POSSIBLE IMPACTS OF THE SPS ON THE SPACE TELESCOPE E. J. Groth The goals of the Space Telescope (ST) as described in the NASA Announcement of Opportunity are to determine: • The constitution, physical characteristics, and dynamics of celestial enti ties • The nature of processes which occur in the extreme physical conditions existing in and between astronomical objects • The history and evolution of the universe • Whether the laws of nature are universal in the space-time continuum. To meet these goals, the ST must be able to detect and measure objects which are several magnitudes fainter than can be observed with ground-based telescopes. The main advantage of the ST is that its 2.4-m aperture produces diffraction limited images; therefore, the background light within a stellar image is reduced several orders of magnitude compared to what can be obtained on the ground. Other advantages of the ST are that it can work in the UV and IR spectral regions; there is no atmospheric absorption and emission or fluctuations in the absorption and emission; and the image size is smaller than 0.1 arcsec (as compared to > 1 arcsec from the ground), which not only increases the S/N for stellar objects by a factor of >20 compared to an identical ground- based telescope but also allows high resolution studies of extended objects. The orbit of the ST is circular and at an altitude of 500 km, an inclination of 28.8° and with a period of 94.5 minutes. The background sources which limit the sensitivity of the ST are: • Zodiacal light (23 mv/arcsec at minimum) • Stray light from Sun, Earth, and Moon (and SPS). The zodiacal light (sunlight scattered from interplanetary dust particles) is a diffuse source with a minimum brightness corresponding to about 23 visual
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