> The idea was conceived in the 1970s. Satellite downlinks weren't that capable and several keyhole satellites still used film. Specifically, the mid 70s KH-9s

> The idea was conceived in the 1970s. Satellite downlinks weren't that capable and several keyhole satellites still used film. Specifically, the mid 70s KH-9s had a re-entry vehicle magazine that carried something like 6 or 7 REVs, and when it ran out the KH-9 became useless. The idea was that the shuttle could service the KH-9s on orbit and replace the magazine. The real reason this became useless was that around the same time CCDs were invented, and KH-11s (from 1976 - still in the design phase of the shuttle) didn't need re-entry vehicles at all. Oddly the USAF still operated KH-9s with their REV cannisters up til 1980. (If you're wondering what happened to KH-10, that was the cancelled 'MOL' program: https://en.wikipedia.org/wiki/Manned_Orbiting_Laboratory https://en.wikipedia.org/wiki/Manned_Orbiting_Laboratory )