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Corona (satellite)

Corona was the name of a series of US military spy satellites, used for photographic surveillance of the Soviet Union, China and other areas from June 1959 (1960) until May 1972. The project name is sometimes given as CORONA, but it is not an acronym.

The satellites were designated KH-1, KH-2, KH-3, KH-4, KH-4A and KH-4B. KH standing for Keyhole and the incrementing number indicating changes in the surveillance instrumentation, such as the change from single panoramic to double panoramic cameras. The KH naming system was first used in 1962 with KH-4 and the earlier numbers were retroactively applied. There were 144 Corona satellites launched, of which 102 returned usable imagery.

The Corona satellites used special 70 mm film with a 24 inch focal length. Initially orbiting at 165 to 460 km the cameras could resolve images down to 7.5 m, the two KH-4 systems improved the resolution to 2.75 m and 1.8 m respectively and used a lower altitude pass.

The initial Corona launches were obscured as part a space technology program called Discoverer. The first test launches were in early 1959, the first launch with a camera was June 1959 as Discoverer 4, which was a 750 kg satellite launched by a Thor Agena rocket. The key issue with the early satellites was the recovery of the exposed film, radio link technology did not exist and so film canisters were returned to earth in capsules, called buckets. The buckets were recovered in mid-air by a specially equipped aircraft during their parachute descent. The first camera-fitted Discoverer missions failed to return usable film, but following repeated recovery tests on August 18, 1960 with Discoverer 14 a bucket was successfully retrieved two days later by a C-119.

The last launch under the Discoverer name was 38 in 1962, after that the launches were entirely secret. The last Corona launch was on May 25, 1972. The best sequence of Corona launches was from 1966 to 1971 when there were 32 consecutive launch-and-film-recoveries.

Corona was officially secret until 1992. On February 22, 1995 an Executive Order declassified the imagery acquired by the Corona and two later programs (Argon and Lanyard).

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