Fifty years ago today — December 20, 1960 — the Discoverer-19 satellite launched from Vandenberg AFB.
(Discoverer-19 “launch cover” postcard, cancelled the day of launch. From the “Unmanned Satellite Philately” site created by Don Hillger and Garry Toth at Colorado State University.)
Part of the CORONA program and listed as an Air Force photoreconnaissance satellite, Discoverer-19 “did not carry a film capsule,” but was launched “as a test for the MIDAS missile-detection system.” MIDAS, the “Missile Detection Alarm System,” was an infrared detection system and precursor to the Defense Support Program and Space-Based Infrared systems.
The National Reconnaissance Office produced an interesting history of MIDAS, declassified in the late 1990s. That history points out that Discoverer-19 carried instruments to measure the background IR radiation emitted by the Earth “to confirm the technical feasibility of the MIDAS concept.”
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