Many scientific justifications for space astronomy have been prepared by individuals and committees during the past three decades or more. The first such report that I am aware of, called “Astronomical Advantages of an Extraterrestrial Observatory”, was written by Lyman Spitzer in September 1946, and although its goals were extremely modest by today’s standards, the report did dwell with enthusiasm on the ultimate goal of a large reflecting telescope 4-6 meters in diameter with diffraction-limited optics put into earth-satellite orbit. The latest study, from which I shall quote liberally, has just been published by the Astronomy Committee of the U. S. National Academy of Sciences, and provides the scientific foundation for space astronomy in the 1980’s. Space Astronomy was initiated about one month after the date of publication of Spitzer’s report, when the first high-altitude rocket was launched to observe the sun’s ultraviolet radiation. Since that time, space astronomy has completed two phases and is about to embark on a third. In Phase 1, which lasted until the beginning of Sputnik, observations were made for a few minutes at a time from high-altitude rockets. In the second phase, which is just ending, observations were made with relatively small instruments in earth-orbiting satellites. The observing programs carried out with rockets and small satellites were called experiments because their capabilities and objectives were limited and their lifetimes were short -from a few minutes to about a year.