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Why would a moon telescope be desirable over a satellite telescope?
by SubiculumCode 2y ago
Why would a moon telescope be desirable over a satellite telescope?
- dagw 2y agoFTA: "Unlike telescopes such as the Hubble and the James Webb, which are made from mirrors and lenses, FarView would comprise a hundred thousand metal antennas made on-site by autonomous robots. It would cover a Baltimore-size swath of the moon." They want to build a radio telescope, not a simple optical telescope.
- SubiculumCode 2y agoThanks. Still, this doesn't answer my question about why build it on the moon and not in space.
- tekla 2y agoI think humans currently have a hard time deploying a 20km by 20km object in space.
- echelon 2y agoTo be fair, we also have this problem on the moon.
- jessriedel 2y agoIt’s easier to deploy in the weightless environment of orbit than on the moon with gravity. Consistent with this, the largest off-Earth structure ever built (the ISS) is in orbit, not on a heavenly body.
- itishappy 2y agoSure, but it's even easier to not have to worry about deploying at all. The largest structures we've built were built in-situ.
- jessriedel 2y agoIt requires deployment either way. The largest ships we have that go to the moon are no larger than those going to orbit.
- avmich 2y agoCan't believe you don't see the other reasons why ISS is on orbit.
- jessriedel 2y agoI think you have misread my comment.
- avmich 2y ago"Consistent with this..." I read as "this cause has significant part in justification that...". ISS obviously is on orbit not because it's easier to build in space than on the surface of a natural satellite - if Earth would have a Deimos orbiting it at height of 1000 km, I see it quite possible that ISS would be on the surface of such satellite, with all ifs and buts - but because ISS is roughly in the closest location to Earth which is still "space" and doesn't require continuous re-launching (like New Shepard). Coming back to the topic, I'd like to see the reasons why both approaches could be beneficial. I see, for example, that for space-based constructions we don't - mostly - have interference from the surface of anything, while for surface-based constructions we have support and resources. Do we have a full analysis which would allow us to say "surface always sux, in-space forewa" or "only l00mers build in space, real men are firmly grounded"? Or, talking about a finer point, deployment only - do we have full justification?
- netcraft 2y agothe size. An optical telescope is limited by the size of the mirror which needs to be one continuous surface (though not necessarily smooth for instance the JWT but I digress), but a radio telescope doesnt, it can be many individual collectors that can be joined together. This enables it to be much larger so it can collect more signal, and the radio waves are much longer so it needs to be much larger. In an extreme example we have used many different radio telescopes together with very precise timing to produce the images of the black holes at the center of M87 and the milky way. But it requires those different clusters of collectors to be stationary - so while you could probably build a swarm of satellites, they would have to stay in very precise distances from each other over time which would be considerably more difficult than planting them on a surface. Also, a big shield like the moon blocking out radio interference coming from the earth is desirable. IANAA, corrections to my understandings welcome
- itishappy 2y agoI'd flip your comment about optical surfaces: they need to be smooth, not continuous, and smoothness is actually not required either! The requirement is a consistent phase relationship, which allows the signals to add together nicely via interference. Rays coming from same direction take the same path to the detector and interfere constructively, while rays coming from different directions tend to cancel. For optical frequencies, the phase is difficult to measure directly, so we instead polish the surfaces down to a fraction of the wavelength of light (so that it all has the same phase). For radio telescope, the frequency is a lot lower, and we actually can measure the phase directly, so we can make our sensors crazy shapes and adjust it by adding delay. If you can change the individual delays (say, via software) you can change how they interfere and therefore change the sensitive direction for your telescope. This is how phased arrays function.
- netcraft 2y agosorry, yeah, thats a much better way of saying it and my smooth vs continuous was just confusing
- 2y ago
- itishappy 2y agoEasier to build it where the materials are than try to launch a city-sized radio telescope.
- BurningFrog 2y agoThey're planning to build this telescope on the Moon, by mining Moon rocks. In space, there are no rocks to mine, so you're have to launch all the material to space, which is wildly impractical/expensive.
- avmich 2y agoI guess local resources are easier to use locally, rather than launching to orbit first? You also have a firm base to mount the antenna, and the process of mounting could be arguably easier.
- zardo 2y agoThe idea is they dig trenches in the shapes of antenna and cast them in place. Its not even as complex as mounting them on the ground.
- jon_richards 2y agoIt’s difficult to keep things spaced out properly in microgravity without scaffolding. See also https://en.m.wikipedia.org/wiki/Project_West_Ford https://en.m.wikipedia.org/wiki/Project_West_Ford
- tekla 2y agoI feel that a 20km wide telescope may have a hard time fitting in a fairing.