Explorer I
Explorer 1 in its orbital configuration, with the launch vehicle's fourth stage attached
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| Mission type | Earth science |
|---|---|
| Operator | Army Ballistic Missile Agency |
| Harvard designation | 1958 Alpha 1 |
| COSPAR ID | 1958-001A |
| SATCAT no. | 00004 |
| Mission duration | 111 days |
| Spacecraft properties | |
| Manufacturer | Jet Propulsion Laboratory |
| Launch mass | 13.97 kilograms (30.8 lb) |
| Dimensions | 80.75 inches (205.1 cm) length 6.00 inches (15.2 cm) diameter |
| Power | 60 watts |
| Start of mission | |
| Launch date | February 1, 1958, 03:48 UTC |
| Rocket | Juno I RS-29 |
| Launch site | Cape Canaveral LC-26A |
| End of mission | |
| Last contact | May 23, 1958 |
| Decay date | March 31, 1970 |
| Orbital parameters | |
| Reference system | Geocentric |
| Regime | MEO |
| Semi-major axis | 7,832.2 kilometers (4,866.7 mi) |
| Eccentricity | 0.140 |
| Perigee | 358 kilometers (222 mi) |
| Apogee | 2,550 kilometers (1,580 mi) |
| Inclination | 33.24° |
| Period | 114.8 minutes |
| RAAN | 334.6171 degrees |
| Argument of perigee | 311.5310 degrees |
| Mean anomaly | 48.3249 degrees |
| Mean motion | 16.275 |
| Epoch | 31 March 1970, 00:50:24 UTC |
| Revolution no. | 58402 |
| Instruments | |
| Cosmic-Ray Detector Micrometeorite Detector Satellite Drag Atmospheric Density |
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Explorer 1 was the first satellite of the United States, launched as part of its participation in the International Geophysical Year. The mission followed the first two satellites the previous year; the Soviet Union's Sputnik 1 and 2, beginning the Cold War Space Race between the two nations.
Explorer 1 was launched on January 31, 1958 at 22:48 Eastern Time (equal to February 1, 03:48 UTC) atop the first Juno booster from LC-26 at the Cape Canaveral Missile Annex, Florida. It was the first spacecraft to detect the Van Allen radiation belt, returning data until its batteries were exhausted after nearly four months. It remained in orbit until 1970, and has been followed by more than 90 scientific spacecraft in the Explorer series.
Explorer 1 was given Satellite Catalog Number 4, and the Harvard designation 1958 Alpha 1, the forerunner to the modern International Designator.
The U.S. Earth satellite program began in 1954 as a joint U.S. Army and U.S. Navy proposal, called Project Orbiter, to put a scientific satellite into orbit during the International Geophysical Year. The proposal, using a military Redstone missile, was rejected in 1955 by the Eisenhower administration in favor of the Navy's Project Vanguard, using a booster advertised as more civilian in nature. Following the launch of the Soviet satellite Sputnik 1 on October 4, 1957, the initial Project Orbiter program was revived as the Explorer program to catch up with the Soviet Union.
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