Discoverer 18, also known as Corona 9013, was an American optical reconnaissance satellite launched on 7 December 1960 at 20:24:00 GMT. It was the first successful, and the third of ten total Corona KH-2 satellites, based on the Agena-B. Background Discoverer 18 was the third of the KH-2 Corona spy satellites, which was distinguished from the predecessor KH-1 series in its incorporation of the improved C' camera, which replaced the C model carried on KH-1 missions. The improved camera had variable image motion compensation so that its carrying satellites could be flown in differing orbits. Like the C camera, the C' was manufactured by Fairchild Camera and Instrument under the supervision of Itek, a defense contractor that specialized in making cameras for spy satellites. The satellite also carried a Transit on Discoverer (TOD) payload Discoverer 16, the first of the KH-2 series, had failed to reach orbit after its launch on 26 October 1960. Discoverer 17, the second of the KH-2 series launched successfully on 12 November 1960 but suffered a payload malfunction. Mission The launch of Discoverer 18 occurred at 20:24:00 GMT on 7 December 1960. A Thor DM-21 Agena-B rocket was used, flying from LC 75-3-4 at the Vandenberg Air Force Base. Upon successfully reaching orbit, it was assigned the Harvard designation 1960 Sigma 1. Discoverer 18 was operated in a low Earth orbit, with a perigee of , an apogee of , 81.5° of inclination, and a period of 93.66 minutes. The satellite had a mass of , and was equipped with a panoramic camera with a focal length of , which had a maximum resolution of . Images were recorded onto film, and returned in a Satellite Recovery Vehicle (SRV), which was recovered three days after the launch. The Satellite Recovery Vehicle used by Discoverer 18 was SRV-508. Discoverer 18 was placed in a near-polar orbit to test spacecraft engineering techniques, to continue the evaluation of the Agena B vehicle, and to attempt separation, deceleration, reentry through the atmosphere, and recovery from the air of an instrument package. The cylindrical Agena B stage carried a telemetry system, tape recorder, receivers for command signals from the ground, a horizon scanner, and a recovery capsule. The capsule was a bowl-shaped configuration in diameter and deep. A conical afterbody increased the total length to about . The recovery capsule payload included the photographic film packs, nuclear track plates, and