Texas astronomers revive idea for 'Ultimately Large Telescope' on the moon
phys.org
phys.org
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
I would like this to be the project that really drives future human presence on the lunar surface.
But the cost difference in landing anything on the moon is massive. Every kilogram of payload sent to low earth orbit takes roughly 15 Kg of fuel. To land a Kg of payload on the moon requires roughly 80 kg of fuel.
https://www.nasa.gov/directorates/spacetech/niac/2020_Phase_...
https://arxiv.org/abs/2007.02946
For the sort of telescope which they propose to use, they reference:
A stable polar orbit is easier to get to and return from the moon.
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.
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.)
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
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.
I was fantasizing some form of active control, without the speed demand of in-atmosphere adaptive optics. This might be needed anyway after micrometeoroid damage.
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.
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."
There are other ideas for large optical telescopes in space like 'painting' part of a balloon with a reflective material. The disadvantages are that these produce spherical rather than parabolic surfaces and would require complex re-imaging optics (like Arecibo). The other is that to observe optical and near-ultraviolet light the surface must be very accurate with deviations less than 15 times the wavelength of the light (so in the 20 nanometer regime). The technology has not been demonstrated for this with a space balloon, but there are plans to use this scheme for far infrared or microwaves where the surface accuracy constraints are less severe.
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?
If I recall correctly, for the apollo program about 30% was for the launch vehicle.
If launch costs decrease by an order of magnitude, reliability of payload can be relaxed, and therefore costs of payload engineering and manufacture decrease.
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.
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...
That is what needs addressing. That level of automatisation is the hard part about space.
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.
Shocking ...
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.
>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.
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.
I fully support such activities.
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/IPSAndOri...
[2] https://en.wikipedia.org/wiki/Interplanetary_Transport_Netwo...
[3] http://www.dept.aoe.vt.edu/~sdross/papers/AmericanScientist2...
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.
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?
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.
Do you have to put money down like with Tesla Full Self Driving?
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.)
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.
That cost is predicated on rapid relaunch, with multiple launches /per-day/. It wouldn't be ten years, more like two to four :)
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.
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.
>Without an independent infrastructure in place at a lunar pole, it would likely be impossible to construct and operate a large liquid-mirror telescope.
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.
Presumably the stuff required to move stuff to make the scope will disturb at least some sand
(I’m not a materials scientist, this is a question not a suggestion)
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".
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.
This would theoretically provide a superior level of clarity versus ground telescopes. And it would allow for viewing of the earth.
Quite a small one, but first of its kind. :)
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".
> 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.
They need to find a solid that does not just sublimates when heated in the void.
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.
Of course it should probably never point at the sun unless they want to melt their sensors.