Could large craters on the moon be used as reflective lenses for radio signals?
Acting like a large radio telescope reflecting radio waves to a satellite positioned over the crater.
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Sign up to join this communityInteresting idea. I think the answer is both yes and no -- yes with a manufactured dish but no in the crater's raw state.
The Arecibo telescope sits in a natural crater, but adds a dish which has a couple of important things required by a radio dish:
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Could large craters on the moon be used as reflective lenses for radio signals?
You'd have to line the surface with something reflective to microwaves, like a metallic mesh, or similar materials.
Secondly, the shape of the crater is probably not quite ideal, so it would have to be adjusted a little, carved up a bit in various places. But it's a good start, and definitely better than starting with a flat ground.
There is also the question of stability - you need to make sure that whatever changes you make (carving a different shape, lining it with mesh) do not affect the stability of the crater, or else various parts may slide or collapse. This is an engineering problem.
Acting like a large radio telescope reflecting radio waves to a satellite positioned over the crater.
Not possible unless the crater is exactly on the equator, and even then it would be tricky.
But a crater like the one in your picture is so strongly curved, the focal length is about the same as the diameter. In other words, if the diameter of the hole is X, the altitude of the receiver is pretty close to X - give or take something like 50% or so, depending on the exact curvature. It might be easier to just build a giant arch over the crater. Again, this is a matter of engineering.
If it works for Arecibo it could be made to work on the Moon, Ceres, and maybe even Mars. The point about sending a prefab is a good one. And using two radio telescopes in tandem separated in space would allow for astronomers to take advantage of the improved angular resolution this affords provided they were arranged so as to allow them to simultaneously focus on the same point. That would be a neat problem in astrophysics! Radio telescopes aimed at the same point simultaneously from the Earth and Mars while they are on opposite sides of their orbits would have incredible resolution.
Yes, Frank Drake looked into this - see page 91 here http://www.lpi.usra.edu/lunar/strategies/objectives/ast_observations_moon.pdf
He calculated that you could make a telescope with diameter 30 km using steel, and up to 60 to 90 km with stronger materials. And no problem with wind loading on the Moon.
I agree that the crater needs to be lined, but you also have the problem of maintaining a satellite in stationary orbit above the crater. Nearly impossible unless the crater is on the equatorial plane. Also, a stationary satellite around the moon would be influenced by the Earth, so you would need to burn fuel to keep the satellite in position.