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Explorer 01
Explorer 1 Mission to Earth

Mission Type: Orbiter
Launch Vehicle: Jupiter C (Juno I)
Launch Site: Cape Canaveral, United States
NASA Center: Jet Propulsion Laboratory
Spacecraft Mass: 13.97 kg
Spacecraft Instruments: 1) Cosmic Ray Detector; 2) Micrometeorite Detector; 3) Satellite Drag Atmospheric Density and 4) Temperature Sensor
Spacecraft Dimensions: 2.03 m long and 0.152 m in diameter
National Space Science Data Center,

NASA Jet Propulsion Laboratory, Explorer 1 History,

Explorer 1 was the first successfully launched U. S. spacecraft. Launched late on 31 January 1958 (10:48 p.m. EST, or 03:48 UTC on 01 February) on an adapted Jupiter-C rocket, Explorer 1 carried instrumentation for the study of cosmic rays, micrometeorites, and for monitoring of the satellite's temperature.

The Jupiter-C launch vehicle consisted of four propulsive stages. The first stage was an upgraded Redstone liquid-fueled rocket. The second, third, and fourth stage rockets consisted of eleven, three, and one (respectively) Sergeant motors. The satellite itself was the fourth stage of the Jupiter-C rocket. It was cylindrical, 2.03 m long and 0.152 m in diameter. Four whip antennas were mounted symmetrically about the mid-section of the rocket. The spacecraft was spin stabilized.

The 4.82 kg instrumentation package was mounted inside of the forward section of the rocket body. A single Geiger-Mueller detector was used for the detection of cosmic rays. Micrometeorite detection was accomplished using both a wire grid (arrayed around the aft section of the rocket body) and an acoustic detector (placed in contact with the midsection). Data from the instruments were transmitted continuously, but acquisition was limited to those times when the spacecraft passed over appropriately equipped ground receiving stations. Assembly of data proceeded slowly also due to the fact that the satellite's spin-stabilized attitude transitioned into a minimum kinetic energy state, that of a flat spin about its transverse axis. This was deduced from the modulation of the received signal, which produced periodic fade-outs of the signal.

Explorer 1 was the first spacecraft to successfully detect the durably trapped radiation in the Earth's magnetosphere, dubbed the Van Allen Radiation Belt (after the principal investigator of the cosmic ray experiment on Explorer 1, James A. Van Allen). Later missions (in both the Explorer and Pioneer series) were to expand on the knowledge and extent of these zones of radiation and were the foundation of modern magnetospheric studies.

Key Dates
1 Feb 1958:  Launch (31 Jan. 1958, 10:48 p.m. EST) (03:48 UT)
23 May 1958:  Last Data Transmitted
31 Mar 1970:  Re-entered Earth's Atmosphere
Status: Successful
Fast Facts
Explorer 01 Facts Dr. Wernher von Braun led the Jet Propulsion Laboratory team (right) that completed Explorer 1's design in only three months.

Explorer 1 completed 58,000 orbits times before returning to Earth in March 1970.

The first U.S. attempt to launch an Earth-orbiting satellite - Vanguard - rose a few feet above the ground but then fell back to Earth and burst into flames.
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Last Updated: 21 May 2013