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Discoverer 2



Discoverer 2 was a cylindrical satellite designed to gather spacecraft engineering data and to attempt ejection of an instrument package from orbit for recovery on Earth. The spacecraft was launched into a 239 km x 346 km polar orbit by a Thor-Agena A booster. The spacecraft was three-axis stabilized and was commanded from Earth. After 17 orbits, on 14 April 1959, a reentry vehicle was ejected. The reentry vehicle separated into two sections, one consisting of the protection equipment, retrorocket and main structure and the other the reentry capsule. It was planned that the capsule would reenter over the vicinity of Hawaii for recovery, but a timer malfunction caused premature capsule ejection and reentry over the north polar region. The capsule was never recovered. The main instrumentation payload remained in orbit and carried out vehicular performance and communications tests.

The spacecraft was 1.5 m in diameter, 5.85 m long and had a mass after second stage separation, including propellants, of roughly 3800 kg. The mass excluding propellants was 743 kg, which included 111 kg for the instrumentation payload and 88 kg for the reentry vehicle. The capsule section of the reentry vehicle was 84 cm in diameter and 69 cm long and held a parachute, test life-support systems, cosmic-ray film packs to determine the intensity and composition of cosmic radiation (presumably as a test for storage of future photographic film), and a tracking beacon. The capsule was designed to be recovered by a specially equipped aircraft during parachute descent, but was also designed to float to permit recovery from the ocean. The main spacecraft contained a telemetry transmitter and a tracking beacon. The telemetry could transmit over 100 measurements of the spacecraft performance, including 28 environmental, 34 guidance and control, 18 second stage performance, 15 communications, and 9 reentry capsule parameters. Electrical power for all instruments was provided by NiCd batteries. Orientation was provided by a cold mitrogen gas jet-stream system, a scanner for pitch attitude, and an inertial reference package for yaw and roll data.

The Discoverer 2 mission successfully gathered data on propulsion, communications, orbital performance, and stabilization. All equipment functioned as programmed except the timing device. Telemetry functioned until April 14, 1959, and the main tracking beacon functioned until April 21, 1959. Discoverer 2 was the first satellite to be stabilized in orbit in all three axes, to be maneuvered on command from the earth, to separate a reentry vehicle on command, and to send its reentry vehicle back to earth.

The Discoverer program was managed by the Advanced Research Projects Agency of the Department of Defense and the U.S. Air Force. The primary goal of the program was to develop a film-return photographic surveillance satellite to assess how rapidly the Soviet Union was producing long-range bombers and ballistic missiles and where they were being deployed, and to take photos over the Sino-Soviet bloc to replace the the U2 spyplanes. It was part of the secret Corona program which was also used to produce maps and charts for the Department of Defense and other US government mapping programs. The goal of the program was not revealed to the public at the time, it was presented as a program to orbit large satellites to test satellite subsystems and investigate the communication and environmental aspects of placing humans in space, including carrying biological packages for return to Earth from orbit. In all, 38 Discoverer satellites were launched by February 1962, although the satellite reconnaissance program continued until 1972 as the Corona project. The program documents were declassified in 1995.

Alternate Names

  • 00014

Facts in Brief

Launch Date: 1959-04-13
Launch Vehicle: Thor
Launch Site: Vandenberg AFB, United States
Mass: 743.0 kg

Funding Agency

  • Department of Defense-Department of the Air Force (United States)


  • Astronomy
  • Surveillance and Other Military

Additional Information

Questions or comments about this spacecraft can be directed to: Dr. David R. Williams.

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