While mostly classified military missions, several Discoverers are known to have contained scientific X-ray counters. The program objectives were to test a system of better orbital control of the Agena B launch vehicle and to collect scientific data concerning electrons, x-rays, and galactic RF radiation. In addition, several biological specimens were exposed to the environment of space while making 33 orbits of the earth. The science unit jettisoned after these 33 orbits and was recovered near Hawaii on 4 September 1961. The spacecraft decayed from orbit and was recovered on 10 September 1961, from the sea.
Information concerning the success of the spacecraft is unknown.
Discoverer 31 was launched on 17 September 1961. The science unit failed to jettison. The spacecraft reentered the atmosphere on 26 October 1961. The science capsule failed to jettison properly and the spacecraft fell silent on 7 December 1962. It was still in orbit as of 1966.