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.
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 missile [3] combined with solid-propellant rocket cluster upper stage to put a satellite into orbit. [2] : 17–18, 43
In 1955, the "Stewart Committee", under the chairmanship of Homer J. Stewart of Jet Propulsion Laboratory (JPL), chose an Naval Research Laboratory (NRL) satellite plan using a rocket based on its Viking rocket (Project Vanguard) for the International Geophysical Year, which would start 1 July 1957. [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] with two shots authorized as a back-up to Vanguard in early November. [2] : 238 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 1 and building Explorer 1 in 84 days. [4] An experiment developed for Vanguard by George Ludwig, [2] : 238 comprising an Anton 314 omnidirectional Geiger tube detector for measuring the flux of high energy charged protons and electrons, was adapted for Explorer 1. [5] Because of the high spin rate of the Explorer 1 rocket, the experiment's tape recorder had to be omitted, which meant that data could only be collected when the satellite was in sight and range of a ground station. [2] : 238
Explorer 1 took off 31 January 1958, becoming America's first satellite. Its Geiger tube worked properly, but acted contrary to expectations. As the satellite ascended in its orbit, the radiation count increased, then abruptly dropped to zero. When the satellite was descending, the tube abruptly began detecting charged particles again. As data could only be received about 15% of the time, it was yet impossible to determine the phenomenon Explorer had detected. [2] : 241–242
The objective of this spacecraft was a continuation of experiments started with Explorer 1. The payload consisted of a micrometeorite detector (a wire grid array and acoustic detector) and the same cosmic ray counter (a Geiger-Müller tube) experiment included on Explorer 1, but this time with an on-board tape recorder to provide a complete radiation history for each orbit, Ludwig having had time to accommodate for the spin-stabilization of the satellite.<Vanguard/>: 241 [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]
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]
Explorer 3 largely confirmed the findings of Explorer 1, with the same zero count returned above an altitude of around 1,000 km (620 mi) to 1,200 km (750 mi). Because of the consistent results, Van Allen hypothesized that the satellites' equipment might have been saturated by unexpectedly high radiation concentrations, trapped in a belt of charged particles by the Earth's magnetic field. Explorer 4, equipped with a lead-shielded counter, flew in July and confirmed the existence of the radiation fields subsequently known as the Van Allen Belts. [2] : 242–243
On 7 May 1958, micrometeorites associated with the Eta Aquariids meteor shower ruptured two of Explorer 3's micrometeorite erosion gauges. [9]
A replica of the spacecraft is currently located in the Smithsonian Institution's National Air and Space Museum, Milestones of Flight Gallery.
Explorer 1 was the first satellite launched by the United States in 1958 and was part of the U.S. participation in the International Geophysical Year (IGY). The mission followed the first two satellites, both launched by the Soviet Union during the previous year, Sputnik 1 and Sputnik 2. This began a Space Race during the Cold War between the two nations.
The Jupiter-C was an American research and development vehicle developed from the Jupiter-A. Jupiter-C was used for three uncrewed sub-orbital spaceflights in 1956 and 1957 to test re-entry nosecones that were later to be deployed on the more advanced PGM-19 Jupiter mobile missile. The recovered nosecone was displayed in the Oval Office as part of President Dwight D. Eisenhower's televised speech on November 7, 1957.
The Juno I was a four-stage American space launch vehicle, used to launch lightweight payloads into low Earth orbit. The launch vehicle was used between January 1958 to December 1959. The launch vehicle is a member of the Redstone launch vehicle family, and was derived from the Jupiter-C sounding rocket. It is commonly confused with the Juno II launch vehicle, which was derived from the PGM-19 Jupiter medium-range ballistic missile. In 1958, a Juno I launch vehicle was used to launch America's first satellite, Explorer 1.
Pioneer 3 was a spin-stabilized spacecraft launched at 05:45:12 GMT on 6 December 1958 by the U.S. Army Ballistic Missile Agency in conjunction with NASA, using a Juno II rocket. This spacecraft was intended as a lunar probe, but failed to go past the Moon and into a heliocentric orbit as planned. It did however reach an altitude of 102,360 km before falling back to Earth. The revised spacecraft objectives were to measure radiation in the outer Van Allen radiation belt using two Geiger-Müller tubes and to test the trigger mechanism for a lunar photographic experiment.
Vanguard 1 is an American satellite that was the fourth artificial Earth-orbiting satellite to be successfully launched, following Sputnik 1, Sputnik 2, and Explorer 1. It was launched 17 March 1958. Vanguard 1 was the first satellite to have solar electric power. Although communications with the satellite were lost in 1964, it remains the oldest human-made object still in orbit, together with the upper stage of its launch vehicle.
Pioneer 4 was an American spin-stabilized uncrewed spacecraft launched as part of the Pioneer program on a lunar flyby trajectory and into a heliocentric orbit making it the first probe of the United States to escape from the Earth's gravity. Launched on March 3, 1959, it carried a payload similar to Pioneer 3: a lunar radiation environment experiment using a Geiger–Müller tube detector and a lunar photography experiment. It passed within 58,983 km (36,650 mi) of the Moon's surface. However, Pioneer 4 did not come close enough to trigger its photoelectric sensor. The spacecraft was still in solar orbit as of 1969. It was the only successful lunar probe launched by the U.S. in 12 attempts between 1958 and 1963; only in 1964 would Ranger 7 surpass its success by accomplishing all of its mission objectives.
Pioneer P-30 was intended to be a lunar orbiter probe, but the mission failed shortly after launch on September 25, 1960. The objectives were to place a highly instrumented probe in lunar orbit, to investigate the environment between the Earth and Moon, and to develop technology for controlling and maneuvering spacecraft from Earth. It was equipped to estimate the Moon's mass and topography of the poles, record the distribution and velocity of micrometeorites, and study radiation, magnetic fields, and low frequency electromagnetic waves in space. A mid-course propulsion system and injection rocket would have been the first United States self-contained propulsion system capable of operation many months after launch at great distances from Earth and the first U.S. tests of maneuvering a satellite in space.
Venera 1, also known as Venera-1VA No.2 and occasionally in the West as Sputnik 8 was the first spacecraft to perform an interplanetary flight and the first to fly past Venus, as part of the Soviet Union's Venera programme. Launched in February 1961, it flew past Venus on 19 May of the same year; however, radio contact with the probe was lost before the flyby, resulting in it returning no data.
Marshall Space Flight Center, located in Redstone Arsenal, Alabama, is the U.S. government's civilian rocketry and spacecraft propulsion research center. As the largest NASA center, MSFC's first mission was developing the Saturn launch vehicles for the Apollo program. Marshall has been the lead center for the Space Shuttle main propulsion and external tank; payloads and related crew training; International Space Station (ISS) design and assembly; computers, networks, and information management; and the Space Launch System. Located on the Redstone Arsenal near Huntsville, MSFC is named in honor of General of the Army George C. Marshall.
Project Vanguard was a program managed by the United States Navy Naval Research Laboratory (NRL), which intended to launch the first artificial satellite into low Earth orbit using a Vanguard rocket as the launch vehicle from Cape Canaveral Missile Annex, Florida.
The Army Ballistic Missile Agency (ABMA) was formed to develop the U.S. Army's first large ballistic missile. The agency was established at Redstone Arsenal on 1 February 1956, and commanded by Major General John B. Medaris with Wernher von Braun as technical director.
Explorer 4 was an American satellite launched on 26 July 1958. It was instrumented by Dr. James van Allen's group. The Department of Defense's Advanced Research Projects Agency (ARPA) had initially planned two satellites for the purposes of studying the Van Allen radiation belts and the effects of nuclear explosions upon these belts, however Explorer 4 was the only such satellite launched as the other, Explorer 5, suffered launch failure.
The Saturn family of American rockets was developed by a team of former German rocket engineers and scientists led by Wernher von Braun to launch heavy payloads to Earth orbit and beyond. The Saturn family used liquid hydrogen as fuel in the upper stages. Originally proposed as a military satellite launcher, they were adopted as the launch vehicles for the Apollo Moon program. Three versions were built and flown: the medium-lift Saturn I, the heavy-lift Saturn IB, and the super heavy-lift Saturn V.
Vanguard 3 is a scientific satellite that was launched into Earth orbit by the Vanguard SLV-7 on 18 September 1959, the third successful Vanguard launch out of eleven attempts. Vanguard rocket: Vanguard Satellite Launch Vehicle-7 (SLV-7) was an unused Vanguard TV-4BU rocket, updated to the final production Satellite Launch Vehicle (SLV).
Explorer 2 was an American unmanned space mission within the Explorer program. Intended to be a repetition of the previous Explorer 1 mission, which placed a satellite into medium Earth orbit, the spacecraft was unable to reach orbit due to a failure in the launch vehicle during launch.
Explorer 6, or S-2, was a NASA satellite, launched on 7 August 1959, at 14:24:20 GMT. It was a small, spherical satellite designed to study trapped radiation of various energies, galactic cosmic rays, geomagnetism, radio propagation in the upper atmosphere, and the flux of micrometeorites. It also tested a scanning device designed for photographing the Earth's cloud cover. On 14 August 1959, Explorer 6 took the first photos of Earth from a satellite.
Explorer 7 was a NASA satellite launched on 13 October 1959, at 15:30:04 GMT, by a Juno II launch vehicle from Cape Canaveral Air Force Station (CCAFS) to an orbit of 573 × 1,073 km (356 × 667 mi) and inclination of 50.27°. It was designed to measure solar X-ray and Lyman-alpha flux, trapped energetic particles, and heavy primary cosmic rays. Secondary objectives included collecting data on micrometeoroid penetration, molecular sputtering and studying the Earth-atmosphere heat balance.
Explorer 5 was a United States satellite with a mass of 17.43 kg (38.4 lb). It was the last of the original series of Explorer satellites built, designed, and operated by the Jet Propulsion Laboratory.
The Redstone family of rockets consisted of a number of American ballistic missiles, sounding rockets and expendable launch vehicles operational during the 1950s and 1960s. The first member of the Redstone family was the PGM-11 Redstone missile, from which all subsequent variations of the Redstone were derived. The Juno 1 version of the Redstone launched Explorer 1, the first U.S. orbital satellite in 1958 and the Mercury-Redstone variation carried the first two U.S. astronauts into space in 1961. The rocket was named for the Redstone Arsenal in Huntsville, Alabama where it was developed.
Explorer S-46 was a NASA satellite with a mass of 41 kg (90 lb). It was the last of the original series of Explorer satellites built, designed, and operated by the Jet Propulsion Laboratory and Army Ballistic Missile Agency (ABMA).
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