Lunar crater observatory

[cdnprodigy]

I want to know if anyone has actually considered using the basin of a polar Lunar impact crater as the platform for a radio or infrared telescope dish. I've read small impact basins tend to be parabolic in geometry, and the basin surface could be turned to glass using a Fresnel Lens mounted on a rover or something. Is anyone aware of the concept being studied anywhere?

 

[rhodan]

That's an interesting concept, but you'd have no control as to where to aim your dish.

 

[harmonicaman]

Well, the world's largest radio telescope at Arecibo, PR, also utilizes a "Fixed" dish, but it's a misconception to believe that it cannot be aimed.<br /><br />This engineering feat is accomplished by mounting the recievers over the dish on a system of moving cables.<br /><br />Here's the Wikipedia description of how the Arecibo Radio Observatory steers the telescope: <br /><br /><i>"It (Arecibo Radio Telescope) is a spherical reflector (as opposed to a parabolic reflector). This form is due to the method used to aim the telescope; the telescope's dish is fixed in place, but the receiver at its focal point is repositioned to intercept signals reflected from different directions by the spherical dish surface. <br /><br />The receiver is located on a 900-ton platform which is suspended 150 m (450 ft) in the air above the dish by 18 cables running from three reinforced concrete towers, one of which is 110 m (365 ft) high and the other two of which are 80 m (265 ft) high (the tops of the three towers are at the same elevation). The platform has a 93 m long rotating bow-shaped track called the azimuth arm on which receiving antennae, secondary and tertiary reflectors are mounted. <br /><br />This allows the telescope to observe any region of the sky within a forty degree cone of visibility about the local zenith (between -1 and 38 degrees of declination)."</i> <br /><br />Image<br /><br />(Back when I was working at Cornell, I had a chance to go to Arecibo, PR. for a tour; but I declined because I'm an idiot...)

 

[rhodan]

<i>...but I declined because I'm an idiot...)</i><br /><br /><img src="/images/icons/smile.gif" /><br /><br />Thanks Harmonicaman, I should have thought of Arecibo, perhaps the most impressive scientific instrument in the world, together with the particle accelerators. It would be a giant engineering feat to build something similar on the Moon though.

 

[cdnprodigy]

The fixed nature of a lunar structure wouldn't work against it. On earth, you need to track a target, but that problem wouldn't exist on a Lunar polar region. You would only get a small region of the sky to view, but the depth of resolution would unmatched. I don't think the structure would be that grand to create, assuming the surface of a crater could form the actual physical "dish" for the telescope. Would melted/sintered/baked lunar regolith would actually reflect enough EM rays to function as a observatory? Perhaps the problem is we really don't know enough about the Moon's composition to answer this question. The interior of an appropriate crater might be metallic enough to reflect or wide variety of EM wavelengths or it might not be...<br />The receiver design of the Arecibo might be the best way to get light to the Fresnel-rover apparatus for the purpose of melting regolith. I'm thinking there might only need to be a two tonne payload for all of this. Total price tag of maybe mid 8 figures on a Falcon IX? Cheapest useful Lunar mission plan I can think of.<br /> I don't know if melted crater interiors are reflective enough, and I don't know if a crater's geometry is telescope quality parabolic, or only roughly irregularly parabolic...

 

[nexium]

Hi cdnprodigy: The moon equivelent of Aricibo would need to track the target at a slower rate, but tracking would be required even at the poles of the moon. Aricibo uses metal mesh to correct for the minor irregularities of the crater. In theory an Earth or Moon crater could be fused to an optically acceptable parabolic or segment of a sphere, but the engineering problems would be enourmous. Perhaps the areas close enough could be silvered and those with error could be painted dull black. Neil

 

[neptune501]

That is very interesting. But, like Rhodan said you have no control over it.

 

[cdnprodigy]

The Moon doesn't rotate. It does revolve around the earth every 27 days. I think this would be slow enough for tracking not to be an issue.<br />The field of view would only be a sliver of the sky, but the magnification would be unsurpassed. I think the topography of the crater basin would be too imprecise for anything but radiowaves. It would actually need to be equatorial or mid-latitude to avoid interference from the earth's surface or auroral sources.<br />Unfortunately, I don't think this idea is feasible anymore. Radio waves need metal, my moon-glass wouldn't cut it. Some asteroids are iron ore rich, but when they impact the moon, it ejects a plume of debris originating from the Lunar surface. This debris settles over the fused metal breccia I would need. <img src="/images/icons/frown.gif" /><br />I don't know how deeply, but even a foot of regolith screw up the plan. I will keep an eye on coming Lunar missions. Maybe there is a portion of the Moon's surface that is metal rich. I remember seeing a false colour map of the Moon that showed regions highly metallic. I f a metallic asteroid impacted such a region, maybe the plume that settled would be metallic enough to facilitate this concept?

 

[cdnprodigy]

The Moon doesn't rotate. lol. I'll have my coffee 1st before posting next time. I meant the Moon doesn't rotate fast enough for a tracking system to be a necessity, I don't think. There is a big difference between a 24 hr rotation and a 27 day rotation.<br /><br />For a near-term lunar mission of this sort to be feasible, it has to be as simple and payload friendly a possible. The mylar tarp and Arecibo positioning systems are all heavy and add failure points.

 

[cdnprodigy]

the weight penalty is for lift-off payload costs. Their telescope costs billions. Mine (if it would have worked) would have been high 8 figures or low 9 figures.