The term "reconnaissance satellite" is preferred, as "spy satellite" often has negative connotations.
In the United States, the most information is available on programs that existed up to 1972. Some information about programs prior to that time is still classified, and a small trickle of information is available on subsequent missions. A few up-to-date reconnaissance satellite images have been declassified on occasion, or leaked, as in the case of KH-11 photographs which were sent to Jane's Defence Weekly in 1985.
Serious satellite studies began with that 1946 RAND study, which showed that it was technically feasible to launch Earth satellites and that using them for reconnaissance -as "observation aircraft" -- would be an obvious mission.
Reconnaissance and surveillance -- the former is active, while the latter amounts to passively observing -- would have three basic functions for both sides during the remainder of the Cold War: technical intelligence collection; targeting; and arms control monitoring and verification.
Unlike other reconnaissancesatellites built for foreign governments, which are supposed to remain under U.S. control, Space Imaging said that it in effect wanted to hand over the satellite's keys with the spacecraft itself.
A spy satellite (officially referred to as a reconnaissancesatellite or recon sat) is an Earth observation satellite or communications satellite deployed for military or intelligence applications.
Until the 1970s and even the 1980s, many reconnaissancesatellites that took photographs would eject canisters of photographic film, which would descend to earth and be retrieved in mid-air as they floated down on parachutes.
A few up-to-date reconnaissancesatellite images have been declassified on occasion, or leaked, as in the case of KH-11 photographs which were sent to Jane's Defence Weekly in 1985.