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 99 successful and four unsuccessful missions as of this writing (March 2023). 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	Explorer 36	1968-002A	1968-01-11	Earth Science Heliophysics
SOLRAD 9	Explorer 37	1968-017A	1968-03-05	Heliophysics
RAE-A	Explorer 38	1968-055A	1968-07-04	Astronomy Heliophysics
AD-C	Explorer 39	1968-066A	1968-08-08	Earth Science
Injun 5	Explorer 40	1968-066B	1968-08-08	Heliophysics
IMP-G	Explorer 41	1969-053A	1969-06-21	Heliophysics
Uhuru	Explorer 42	1970-107A	1970-12-12	Astronomy
IMP-I	Explorer 43	1971-019A	1971-03-13	Astronomy Heliophysics
SOLRAD 10	Explorer 44	1971-058A	1971-07-08	Heliophysics
S-Cubed A	Explorer 45	1971-096A	1971-11-15	Heliophysics
Meteoroid Technology Satellite	Explorer 46	1972-061A	1972-08-13	Planetary Science
IMP-H	Explorer 47	1972-073A	1972-09-23	Heliophysics
SAS-B	Explorer 48	1972-091A	1972-11-15	Astronomy
RAE-B	Explorer 49	1973-039A	1973-06-10	Astronomy Heliophysics Planetary Science
IMP-J	Explorer 50	1973-078A	1973-10-26	Heliophysics
AE-C	Explorer 51	1973-101A	1973-12-16	Earth Science Heliophysics
Hawkeye 1	Explorer 52	1974-040A	1974-06-03	Heliophysics
SAS-C	Explorer 53	1975-037A	1975-05-07	Astronomy
AE-D	Explorer 54	1975-096A	1975-10-06	Earth Science Engineering Heliophysics
AE-E	Explorer 55	1975-107A	1975-11-20	Earth Science Heliophysics
ISEE 1	Explorer 56	1977-102A	1977-10-22	Astronomy Heliophysics
IUE	Explorer 57	1978-012A	1978-01-26	Astonomy Heliophysics Planetary Science
HCMM	Explorer 58	1978-041A	1978-04-26	Earth Science
ISEE 3	Explorer 59	1978-079A	1978-08-12	Astronomy Heliophysics Planetary Science
SAGE	Explorer 60	1979-013A	1979-02-18	Earth Science
Magsat	Explorer 61	1979-094A	1979-10-30	Heliophysics
Dynamics Explorer 1	Explorer 62	1981-070A	1981-08-03	Heliophysics
Dynamics Explorer 2	Explorer 63	1981-070B	1981-08-03	Earth Science Heliophysics
SME	Explorer 64	1981-100A	1981-10-06	Earth Science Heliophysics
AMPTE/CCE	Explorer 65	1984-088A	1984-08-16	Heliophysics
COBE	Explorer 66	1989-089A	1989-11-18	Astronomy
EUVE	Explorer 67	1992-031A	1992-06-07	Astronomy
WIRE, Failed	Explorer 75	1999-011A	1999-03-05	Astronomy
TERRIERS, Failed	Explorer 76	1999-026A	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
TESS	Explorer 95	2018-038A	2018-04-18	Astronomy
ICON	Explorer 96	2019-068A	2019-10-11	Heliophysics

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
IXPE	Explorer 97	2021-121A	2021-12-09	Astronomy

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
ISS	NICER	1998-067A	2017-06-03	Astronomy
SES 14	GOLD	2018-012B	2018-01-25	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) had been operational just over two years and one year, respectively.