Explorer program
Encyclopedia
The Explorer program is a United States space exploration program that provides flight opportunities for physics, heliophysics
Heliophysics
Heliophysics is a word coined by Dr. George Siscoe of Boston University and subsequently used by the NASA Science Mission Directorate to encompass the study of the system composed of the Sun's heliosphere and the objects that interact with it—most notably, but not limited to, planetary atmospheres...

, and astrophysics
Astrophysics
Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties of celestial objects, as well as their interactions and behavior...

 investigations from space. Over 90 space missions have been launched from 1958 to 2011, and it is still active. Starting with Explorer 6
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...

, it has been a NASA program, and they have worked with a variety of other institutions and business, including many international collaborations. Currently, the major subprograms are Small Explorer program
Small Explorer program
The Small Explorer program is an effort within NASA to fund space exploration missions that cost no more than $120 million.- Program history :...

 (SMEX) and Medium Explorer Program (MIDEX).

Currently running programs as of 2011 include THEMIS
Themis
Themis is an ancient Greek Titaness. She is described as "of good counsel", and is the embodiment of divine order, law, and custom. Themis means "divine law" rather than human ordinance, literally "that which is put in place", from the verb τίθημι, títhēmi, "to put"...

/Artemis, 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 a Delta II 7320-10C expendable launch vehicle. Swift is managed by the NASA Goddard Space Flight Center, and was developed by an international...

, GALEX
GALEX
The Galaxy Evolution Explorer is an orbiting ultraviolet space telescope launched on April 28, 2003. A Pegasus rocket placed the craft into a nearly circular orbit at an altitude of and an inclination to the Earth's equator of 29 degrees....

, RHESSI
Reuven Ramaty High Energy Solar Spectroscopic Imager
Reuven Ramaty High Energy Solar Spectroscopic Imager is the sixth mission in the line of NASA Small Explorer missions...

, ACE
Advanced Composition Explorer
Advanced Composition Explorer is a NASA 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...

, 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...

, IBEX
Interstellar Boundary Explorer
Interstellar Boundary Explorer is a NASA satellite that will make the first map of the boundary between the Solar System and interstellar space. The mission is part of NASA's Small Explorer program. The IBEX satellite was launched with a Pegasus-XL rocket on October 19, 2008, at 17:47:23 UTC...

. Some additional missions that may be in hibernation or reduced function include 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...

, ISEE-3/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 ESRO/ESA to study the interaction between the Earth's magnetic field and the...

, 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...

, and WISE
Wide-field Infrared Survey Explorer
Wide-field Infrared Survey Explorer is a NASA infrared-wavelength astronomical space telescope launched on December 14, 2009, and decommissioned/hibernated on February 17, 2011 when its transmitter was turned off...



Some of the latest planned missions include IRIS
Interface Region Imaging Spectrograph
The Interface Region Imaging Spectrograph is a planned space probe to observe the Sun by NASA. It is a NASA Small Explorer program mission to investigate the physical conditions of the solar limb, particularly the chromosphere of the Sun...

, GEMS (SMEX)
Gravity and Extreme Magnetism SMEX
The Gravity and Extreme Magnetism SMEX mission is a planned space observatory. The main scientific goal of GEMS is to be the first mission to systematically measure the polarization of cosmic X-Ray sources...

, and NuSTAR
Nuštar
Nuštar is a village in eastern Croatia, located northeast of Vinkovci and west of Vukovar, on the route D55. The population of Nuštar is 3,639, with a total of 5,772 people in the municipality, which also includes the nearby villages of Cerić and Marinci .90.79% declare themselves Croats...

.

Launchers have included Jupiter C/Juno I
Juno I
The Juno I was a four-stage American booster rocket which launched America's first satellite, Explorer 1, in 1958. A member of the Redstone rocket family, it was derived from the Jupiter-C sounding rocket...

, Juno II
Juno II
Juno II was an American space launch vehicle used during the late 1950s and early 1960s. It was derived from the Jupiter missile, which was used as the first stage.-Development:...

, various Thor rockets such as Thor-Able
Thor-Able
The Thor-Able was an American expendable launch system and sounding rocket used for a series of re-entry vehicle tests and satellite launches between 1958 and 1960. It was a two stage rocket, consisting of a Thor IRBM as a first stage, and a Vanguard-derived Able second stage. On some flights, an...

, Scout, various Delta and Delta II
Delta II
Delta II was an American space launch system, originally designed and built by McDonnell Douglas. Delta II is part of the Delta rocket family and was in service from 1989 until November 1, 2011...

 rockets (see Delta rocket family), and Pegasus.

History

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 endeavour. 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 an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...

 during the International Geophysical Year
International Geophysical Year
The International Geophysical Year was an international scientific project that lasted from July 1, 1957, to December 31, 1958. It marked the end of a long period during the Cold War when scientific interchange between East and West was seriously interrupted...

; however, 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 from Cape Canaveral Missile Annex, Florida....

. The Explorer program was later reestablished to catch up with the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

 after that nation's launch of Sputnik 1
Sputnik 1
Sputnik 1 ) was the first artificial satellite to be put into Earth's orbit. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957. The unanticipated announcement of Sputnik 1s success precipitated the Sputnik crisis in the United States and ignited the Space...

 on October 4, 1957. (See: Sputnik crisis
Sputnik crisis
The Sputnik crisis is the name for the American reaction to the success of the Sputnik program. It was a key event during the Cold War that began on October 4, 1957 when the Soviet Union launched Sputnik 1, the first artificial Earth satellite....

) 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. It is believed that most of the particles that form the belts come from solar wind, and other particles by cosmic rays. It is named after its discoverer, James...

.

The Explorer program was transferred to NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

, which continued to use the name for an ongoing series of relatively small space missions, typically an artificial satellite with a science focus. Over the years, NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 has launched a series of Explorer spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

 carrying a wide variety of scientific investigations.

Explorer satellites have made important discoveries: Earth's magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...

 and the shape of its gravity field
Gravitational field
The gravitational field is a model used in physics to explain the existence of gravity. In its original concept, gravity was a force between point masses...

; the solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

; properties of micrometeoroids raining down on the Earth; much about ultraviolet, cosmic, and X-rays from the solar system and universe beyond; ionospheric physics
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...

; Solar plasma
Solar flare
A solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up to 6 × 1025 joules of energy . The flare ejects clouds of electrons, ions, and atoms through the corona into space. These clouds typically reach Earth a day...

; solar energetic particles
Solar Energetic Particles
Solar Energetic Particles are high-energy particles coming from the Sun which had been first observed in the early 1940s. They consist of protons, electrons and heavy ions with energy ranging from a few tens of keV to GeV...

; and atmospheric physics. These missions have also investigated air density, radio astronomy, geodesy, and gamma ray astronomy. Various space telescopes have made a variety of discoveries, including the first known Earth Trojan asteroid
Earth Trojan asteroid
Earth trojans are asteroids that orbit in the vicinity of the Earth-Sun Lagrangian points and . They are named after the Trojan asteroids that are associated with the analogous Lagrangian points of Jupiter....

.

The Explorers Program Office at Goddard Space Flight Center in Greenbelt, Maryland
Greenbelt, Maryland
Greenbelt is a city in Prince George's County, Maryland, United States. Contained within today's City of Greenbelt is the historic planned community now known locally as "Old Greenbelt" and designated as the Greenbelt Historic District...

, provides management of the multiple scientific exploration missions in the Explorer space flight program. The missions are characterized by relatively moderate cost, and by small to medium sized missions that are capable of being built, tested and launched in a short time interval compared to the large observatories.

Explorer categories have included MIDEX, SMEX, UNEX, and others. A subprogram called Missions of Opportunity (MO) has funded instruments on non-NASA missions.

Spacecraft by year

Explorer name numbers can be found in the NSSDC master catalog, typically assigned to each spacecraft in a mission. However, one source says they were not officially assigned after 1975.
Explorer Missions
# Name(s) 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. It is believed that most of the particles that form the belts come from solar wind, and other particles by cosmic rays. It is named after its discoverer, James...

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 nuclear test
Operation Argus
Operation Argus was a series of nuclear weapons tests and missile tests secretly conducted during August and September 1958 over the South Atlantic Ocean by the United States's Defense Nuclear Agency, in conjunction with the Explorer 4 space mission. Operation Argus was conducted between the...

 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 launched atop a Jupiter-C rocket on August 24, 1958 from Launch Complex 5, but failed when the rocket's booster collided with its second stage after separation, causing the upper stage firing angle to be off.- References :...

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 Explorer 6
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...

 (S-2 (Able 3))
August 7, 1959 Magnetosphere research October 6, 1959 July 1, 1961
7 Explorer 7
Explorer 7
Explorer 7 was launched October 13, 1959 at 10:36 a.m. Eastern Time by a Juno II rocket from Cape Canaveral Air Force Station to an orbit of 573 km by 1073 km and inclination of 50.27°. It was designed to measure solar x-ray and Lyman-alpha flux, trapped energetic particles, and heavy...

 (S 1A)
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 Explorer 8
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....

 (S 30)
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 Explorer 10
Explorer 10
Explorer 10 was an American Earth-orbital satellite that investigated Earth's magnetic fields and nearby plasma...

 (P 14)
March 25, 1961 Investigated field magnetic field between the Earth and Moon March 25, 1961 June 1, 1968
11 Explorer 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
Explorer 14
Explorer 14 is a spin-stabilized, solar-cell-powered spacecraft instrumented to measure cosmic-ray particles, trapped particles, solar wind protons, and magnetospheric and interplanetary magnetic fields. A 16-channel PFM/PM time-division multiplexed telemeter was used. The time required to sample...

 (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 In orbit
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 In Lunar orbit
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-A , SAS 1, or Explorer 42.The observatory was launched on 12 December 1970 into an initial orbit of about 560 km apogee, 520 km...

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 Small Astronomy Satellite 2, 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 October 7, 2006 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 Small Astronomy Satellite 3 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...

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. The satellite was a collaborative project between NASA, the UK Science Research Council and the European Space Agency...

January 26, 1978 Ultraviolet astronomy September 30, 1996 In orbit
58 HCMM (AEM-A, Applications Explorer Mission-A, Heat Capacity Mapping Mission
Heat Capacity Mapping Mission
The Heat Capacity Mapping Mission was the first Applications Explorer Mission. HCMM provided comprehensive, accurate, high-spatial-resolution thermal surveys of the surface of the Earth....

)
April 26, 1978 Thermal mapping of the earth September 30, 1980 December 22, 1981
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 ESRO/ESA to study the interaction between the Earth's magnetic field and the...

)
August 12, 1978 Magnetospheric research Hibernation In heliocentric orbit
Heliocentric orbit
A heliocentric orbit is an orbit around the Sun. All planets, comets, and asteroids in our Solar System are in such orbits, as are many artificial probes and pieces of debris. The moons of planets in the Solar System, by contrast, are not in heliocentric orbits as they orbit their respective planet...

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...

 (Solar Mesosphere Explorer)
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 In orbit
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 January 30, 2002
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 June 30, 2004 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...

December 30, 1995 X-ray astronomy Operational
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 NASA 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...

August 25, 1997 Solar/interplanetary/interstellar particle research Operational In L1 orbit
Lissajous orbit
In orbital mechanics, a Lissajous orbit, , named after Jules Antoine Lissajous, 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...

72 SNOE February 26, 1998 Atmospheric research December 13, 2003 December 13, 2003
73 TRACE
TRACE
TRACE was 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 June 21, 2010 (Hibernation) 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 was 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...

March 5, 1999 Infrared astronomy, primary mission failed due to loss of coolant No Survey, limited secondary mission May 10, 2011
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 Contact lost
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 In orbit
80 WMAP June 30, 2001 Microwave astronomy October 2010 In L2 orbit
Lissajous orbit
In orbital mechanics, a Lissajous orbit, , named after Jules Antoine Lissajous, 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...

81 RHESSI February 5, 2002 X-ray and gamma ray solar flare imaging Operational In orbit
82 CHIPSat
CHIPSat
CHIPSat is a now-decommissioned, but still-orbiting, microsatellite. It was launched on January 12, 2003 from Vandenberg Air Force Base aboard a Delta II with the larger ICESat, and had an intended mission duration of one year...

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 launched on April 28, 2003. A Pegasus rocket placed the craft into a nearly circular orbit at an altitude of and an inclination to the Earth's equator of 29 degrees....

April 28, 2003 Ultraviolet astronomy Operational 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 a Delta II 7320-10C expendable launch vehicle. Swift is managed by the NASA Goddard Space Flight Center, and was developed by an international...

November 20, 2004 Gamma ray astronomy Operational In orbit
85 THEMIS
THEMIS (satellite)
The Time History of Events and Macroscale Interactions during Substorms mission was originally 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...

 A
February 17, 2007 Magnetospheric research Operational In orbit
86 THEMIS
THEMIS (satellite)
The Time History of Events and Macroscale Interactions during Substorms mission was originally 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...

 B (ARTEMIS P1)
February 17, 2007 Magnetospheric research Operational In orbit
87 THEMIS
THEMIS (satellite)
The Time History of Events and Macroscale Interactions during Substorms mission was originally 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...

 C (ARTEMIS P2)
February 17, 2007 Magnetospheric research Operational In orbit
88 THEMIS
THEMIS (satellite)
The Time History of Events and Macroscale Interactions during Substorms mission was originally 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...

 D
February 17, 2007 Magnetospheric research Operational In orbit
89 THEMIS
THEMIS (satellite)
The Time History of Events and Macroscale Interactions during Substorms mission was originally 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...

 E
February 17, 2007 Magnetospheric research Operational In orbit
90 AIM
Aeronomy of Ice in the Mesosphere
The Aeronomy of Ice in the Mesosphere is a satellite to conduct a 26-month study of noctilucent clouds . It is the ninetieth Explorer program mission and is part of the NASA-funded Small Explorer program...

April 25, 2007 Noctilucent cloud observation Operational In orbit
91 IBEX
Interstellar Boundary Explorer
Interstellar Boundary Explorer is a NASA satellite that will make the first map of the boundary between the Solar System and interstellar space. The mission is part of NASA's Small Explorer program. The IBEX satellite was launched with a Pegasus-XL rocket on October 19, 2008, at 17:47:23 UTC...

October 19, 2008 Mapping the boundary between the Solar System and interstellar space. Operational In orbit
92 WISE
Wide-field Infrared Survey Explorer
Wide-field Infrared Survey Explorer is a NASA infrared-wavelength astronomical space telescope launched on December 14, 2009, and decommissioned/hibernated on February 17, 2011 when its transmitter was turned off...

December 14, 2009 Infrared astronomy February 17, 2011
Hibernation
In orbit

Spacecraft by name

Explorer missions in the NSSDC master catalog listing. http://nssdc.gsfc.nasa.gov/nmc/SpacecraftQuery.jsp This does not include Missions of Opportunity (MO), but does include some spacecraft with launch failures or were cancelled.

Other missions

Examples of cancelled missions, include:
  • Owl 1
  • Owl 2
  • MSS A
  • CATSAT (STEDI 3)
  • IMEX (UNEX 2)
  • FAME (MIDEX 4)
    Full-sky Astrometric Mapping Explorer
    Full-sky Astrometric Mapping Explorer was a proposed astrometric satellite designed to determine with unprecedented accuracy the positions, distances, and motions of 40 million stars within our galactic neighborhood...

     
  • SPIDR (SMEX 8)


Many more missions are proposed, but not selected. For example in 2011, the overall explorer program received 22 full missions solicitations, 20 Missions of Opportunity, and 8 USPI.

Another type of program called missions of opportunity (MO), which adds small missions to other spacecraft, such as an additional instrument. Examples of this include Astro-H
ASTRO-H
Astro-H is a planned X-ray astronomy satellite under development by the Japan Aerospace Exploration Agency . It is expected to be launched in 2014 into the 550 km height orbit around earth. Launch vehicle will be the H-IIA.With a planned weight of 2.4 t, Astro-H will be the heaviest Japanese...

, CINDI
CINDI
CINDI, or the Coupled Ion-Neutral Dynamics Investigation is a NASA mission of opportunity payload aboard the C/NOFS satellite. Mission of opportunity is part of the Explorer program.-External links:**...

, TWINS
TWINS
Two Wide-Angle Imaging Neutral-Atom Spectrometers are a pair of NASA instruments aboard two United States National Reconnaissance Office satellites in Molniya orbits. TWINS was designed to provide stereo images of the Earth's ring current. The first instrument, TWINS-1, was launched aboard USA-184...

, and HETE-2.

See also

  • Tom Krimigis
    Stamatios Krimigis
    Stamatios M. Krimigis is a Greek-American scientist in space exploration. He has contributed to the majority of the United States' unmanned space exploration programs of the Solar system and beyond. He has contributed to exploration missions to almost every planet of our solar system...

  • Small Explorer program
    Small Explorer program
    The Small Explorer program is an effort within NASA to fund space exploration missions that cost no more than $120 million.- Program history :...

  • Discovery program
    Discovery Program
    NASA's Discovery Program is a series of lower-cost, highly-focused American scientific space missions that are exploring the Solar System. It was founded in 1992 to implement then-NASA Administrator Daniel S. Goldin's vision of "faster, better, cheaper" planetary missions...

  • New Frontiers program
    New Frontiers program
    The New Frontiers program is a series of space exploration missions being conducted by NASA with the purpose of researching several of the Sun's planets including Jupiter, Venus, and the dwarf planet Pluto...


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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