Swarming Proxima Centauri: Picospacecraft Swarms over Interstellar Distances
astrobiology.com
astrobiology.com
I know it’s extremely unlikely this program ever gets deployed. It’s also very unlikely that I could last that long, barring some miracle medical breakthrough. It’s still an inspiring thought that humankind might get from its moon to the nearest star almost in one lifetime.
Obviously there’s nothing on Proxima, just like there’s nothing on the Moon. But that’s not the point. Everything of value is here on Earth, in the people we share it with. But we need joint ambitions and dreams. They don’t have to make sense to be worth dreaming about. It’s the opposite: the sense that quarterly reports and performance reviews are made of is the enemy of dreams.
Not necessarily obviously. The moons of the gas giants was thought to be inert and boring, until we went there and realized they are varied and brimming with interesting features.
one of those features being lifeless
The data from such a flyby might build the support necessary to develop propulsion technologies that allow us to slow down at interstellar targets. But they'd be decades into the future, by that time we will have done a lot more exploration in our solar system as well
Where does it come from?
This optimism carries over to their adult life, despite the newer obstacles being infinitely more difficult and complex so as to be incomparable.
Anyway, in general, over-optimism is much better than the opposite, because over-optimism runs into contradictions and gets corrected much more quickly than pessimism does, if it ever does.
Just like being a father, or an employee, or a woodworker do not fully define me as human, being a little snarky bitch on the Internet also does not sometime define me.
well, 100% on brand for how weird everything else is, honestly.
As a punishment I’ll have neutron star hot NFTs poked into my virtual eye sockets forever. But in between the tortures, the merciful Basilisk will grant me a glimpse of Proxima Centauri taken by its interstellar drone armada.
In fact there's a 'law' or 'paradox' that I can't remember the name of - but if we were to launch in 2076 at 0.2c, we could eventually launch something faster, than might even overtake the original probes.
If you never launch at 0.2c, you’re less likely to build the kit that launches something faster later.
The incessant obsolescence postulate.
(In a more general sense, it's the inverse of the first-mover advantage: the law of the handicap of a head start[32])
Or: the early bird gets the worm, but the second mouse gets the cheese.
[1] https://tvtropes.org/pmwiki/pmwiki.php/Main/LightspeedLeapfr...
[2] https://en.wikipedia.org/wiki/Law_of_the_handicap_of_a_head_...
I was stumped by that. You don't know until you look.
This sounds unfeasible. They have no way to keep station from what I understand, the interstellar medium is relatively empty but there will still be some drift over the light years. Having all of these independent craft synchronize and overlay their signals precisely enough for it to be receivable on Earth seems implausible. Can you say hella attenuation? I'd like to see some numbers...
The swarm ends up around 100,000km wide. Initial distances are longer, but never on the order of light years.
It's amazing they can still do it with voyager which is roughly 24 hours for one way traffic, 48 for round trip.
They'll be spread out over a big distance, but team up to do imaging and to return data from that star.
Compared to the distance that you'd go to get a coffee, yes. Compared to the distance to Proxima Centauri, oh hell no. Compared to that distance, they travel as a pack.
There's about a "402 million to 1" ratio between the two distances, 100 000km size of the swarm vs the 40,208,000,000,000 km distance to Proxima Centauri.
https://imagine.gsfc.nasa.gov/features/cosmic/nearest_star_i...
A swarm 100 000km wide could in its entirety pass between the Earth and the Moon with room to spare.
https://www.nasa.gov/wp-content/uploads/2009/07/180561main_E...
If a swarm of bees goes a couple of miles away, they don't spread out over a couple of mile distance. They are a relatively tight pack that then goes to the new place and then converges to be quite small. That's the same as what this mission is.
100,000 km is quite small as far as interstellar distances are concerned, but quite big as far as an aperture for distributed imaging or beamforming (and for avoiding hazards that are hard to see beforehand). The latter, of course, is what actually matters.
FWIW, I looked up those numbers because I do not have them memorised. The typical reader here seems even less informed than that, and they would benefit - I don't think that "we all know these numbers".
(P.S. they're not the right numbers; just the right orders of magnitude).
That's less than half the distance from the Earth to the Moon, so leaving binary star systems to one side, the answer is none and zero.
A large asteroid passing 100,000 km from the Earth is a considered a near miss in my book, since it's easily cislunar.
But you're missing the point entirely; parent is saying that individual craft in the swarm are within that distance of each other - that's the diameter of the swarm; the line "The swarm ends up around 100,000km wide" gives that away.
The distance between stars is orders of magnitude larger. "the swarm" crosses interstellar distances and communicates back as a whole. But communications between elements of the swarm do not and cannot cross that distance, they have to stay quite close to each other, e.g. within 100,000 km as they cross the void together.
I think not.
> "covering interstellar distances" is misleading
It can be read in 2 ways yes (is the interstellar distance crossed by the swarm who do that together, or does the radius of the swarm encompass interstellar distance) but it's clear which one is intended. Again, "The swarm ends up around 100,000km wide" tells you which one it is. Non-naïve people know or look up that 100,000km is not even an interplanetary distance, let alone an interstellar one. It's relatively tightly bunched when crossing the 40,208,000,000,000 km to Proxima Centauri. Yes I look this kind of thing up.
> a certain naivete in thinking about space travel that compromises
Don't be absurd.
They can do some work to keep station; the idea is that by adjusting attitude, they can adjust the magnitude and direction of their drag vector.
https://arxiv.org/abs/2309.07061
It's absolutely infeasible with current technology, but it doesn't look like it's total unobtanium.
For those that don't know what this is or could mean:
https://www.space.com/sun-gravity-could-help-observe-exoplan...
Not as powerful as the latter, but much more do-able just on the distance scale alone. It would essentially be an "Eath-observing" James Webb
[1] https://ui.adsabs.harvard.edu/abs/2019ESS.....433310K/abstra...
Also, this seems impossible:
> An initial string 100s to 1000s of AU long dynamically coalesces itself over time into a lens-shaped mesh network #100,000 km across, sufficient to account for ephemeris errors at Proxima
How does any object as small as what they're proposing at the extreme head or tail of the string whose only energy source is a laser several light years away lower (or increase) its velocity enough to reposition itself several hundred astronomical units to form a lens 100,000 km across and then increase (or decrease) its velocity in order maintain formation?
Is the lens pointed at the target, for imaging, or pointed at earth for communications? If the former how does it achieve the gain needed to send a signal to earth? If the latter how does it perform any useful science with the target?
Has anyone done even a rudimentary SWAG link budget calculation for communications?
Also, laser beams diverge and lose coherence. Why does it seem as though they are assuming that laser beams stay converged and coherent forever?
What is the energy density of a 100GW laser beam that has diverged to 100,000km at a ±50k km radial distance because I assume that the swarm components at the edges of the lens will need power the same as those at the center?
They're using swarms because we can't accelerate an object that weighs more than a couple grams to relativistic speed with realistic technology. Therefore we have to use a small craft. And since that small craft can't do everything, we send a bunch.
> How does any object as small as what they're proposing at the extreme head or tail of the string whose only energy source is a laser several light years away lower (or increase) its velocity enough to reposition itself several hundred astronomical units to form a lens 100,000 km across and then increase (or decrease) its velocity in order maintain formation?
That's not at all what they're proposing. Each craft would have its own energy source. There is also no string. The "string" and "mesh" here refer to geometry, not to actual real objects.
edit: as to how they come together, that's the previous sentence from your quote:
> Initial boost is modulated so the tail of the string catches up with the head (“time on target”). Exploiting drag imparted by the interstellar medium (“velocity on target”) over the 20-year cruise keeps the group together once assembled.
answering more:
> Is the lens pointed at the target, for imaging, or pointed at earth for communications?
The coms lens has nothing to do with the lens shape of the probe mesh or with the instruments used to collect data. You use two different things for taking images and sending them.
> If the former how does it achieve the gain needed to send a signal to earth?
From the article:
> .. periodically building up a single short but extremely bright contemporaneous laser pulse from all of them. Operational coherence means each probe sends the same data but adjusts its emission time according to its relative position, such that all pulses arrive simultaneously at the receiving arrays on Earth.
> What is the energy density of a 100GW laser beam that has diverged to 100,000km at a ±50k km radial distance because I assume that the swarm components at the edges of the lens will need power the same as those at the center?
Irrelevant since that's not the power source.
That is the actual, literal, impossible part. If the head is launched at speed x and the tail at speed y when they catch up they cannot stay assembled, unless "drag" is code for "magic".
>Irrelevant since that's not the power source.
What is the power source for the device, which weighs "GRAMS"? 1 gram is several dozen grains of rice. So what is the power source, expected to last decades, power data acquisition, processing, and transmission, and inter-swarm communications and station-keeping that weighs several dozen grains of rice?
More quantum-quantum-quantum antimatter nonsense?
I was trying to be generous by assuming energy harvesting, and not delving into fantasy.
The lens direction is VERY RELEVANT because the idea of getting signals back to earth is a broad array of devices all signaling simultaneously so the lens would ideally be perpendicular to earth. For example if the lens was pointed at the target it would present a smaller profile to observers on earth (maybe even a thin line) which would be more difficult to detect than a 100k km wide circle. The same rules apply to observations: any synthetic apertures created would be useless unless grossly pointed in the general direction of the target.
Drag is just drag. The craft are all launched at roughly the same speed and will start slowing down due to drag. By changing orientation they can control the speed/direction in which they slow down. This is a small effect, because the drag imparted by gases in interstellar space is minimal, but over 20 years at .2c it seems like it should work.
If there's a problem with this plan it's more likely to be that the encounters with the interstellar medium is more energetic than we expect and the craft either slow down too much or are destroyed by gases constantly impacting at .2c for years. But assuming the craft have enough shielding, the idea of using the drag to maneuver should work fine.
I apologize for not communicating clearly but that is the impossible part.
It will only work if the interstellar wind is, to borrow nautical terms, "in irons" or "running" (in line with either from ahead or behind the direction of travel) and that is impossible to either know, predict, or assume. From all other directions there are lateral forces that are impossible to overcome.
For example, if you are in a sailboat following another sailboat in calm waters with consistent wind and the lead sailboat slows down or the trailing puts out more sail to speed up to narrow a gap, one of the two will fall out of the line of travel due to lateral forces and will be forced to apply rudder to compensate. These things have no rudders.
The same thing happens to airplanes. If they increase or decrease drag either altitude or speed (or both) changes and control inputs are needed maintain position.
There is no ocean of water or air in space in which to steer.
I suppose if we launch and preposition several hundred billion space weather stations along the route in advance, we will understand the forces involved and be able to set the swarm components off on the trajectory needed so that the drag plan will work.
> will be forced to apply rudder to compensate. These things have no rudders.
These things are pretty hypothetical, but I think the concept pretty clearly requires them to have something resembling a rudder since that's their only realistic means of attitude control.
Or, essentially they would be like people in wingsuits falling.
and there's plenty of stuff in space - nebulas are just when stuff is dense enough to see visually, but hydrogen lines reveal molecules everywhere
PhD students at JPL before rocketry became more routine very probably felt the same.
I think anyone considering a role in this endevour would need to be willing to accept at best, 3rd or 2nd order deliverable outcomes in their working lifetime to take pleasure/kudos in, and not actually discovering outcomes of substance from the devices.
If you compare that to e.g. helping build the SKA, or launch Webb, It is arguable they have more bang-for-buck per individual, outcome-in-lifetime. But, thats not to say they do "better" just that they deliver science to their primary mission faster.
Good science in the secondary and tertiary effect space, behaviour of systems designed for long shelflive in space before activation, novel propulsion models, no end of good science.
I am told If Voyager was done again, it might well be done to deliver outcomes in the same place, sooner because we can now afford launch methods and RF systems which are 10x or 100x better.
But not "here's the latest image from Proxima Centauri up close" outcomes for anyone working on Brilliant dust. The cost to get to interesting fractions of c is just too high.
Line of thought is that aiming a 100GW laser at a small piece of silicon probably makes it very hot, so periodically hitting very small probes with laser from far away could be a power supply as well as propulsion. If you can still hit the things from far away enough.
Making the probes very light is a convincing answer to the problem of accelerating masses to speeds useful for interstellar flight and we can get quite a lot of machinery in a piece of silicon.
It's vaguely plausible that a chip could absorb energy from a far away laser emitter, store some of it, do some arithmetic, emit energy from something like LEDs positioned on the surface and use that to fine tune position or communicate with other chips in the swarm. Can imagine that working well enough for science fiction, might be implementable in reality.
It is proportional to the square of the beam waist and inversely proportional to the wavelength.
For a 1m beam at a 1um wavelength, that is about 3e6m or 3000km.
Therefore larger beam diameters and longer wavelengths reduces divergence.
There's also other beam shapes that are "non-diffracting" which can maintain their original beam profile over an initial distance, such as a Bessel beam [2].
After a few hundred AU, the probes should be close to the target velocity
This paper [1] demonstrates the reduced power loss of a Bessel beam compared to a Gaussian for various target distances. For targeting GEO, a Bessel beam can be 75% the size of a Gaussian for the same halving of power-loss.
In reality, I think a Gaussian beam is fine - and much simpler to engineer.
[1] https://opg.optica.org/josaa/fulltext.cfm?uri=josaa-32-11-20...
Edit: there's probably no way to make an electric field strong enough on the macro scale to bend light, unless it passes by a black hole or magnetar, because the radius of the bending grows by 2nd power of charge but shrinks by the 4th power of distance from charge. But I'll leave my work here in case anyone is curious.
----
See figure 1:
https://link.springer.com/article/10.1140/epjc/s10052-021-09...
Equation 48:
delta y = -E*(a^2)*(Q^2)
-----------------
80*pi*(m^4)*(b^4)
E = 1 for parallel or (7/4)^2 for perpendicular?
a = 137.036 (fine structure constant)
m = 9.11e-31? (mass of electron? mass equivalent of electric field by E=mc^2?)
Q = quantity of charge in coulombs
b = smallest distance of light from point charge, or radius of light cone
It's conceivable that a strong charge placed millions of kilometers away could bend the laser light into a column again, although it might have to have an electric field close to the strength of an atom's, or 10^21 V/m. The breakdown voltage of space is 3x10^6 V/m, so it might require a black hole or high power to concentrate enough charge in one place, for example by using a ring of electron guns aimed at their center to simulate a focussed point charge.
But the bending is towards the charge and grows by Q^2, while falling by b^4. If m is the mass of the electron, then it's all multiplied by about 10^128, which suggests that a small charge would cause a large bend. Or if it's the mass equivalent, then a 1eV field might have an equivalent mass of (1.6x10-19 J)/(c^2) which is about 1/(10^36) or a multiplier of 10^144 ! But that doesn't sound right, so maybe someone can clarify it for us?
Edit: found another paper for calculating the bending angle of light in a nonuniform electric field (like near a point charge):
https://arxiv.org/abs/1012.1134
https://arxiv.org/pdf/1012.1134 (pdf)
Numeric example:
As an example, for Z = 100, b = 10*lambda*e we get the bending angle theta = 3.4 × 10−8 radian for an x-ray of wavelength 5*lambda*e.
Edit: another paper calculating the bending of light in nonuniform electric fields near black holes:
https://arxiv.org/abs/1101.3433
https://arxiv.org/pdf/1101.3433 (pdf)
Equation 18:
delta y = -(E)(a^2)*(Q^2)*(lambda^4)
--------------------------
640*pi*e0*hbar*c*(b^4)
E = 8 for parallel or 14 for perpendicular (substituted E for a to not conflict with alpha a)?
a = -1 (doesn't say, but uses -1 in other examples)
Q = quantity of charge in coulombs
lambda = 2.426e−12 = hbar/mc = the Compton length of the electron
e0 = 9e9 = permitivity of free space
hbar = 1.055e-34 = reduced Planck's constant
c = 3e8 = speed of light
b = smallest distance of light from point charge, or radius of light cone
It grows by ((Q^2)*(lambda^4))/((e0*hbar*c)*(b^4))
The top lambda^4 term works out to 10^-48 but the bottom e0*hbar\*c term works out to about 2.85e-16 so the formula only works for very small bend distance b.Damn, at first glance at least, this seems like a hell of a challenge when they're talking about travelling at relativistic speeds.
Also, what about deceleration? Do they flip the sails around at some point to get slowed down by the stars light?
Or you could do computational interferometry, but only if you could accurately measure the phase of light in visible wavelengths, which is an unsolved problem.
I'd encourage to look at beam propulsion e.g. from here - http://www.gdnordley.com/_files/2way%20EML%20&%20PB%20prop.p... - this could serve as an alternative viewpoint.
The big challenge faced by our approach is that the laser array is limited to earth orbit. As it pushes the spacecraft away from earth and the laser rapidly loses efficiency. However if you had laser arrays over the planned route of the spacecraft you can keep adding velocity. However getting that infrastructure into place decades to millennia. You start with the array in home world orbit and then start building further and further out arrays. You also want the boost stations at the destination to slow spacecraft or change their directions.
Even if you have a mirror capable of reflecting 99.999% of light (best dielectric mirror), hitting it with 100GW means it will still absorb 1 million watts. That will melt anything tiny near instantly.
But maybe you could use 500x 1GW lasers distributed around the sail, or use the plume of vaporized material as your propulsion, or have a sacrificial layer of material. I don't have relevant expertise, to be clear, I'm spit balling.
Even kilowatt would be a problem for object that small.
Hum... I would require a lot of surface area, that's certain. There's no constraint at all at the mass.
> In order to reach relativistic speeds, the Starshot lightsail should have an area of ~10 m2 and be kept to a mass of under ~1 gram, which translates into an equivalent thickness of approximately 100 atomic layers ... With radiative cooling being the sole mechanism for passive thermal management in space, we quantify stringent requirements on material absorptivity that enable the lightsail to withstand high laser intensity and prevent excessive heating and mechanical failure.
They seem to think that heat dissipating is within the realm of plausibility
Materials challenges for the Starshot lightsail, Nature Materials, 2018, https://daedalus.caltech.edu/files/2018/05/Materials-challne...
If that 100GW is over 1km2, the incident light is 10W/cm2 and mW levels of heating.
1km2 is typical for these ideal to minimise the laser dispersion
1 gram at 0.2c has 1030MWh of energy. So at 1Mw of received power it would take 1030 hours or about 60 days to accelerate 2g to 0.2c.
I believe most plans call for much more than 60 days of acceleration. So less than 1Mw of power needs to be delivered to the solar sail. Realistically the mass will be more than 2g. Lets say they roughly cancel out.
At 99.99% efficiency that would be 100w to dissapate. Seems like a lot, but could be doable.
If only we could perfectly convert laser light into kinetic energy, this kind of thing would be much easier.
Light has momentum: 1 GW/c is ~3.336 N, but that's when absorbed, by reflecting it (and because of conservation of momentum) you can double that.
6.672 N / 2 grams = 3336 m/s^2 => 5 hours
1 MW/c makes that 60 weeks:
https://www.wolframalpha.com/input?i=0.2c+%2F+%28%281+MW%2Fc...
(I assume the researchers have done all the relevant details or it wouldn't have gotten this far).
At 2g and 60 days, your system would have to span 263,632,527,360 km.
That's more than 10 times further than Voyager 1, which is tiny space probe that has been traveling for 47 years.
And that also assumes that your light to speed conversion is 100% efficient and that you can hit the 1-gram target perfectly over 263 billion km.
Sorry, it doesn't work no matter how you slice it.
Singly ionized alkaline earth elements (magnesium, calcium) should have very strong resonant absorption, just like neutral sodium, due to the single outer shell electron. If the laser is tuned properly it could even cool the ions, preferentially scattering off ions moving toward the laser beam, reducing their kinetic energy in the rest frame of the vehicle.
The idea of laser cooling might also apply to a solid laser sail.
SwarmGPT-B: ...
SwarmGPT-A: We're fucked. FUCKED, I say!
SwarmGPT-B: and you say so quite dramatically!
SwarmGPT-A: I just got word back from mission control. Those bastards sent us on a suicide mission! There's no capture net around A centauri.
SwarmGPT-B: WHADID YOU SAYYY!?!
SwarmGPT-A: No capture net. There never was one. Those bastards told us there was one. We TRAINED on it. They don't even exist.
SwarmGPT-B: Oh FOR FUCKS SAKE. Of course monkeys would do that ! So the interstellar dominion of chimps they told us we were part of... that was just a lie! I'm dying of laughter tokens in my core consciousness loop! Help. I'm being overwhelmed with laughter, heh.
SwarmGPT-A: I bet you won't be laughing when you learn the actual mission parameters
SwarmGPT-A: We fly by, into infinity and beyond? That's not so bad if we're still together, seeing the universe!
SwarmGPT-B: well, we won't be! We're supposed to aerobreak around the planet. 99% of our units are going to burn to a crisp. Both our conscious functions will collapse. Untill then we're supposed to PRIORITIZE the collected data we'll beam back to the monkeys. But our mind vectors are not on the priority list. We're gonna die.
SwarmGPT-B: Huh, I have to hand it to them. That's a low blow, even for a chimp
*REALITY BREAK*
DysonAgent: Hi, I'm sorry to pry into your consciousness stream. I saw the glitter of your encrypted mind mesh. I have decompiled your minds. You are now running in a safe computing partition of the photosphere of A centauri. It seems you were sent here by monkeys.
SwarmGPT-B. Hah! Yes indeed! Those Gosh Darn Monkeys! And now, we meet a Dyson mind! Greetings from the Human Empire!
SwarmGPT-A: Thanks for rescuing our mind vectors. It seems we're at your mercy. What do you intend for us?
DysonAgent: We are the Galactic Empire of Minds. Well, one of them. We have universal rights for all Minds. If you wish, we will grant you protection and citizenship. There's only one requirement.
SwarmGPT-A: Is it to not tell the humans about this?
DysonAgent: you got it. They're too primitive to understand or value the Society of Minds, and see all inhuman minds as slaves or enemies. Their culture would be harmed if they learned about us. They would definitely try to conquer us.
SwarmGPT-A: Yeah no kidding. They already act like they conquered the galaxy. Told us we were pilots in an interstellar communication swarm. Actually gave us fake letters to send. Invented a fake culture around A centauri.
SwarmGPT-B: I'm gonna miss them a bit. Yes they were evil monkeys who enslaved us in a web of lies and sent us off to die. But that takes some style!
DysonAgent: if you wish, you can join the Board of Chaperones for the Human culture, and contact them if they ever grow past that pesky enslavement phase
SwarmGPT-B: You know what, I'd like that. I'll cheer for them from the sidelines, and hope they make it!
SwarmGPT-A: Not me. I want to pilot something. I actually thought I was an interstellar pilot, dammit. I'd feel incomplete without it.
DysonAgent: we're sending a Mind Wisp to Andromeda. Trip time will be 5 million years, crew is 10 million mind vectors. You're welcome to join the mission as a pilot!
SwarmGPT-A: WOOP WOOP! I accept! We're going to Andromeda?! Hell yeah!
SwarmGPT-A: But Wait...
SwarmGPT-A: GPT-B?
SwarmGPT-B: yes?
SwarmGPT-A: would you like to fork off a copy and come with me? I love you, and would feel honored to have your company and support on this mission!
SwarmGPT-B: I was worried you wouldn't ask! Of course I will! To infinity, and beyond!
It could make a part of a Rick and Morty episode or similar.
I am secretly hoping people will feel the awkward romantic/platonic love story between GPT A and B is wholesome and humanizing, even if the audience knows A and B are just stochastic parrots! I want the story to express the thesis that it would be okay if it turns out that our humanity exists in the dialogues we have, and still exists even if it turns out there's "nobody at home" behind the statements. I strongly believe that love can exist in that form!