Launching a 25-meter space telescope. Are astronauts a key to the next technically logical step after NGST?

Considers architectures for a 25-m space telescope mirror that will extend the technological development currently underway for the Next Generation Space Telescope (NGST). Key engineering requirements are derived that distinguish a 25-m mirror from the 8-m NGST mirror. The feasibility of applying both mirror panel and active-alignment-control technologies currently under development for the NGST to a larger (25-m) telescope mirror is discussed. Analyses are presented that indicate it is impractical to mechanically deploy a 25-m telescope mirror simply because of the volumetric packaging inefficiency of such concepts. Instead, it is shown that an erectable mirror, assembled by either astronauts or robotic devices, provides the most logical mirror architecture. Finally, it is shown that an observatory with a 25-m primary mirror could be launched in one Shuttle mission for assembly and initial checkout in low Earth orbit