Recipe for Giant Lunar Telescopes
Written by Nancy Atkinson
Someone has finally figured out something useful for all the dust on the moon's surface: mix it with some epoxy and a pinch of carbon to create giant telescope mirrors. "We could make huge telescopes on the moon relatively easily, and avoid the large expense of transporting a large mirror from Earth," said Peter Chen at a press conference today at the American Astronomical Society meeting. "Since most of the materials are already there in the form of dust, you don't have to bring very much stuff with you, and that saves a ton of money."
Chen and is team had been working with carbon-fiber composite materials to produce high-quality telescope mirrors. But then they decided to try an experiment. They substituted tiny carbon nanotubes for the carbon-fiber composites, and mixed in epoxies with crushed rock that has the same
composition and grain size as lunar dust, they discovered to their surprise that they had created a very strong material with the consistency of concrete. This material can be used instead of glass to
make mirrors.
Then they spun their concoction at room temperature to create a 12-inch-wide telescope mirror form, which they then coated with aluminum to create a highly reflective surface.
"Our method could be scaled-up on the moon, using the ubiquitous lunar dust, to create giant telescope mirrors up to 50 meters in diameter," said collaborator Douglas Rabin. Currently the world's largest optical telescope is the 10.4-meter Gran Telescopio Canarias in the Canary Islands, so this would be quite a step up.
Like liquid mirror telescopes, these large telescopes on the moon have definite advantages. With a stable platform, and no atmosphere to absorb or blur starlight, the monster scope could record the spectra of extra solar terrestrial planets and detect atmospheric biomarkers such as ozone and methane. Two or more such telescopes spanning the surface of the Moon can work together to take direct images of Earth-like planets around nearby stars and look for brightness variations that come from oceans and continents.
"Constructing giant telescopes provides a strong rationale for doing astronomy from the moon," says Chen. "We could also use this on-site composite material to build habitats for the astronauts, and mirrors to collect sunlight for solar-power farms."
Filed under: Astronomy
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June 4th, 2008 at 2:30 pm
I seem to recall that the lunar soil is rich in He-3 (because of the solar wind, presumably). Am I misremembering? If we ever get fusion to work there might be a further incentive in mining that, right?
June 4th, 2008 at 2:40 pm
Hope it can handle the thousands of sand grain sized meteorites hitting it all the time… maybe they should go with a liquid mirror so it can get it's shape back after an impact.
June 4th, 2008 at 4:06 pm
You are probably correct in that the mirror will take conciderable damage from dust meteorites, but a spun mirro made on location could be replaced by another once it have degraded to much, so the concept is still very good.
June 4th, 2008 at 5:52 pm
Interesting, this sounds like a step on the way to finding a good solution to what has seemed an insurmountable problem. Keep on working it.
June 4th, 2008 at 7:04 pm
I am not quite sure if microsopic meteorits would be of a considerably higher risk for a telescope on the Moon, than they are for example for the Hubble. Well, the gravitation of the Moon may attract little bit more of them, but I wonder if it is really that bad.
June 4th, 2008 at 7:33 pm
How is building a telescope on the Moon a _good_ idea? Don't get me wrong, I fully support a lunar observatory, but building the telescope in situ probably doesn't make much sense. Instead of carting up the mirror from Earth, you'd have to cart up the machines and equipment to _make_ the mirror, and that would be considerably more costly than assembling a multi-facetted mirror built on Earth to give the equivalent diameter of a single piece.
Think about it. You'd have to send up the machines to collect the lunar regolith. You'd have to send up the machines to hold the regolith in place. You'd have to send up the epoxy. You'd have to send up a machine to pour the epoxy. You'd have to send up a machine to spin the whole assembly. You'd have to send up a machine that could heat aluminum to the melting point, and you'd have to do it in a controlled thermal/atmospheric environment. Then you'd still have to transport it to the assembly it needs to be mounted on. Why not skip all that and just send up segments and assemble them in-situ?
Peace,
Drew
June 4th, 2008 at 7:42 pm
I agree with Drew. What has Hubble cost us? Isn't it something like seven billion and counting. When you could have built OWL on earth and used adaptive optics to remove atmospheric interference. The result would be an order of magnitude better at a fraction of the cost. Plus its a helluva lot easier to upgrade and maintain!!
June 4th, 2008 at 7:54 pm
man power for dust collection (which even for a machine wouldn't weigh more than a mirror, doesn't even have to be big, just have the machine run on solar and let it run for a month if necessary), machine to spin = less mass than actual 50 foot lens, which is 50 feet in at least 2 orthogonal directions, don't even know how your going to fit at on a shuttle. Molds are light weight and can be pieced together from scratch. Melting aluminum = solar power once again (you fail to realize that its about 1 Au from the sun and no atmosphere to weaken solar rays).
But why just optical? I would like to see multi layered inputs from the telescope seeing how so much time will be put into it.
June 4th, 2008 at 10:12 pm
@Flaming Pope:
Man power for dust collection?! What a waste! Consider how big a 50' mirror is. That's 150 square feet of surface area. Imagine collecting enough sand to cover 150 square feet to a depth of a couple inches. Now do that on the Moon wearing a suit with limited air, limited time, and multiple priorities. Would you really spend valuable time sending astronauts out on errands to collect dust in buckets?!
I was ignoring power production (except for a few select places like the rim of Shackleton Crater, solar power on the Moon only works 14 out of 28 earth-days) because the power requirements are moot – operating the telescope and support equipment will require power, so some sort of electrical power generation on the Moon must occur regardless of where the telescope is assembled.
A machine to spin the mirror in assembly may be less mass than the 50' mirror itself, but it must be at least 50' in diameter to hold a 50' mirror without allowing material to slough off the sides when spun and to maintain a uniform surface across the mirror. Forget _fitting_ it on a rocket (who said anything about the Shuttle? Shuttle can't get to the Moon anyway, and I made no mention of actual payload size requirements for launch vehicles). My point is that when you add up all the equipment required to build a mirror on the Moon versus assemble a mirror from components manufactured on Earth, it is more energy efficient (launch vehicle, not power generation on the Moon) and thus cost effective to manufacture it on Earth and assemble it on the Moon than to manufacture a single solid mirror on the Moon.
However, lunar manufacturing may have an advantage over terrestrial manufacturing when considering economies of scale. If more than one mirror is to be produced with little or no transport over the lunar surface, it may be more efficient to manufacture it on the Moon.
Peace
June 4th, 2008 at 10:15 pm
Oops. Area of a circle is πr^2, not 2πr. Duh!
Try 1963 square feet.
Peace
June 5th, 2008 at 3:24 am
…and projected size is 50 meters, not 50 feet.
June 5th, 2008 at 5:43 am
Hey NASA! I believe it in the best interest of main street America that you put Drew and Brad on your payroll as senior science advisors. Why you ask? Well, both gentlemen exhibit more common sense in their posts than the team working on this "lunar telescope" folly. My gawd! What are these NASA "lunar telescope" guys smoking when spending our tax dollars?
June 5th, 2008 at 6:17 am
Wow, you guys realize that transporting 1 set of machines means you can manufacture any number of mirrors right? Oh and the same machines that manufacture the mirrors are the SAME machines that manufacture other regolith "concrete". The only difference is the form and the coating.
Who are the ones smoking crack?
Think before you open your pie holes.
June 5th, 2008 at 8:23 am
@Drew
I'm not quite sure if the scientists are suggesting to produce a 50-metre diameter mirror that could then be spun inside a ~ 50-metre diameter spinning-type machine as this would require huge, huge amounts of machinery (so I agree with you on that count). Before I go on, just a note about your corrected calculations which seem, I think, to suggest you' re looking at 50 foot diameter mirrors, but as far as I know they're talking about ~ 50-metre diameter mirrors (and upwards). This would then make the overall area using πr^2 as ~ 1963 sq. metres not 1963 sq. feet (1963 sq. metres is much, much greater than 1963 sq. feet).
I think, however, that the scientists may not be be looking at producing just one huge 50-metre diamter mirror as a whole, but rather a mirror made up of several smaller, segmented mirrors, say, a metre across, which would then be conjoined together to produce the larger 50-metre diameter mirror. These segemented type mirrors have been made on Earth (e.g.the Hobby-Eberly telescope made up of 91segmented mirrors each a ~ metre in diameter across), and so it would be possible to produce the mirror sizes they suggest. Just imagine, therefore, an astronaut spinning smaller 1-metre-diameter mirrors at a future lunar base, where the euipment used to do so wouldn't be that much big, and as the moon's gravity is 1/6 that of Earth's, assembling them together would be somewhat easier. However, I do agree that trying to do such work in those awkward, confining suits that astronauts have to wear isn't going to be a walk in the park. Still, they've [the astronauts] have tackled far more difficult jobs in the past in space, and on the Moon, so, it's as well to remain optimistic to someday see them building these huge 50-metre diameter telescopes that they are proposing.
John — http://www.moonposter.ie
June 5th, 2008 at 10:38 am
Back @ Drew:
Your still thinking like a down to earth human, when you should be thinking space man.
I referred to spin like a concrete mixer, (which is quite small no matter how you look at it)- this along with molds instead of one gigantic fabricator. And I'm saying small since you can have the machines run for any length of time.
14 out of 28 days is plenty, either have panels on both sides of the moon, a back up storage unit, or simply build two telescopes with the equipment at hand.
And size is of no matter where it be micro meters, feet, kilo meters, just let machines run for any indefinite amount of time and readjust the molds. Lastly I was joking about the manpower- but it is doable, maybe with a smaller scale mirror for testing the idea first on the moon before implicating it.
Why is every1 thing about large machinery? All you need are small ones which run for a longer period of time, like ion engines, small amounts at a time but effective
June 5th, 2008 at 11:35 am
I like a radio telescope on the far side of the moon. It would be protected from the earth (communication via satt. would be required), and would use the natural shape of a crater to form a large (100 meter for example) collector. I wonder if a simple metal mesh could be placed in a crater to create such a telescope? One could roll it up and send it to the moon. Optical telescopes on the moon seem very hard to construct, the technology seems a ways off that is.
June 5th, 2008 at 12:29 pm
Hello Dude, Wow! You figured it out! However, wouldn't it make more economic and technical sense to manufacture a segmented mirror on earth and transport it to the surface of the moon for assembly? Why screw around with transporting lens making machinery! OK, so maybe NASA's science engineers may not be smoking what-ever it is they might smoke. Those guys are misguided and not thinking clearly. It's frustrating to see our tax dollars "go up in smoke", err . . . wasted.
June 6th, 2008 at 4:53 am
Some of the posters seem to be talking as though the whole mirror was going to be cast in one go. I would assume the 50 meter telescope would be built out of small segments. At that sort of scale, a 10 cm square segment is within a quarter of a wave of being flat. Perhaps they would use larger tiles – say spinning hexagons 1 meter across. I don't see any problem with making these. What I do see is the problem making something that supports and points all of this the size of the Jodrell Bank radio telescope. Unless we are just finding some convenient crater and polishing up the sides like Arecibo. Have a look at OWL to see the sort of thing involved. On earth, the point and support structure would weigh 14000 tons. On the moon, the dead weight will be a lot smaller, and the vibrations will be less, but it will probably still weigh a lot more than the mirror elements themselves.
Now, if you could assemble the thing in space, then everything could be less massive. You might make the mirror and some of the struts on the moon, and then launch them from there to somewhere in space where they can be assembled. The final stages of the optics would come from earth.
Anyhow, thinking is cheap: stuffing up a space station or trying to set a man on Mars without doing the thinking is what eats the resources. There is no rush to sort out a moon telescope anyway. We will have to see if the OWL can be built first, and that ought to happen on Earth (on the Antarctica dome if we are allowed). We see how that goes before we try making one where we can't repair it.
June 6th, 2008 at 7:09 am
One thing some of the posters might be forgetting is that they won't just be building mirrors on the moon – they intend to actually build a space colony there, so whatever equipment they need to do that, can be used to build the mirrors. I'm sure the smart folks at nasa realize what it will take to build these things, and are considering that when making these proposals. If there is a colony on the moon, it makes sense to have those in the colony doing useful things, like building and maintaining telescopes for one thing. If putting a colony on the moon makes sense (I'm not sure it does), then so does making telescopes.
June 7th, 2008 at 9:43 am
Sure, if ALL you are going to be doing is setting up ONE astronomical telescope, it makes sense to transport it from Earth & assemble it either on the lunar surface or in free space. On the other hand, if you are interested in a real observatory with multiple instruments, or if you are going to the Moon for (God forbid!) some extended period, or with multiple goals, transporting materials-processing & manufacturing equipment rapidly becomes more economical than transporting finished parts and supplies.
June 8th, 2008 at 7:54 pm
It doesn't make any sense to transport any kind of machinery to the surface of the moon to manufacture anything. The proponents of this folly have absolutely no idea of what is involved in the simplest manufacturing process, especially on the moon. For example, it would take a small factory and dozen or so people to produce, say, a hand full of small functional $100 on earth telescopes. Not to mention the power requirements and life support systems, ad infinitum. And to colonize the moon for some meaningful purpose even for a few weeks aint going to happen in this or the next century, if ever.. There is simply no reasonable return on investment even for military defense purposes. Scientific curiosity is great! But at a cost of tens of billions of dollars to verify the presense of water or microbial life on the moon is totally ludicrous. We have enough mystery here on earth to keep viturally all scientific disciplines busy for centuries.