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Explorer program

Explorer program

Overview
The Explorer program was the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

's first successful attempt to launch an artificial satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavor. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

. It began as a U.S. Army proposal to place a scientific satellite into orbit
Orbit
In physics, an orbit is the gravitationally curved path of one object around a point or another body, for example the gravitational orbit of a planet around a star....

 during the International Geophysical Year
International Geophysical Year
The International Geophysical Year was an international scientific effort that lasted from July 1, 1957, to December 31, 1958.The IGY encompassed eleven Earth sciences: aurora and airglow, cosmic rays, geomagnetism, gravity, ionospheric physics, longitude and latitude determinations , meteorology,...

. That proposal was rejected in favor of the U.S. Navy's Project Vanguard
Project Vanguard
Project Vanguard was a program managed by the United States Naval Research Laboratory , which intended to launch the first artificial satellite into Earth orbit using a Vanguard rocket as the launch vehicle....

. It was revived as a crash program  to catch up with the Soviet Union
Soviet Union
The Union of Soviet Socialist Republics was a constitutionally socialist state that existed in Eurasia from 1922 to 1991. The name is a translation of the , tr. Soyuz Sovetskikh Sotsialisticheskikh Respublik, abbreviated СССР, SSSR. The common short name is Soviet Union, from , Sovetskiy Soyuz...

 after that nation's launch of Sputnik 1
Sputnik 1
Sputnik 1 was the first Earth-orbiting artificial satellite. It was launched into an elliptical low earth orbit by the Soviet Union on 4 October 1957, and was the first in a series of satellites collectively known as the Sputnik program...

 on October 4, 1957. (See: Sputnik crisis
Sputnik crisis
The Sputnik crisis was a turning point of the Cold War that began on October 4, 1957 when the Soviet Union launched the Sputnik 1 satellite. The United States had believed itself to be the world leader in space technology and thus the leader in missile development. The surprise of the Sputnik...

) Explorer 1 was launched January 31, 1958.
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Encyclopedia
The Explorer program was the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

's first successful attempt to launch an artificial satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavor. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

. It began as a U.S. Army proposal to place a scientific satellite into orbit
Orbit
In physics, an orbit is the gravitationally curved path of one object around a point or another body, for example the gravitational orbit of a planet around a star....

 during the International Geophysical Year
International Geophysical Year
The International Geophysical Year was an international scientific effort that lasted from July 1, 1957, to December 31, 1958.The IGY encompassed eleven Earth sciences: aurora and airglow, cosmic rays, geomagnetism, gravity, ionospheric physics, longitude and latitude determinations , meteorology,...

. That proposal was rejected in favor of the U.S. Navy's Project Vanguard
Project Vanguard
Project Vanguard was a program managed by the United States Naval Research Laboratory , which intended to launch the first artificial satellite into Earth orbit using a Vanguard rocket as the launch vehicle....

. It was revived as a crash program  to catch up with the Soviet Union
Soviet Union
The Union of Soviet Socialist Republics was a constitutionally socialist state that existed in Eurasia from 1922 to 1991. The name is a translation of the , tr. Soyuz Sovetskikh Sotsialisticheskikh Respublik, abbreviated СССР, SSSR. The common short name is Soviet Union, from , Sovetskiy Soyuz...

 after that nation's launch of Sputnik 1
Sputnik 1
Sputnik 1 was the first Earth-orbiting artificial satellite. It was launched into an elliptical low earth orbit by the Soviet Union on 4 October 1957, and was the first in a series of satellites collectively known as the Sputnik program...

 on October 4, 1957. (See: Sputnik crisis
Sputnik crisis
The Sputnik crisis was a turning point of the Cold War that began on October 4, 1957 when the Soviet Union launched the Sputnik 1 satellite. The United States had believed itself to be the world leader in space technology and thus the leader in missile development. The surprise of the Sputnik...

) Explorer 1 was launched January 31, 1958. Besides being the first U.S. satellite, it is known for discovering the Van Allen radiation belt
Van Allen radiation belt
The Van Allen radiation belt is a torus of energetic charged particles around Earth, which is held in place by Earth's magnetic field. This field is not uniformly distributed around the Earth. On the sunward side, it is compressed because of the solar wind, while on the other side it is elongated...

.

Explorer at NASA


The Explorer program was taken over by NASA
NASA
The National Aeronautics and Space Administration is an agency of the United States government, responsible for the nation's public space program. NASA was established by the National Aeronautics and Space Act on July 29, 1958, replacing its predecessor, the National Advisory Committee for...

, which continued to use the name for robotic spacecraft missions.

Over the years, NASA
NASA
The National Aeronautics and Space Administration is an agency of the United States government, responsible for the nation's public space program. NASA was established by the National Aeronautics and Space Act on July 29, 1958, replacing its predecessor, the National Advisory Committee for...

 has launched a series of "Explorer" spacecraft
Spacecraft
A spacecraft is a craft or machine designed for spaceflight. On a sub-orbital spaceflight, a spacecraft enters space then returns to the Earth. For an orbital spaceflight, a spacecraft enters a closed orbit around the planetary body. Spacecraft used for human spaceflight carry people on board as...

 carrying a wide variety of scientific investigations. The list below identifies the 79 successful missions as of December 2004. As of this writing, Explorers 50 (IMP-8), 68-71, 73-74, 79-83 (SAMPEX, RXTE, FAST, ACE, TRACE, SWAS, WMAP, RHESSI, CHIPSat, GALEX and SWIFT) are still operating.

NASA's Explorer spacecraft series not only is the longest running series of spacecraft, it has produced highly-durable, well-engineered spacecraft as well. Of the 79 successful Explorer missions depicted, five of them had missions that lasted 10 or more years, the longest of which (IMP-8) has been operational for over 26 years now and still produces valuable information about the solar wind. NASA's IUE
International Ultraviolet Explorer
The International Ultraviolet Explorer was an astronomical observatory satellite primarily designed to take ultraviolet spectra...

 spacecraft operated for 19 years and produced copious amounts of data for the astronomical community. The ISEE 3/ICE spacecraft operated for 14 years. As of March 2000, of the ten operational Explorer missions, SNOE and TRACE have operated for about two years, ACE two and a half years, FAST for about three and a half, RXTE for over four, EUVE and SAMPEX for nearly eight, and IMP 8 for more than 26. SWAS has been operational for slightly more than one year, having been launched in early December 1998.

Energetic Particle Explorers
Explorers 12, 14, 15 and 26 were the S 3 series of spacecraft, known as Energetic Particle Explorers. They were spin-stabilized
Spin-stabilized satellite
A spin-stabilized satellite is a satellite which has the motion of one axis held fixed by spinning the satellite around that axis, using the gyroscopic effect.The attitude of a satellite or any rigid body is its orientation in space...

, solar-cell-powered spacecraft instrumented to measure cosmic ray
Cosmic ray
Cosmic rays are energetic particles originating from outer space that impinge on Earth's atmosphere. Almost 90% of all the incoming cosmic ray particles are protons, almost 10% are helium nuclei , and slightly under 1% are heavier elements and electrons...

 particles, trapped particles, solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the sun. It consists mostly of electrons and protons with energies of about 1 keV. The stream of particles varies in temperature and speed with the passage of time...

 proton
Proton
The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H+...

s, and magnetospheric
Magnetosphere
A magnetosphere is a highly magnetized region around and possessed by an astronomical object. Earth is surrounded by a magnetosphere, as are the magnetized planets Mercury, Jupiter, Saturn, Uranus, and Neptune. Jupiter's moon Ganymede is magnetized, but too weak to trap solar wind plasma. Mars has...

 and interplanetary magnetic field
Magnetic field
Magnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges...

s.

Mission History


Explorer Missions
Explorer Name Launch Date Mission End of Data Re-Entry
1 Explorer 1 January 31, 1958 Energetic particle studies, discovered the Van Allen radiation belt
Van Allen radiation belt
The Van Allen radiation belt is a torus of energetic charged particles around Earth, which is held in place by Earth's magnetic field. This field is not uniformly distributed around the Earth. On the sunward side, it is compressed because of the solar wind, while on the other side it is elongated...

May 23, 1958 March 31, 1970
2 Explorer 2
Explorer 2
Explorer 2 was to be a repeat of the Explorer 1 mission. However, due to a failure in the rocket during launch, the spacecraft did not reach orbit....

March 5, 1958 Failed to achieve orbit - -
3 Explorer 3 (Gamma 1)
Explorer 3
Explorer 3 was an artificial satellite of the Earth, nearly identical to the first United States artificial satellite Explorer 1 in its design and mission...

March 26, 1958 Energetic particle studies June 27, 1958 June 27, 1958
4 Explorer 4
Explorer 4
Explorer 4 was a US satellite launched on July 26, 1958. It was instrumented by Dr. James van Allen's group. The Department of Defense's Advanced Research Projects Agency had initially planned two satellites for the purposes of studying the Van Allen radiation belts and the effects of nuclear...

July 26, 1958 Energetic particle studies October 5, 1958 October 23, 1959
5 Explorer 5
Explorer 5
Explorer 5 was a United States satellite with a weight of 17.24 kg.It fired off from a Jupiter-C rocket on August 24, 1958, but failed as the rocket's booster collided with its second stage after separation, causing the upper stage firing angle to be off....

August 24, 1958 Failed to achieve orbit - -
7x Explorer 7x (S 1) July 16, 1959 Measure earth's radiation balance, destroyed by range safety - -
6 S-2 (Able 3)
Explorer 6
Explorer 6 was a United States satellite launched on August 7, 1959. It was a small, spheroidal satellite designed to study trapped radiation of various energies, galactic cosmic rays, geomagnetism, radio propagation in the upper atmosphere, and the flux of micrometeorites...

August 7, 1959 Magnetosphere research October 6, 1959 July 1, 1961
7 S 1A
Explorer 7
Explorer 7 was launched October 13, 1959. It was designed to measure solar x-ray and Lyman-alpha flux, trapped energetic particles, and heavy primary cosmic rays....

October 13, 1959 Energetic particle studies August 24, 1961 In orbit
-- S 46 March 23, 1960 Analyze electron and proton radiation energies, failed to achieve orbit - -
8 S 30
Explorer 8
Explorer 8 is a U.S. research satellite launched on November 3, 1960. It confirmed the existence of a helium layer in the upper atmosphere....

November 3, 1960 Measured atmospheric composition of the ionosphere December 27, 1960 In orbit
-- S 56 December 4, 1960 Atmospheric density measurements, failed to achieve orbit - -
9 S 56A February 16, 1961 Atmospheric density measurements April 9, 1964 April 9, 1964
-- S 45 February 24, 1961 Ionosphere research, failed to achieve orbit - -
10 P 14 March 25, 1961 Investigated field magnetic field between the earth March 27, 1961 June 1, 1968
11 S 15 April 27, 1961 Gamma ray astronomy November 17, 1961 In orbit
-- S 45A May 25, 1961 Ionosphere research, failed to achieve orbit - -
-- S 55 (Meteoroid Satellite-A, Micrometeorite Explorer) June 30, 1961 Micrometeoroid research, failed to achieve orbit - -
12 EPE-A (S 3, Energetic Particle Explorer-A) August 16, 1961 Energetic particle research December 6, 1961 September 1, 1963
13 S 55A August 25, 1961 Micrometeoroid research August 28, 1961 August 28, 1961
14 EPE-B (Energetic Particle Explorer-B) October 2, 1962 Energetic particle research August 11, 1963 July 1, 1966
15 EPE-C (Energetic Particle Explorer-C) October 27, 1962 Energetic particle research January 30, 1963 January 15, 1978
16 S 55B December 16, 1962 Micrometeoroid research July 22, 1963 November 24, 1966?
17 AE-A (Atmosphere Explorer-A)
Explorer 17
Explorer 17 was a United States satellite, launched at Cape Canaveral from LC-17B on a Delta-B booster, on April 3, 1963, to study the Earth's upper atmosphere. It was the first satellite of five Atmosphere Explorers.- Technical specifications :Explorer 17 was a spin-stabilized sphere 0.95 m in...

April 3, 1963 Atmospheric research July 10, 1963 November 24, 1966?
18 IMP-A (IMP 1, Interplanetary Monitoring Platform-A) November 27, 1963 Magnetospheric research May 10, 1965 December 30, 1965
19 AD-A (Atmospheric Density-A) December 19, 1963 Atmospheric density measurements May 10, 1981 May 10, 1981
20 IE-A (S 48, TOPSI, Ionosphere Explorer-A) August 25, 1964 Ionosphere research December 29, 1965 In orbit
21 IMP-B (IMP 2, Interplanetary Monitoring Platform-B) October 4, 1964 Magnetospheric research October 13, 1965 January 30, 1966
22 BE-B (S 66, Beacon Explorer-B) October 10, 1964 Ionospheric and geodetic research February 1970 In orbit
23 S 55C (Explorer 23) November 6, 1964 Micrometeoric research November 7, 1965 June 29, 1983
24 AD-B (Atmospheric Density-B) November 21, 1964 Atmospheric density measurements October 18, 1968 October 18, 1968
25 Injun 4
Injun (satellite)
The Injun program was a series of six satellites designed and built by researchers at the University of Iowa. They were intended to observe various radiation and magnetic phenomena in the ionosphere and beyond....

 (IE-B, Ionosphere Explorer-B)
November 21, 1964 Ionospheric research December 1966 In orbit
26 EPE-D (Energetic Particle Explorer-D) December 21, 1964 High energy particle observations December 27, 1967 In orbit
27 BE-C (Beacon Explorer-C) April 29, 1965 Magnetospheric research July 20, 1973 In orbit
28 IMP-C (IMP 3, Interplanetary Monitoring Platform-C) May 29, 1965 Magnetospheric research May 12, 1967 July 4, 1968
29 GEOS 1 (GEOS-A) November 6, 1965 Geodetic earth monitoring June 23, 1978 In orbit
30 SOLRAD 8 (SE-A) November 19, 1965 Solar radiation monitoring
(Cover for covert ELINT mission)
November 5, 1967 In orbit
31 DME A November 29, 1965 Ionospheric research October 1 1969 In orbit
32 AE-B (Atmosphere Explorer-B)
Explorer 32
Explorer 32—also known as Atmosphere Explorer-B —was a satellite launched by the United States to study the Earth's upper atmosphere. It was launched from Cape Canaveral on a Delta-C1 rocket, on 25 May 1966...

May 25, 1966 Atmospheric research March 1967 February 22, 1985
33 IMP-D (AIMP 1, Anchored IMP 1, Interplanetary Monitoring Platform-D)
Explorer 33
Explorer 33 was a spacecraft launched by NASA on July 1, 1966 on a mission of scientific exploration. Originally intended for a lunar orbit, mission controllers worried that the spacecraft's trajectory was too fast to guarantee lunar capture...

July 1, 1966 Magnetospheric research September 21, 1971 In orbit
34 IMP-F (IMP 4, Interplanetary Monitoring Platform-F) May 24, 1967 Magnetospheric research May 3, 1969 May 3, 1969
35 IMP-E (AIMP-E, AIMP 2, Anchored IMP 2, Interplanetary Monitoring Platform-E)
Explorer 35
Explorer 35 was a spin-stabilized spacecraft instrumented for interplanetary studies, at lunar distances, of the interplanetary plasma, magnetic field, energetic particles, and solar X rays. It was launched into an elliptical lunar orbit. The spin axis direction was nearly perpendicular to the...

July 19, 1967 Magnetospheric research June 24, 1973 ?
36 GEOS 2 (GEOS-B) January 11, 1968 Geodetic earth monitoring July 1, 1982 In orbit
37 Solrad 9 (SE B) March 5, 1968 Solar radiation monitoring
(Cover for covert ELINT mission)
April 30, 1974 November 16, 1990
38 RAE-A (RAE 1, Radio Astronomy Explorer-A) July 4, 1968 Radio astronomy ? In orbit
39 AD-C (Atmospheric Density-C) August 8, 1968 Atmospheric density measurements June 23, 1971 June 22, 1981?
40 Injun 5
Injun (satellite)
The Injun program was a series of six satellites designed and built by researchers at the University of Iowa. They were intended to observe various radiation and magnetic phenomena in the ionosphere and beyond....

 (Injun C, IE-C, Ionosphere Explorer-C)
August 8, 1968 Magnetospheric Research June 1971 In orbit
41 IMP-G (IMP 5, Interplanetary Monitoring Platform-G) June 21, 1969 Magnetospheric research December 23, 1972 December 23, 1972
42 SAS-A (Small Astronomy Satellite-A, SAS 1)
Uhuru (satellite)
Uhuru was the first satellite launched specifically for the purpose of X-ray astronomy. It was also known as the X-ray Explorer Satellite, SAS-1 , or Explorer 42.The observatory was launched on 12 December 1970 into an initial orbit of about 560 km apogee, 520 km perigee, 3 degrees...

December 12, 1970 X-Ray Astronomy January 4, 1975 April 5, 1979
43 IMP-H (IMP 6, Interplanetary Monitoring Platform-H) March 13, 1971 Magnetospheric research October 2, 1974 October 2, 1974
44 Solrad 10 (SE-C, SOLRAD-C) July 8, 1971 Solar radiation monitoring
(Cover for covert ELINT mission)
June 30, 1973 December 15, 1979
45 SSS-A (S-Cubed A) November 15, 1971 Magnetospheric research September 30, 1974 January 10, 1992
46 Meteoroid Technology Satellite (MTS, METEC) August 13, 1972 Micrometeoroids research November 4, 1974 November 2, 1979
47 IMP-I (IMP 7, Interplanetary Monitoring Platform-I) September 23, 1972 Magnetospheric research October 31, 1978 In orbit
48 SAS-B (Small Astronomy Satellite-B, SAS 2)
Second Small Astronomy Satellite
The Second Small Astronomy Satellite, also known also as SAS-2, SAS B or Explorer 48, was a NASA gamma ray telescope. It was launched on 15 November 1972 into low Earth orbit with a periapsis of 443 km and an apoapsis of 632 km)...

November 15, 1972 X-Ray Astronomy June 8, 1973 August 20, 1980
49 RAE-B (RAE 2, Radio Astronomy Explorer-B)
Explorer 49
Explorer 49 was a 328 kilogram satellite launched on June 10 1973 for longwave radio astronomy research. It had four 230-meter long X-shaped antenna elements, which made it one of the largest spacecraft ever built....

June 10, 1973 Radio astronomy April 26, 1977 In Lunar orbit
50 IMP J (IMP 8, Interplanetary Monitoring Platform-J) October 26, 1973 Magnetospheric research Operational (34 years) In orbit
51 AE-C (Atmosphere Explorer-C) December 16, 1973 Atmospheric research ? December 12, 1978
52 Hawkeye 1, Injun 6 (IE-D, Ionosphere Explorer-D)
Explorer 52
Explorer 52 was a US satellite launched on June 3, 1974 from Vandenberg Air Force Base on a Scout booster.This satellite was also known as:* Hawkeye 1* IE D* Injun 6* Injun F* Neutral Point Explorer* 07325...

June 3, 1974 Magnetospheric research April 28, 1978 April 28, 1978
53 SAS-C (Small Astronomy Satellite-C, SAS 3)
Third Small Astronomy Satellite
The Third Small Astronomy Satellite was a NASA X-ray astronomy space telescope. It functioned from May 7, 1975 to April 1979. It covered the X-ray range with four experiments on board. The satellite, built by the Johns Hopkins University Applied Physics Laboratory , was proposed and operated by...

May 7, 1975 X-Ray Astronomy April 7, 1979 April 9, 1979
54 AE-D (Atmosphere Explorer-D) October 6, 1975 Atmospheric research January 29, 1976 March 12, 1976
55 AE-E (Atmosphere Explorer-E) November 20, 1975 Atmospheric research September 25, 1980 June 10, 1981
56 ISEE 1 & 2 (International Sun-Earth Explorer-A & B) October 22, 1977 Magnetospheric research September 26, 1987 September 26, 1987
57 IUE
International Ultraviolet Explorer
The International Ultraviolet Explorer was an astronomical observatory satellite primarily designed to take ultraviolet spectra...

January 26, 1978 Ultraviolet astronomy September 30, 1996 In orbit
58 HCMM (AEM-A, Applications Explorer Mission-A, Heat Capacity Mapping Mission) April 26, 1978 Thermal mapping of the earth September 30, 1980 ?
59 ISEE 3 (International Sun-Earth Explorer-C, ICE
International Cometary Explorer
The International Cometary Explorer spacecraft was originally known as International Sun/Earth Explorer 3 satellite, launched August 12, 1978. It was part of the ISEE international cooperative program between NASA and ESA to study the interaction between the Earth's magnetic field and the solar...

)
August 12, 1978 Magnetospheric research May 5, 1997 In heliocentric orbit
Heliocentric orbit
A heliocentric orbit is an orbit around the Sun. In our Solar System, all planets, comets, and asteroids are in such orbits, as are many artificial probes and pieces of debris. Ganymede, by contrast, is not in a heliocentric orbit as it orbits Jupiter...

60 SAGE (AEM-B, Applications Explorer Mission-B, Stratospheric Aerosol and Gas Experiment) February 18, 1979 Stratospheric aerosol and ozone data January 7, 1982 April 11, 1989
61 MAGSAT
Magsat
Magsat spacecraft was launched in the fall of 1979 and ended in the spring of 1980. The mission was to map the Earth's magnetic field, the satellite has two magnetometers...

 (AEM-C, Applications Explorer Mission-C, Magnetic Field Satellite)
October 30, 1979 Mapped the near surface magnetic field of the Earth May 6, 1980 June 11, 1980
62 DE 1
Dynamics Explorer
Dynamics Explorer was a NASA mission, launched on August 3, 1981 and terminated on February 28, 1991. It consisted of two unmanned satellites, DE-1 and DE-2, whose purpose was to investigate the interractions between plasmas in the magnetosphere and those in the ionosphere...

 (DE-A, Dynamics Explorer-A)
August 3, 1981 Magnetospheric research February 28, 1991 In orbit
63 DE 2
Dynamics Explorer
Dynamics Explorer was a NASA mission, launched on August 3, 1981 and terminated on February 28, 1991. It consisted of two unmanned satellites, DE-1 and DE-2, whose purpose was to investigate the interractions between plasmas in the magnetosphere and those in the ionosphere...

 (DE-B, Dynamics Explorer-B)
August 3, 1981 Magnetospheric research 1983 February 19, 1983
64 SME
Solar Mesosphere Explorer
The Solar Mesosphere Explorer was an United States unmanned spacecraft to investigate the processes that create and destroy ozone in Earth's upper atmosphere. The mesosphere is a layer of the atmosphere extending from the top of the stratosphere to an altitude of about 80 kilometers...

October 6, 1981 Atmospheric research April 4, 1989 March 5, 1991
65 AMTPE/CCE (Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer) August 16, 1984 Magnetospheric research July 12, 1989 ?
66 COBE
COBE
The Cosmic Background Explorer , also referred to as Explorer 66, was a satellite dedicated to cosmology. Its goals were to investigate the cosmic microwave background radiation of the universe and provide measurements that would help shape our understanding of the cosmos.This work provided...

November 18, 1989 Microwave astronomy December 23, 1993 In orbit
67 EUVE
Extreme Ultraviolet Explorer
The Extreme Ultraviolet Explorer was a space telescope for ultraviolet astronomy, launched on June 7, 1992. With instruments for UV radiation between wavelengths of 7 and 76 nm, the EUVE was the first satellite mission especially for the short-wave ultraviolet range...

June 7, 1992 Ultraviolet astronomy January 30, 2002 In orbit
68 SAMPEX
Solar Anomalous and Magnetospheric Particle Explorer
The Solar Anomalous and Magnetospheric Particle Explorer satellite was launched in July 1992 into a low earth orbit at an altitude of 520 by 670 km and 82 degrees inclination. The satellite, which has far exceeded its expected three-year lifetime, has primarily operated in a three-axis...

July 3, 1992 Magnetospheric research operational? In orbit
69 RXTE
Rossi X-ray Timing Explorer
The Rossi X-ray Timing Explorer is a satellite that observes the time structure of astronomical X-ray sources. The RXTE has three instruments --the Proportional Counter Array, the High-Energy X-ray Timing Experiment , and one instrument called the All Sky Monitor. The RXTE observes X-rays from...

December 30, 1995 X-ray astronomy Operational (11 years) In orbit
70 FAST
Fast Auroral Snapshot Explorer
The Fast Auroral Snapshot Explorer was launched from Vandenberg Air Force Base on board a Pegasus XL rocket on August 21, 1996. One in the series of NASA's Small Explorer spacecraft, FAST was designed to observe and measure the plasma physics of the auroral phenomena which occur around both poles...

August 21, 1996 Auroral phenomena operational? In orbit
71 ACE
Advanced Composition Explorer
Advanced Composition Explorer is a space exploration mission being conducted as part of the Explorer program to study matter in situ, comprising energetic particles from the solar wind, the interplanetary medium, and other sources. Real-time data from ACE is used by the Space Weather Prediction...

August 25, 1997 Solar/interplanetary/interstellar particle research Operational (11 years) In L1 orbit
Lissajous orbit
In orbital mechanics, a Lissajous orbit is a quasi-periodic orbital trajectory that an object can follow around a Lagrangian point of a three-body system without requiring any propulsion. Lyapunov orbits around a libration point are curved paths that lie entirely in the plane of the two primary...

72 SNOE February 26, 1998 Atmospheric research December 13, 2003 December 13, 2003
73 TRACE
TRACE
TRACE is a NASA space telescope designed to investigate the connections between fine-scale magnetic fields and the associated plasma structures on the Sun by providing high resolution images and observation of the solar photosphere and transition region to the corona...

April 2, 1998 Solar observatory Operational (10 years) In orbit
74 SWAS
Submillimeter Wave Astronomy Satellite
The Submillimeter Wave Astronomy Satellite was an astronomical observatory launched on December 5, 1998 as part of the Small Explorer program within NASA...

December 6, 1998 Submillimeter astronomy July 2004 hibernation
August 2005 after Deep Impact sub-mission
In orbit
75 WIRE
Wide Field Infrared Explorer
The Wide Field Infrared Explorer is a satellite launched on 5 March 1999 on the Pegasus XL rocket into a polar orbit between 409 km and 426 km above the Earth's surface. WIRE was intended to be a four-month infrared survey of the entire sky, specifically focusing on starburst galaxies and luminous...

March 5 1999 InfraRed astronomy, primary mission failed due to loss of coolant operational? In orbit
76 TERRIERS May 18 1999 Atmospheric research, satellite failed shortly after achieving orbit May 18 1999 In orbit
77 FUSE
Far Ultraviolet Spectroscopic Explorer
The Far Ultraviolet Spectroscopic Explorer is a space-based telescope operated by the Johns Hopkins University Applied Physics Laboratory. FUSE was launched on a Delta II rocket on June 24, 1999, as a part of NASA's Origins program...

June 23 1999 Ultraviolet astronomy October 18, 2007 In orbit
78 IMAGE
IMAGE
IMAGE , or Explorer 78, was a NASA MIDEX mission that studied the global response of the Earth's magnetosphere to changes in the solar wind...

March 25, 2000 Magnetospheric research December 18, 2005 In orbit
79 HETE-2
High Energy Transient Explorer
The High Energy Transient Explorer was an American astronomical satellite with international participation . The prime objective of HETE was to carry out the first multiwavelength study of gamma-ray bursts with UV, X-ray, and gamma-ray instruments mounted on a single, compact spacecraft...

October 9, 2000 UV, X-Ray, and gamma ray astronomy Operational (7 years) In orbit
80 WMAP June 30, 2001 Microwave astronomy Operational (6 years) In L2 orbit
Lissajous orbit
In orbital mechanics, a Lissajous orbit is a quasi-periodic orbital trajectory that an object can follow around a Lagrangian point of a three-body system without requiring any propulsion. Lyapunov orbits around a libration point are curved paths that lie entirely in the plane of the two primary...

81 RHESSI February 5, 2002 X-ray and gamma ray solar flare imaging Operational (6 years) In orbit
82 CHIPSat
CHIPSat
CHIPSat is a microsatellite. It was launched aboard a Delta II alongside the larger ICESat. CHIPSat is the first of NASA's University-Class Explorers mission. The primary science objective was to study the million-degree gas in the interstellar medium...

January 13, 2003 Ultraviolet spectroscopy and astronomy April 11, 2008 In orbit
83 GALEX
GALEX
The Galaxy Evolution Explorer is an orbiting ultraviolet space telescope that was launched on April 28, 2003. A Pegasus rocket placed GALEX into a nearly circular orbit at an altitude of 697 km and an inclination to the Earth's equator of 29 degrees.The first observation was dedicated to the...

April 28, 2003 Ultraviolet astronomy Operational (5 years) In orbit
84 SWIFT
Swift Gamma-Ray Burst Mission
The Swift Gamma-Ray Burst Mission consists of a robotic spacecraft called Swift, which was launched into orbit on 20 November 2004, 17:16:00 UTC on the Delta II 7320-10C series expendable launch vehicle...

November 20, 2004 Gamma ray astronomy Operational (3 years) In orbit
85 THEMIS
THEMIS (satellite)
The THEMIS mission uses a constellation of five NASA satellites to study energy releases from Earth's magnetosphere known as substorms, magnetic phenomena that intensify auroras near Earth's poles...

February 17, 2007 Magnetospheric research Operational In orbit
86 THEMIS
THEMIS (satellite)
The THEMIS mission uses a constellation of five NASA satellites to study energy releases from Earth's magnetosphere known as substorms, magnetic phenomena that intensify auroras near Earth's poles...

February 17, 2007 Magnetospheric research Operational In orbit
87 THEMIS
THEMIS (satellite)
The THEMIS mission uses a constellation of five NASA satellites to study energy releases from Earth's magnetosphere known as substorms, magnetic phenomena that intensify auroras near Earth's poles...

February 17, 2007 Magnetospheric research Operational In orbit
88 THEMIS
THEMIS (satellite)
The THEMIS mission uses a constellation of five NASA satellites to study energy releases from Earth's magnetosphere known as substorms, magnetic phenomena that intensify auroras near Earth's poles...

February 17, 2007 Magnetospheric research Operational In orbit
89 THEMIS
THEMIS (satellite)
The THEMIS mission uses a constellation of five NASA satellites to study energy releases from Earth's magnetosphere known as substorms, magnetic phenomena that intensify auroras near Earth's poles...

February 17, 2007 Magnetospheric research Operational In orbit
90 AIM
Aeronomy of Ice in the Mesosphere
Aeronomy of Ice in the Mesosphere is a NASA-funded satellite being used to conduct a 26-month study of noctilucent clouds . On April 25, 2007 AIM was boosted into a 600 km high polar orbit by a Pegasus-XL rocket, which was air-launched from a Lockheed L-1011 aircraft.The noctilucent clouds AIM is...

April 25, 2007 Noctilucent cloud observation Operational In orbit


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