[HN Gopher] Texas astronomers revive idea for 'Ultimately Large ...
___________________________________________________________________
Texas astronomers revive idea for 'Ultimately Large Telescope' on
the moon
Author : dnetesn
Score : 166 points
Date : 2020-11-17 11:49 UTC (11 hours ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| moralsupply wrote:
| The major issue with a telescope in the moon would be the very
| fine sand in moon's surface that would cause mechanical failures
| evan_ wrote:
| Would it? With no wind, the sand mostly stays on the ground.
| When it does get kicked up by something, it goes right back
| down since there's no atmosphere.
| NikolaeVarius wrote:
| What. Things come down because of gravity, not because the
| pretense of an atmosphere.
|
| Presumably the stuff required to move stuff to make the scope
| will disturb at least some sand
| SlipperySlope wrote:
| Early moon mission demonstrated that rock and feather fell
| at the same speed.
|
| Ergo, ultra fine dust will fall to the moon's surface at
| the same rate as a boulder.
|
| Dust will stick with static electricity however much better
| on the moon - so your point has an even better
| justification.
| lstodd wrote:
| The point of lacking any atmosphere is that dust is not
| getting blown around. It just goes down.
| snowwrestler wrote:
| US astronauts found that static charge made the regolith
| stick to everything that came near it. Basically anything
| that moved across the surface got quickly coated. And because
| there is no weathering on the moon, the particles could be
| extremely small and sharp, which made it difficult to exclude
| or expel them. Apollo suits at the Smithsonian are still gray
| with embedded regolith. Conservators try to minimize flexing
| as the embedded sharp particles chew up the fabric fibers
| over time.
| IronRanger wrote:
| Moon dust is basically like asbestos:
|
| https://www.businessinsider.com/moon-dust-is-toxic-2012-7
| ben_w wrote:
| If it's electrostatic (rather than, say, van der Waals
| forces), could it not be dealt with by big sheets of metal
| and a high voltage supply?
| metalliqaz wrote:
| It's hard to imagine how this could be easier or cheaper than
| just launching another space telescope. I see from the article
| that it uses a spinning liquid mirror, so yes, that would require
| gravity to work, but how many extra launches would it take to get
| the telescope to the moon and _also_ the lander equipment.
| mannykannot wrote:
| The thinking might be that if we are going to return to the
| moon, then the more we have in the way of useful projects to do
| there, the better.
|
| The JWST is not exactly going smoothly, and telescopes of that
| size will not be powerful enough to study the era of the first
| stars.
| sbierwagen wrote:
| It absolutely would not be easier or cheaper. It would be a
| larger, more capable instrument than the JWST. From the paper:
| https://iopscience.iop.org/article/10.1086/588034
|
| >Without an independent infrastructure in place at a lunar
| pole, it would likely be impossible to construct and operate a
| large liquid-mirror telescope.
| mkoubaa wrote:
| Launch a mining and manufacturing unit and built it along with
| anything else we need on the moon
| metalliqaz wrote:
| That technology doesn't exist...
| m4rtink wrote:
| Until someone starts working on it, no technology usually
| exists.
| metalliqaz wrote:
| Yeah, well, right now a mining and manufacturing
| operation on Earth weighs more than the entirety of
| everything humankind has ever lifted into space, by at
| least an order of magnitude, probably several orders of
| magnitude. And it still relies on a worldwide
| transportation network to move materiel. We could build
| 10 JWST and still come in well under budget compared to
| developing that tech.
| nitrogen wrote:
| Watching Cody's Lab on YouTube, it seems people used to
| mine and refine (distill) some metals with what looks
| like less than a ton of equipment.
| helsinkiandrew wrote:
| I assume (its a shame the article didn't go into this) that the
| telescope would basically be a big fabric structure and it and
| the liquid mirror can be easily transported and set up without
| humans.
|
| The magnification of the 100M mirror make up for the lack of
| being able to point it anywhere at a much reduced cost than a
| 'traditional' space telescope.
| Jyaif wrote:
| How would they keep the liquid from evaporating? Would they need
| to enclose it?
| mrfusion wrote:
| Could it be a liquid like mercury? Would that evaporate?
| rtkwe wrote:
| Mercury does still have a vapor pressure and evaporates at
| room temperature so it could evaporate some but it would be
| in the shade so it would need warming to remain liquid more
| than cooling so the evaporation rate could be controlled and
| would probably be very very slow around it's freezing point.
| postalrat wrote:
| If its highly reflective maybe it won't heat up much in
| sunlight.
| lstodd wrote:
| It can't be in sunlight, or the telescope would be useless.
|
| The problem would be more in choosing a material that has low
| enough melting point so that making up for the radiative loss
| to keep it melted wouldn't be a big issue and at the same
| time vapor losses can be managed. Which is why they propose
| separate materials for the mirror body and its surface I
| guess.
| postalrat wrote:
| Why would it be useless? I'm sure dark is preferable but
| there isn't an atmosphere on the moon and most of light
| should reflect away from the sensor.
|
| Of course it should probably never point at the sun unless
| they want to melt their sensors.
| janmo wrote:
| If the liquid is kept in the shadow it will be at a temperature
| of zero kelvin (-273 degC). I guess that at this temperature
| mercury won't evaporate.
| kingbirdy wrote:
| Won't it still boil due to the near-zero pressure?
| jandrese wrote:
| Depends how cold you can keep it. Even if it doesn't boil
| it could sublimate away if not kept extremely cold.
| henearkr wrote:
| Then on the contrary how do they keep it from freezing?
| NikolaeVarius wrote:
| By heating it
| sp332 wrote:
| Permanently shaded regions don't get much below 25K, maybe up
| to 70K. http://lroc.sese.asu.edu/posts/979 Still good enough
| for mercury of course.
| VMG wrote:
| I hoped this would be about converting a meteorite crater into a
| mirror
| Out_of_Characte wrote:
| It might still be, creating a disk of 100m in diameter on the
| moon would need all the help you can get. There aren't exactly
| alot of bulldozers on the moon.
| BlueTemplar wrote:
| You could a bit like in Arecibo, and pick a properly-sized
| crater ?
| mturk wrote:
| The article suggests they will be able to "unambiguously
| identify" Population III stars, which would be absolutely
| incredible.
| detritus wrote:
| For anyone else unfamiliar with the term, here's a link to an
| explanation: https://kipac.stanford.edu/highlights/population-
| iii-stars-u...
|
| Particularly - "Astronomers grouped stars in the order they
| were observed, so Pop I stars are present-day stars, with Pop
| II stars being one generation older. Pop III stars are the
| hypothesized oldest stars in existence."
| api wrote:
| I've thought for a long time that this would be a great science
| mission for a manned lunar landing or a series of them. This is
| probably something too complex and large to robotically assemble
| on the Moon, and a human mission could also use in-situ lunar
| resources (e.g. lunar concrete) to help build such a thing. You
| could build a _massive_ telescope up there that would be able to
| outperform anything we currently have by many factors.
|
| Even better would be an array of them precisely positioned and
| bound together.
|
| I wonder how big you'd have to go to actually _see_ exoplanets?
| Wow.
| janmo wrote:
| There is also the interesting idea of building a radio telescope
| on the moon.
| https://en.wikipedia.org/wiki/Lunar_Crater_Radio_Telescope
| rozab wrote:
| I think this might have been posted on HN recently. To me this
| is a far more appealing project. It could require very little
| payload weight, and it achieves something that is only really
| possible on the moon.
|
| I would like this to be the project that really drives future
| human presence on the lunar surface.
| dylan604 wrote:
| According other headlines, they are going to need to create a
| radio free zone on the moon as they are talking about
| installing a 4G network.
| NikolaeVarius wrote:
| They build on the far side to address this.
| jvanderbot wrote:
| One sign that this is a good idea, is multiple different
| instantiations and simultaneous teams working on it.
|
| 1. NASA STMD study with robotic assembly:
| https://www.nasa.gov/directorates/spacetech/niac/2020_Phase_...
|
| 2. Article on the basics + decadal survey paper:
| https://phys.org/news/2020-10-moon-seti.html
|
| 3. Recent lecture on the "FARSIDE" mission concept at Caltech:
| https://kiss.caltech.edu/lectures/2020_Hallinan.html
|
| "There is some urgency in establishing a lunar far-side radio-
| quiet reserve before we get the burgeoning problem we have in
| Earth orbit with optical interference from communications
| satellites. We are already concerned about the Chinese
| communications satellites--so this needs to be a global consensus
| now!" -- Dr. Pete Worden, the Chairman Breakthrough Prize
| Foundation and the former director of NASA's Ames Research Center
| hikerclimb wrote:
| Hopefully this doesn't work
| _Microft wrote:
| Arxiv paper linked at the bottom of the article:
|
| https://arxiv.org/abs/2007.02946
|
| For the sort of telescope which they propose to use, they
| reference:
|
| https://iopscience.iop.org/article/10.1086/588034
| mnw21cam wrote:
| > To study the first stars, it would stare at the same patch of
| sky continuously, to collect as much light from them as possible
|
| I hate to be the one to spoil the party, but the moon _rotates_.
| The main problem with a rotating liquid mirror is that you don 't
| get to choose the axis of the parabola, and that axis rotates as
| the moon orbits the Earth.
|
| You may be able to get a decent view of stars drifting through
| the view, and with enough orbits you could build up a decent
| picture, but that's different from staring "at the same patch of
| sky continuously".
| rthomas6 wrote:
| Surely these career scientists have considered this problem
| that you came up with seconds after reading a press release
| about the idea.
| deliveryboyman wrote:
| The paper mentions this limitation. You really think a team of
| scientists would not recognize this?
| teraflop wrote:
| As others have pointed out, this was considered. Here is the
| relevant excerpt from the paper:
|
| > To avoid an articulating mount, the telescope would be placed
| at the lunar pole, constantly pointing at the zenith. [...] The
| limit on exposure time is then given by the precession of the
| moon, and is of the order of several days. This can only be
| extended by the addition of some active tracking facility, for
| example a moving prime focus platform.
| shireboy wrote:
| Why stop with one? Wouldn't a network of 3-4 spread across the
| dark side of the moon and networked together be even better?
| VMG wrote:
| there is no dark side of the moon (except for a pretty cool
| album)
| Out_of_Characte wrote:
| The moon is tidally locked to earth, that's what's called the
| 'dark side' of the moon from earth's perspective.
| AnIdiotOnTheNet wrote:
| As a matter of fact, it's all dark.
|
| But seriously, the "dark side" of the moon is the side we can
| never see from earth. It isn't literally dark so much as just
| unseen. Consider similar usages like "dark energy" or "a shot
| in the dark".
| BitwiseFool wrote:
| But there are craters near the poles where sun never shines
| and I assume that's what they mean.
| pdabbadabba wrote:
| Isn't it true that the far side is darker? The near side will
| be illuminated either by the sun directly or by light
| bouncing off the earth. The far side is also, of course,
| intermittently illuminated by the sun. But when it isn't,
| wouldn't it be much darker?
| inglor_cz wrote:
| Albedo of the rocks matters.
|
| Almost all the lunar maria, which are very dark, are on the
| near side. So, in those places, you get some extra light
| from the Earth, but less of it is going to be reflected
| from the ground towards your eyes.
|
| The far side is mostly highlands, with albedo twice as
| high.
| ben_w wrote:
| That is interesting, but does it matter? No atmosphere to
| diffuse the light reflecting off the ground and in so
| doing interfere with a telescope.
| dmead wrote:
| maybe you can't use Interferometry for this? if they can get
| the oldest light with just one, theres no benefit to adding
| more.
| petschge wrote:
| Interferometry at optical wavelength is very hard. Doing it
| remotely is currently impossible.
| jandrese wrote:
| Are you putting them on the dark side to reduce light pollution
| from Earth? It's going to complicate communication since you'll
| need a relay to bounce signals off of when talking with it.
| dharmab wrote:
| You only need one because the moon moves. You can take multiple
| measurements at different parts of the earth and moon orbit.
| uCantCauseUCant wrote:
| My biggest problem is with the outdated concept of optics used in
| telescopes today. There is usually a large mirror and lenses
| which should be redundant.
|
| A NN trained on the physics simulation of a wobbling droplet of
| e.g. mercury should be able to use this "predictable,
| deterministic" partial mirror, to glimps everything needed to
| see. If a ferro-fluid with electromagnetic actuators is used-the
| shape of the mirror could be even modified by the observer NN in
| realtime, to sharpen, or block parts of the mirror.
|
| If this would be acceptable to the astronomic community - we
| could mass produce Hubbles.
| jsnider3 wrote:
| I look forward to the Supremely Ultimate Large Telescope being
| built on Ceres.
| m4rtink wrote:
| To The MAX!
| NikolaeVarius wrote:
| Solar system sized radio interferometry telescope please
| DanielBMarkham wrote:
| I have a space commercialization question.
|
| SpaceX is purportedly at some point going to be able to put 100
| tons in LEO for around 100M. I'll roughly assume with a second
| launch full of fuel, a purchaser with the right gear could put
| close to 100 tons on the lunar surface for 200M or so, once they
| get the kinks out and the price down.
|
| So why not just pre-purchase 20 of these for your favorite lunar
| project, such as the ULT? If they bring prices down you get a
| cool lunar base. If they don't, you don't pay. That much payload
| delivered to the moon for $4B would be an incredible bargain, and
| it also serves to further incentivize SpaceX.
|
| I'm sure I have something about the economics wrong, but I don't
| know what. Seems to me like we should be _very_ close to a lot of
| back-burner space projects getting off the drawing boards.
|
| What don't I understand?
| 317070 wrote:
| Imagine the same project (Lunar base? Moon telescope? Rocket
| fuel harvester?) but in the Sahara. Now add the constraint that
| you want it there, but without ever having any humans on site.
|
| That is what needs addressing. That level of automatisation is
| the hard part about space.
| travisporter wrote:
| I smell an XPrize!
| vorpalhex wrote:
| Is robotics (longterm) a solution here, and if so, what level
| of autonomy do we need?
|
| Latency between Earth and the Moon is just enough to make
| realtime command a bit too rough to use I'd imagine, so I
| imagine we'd need at least low level autonomous tasks of
| "move resources from landing pad to storage" and "prepare
| build site" with enough intelligence to detect when these
| tasks hit an exception.
|
| On top of that, I suspect we'd need enough robotic automation
| to be able to build, maintain and run whatever the thing is.
| That probably means several specialized robots (packing dirt
| for a foundation, deploying construction pieces, a crane) as
| well as some general robots for when things do go off script
| (haul away a broken robot, right a fallen pylon, remove
| debris).
|
| Does this feel like something achievable in the next decade
| or two? Are there large pieces we're missing?
| kevin_thibedeau wrote:
| Robotics in hard vacuum with abrasive soil, extreme
| temperature fluctuations, and bullets raining down. We
| don't deal with that on Earth.
| m4rtink wrote:
| Some of the deep sea robots used on oil and gas rigs come
| close IMHO.
| inglor_cz wrote:
| Except for abrasive soil, all the challenges exist on the
| orbit as well. And various satellites seem to cope.
|
| If attrition of the robots turns out to be a factor, it
| could still be solved like this: expect that an average
| robot can survive 6 months on the lunar surface. So send
| twenty of them to the remote base, build a cave for the
| reserve robots and "burn" through the reserve slowly.
| Every 4-5 years, send a human crew to replace or repair
| the dead robots.
|
| Can be done, the main question is the price tag.
| retrac wrote:
| Indeed. Slightly tangential, but when you start thinking
| about a Mars colony -- but here on Earth -- a self-sufficient
| hermetically-sealed environment somewhere underground -- it
| really starts to drive the scope of the problem home.
|
| We don't really know how to create a self-contained ecosystem
| here on Earth, with everything on-hand. And the residents
| won't even all die if someone accidentally pokes a hole in
| the wall in the Antarctic prototype base.
| AnIdiotOnTheNet wrote:
| Indeed. If we're going to be serious about extraterrestrial
| colonies we should be workshopping our solutions right now
| here at home where the problems and consequences are orders
| of magnitude lesser.
| tzs wrote:
| One approach is to not try to make our colonies self-
| sufficient. Instead send a study stream of cargo missions
| to resupply them.
|
| At first, that seems completely impractical due to the
| enormous fuel costs but it turns out that if you are in
| this for the long term there is a way around that.
|
| Getting around the solar system is expensive if you are in
| a hurry, but if you can take your time it can be cheap.
|
| It is not just actual planetary bodies that a spacecraft
| can orbit. It turns out there are also orbits around
| Lagrange point. Some stable, some unstable.
|
| If you want to get from planet A to planet B cheaply and
| aren't in a hurry, what you can do is first put your cargo
| container in an orbit around an appropriate A/Sun Lagrange
| point, then nudge it into a carefully chosen unstable
| orbit.
|
| The unstable orbit gets farther and farther away from the
| Lagrange point. At some point, it crosses an unstable B/Sun
| Lagrange orbit, with a low enough delta-V between the two
| that a nudge can move it from the former to the later.
|
| It then gets closer and closer to that B/Sun Lagrange
| point, until you reach a point where another nudge can move
| it into the same orbit as B, just ahead or behind. Another
| nudge gets it to B.
|
| How long this takes depends on A and B, and it is all over
| the place. Some combinations take a decade or two. Some
| take hundreds of years. Some take thousands.
|
| This then is a plan for a long term thinking civilization
| to colonize their solar system (I'm going to assume that
| they also call their planet "Earth" and a major moon of it
| "Moon"). First, get yourself a serious presence in Earth
| orbit and Moon orbit, and maybe also on the Moon. Anything
| you can make in one of those places that is needed for your
| deep space missions is a win because you won't have to get
| it out of Earth's gravity well.
|
| When you've got to the point that you can produce a steady
| stream of unmanned space cargo containers loaded with non-
| perishable items in Earth orbit or Moon orbit, you can
| start moving them to appropriate Lagrange points, and
| nudging them into appropriate unstable orbits for the
| places you want to colonize.
|
| It will take a long time, but when you have a good number
| of shipments accumulated at a place you want to colonize,
| you then send your colonists using the fast, expensive
| route. Note that your colonists only need to take enough
| supplies for the trip itself. (And they don't need to take
| return fuel if not everyone is going to stay, as that can
| be included in the pre-sent cargo).
|
| Here are a few articles on this [1][2][3].
|
| [1] http://www.gg.caltech.edu/~mwl/publications/papers/IPSA
| ndOri...
|
| [2] https://en.wikipedia.org/wiki/Interplanetary_Transport_
| Netwo...
|
| [3] http://www.dept.aoe.vt.edu/~sdross/papers/AmericanScien
| tist2...
| SlipperySlope wrote:
| Phobos is the high ground. Get there and plant the flag.
| inglor_cz wrote:
| There is a saying that once you reach the orbit (here, on
| Earth), you are halfway to anywhere.
|
| Lifting objects from Earth's gravity well is expensive.
| There would be a better case for building extensive
| industrial base on the Moon, with its 0.16g gravity, and
| supplying all the distant bases from there.
|
| You can, for example, plausibly build a space elevator on
| the Moon [1] with contemporary materials (even Kevlar
| would suffice), thus lowering the price tag enormously.
|
| [1] https://en.wikipedia.org/wiki/Lunar_space_elevator
| travisoneill1 wrote:
| Doesn't really change anything because you are pretty
| much out of the Earth's gravity well by the time you get
| to the moon.
| ben_w wrote:
| Sure it does -- you shuttle humans up to LEO at the
| current SpaceX Dragon cost, and instead of docking to the
| ISS they dock to the full-size replica of the Enterprise
| that an eccentric billionaire 3D printed on 16 Psyche and
| filled with space-grown food, plants, and spandex
| costumes.
| dwaltrip wrote:
| To be fair, we have never had a reason to do so. It is a
| hard problem, but it isn't impossible.
| 0xffff2 wrote:
| Of course we have reason to do so (to test whether we can
| do it) and projects like Biosphere 2 suggest that while
| it's not impossible, it is for the time being unsolved.
| dwaltrip wrote:
| I meant other than purposes related to space exploration
| and general scientific research.
|
| I fully support such activities.
| michael1999 wrote:
| Nobody has ever constructed an independent human-
| compatible biosphere. We have 0 evidence that it is
| possible at a practical scale. N=1.
| jandrese wrote:
| There was the Biosphere II project from the 90s, but it
| ultimately failed.
|
| https://en.wikipedia.org/wiki/Biosphere_2
| hvdfhbj wrote:
| Really more of a PR spectacle than a worthwhile
| experiment.
|
| Including humans seems to have caused most of the
| problems there. If you actually wanted to experiment with
| closed biological systems in a useful way then I'd
| recommend doing a bunch of trials with a less
| cantankerous species of large omnivorous mammal, like the
| goat.
| heymijo wrote:
| _Biosphere 2 was originally meant to demonstrate the
| viability of closed ecological systems to support and
| maintain human life in outer space_ [0]
|
| > _including humans seem to have caused most of the
| problems_
|
| I chuckled a bit at your reply hvd.
|
| The hardest, seemingly intractable problems in the world
| aren't engineering problems, they are human ones. If we
| want to level up as a species those are the ones we will
| need to figure out how to solve.
| asimpletune wrote:
| I don't know if I'd call it a total failure. There's a
| pretty cool documentary about it an Apple TV+. I think if
| they had communicated the caveats better and more
| honestly then it would have been a success on the grounds
| of being a baby step towards the direction of the more
| ultimate case. I'd say the biggest success was showing
| that even with all the resources on earth available, this
| problem is non-trivial.
| michael1999 wrote:
| Low oxygen, low food, crashed ecosystem. Interesting
| science, but a total failure at demonstrating the
| feasibility of a closed ecosystem.
| BurningFrog wrote:
| Run by Steve Bannon, of all people!
| asimpletune wrote:
| I believe bannon came in after the experiment had already
| concluded.
| andrewem wrote:
| From reading the Wikipedia article, it sounds like "run
| by" overstates his role, but wow nevertheless.
| TLightful wrote:
| "Steve Bannon left Biosphere 2 after two years, but his
| departure was marked by an 'abuse of process' civil
| lawsuit filed against Space Biosphere Ventures by the
| former crew members who had broken in.[70] Leading
| managers of Biosphere 2 from the original founding group
| stated both abusive behaviour by Bannon and others, and
| that the bankers' actual goal was to destroy the
| experiment."
|
| Shocking ...
| lozaning wrote:
| There was still some very cool engineering that went into
| making what it was supposed to be. Check out this video
| on the 'south lung' youtube.com/watch?v=Wind4fjbt_k
|
| Because they didnt want air going in or out of the
| biosphere they had to figure out a way to account for the
| massive change in volume as the air temperature inside
| changes between super hot days and cold nights, otherwise
| you'd blow the windows out of the thing during the day.
| cma wrote:
| > If they don't, you don't pay.
|
| Do you have to put money down like with Tesla Full Self
| Driving?
| azernik wrote:
| More like 5+ launches to get it refueled - the payload of
| Starship is MUCH smaller than its fuel load.
| dpifke wrote:
| Musk is claiming that Starship launches will be closer to $10M
| than $100M:
|
| https://twitter.com/elonmusk/status/1328770804222468097
|
| (I've heard some ad hominem attacks that this will never
| happen, but haven't seen any actual evidence that it's
| impossible.)
| DanielBMarkham wrote:
| This continues to befuddle me.
|
| So let's assume Musk nails it and can do this for $10M.
| Instead of my 20, imagine 200 100-ton landings of cargo on
| the moon, say over the period of ten years.
|
| Instead of everybody sitting on Earth, trying to design-
| session-out the perfect lunar base, why not just keep
| regularly-delivering supplies, then learn how to build a
| lunar base while on the moon, figuring it out as you go?
| After all, just like SpaceX, we're not trying to build _a_
| lunar base. We 're trying to build a _factory for
| constructing lunar bases_ , eventually hundreds of them.
| Solving the modular/generic problem is what we want to do,
| not build another Space Shuttle.
|
| Perhaps I'm wrong, but it seems like most of the people here,
| indeed most of the aerospace industry, naturally prefer these
| big, lumbering, paperwork-heavy, long-lasting bureaucratic
| programs. But without enough regularly-arriving supplies, why
| try to solve something up-front, all-at-once, and perhaps
| years or decades ahead of time when you can just figure out
| the bare minimum of things you need just as you need them?
|
| But like I said, I'm probably missing something. I've been
| saying for 20+ years that our real problem is cost-to-LEO.
| Now that we're just barely beginning to address that, the
| next problem very well may likely be changing the way we
| think of large space-based programs. That could very well end
| up being a bigger problem than cost over the long run.
|
| ADD: Seems to me that the Starship is a solution to
| delivering _humans_ to space. We need reusable heat shields,
| booster packs, and payload capsules, along with an Earth-
| based mass-driver, to truly drive down cargo rates another
| 100x. At that point we 'll begin seriously talking about
| becoming a space-faring species.
| peterpost2 wrote:
| The cost of rocket launches is not the largest part of creating
| a lunar base, designing and manufactoring all the landers,
| base, electronics, software etc. is the larger part of it.
|
| If I recall correctly, for the apollo program about 30% was for
| the launch vehicle.
| ethbr0 wrote:
| It seems like this would be somewhat of an interrelated
| valuation.
|
| If launch costs decrease by an order of magnitude,
| reliability of payload can be relaxed, and therefore costs of
| payload engineering and manufacture decrease.
| m4rtink wrote:
| If mass reduction is no longer super critical, you can use
| heavier but cheaper materials that provide the needed
| strength.
|
| There could be other knock off effect of cheaper and more
| frequent space launch - you can send multiple versions and
| see which works the best, ship prototypes back for
| extensive evaluation, send robots or people to fix broken
| things.
|
| A lot of things are done differently if you have just a
| couple super expensive shots per decade & everything needs
| to work without external help at the first time.
| NickM wrote:
| I would assume engineering and building one of these things is
| non-trivial, and there may also be certain aspects tailored to
| the specific launch vehicle, so it's not like as soon as SpaceX
| proves they can do what they plan to do that you can just pop a
| telescope on a rocket and go.
| _Microft wrote:
| Launch providers list the characteristics of their vehicle
| and the customer has to ensure to stay within the
| constraints.
|
| SpaceX is special (or used to be special, maybe others have
| followed suit by now?) in that they make this information
| public. See here what loads, accelerations or vibrations the
| payload has to withstand during a launch on a Falcon 9 or
| Falcon Heavy launch vehicle:
|
| https://www.spacex.com/media/Falcon_Users_Guide_082020.pdf#p.
| ..
| remote_phone wrote:
| They missed such a good opportunity to call it the "Unearthly
| Large Telescope"!
| ChuckMcM wrote:
| Or simply the BFT, but I expect it will be something "Lunar
| Telescope" or something "Lunar Observatory" (which implies
| people present as I recall)
| ilaksh wrote:
| I think it would be a nice idea to have several more normal
| telescopes on the moon with an internet site that would allow you
| to rent time and operate them remotely somehow. And maybe one or
| two really big visible light ones.
|
| This would theoretically provide a superior level of clarity
| versus ground telescopes. And it would allow for viewing of the
| earth.
| m4rtink wrote:
| There is already one in place:
| https://www.newscientist.com/article/dn28323-china-has-had-a...
| https://en.wikipedia.org/wiki/Chang%27e_3#Lunar-based_ultrav...
|
| Quite a small one, but first of its kind. :)
| csunbird wrote:
| Forgive me for my ignorance, since my knowledge of advanced
| physics and orbital mechanics are limited to KSP, can't we build
| something like this on orbit, thus saving a lot of headache from
| landing and constructing on the moon?
|
| A stable polar orbit is easier to get to and return from the
| moon.
| [deleted]
| rtkwe wrote:
| The core of it is a liquid mirror which is harder to do in
| space because to shape it into a parabola you need spin and a
| down which would require constant acceleration since it want's
| to look at a single point in space. Also long duration attitude
| holding is harder in space than it is on the ground.
|
| If we wanted to build something similar in space it's
| essentially a 5x larger James Webb Space Telescope which is
| having some trouble last I heard with it's folding mechanism so
| building one 5 times larger to fit into a faring is a big task.
| abecedarius wrote:
| OTOH in zero g a mirror needn't support its own weight. A
| shade would eliminate temperature fluctuation. Naively I'd
| expect it should be practical for a very large, very
| lightweight telescope mirror to be built in situ in space
| instead of trying to launch and unfold one built on Earth.
|
| I guess the big problem for that right now is that for humans
| to do the building, it'd have to be in low orbit, a less-
| than-ideal environment for a long-lived scientific
| instrument. (Just kibbitzing, am not a rocket scientist.)
| handol wrote:
| I expect it would be much harder to put a mirror factory in
| orbit than a mirror.
| csunbird wrote:
| I mean the construction can be done on low earth orbit,
| then the satellite telescope can do a transfer to a higher
| orbit. Again, forgive my ignorance :)
| rtkwe wrote:
| We've only built a tiny number of things in orbit and
| haven't yet built something that then gets sent off
| somewhere like a shipyard. It's all been stations that are
| then left basically where they [0] are so we don't really
| have the experience of how to do that yet. Also that takes
| a long time because it's just slow to move around in space.
|
| It does need to support it's own mass through during
| maneuvering and pointing operations as well so it can't be
| completely flimsy. Also you'd want to get further from the
| earth to avoid all that drag from a huge mirror in LEO.
|
| [0] Beyond periodic small orbit boosting burns
| abecedarius wrote:
| Pointing needn't be at all quick, as long as you're not
| trying to catch a gamma-ray burst in the act or the like.
| Agreed about the badness of LEO.
|
| Another problem: a very large mirror is a significant
| target for micrometeoroids. It'd need to be made able to
| keep going after losing little patches.
| [deleted]
| Fumtumi wrote:
| We are already doing this with James Webb Space Telescope. That
| one will be further away from sun than earth and moon.
| NikolaeVarius wrote:
| JWST is not being assembled in space
| Fumtumi wrote:
| yeah my fault; I interpreted the question as 'hey sounds
| difficult to do that, can't we make it easier?' in sense of
| the person asking without knowing the JWST exists.
| Rebelgecko wrote:
| Normally liquid mirror telescopes depend on having some amount
| of gravity to work correctly (the liquid needs to pool in a
| certain way). There's workarounds to do this in space but it
| gets really complicated.
|
| Other issues with space based telescopes:
|
| They need fuel + thrusters to go where you want them to be (or
| just to maintain their orbit!)
|
| Heat dissipation is a big problem. Being able to use the whole
| moon as a thermal flywheel could help out a lot. In space you
| can use things like cryocoolers to regulate temps, but they
| cause vibrations which can be problematic if you need your
| telescope to remain steady. If this requires refrigeration, you
| can put the vibrating parts far enough away from the telescope
| that they don't move it. Putting the thing in a crater probably
| helps regulate temps too (less direct sun)
|
| Humanity in general is better at building and maintaining
| things on solid ground. If you drop a bolt on the moon, you
| lean over and pick it up. If you drop a bolt in orbit, you have
| to worry about it damaging your spacecraft at the next
| conjunction.
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