Explorer 1 Credit - NASA

Discovered Van Allen radiation belts. Spacecraft engaged in research and exploration of the upper atmosphere or outer space.

Typical orbit: 266 x 2329 km, 33.3 deg inclinaton. Mass: 5.00 kg (11.00 lb).

• 1954 June 25 - Project Orbiter begun. - Launch Vehicle: Redstone.
  In a meeting, Dr. Wernher von Braun, Frederick C. Durant III, Alexander Satin, David Young, Dr. Fred L. Whipple, Dr. S. Fred Singer, and Commander George W. Hoover agreed that a Redstone rocket with a Loki cluster as the second stage could launch a satellite into a 200-mile orbit without major new developments. This became a joint Army-Navy study project after meeting at Redstone Arsenal on August 3. Project Orbiter was a later outgrowth of this proposal and resulted in the launching of Explorer I on January 31, 1958.

• 1954 August 15 - Von Braun proposes launch of US satellite. - Program: Explorer. Launch Vehicle: Redstone.
  Von Braun report 'A Minimum Satellite Vehicle Based on Components Available from Developments of the Army Ordnance Corps' in response to June Pentagon meeting proposes $ 100,000 to launch satellite by Redstone.

• 1955 August 24 - Redstone recommended as satellite launcher. - Program: Explorer. Launch Vehicle: Redstone.
  Research and development Policy Council (DOD) unanimously recommended that the time-risk factor in the scientific satellite program be brought to the attention of the Secretary of the Defense for determination as to whether a Redstone backup program was indicated.

• 1957 October 5 - Von Braun promises first US satellite in 60 days. - Program: Explorer. Launch Vehicle: Redstone.
  Von Braun briefs Secretary of Defence McElroy on Jupiter-C/Redstone for immediate US satellite launch. Promises launch in 60 days. Medaris says 90.

• 1958 February 1 - Explorer 1 - Program: Explorer. Launch Site: Cape Canaveral. Launch Complex: LC26A. Launch Vehicle: Redstone. Mass: 5.00 kg (11.00 lb). Perigee: 347 km (215 mi). Apogee: 1,859 km (1,155 mi). Inclination: 33.20 deg. Period: 107.20 min.
  Explorer I, the first U.S. earth satellite, was launched by a modified Army Ballistic Missile Agency Jupiter-C. Explorer I, developed by the Jet Propulsion Laboratory, carried the U.S.-IGY (International Geophysical Year) experiment of James A. Van Allen and resulted in the discovery of the radiation belt around the earth.

• 1958 March 5 - Explorer 2 - Program: Explorer. Launch Site: Cape Canaveral. Launch Complex: LC26A. Launch Vehicle: Redstone. FAILURE: Fourth Stage failed to ignite. Mass: 5.00 kg (11.00 lb).
  

• 1958 March 26 - Explorer 3 - Program: Explorer. Launch Site: Cape Canaveral. Launch Complex: LC5. Launch Vehicle: Redstone. Mass: 5.00 kg (11.00 lb). Perigee: 186 km (115 mi). Apogee: 2,799 km (1,739 mi). Inclination: 33.40 deg. Period: 115.70 min.
  Radiation, micrometeoroid data.