Explorer 4

USA

Spacecraft n°: 15

USA satellite n°: 11

Launch data:

Designation	00009 / 1958Eps 1 / 58005A
Launch date	26 Jul 1958 - 15:00:57 UT
Launch site	CC, LC5
Launch vehicle	Jupiter C (Juno 1)
Mission	Scientific: ionosphere study
Earth orbit on 26 Jul 1958:
Perigee/Apogee	263 x 2213 km
Eccentricity	0.128
Inclination	50,30°
Period	110,18 min

Description

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-Mueller tubes and the cesium 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.

Spacecraft data:

Prime contractor	Jet Propulsion Laboratory (JPL)
Operator	NASA
Platform
Mass at launch	17,5 kg
Payload	8 kg
Basic shape	Cylinder
Dimension	2.03 long 0.15 dia
Equipment	Cosmic-ray detection package, temperature sensors micrometeorite impact microphone, micrometeorite erosion gauges

End of life

Decay	23 Oct 1959
Lifetime	454 days

Ref.: #1, #2, #7, #14, #15, #27, #206 - update: 10.07.04

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