* Astronomy

First Spy Satellites: "Corona Project Overview" 1995 National Reconnaissance Office

The Corona satellites were designated KH-1, KH-2, KH-3, KH-4, KH-4A and KH-4B. KH stood for "Key Hole" or "Keyhole" (Code number 1010),[1] and the incrementing number indicated 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 photographs.
The Corona program was officially classified top secret until 1992. Then, on February 22, 1995, the photos taken by the Corona satellites, and also by two contemporary programs (Argon and KH-6 Lanyard) were declassified under an Executive Order signed by President Bill Clinton.
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