Orbiting Solar Observatory
From Memory Alpha, the free Star Trek reference
The Orbiting Solar Observatory, or OSO, was a 20th century series of satellites used by NASA for studying the physical properties of the Sun.
A black-and-white drawing of the satellite was stored in the USS Enterprise library computer. This drawing was retrieved by the Talosians when they accessed the starship's computers in 2254. (TOS: "The Cage")
