Eyes in space
One of my major interests outside of social science is space-based observatories and exoplanet detection. I've long thought that we need to figure out a way to manufacture monolithic telescope mirrors in space, and I've thought of a couple of different ways to do that. But I did not think of this:
"Under his plan, a 3-D-manufacturing vendor will fabricate an unpolished mirror blank appropriate for his two-inch instrument. He then will place the optic inside a pressure chamber filled with inert gas. As the gas pressure increases to 15,000 psi, the heated chamber in essence will squeeze the mirror to reduce the surface porosity — a process called hot isostatic pressing."
This is excellent. The reason why we need to manufacture mirrors in space is that we need more aperture, and we're limited in the size of mirror/telescope that we can launch into space. Hubble is 2.4 meters. As far as I know, this is the largest monolithic mirror we have in space. The upcoming James Webb Telescope is 6.5 meters, but it's segemented, not monolithic. The mirror is folded for the trip up. Segmented mirrors allow a larger aperture, but they won't reflect as much light as a monolithic -- I think they might only be as good a monolithic mirror of about half the size, but I'm not sure if there's a consistent factor conversion there.
For reference, the largest mirrors anyone has made are in the 8.4 meter ballpark that you see in the Large Binocular Telescope, for example. They're incredibly hard to make, and very massive. Earth's gravity is a major constraint on making larger mirrors with the required level of precision and stability. Making them in space eliminates a lot of constraints. (The huge next-generation terrestrial telescopes you hear about all use segmented mirrors, like the creatively named European Extremely Large Telescope and the proposed Overwhelmingly Large Telescope.)
Why do we need larger telescopes in space? So we can see more. If it were in space, and with IR, the LBT would be able to directly image exoplanets and characterize their atmospheres. Space-based telescopes are far more sensitive than terrestrial, since they don't have to deal with the distortion and IR blocking of earth's atmosphere (Hubble is about as good as the LBT, even though it's much smaller, because it's in space.) We might be able to infer, with some confidence, the presence of life on exoplanets by the composition of their atmospheres, depending on a few things (FYI, an exoplanet is a planet outside of our solar system, a planet orbiting another star, or in rare cases flying alone through interstellar space.) Almost nothing would be more significant in human history than the discovery of life elsewhere.
A larger telescope would also allow us to observe much older stars and galaxies, and possibly see the very first galaxies form (astronomy is another word for time travel...) In fact, this is precisely what we expect the James Webb to do. But it would be so much better if it were a monolithic mirror.
8/29/2014 07:31:09 am
I'm not sure 3d printing is intended to manufacture mirrors in space. It's just a cost reduction technique. As a simple minded engineer I'd say the best option is to develop a 21st Century version of the Saturn V, and a very large mother airplane to allow two stage booster space launchings from 15000 meters elevation... With those two in hand we can put giant mirrors in space.
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José L. Duarte
Social Psychology, Scientific Validity, and Research Methods.