Small Astronomy Satellite
A NASA series of three small satellites devoted to X-ray and gamma-ray astronomy. SAS-1, also known as Explorer 42, was renamed Uhuru after launch in 1970. It was the first X-ray satellite, and performed the first X-ray sky survey. SAS-2, otherwise known as Explorer 48, was a gamma-ray mission, launched in 1972 November. The last of the series, SAS-3, or Explorer 53, was launched in 1975 May to study individual X-ray sources.
http://heasarc.gsfc.nasa.gov/docs/uhuru/uhuru.html Information page on SAS 1 at Goddard Space Flight Center.
http://heasarc.gsfc.nasa.gov/docs/sas2/sas2.html Information page on SAS 2 at Goddard Space Flight Center.
http://heasarc.gsfc.nasa.gov/docs/sas3/sas3.html Information page on SAS 3 at Goddard Space Flight Center.