Inner workings: Hubble's quarter century in orbit has opened a universe of possibilities.

When the Hubble Space Telescope was deployed from Space Shuttle Discovery on April 25, 1990, few knew just how far-reaching its impact would be on astronomy, cosmology, and public appreciation of the universe. “It has given us views of the universe that we have never seen before and provided a wealth of data for astronomers around the world to ponder,” says Ken Sembach, head of the Hubble Mission Office at the Space Telescope Science Institute. Hubble also laid the foundation for a new generation of space telescopes. But such lofty achievements took plenty of study and political will. The telescope had a troubled beginning because of repeated questions about its price tag and mission, not to mention a faulty mirror. Hubble’s origins stretch back nearly three decades before its launch. In 1962, a National Academy of Sciences report recommended the creation of a large space-telescope study program to complement its orbiting astronomical observatories program: “Consideration should be given to the desirability of a large space telescope, and the technical problems associated with it, as the next step beyond the present orbiting astronomical observatories program” (1). This new breed of telescope would have a much larger aperture than existing orbiting astronomical observatories and be capable of “stellar and nebular studies through the entire spectral range from soft X rays to infrared.”However, the budgets and the technological capabilities of the time presented challenges for a large-aperture space telescope. Recommendations at the Academy’s 1965 Space Science Board added some specifics: “We conclude that a space telescope of very large diameter, with a resolution corresponding to an aperture of at least 120 inches, detecting radiation between 800 Å and 1 mm, and requiring the capability of man in space, is becoming technically feasible, and will be uniquely important to the solution of the central astronomical problems of our era” (2) (Figs. 1 and 2). This led to the Large Space Telescope program, later to be known as the Hubble Space Telescope, named for Edwin Hubble, discoverer of the relationship between distance and velocity for receding galaxies (3). By 1970, Congress still balked at the price tag and didn’t pay much attention. But after advocates, including astronomers John Bahcall and Lyman Spitzer, in 1974 obtained a letter from the National Research Council’s decadal survey of astronomy committee saying that an updated 1970 survey would rank the project higher. That gave them the leverage they needed to convince Congress. The initial proposed launch date was 1983. But technical delays, budget problems, and the 1986 Space Shuttle Challenger disaster pushed the launch to 1990. Then came a series of difficult servicing missions beginning in 1993 to install corrective optics for the incorrectly ground main mirror and upgrade various components. Hubble was designed to be serviceable, but these weren’t easy fixes. Nevertheless, astronauts made the repairs and boosted the telescope to a higher orbit to compensate for the atmospheric drag that had gradually brought it closer to Earth. “There are moments you look back on, and see that they are pivotal moments that made the mission what it is,” says Sembach.