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NASA's Explorer Program Satellites

Over the years, NASA has launched a series of "Explorer" spacecraft carrying a wide variety of scientific investigations. The sections below identify the 89 successful and four unsuccessful missions as of this writing (August 2014). Each list identifies the common name (different than "Explorer N" for most), what its Explorer name is, the international (COSPAR) launch ID, and its launch date.

Explorers

Explorer missions are large craft that are, by definition, not to exceed a cost of $200 million for development, launch services, and mission operations and data analysis, exclusive of the launch vehicle.

Spacecraft Name Explorer Number COSPAR ID Launch Date Science Disipline(s)
Explorer 1 Explorer 1 1958-001A 1958-02-01 Earth Science
Heliophysics
Explorer 2 Explorer 2 Failed 1958-03-05 Heliophysics
Explorer 3 Explorer 3 1958-003A 1958-03-26 Astronomy
Heliophysics
Explorer 4 Explorer 4 1958-005A 1958-07-26 Heliophysics
Explorer 5 Explorer 5 Failed 1958-08-24 Heliophysics
Explorer 6 Explorer 6 1959-004A 1959-08-07 Heliophysics
Explorer 7 Explorer 7 1959-009A 1959-10-13 Earth Science
Heliophysics
Explorer 8 Explorer 8 1960-014A 1960-11-03 Earth Science
Heliophysics
Planetary Science
Explorer 9 Explorer 9 1961-004A 1961-02-16 Earth Science
P 14 Explorer 10 1961-010A 1961-03-25 Heliophysics
S 15 Explorer 11 1961-013A 1961-04-27 Astronomy
Heliophysics
EPE-A Explorer 12 1961-020A 1961-08-16 Heliophysics
S 55A Explorer 13 1961-022A 1961-08-25 Planetary Science
EPE-B Explorer 14 1962-051A 1962-10-02 Heliophysics
EPE-C Explorer 15 1962-059A 1962-10-27 Heliophysics
S 55B Explorer 16 1962-070A 1962-12-16 Planetary Science
AE-A Explorer 17 1963-009A 1963-04-03 Earth Science
Heliophysics
IMP-A Explorer 18 1963-046A 1963-11-27 Heliophysics
AD-A Explorer 19 1963-053A 1963-12-19 Earth Science
IE-A Explorer 20 1964-051A 1964-08-25 Astronomy
Heliophysics
IMP-B Explorer 21 1964-060A 1964-10-04 Heliophysics
BE-B Explorer 22 1964-064A 1964-10-10 Earth Science
Heliophysics
S 55C Explorer 23 1964-074A 1964-11-06 Planetary Science
AD-B Explorer 24 1964-076A 1964-11-21 Earth Science
Injun 4 Explorer 25 1964-076B 1964-11-21 Heliophysics
EPE-D Explorer 26 1964-086A 1964-12-21 Heliophysics
BE-C Explorer 27 1965-032A 1965-04-29 Earth Science
Heliophysics
IMP-C Explorer 28 1965-042A 1965-05-29 Heliophysics
GEOS 1 Explorer 29 1965-089A 1965-11-06 Earth Science
SOLRAD 8 Explorer 30 1965-093A 1965-11-19 Heliophysics
DME-A Explorer 31 1965-098B 1965-11-29 Heliophysics
AE-B Explorer 32 1966-044A 1966-05-25 Earth Science
Heliophysics
IMP-D Explorer 33 1966-058A 1966-07-01 Astronomy
Heliophysics
Planetary Science
IMP-F Explorer 34 1967-051A 1967-05-24 Heliophysics
IMP-E Explorer 35 1967-070A 1967-07-19 Heliophysics
Planetary Science
GEOS 2 1968-002A Explorer 36 1968-01-11 Earth Science
Heliophysics
SOLRAD 9 1968-017A Explorer 37 1968-03-05 Heliophysics
RAE-A 1968-055A Explorer 38 1968-07-04 Astronomy
Heliophysics
AD-C 1968-066A Explorer 39 1968-08-08 Earth Science
Injun 5 1968-066B Explorer 40 1968-08-08 Heliophysics
IMP-G 1969-053A Explorer 41 1969-06-21 Heliophysics
Uhuru 1970-107A Explorer 42 1970-12-12 Astronomy
IMP-I 1971-019A Explorer 43 1971-03-13 Astronomy
Heliophysics
SOLRAD 10 1971-058A Explorer 44 1971-07-08 Heliophysics
S-Cubed A 1971-096A Explorer 45 1971-11-15 Heliophysics
Meteoroid Technology Satellite 1972-061A Explorer 46 1972-08-13 Planetary Science
IMP-H 1972-073A Explorer 47 1972-09-23 Heliophysics
SAS-B 1972-091A Explorer 48 1972-11-15 Astronomy
RAE-B 1973-039A Explorer 49 1973-06-10 Astronomy
Heliophysics
Planetary Science
IMP-J 1973-078A Explorer 50 1973-10-26 Heliophysics
AE-C 1973-101A Explorer 51 1973-12-16 Earth Science
Heliophysics
Hawkeye 1 1974-040A Explorer 52 1974-06-03 Heliophysics
SAS-C 1975-037A Explorer 53 1975-05-07 Astronomy
AE-D 1975-096A Explorer 54 1975-10-06 Earth Science
Engineering
Heliophysics
AE-E 1975-107A Explorer 55 1975-11-20 Earth Science
Heliophysics
ISEE 1 1977-102A Explorer 56 1977-10-22 Astronomy
Heliophysics
IUE 1978-012A Explorer 57 1978-01-26 Astonomy
Heliophysics
Planetary Science
HCMM 1978-041A Explorer 58 1978-04-26 Earth Science
ISEE 3 1978-079A Explorer 59 1978-08-12 Astronomy
Heliophysics
Planetary Science
SAGE 1979-013A Explorer 60 1979-02-18 Earth Science
Magsat 1979-094A Explorer 61 1979-10-30 Heliophysics
Dynamics Explorer 1 1981-070A Explorer 62 1981-08-03 Heliophysics
Dynamics Explorer 2 1981-070B Explorer 63 1981-08-03 Earth Science
Heliophysics
SME 1981-100A Explorer 64 1981-10-06 Earth Science
Heliophysics
AMPTE/CCE 1984-088A Explorer 65 1984-08-16 Heliophysics
COBE 1989-089A Explorer 66 1989-11-18 Astronomy
EUVE 1992-031A Explorer 67 1992-06-07 Astronomy
WIRE, Failed 1999-011A Explorer 75 1999-03-05 Astronomy
TERRIERS, Failed 1999-026A Explorer 76 1999-05-18 Heliophysics

Medium-Class Explorers (MIDEX)

Medium-class explorer (MIDEX) missions are craft that are, by definition, not to exceed a cost of $180 million for development, launch services, and mission operations and data analysis, exclusive of the launch vehicle.

Spacecraft Name Explorer Number COSPAR ID Launch Date Science Disipline(s)
XTE Explorer 69 1995-074A 1995-12-30 Astronomy
ACE Explorer 71 1997-045A 1997-08-25 Heliophysics
FUSE Explorer 77 1999-035A 1999-06-24 Astronomy
IMAGE Explorer 78 2000-017A 2000-03-25 Heliophysics
WMAP Explorer 80 2001-027A 2001-06-30 Astronomy
Swift Explorer 84 2004-047A 2004-11-20 Astronomy
THEMIS-A Explorer 85 2007-004A 2007-02-17 Heliophysics
THEMIS-B Explorer 86 2007-004B 2007-02-17 Heliophysics
THEMIS-C Explorer 87 2007-004C 2007-02-17 Heliophysics
THEMIS-D Explorer 88 2007-004D 2007-02-17 Heliophysics
THEMIS-E Explorer 89 2007-004E 2007-02-17 Heliophysics
WISE Explorer 92 2009-071A 2009-12-14 Astronomy

Small Explorers (SMEX)

Small explorer missions are craft that are, by definition, not to exceed a cost of $120 million for development, launch services, and mission operations and data analysis, exclusive of the launch vehicle.

Spacecraft Name Explorer Number COSPAR ID Launch Date Science Disipline(s)
SAMPEX Explorer 68 1992-038A 1992-07-03 Astronomy
Heliophysics
FAST Explorer 70 1996-049A 1996-08-21 Heliophysics
TRACE Explorer 73 1998-020A 1998-04-02 Heliophysics
SWAS Explorer 74 1998-071A 1998-12-06 Astronomy
RHESSI Explorer 81 2002-004A 2002-02-05 Heliophysics
GALEX Explorer 83 2003-017A 2003-04-28 Astronomy
AIM Explorer 90 2007-015A 2007-04-25 Heliophsyics
IBEX Explorer 91 2008-051A 2008-10-19 Heliphysics
NuSTAR Explorer 93 2012-031A 2012-06-13 Astronomy
IRIS Explorer 94 2013-033A 2013-06-28 Heliophysics

University-Class Explorers (UNEX)

University-class explorer missions are craft that are, by definition, not to exceed a cost of $15 million for development, launch services, and mission operations and data analysis, exclusive of the launch vehicle.

Spacecraft Name Explorer Number COSPAR ID Launch Date Science Disipline(s)
SNOE Explorer 72 1998-012A 1998-02-26 Heliophysics
CHIPS Explorer 82 2003-002B 2003-01-13 Astronomy

Missions of Opportunity

Missions of Opportunity (MO) investigations are characterized as being part of a non-NASA space mission of any size and having a total NASA cost of under $55 million. These missions are conducted on a no-exchange-of-funds basis with the organization sponsoring the mission. As a result, these investigations are not always assigned an Explorer number.

Spacecraft Name Investigation COSPAR ID Launch Date Science Disipline(s)
HETE 2 Explorer 79 2000-061A 2000-10-09 Astronomy
Suzaku 2 Guest Observer Facility 2005-025A 2005-07-10 Astronomy
USA 184 TWINS 1 2006-027A 2006-06-28 Heliophysics
USA 200 TWINS 2 2008-010A 2008-03-13 Heliophysics
C/NOFS CINDI 2008-017A 2008-04-16 Heliophysics

A long-lived series of long-lived spacecraft

NASA's Explorer spacecraft series is not simply the longest running series of spacecraft, it has produced highly-durable (i.e., well-engineered) spacecraft as well. The diagram (current as of Feb. 1998) illustrates this point very clearly. Of the 73 successful Explorer missions depicted, fully five of them had had missions which lasted 10 or more years, the longest of which (IMP 8) had been operational for over 26 years and produced valuable information about the solar wind for several more years. (NASA retired IMP 8 in October 2001 after 28 years of continuous operation.)

NASA's IUE spacecraft operated for 19 years and produced copious amounts of data for the astronomical community. The ISEE 3/ICE spacecraft also operated for 19 years.

As of August 2014, of the 13 operational Explorer missions, ACE has operated for 17 years, followed by RHESSI (13 years), Swift (10 years), the five THEMIS spacecraft (7.5 years), AIM (7 years), IBEX (6 years), and WISE (5 years). The two newest Explorers (NuSTAR and IRIS) have been operational just over two years and one year, respectively.

Other Sources of Explorer Information

Explorers Program (NASA GSFC)

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