Discoverer 31 was a USAF photographic surveillance satellite designed to assess how rapidly the Soviet Union was producing long-range bombers and ballistic missiles, and where they were being deployed. It was part of the Corona program which was also used to produce maps and charts for the Department of Defense and other US government mapping programs. The satellite used a film canister that was returned to earth in a capsule (a.k.a. bucket) for evaulation. These capsules were designed to be recovered by a specially equipped aircraft during parachute descent, but were also designed to float to permit recovery from the ocean. All film were black and white. Discoverer 31's film capsule recovery failed.