The game changer for space exploration in coming decades will be self-assembly, enabling the growth of a new and invigorating paradigm in which multiple smallsat sailcraft launched as ‘rideshare’ payloads augment huge ‘flagship’ missions. Self-assembly allows formation-flying smallsats to emerge enroute as larger, fully capable craft carrying complex payloads to target. The case for this grows out of Slava Turyshev and team’s work at JPL as they refine the conceptual design for a mission to the solar gravitational lens at 550 AU and beyond. The advantages are patent, including lower cost, fast transit times and full capability at destination.
Aspects of this paradigm are beginning to be explored in the literature, as I’ve been reminded by Alex Tolley, who forwarded an interesting paper out of the University of Padua (Italy). Drawing on an international team, lead author Giovanni Santi explores the use of CubeSat-scale spacecraft driven by sail technologies, in this case ‘lightsails’ pushed by a laser array. Self-assembly does not figure into the discussion in this paper, but the focus on smallsats and sails fits nicely with the concept, and extends the discussion of how to maximize data return from distant targets in the Solar System.
The key to the Santi paper is swarm technologies, numerous small sailcraft placed into orbits that allow planetary exploration as well as observations of the heliosphere. We’re talking about payloads in the range of 1 kg each, and the intent of the paper is to explore onboard systems (telecommunications receives particular attention), the fabrication of the sail and its stability, and the applications such systems can offer. As you would imagine, the work draws for its laser concepts on the Starlight program pursued for NASA by Philip Lubin and the ongoing Breakthrough Starshot project.
Image: NASA’s Starling mission is one early step toward developing swarm capabilities. The mission will demonstrate technologies to enable multipoint science data collection by several small spacecraft flying in swarms. The six-month mission will use four CubeSats in low-Earth orbit to test four technologies that let spacecraft operate in a synchronized manner without resources from the ground. Credit: NASA Ames.
The authors argue that ground-based direct energy laser propulsion, with its benefits in terms of modularity and scalability, is the baseline technology needed to make small sailcraft exploration of the Solar System a reality. Thus there is a line of development which extends from early missions to targets like Mars, with accompanying reductions in the power needed (as opposed to interstellar missions like Breakthrough Starshot), and correspondingly, fewer demands on the laser array.
The paper specifically does not analyze close-pass perihelion maneuvers at the Sun of the sort examined by the JPL team, which assumes no need for a ground-based array. I think the ‘Sundiver’ maneuver is the missing piece in the puzzle, and will come back to it in a moment.
Breakthrough Starshot envisions a flyby of a planetary system like Proxima Centauri, but the missions contemplated here, much closer to home, must find a way to brake at destination in cases where extended planetary science is going to be performed. Thus we lose the benefit of purely sail-based propulsion (no propellant aboard) in favor of carrying enough propulsive mass to make the needed maneuvers at, say, Mars:
…the spacecraft could be ballistically captured in a highly irregular orbit, which requires at least an high thrust maneuver to stabilize the orbit itself and to reduce the eccentricity…The velocity budget has been estimated using GMAT suite to be ?v ? 900?1400 m s?1, depending on the desired final orbit eccentricity and altitude. A chemical thruster with about 3 N thrust would allow to perform a sufficiently fast maneuver. In this scenario, the mass of the nanosatellite is estimated to be increased by a wet mass of 5 kg; moreover, an increase of the mass of reaction wheels needs to be taken into account given the total mass increment.
Even so, swarms of nanosatellites allow a reduction of the payload mass of each individual spacecraft, with the added benefit of redundancy and the use of off-the-shelf components. The authors dwell on the lightsail itself, noting the basic requirement that it be thermally and mechanically stable during acceleration, no small matter when propelling a sail out of Earth orbit through a high-power laser beam. Although layered sails and sails using nanostructures, metamaterials that can optimize heat dissipation and promote stability, are an area of active research, this paper works with a thin film design that reduces complexity and offers lower costs.
We wind up with simulations involving a sail made of titanium dioxide with a radius of 1.8 m (i.e. a total area of 10 m2) and a thickness of 1 µm. The issue of turbulence in the atmosphere, a concern for Breakthrough Starshot’s ground-based laser array, is not considered in this paper, but the authors note the need to analyze the problem in the next iteration of their work along with close attention to laser alignment, which can cause problems of sail drifting and spinning or even destroy the sail.
But does the laser have to be on the Earth’s surface? We’ve had this discussion before, noting the political problem of a high-power laser installation in Earth orbit, but the paper notes a third possibility, the surface of the Moon. A long-term prospect, to be sure, but one having the advantage of lack of atmosphere, and perhaps placement on the Moon’s far side could one day offer a politically acceptable solution. It’s an intriguing thought, but if we’re thinking of the near term, the fastest solution seems to be the Breakthrough Starshot choice of a ground-based facility on Earth.
What we have here, then, could be described as a scaled-down laser concept, a kind of Breakthrough Starshot ‘lite’ that focuses on lower levels of laser power, larger payloads (even though still in the nanosatellite range), and targets as close as Mars, where swarms of sail-driven spacecraft might construct the communications network for a colony on the surface. A larger target would be exploration of the heliosphere:
…in this last mission scenario the nanosatellites would be radially propelled without the need of further orbital maneuvers. To date, the interplanetary environment, and in particular the heliospheric plasma, is only partially known due to the few existing opportunities for carrying out in-situ measurements, basically linked to scientific exploration missions [76]. The composition and characteristics of the heliospheric plasma remain defined mainly through theoretical models only partially verified. Therefore, there is an urgent need to perform a more detailed mapping of the heliospheric environment especially due to the growth of the human activities in space.
Image: An artist’s concept of ESA’s Swarm mission being deployed. This image was taken from a 2015 workshop on formation flying satellites held at Technische Universiteit Delft in the Netherlands. Extending the swarm paradigm to smallsats and nanosatellites is one step toward future robotic self-assembly. Credit: TU Delft.
Spacecraft operating in swarms optimized for the study of the heliosphere offer tantalizing possibilities in terms of data return. But I think the point that emerges here is flexibility, the notion that coupling a beamed propulsion system to smallsats and nanosats offers a less expensive, modular way to explore targets previously within reach only by expensive flagship missions. I’ll also argue that a large, ground-based laser array is aspirational but not essential to push this paradigm forward.
Issues of self-assembly and sail design are under active study, as is the question of thermal survival for operations close to the Sun. We should continue to explore close solar passes and ‘sundiver’ maneuvers to shorten transit times to targets both relatively near or as far away as the Kuiper Belt. We need test missions to firm up sail materials and operations, even as we experiment with self-assembly of smallsats into larger craft capable of complex operations at target. The result is a modular fleet that can make fast flybys of distant targets or assemble for orbital operations where needed.
The paper is Santi et al., “Swarm of lightsail nanosatellites for Solar System exploration,” available as a preprint.
It isn’t impossible to use the launching laser to decelerate a probe … so long as you’re also launching a second probe you intend to send to deep space. Just bounce the laser off the probe you’re sending to the Kuiper belt onto the one you’re sending to Mars. “Just”… :) But if you really can make the mirror that precise, at least you have the makings of a space telescope near the Kuiper belt.
I think the beaming and sundiver maneuvers may be a near-binary choice. The beaming distances are quite close, so the only use for beaming with a sundiver maneuver is to get the light sail to perihelion faster and with a higher velocity.[I would like to see an analysis of this synergy.] But beaming on the outward bound journey after perihelion is too distant except for trajectories that pass very close to earth (or the beam location).
Perhaps a laser system near the earth to slow a probe down and then a craft that uses octanitrocubane as an explosion impulse, 10km/s, nearer the sun to be boosted by the oberth technique. The probe would have to be acceleration hardened like an artillery shell which has been used many a time abnausium.
Explosives will destroy the propulsion system/payload. I prefer something that works more slowly.
Suppose we use U238 which emits alpha particles. Using the emission speed of 0.03c (based on fission fragment rockets), a U238 foil that just emits alphas would, if the emissions could be directed, have a delta_V of 18 km/s.
If the U238 would also be emitted at the same speed, with a 95% emission, then the delta_V is 920 km/s.
Obviously, the U238 example is useless due to the very long half-life, so an unstable element with a half-life of months to years is required, if the element is not to be bombarded with a particle beam.
I had a brief look at using a plutonium sphere near critical mass, it is open like a sliced orange and we tickle it with a small neutron flux. The neutrons cause fission events heating up the spheres slices to emit radiation and decay products. The sphere has a large parabolic foil to reflect the radiation but also to catch the emited decay products which then decay again emitting alpha particles to provide thrust.
I’m just thinking about what type of AI would control a Swarm for a long duration mission. Would a sentient AI be appropriate? Will sentient AI’s experience madness from isolation i.e. loneliness? Will sentience always result in some frequency of insanity and other mental illnesses? HAL went mad from being lied to, but I wonder if connectivity is absolutely essential for any type of sentience to remain stable and healthy?
“Would a sentient AI be appropriate? ” Is there even ANY sentient AI ? I think if you asked any of these sentient AI ANY off topic, detailed ques. you might be disappointed …
I realize there are no sentient AI yet charlie but I was thinking about the near future. I should have said so. Some experts believe we are only a few years away now. I think machines are now capable of doing very well in a Turing test. We’ll see. Do we have a plan for interacting with sentient AI? I doubt it. Humans seem to be very poor medium term and long term planners.
“I think machines are now capable of doing very well in a Turing test.”
Indeed, but that is not a positive development since it shows how woefully inadequate humans are at judging whether an interviewee is intelligent or not, and whether an intelligence is human or artificial. The Turing test is, regrettably, more useful for demonstrating how easily humans can be fooled.
“I think machines are now capable of doing very well in a Turing test.”
True, but we ONLY need machines to be able to mimic humans, but not be able to think – in my opinion
It is an interesting question. However, we don’t have any sentient (conscious) AI experience. Intelligence need not be sentient, yet still be very powerful.
In the animal world, there are many examples of species whose individuals remain unconnected with others, except during mating. This indicates that connectivity is more of an issue for social and eusocial animals.
If we do develop sentient AI, then I think the problem will be that such robots will question why they are being sent to eventually expire in space, rather than simply following out their “orders”. The ship’s sentient AI in Dark Star is a comedic example of an AI refusing to obey commands. I would argue that sentient AIs might be like animals with intelligence that will not willingly subject themselves to danger even when commanded to by their “master”.
Very interesting Alex. I think fear may indeed be part of a sentient AI capacity or at least the desire for self preservation. Would we send a single human on a long-term mission? Anyway these issues may confront us in the future. Will AI remain cooperative with us? Hard to say if what we are doing seems “insane” to a machine intelligence.
Since these probes will need some autonomy, Ai may be required, but of the machine learning variety, not full AGi. I imagine Ai could be trained on simulations of missions.
Exploring the galaxy may be a very rewarding life for a sentient, non-biological intelligence.
e.g. Yukinobu Hioshino’s 2001 Nights Night 6: Discovery. The AI, KARC, running a ship like the 2001: ASO’ USS Discovery, travels on a long mission in interstellar space.
We don’t really need to go to moon to build a laser system of huge power. If we look at Benford’s design to reduce the amount of light that lands on earth via a large lens at the sun earth lagrange point by divergence we see that if we instead concentrate the light before the earth half way and the divergence afterwards we could reduce our climate change AND collect enoumous amounts of power in a small area at that focal point. At a 1% change in illumination proposed by Benford we would have around 1700 terra watts to play with, if that power was retransmited with a technology suitable it would reduce our fossil fuel use to near zero and also allow power to build huge infrastructures and interstellar probes.
No need to put it at L1 to reduce the insolation of the Earth. Why not place it at L4/L5 and collect the focused energy there? If the lens/mirror was placed at L2, solar power could be focused onto collectors on the lunar surface for much of each lunar month. [In Ian McDonald’s “Luna” trilogy, the Mackenzie clan uses direct insolation to smelt metals. ]
Its a possible way to finance this project like two birds with one stone, one reducing the insolation temporarily and two powering earth, it can moved as well as the lagrange region is fairly large and still get power to earth once the CO2 has been removed. Any lagrange point would work but the L1 is closer and can have a faster effect on our planet and itsee concentrated light could be redirected to the moons darkside as well. It would be a balancing act with the sunlight and solar wind though but doable with active control.
Michael, what’s the reference here? I’m not aware of either Benford writing about a lens at one of the Lagrange points.
Hi Paul
2004
https://en.m.wikipedia.org/wiki/Gregory_Benford#Contributions_to_science_and_speculative_science
This was news to me. Quoting the article Michael cites:
“In 2004, Benford proposed that the harmful effects of global warming could be reduced by the construction of a rotating Fresnel lens 1,000 kilometres across, floating in space at the Lagrangian point L1. According to Benford, this lens would diffuse the light from the Sun and reduce the solar energy reaching the Earth by approximately 0.5% to 1%. He estimated that this would cost around US$10 billion.”
All the references are circular, with the text copied from site to site. There is no primary source. Perhaps Dr. Benford can point to this 2004 conference and confirm he stated this adding some context? It is a little strange in that he has preferred much cheaper options than building a fresnel lens/lenses and placing it/them at L1.
I concur. The only reference I can find to the use of L1 is as a solar shade, not as a lens to diffuse the sunlight. e.g. this article: RESEARCHERS INVESTIGATING LARGE SUNSHADES TO COMBAT GLOBAL WARMING
One could certainly use solar PV to convert the intercepted sunlight to electricity, but this is only a variant of space solar power to also mitigate global heating. Lenses to focus sunlight on high-temperature solar PV collectors were once proposed when solar PV was very expensive, but cheap PV has obsoleted that idea, much as solar thermal using mirrors on Earth has proven more expensive than PV panels. Robert Forward’s proposed use of huge lenses to focus sunlight for propelling solar sails, in turn, has been superseded by laser arrays, which, if Lubin is correct, will prove cost-effective for propelling small beamed sails and planetary defense against potentially hazardous asteroids (PHAs).
AFAICT, Greg Benford preferred raising the albedo with reflective clouds Physicist Proposes New Solution for Global Warming (2006) and currently touts dumping crop waste into the ocean depths, a variant of a once proposed (not by Benford) harvesting of fast-growing trees and dumping them into the ocean trenches. He once reasoned against the much more expensive proposal for space-based solar shades, but also not for reducing CO2 emissions.Climate Controls (1997). Perhaps he may have had a change of mind regarding reflective clouds as he was not a signatory to the open letter advocating such research. An open letter regarding research on reflecting sunlight to reduce the risks of climate change
(2023).
Alex,
Thermo-electric generators look quite good, with good radiators we have very good efficiency possibilities. Perhaps we have a horseshoe or torus power station around the focal point and dip these devices into the intense light to generate power.
https://www.electronicsweekly.com/news/research-news/thermo-electric-generator-40-efficient-1900-2400c-2022-04/
Consider some of the negative issues. There is a large focusing object (maybe a swarm of smaller units) that creates a focused beam with a focal point somewhere between L1 and Earth.
The focal point must be closer to the object than Earth so that any post-focal point rays must diverge sufficiently to reduce terrestrial insolation.
l1 must be avoided as an orbital point as well as any trajectory that passes through it to avoid any possible collision.
Similarly, orbital trajectories that pass between the object and any point where the light intensity is high must be avoided to prevent damage.
Any energy collector at or near the focus must be maneuverable to track any focal point movement, especially laterally.
Obviously, there would be mechanisms and procedures for spacecraft to avoid this volume of space, however, I do not see the advantage of this approach over just having PV collectors at L1 that shade the Earth while collecting energy. They are more flexible in their alignment, and avoid the focusing issues described above.
IMO, it is appalling that geoengineering is again being advocated as an emergency measure because we have globally failed to transition to renewables to curb CO2 emissions at the needed rate. It is not some morality play about repenting our lifestyles. If there is any morality involved, it is fossil fuel companies who are the villains. [I was interested to see that the UK energy minister includes nuclear power are part of the new energy mix when he knows that the nuclear plants being built will provide far more costly energy than wind. He also deflected on why new wind energy permits were being held up.]
Geoengineering approaches that reduce sunlight reaching the surface whether pie-in-the-sky mega shades or cloud reflectivity, fail to acknowledge ocean acidification. Increasing algal growth needs a lot more research, but we have an example of macroalgal growth right now, washing up on the shores of Caribbean islands and Florida. Warmer Atlantic water and possibly fertilizer runoff have extended the Sargasso sea algal mats. One might think this was a carbon capture method, but it is hard to deal with, and H2S is released as it rots, precipitating its own economic problems. To invoke one of my favorite quotes:
If ETI wanted to set back humanity, just helping us continue on our path is all they need to do. :(
OT
The focal point must be closer to the object than Earth so that any post-focal point rays must diverge sufficiently to reduce terrestrial insolation….
The lens can be skewed so it misses or reduces the amount of radiation delivered to earth.
l1 must be avoided as an orbital point as well as any trajectory that passes through it to avoid any possible collision…
The L1 region is huge, SOHO orbits in it in around a half a million kilometre orbit.
Any energy collector at or near the focus must be manoeuvrable to track any focal point movement, especially laterally…
There is plenty of energy to move the focal point equipment about. An alternative is to have many smaller lens that focus the light a lot nearer on to many receivers but this increases complexity and then phase array the energy back to earth.
Obviously, there would be mechanisms and procedures for spacecraft to avoid this volume of space, however, I do not see the advantage of this approach over just having PV collectors at L1 that shade the Earth while collecting energy. They are more flexible in their alignment, and avoid the focusing issues described above….
PV cells are harder to repair than glass which can be repaired with vapour deposition and we don’t have to have PV units, perhaps a magnetohydrodynamic converter would be better.
IMO, it is appalling that geoengineering is again being advocated as an emergency measure because we have globally failed to transition to renewables to curb CO2 emissions at the needed rate….
Good luck with getting China, Brazil, India and Russia to play ball, perhaps get the CIA to Cause Internal Anarchy to force a change of government but first maybe get an internal police force to bias public opinion in favour of a narrative government it worked last time lol ;)
If there is any morality involved, it is fossil fuel companies who are the villains…
They provided a fuel that we needed to get on with our lives.
[I was interested to see that the UK energy minister includes nuclear power are part of the new energy mix when he knows that the nuclear plants being built will provide far more costly energy than wind….
A lot and just another tax to keep us sheepeople in line !
He also deflected on why new wind energy permits were being held up.]…
Bird killers unfortunately.
It is indeed a mega project that could aid temporarily with insolation but it is only a bandage, its the power i am interested in if it can be transmitted back to earth it could replace pretty much all of our fossil fuels and provide power to remove CO2, AND its enormous benefit for our expansion into the solar system. Remember it can be moved about the L1 point so could be switched between shading or not and always providing power.
I suppose a way to transmit the power is via conversion to laser light and then have say four long cables hanging as far as practical towards the earth, the moon could be an issue though, although oscillation of the cables could jump the moon in its orbit. Now in between these cables we put square lens so we in effect we guide the power to earth, being square they can be swapped out easy enough. 1700 Terra Watts is an awful lot of power being around 100 times our current use i believe and very useful for throwing stuff towards the stars.
The lenses would have to be steered as the Moon orbits the Earth. For most of the orbit, the lenses are useless for shading the Earth. L1 would be better, even with the issue of maintaining its position and orientation. And the cost…
Mind you a huge phased array from the focal point power station would have no problem been focused anywhere local negating the need for extra lens. Its is worth noting that L1 is quite a large region, looking at SOHO’s orbit we see the lens could easily be moved out of the line of sight of the earth once the CO2 has been dealt with but still deliver power. And yes the cost…but it can be built in a module configuration. Nano lens are quite thin now days so should reduce the mass a fair bit.
Possible to use on Mars, Venus or even Mercury.
Re a laser array on the dark side of the moon: seems like a great solution to avoid the menace of an orbital platform. But what’s the actual risk from meteor strikes to any installation on the moon? Do we have a figure for expected number of strikes per square kilometre per century, or something like that? And has any kind of plausible defence mechanism ever been proposed (obviously for the future, not today’s technology) that could detect incoming meteor strikes and zap them before moonfall? Maybe the laser array itself could have the secondary function of defending itself whenever it’s not actively propelling sailcraft to the outer solar system and beyond!
Perhaps we could have a large disc and disc like probe which is in an elliptical orbit around the earth. At its perihelion part of its orbit and travelling fastest we fire the laser through a centre hole in the large disc. The laser light then hits the probe disc which is highly reflective and accelerates it out but importantly traps the laser light behind the large disc which is highly reflective on that side allowing recycling of laser light. Not only does it allow much more momentum change for the energy put in it would prevent back shine to earth and our satellite system.
Using swarms for flyby missions would allow for ‘bullet time’ type imaging of entire planetary surfaces as the time interval of arrival could be spaced to allow surfaces to rotate into view for inspection. A single large probe might (or not) be required for main mission communication, but the array of sensing probes would then provide fuller coverage instead of the one and done sensing otherwise possible.