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.

Expand

EWLINE Explorer Missions Spacecraft Name Explorer # NSSDC ID Launch Date Launch Vehicle 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...   Explorer 71 1997-045A 1997-08-25 Delta II 7920 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...   Explorer 90 2007-015A 2007-04-25 Pegasus XL AD-A Explorer 19 1963-053A 1963-12-19 Scout AD-B Explorer 24 1964-076A 1964-11-21 Scout AD-C Explorer 39 1968-066A 1968-08-08 Scout AE-A Explorer 17 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...   1963-009A 1963-04-03 Thor-Delta AE-B Explorer 32 1966-044A 1966-05-25 Delta AE-C Explorer 51 1973-101A 1973-12-16 Delta AE-D Explorer 54 1975-096A 1975-10-06 Delta AE-E Explorer 55 1975-107A 1975-11-20 Delta AMPTE/CCE Explorer 65 1984-088A 1984-08-16 Delta BE-B Explorer 22 1964-064A 1964-10-10 Scout BE-C Explorer 27 1965-032A 1965-04-29 Scout CHIPS 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...   Explorer 82 2003-002B 2003-01-13 Delta II 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...   Explorer 66 1989-089A 1989-11-18 Delta DME-A Explorer 31 1965-098B 1965-11-29 Thor-Agena B Dynamics Explorer 1 Explorer 62 1981-070A 1981-08-03 Delta Dynamics Explorer 2 Explorer 63 1981-070B 1981-08-03 Delta 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...   Explorer 67 1992-031A 1992-06-07 Delta II Explorer 1  Explorer 1 1958-001A 1958-02-01 Jupiter C (Juno I) 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....   Explorer 2 EXPLR2 1958-03-05 Jupiter C (Juno I) Explorer 3 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...   Explorer 3 1958-003A 1958-03-26 Juno 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...   Explorer 4 1958-005A 1958-07-26 Juno 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 :...   Explorer 5 EXPLR5 1958-08-24 Jupiter C (Juno I) 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...   Explorer 6 1959-004A 1959-08-07 Thor-Able 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...   Explorer 7 1959-009A 1959-10-13 Juno Explorer 7X Explorer 7x EXP-7X 1959-07-16 Juno 2 (Juno II) 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....   Explorer 8 1960-014A 1960-11-03 Juno Explorer 9 Explorer 9 Explorer 9, known as S-56A before launch, was an American satellite which was launched in 1961 to study the density and composition of the upper thermosphere and lower exosphere. It was a reflight of the failed S-56 mission, and consisted of a , balloon which was deployed into a medium Earth orbit...   Explorer 9 1961-004A 1961-02-16 Scout Explorer 12 Explorer 12 1961-020A 1961-08-16 Thor-Delta Explorer 14 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...   Explorer 14 1962-051A 1962-10-02 Thor-Delta Explorer 15 Explorer 15 1962-059A 1962-10-27 Thor-Delta Explorer 26 Explorer 26 1964-086A 1964-12-21 Delta Explorer 33 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...   Explorer 33 1966-058A 1966-07-01 Delta Explorer 35 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...   Explorer 35 1967-070A 1967-07-19 Delta Explorer S45 Explorer S45 EXS-451 1961-02-24 Juno Explorer S45A Explorer S45A EXS-452 1961-05-24 Juno 2 (Juno II) Explorer S55 Explorer S55 EXS-55 1961-06-30 Scout FAST FAST -Primary meanings:Fast may refer to:* Fast as in high speed or velocity, may be used with anything that has a speed.* Fasting, abstaining from foodSlang:* Fast, a slang term for someone who is sexually promiscuous-Sports:...   Explorer 70 1996-049A 1996-08-21 Pegasus XL FUSE Fuse The word fuse has several meanings:* Fuse , a device used in electrical systems to protect against excessive current....   Explorer 77 1999-035A 1999-06-24 Delta II 7320 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....   Explorer 83 2003-017A 2003-04-28 Pegasus XL GEOS 1 Explorer 29 1965-089A 1965-11-06 Delta GEOS 2 Explorer 36 1968-002A 1968-01-11 Delta Hawkeye 1 Explorer 52 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...   1974-040A 1974-06-03 Scout HCMM 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....   Explorer 58 1978-041A 1978-04-26 Scout-F HETE 2 Explorer 79 2000-061A 2000-10-09 Pegasus IBEX  Explorer 91 2008-051A 2008-10-19 Pegasus XL IE-A Explorer 20 1964-051A 1964-08-25 Scout 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...   Explorer 78 2000-017A 2000-03-25 Delta II 7326 IMP-A Explorer 18 1963-046A 1963-11-27 Thor-Delta IMP-B Explorer 21 1964-060A 1964-10-04 Delta IMP-C Explorer 28 1965-042A 1965-05-29 Delta IMP-F Explorer 34 1967-051A 1967-05-24 Delta IMP-G Explorer 41 1969-053A 1969-06-21 Delta IMP-H Explorer 47 1972-073A 1972-09-23 Delta IMP-I Explorer 43 1971-019A 1971-03-13 Delta IMP-J Explorer 50 1973-078A 1973-10-26 Delta Injun 4 Explorer 25 1964-076B 1964-11-21 Scout Injun 5 Explorer 40 1968-066B 1968-08-08 Scout ISEE 1 Explorer 56 1977-102A 1977-10-22 Delta ISEE 3 Explorer 59 1978-079A 1978-08-12 Delta IUE  Explorer 57 1978-012A 1978-01-26 Delta Magnetic Storm Satellite cancelled Explorer-A MSS-A Scout? 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...   Explorer 61 1979-094A 1979-10-30 Scout Meteoroid Technology Satellite Explorer 46 1972-061A 1972-08-13 Scout P 14 Explorer 10 1961-010A 1961-03-25 Thor-Delta RAE-A Explorer 38 1968-055A 1968-07-04 Delta RAE-B Explorer 49 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....   1973-039A 1973-06-10 Delta RHESSI  Explorer 81 2002-004A 2002-02-05 Pegasus XL S 15 Explorer 11 1961-013A 1961-04-27 Juno S 46A Explorer S-46 EXS-46 1960-03-23 Juno 2 (Juno II) S 55A Explorer 13 1961-022A 1961-08-25 Scout S 55B Explorer 16 1962-070A 1962-12-16 Scout S 55C Explorer 23 1964-074A 1964-11-06 Scout S 56 Explorer S-56 EXS-56 1960-12-04 Scout S-Cubed A Explorer 45 1971-096A 1971-11-15 Scout SAGE Explorer 60 1979-013A 1979-02-18 Scout SAMPEX  Explorer 68 1992-038A 1992-07-03 Scout SAS-B Explorer 48 1972-091A 1972-11-15 Scout SAS-C Explorer 53 1975-037A 1975-05-07 Scout 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...   Explorer 64 1981-100A 1981-10-06 Delta SNOE Explorer 72 1998-012A 1998-02-26 Pegasus XL SOLRAD 8  Explorer 30 1965-093A 1965-11-19 Scout SOLRAD 9  Explorer 37 1968-017A 1968-03-05 Scout SOLRAD 10  Explorer 44 1971-058A 1971-07-08 Scout SWAS  Explorer 74 1998-071A 1998-12-06 Pegasus XL 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...   Explorer 84 2004-047A 2004-11-20 Delta II TERRIERS Explorer 76 1999-026A 1999-05-18 Pegasus THEMIS-A Explorer 85 2007-004A 2007-02-17 Delta II 7925 THEMIS-B Explorer 86 2007-004B 2007-02-17 Delta II 7925 THEMIS-C Explorer 87 2007-004C 2007-02-17 Delta II 7925 THEMIS-D Explorer 88 2007-004D 2007-02-17 Delta II 7925 THEMIS-E Explorer 89 2007-004E 2007-02-17 Delta II 7925 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...   Explorer 73 1998-020A 1998-04-02 Pegasus XL Uhuru 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...   Explorer 42 1970-107A 1970-12-12 Scout WIRE Wire A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...   Explorer 75 1999-011A 1999-03-05 Pegasus XL WISE Wise -People:* Audrey Wise , United Kingdom politician* Bob Wise , American politician* Brownie Wise , American saleswoman who developed "party plan" marketing*Christopher Wise , American author...   Explorer 92 2009-071A 2009-12-14 Delta II WMAP  Explorer 80 2001-027A 2001-06-30 Delta II X-Ray Timing Explorer 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...   Explorer 69 1995-074A 1995-12-30 Delta II 7920

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

• NASA Explorer program missions page
• NSSDC List of Explorer missions from 1 to 77
• Explorer Program Profile by NASA's Solar System Exploration
• 1957 Video (30 minutes) on launch and impact of Explorer
• Master list of Names, Initialisms, and Abbreviations for un-manned satellites
• U.S. Space Objects Registry
• Explorer Program at Gunters Space Page (detailed list of explorer missions