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| Organization: | Army Ballistic Missile Agency |
| Major Contractors: | Jet Propulsion Laboratory |
| Mission Type: | Earth Science |
| Satellite of: | Earth |
| Launch: | March 26, 1958 at 17:31:00 UTC |
| Launch Vehicle: | Jupiter-C |
| Decay: | June 27, 1958 |
| Mission Duration: | 93 days |
| Mass: | 14.1 kg |
| NSSDC ID: | 1958-003A |
| Webpage: | NASA NSSDC Master Catalog |
| Orbital elements | |
|---|---|
| Semimajor Axis: | 7,870.7 km |
| Eccentricity: | .165894 |
| Inclination: | 33.38° |
| Orbital Period: | 115.7 minutes |
| Apogee: | 2,799 km |
| Perigee: | 186 km |
| Orbits: | ~1,160 |
| Instruments | |
| Geiger-Mueller detector : | Detection of cosmic rays |
| Wire grid array : | Micrometeorite detection |
| Acoustic detector : | Micrometeorite detection |
Explorer-III was nearly identical to Explorer I in design and mission.
The satellite was launched from Cape CanaveralCape Canaveral is a strip of land in Brevard County, Florida, near the center of the Atlantic coast. It is part of Merritt Island, in a region known as the Space Coast, and is the site of the Kennedy Space Center, and the Cape Canaveral Air Force Station. (now Kennedy Space Center) in FloridaFlorida is a southern state in the United States. It is known as the Sunshine State. Florida" is a Spanish adjective which means "flowery". It was discovered by Spanish explorers during the Easter season, which is called Pascua Florida in Spanish. Postal at 17:31:00 UTC on March 26, 1958, by the Jupiter-C vehicle.
The Jupiter-C has its origins in the United States Army's Project OrbiterProject Orbiter was a proposed spacecraft, an early competitor to Project Vanguard. It was jointly run by the United States Army and United States Navy. It was ultimately rejected by the Ad Hoc Committee on Special Capabilities, which selected proceeding in 1954. The project was canceled in 1955, however, when the decision was made to proceed with Project Vanguard.
Following the launch of the Soviet Sputnik I on October 4, 1957, ABMA was directed to proceed with the launching of a satellite using the Jupiter-C, which had already been flight-tested in nose-cone re-entry tests for the Jupiter IRBM ( intermediate-range ballistic missile). Working closely together, ABMA and JPL completed the job of modifying the Jupiter-C and building the Explorer-I in 84 days.