Technicians in a clean room at NASA’s Kennedy Space Center in Cape Canaveral, Florida, check out the Orbiting Astronomical Observatory 2 before the mission’s Dec. 7, 1968, launch.
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.[3] An Atlas-Centaur rocket launched it into a nearly circular 750-kilometre (470 mi) altitude Earth orbit.[4] Data was collected in ultraviolet on many sources including comets, planets, and galaxies.[3][5] It had two major instrument sets facing in opposite directions; the Smithsonian Astrophysical Observatory (SAO) and the Wisconsin Experiment Package (WEP).[5] One discovery was large halos of hydrogen gas around comets,[5] and it also observed Nova Serpentis, which was a nova discovered in 1970.[3]
Celescope: Smithsonian Astrophysical Observatory
The Smithsonian Astrophysical Observatory, also called Celescope, had four 12 inch (30.5 cm) Schwarzschild telescopes that fed into Uvicons.[6] The Uvicon was an ultra-violet light detector based on the Westinghouse Vidicon.[7] Ultraviolet light was converted into electrons which were in turn converted to a voltage as those electrons hit the detection area of the tube.[8] There has been a Uvicon in the collection of the Smithsonian Institution since 1973.[7]
Various filters, photocathodes, and electronics aided in collecting data in several ultraviolet lightpassbands.[6] The detectors showed a gradual loss of sensitivity[9] and the experiment was turned off in April 1970.[6] By the time it finished about 10 percent of the sky was observed[6] resulting in a catalog of 5,068 UV stars.[9]
Wisconsin Experiment Package
The Wisconsin Experiment Package had seven different telescopes for ultraviolet observations.[10] For example, there was a nebular photoelectric photometer fed by a 16-inch (40.64 cm) telescope with a six-position filter wheel[10] that unfortunately failed a few weeks after launch.[9]
In addition to the Celescope's catalog of UV stars, the WEP observed comet Tago-Sato-Kosaka and found it to be surrounded by a cloud of hydrogen, confirming that the comet was largely made up of water, and detected the 2175-angstrom bump, an increase in UV absorption at that wavelength that is still not fully explained.[9]
Spacecraft bus
The observatory was built in the shape of an octagonal prism. It measured about 10 by 7 ft (3.0 by 2.1 m) and weighed 4,400 lb (2,000 kg).[11]
Payloads are separated by bullets ( · ), launches by pipes ( | ). Crewed flights are indicated in underline. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in (brackets).
