Author - Kevin Ringer - August 1996
I was very interested in the Horizon tv programme concerning extra solar planets. The NASA administrator, Daniel Goldin, stated his desire to see photos of such planets and stated a telescope the size of the moon would be required to take such photos. This started me thinking about ways of putting large telescopes into space.
Imagine a huge umbrella, up to the length of a shuttle's cargo bay. The central pole of the umbrella carries all the optics, guidance etc., necessary for a reflecting space telescope. Each arm of the umbrella contains a long, thin segment of mirror. Once ejected from the shuttle, the umbrella opens and small adjusters along the length of the underside of each mirror keeps the mirrors in perfect alignment. The lack of gravity would alleviate many of the stesses on the mirror, distortions occuring mainly due to the Sun's heat. To compensate for the gaps between each arm, the umbrella rotates around the axis of the central pole, taking longer exposures, allowing mirrors to move through the gaps.
To keep costs down, the number of arms could be reduced, increasing the necessary exposure time but permitting the construction of a fully functioning telescope at less cost.
A 10M central pole would produce a mirror approaching 20M in diameter. If the mirror on each arm was, for instance, 0.5M, then exposure time would increase by a factor of 125 ([2pi r]/mirrror width), for a one arm telescope, a factor of 62 for a two arm one, etc..
Maybe I have missed some vital point but it does appear that large telescopes can be put into orbit, the only downside being dramatic increases in exposure time.