Here's a quick look at NASA's "Great Observatories," a series of four space-borne observatories designed to conduct astronomical studies over many different wavelengths:
1. Hubble Space Telescope (HST) was launched on the space shuttle in 1990. A 2.4-meter telescope for observing in the near-ultraviolet, visual, and near-infrared wavelengths (1150 A to 1 mm), HST will probably be used beyond its planned mission end in 2005.
2. Compton Gamma-Ray Observatory (CGRO) was launched on the shuttle in 1991. CGRO collects data from 30 keV to 30 GeV, and studies some of the most violent physical processes in the Universe: solar flares, gamma-ray bursts (which for a few seconds can generate more energy than an entire galaxy), pulsars, nova and supernova explosions, black holes, and quasars.
3. Advanced X-Ray Astrophysics Facility (AXAF) will be launched on the shuttle and boosted into high-earth orbit in early 1999 to observe black holes, quasars, and high-temperature gases. AXAF was recently renamed the Chandra X-ray Observatory in honor of the late Indian-American Nobel laureate, Subrahmanyan Chandrasekhar, one of the foremost astrophysicists of the twentieth century.
4. Space InfraRed Telescope Facility (SIRTF), currently in development, will start its 2.5 to 5-year mission in December 2001 on a Delta rocket. A 0.85-meter telescope for imaging and spectroscopy in the 3 to 180 micron wavelength range, SIRTF will observe the far reaches of the Universe and conduct large-area imaging and spectroscopic surveys.
A sister program for SIRTF is the Stratospheric Observatory for Infrared Astronomy (SOFIA), the next-generation airborne infrared observatory. A 2.5-meter telescope aboard a customized Boeing 747 airplane, SOFIA will make over 100 high-altitude flights annually over 20 years starting in late 2001. It will perform targeted observations, especially in the Milky Way Galaxy and in the Solar System, within the wavelength range of 0.3 micron to 1.6 millimeter.
The successor to HST will be the Next Generation Space Telescope (NGST), which is planned for launch in 2007 aboard an Atlas-class rocket on a 10-year mission. 3 different preliminary designs are being considered. It will detect wavelengths in the range 0.5 to 30 microns, and be optimized for the 1 to 5 micron region. To keep its infrared detectors cold and away from Earth's reflected sunlight, NGST will probably be located at L2, the stable Lagrangian orbital point which remains on the opposite side of the earth from the sun. With an 8- to 9-meter mirror, NGST will see objects 400 times fainter than large ground-based infrared telescopes (such as Keck or Gemini) or the current generation of space-based infrared telescopes (ISO, NICMOS or SIRTF), with a spatial resolution comparable to HST. It is a key part of NASA's Origins Program, which will use a series of new, low-cost observatories in space and on the ground to investigate the origins of galaxies, stars, and planets -- and of life itself.
The Chandra X-ray Observatory was succcessfully launched from the Space Shuttle in July, 1999.
The Compton Gamma-Ray Observatory was safely de-orbited and entered the Earth's atmosphere on June 4, 2000.
SIRTF (renamed the Spitzer Space Telescope) was succcessfully launched aboard a Delta rocket on August 25, 2003.
NASA press release 9/4/02: "SOFIA is scheduled to arrive at NASA Ames in May or June of 2004 for its final flight tests and is scheduled to begin full-scale astronomical observations in late 2004."