Discoverer 18, also known as Corona 9013, was an American optical reconnaissance satellite which was launched on 7 December 1960 at 20:24:00 GMT. It was a KH-2 9013 satellite, based on an Agena-B. 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, which was recovered three days after the launch. The Satellite Recovery Vehicle used by Discoverer 18 was SRV-508. Discoverer 18 was a satellite 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 satellite's scientific experiment package of radiation dosimeters, infrared radiometers, and microwave band detectors was identical to that of DISCOVERER 17, with the addition of photographic film packs sensitive to neutrons, x-rays and gamma rays, and nuclear track plates. The spacecraft carried external lights for optical tracking from ground camera stations. 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 biological specimens. A Thiokol retrorocket was mounted at the end of the afterbody to decelerate the capsule out of orbit. An monitoring system was included in the capsule to report on selected events, such as the firing of the retrorocket, jettisoning of the heat shield, and others. The recovery capsule was ejected, reentered the atmosphere, and was retrieved in mid-air near Hawaii by a C-119 aircraft at altitude after 48 orbits. The Agena B stage remained in orbit until 2 April 1961, when it reentered the atmosphere and burned up. Useful scientific data were obtained from the satellite. Experience Nuclear Emulsion, was two groups of films coated with nuclear emulsions, arranged horizontally and vertically, were used to measure the intensity and direction of cosmic radiation and to distinguish among electrons, protons, and heavier charged particles. These emulsions were sensitive to neutrons, x-rays, and gamma rays. Nuclear track plates were also included in the experiment package. Neutron density was measured by changes induced in a metallic bismuth detector. The experiment was contained in the recovery capsule, which was retrieved in mid-air after 48 orbits.
