The SAS-1 satellite, launched from a platform called San Marco off the coast of Kenya in 1970 December and named Uhuru after the Swahili for Freedom; also known as Explorer 42. It carried out the first survey of the X-ray sky. In all it discovered 339 sources before it ceased working in 1973 April.
http://heasarc.gsfc.nasa.gov/docs/uhuru/uhuru.html Information page at Goddard Space Flight Center.
Subjects: Astronomy and Astrophysics.