Why put telescopes in orbit?Putting telescopes into orbit is exceedingly expensive. They are incredibly difficult to service when things go wrong, and we are limited to only a few meters (recall the Keck is 10-m) for the primary, in order for the system to fit in the Space Shuttle.. So why do it?
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Atmospheric transmission
Only a narrow region of the optical and near-infrared and the radio can be observed from the ground. Gamma-ray, X-ray, UV, and most Infrared observatories must be placed above Earth's atmosphere.
Atmospheric Seeing
Light from a distant source
may travel for a billion years only to get blurred in
the final one-trillionth of a second, passing through
our atmosphere!
NASA is the main provider of space-based astronomy
missions in the U.S. Currently 33 missions are operating,
23 are in development. They, listed here, include cosmological, astronomical,
solar and planetary studies. Even the Keck Telescopes are
partially funded by NASA (for planetary work).
You can view the location over Earth of many of the current missions live at this website
Major Space Observatories
Infrared: Infrared Astronomy Satellite (IRAS) 1980s, Space Infrared Telescope Facility (SIRTF), to launch 2002.
Ultraviolet: Hubble Space Telescope(HST), Far Ultraviolet Explorer (FUSE), Extreme Ultraviolet Explorer (EUVE). SOHO (Solar)
Gamma and X-rays: Chandra Mission, Rosse X-ray Timing Explorer (RXTE), Yohkoh (Solar).
The Next Generation Space Telescope (NGST)
HST is expected to finish it's mission by 2008 or possibly as
late as 2010. NGST is designed to replace HST, launching in
2009, with an expected life time of 5-10 years. NGST will be
optimized for infrared observations. It is hoped that it will
have the sensitivity to view the very edge of our observable
universe, witnessing the birth of the first stars and galaxies
in our universe, 15 billion years ago.
Because of the long time-scale for such a project, ideas which are not entirely feasible are considered, since we expect the technology to continue to advance in the meantime.