Explorer 4

Infobox Spacecraft
Name = Explorer 4


Organization = Army Ballistic Missile Agency
Major_Contractors = Jet Propulsion Laboratory
Mission_Type = Earth science
Satellite_Of = Earth
Launch = July 26, 1958 at 15:07 UTC
Launch_Vehicle = Jupiter-C
Decay = October 23, 1959
Mission_Duration = 71 days
NSSDC_ID = 1958-005A
Webpage = [http://nssdc.gsfc.nasa.gov/database/MasterCatalog?sc=1958-005A NASA NSSDC Master Catalog]
Mass = 25.5 kg
Semimajor_Axis = 7,616.2 km
Eccentricity = .127936
Inclination = 50.3°
Orbital_Period = 110.2 minutes
Apoapsis = 2,213 km
Periapsis = 263 km
Orbits = ~5,930

Explorer 4 (satellite 1958 epsilon) was a US satellite launched on July 26, 1958. It was instrumented by Dr. James van Allen's group. The Department of Defense's Advanced Research Projects Agency had initially planned two satellites for the purposes of studying the Van Allen radiation belts and the effects of nuclear explosions upon these belts (and the Earth's magnetosphere in general), however Explorer 4 was the only such satellite launched.

Explorer 4 was a cylindrically shaped satellite instrumented to make the first detailed measurements of charged particles (protons and electrons) trapped in the terrestrial radiation belts. An unexpected tumble motion of the satellite made the interpretation of the detector data very difficult. The low-power transmitter and the plastic scintillator detector failed September 3, 1958. The two Geiger-Müller tubes and the caesium iodide crystal detectors continued to operate normally until September 19, 1958. The high-power transmitter ceased sending signals on October 5, 1958. It is believed that exhaustion of the power batteries caused these failures. The spacecraft decayed from orbit after 454 days on October 23, 1959.

See also

* Operation Argus

External links

* [http://nssdc.gsfc.nasa.gov/multi/explorer.html NASA's Explorer Missions]