together at the entrance of the fusion reactor. A magnetic dipole field as on Earth where all field lines focus on the poles would do the job. Indeed, the fast protons from the solar wind are guided towards the poles along the field lines, creating auroras. But they are trapped, bouncing between north and south, never reaching the magnetic poles. The reason is rather technical: Dipole fields change too rapidly along the path of a proton in order to keep it on track.
Fishback simply assumed a sufficiently slow field variation along the flight direction, Bz=B0/(1+ ? z) with a „very small“ ?. Everything else derives from there, in particular the parabolic shape of the magnetic field lines. Interestingly, throughout the text one looks in vain for field strengths, let alone a blueprint of the apparatus. The only hint to the visual appearance of the device is a drawing of a long, narrow paraboloid that would suck the protons into the fusion chamber. As a shortcut to what the author called the region dominated by the ramjet field I use here the term „Fishback solenoid“.
Fig. 1 is adapted from the original [5]. I added the coils that would create the appropriate field. Their distance along the axis indicates the decreasing current as the funnel widens. Protons come in from the right. Particles outside the scooping area As are rejected by the field. The mechanical support of the coils is indicated in blue. It constitutes a considerable portion of the ship’s mass, as we shall see below.
Fig. 1: Fishback solenoid with parabolic field lines. The current carrying coils are symbolized in red. The mechanical support is in blue. The strong fields exert hoop stress on the support that contributes considerably to the ship’s mass. Adapted from [5].
Searching for scientific publications that build upon Fishback’s proposal, Scopus renders 6 citations up to this date (April 2021). Some of them deal with the mechanical stress of the magnetic field, another aspect of Fishback’s paper that I discuss in the following, but as far as I could see the paraboloidal field was not studied in the 50 years since. This is surprising because normally authors continue research when they have a promising idea, and others jump on the subject, from which follow-up publications arise, but J. F. Fishback published only this one paper in his lifetime. [On Fishback and his tragic destiny, see John Ford Fishback and the Leonora Christine, by A. A. Jackson].
Solving the dynamic equation for protons in the Fishback field proves that the concept works. The particles are guided along the parabolic field lines toward the reactor as shown in the numerical simulation Fig. 2.
Fig.2: Proton paths in an (r,z)-diagram. r is the radial distance from the symmetry axis, z is the distance along this axis. The ship flies at 0.56 c (?=0.56) in positive z-direction. In the ship’s rest frame, protons arrive with a kinetic energy of 194 MeV from the top. Left: Protons entering the field at z=200 km are focussed to the reactor mouth at the coordinate origin, gyrating over the field lines. Particles following the red paths make it to the chamber; protons following the black lines spiral back. The thick grey parabola separates the two regimes. Right: Zoom into the first 100 m in front of the reactor mouth of radius 10 m. Magnetic field lines are drawn in blue.
The reactor intake is centered at (r,z)=(0,0). In the ship’s rest frame the protons arrive from top – here with 56 % of light speed, the maximum speed of the EXODUS in my novel [8]. Some example trajectories are drawn. Protons spiral down the magnetic field lines as is known from earth’s magnetic field and enter the fusion chamber (red lines). The scooping is well visible. The reactor mouth has an assumed radius of 10 m. A closer look into the first 100 m (right figure) reveals an interesting detail: Only the first two trajectories enter the reactor. Protons travelling beyond the bold grey line are reflected before they reach the entrance, just as charged particles are bouncing back in the earth’s field before they reach the poles. From the Figure it is evident that at an axial length of 200 km of the Fishback solenoid the scoop radius is disappointingly low – only 2 km. Nevertheless, the compression factor (focussing ions from this radius to 10 m) of 1:40.000 is quite remarkable.
The adiabatic condition mentioned above allows a simple expression for the area from which protons can be collected. The outer rim of this area is indicated by the thick grey line in Fig. 2. The supraconducting coils of the solenoid should ideally be built following this paraboloid, as sketched in Fig. 1. Tuning the ring current density to
yields a result that approximates Fishback‘s field closely.
What does it mean in technical terms? Let me discuss an idealized example, having in mind Poul Anderson’s novel. The starship Leonora Christina accelerates at 1 g, imposing artificial earth gravity on the crew. Let us assume that the ship‘s mass is a moderate 1100 tons (slightly less than 3 International Space Stations). For 1 g acceleration on board, we need a peak thrust of ~11 million Newton, about 1/3 of the first stage of the Saturn V rocket. The ship must be launched with fuel on stock because the ramjet operates only beyond a given speed, often taken as 42 km/s, the escape velocity from the solar system. In the beginning, the thrust is low. It increases with the ship’s speed because the proton throughput increases, asymptotically approaching the peak thrust.
Assuming complete conversion of fusion energy into thrust, total ionisation of hydrogen atoms, and neglecting drag from deviation of protons in the magnetic field, at an interstellar density of 106 protons/m3, the „fuel“ collected over one square kilometer yields a peak thrust of 1,05 Newton, a good number for order-of-magnitude estimates. That makes a scooping area of ~10 million square km, which corresponds to an entrance radius of about 1800 km of the Fishback solenoid. From Fig. 2, it is straightforward to extrapolate the bold grey parabola to the necessary length of the funnel – one ends up with fantastic 160 million km, more than the distance earth – sun. (At this point it is perhaps worth mentioning that this contribution is a physicist’s treatise and not that of an engineer.)
Plugging the scooping area into the relativistic rocket equation tells us which peak acceleration is possible. The results are summarised in Table 1. For convenience, speed is given in units of the light speed, ß=v/c. Additionally, the specific momentum ß? is given where
is the famous relativistic factor. (Note: The linear momentum of 1 kg of matter would be ß? c.) Acceleration is in units of the earth gravity acceleration, g=9.81 m/s2.
Under continuous acceleration such a starship would pass Proxima Centauri after 2.3 years, arrive at the galactic center after 11 years, and at the Andromeda galaxy after less than 16 years. Obviously, this is not earth time but the time elapsed for the crew who profit from time dilation. There is one problem: the absurdly long Fishback solenoid. Even going down to a scooping radius of 18 km, the supraconducting coils would reach out 16,000 km into flight direction. In this case the flight to our neighbour star would last almost 300 years.
Table 1: Acceleration and travel time to Proxima Centauri, the galactic center, and the Andromeda galaxy M31, as a function of scooping area. ß? is the specific momentum at the given ship time. A ship mass of 1100 tons, reactor entrance radius 10 m, and constant acceleration from the start was assumed. During the starting phase the thrust is low, which increases the flight time by one to several years depending on the acceleration.
Fishback pointed out another problem of Bussard ramjets [5]. The magnetic field exerts strong outward Lorentz forces on the supraconducting coils. They must be balanced by some rigid support, otherwise the coils would break apart. When the ship gains speed, the magnetic field must be increased in order to keep the protons on track. Consequently, for any given mechanical support there is a cut-off speed beyond which the coils would break. For the Leonora Christina a coil support made of a high-strength „patented“ steel must have a mass of 1100 tons in order to sustain the magnetic forces that occur at ?=0,74.
Table 2: Cut-off speeds ?c and cut-off specific momenta (ß?)c (upper bounds) for several support materials. (ß?)F from [5], (ß?)M from [7]. ?y/? is the ratio of the mechanical yield stress to the mass density of the support material. Bmax is the maximum magnetic field at the reactor entrance at cut-off speed. A scooping area of 10 million km2 was assumed, allowing a maximum acceleration of ~1 g for a ship of 1100 tons. Values in italics for Kevlar and graphene, unknown in the 1960s, were calculated based on equations given in [7].
But we assumed above that this is the ship‘s entire mass. That said, the acceleration must drop long before speeding at 0,74 c. The cut-off speed ?c=0,74 is an upper bound (for mathematicians: not necessarily the supremum) for the speed at which 1 g acceleration can be maintained. Lighter materials for the coil support would save mass. Fishback [5] calculated upper bounds for the speed at which an acceleration of 1 g is still possible for several materials such as aluminium or diamond (at that time the strongest lightweight material known). Values are shown in Table 2 together with (ß?)c.
Martin [7] found some numerical errors in [5]. Apart from that, Fishback used an optimistically biased (ß?)c. Closer scrutiny, in particular the use of a more realistic rocket equation [6], results in more realistic upper bounds. Using graphene, the strongest material known, the specific cut-off momentum is 11,41. This value would be achieved after a flight of three years at a distance of 10 light years. After that point, the acceleration would rapidly drop to values making it hopeless to reach the galatic center in a lifetime.
In conclusion, the interstellar magnetic ramjet has severe construction problems. Some future civilization may have the knowhow to construct fantastically long Fishback solenoids and to overcome the minimum mass condition. We should send a query to the guys who flashed the BLC1 signal from Proxima Centauri. The response is expected in 8.5 years at the earliest. In the meantime the educated reader may consult a tongue-in-cheek solution that can be found in my recent scientific novel [8].
Acknowledgements
Many thanks to Al Jackson for useful comments and for pointing out the source from which Poul Anderson got the idea for Tau Zero, and to Paul Gilster for referring me to the seminal paper of John Ford Fishback.
References
[1] Robert W. Bussard: Galactic Matter and Interstellar Flight. Astronautica Acta 6 (1960), 1-14.
[2] Poul Anderson: Tau Zero. Doubleday 1970.
[3] Carl Sagan: Direct contact among galactic civilizations by relativistic inter-stellar space flight, Planetary and Space Science 11 (1963) 485-498.
[4] Eugen Sänger: Zur Mechanik der Photonen-Strahlantriebe. Oldenbourg 1956.
[5] John F. Fishback: Relativistic Interstellar Space Flight. Astronautica Acta 15 (1969), 25-35.
[6] Claude Semay, Bernard Silvestre-Brac: The equation of motion of an interstellar Bussard ramjet. European Journal of Physics 26 (1) (2005) 75-83.
[7] Anthony R. Martin: Structural limitations on interstellar space flight. Astronautica Acta 16 (6) (1971) 353-357.
[8] Peter Schattschneider: The EXODUS Incident. Springer 2021,
ISBN: 978-3-030-70018-8. https://www.springer.com/de/book/9783030700188#aboutBook
by Paul Gilster | Jul 7, 2021 | Astrobiology and SETI |
I sometimes rely on nudges from my software to remind me of directions I’ve been meaning to take in a Centauri Dreams article. Seeing that Caleb Scharf has a new book out (The Ascent of Information), I was setting about ordering it when I noticed how many notes I had on my hard disk related to Scharf’s work, a reminder of how provocative I find his writings. That took me back to a 2018 article called The Selfish Dataome, and also to the recent article The Origin of Technosignatures, which appeared a few days ago in Scientific American.
Scharf (Columbia University) has the habit of asking questions no one else seems to have thought of. So let’s kick this around a bit. The notion of a ‘dataome’ is about external things that a species generates. Scharf defines it as:
a deeper way to quantify intelligent life, based on the external information that a species generates, utilizes, propagates and encodes in what we call technology—everything from cave paintings and books to flash drives and cloud servers and the structures sustaining them.
Here we go beyond biology to ask why technology comes to exist in the first place. But this gets into some deep philosophizing that is beyond my pay grade, so I’ll pause to look at the numbers in our current dataome, which are staggering. They inspire in me that punchy effect I can feel when contemplating galaxies full of stars and planets. In 2018, according to Scharf, we generated 2.5 quintillion bytes of data a day or — I like this — a billion billion bytes for every planetary rotation. Much of that data hangs around in our daily lives.
Think of YouTube’s holdings, for example, or the GIFs you occasionally get from your friends, the scientific papers we keep talking about in these pages, the emails that pester your bulging mailbox, the albums of photos of the kids in the family room, the collection of black and white movies on ancient VCR tapes (well, that’s my collection, but I assume you have something similar). This is all folded into a dataome, which to Scharf is analogous to a genome, and one that may, as per Richard Dawkins, somehow perpetuate itself. What compels us, in other words, to keep all these things?
To address the question in his older article, Scharf in 2018 looked at the writings of William Shakespeare. You’d think these would be easy to define: The gorgeous sonnets, the 37 plays, the 835,997 words comprising the complete works (with a small handful whose authorship is disputed). But the question is how all this has propagated over the centuries. Two to four billion physical copies, by Scharf’s estimates, of the works, meaning hundreds of billions of sheets of paper covered by more than a quadrillion letters, have been produced. All of this involves energy production, even in reading.
Thus Scharf on energy use:
Across time these billions of volumes have been physically lifted and transported, dropped and picked up, held by hand, or hoisted onto bookshelves. Each individual motion has involved a small expenditure of energy, maybe a few Joules. But that has added up across the centuries. It’s possible that altogether the simple act of human arms raising and lowering copies of Shakespeare’s writings has expended well over 4 trillion Joules of energy. That’s equivalent to combusting several hundred thousand kilograms of coal.
And that’s just for the physical production of the actual Shakepearean canon. Add this:
Additional energy has been utilized every time a human has read some of those 835,997 words and had their neurons fire. Or spoken them to a rapt audience, or spent tens of millions of dollars to make a film of them, or turned on a TV to watch one of the plays performed, or driven to a Shakespeare festival. Or for that matter bought a tacky bust of “the immortal bard” and hauled it onto a mantelpiece. Add in the energy expenditure of the manufacture of paper, books, and their transport and the numbers only grow and grow.
I have a lot of Shakespeare in the house myself. In addition to the various printed editions of his works I’ve accumulated since grad school, I also keep the Oxford and the recent Modern Library editions on my ebook readers (a Kindle Oasis and a Kobo Aura One). I like to think I’m saving a few trees: Scharf points out that given US paper production statistics (based on 2006 data), 28,000 Joules of energy were used per gram of final material. US paper production ran to 99.5 million tons of pulp and paper that year.
Here again the question of why we keep things: I read a lot of library books downloaded onto my e-readers. Talking this over with a bookish friend, he told me that wouldn’t work for him. He had to have a physical object on his shelf that he owned. Why?
If you think of this in terms of symbiosis, we are creating a burden of energy use to feed our dataome that continues to grow, and it’s a reasonable question to ask whether we are drawing the kind of benefit from it that we might. What are all those Facebook posts worth? But unlike our situation with the ‘selfish gene,’ this human-dataome symbiosis is something we can manage, even if we haven’t really examined its evolution or analyzed its function in the overall growth of the species. I assume this is what Scharf will be doing in his new book, which I will be discussing here later.
In the more recent article, though, Scharf questions whether these concepts have value in how we deal with technosignatures and the ongoing expansion of SETI toward artifacts and technologies. I’ve often thought in terms of the Drake Equation that the L factor — the longevity of a technological civilization — is embedded in the question of whether technology actually offers an evolutionary advantage. In the short term, the answer seems obvious, but not if the inevitable outcome of burgeoning high tech is putting tools of species destruction in the hands of an ever larger number of people.
Scharf argues that a search for technosignatures can be considered more broadly a search for extraterrestrial dataomes, for the former grow out of the latter. He suggests that we consider something like a Dyson sphere as a consequence of a process that is itself Darwinian:
…the arrival of a dataome on a world represents an origin event. Just as the origin of biological life is, we presume, represented by the successful encoding of self-propagating, evolving information in a substrate of organic molecules. A dataome is the successful encoding of self-propagating, evolving information into a different substrate, and with a seemingly different spatial and temporal distribution— routing much of its function through a biological system like us. And like other major origin events it involves the wholesale restructuring of the planetary environment, from the utilization of energy to fundamental chemical changes in atmospheres or oceans.
This plays into our plans to examine planetary atmospheres for environmental factors that could be the consequences of these kinds of energy transformations. Thus it would behoove us to consider the relationship between the dataome we move in and the biological life — ourselves — that interacts with it, questioning in what ways the interests of the two are aligned and where they may be coming out of joint. (Sorry, I had to get Hamlet in there, what with all this talk about Shakespeare: “The time is out of joint. O cursed spite, that I was born to set it right!” The Bard is timeless).
I’m not sure how we examine a balance like this in Darwinian terms, but we wrestle daily with consequences like social networks changing discourse and affecting public policy, or the widespread propagation of cultural memes via cable and streaming TV. Scharf sees carbon emissions as one consequence of the dataome’s insatiable demand for energy, so industrial pollution is an inevitable offshoot. I think we need to ask whether the idea of a dataome can offer us anything predictive about what another species might do as it encodes and propagates its own information.
Scharf asks the question in these essays but it’s clear we are only at the beginning of what may be a long conversation. I’m having trouble seeing how parsing the growth of data this way gives us tools beyond the factors we’re already using to search for technosignatures, but the key may be in the idea that a dataome resembles a living rather than an inert system. If genes can be selfish, can data be the same? Just how much control do we have over a dataome when it reaches planetary dimensions?
As we ourselves don’t know the outcomes of such growth, its manifestations in a technosignature will be hard to imagine. Let’s see where Scharf goes with this next.
