FIGURE 4.2 The power of SIRTF compared with existing telescopes and with the European ISO mission. “Astronomical capability” is defined as (facility lifetime) × (efficiency) × (number of detectors)/(sensitivity)2 and is normalized at various wavelengths to the capabilities of NASA 's 3-m telescope on Mauna Kea, IRAS, or the KAO. The figure shows how much more quickly SIRTF would be able to map or survey a region of sky to a particular flux limit than would other telescopes.

the private 10-m Keck telescope in three ways: (1) it will be accessible to all U.S. astronomers, whereas the Keck telescope will be available to only about 3 percent of the national astronomical community; (2) it will be the only large telescope in the world optimized for performance in the infrared; and (3) it will use adaptive optics to achieve the maximum possible spatial resolution in the near-infrared.

The third telescope needed to cover this factor-of-1,000 range in wave-lengths is the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA), a moderate-sized 2.5-m telescope. Mounted in a Boeing 747 aircraft, SOFIA will fly over 100 8-hour missions per year. At altitudes of 41,000 ft, above 99 percent of the water vapor in the earth's atmosphere, SOFIA will open the wavelength range from 30 to 350 µm to routine observation and make valuable contributions at still longer wavelengths. In particular, spectral observations at these wavelengths hold the key to understanding the physics in regions of high density and moderate temperature that characterize the primitive nebulae around newly formed stars, and the cores of infrared-luminous galaxies and quasars. SOFIA's capability for diffraction-limited imaging and high-resolution spectroscopy at wavelengths inaccessible from the ground will complement SIRTF's great sensitivity at infrared and submillimeter wavelengths. SOFIA is a joint project with Germany, which will supply the telescope system and support about 20 percent of the operations. NASA and the German space agency

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