Explorer 51, also known as Atmosphere Explorer-C or AE-C, was a NASA upper-atmosphere research satellite launched on December 16, 1973. Its suite of 14 instruments measured thermospheric neutral composition, density, temperature, energy transfer, ionospheric chemistry, and photochemical processes over altitudes from roughly 150 to 4,000 kilometers, with merged science data through December 1978.
Future launches and major activity directly linked to this vehicle family.