The National Aeronautics and Space Administration's (NASA) Astro-1 Observatory was launched aboard space shuttle Columbia on 2 December 1990, beginning a 9-day mission whose technical problems were widely reported in the press, but whose scientific achievements are just now coming into focus. Mounted on two steerable platforms in the cargo bay were three telescopes designed to perform various measurements in the ultraviolet (UV) band of the spectrum and one telescope designed to study astronomical X-ray sources (Table 1). Also on board was a crew of seven astronauts, including four astronomers who had been waiting for this flight since 1984.
One of the Astro-1 instruments was the Hopkins Ultraviolet Telescope (HUT), designed to study stars, planets, nebulae, galaxies, and quasars in a largely unexplored region of the spectrum-the far- and extreme-UV bands (Davidsen et al. 1992). Important clues to the nature of these objects are potentially available in this spectral region, which is not accessible to other observatories, including the Hubble Space Telescope. During the Astro-1 mission, HUT obtained UV spectrophotometry of 77 objects at wavelengths extending from 1850 Å to the Lyman limit at 912 Å, where the interstellar medium becomes opaque because of photoelectric absorption by atomic hydrogen, and detected a few nearby objects at wavelengths as short as 400 Å. Part of the scientific and technical motivation for this mission and a few of the numerous results derived from the first year of analysis of these data are discussed in this article.