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The Engineering and Logistics of Building the Giant Magellan Telescope (theconversation.com)
New submitter Kenneth Stephen writes: Astronomers have always wanted bigger and better telescopes. Building such telescopes today come with many challenges that require high precision work to resolve. This story describes the design thinking that is being applied to the construction and deployment of the Giant Magellan Telescope. From the article: "One of the challenges of using a large mirror is that it tends to bend under its own weight and the force of wind. The mirror is exposed to wind like a sail on a yacht, but it can only bend by about 100 nanometers before its images become too blurry. The best way to overcome this problem is to make the mirror as stiff as is practical, while also limiting its weight. We accomplish this feat by casting the mirror into a lightweight honeycomb structure. Each mirror has a continuous glass facesheet on top and an almost continuous backsheet, each about one inch thick. Holding the two sheets together is a honeycomb structure consisting of half-inch-thick ribs in a hexagonal pattern. Our honeycomb mirrors are 70 centimeters thick, making them stiff enough to withstand the forces of gravity and wind. But they’re 80 percent hollow and weigh about 16 tons each, light enough that they don’t bend significantly under their own weight."
If the Astronomers would stop harassing women they would probably get it built faster. - Ethan (StartsWithABang)
One of the challenges of using a large mirror is that it tends to bend under its own weight and the force of wind.
I think it's a scandal that we aren't building a massive telescope in space, where you don't have to worry about gravitational sagging or gusts of wind... (or clouds, atmospheric distortions, light pollution, etc.). When we think of near-future space program ambitions, everybody talks about sending people to Mars. But we would learn so much more from building and using a kilometer-scale telescope mirror in orbit. From the article, it's clear that even terrestrial telescope mirrors now consist of a thin glass sheet with scaffolding behind it. Isn't it time to think about how to build that kind of thing in space, where the scaffolding requirements would be much smaller? It's inevitable that for a certain size of mirror, it will actually more expensive to build it on Earth than in space, for the reasons mentioned in the article. So come on, let's get some courageous nerds like Elon Musk on the job and build a telescope that could actually resolve extrasolar planets and see the formation of the first galaxies. Compared to this, people on Mars seems like a vanity project.
The South pole of the Moon is quite a good site. There are mountains permanently lit (for power) and crater bottoms in permanent shadow a few hundred meters away (for the telescopes). Having a large mass (like the moon) to anchor you against vibration from your own systems, light pressure, etc. and serve as a heat sink has considerable advantages.
See http://citeseerx.ist.psu.edu/v...