Really Big Telescopes

Here's how to build a really huge telescope (for actually imaging stars around other planets). Take two circular sheets of plastic, attach them together around the edge, and launch the assembly into space, where it inflates into a rough parabola. Then fill it with a couple of tons of mercury. Start the thing spinning and use a solar sail, ion thruster or what have you to accelerate the thing toward the star you wish to observe. The combination of spin and acceleration will form the mercury's surface into a perfect parabola on the back wall of the bubble. Note that the 1/4-wave uniformity requirement only applies to the mirror itself, not to the very thin layer of transparent mylar on the front that's keeping your mercury from boiling off: that's optically unimportant as long as it's very thin. Temperature controls will be a problem. So will finding a clear million kilometers to hold this drag race. Apodizing the mirror is probably impossible. But the prettiest part of this idea is that if you see something you like at the star ahead, you can just continue "straight on till morning", and in a couple zillion years, you'll be there!

December 11, 1995

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