Orbiting Astronomical Observatory 2

The Orbiting Astronomical Observatory 2 (OAO-2, nicknamed Stargazer) was the first successful space telescope (first space telescope being OAO-1, which failed to operate once in orbit), launched on December 7, 1968. An Atlas-Centaur rocket launched it into a nearly circular 750-kilometer (470 mi) altitude Earth orbit. Data was collected in ultraviolet on many sources including comets, planets, and galaxies. It had two major instrument sets facing in opposite directions; the Smithsonian Astrophysical Observatory (SAO) and the Wisconsin Experiment Package (WEP). One discovery was large halos of hydrogen gas around comets, and it also observed Nova Serpentis, which was a nova discovered in 1970.

The Smithsonian Astrophysical Observatory, also called Celescope, had four 12 inch (30.5 cm) Schwarzschild telescopes that fed into Uvicons. Various filters, photocathodes, and electronics aided in collecting data in several ultraviolet light passbands. The experiment was completed in April 1970. By the time it finished about 10 percent of the sky was observed. The Uvicon was an ultra-violet light detector based on the Westinghouse Vidicon. Ultraviolet light was converted into electrons which were in-turn converted to a voltage as those electrons hit the detection area of the tube. There has been a Uvicon in the collection of the Smithsonian Institution since 1973. The Wisconsin Experiment Package had eleven different telescopes for ultraviolet observations. For example, there was a photoelectric photometer fed by a 16-inch (40.64 cm) telescope with a six-position filter wheel.WEP observed over 1200 targets in ultraviolet light before the mission ended in early 1973. The observatory was overall about 10 ft by 7 in the shape of an octagonal prism and it weighed 4400 pounds.