An ongoing series of US scientific spacecraft. Explorer 1, launched on 1958 January 31, was the first successful US satellite; it discovered the Earth’s Van Allen Belts. Later Explorers have included the International Ultraviolet Explorer and the Cosmic Background Explorer. A concurrent Small Explorer Program (SMEX), consisting of simpler, cheaper satellites, began in 1992 with the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX). These were later later joined by the Medium-class Explorer (MIDEX) series, the first of which was the Far Ultraviolet Spectroscopic Explorer (FUSE).

http://explorers.gsfc.nasa.gov Official Explorer program website.

http://nssdc.gsfc.nasa.gov/multi/explorer.html Complete listing of Explorer missions.