Future Designs for Space-based Observatories

A NASA appointed "HST and Beyond" Committee studied possible missions and programs for Optical-UV astronomy in space for the first decades of the 21st century. The report contains several grand goals, like "mission to the early universe" and "search for other planets" that could have broad appeal to the public and serve as a umbrella to many of the programs that are perceived to be important to the astronomical community.One group thought a likely successor to HST to be a 6-m reflector in high-earth orbit. Even if we ignore for the time being the difficulty in starting on such an ambitious project in the circumstances of NASA's current budget restraints, it is unresolved whether this is the kind of project that best suits the astronomical community's scientific interests. For example, given a fixed budget a general-purpose, long-lived observatory could be more cost effective for astronomy than a string of COBE-size missions with well-set and limited scientific goals, or even greater number of still smaller missions, like the Explorer series.

There is AIM, a NASA development program that seeks to develop a space platform for astrometric interferometry that would give positions of stars down to 17th magnitude or fainter to an accuracy of better than 10 micro-arcseconds. It would promise to give "a distance to any star in the Milky Way galaxy" But if this route were to be selected, we could forego, for a decade or more, the general capability to point at a particular object and take a picture or take an ultraviolet spectrum with the 0.1 arcsecond resolution, a standard set by the Hubble Space Telescope.

An aerospace consortium has proposed Adapt, a 4-meter diffraction limited "demonstrator" to low earth orbit within 3 years on a Proton rocket, at relatively low cost. The proposers seek astronomical involvement to establish "dual use" and would release the telescope to astronomers for the final 4 years of a projected 5 year lifetime.

These missions involve genuinely new technology. This seems to hold greater attraction to NASA than an enhancement of scientific capabilities, even considering the substantial scientific payoffs of a more powerful version of HST. This relationship of the astronomical community with NASA has already become and will continue to be a point of discussion for the committee. NASA's admitted goal is "to build hardware and fly it" and not necessarily to do science.