Explorer 3
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 Juno I rocket with Explorer 3 satellite | |
| Names | Explorer III 1958 Gamma |
|---|---|
| Mission type | Earth science |
| Operator | JPL / U.S. Army Ordnance |
| Harvard designation | 1958 Gamma |
| COSPAR ID | 1958-003A |
| SATCAT no. | 00006 |
| Mission duration | 93 days (achieved) 120 days (planned) |
| Spacecraft properties | |
| Spacecraft | Explorer III |
| Spacecraft type | Science Explorer |
| Bus | Explorer 1 |
| Manufacturer | Jet Propulsion Laboratory |
| Launch mass | 14.1 kg (31 lb) |
| Payload mass | 8.4 kg (19 lb) |
| Dimensions | 203 cm (80 in) length 15.2 cm (6.0 in) diameter |
| Power | 60 watts |
| Start of mission | |
| Launch date | 26 March 1958, 17:38:01 GMT |
| Rocket | Juno I (RS-24) |
| Launch site | Atlantic Missile Range, LC-5 |
| Contractor | Army Ballistic Missile Agency |
| Entered service | 26 March 1958 |
| End of mission | |
| Last contact | 28 June 1958[1] |
| Decay date | 28 June 1958[1] |
| Orbital parameters | |
| Reference system | Geocentric orbit[1] |
| Regime | Medium Earth orbit |
| Perigee altitude | 186 km (116 mi) |
| Apogee altitude | 2,799 km (1,739 mi) |
| Inclination | 33.38° |
| Period | 115.70 minutes |
| Instruments | |
| Cosmic Ray counter Micrometeorite detector | |
Explorer Program | |
Explorer 3 (Harvard designation 1958 Gamma) was an American artificial satellite launched into medium Earth orbit in 1958. It was the second successful launch in the Explorer program, and was nearly identical to the first U.S. satellite Explorer 1 in its design and mission.
Background
[edit]Explorer 3 was the third satellite in the Explorer small satellite series, which started with Explorer 1, America's first artificial satellite.[2]: 288 The Explorer program was a direct successor to the Army Ballistic Missile Agency (ABMA)'s Project Orbiter, initiated in November 1954 to use a slightly modified Redstone (a 200 miles (320 km) range surface-to-surface missile developed the prior year)[3] combined with upper stages employing 31 Loki solid-propellant rockets (later changed to higher powered Sergeants) to put a satellite into orbit.[2]: 17–18, 43
In 1955, the Eisenhower Administration commissioned the "Stewart Committee", under the chairmanship of Homer J. Stewart of Jet Propulsion Laboratory (JPL), to coordinate the development of an artificial satellite and launcher for the International Geophysical Year, which would start 1 July 1957. The Stewart Committee favored an Naval Research Laboratory (NRL) plan based on its Viking rocket (Project Vanguard) citing the Navy's impressive planned Minitrack communications technology and network as well as both the civilian nature and the greater growth potential of the Viking/Vanguard rocket.[2]: 43, 51–56 Nevertheless, ABMA hoped Redstone-Orbiter could still be used as a backup orbital system. Reentry tests that year conducted with the newly developed, Redstone-based Jupiter-C, further strengthened ABMA confidence in their vehicle as an orbital launcher.
Following the launch of the Soviet satellite Sputnik 1 on 4 October 1957, Project Orbiter was revived.[4] The failure of America's first attempted Vanguard launch on 9 December 1957, cleared the way for an "Explorer" (as the crash program was dubbed) to be the first American satellite.[2]: 74, 199–200, 212–213
Working closely together, ABMA and JPL completed the job of modifying the Jupiter-C to the Juno I and building Explorer I in 84 days.[4]
Launch
[edit]The satellite was launched from Cape Canaveral Missile Test Center of the Atlantic Missile Range (AMR), in Florida at 17:38:01 GMT on 26 March 1958 by the Juno I launch vehicle.[5] The Juno I had its origins in the United States Army's Project Orbiter in 1954. The project was canceled in 1955 when the decision was made to proceed with Project Vanguard.
Following the launch of the Soviet Sputnik 1 on 4 October 1957, Army Ballistic Missile Agency (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 Jet Propulsion Laboratory (JPL) completed the job of modifying the Jupiter-C to the Juno I and building the Explorer I in 84 days.
Spacecraft
[edit]
Explorer 3 was launched in conjunction with the International Geophysical Year (IGY) by the U.S. Army (Ordnance) into an eccentric orbit. The objective of this spacecraft was a continuation of experiments started with Explorer 1. The payload consisted of a cosmic ray counter (a Geiger-Müller tube) and a micrometeorite detector (a wire grid array and acoustic detector). The Explorer 3 spacecraft was spin-stabilized and had an on-board tape recorder to provide a complete radiation history for each orbit..[1]
Its total weight was 14.1 kg (31 lb), of which 8.4 kg (19 lb) was instrumentation. The instrument section at the front end of the satellite and the empty scaled-down fourth-stage rocket casing orbited as a single unit, to be spun around its long axis at 750 revolutions per minute. Data from these instruments would be transmitted to the ground by a 60 milliwatt transmitter operating on 108.03 MHz and a 10 milliwatt transmitter operating on 108.00 MHz.[1]
Transmitting antennas consisted of two fiberglass slot antennas in the body of the satellite itself. The four flexible whip antennas of Explorer 1 were removed from the design.[6] The external skin of the instrument section was painted in alternate strips of white and dark green to provide passive temperature control of the satellite. The proportions of the light and dark strips were determined by studies of shadow-sunlight intervals based on firing time, trajectory, orbit, and orbital inclination.[1]
Electrical power was provided by Mallory type RM Mercury batteries that made up approximately 40% of the payload weight. These provided power that operated the high power transmitter for 31 days and the low-power transmitter for 105 days. Because of the limited space available and the requirements for low weight, the Explorer 3 instrumentation was designed and built with simplicity and high reliability in mind.[1]
Launch and orbit
[edit]Explorer 3 was launched at 17:38:03 GMT on 26 March 1958 from Cape Canaveral Launch Complex 5[7] via the same type of modified Jupiter-C (Juno 1) as the prior two Explorers. A guidance system orbit placed the satellite into an orbit with a higher apogee and lower perigee than planned: 1,735 mi (2,792 km) and 125 mi (201 km), respectively. The ensuing orbital decay made for a comparatively short lifespan: initial estimates placed it at 4.6 months.[8] In fact, the satellite reentered the atmosphere on 28 June 1958, after just 93 days of operation;[1] by the week before reentry, Explorer 3's apogee had dropped to 375 mi (604 km) and the perigee to 99 mi (159 km).[9]
Mission results
[edit]Explorer 3 was completely successful.[1] The discovery of the Van Allen radiation belt by the Explorer satellites was considered to be one of the outstanding discoveries of the International Geophysical Year (IGY).[4]
On 7 May 1958, micrometeorites associated with the Eta Aquariids meteor shower ruptured two of Explorer 3's micrometeorite erosion gauges.[9]
Status
[edit]A replica of the spacecraft is currently located in the Smithsonian Institution's National Air and Space Museum, Milestones of Flight Gallery.
See also
[edit]
References
[edit]- ^ a b c d e f g h i "Trajectory: Explorer-3 1958-003A". NASA. 14 May 2020. Retrieved 15 February 2021.
This article incorporates text from this source, which is in the public domain.
- ^ a b c d Constance Green and Milton Lomask (1970). Vanguard — a History. Washington D.C.: National Aeronautics and Space Administration. pp. 17–18. ISBN 978-1-97353-209-5. OCLC 747307569. SP-4202. Archived from the original on 3 March 2016. Retrieved 21 February 2021.
- ^ "Installation History 1953 - 1955". U.S. Army Aviation and Missile Life Cycle Management Command. 2017. Archived from the original on 2 February 2023. Retrieved 1 February 2021.
- ^ a b c "Explorer Info". NASA History. NASA. Retrieved 20 October 2024.
- ^ "About the Mission". JPL. NASA. Retrieved 24 June 2017. This article incorporates text from this source, which is in the public domain.
- ^ Pilkington, W. C. (5 September 1958). "Vehicle Motions as Inferred from Radio-signal – Strength Records". NASA. Retrieved 18 October 2018. This article incorporates text from this source, which is in the public domain.
- ^ McDowell, Jonathan. "Launch Log". Jonathan's Space Report. Retrieved 20 October 2024.
- ^ "Explorer III Orbit". Aviation Week and Space Technology. McGraw Hill Publishing Company. 31 March 1958. p. 27. Retrieved 20 October 2024.
{{cite magazine}}: CS1 maint: url-status (link) - ^ a b "Army Evaluates Data From Explorer III". Aviation Week and Space Technology. McGraw Hill Publishing Company. 30 June 1958. p. 19. Retrieved 19 October 2024.
{{cite magazine}}: CS1 maint: url-status (link)
External links
[edit]- Big Picture: Army Satellites – Explorer 1, Explorer 2 and Explorer 3 on YouTube
- Data Sheet, Department of Astronautics, National Air and Space Museum, Smithsonian Institution.
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