Discoverer 3 was an American optical reconnaissance satellite launched on 3 June 1959 at 20:09:20 GMT, the third of three test flights of the Corona KH-1 spy satellite series. The first Discoverer mission to carry live animal passengers, Discoverer 3 was lost when its carrying Agena-A booster crashed into the Pacific Ocean.

The Corona program was a series of American strategic reconnaissance satellites produced and operated by the Central Intelligence Agency (CIA) Directorate of Science & Technology with substantial assistance from the U.S. Air Force. The CORONA satellites were used for photographic surveillance of the Soviet Union (USSR), China, and other areas beginning in June 1959 and ending in May 1972.