instruments, the Space Telescope Imaging Spectrometer (STIS) and the Near-Infrared Camera and Multi-Objective Spectrometer (NICMOS). Both of these instruments can also be fitted with appropriate optics to remove the aberrations in the HST images and so achieve the high spatial resolution possible with an orbiting telescope. These new instruments will greatly enhance the power of the HST observatory. STIS will increase the speed with which some critical ultraviolet and visible-light observations can be made by a factor as large as 100 or more and will make possible spatially resolved spectroscopy. NICMOS will use two-dimensional arrays for imaging faint, complex fields with 0.1-arcsecond spatial resolution, and for spectroscopy with frequency resolution up to 10,000 at near-infrared wavelengths. In this wavelength range, the background radiation affecting HST is 100 times smaller than that affecting terrestrial telescopes, which must observe through the earth's time-variable atmosphere.

  • The committee considers the prompt installation of the new WF/PC to be of critical importance to space astronomy. Corrective optics may restore most of the capabilities of the other instruments. All three second-generation instruments (WF/PC, STIS, and NICMOS) must be installed and work well in order for HST to attain its full scientific goals.

GAMMA RAY OBSERVATORY

The Gamma Ray Observatory will study a broad range of topics, including accretion processes around neutron stars, the origin of gamma-ray bursts, nucleosynthesis in supernovae, interactions of cosmic rays with interstellar matter, and energy production by giant black holes in galactic nuclei. GRO's instruments have sensitivities and angular resolutions more than an order of magnitude better than those available on previous missions. The expected value of GRO's dataset mandates a vigorous, peer-reviewed program of investigations by the broad astronomical community.

ADVANCED X-RAY ASTROPHYSICS FACILITY

The Advanced X-ray Astrophysics Facility, the number-one-priority major new program recommended by the Field Committee in 1982, will return the United States to preeminence in x-ray astronomy, a field pioneered by NASA's earliest x-ray-detecting sounding rockets and satellites. Construction of AXAF is under way, with a launch planned for the latter part of the 1990s. AXAF will have a major impact on almost all areas of astronomy, including studies of the coronae of nearby stars, mapping of energetic galaxies, and detection of hot gas within distant clusters of galaxies. AXAF has a strong technical and scientific heritage from previous x-ray missions; in many ways, it is a scaled-up version of the successful Einstein Observatory launched more than a decade ago. This



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