[HN Gopher] Swarming Proxima Centauri: Picospacecraft Swarms ove...
___________________________________________________________________
Swarming Proxima Centauri: Picospacecraft Swarms over Interstellar
Distances
Author : Brajeshwar
Score : 259 points
Date : 2024-05-19 14:33 UTC (1 days ago)
(HTM) web link (astrobiology.com)
(TXT) w3m dump (astrobiology.com)
| MR4D wrote:
| Seems like this would be easy to test around the asteroid belt,
| and pretty much doable with today's technology.
| PicassoCTs wrote:
| Fire it directly towards the sun, let it de accelerate with solar
| sail.
| davedx wrote:
| > A swarm whose members are in known spatial positions relative
| to each other, having state-of-the-art microminiaturized clocks
| to keep synchrony, can utilize its entire population to
| communicate with Earth, 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. This effectively multiplies the power from any
| one probe by the number N of probes in the swarm, providing
| orders of magnitude greater data return.
|
| 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...
| uoaei wrote:
| Can you say relativistic corrections hell? "Over lightyears"
| means it takes literally years for these things to coordinate
| moves with each other, to say nothing of post-launch
| coordination messages from Earth.
| mlyle wrote:
| > "Over lightyears" means it takes literally years for these
| things to coordinate moves with each other
|
| The swarm ends up around 100,000km wide. Initial distances
| are longer, but never on the order of light years.
| maxrecursion wrote:
| Yeah, I think he missed the part where it discussed the
| swarm would have to be mostly autonomous since
| communicating back to earth for any sort of management
| commands is completely out of the question.
|
| It's amazing they can still do it with voyager which is
| roughly 24 hours for one way traffic, 48 for round trip.
| uoaei wrote:
| I'm not sure "swarm over interstellar distances" makes any
| sense here, then. How many stars are within 100,000 km of
| each other and what percentage of stars does that
| represent?
| mlyle wrote:
| The idea is, you launch a large number of probes,
| accelerated one by one, working so that they'll arrive at
| the same time to the same star (Proxima Centauri). If you
| lose a bunch, no problem.
|
| They'll be spread out over a big distance, but team up to
| do imaging and to return data from that star.
| SideburnsOfDoom wrote:
| > They'll be spread out over a big distance
|
| 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_sta
| r_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...
| mlyle wrote:
| Yes, of course. We all know these numbers. I _teach_ a
| space engineering class where students chirp out in
| recitation "400km to LEO, 40,000 km to GEO, 400,000 km
| to the moon". The degree of "well acktually" trying to be
| pedantic here is unnecessary.
|
| 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.
| SideburnsOfDoom wrote:
| My apologies, I was not trying to be pedantic or to
| correct you. It's for other readers too and does not
| contradict, really.
|
| 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".
| mlyle wrote:
| Seems like I should be the one apologizing; it's hard to
| know tone online, and I thought you were trying to assert
| it wasn't a swarm like the other people. Sorry about
| that.
|
| (P.S. they're not the right numbers; just the right
| orders of magnitude).
| SideburnsOfDoom wrote:
| > How many stars are within 100,000 km of each other and
| what percentage of stars does that represent
|
| 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.
| uoaei wrote:
| You're missing the point entirely: framing the swarm as
| "covering interstellar distances" is misleading and
| betrays a certain naivete in thinking about space travel
| that compromises the reporting on this plan.
| SideburnsOfDoom wrote:
| > You're missing the point entirely
|
| 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-naive 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.
| mlyle wrote:
| Bees swarm over distances of miles. But the swarm doesn't
| stretch out miles. They form a dense group that moves
| somewhere miles away.
| MarkusQ wrote:
| Ships _spread out_ over 100,000km will literally cover
| interstellar distances as a swarm by _traveling to
| another star_. That's the whole point. A bunch of insects
| can swarm a thousand km from the time it forms to when it
| breaks up, even if the swarm itself is never more than a
| couple of km in diameter.
| mlyle wrote:
| They don't need to keep exact position; they just need to know
| their relative distance offsets from Earth to synchronize
| pulses.
|
| 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.
| nynx wrote:
| station keeping is definitely possible. each craft could use
| its comms laser for impulse
| qnleigh wrote:
| I agree. Sounds like the plan is to have the signals from each
| probe add up coherently, which means the laser pulses need to
| be coherent with each other. The wavelength of optical light is
| 100s of nanometers, so that is the level of precision required
| spatially, relative to the much much larger probe spacing that
| they quote. This (plus the required temporal coherence) is
| probably not possible without the probes actively locking their
| lasers to each other, but now each probe needs the optics to
| send and detect the optical signal from at least its nearest
| neighbors. I can't say if this is impossible given the weight
| restrictions, but it sounds rough.
| golol wrote:
| This is what I want Starship to succeed for.
| tootie wrote:
| I'm confused about these gram-scale devices that have so many
| capabilities in board. And is the laser terrestrial or deployed
| to space?
| bwanab wrote:
| If we think we're being visited by aliens, then this suggests
| that this is the kind of thing we should be on the lookout for
| here.
| Jerrrrry wrote:
| There have been a couple candidates, so damning a lot of
| astronomers would rather not talk about it.
| EthanHeilman wrote:
| I don't think we should expect alien mission architectures are
| likely to look like this in terms of mass or size unless we are
| very near the homeworld of the aliens and they have just
| started exploration. A civilization that has been building
| systems like this for 100s to 1000s of years would have
| deployed lasers along the flight path of the spacecraft
| allowing significantly higher and more efficient payloads.
|
| 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.
| jimmcslim wrote:
| Like that meteor in Portugal last night? If one of these
| probes, albeit very small in mass, but travelling very fast,
| what is the energy released on impact?
| foota wrote:
| On a similar vein, I have a deep yearning for a solar gravity
| lens to be used to image exo planets within my lifetime. I've got
| a long time, but it's frustrating to see so little movement on
| big astronomy projects like these.
| dylan604 wrote:
| so little <public> movement. there is a concept of decadal
| projects where they are being iterated on in working groups or
| just smaller groups in general. they may not get much public
| discussion on purpose. the ideas just might not be viable yet,
| but then some new tech comes along and an old idea gets pulled
| back out of the drawer. also, so ideas are so fantastical, they
| receive immediate negative blow back which makes it impossible
| for congress critters to get on board and fund them. luckily,
| the public success of JWST (even after all of the delays) has
| helped put a positive look on some of these projects. just hope
| that Boeing is not attached to it
| foota wrote:
| I'll hold faith then :)
| patrick0d wrote:
| All you need to do to see some change is pick a goal and commit
| a long time towards it. So if you have a long time maybe you
| can help with this project that you would like to see.
| kilroy123 wrote:
| Same here! One of my dream projects to see happen before I die.
|
| For those that don't know what this is or could mean:
|
| https://www.space.com/sun-gravity-could-help-observe-exoplan...
| kemmishtree wrote:
| You've got a long time--Will you please kindly take personal
| responsibility to ensure we see images of seasonal foliage
| changes in vast forests on superearths hundreds of light years
| away using billions of solar gravity lensing observatories
| built and launched by self-replicating processes? Also don't be
| a slacker and get first lens light by 2050?
| was_a_dev wrote:
| What about the Terrascope [1] concept instead? Using the
| Earth's atmoshpere as a refractive lens. This requires a
| telescope of L2 rather than some 540AU away for a solar gravity
| lens.
|
| 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...
| bibelo wrote:
| Three Body Problem
| can16358p wrote:
| Same came to my mind though even accelerating few grams is
| challenging, and _SPOILERS FROM HERE_ sending something like a
| human brain like in a capsule would definitely not be
| achievable with something like this with our understanding of
| technology and science. Yet, I 'd love to see how nuclear
| detonations in space like in 3BP would play out in real world.
| pavlov wrote:
| I was born 11 years after the Moon landing. Theoretically, if I
| lived to be 120, I might see the data from this Proxima swarm
| fly-by. (Assuming a 2076 launch, twenty years travel time at
| 0.2c, and four years for the information return trip.)
|
| 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.
| tokai wrote:
| >Obviously there's nothing on Proxima, just like there's
| nothing on the Moon.
|
| 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.
| dylan604 wrote:
| > they are varied and brimming with interesting features.
|
| one of those features being lifeless
| zardo wrote:
| For all we know Europa and Enceledous could support
| millions of tons of biomass.
| idlewords wrote:
| Right now Enceladus is the most likely target for extant
| life in the solar system, and is one of four moons with a
| subsurface water ocean. We know almost nothing about them.
| greggsy wrote:
| In order to make any of these interstellar dreams at all
| useful, we'd need to master the ability to explore the
| full gamut of what a solar system can offer. It's just
| not sexy enough to make headlines.
| wongarsu wrote:
| Most proposed interstellar missions (including the
| article) are just flybys. We won't learn much more about
| how to do flybys by observing our own solar system.
|
| 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
| cortesoft wrote:
| Life isn't the only interesting thing
| phkahler wrote:
| We could send tardigrades ;-)
| euroderf wrote:
| Assuming bombardment by radiation, they might quickly
| evolve into our superiors.
| Teever wrote:
| Such confidence, such hubris.
|
| Where does it come from?
| samplatt wrote:
| Many humans spend their formative years learning that
| they can overcome most obstacles with enough effort and
| willpower.
|
| This optimism carries over to their adult life, despite
| the newer obstacles being infinitely more difficult and
| complex so as to be incomparable.
| oasisaimlessly wrote:
| That's not relevant to assuming that the rest of the
| solar system is lifeless; I'm assuming you didn't see
| what GP was replying to.
|
| 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.
| bunabhucan wrote:
| In 2124 someone will synthesize your consciousness from this
| and other posts and tell "you" about the results.
| idlewords wrote:
| Please don't synthesize my consciousness from Hacker News
| posts.
| Loughla wrote:
| Or my online presence in totality, to be honest. Who I am
| online is only a small part of who I am.
|
| 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.
| ben_w wrote:
| On the internet, I'm a wolf. So synthesising a persona
| from my digital presence would be...
|
| well, 100% on brand for how weird everything else is,
| honestly.
| jon_richards wrote:
| By asking that, you just guarantee your synthesized
| consciousness will be miserable.
| idlewords wrote:
| Well, at least it will be accurate.
| konstantinua00 wrote:
| too late, my imagination is fuuuming
| pavlov wrote:
| It's going to be Roko's Basilisk who is angry at me for
| making fun of cryptocurrency on HN and therefore delaying the
| Buttcoin Singularity by 3.7 minutes.
|
| 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.
| PhasmaFelis wrote:
| My favorite thing about Roko's Basilisk is how a bunch of
| hard-nosed rationalists using remorseless logic somehow
| managed to conclude that God is real and will torture you
| in Hell forever if you sin.
| mensetmanusman wrote:
| a zip file of his consciousness is still a zip file :)
| DrBazza wrote:
| The trouble with being at the beginning of space travel is that
| we will get better and faster at it.
|
| 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.
| JumpCrisscross wrote:
| > _if we were to launch in 2076 at 0.2c, we could eventually
| launch something faster_
|
| If you never launch at 0.2c, you're less likely to build the
| kit that launches something faster later.
| avensec wrote:
| > In fact there's a 'law' or 'paradox' that I can't remember
| the name of
|
| The incessant obsolescence postulate.
| anvandare wrote:
| I think you're thinking of the Lightspeed Leapfrog trope[1].
|
| (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/LightspeedLea
| pfr...
|
| [2] https://en.wikipedia.org/wiki/Law_of_the_handicap_of_a_he
| ad_...
| andy99 wrote:
| We launched the first Voyager in the 70s. 50 years on do we
| have anything catching up to it?
| JoeAltmaier wrote:
| Obviously there's nothing...
|
| I was stumped by that. You don't know until you look.
| JonChesterfield wrote:
| What's the range on a laser, in terms of how far away is the beam
| still fairly narrow if it doesn't hit anything? Function of the
| geometry of the emitter?
|
| 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.
| was_a_dev wrote:
| For a Gaussian laser beam, a good metric is the Rayleigh
| distance, which is the distance where the beam diverges to
| sqrt(2) of it's initial beam size (waist) [1].
|
| 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].
|
| [1] https://en.m.wikipedia.org/wiki/Rayleigh_length
|
| [2] https://en.wikipedia.org/wiki/Bessel_beam
| JonChesterfield wrote:
| Thanks for the link. What I'm getting is we think emitting
| light that doesn't spread out over distance can be done with
| unbounded power, thus we can probably aspire to make ones
| that cross greater distances by spending more power on the
| creation and a degree of inventing new materials. Sound about
| right to you?
| was_a_dev wrote:
| I think for the any initial project, we'll have to resort
| to 1km scale laser arrays. These would allow for a beam
| with a low dispersion so there can be a good initial
| acceleration.
|
| After a few hundred AU, the probes should be close to the
| target velocity
| perihelions wrote:
| I don't believe that Bessel beam is a workaround for the
| diffraction limit in the far-field. That diffraction limit is
| a universal law for any optical system with a finite-size
| aperture (i.e. the size of the focusing mirror array). To the
| extent you're approximating a Bessel beam in the real,
| physical world, we're still stuck with finite apertures, so
| it's the same law.
| was_a_dev wrote:
| I agree. It would depend on the definition of "far-field"
| in this example, even for a quasi-Bessel beam there is a
| near region that maybe useful for this example given a
| large enough aperture.
|
| 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...
| zackmorris wrote:
| On a whim I looked up whether magnets or electric fields can
| refract light, and while they generally can't, strong
| electric charges can:
|
| 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
|
| Unfortunately the math is not written well IMHO, and it
| doesn't have any numeric examples, so the reader is forced to
| understand the entire paper before drawing conclusions.
|
| 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 x 10-8
| radian for an x-ray of wavelength 5*lambda*e.
|
| Probably a larger "impact parameter b, over which distance
| the bending occurs mostly" requires a proportionately larger
| electric field or point charge.
|
| 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.
| bufferoverflow wrote:
| Every high power laser propulsion proposal I have seen requires
| magical materials that don't exist, and aren't likely to exist
| any time soon.
|
| 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.
| maxbond wrote:
| And that megawatt will be absorbed in a tiny surface area, no?
| Given that it's a laser? So even though the sail has plenty of
| surface area to reject heat, it won't be able to conduct it
| faster than it vaporizes.
|
| 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.
| bufferoverflow wrote:
| 1 megawatt of continuously absorbed power would require a lot
| of mass to dissipate without melting. But since we're talking
| about gram-sized objects, there's no chance.
|
| Even kilowatt would be a problem for object that small.
| marcosdumay wrote:
| > 1 megawatt of continuously absorbed power would require a
| lot of mass to dissipate without melting
|
| Hum... I would require a lot of surface area, that's
| certain. There's no constraint at all at the mass.
| EthanHeilman wrote:
| Starshot which is the above proposal is likely based uses
| 10 meter square solar sails that are 100 atoms thick.
|
| > 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...
| barbegal wrote:
| It's a nice idea but surely any variation in mass of the
| lightsail will result in significant forces which will
| literally pull the sail apart. And with a thickness of
| 100 atoms that variation might be just a few atoms. I
| can't see how this can be manufactured to take such high
| forces and be so light and thin.
| EthanHeilman wrote:
| That's why it is a research project, it is hard to do.
| rocqua wrote:
| No, lasers are rather inaccurate over large distances. So it
| would be very uniformly spread.
| jerf wrote:
| "Laser" actually refers only to the generation technique and
| the resulting _phase_ coherence of the resulting photons.
| Lasers don 't have to be particularly tightly focused. In
| fact if you've got a laser pointer at home, there's may be a
| lens on it you can take off, and there will be quite a spread
| on it. It is focused down by a lens and if you look carefully
| at the resulting spot you can see interference speckles from
| the focusing lens. Without the lens the laser will lack those
| speckles and you'll get a uniform, much larger spot from the
| raw laser.
| was_a_dev wrote:
| Is a single probe subject to 100 GW? Isn't that just the output
| power of the laser array.
|
| 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
| rocqua wrote:
| But you don't need to hit the sails with 100GW to get a few
| grams of weight up to relativistic speeds right?
|
| 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.
| ben_w wrote:
| > 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.
|
| 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).
| pfdietz wrote:
| I've thought the better idea would be to tune the laser beam to
| resonantly scatter off certain ions that are kept trapped in a
| magnetic field.
|
| 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.
| snakeyjake wrote:
| Swarms for this application seem inefficient to me because they
| duplicate so much of the mass-- mass that could be used not as
| single basket but as adequate redundancy in a single craft.
|
| 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?
| dj_mc_merlin wrote:
| > Swarms for this application seem inefficient to me because
| they duplicate so much of the mass-- mass that could be used
| not as single basket but as adequate redundancy in a single
| craft.
|
| 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.
| snakeyjake wrote:
| >> 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.
|
| 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.
| lukeschlather wrote:
| > 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".
|
| 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.
| snakeyjake wrote:
| > By changing orientation they can control the
| speed/direction in which they slow down.
|
| 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.
| lukeschlather wrote:
| I think the analogy would be more like craft falling
| through the atmosphere. I found one NASA article that
| says interstellar wind speed is 26 km/s, which is four
| orders of magnitude smaller than .2c. Practically
| speaking I think you can model it as a constant .2c
| headwind.
|
| > 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.
| konstantinua00 wrote:
| I don't think you need to worry about winds when
| travelling at 0.2c...
|
| 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
| downrightmike wrote:
| I'd like to see a stellaser. Asimov wrote about them, but we'd
| just need to get one close enough to the Sun and have unlimited
| power to the darker parts of space
| GartzenDeHaes wrote:
| Could be a cover project for something classified, such as a
| ground based laser paired with an orbital mirror on lets say an
| X-37 or something.
| bluerooibos wrote:
| > synchronizing probes' on-board clocks with Earth and with each
| other to support accurate position-navigation-timing (PNT).
|
| 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?
| minitoar wrote:
| No, it's a relativistic flyby.
| avmich wrote:
| > Tiny gram-scale interstellar probes pushed by laser light are
| likely to be the only technology capable of reaching another star
| this century.
|
| 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.
| pfdietz wrote:
| If a large number of probes can be kept optically coherent, then
| so can separate mirrors here in the Solar System. A telescope
| 100,000 km across (the size of this swarm) could resolve features
| a fraction of a km across at Proxima Centauri.
| mr_toad wrote:
| The trouble is you need to keep the elements of an optical
| telescope very very precisely aligned - a precision on the
| order of the wavelength of light, which is impractical in
| space.
|
| 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.
| pfdietz wrote:
| Correct me if I'm wrong, but doesn't this interstellar swarm
| scheme require onboard clocks accurate to 1/frequency of the
| the light being used? Which is equivalent to the accurate
| measurement of phase.
| mchouza wrote:
| They don't, see https://arxiv.org/abs/2309.07061 . The
| basic idea is to use "picosecond-level" synchronization to
| improve the signal-to-noise ratio. They mention that a
| truly phase-coherent swarm would perform much better but
| they consider that a longer term prospect (section 2.1.4).
| wwarner wrote:
| I think LISA Pathfinder showed that it's possible to phase
| lock lasers over very long distances as long as they are in a
| stable orbit. It's basically a metal cube in freefall
| surrounded a proximity sensor, so that as the sensor drifts
| toward the cube, but long before making direct contact, the
| apparatus can adjust it's position. The experiment
| demonstrated that the system can be used to keep mirrors
| precisely separated over large distances in support of
| gravitational wave detection. I would think something like
| this could be adapted to align lots of things that are in a
| stable orbit.
| barfbagginus wrote:
| SwarmGPT-A: We're fucked.
|
| 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!
| can16358p wrote:
| Frankly reading this was lovely!
|
| It could make a part of a Rick and Morty episode or similar.
| barfbagginus wrote:
| Thank you! It was kind of a data dump, and DysonAgent feels
| like a somewhat abrupt and creepy deus ex machina with no
| character development. But I love that kind of stuff! I'm
| glad you enjoyed it!
|
| 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!
| konstantinua00 wrote:
| I thought the punchline would be "we are intergalactic empire
| and are sending mind mails to another galaxy, there's a capture
| net on the other side"
| ggm wrote:
| People who host pitch-drop experiments don't do it with an
| expectation of a definitive outcome inside their lifetime.
|
| 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.
| system2 wrote:
| Imagine killing bunch of Proxima Centauri people with our gram
| nanobots by accident and not even knowing it. That would really
| puzzle them.
| hacker_88 wrote:
| Have they thought of exploding nukes to propel the Craft with
| radiation
| dustfinger wrote:
| If it is only feasible to accelerate low mass objects to the
| speed of light, no matter the level of technological advancement,
| then it might be the case that highly intelligent and technically
| advanced beings have reduced the mass of their own bodies to
| explore galaxies. Maybe the most advanced and intelligent beings
| are mere grams in mass. It would make for an interesting sci-fi
| at the very least ;-)
| dhosek wrote:
| Or they've cryonically frozen their brains and put them in
| ships powered by nuclear explosions enabling them to travel at
| 0.2 _c_ assuming that the aliens at the other end of the trip
| will be curious enough to reanimate the brains and build them
| new bodies.
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