Explorer 4
Explorer 4
|
|
| Mission type | Earth science |
|---|---|
| Operator | Army Ballistic Missile Agency |
| Harvard designation | 1958 Epsilon 1 |
| SATCAT № | 9 |
| Mission duration | 71 days |
| Spacecraft properties | |
| Manufacturer | Jet Propulsion Laboratory |
| Launch mass | 25.50 kilograms (56.2 lb) |
| Start of mission | |
| Launch date | July 26, 1958, 15:00:57 UTC |
| Rocket | Juno I |
| Launch site | Cape Canaveral LC-5 |
| End of mission | |
| Last contact | October 5, 1958 |
| Decay date | October 23, 1959 |
| Orbital parameters | |
| Reference system | Geocentric |
| Regime | Medium Earth |
| Semi-major axis | 7,616.2 kilometers (4,732.5 mi) |
| Eccentricity | 0.1279360055923462 |
| Perigee | 263 kilometers (163 mi) |
| Apogee | 2,213 kilometers (1,375 mi) |
| Inclination | 50.29999923706055 degrees |
| Period | 110.20 minutes |
| RAAN | 82.42 degrees |
| Argument of perigee | 57.72 degrees |
| Mean anomaly | 303.52 degrees |
| Mean motion | 15.52 |
| Epoch | 2 October 1959, 06:53:14 UTC |
| Revolution number | 6070 |
Explorer 4 was an American 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 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.
Contents
Mission
Launched from a Juno I rocket, the mission remained secret from the public for six months.[1]
The satellite telemetry was analyzed for three Operation Argus nuclear weapons tests at high altitude. The satellite was also on orbit for very first high-altitude_nuclear_explosions, the 3.8 mT Operation_Hardtack_I shots, which were launched a few days after Explorer 4. All five nuclear tests produced relatively small, persistent artificial radiation belts resulting from the explosions.
| Explosion | Location | Date | Yield (approximate) | Altitude | Nation of Origin |
|---|---|---|---|---|---|
| Hardtack Teak | Johnston Island (Pacific) | 1958-08-01 | 3.8 megatons | 76.8 km (47.7 mi) | United States |
| Hardtack Orange | Johnston Island (Pacific) | 1958-08-12 | 3.8 megatons | 43 km (27 mi) | United States |
| Argus I | South Atlantic | 1958-08-27 | 1-2 kilotons | 200 km (120 mi) | United States |
| Argus II | South Atlantic | 1958-08-30 | 1-2 kilotons | 256 km (159 mi) | United States |
| Argus III | South Atlantic | 1958-09-06 | 1-2 kilotons | 539 km (335 mi) | United States |
An unexpected tumble motion of the satellite made the interpretation of the detector data very difficult. The tumble should have been expected, as both Explorer 1 and Explorer 3, of similar design, did the same. The satellite also assumed a high eccentricity orbit similar to its sister satellites.
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
References
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External links
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