[HN Gopher] Mission to reach and operate at the focal region of ...
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Mission to reach and operate at the focal region of the solar
gravitational lens
Author : WithinReason
Score : 199 points
Date : 2022-07-28 10:22 UTC (6 hours ago)
(HTM) web link (arxiv.org)
(TXT) w3m dump (arxiv.org)
| garettmd wrote:
| Can someone ELI5 for me?
| MattPalmer1086 wrote:
| Use the sun's gravity as a giant lens (bends light) so you can
| see a really long way away.
|
| But the focal point of this lens is about 500 times the
| distance of the earth to the sun, so difficult to get to.
| walnutclosefarm wrote:
| It's an interesting idea, and why not write a paper about it and
| try to get it published? Every academic needs papers with their
| name on them, and thinking about this had to be fun, if you don't
| have anything useful to do with your time.
|
| But as an actual scientific investment, in my opinion, it belongs
| pretty near the bottom of pile of things we should spend our
| astronomy / cosomology / astrophysics budget on. The cost per
| unit of new information is just way too large, and the risk of
| mission failure too high, to justify making it a priority.
| superkuh wrote:
| It's not a new idea and there already have been dozens of
| papers, and entire books (http://erewhon.superkuh.com/library/S
| pace/Spacecraft/Deep%20...), published about using the solar
| gravitational focus as a lens and sending a spacecraft there.
| In fact NASA was already funding early mission studies like the
| Heliopause Electrostatic Rapid Transit System (HERTS) a decade
| ago.
|
| And not only is it good for planetary sciences, it's good for
| cosmology too since it enables looking at the truly small scale
| structure of the cosmic microwave background. A mission to the
| gravitational focal line opposite some star should be one of
| the highest priorities.
|
| http://erewhon.superkuh.com/library/Space/Spacecraft/Diffrac...
|
| http://erewhon.superkuh.com/library/Space/Spacecraft/Direct%...
|
| http://erewhon.superkuh.com/library/Space/Spacecraft/Image%2...
|
| http://erewhon.superkuh.com/library/Space/Spacecraft/Mission...
|
| http://erewhon.superkuh.com/library/Space/Spacecraft/Photome...
|
| http://erewhon.superkuh.com/library/Space/Spacecraft/Resolve...
| JoeDaDude wrote:
| Claudio Maccone's proposal, to put a radio telescope at the
| solar focal point for SETI or communications purposes, is
| included as a chapter titled "Radio Links enabled by
| Gravitational lenses of the Sun and Stars" in the book
| Communications with Extraterrestrial Intelligence edited by
| Douglas Vakoch [1].
|
| [1]. https://www.seti.org/book/communications-
| extraterrestrial-in...
| bowsamic wrote:
| Are you a physicist? This sounds like the opinion of a non-
| physicist. In physics we usually work on and publish basically
| any idea possible, just so that we have a full picture of what
| actually is possible and what the challenges are. Of course
| it's better if it's practical but that's not a necessity
| pmayrgundter wrote:
| "Using a meter-class telescope one can produce images of the
| exoplanet with a surface resolution measured in tens of
| kilometers and to identify signs of habitability."
|
| Here's gmaps satellite view at ~10km/px
|
| EDIT: fixed permalink
| https://www.google.com/maps/@41.4220797,-93.7912673,6877284m...
|
| also: https://imgur.com/a/JwHmaIY
|
| Wow.
| bartread wrote:
| That link just opens a standard map of the whole globe in a
| flat projection - I think you might need to use the sharing
| link generator to share what you intended.
| simias wrote:
| I think that's what they wanted? Although it's still a
| strange way to communicate that given that it'll change
| wildly based on screen resolution. A screenshot would
| probably be a better idea.
| rchard2scout wrote:
| I'm not sure if it's possible to easily share the correct
| settings in an URL, but:
|
| In the Layers menu, set it to Satellite, Globe view, and turn
| off Labels. Then, zoom until the earth is ca. 1275 pixels
| wide
| abhaynayar wrote:
| I think the link intended to show 10 km/pixel, to give an
| idea of what it would look like. It shows a scale of length
| 1000 km to me, if it is 10 km/pixel then there should be a
| 100 pixels within that length, which seems okay as a sanity
| check. But yeah, it depends on the screen resolution as well.
| pmayrgundter wrote:
| Thanks, fixed!
| p1mrx wrote:
| When you can resolve territorial borders and labels, that's a
| pretty strong sign of intelligent life.
| codethief wrote:
| I think you might want to switch to satellite view. There are
| definitely human-made structures that you can recognize at
| 10km/px.
| pmayrgundter wrote:
| Weird, fix didn't work either :( Just use the imgur :)
| phkahler wrote:
| Didn't they say the spacecraft will have to move around to get
| each pixel? That means the planet would turn between pixels and
| you wouldn't get a coherent image. It would also take a very
| long time to cover 10's of thousands of pixels. May need to
| send many imagers and combine the results...
| jackmott wrote:
| WithinReason wrote:
| I wonder if you could use just 1 spacecraft and actually
| exploit the rotation of the planet to "scan" the planet
| surface in 1 dimension. The movement of your telescope would
| provide the other dimension, so in a slow fly-through you
| could get a 2D image of the planet surface. So e.g. imaging a
| 12000 km (Earth-size) planet at 10 km/pixel would take 1200
| planet rotations, each providing a row of pixels, taking
| about 3 years assuming it's rotating at the speed of Earth.
| You would just have to know ahead of time the orientation of
| the planet's axis of rotation so you approach the "focal
| region" from the right angle.
| Brian_K_White wrote:
| Before I read this... "focal region" sounds nonsensical to me.
| Surely the focal length and direction depends on the thing you
| want to look at? The "focal region" would be something like a
| sphere starting some distance from the sun and extending out in
| all directions to infinity?
| WithinReason wrote:
| I think that's why it's called a focal _region_ instead of a
| focal _point_.
| simias wrote:
| Given the scales we're talking about I presume that everything
| you want to look at is effectively "at infinity", as such I
| expect that you consider where two parallel rays would meet due
| to solar lensing and that's your focal region.
| Orothrim wrote:
| I don't believe so, I believe that the size and gravity of the
| sun have a gravitational effect on space an result in a
| focusing of light at 500+AU distance from the sun. Hence the
| focal region is around this sphere and is where you would "sit"
| to use the sun as a lens and get information about the universe
| on the opposite side of the sun.
|
| https://en.wikipedia.org/wiki/Solar_gravitational_lens
| krisoft wrote:
| > Surely the focal length and direction depends on the thing
| you want to look at?
|
| Yes.
|
| And "aiming" your observatory involves moving it on that
| sphere. Given the distances involved that is pretty much either
| impossible or time prohibitive.
|
| The region starts at 548 AU from the Sun. So 548 times the
| average Sun-Earth distance.
|
| In an ideal world you would teleport your camera to this
| location instantaneously, take a picture and then teleport to
| the next location to look at something else.
|
| We don't know how to do that. The distances are immense.
|
| So instead we pick a target, and send out a satellite or
| satellites on the opposite vector from it to take a peek. There
| is a single point where the target will be in perfect focus,
| but in practice (as the paper shows) the target is "in-focus"
| enough in a larger region that your satellites can take a
| picture while they fly through the region around the ideal
| point.
| adg001 wrote:
| It seems there are a pretty good deal of ideas for ever more
| sophisticated imaging technologies. That's nice. However it would
| be more reassuring to come up, at the same time (or in due
| course), with a similar supply of clever ideas for more
| sophisticated rocket engines, or, more likely, with a long series
| of fundamental contributions to our understanding of physics and
| biology. The ambition of the proposed mission is to reach a focal
| region ~548-900 AU away in order to image exoplanets which are
| distant up to 100 light years. I am sorry to have to remind us
| all about this, but given the extenuating long journey to reach a
| region that is not any closer than 548 AU, it would be even more
| "painful" to discover even more distant exoplanets which would
| remain beyond reach for all practical purposes - As per me
| discoveries of such level should remind us to reaffirm our
| commitment to take care of the only planet we can live for the
| foreseeable future.
| [deleted]
| cptaj wrote:
| Astronomy still provides useful insights regardless of whether
| we can reach those places or not.
|
| That said, we are indeed researching ever more advanced
| propulsion technologies!
|
| We've made great strides in electric propulsion, which is far
| more efficient for long voyages than chemical rockets. This
| tech is already in wide use today in satellites and probes of
| all kinds.
|
| We're ramping up research in nuclear rocket propulsion again.
| There are several branches here: nuclear electric, nuclear
| thermal and nuclear pulse. Of these, the last one is the least
| developed since it basically means using nuclear explosions to
| boost you, but it has the most promise for futuristic spaceship
| drives.
|
| There's also the possibility of using antimater pulse drives
| but that's a hairy can of worms. Very hard to produce the fuel
| in enough quantities.
| lstodd wrote:
| 30 years.. I wouldn't be surprised when a bigger and better
| telescope launched 10 years later arrives there 15 years before
| this crazy contraption.
| abecedarius wrote:
| On that timescale my bet would be on very large telescopes
| built in space nearer us (supplanting the ones built on Earth
| and launched then unfolded). This wouldn't perfectly substitute
| for a solar gravitational lens scope, but it could do a hell of
| a lot.
| Cthulhu_ wrote:
| Maybe, but only if there's a big leap in propulsion technology,
| and as far as I know there's not been anything big in that
| regard in the past 50-odd years. Closest thing is probably
| reusable rockets to reduce cost.
| skykooler wrote:
| There's a few things that could be used to complete the
| mission significantly faster with basically-current tech
| (e.g. NERVA, or Project Orion), but even for deep-space
| missions they are unlikely to see use any time soon.
| sandworm101 wrote:
| A much better idea is the terrascope, using Earth's upper
| atmosphere as a refracting lens. This wouldn't require a multi-
| decade mission, nor a huge sunshield.
|
| https://arxiv.org/abs/1908.00490
| [deleted]
| TomGullen wrote:
| An excellent video on this:
| https://www.youtube.com/watch?v=jgOTZe07eHA
|
| Earths atmosphere and weather affects this sort of telescope
| IIRC and will filter out some lightwaves but seems like a much
| easier win
| jcims wrote:
| Couple of examples shot from the ISS -
| https://www.youtube.com/watch?v=1t8UNxY2bgQ
| someguydave wrote:
| the sunshield would not be huge at 900 AU
| londons_explore wrote:
| The fact that this telescope takes 30+ years to get into position
| and take a photo, and that it in its lifespan can only look at a
| single planet, is a real disadvantage...
| est31 wrote:
| You just have to mass produce these things and send them to
| interesting targets in parallel.
| mabbo wrote:
| 2042: Earth receives a message from an alien intelligent species
| 32 light years away.
|
| 2109: Aliens receive a reply, which includes a map of their own
| world, including where their largest cities are located.
|
| I'm just saying, this is totally a possibility! We can creep on
| the neighbours!
| multiplegeorges wrote:
| > Aliens receive a reply, which includes a map of their own
| world, including where their largest cities are located.
|
| I think we'd interpret this as a threat, maybe, like a target
| map. They might too.
|
| Probably best to reply with something more innocuous, like the
| Fibonacci sequence.
| dylan604 wrote:
| yeah, that was my reaction as well.
|
| "We hear you, and just letting you know, we know where you
| live and have started targeting solutions. Just so you know,
| we're all armed down here!"
| causality0 wrote:
| _solar sailing technologies and in-space aggregation of
| modularized functional units to form mission capable spacecraft_
|
| Am I alone in thinking this is somewhat pointless to discuss
| before the prerequisite technology is developed? It's a bit like
| "how to keep your sentient sexbot from deciding to murder you".
| Like if we could do those things in the first place there would
| be a thousand applications with a better return on investment
| than this.
| krisoft wrote:
| > Am I alone in thinking
|
| Probably not. Most people have trouble thinking long term.
|
| > this is somewhat pointless to discuss before the prerequisite
| technology is developed?
|
| People wouldn't develop said prerequisite technologies if there
| are no applications for it. This paper shows that if we would
| have those technologies we could get this neat thing.
|
| > there would be a thousand applications with a better return
| on investment than this.
|
| Name them.
| TremendousJudge wrote:
| I'd say it's pretty useful to discuss hypotheticals of all
| kinds. In this case, generating ideas for uses of a technology
| that is under development might increase interest and therefore
| funding, or recruit new people to the cause, and generate new
| ideas that may be useful for the active development of the
| technology.
| croo wrote:
| Well, Diffe Whitfield envisioned an internet highway around
| 1974 then went on to find out how can we keep secrets when
| everyone has a computer in his home.
| rendall wrote:
| > _somewhat pointless to discuss before the prerequisite
| technology is developed_
|
| From the article "The study reveals elements of such a
| challenging mission, but it is _nevertheless found to be
| feasible with technologies that are either extant or in active
| development._ " (emph. mine)
|
| It's pointless to discuss the application of technologies in
| active development?
|
| > _there would be a thousand applications with a better return
| on investment than this_
|
| You veered into a baffling non-sequitur, there. ROI in a unique
| science mission to image an exoplanet 100 l.y. distant to a
| resolution of 10s km for potential human habitation? The
| successful ROI is incalculable.
| nautilius wrote:
| Yeah, have you heard of that Patent clerk in Switzerland who
| wrote about what changes when we ride on a train close to the
| speed of light - even though we're still not capable of
| building a train that fast, more than a century after. What a
| waste.
| sp332 wrote:
| This would also work for radio waves, right? We would be able to
| listen in on radio broadcasts from a distant planet.
| hamter wrote:
| For those like me who need some kind of reference for the
| distances mentioned (548-900 AU), Voyager 1 is 156.5 AU from
| earth today.
| scotty79 wrote:
| I wonder how much faster we could get there with solar sail and
| laser boost from Earth
| ben_w wrote:
| Without specifying the size of the laser, anything from "even
| slower" to "whole trip in just under 16 days".
|
| https://en.wikipedia.org/wiki/Breakthrough_Starshot
|
| http://www.wolframalpha.com/input/?i=548%20AU%2F0.2c
| lazide wrote:
| Hah, the latter number requiring some significant percent
| of earths mass being converted to energy or something?
| vilhelm_s wrote:
| Not really, it's the velocity the "Breakthrough Starshot"
| probes would reach. They propose[1] that launching each
| probe would take 84 GWh, which is not super much (about
| 15 times more than a space shuttle launch), but of course
| the Starshot probes would be much lighter than this
| proposed telescope so it's not directly comparable.
|
| [1] https://youtu.be/KIDuXQHt8pk?t=1562
| zardo wrote:
| Accelerating a meter class telescope to .2 c is well
| beyond our current capabilities, but it's nothing like
| _that_ fast.
| MattPalmer1086 wrote:
| There's a nice article on centauri dreams just published
| looking at solar and nuclear options for such a mission.
|
| https://www.centauri-dreams.org/2022/07/26/getting-there-
| qui...
| pavel_lishin wrote:
| One issue would be slowing down when you get there.
|
| You'd need to carry a deployable/detachable mirror with you
| to reflect the laser back at the craft, but that mirror
| itself would also get accelerated further out, which means
| having to correct for that, etc., etc.
| tokamak-teapot wrote:
| With a solar sail you can just start tacking, right?
| tgarv wrote:
| I think a solar sail mostly works at a broad reach or a
| run, so it would be more of a jibe than a tack ;)
| sp332 wrote:
| For this mission, you don't need to slow down or stop. Just
| keep taking image data starting at 548 AU and keep going
| until you're at 900 AU.
| Cerium wrote:
| I thought you have to move laterally to get the pixels?
| "The data are acquired pixel-by-pixel while moving an
| imaging spacecraft within the image."
| scottmsul wrote:
| The fastest way there would probably be with a nuclear
| propulsion engine, as researched in Project Orion.
|
| https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls.
| ..
| dublin wrote:
| Yeah, the solar lensing point is WAY the hell out there: since
| 1 AU is 8 light-minutes, so the 548 AU minimum works out to 73
| light-hours away. When LIGHT takes half a week to make a one-
| way trip, you're in the deep space boondocks, folks.
|
| I haven't read the paper yet, but this thing would have to have
| a fair amount of nuclear power, and comms would be a challenge
| as well. As the abstract mentions, though, while the project
| has a high degree of difficulty, there appear to be no complete
| technology showstoppers to actually doing this, so it's at
| least as doable (and considerably cheaper than) a von Braun-
| style centrifugal space station in Earth orbit.
|
| It'll be interesting to see if the idea gets any traction...
| quirkot wrote:
| For those looking for a live look at Voyager status:
| https://voyager.jpl.nasa.gov/mission/status/
| [deleted]
| alexpotato wrote:
| The solar system explorer view they have on that page is
| fantastic!
|
| I recommend clicking on the "solar system" toggle in the
| bottom middle of the view. It gives you a real sense of the
| planets, probes, asteroids etc that are flying around our
| solar system.
|
| Also reminds me of looking at air traffic control maps and
| what that might look like once intra-solar system space
| travel becomes routine.
| MichaelMoser123 wrote:
| An interview with Dr. Slava Turyshev, who is one of the authors
| of the paper. They are talking about the project
|
| https://www.youtube.com/watch?v=lqzJewjZUkk
| [deleted]
| femto wrote:
| I wonder if a cluster of stars can be treated as a MIMO
| scattering channel for more distant unknown objects? If so, it
| should be possible to resolve details in the unknown object. I
| guess the geometry would have to be such that there is
| appreciable signal from each star/scatterer (ie. sort of
| colinear), but there would be no requirement to be on a focal
| line?
| londons_explore wrote:
| You should also be able to use the fact that empty space is
| (very nearly) black to constrain any optimization algorithm.
| pmayrgundter wrote:
| Neat idea!
| femto wrote:
| I guess one problem could be that the scatterers/stars are
| luminous, so their own emissions might overpower the
| scattered signal? Maybe a cluster of darker objects? Or maybe
| luminous objects are okay if the scattered waves are coming
| from dark regions surrounding the scatterers and have enough
| angular separation that they can be resolved from the
| scatterer's own emissions?
| pmayrgundter wrote:
| hmm.. right.. if the angle of deflection is low and the
| star is close enough that its light and deflected light
| show up very close together. My intuition is this is not
| the case... remember Eddington's test of relativity was for
| deflection of starlight around our Sun. We're really close,
| yet it was observable with the moon obscuring the main
| sunlight.
|
| the article[1] says "For light grazing the surface of the
| sun, the approximate angular deflection is roughly 1.75
| arcseconds." So, what, we take the arcsin of 1.75
| arcseconds to get the apparent divergence ratio, and
| multiply that by distance to stars? As long as that value
| is larger than the aperture of your camera, then you don't
| get competing light? Or maybe you'd need something like the
| TESS satellite, where you have a screen specially created
| to only allow certain beam transits into your detector.
|
| I've worked with a nearest 10k stars database
| (https://celestiary.github.io/, zoom way out) and the edge
| of that is about 2k light years away. So very roughly,
| let's say there's 1/8th of those in a certain direction...
| so you get.. what? some 2k sample points towards some
| distant object? But really most of them wouldn't deflect
| that object's light towards Earth, but usually over or
| undershoot.
|
| Don't really know how to put these together quickly, but is
| giving me some good food for thought!
|
| [1]https://en.wikipedia.org/wiki/Eddington_experiment
| everyone wrote:
| Video about it by launchpad astronomy
| https://youtu.be/NQFqDKRAROI
| ramraj07 wrote:
| There's a ton of astronomy YouTube channels but this is now my
| favorite, dethroned pbs space time. The video that converted me
| was his supernova explanation https://youtu.be/RZkR9zdUv-E -
| for all the content out there no one else has anything this
| good about supernovae.
| WithinReason wrote:
| Starshade deploying:
|
| https://exoplanets.nasa.gov/resources/1015/flower-power-nasa...
|
| "The "petals" of the "sunflower" shape of the starshade are
| designed to eliminate the diffraction that is the central
| feature of an Aragoscope."
|
| "The starshade is a spacecraft designed by Webster Cash, an
| astrophysicist at the University of Colorado at Boulder's
| Center for Astrophysics and Space Astronomy. The proposed
| spacecraft was designed to work in tandem with space telescopes
| like the James Webb Space Telescope, which did not use it, or a
| new 4-meter telescope."
|
| https://en.wikipedia.org/wiki/New_Worlds_Mission
| SideburnsOfDoom wrote:
| I think I've read about using a swarm of these probes "at the
| focal region of the solar gravitational lens" (i.e. in spherical
| shell starting 548 AU from the Sun) in A Sci-Fi novel.
|
| I think this one:
| https://www.goodreads.com/book/show/13039884-existence
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