The primary goal of the satellites was to replace the U-2 spyplane in surveilling the Sino-Soviet Bloc, determining the disposition and speed of production of Soviet missiles and long-range bombers assess.

The KH-1 payload included the C (for Corona) single, vertical-looking, panoramic camera that scanned back and forth, exposing its film at a right angle to the line of flight.

[4] Previously, Discoverer 1, which carried neither camera nor film capsule, was launched 28 February 1959 after a failed attempt on 21 January 1959.

This attempt was aborted when biomedical telemetry ceased from the SRV and, upon opening the capsule, it was discovered that the payload, four black mice, had poisoned themselves by gnawing at the Krylon coating of their cages.

Discoverer III sent telemetry data for 13 minutes, reaching a range of 1,200 miles (1,900 km) downrange and a speed of nearly 18,000 mph (29,000 km/h), before abruptly going silent.

[7]: 53–54 The loss of the mice at sea, compounded by a Jupiter suborbital shot failure on May 29 resulting in the death of the payload monkey, Able, generated complaints from a British humane society and several American newspapers.

[7]: 245  CORONA was declassified in 1995,[7]: 14  and a formal acknowledgement of the existence of US reconnaissance programs, past and present, was issued in September 1996.