Explorer 1
Explorer 1 — the first United States satellite (1 February 1958). Built by JPL and launched by Wernher von Braun's US Army team on a Juno I rocket, it carried a cosmic-ray detector whose puzzling readings revealed the Van Allen radiation belts, the first great discovery of the Space Age. It fell silent in May 1958 and re-entered the atmosphere in 1970. (Its orbit here is representative of the initial 358 × 2,550 km elliptical path — the real orbit decayed over the years.)
Key facts
Mission & specifications
Mission
- Operator
- NASA / JPL
- Launched
- February 1, 1958
- Status
- Completed
Trajectory
- Distance from the Sun
- 1.01 AU
- Distance from Earth
- 16,262 km
- Distance from Venus
- 0.594 AU
Mission
Explorer 1 was America's answer to a shock. When the Soviet Union orbited Sputnik in October 1957, the United States had no satellite of its own and a very public failure behind it — the Navy's Vanguard had toppled and exploded on the pad that December. The job passed to Wernher von Braun's US Army rocket team in Huntsville and to the Jet Propulsion Laboratory in California, who had a booster and a satellite very nearly ready. On the night of 31 January 1958, a Juno I rocket lifted Explorer 1 from Cape Canaveral, and early on 1 February (UTC) it reached orbit — the first US satellite. Its single science instrument, a cosmic-ray detector built by James Van Allen, behaved strangely: at high altitude its count rate fell to zero. Van Allen realised the counter was not failing but being saturated — swamped by intense radiation. Explorer 1 had discovered the belts of charged particles trapped in Earth's magnetic field, now named for him: the first major scientific discovery of the Space Age. The little satellite fell silent in May 1958 and finally re-entered the atmosphere in 1970, but it had announced that the United States, too, could reach and study space.
Images
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