Descrizione : Discoverer 21, also known as RM-2, was an American satellite which was launched in 1961. It was a technology demonstration spacecraft, based on an Agena-B.
Upon successfully reaching orbit, it was assigned the Harvard designation 1961 Zeta 1.
Discoverer 21 was operated in a low Earth orbit, with a perigee of 243 kilometres (151 mi), an apogee of 1,026 kilometres (638 mi).
It remained in orbit until 20 April 1962, when it decayed and reentered the atmosphere.