KH-9

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Codenamed Hexagon, the KH-9 was a photographic reconnaissance satellite used by the United States. Twenty launches were attempted from June 1971 to April 1986, and all but one were successful. The satellite was popularly known as the Big Bird.

The KH-9 was originally conceived in the early 1960s as a replacement for the Corona search satellites. The goal was to search large areas of the earth with a medium resolution camera. The KH-9 carried two main cameras, although a mapping camera was also carried on several missions. The photographic film from the cameras was sent to recoverable reentry vehicles and returned to earth, where the capsules were caught in mid-air by an aircraft. Four reentry vehicles were carried on most missions, with a fifth added for missions that included a mapping camera.

Over the duration of the program the lifetime of the individual satellites increased steadily. The final KH-9 operated for up to 275 days. Different versions of the satellite varied in mass, most weighed 11,400 kilograms or 13,300 kg. Satellites were manufactured by Lockheed and the camera was designed by Itek, but produced by Perkin-Elmer. There were 21 launch attempts and one failure.

The KH-9 was never a backup project for the KH-10 Manned Orbiting Laboratory. It was developed solely as a replacement for the Corona search system.