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Rotating Mercury Lunar Observatory
Fraser Cain writes "Universe Today is reporting on a proposal under consideration by NASA from Dr. Robert Angel at the University of Arizona. He wants to build a 100-meter liquid mirror telescope into a crater on the Moon. It would only be able to look at a specific spot in the sky, but the view would bury Hubble's Deep Field Survey." The challenges of off-Earth construction are left as an exercise for the reader.
Is it true that they are saving money by using Lake Erie as the mercury source?
That's no moon...
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Even if they could keep it clean during construction, how would they keep it from getting contaminated with lighter-than-mercury space dust over time?
The moon's atmosphere is basically hard vacuum. Sure, there are a few air molecules here and there, but certainly nothing that could lift and transport dust particles.
So, short of nearby meteorite impacts kicking up dust and micrometeorites falling to the surface, there really isn't any way for dust to get on the mirror in the first place. And keep in mind that even such dust as would be sent up by the occasional meteorite wouldn't hang around in the air the way it would on Earth, because there isn't any air. It would just trace a parabolic arc and fall straight back down (well, it wouldn't be quite that simple due to the the gases released by the meteorite's own impact, but you get the point).
I very much doubt that the minute quantities of dust that would find their way onto the mirror would present a significant problem.
ZFS: because love is never having to say fsck
I used to imagine a telescope of a pan filled with mercury, spinning, and attached to the lens assembly via rods on top, and the whole device turning to create gravity for the mercury so it stays in the pan, while the whole telescope like a lighthouse scans the skies.
The moon will allow greater sized assemblies, and gravity doesnt have to be induced. The problem is the lack of control, which can be offset by building multiple telescopes at various lattitudes.
So whats difficult? A large container which can carry mercury, even a large plastic bag in a satellite dish mesh can do. The structure will sit on a motor that spins. The motor will not induce any vibrations into the mercury pan, for the former telescope I had a magnetic levitation rotation device, or at least a string that dangles the pan while magnets rotate it. The magnets cannot be in two D structures like regular motors since thats vibration there, so a uniform magnetic field is applied while current is passed between the center of the pan and its sides to allow for a continuous DC motor. If the current can be passed with no contacts, we can achieve real smooth rotations and no frictions or vibrations... again magnetic levitation would be a great idea here since the moon can be cold enough for ceramic superconductors, and clear enough for solar panels to power the thing.
The smaller we make the mercury pan, the more vibration prone it gets as we increase the resolution, so we can expect moon earthquakes to be a problem whenever something hits the surface. Shouldnt be frequent enough to cause a problem...
Unlike Hubble, the structure should be radiation-hardened, low-maintenance, no mechanical parts, no chemical reserves object, except for the mercury container. If spun fast enough, the container can reflect light from greated angles removing the problem of lack of control.
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First off, this far outstrips our present launch capability. Second, we would require a much more reliable method of sending things into space before we decided to send up a significant amount of liquid mercury, given that a failed launch of a rocket carrying a large tank of mercury would be a major ecological disaster. It's a great idea in theory- pouring a bunch of liquid into a bowl would be certainly preferable to the tremendous amount of skill and effort required to properly build and polish large telescope mirrors- but I'm not sure how long it would be before this idea becomes even remotely practical.
"FDA staff reviewers expressed concern about the number of patients who were left out of the study because they died."
Has any one though of starting with a spinning liquid mecury mirror, letting it freeze, and then using it as a conventional telescope mirror. You could even remelt and respin it should it become contaminated. More complicated yes, but also more useful....
Part of the idea with a polar crater is to protect the instrument from temperature variations, something you would get a lot of on a monthly basis with a mirror anywhere else on the Moon. Tycho sits in sunlight for two weeks, then in darkness for two weeks. That's not a stable environment.
Also, a telescope made with a liquid mirror can be aimed in one direction only, towards zenith. Even the slow, monthly rotation of the Moon wouldn't allow for significant exposure times without motion blur, something you don't want when photographing distant galaxies spanning less than an arc second in the sky. The celestial poles are the only two spots in the sky that don't move around (they merely rotate), allowing for arbitrarily long exposures (the article suggests a year) using a camera synchronized with the sky.
If Celestia has the correct orientation of the Moon, the lunar axis points at constellation Draco in the northern hemisphere and at constellation Dorado in the south, the latter including the Large Magellanic Cloud. However, I don't know what particular deep sky objects would be visible using a telescope such as the proposed one at either pole.