Discoverer 12, a development model of the KH-1 Corona reconnaissance satellite without a camera, was launched into a polar orbit by a Thor-DM18 Agena-A booster. Operating in a three-axis stabilized mode and controlled from Earth, it conducted 17 orbits before ejecting a reentry vehicle on April 14, 1959. This vehicle, composed of protection equipment, retrorocket, and main structure, separated into two sections, with the reentry capsule intended for recovery over Hawaii. However, a timer malfunction led to premature capsule ejection and reentry over the north polar region, resulting in the capsule's loss. Despite this setback, the main instrumentation payload continued orbiting, facilitating vehicular performance and communications tests.