Popular name for the U.S. low-altitude spy satellite that combined infrared photo and signal intelligence capabilities. First launched on June 15, 1971 by a Titan 3D booster, the Big Bird satellite weighed 15 tons, was 55 feet long, and housed two KH-9 series cameras that were able to distinguish objects as small as eight inches from an altitude of 90 miles. This was the first U.S. reconnaissance satellite that could photograph such small objects. Each camera had two film canisters to be parachuted to earth for aerial recovery.

The Big Bird satellites were launched at the rate of about two a year from 1971 to 1984; 19 successful launches were followed by one failure, on April 18, 1986, in which the booster exploded after takeoff. The Big Bird's major limitation was its relatively short life span, which started out at some 52 days; by 1978 it was extended to 179 days (the average orbital life was 138 days with a maximum of 275 days achieved in 1983).