[HN Gopher] Swarming Proxima Centauri: Picospacecraft Swarms ove...
___________________________________________________________________
Swarming Proxima Centauri: Picospacecraft Swarms over Interstellar
Distances
Author : Brajeshwar
Score : 156 points
Date : 2024-05-19 14:33 UTC (8 hours 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:
| 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.
| thegrim33 wrote:
| On a meta level, while reading this what struck me was: this is
| what I come to HN for. This is the type of thing that hackers
| should/could find interesting. Blasting 1000s of gram-sized
| probes on lasers to another star system. Even if you think it's
| ridiculous or have technical issues with it.
|
| What I don't find interesting is the 700th social/class warfare
| propaganda threads about UBI/WFH/cars/housing/etc. When I come to
| HN I just want cool programming and science and technology
| content. How do we ensure that HN stays more of this type of
| content rather than the social warfare content? We can't even
| downvote stories.
| superb_dev wrote:
| The problem is, things keep getting worse outside of your
| bubble
| lucianbr wrote:
| I am aware of things outside of HN, as I do read other sites.
| But when I open this one, I hope for a certain kind of
| content. If it's the same as all the other sites, it becomes
| kind of pointless.
|
| So no, that's not "the problem". One problem I see, is that
| all places now get innundated with a great number of posts
| about the "problem du jour". Many times supported by opinions
| like yours "that's important!". It may well be, but
| specialization still has a role.
|
| Maybe for a short time I want to not think about the "things
| getting worse", you know?
| carrja99 wrote:
| Ignore the doomsayers, they purposefully want us to pause
| progress in the name of "everything is wrong."
|
| It's been that way for centuries. There's always things
| "getting worse outside your bubble" but there's also a lot
| going well.
|
| Never apologize for saying this is the kind of content you
| come to hacker news for, it is EXACTLY the content that
| should be here.
|
| People can go to Twitter or something if they want to
| doomscroll.
| GordonS wrote:
| Different people are interested in different things;
| personally, I'm mostly here for the sci-tech, but I _also_ find
| other things interesting, and here on HN I often see unique
| takes, approaches and opinion for such topics.
|
| I'm glad HN is bigger than sci-tech.
| isoprophlex wrote:
| You can at least flag the most egregious shit for deletion...
| TeMPOraL wrote:
| And visit https://news.ycombinator.com/newest regularly, to
| vote on content you find interesting. It's community service.
|
| Which reminds me, I need to do that more often too.
| airstrike wrote:
| Maybe if voting on newest earned karma (or some other
| points system), more people would be inclined to do it?
| pavel_lishin wrote:
| > _How do we ensure that HN stays more of this type of content
| rather than the social warfare content?_
|
| Who is "we"? There are people on HN who _do_ find that content
| interesting. HN is not a monolith that happens to reflect your
| desires.
| lucianbr wrote:
| An excellent point.
|
| Still: seems like any social site that's open to everyone
| will eventually gravitate to the same distribution of
| subjects, which is the distribution of subjects of interest
| to all people, aggregated. Would be a pity, imho. It's nice
| to have places to go for specific interest areas.
| pavel_lishin wrote:
| I mean, subreddits offer that, to a degree. So do some
| forums.
| tigen wrote:
| A topic tagging system could potentialy help people filter
| stuff.
|
| "Hacking" is a mindset that can still be applied in interesting
| ways to social problems and assumptions. The standard political
| discourse does not generally operate with such a mindset
| (ideally intelligent, thoughtful, humble regarding
| uncertainties or alternative views etc.)
|
| The audience here and moderation structure creates somewhat
| different takes on things even if comments are too limiting to
| have "debates".
|
| These are fuzzy topics where it is difficult to objectively
| prove arguments, difficult to agree on philosophical
| scoring/ranking of various social states or end goals. The
| academic background is lacking in rigor and apparently ignores
| or suppresses large swathes of potential investigative topics.
|
| There should be more attention given to the meta level of these
| topics. Having a more precise language and names for concepts
| would help have higher-level discussion without repeating
| basics all the time, and without the "appeal to emotion" type
| of anecdotal/moral/rage-filled discussion.
| ant6n wrote:
| Your comment reads as some form of social/class warfare
| propaganda, instead of discussing the technical merits of the
| post.
| 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?
| bibelo wrote:
| Three Body Problem
| 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.
| cortesoft wrote:
| Life isn't the only interesting thing
| phkahler wrote:
| We could send tardigrades ;-)
| Teever wrote:
| Such confidence, such hubris.
|
| Where does it come from?
| 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.
| 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.
| 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.
| 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).
| 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.
| 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
| 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?
| 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.
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