Discoverer 9 was an American military reconnaissance satellite, launched in 1960 as a part of the Discoverer program. The satellite was launched on 4 February 1960, at 18:51 UTC, from Vandenberg Air Force Base on the Thor-Agena launch vehicle. The Thor cut off 20 seconds early and left the Agena without sufficient velocity or attitude control. It began tumbling and the engine shut down after only 20 seconds of operation, sending the payload into the Pacific Ocean. Cause of the failure was thought to be due to an improper pad umbilical disconnect at liftoff that allowed helium pressure gas to escape from the Agena.