 Explorer 4 instruments | |
| Names | Explorer IV 1958 Epsilon 1 |
|---|---|
| Mission type | Earth science |
| Operator | JPL / Army Ballistic Missile Agency |
| Harvard designation | 1958 Epsilon 1 |
| COSPAR ID | 1958-005A |
| SATCAT no. | 00009 |
| Mission duration | 71 days (achieved) |
| Spacecraft properties | |
| Spacecraft | Explorer IV |
| Spacecraft type | Science Explorer |
| Bus | Explorer 1 |
| Manufacturer | Jet Propulsion Laboratory |
| Launch mass | 25.50 kg (56.2 lb) |
| Dimensions | Cylinder: 94.6 cm (37.2 in) long, 16.5 cm (6.5 in) in diameter, Total length with attached rocket motor: 2.05 m (6 ft 9 in) |
| Start of mission | |
| Launch date | 26 July 1958, 15:00:57 GMT |
| Rocket | Juno I (RS-24) |
| Launch site | Cape Canaveral, LC-5 |
| Contractor | Army Ballistic Missile Agency |
| Entered service | 26 July 1958 |
| End of mission | |
| Last contact | 5 October 1958 |
| Decay date | 23 October 1959 |
| Orbital parameters | |
| Reference system | Geocentric orbit[1] |
| Regime | Medium Earth orbit |
| Perigee altitude | 263 km (163 mi) |
| Apogee altitude | 2,213 km (1,375 mi) |
| Inclination | 50.30° |
| Period | 110.20 minutes |
| Instruments | |
| Charged Particle Detector | |
Explorer program | |
Explorer 4 was an American satellite launched on 26 July 1958. It was instrumented by Dr. James van Allen's group. The Department of Defense's Advanced Research Projects Agency (ARPA) 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 as the other, Explorer 5, suffered launch failure.
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.