Editing Explorers Program (section)

== Classes ==
=== Medium-Class  (MIDEX) ===
{| class="wikitable"
|+List of MIDEX missions<ref>{{cite web |url=http://explorers.gsfc.nasa.gov/midex.html |title=Explorers Program |website=explorers.gsfc.nasa.gov |access-date=8 April 2016 |archive-url=https://web.archive.org/web/20160323014953/http://explorers.gsfc.nasa.gov/midex.html |archive-date=23 March 2016 |url-status=dead}} {{PD-notice}}</ref><ref name=":0" /><ref>{{cite web |url=https://explorers.larc.nasa.gov/MIDEX/MIDEX.html |title=Medium-class Explorers (MIDEX) |publisher=Explorers.larc.nasa.gov |access-date=28 April 2018}} {{PD-notice}}</ref> 
|-
! Name
! MIDEX<br/>number
! Explorer<br/>number
! Launch (UTC)
! Status
|-
| [[Rossi X-ray Timing Explorer|RXTE]]
| 
| Explorer-69
| 30 December 1995
| Ended in 2012 / Reentered on 30 April 2018 
|-
| [[Advanced Composition Explorer|ACE]]
| 
| Explorer-71
| 25 August 1997
| {{success|'''Operational'''}}
|-
| [[Far Ultraviolet Spectroscopic Explorer|FUSE]]
| MIDEX-0
| Explorer-77
| 23 June 1999
| Ended in 2007
|-
| [[IMAGE (spacecraft)|IMAGE]]
| MIDEX-1
| Explorer-78
| 25 March 2000
| Lost contact in 2005. Partial contact reestablished in January 2018
|-
| [[Wilkinson Microwave Anisotropy Probe|WMAP]]
| MIDEX-2
| Explorer-80
| 30 June 2001
| Ended in 2010
|-
| [[Neil Gehrels Swift Observatory|Swift]]
| MIDEX-3
| Explorer-84
| 20 November 2004
| {{success|'''Operational'''}}
|-
| [[Full-sky Astrometric Mapping Explorer|FAME]]
| MIDEX-4
| {{center|—}}
| ''Scheduled for 2004''
| Cancelled in 2002 (cost)
|-
| [[THEMIS (satellite)|THEMIS]] A
| MIDEX-5A
| Explorer-85
| 17 February 2007
| {{success|'''Operational'''}}
|-
| [[THEMIS (satellite)|THEMIS]] B
| MIDEX-5B
| Explorer-86
| 17 February 2007
| {{success|'''Operational'''}}
|-
| [[THEMIS (satellite)|THEMIS]] C
| MIDEX-5C
| Explorer-87
| 17 February 2007
| {{success|'''Operational'''}}
|-
| [[THEMIS (satellite)|THEMIS]] D
| MIDEX-5D
| Explorer-88
| 17 February 2007
| {{success|'''Operational'''}}
|-
| [[THEMIS (satellite)|THEMIS]] E
| MIDEX-5E
| Explorer-89
| 17 February 2007
| {{success|'''Operational'''}}
|-
| [[Wide-field Infrared Survey Explorer|WISE / NEOWISE]] 
| MIDEX-6
| Explorer-92
| 14 December 2009
| Mission operations Completed on 31 July 2024.<ref>{{Cite web|url=https://www.nasa.gov/missions/neowise/nasas-neowise-infrared-heritage-will-live-on/|title=NASA’s NEOWISE Infrared Heritage Will Live On - NASA|date=1 July 2024}}</ref> Reentered on 2 November 2024

|-
| [[Transiting Exoplanet Survey Satellite|TESS]]
| MIDEX-7
| Explorer-95
| 18 April 2018
| {{success|'''Operational'''}}
|-
| [[Ionospheric Connection Explorer|ICON]]
| MIDEX-8
| Explorer-96
| 11 October 2019 
| {{success|'''Operational'''}}
|-
| [[SPHEREx]]
| MIDEX-9<!--The sequential number, but needs a reference-->
| 
| 12 March 2025 
|  {{success|'''Operational'''}}
|-
| [[Multi-slit Solar Explorer|MUSE]]
| MIDEX-10<!--The sequential number, but needs a reference-->
| 
| 2027 
| {{pending|In development}}
|-
| [[HelioSwarm]]
| MIDEX-11<!--The sequential number, but needs a reference-->
| 
| 2028 
| {{pending|In development}}
|-
| [[UVEX]]
| MIDEX-12<!--The sequential number, but needs a reference-->
| 
| 2030 
| {{pending|In development}}
|}

=== Small Explorers (SMEX) ===
The Small Explorers class was implemented in 1989 specifically to fund space exploration missions that cost no more than {{US$|120 million}}.<ref name=missions/><ref name="IEEE" /> The missions are managed by the Explorers Project at the [[Goddard Space Flight Center]] (GSFC).<ref name="welcome" />

The first set of three SMEX missions were launched between 1992 and 1998. The second set of two missions were launched in 1998 and 1999. These early missions were managed by the Small Explorers Project Office at Goddard Space Flight Center. In early 1999, that office was closed and with the announcement of opportunity for the third set of SMEX missions NASA converted the program so that each mission was managed by its [[Principal investigator|Principal Investigator]], with oversight by the GSFC Explorers Project.<ref name="welcome" />

NASA funded a competitive study of five candidate heliophysics Small Explorers missions for flight in 2022. The proposals were Mechanisms of Energetic Mass Ejection – eXplorer (MEME-X), Focusing Optics X-ray Solar Imager (FOXSI), Multi-Slit Solar Explorer (MUSE), Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS), and Polarimeter to Unify the Corona and Heliosphere (PUNCH).<ref>{{cite web |url=https://www.nasa.gov/press-release/nasa-selects-proposals-to-study-sun-space-environment |title=NASA Selects Proposals to Study Sun, Space Environment |publisher=NASA |first=Dwayne |last=Brown |date=28 July 2017 |access-date=7 December 2017}} {{PD-notice}}</ref><ref>{{cite web |url=https://nspires.nasaprs.com/external/viewrepositorydocument/cmdocumentid=524225/solicitationId=%7BA0C496AC-9B9D-8F7D-A506-B1695BF9BDE8%7D/viewSolicitationDocument=1/2016%20Helio%20SMEX%20AO_amend1_clarify.pdf |title=Announcement of Opportunity: Heliophysics Explorers Program, 2016 Small Explorers (SMEX) |publisher=NASA |date=13 July 2016 |id=NNH16ZDA005O}} {{PD-notice}}</ref><ref>{{cite web |url=https://explorers.larc.nasa.gov/HPSMEX/pdf_files/8_SMEX-AO-2016Helio-CSR-Kickoff-LSP-MENDOZA-HILL.pdf |title=Heliophysics Small Explorers 2016 Announcement of Opportunity: Concept Study Report Kickoff |publisher=NASA{{\}}Launch Services Program |first=Alicia |last=Mendoza-Hill |date=25 August 2017}} {{PD-notice}}</ref> In June 2019 NASA selected TRACERS and PUNCH for flight.<ref>{{cite web |url=https://www.nasa.gov/press-release/nasa-selects-missions-to-study-our-sun-its-effects-on-space-weather |title=NASA Selects Missions to Study Our Sun, Its Effects on Space Weather |publisher=NASA |date=20 June 2019 |url-status=live |archive-url=https://web.archive.org/web/20231031190231/https://www.nasa.gov/news-release/nasa-selects-missions-to-study-our-sun-its-effects-on-space-weather/ |archive-date=31 October 2023}} {{PD-notice}}</ref>

{| class="wikitable"
|+List of SMEX missions <ref name=":0">{{cite web |url=http://space.skyrocket.de/doc_sat/explorer.htm |title=Explorers Program |website=space.skyrocket.de |access-date=8 April 2016}}</ref><ref>{{cite web |url=http://explorers.gsfc.nasa.gov/smex.html |title=Operational Small Explorers (SMEX) Missions |website=Explorers Program |access-date=8 April 2016 |archive-url=https://web.archive.org/web/20160325193350/http://explorers.gsfc.nasa.gov/smex.html |archive-date=25 March 2016 |url-status=dead}} {{PD-notice}}</ref>
|-
! Name
! SMEX<br/>number
! Explorer<br/>number
! Launch (UTC)
! End of<br/>mission
! Status
|-

| [[Solar Anomalous and Magnetospheric Particle Explorer|SAMPEX]]
| SMEX-1
| Explorer-68
| 3 July 1992
| 30 June 2004
| Reentered on 13 November 2012
|-

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| [[TOMS]]-EP
| 
| 
| 2 July 1996
| <ref>{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1996-037A |title=NASA - NSSDCA - Spacecraft |publisher=NASA |date=21 March 2017 |access-date=20 April 2018}} {{PD-notice}}</ref>
-->
|-

| [[Fast Auroral Snapshot Explorer|FAST]]
| SMEX-2
| Explorer-70
| 21 August 1996
| 4 May 2009
| 
|-

| [[Submillimeter Wave Astronomy Satellite|SWAS]]
| SMEX-3
| Explorer-74
| 6 December 1998
| 21 July 2004
| 
|-

| [[TRACE]]
| SMEX-4
| Explorer-73
| 2 April 1998
| 21 June 2010
| 
|-

| [[Wide Field Infrared Explorer|WIRE]]
| SMEX-5
| Explorer-75
| 5 March 1999
| {{n/a}}
| Spacecraft equipment failure; reentered on 10 May 2011
|-

| [[Reuven Ramaty High Energy Solar Spectroscopic Imager|RHESSI]]
| SMEX-6
| Explorer-81
| 5 February 2002
| April 2018
| Deorbited on 20 April 2023
|-

| [[GALEX]]
| SMEX-7
| Explorer-83
| 28 April 2003
| May 2012
| Decommissioned on 28 June 2013
|-

| SPIDR
| SMEX-8
| {{center|—}}
| ''Scheduled for 2005''
| {{n/a}}
| Cancelled in 2003 due to poor instrument sensitivity <ref>{{cite web |url=http://www.spacetoday.net/Summary/1695 |title=NASA cancels space science mission |website=spacetoday.net |date=4 June 2003 |access-date=28 April 2018 |url-status=live |archive-url=https://web.archive.org/web/20190427111301/http://www.spacetoday.net/Summary/1695 |archive-date=27 April 2019}}</ref>
|-

| [[Aeronomy of Ice in the Mesosphere]] (AIM)
| SMEX-9
| Explorer-90
| 25 April 2007
| 19 August 2024
| Reentered on 19 August 2024
|-

| [[Interstellar Boundary Explorer|IBEX]]
| SMEX-10
| Explorer-91
| 19 October 2008
| 
| {{success|'''Operational'''}}
|-

| [[NuSTAR]]
| SMEX-11
| Explorer-93
| 13 June 2012
| 
| {{success|'''Operational'''}}
|-

| [[Interface Region Imaging Spectrograph|IRIS]]
| {{nowrap|SMEX-12}}
| {{nowrap|Explorer-94}}
| 28 June 2013
| 
| {{success|'''Operational'''}}
|-

| [[Gravity and Extreme Magnetism|GEMS]]
| SMEX-13
| {{center|—}}
| ''Scheduled for 2014''
| {{n/a}}
| Cancelled in 2012 due to expected cost overruns<ref>{{cite web |last1=Berger |first1=Brian |first2=Dan |last2=Leone |agency=Space News |url=https://www.space.com/16041-gems-spacecraft-nasa-cancellation.html |title=GEMS Spacecraft Team Appeals NASA Cancellation Decision |publisher=Space.com |date=7 June 2012 |access-date=28 April 2018}}</ref>
|-

| [[Imaging X-ray Polarimetry Explorer]] (IXPE)
| SMEX-14
| {{nowrap|Explorer-97}}
| 9 December 2021
| 
| {{success|'''Operational'''}}
|-

| [[Polarimeter to Unify the Corona and Heliosphere|PUNCH]]
| SMEX-15
| 
| 12 March 2025<ref name="nasa-lspedu">{{cite web |url=https://public.ksc.nasa.gov/lspeducation/upcoming-missions/ |title=Upcoming Missions |work=[[NASA Launch Services Program]] |date=1 July 2024 |access-date=3 August 2024}}</ref>
| 
| {{pending|Launched}}<ref name="nasa-20220803">{{cite web |last=Oxford |first=Clarence |url=https://www.spacedaily.com/reports/NASAs_PUNCH_Mission_Commences_Study_of_Solar_Wind_999.html |title=NASA's PUNCH Mission Commences Study of Solar Wind |date=13 March 2025 |access-date=19 March 2025 |work=Space Daily}} {{PD-notice}}</ref>
|-

| [[Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites|TRACERS]]
| SMEX-16
| 
| April 2025<ref>{{cite web |last=Foust |first=Jeff |url=https://spacenews.com/nasa-selects-spacex-for-rideshare-launch-of-smallsat-mission/ |title=NASA selects SpaceX for rideshare launch of smallsat mission |work=SpaceNews |date=30 September 2023 |access-date=1 October 2023 |url-status=live |archive-url=https://archive.today/20231219234720/https://spacenews.com/nasa-selects-spacex-for-rideshare-launch-of-smallsat-mission/ |archive-date=19 December 2023}}</ref>
| 
| {{pending|In development}}
|-

| [[Compton Spectrometer and Imager|COSI]]
| SMEX-17
| 
| August 2027<ref>{{cite press release |url=https://www.nasa.gov/news-release/nasa-awards-launch-services-contract-for-space-telescope-mission/ |title=NASA Awards Launch Services Contract for Space Telescope Mission |work=NASA |date=2 July 2024 |access-date=3 July 2024}} {{PD-notice}}</ref>
| 
| {{pending|In development}}
|}

<gallery>
File:SAMPEX 3.jpg|SAMPEX
File:RHESSI.jpg|RHESSI
File:IBEX spacecraft.jpg|IBEX
File:IXPE-artist-rendition.jpg|IXPE
</gallery>

=== University-Class Explorers (UNEX) ===
{| class="wikitable"
|+List of UNEX missions<ref name=":1">{{cite web |url=http://explorers.gsfc.nasa.gov/unex_mo_intern.html |title=Explorers Program |website=explorers.gsfc.nasa.gov |access-date=2016-04-08 |archive-url=https://web.archive.org/web/20160322091118/http://explorers.gsfc.nasa.gov/unex_mo_intern.html |archive-date=22 March 2016 |url-status=dead}} {{PD-notice}}</ref>
|-
! Name
! UNEX number
! Explorer<br/>number
! Launch (UTC)
! Status
|-
| [[Student Nitric Oxide Explorer|SNOE]]
| UNEX-1
| Explorer-72
| 26 February 1998
| Ended in 2000
|-
| IMEX
| UNEX-2
| {{center|—}}
| ''Scheduled for 2003''
| Cancelled before 2005 (cost)<ref name="nap">{{cite book |url=https://www.nap.edu/read/11530/chapter/8#54 |title=6 Lessons Learned from PI-Led Mission Experiences &#124; Principal-Investigator-Led Missions in the Space Sciences &#124; The National Academies Press |doi=10.17226/11530 |publisher=Nap.edu |date=2006 |isbn=978-0-309-10070-0 |access-date=28 April 2018}}</ref>

|-
| [[Cosmic Hot Interstellar Plasma Spectrometer|CHIPS]]
| UNEX-3
| Explorer-82
| 12 January 2003
| Ended in 2008
|}

=== Missions of Opportunity (MO) ===
Missions of Opportunity (MO) are investigations characterized by 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. NASA solicits proposals for Missions of Opportunity on SMEX, MIDEX and UNEX investigations.<ref>[https://explorers.gsfc.nasa.gov/missions.html Explorers Missions: Missions of Opportunity (MO)] NASA [[Goddard Space Flight Center]] (GSFC). Accessed on 18 August 2019. {{PD-notice}}</ref>

{| class="wikitable"
|+List of MO<ref name=":1" />
|-
! Name
! Launcher (mission)
! Launch (UTC)
! Status
|-
| [[HETE-2]]
| NASA (Explorer-79)
| 9 October 2000
| Ended in 2008<ref>{{cite web |url=https://heasarc.gsfc.nasa.gov/docs/hete2/hete2.html |title=The HETE-2 Satellite |publisher=NASA |access-date=28 April 2018}} {{PD-notice}}</ref>
|-
| [[INTEGRAL]]
| [[ESA]]<ref>{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=2002-048A |title=NASA - NSSDCA - Spacecraft |publisher=NASA |access-date=20 April 2018}} {{PD-notice}}</ref>
| 17 October 2002
| {{success|'''Operational'''}}
|-
| [[Suzaku (satellite)|Suzaku]] (Astro-E2)
| [[JAXA]]<ref>{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=2005-025A |title=NASA - NSSDCA - Spacecraft |publisher=NASA |date=21 March 2017 |access-date=20 April 2018}} {{PD-notice}}</ref>
| 10 July 2005
| Ended in 2015
|-
| [[TWINS]]
| [[National Reconnaissance Office|NRO]] ([[USA-184]];<ref>{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=2006-027A |title=NASA - NSSDCA - Spacecraft |publisher=NASA |access-date=2018-04-20}} {{PD-notice}}</ref><br/>[[USA-200]]<ref>{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=2008-010A |title=NASA - NSSDCA - Spacecraft |publisher=NASA |access-date=2018-04-20}} {{PD-notice}}</ref>)
| TWINS-1: 28 June 2006<br/>TWINS-2: 13 March 2008
| {{success|'''Operational'''}}
|-
| [[CINDI]]
| [[DoD]] ([[C/NOFS]])<ref>{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=2008-017A |title=NASA - NSSDCA - Spacecraft |publisher=NASA |date=2017-03-21 |access-date=2018-04-20}} {{PD-notice}}</ref>
| 16 April 2008
| Ended in 2015
|-
| [[Hitomi (satellite)|Hitomi]] (Astro-H)
| [[JAXA]]<ref>{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=2016-012A |title=NASA - NSSDCA - Spacecraft |publisher=NASA |date=2017-03-21 |access-date=2018-04-20}} {{PD-notice}}</ref>
| 17 February 2016 
| {{failure|Failed}}
|-
| [[Neutron Star Interior Composition Explorer|NICER]]
| [[ISS]] ([[SpaceX CRS-11|CRS-11]])
| 3 June 2017
| {{success|'''Operational'''}}
|-
| [[Global-scale Observations of the Limb and Disk|GOLD]]
| [[SES (company)|SES]] ([[SES-14]])
| 25 January 2018
| {{success|'''Operational'''}}
|-
| [[X-Ray Imaging and Spectroscopy Mission|XRISM]]
| [[JAXA]]
| 6 September 2023
| {{success|'''Operational'''}}
|-
| [[Atmospheric Waves Experiment|AWE]]
| [[ISS]] ([[SpaceX CRS-29|CRS-29]])
| December 2023
| {{success|'''Operational'''}}
|-
| [[GUSTO (telescope)|GUSTO]]
| [[NASA]] ([[high-altitude balloon]])
| 31 December 2023
| Ended on 26 February 2024<ref>{{cite web |last=Littleton |first=Olivia F. |url=https://www.nasa.gov/missions/scientific-balloons/nasa-scientific-balloons-ready-for-flights-over-antarctica/ |title=NASA Scientific Balloons Ready for Flights Over Antarctica |work=[[NASA]] |date=27 February 2024 |access-date=3 August 2024}}</ref>
|-
| [[Sun Radio Interferometer Space Experiment|SunRISE]]
| [[NASA]] ([[Maxar]] satellite)
| 2024
| {{pending|In development<ref>{{cite web |last=Ng |first=Joy |url=https://blogs.nasa.gov/sunspot/2021/09/09/nasas-sunrise-mission-studying-solar-particle-storms-moves-toward-launch/ |title=NASA's SunRISE Mission Studying Solar Particle Storms Moves Toward Launch |work=NASA |date=9 September 2021 |access-date=9 September 2021}} {{PD-notice}}</ref><ref>{{cite press release |last1=Hautaluoma |first1=Grey |last2=Fox |first2=Karen |url=https://www.nasa.gov/press-release/nasa-selects-mission-to-study-causes-of-giant-solar-particle-storms |title=NASA Selects Mission to Study Causes of Giant Solar Particle Storms |publisher=NASA |date=30 March 2020 |access-date=31 March 2020}} {{PD-notice}}</ref>}}
|-
| [[Electrojet Zeeman Imaging Explorer|EZIE]]
| [[NASA]], [[JHUAPL]]
| 2024
| {{pending|In development<ref>{{cite press release |url=https://www.jhuapl.edu/PressRelease/201229-NASA-selects-EZIE-heliophysics |title=Johns Hopkins APL Space Weather Mission Selected by NASA |publisher=JHUAPL |date=29 December 2020 |access-date=30 December 2020}}</ref>}}
|-
| [[Solar-C EUVST]]
| [[JAXA]]
| July 2028
| {{pending|In development<ref>{{cite press release |last1=Hautaluoma |first1=Grey |last2=Frazier |first2=Sarah |url=https://www.nasa.gov/press-release/nasa-approves-heliophysics-missions-to-explore-sun-earth-s-aurora |title=NASA Approves Heliophysics Missions to Explore Sun, Earth's Aurora |publisher=NASA |date=29 December 2020 |access-date=30 December 2020}} {{PD-notice}}</ref><ref>{{cite conference |last=Shimizu |first=Toshifumi |url=https://agu.confex.com/agu/fm23/meetingapp.cgi/Paper/1295860 |title=SH54A-03 The SOLAR-C EUVST mission: Coronal physics advanced by novel EUV spectroscopy |conference=American Geophysical Union (AGU23) |date=15 December 2023 |access-date=26 December 2023}}</ref>}}
|-
| [[Contribution to ARIEL Spectroscopy of Exoplanets|CASE]]
| [[ESA]] ([[Cosmic Vision]] [[ARIEL|M4]])
| 2029
| {{pending|In development<ref>{{cite web |last=Landau |first=Elizabeth |url=https://www.nasa.gov/feature/jpl/nasa-instrument-to-probe-planet-clouds-on-european-mission |title=NASA Instrument to Probe Planet Clouds on European Mission |publisher=NASA |date=8 November 2019 |access-date=12 November 2019}} {{PD-notice}}</ref><ref>{{Cite journal |arxiv=1906.02820 |doi=10.1088/1538-3873/ab2d54 |title=Constraining Exoplanet Metallicities and Aerosols with the Contribution to ARIEL Spectroscopy of Exoplanets (CASE) |journal=Publications of the Astronomical Society of the Pacific |volume=131 |issue=1003 |pages=094401 |year=2019 |last1=Zellem |first1=Robert T. |display-authors=et al. |bibcode=2019PASP..131i4401Z |s2cid=174801052}} {{PD-notice}}</ref>}}
|}

=== Beacon Explorers{{anchor|Beacon}} ===
Three satellites were planned in this series: [[Beacon Explorer-A]], [[Beacon Explorer-B]], [[Beacon Explorer-C]].

=== GEOS series ===
A series of three Geodetic Earth Orbiting Satellite (GEOS) were put in orbit: [[GEOS 1]], [[GEOS 2]], [[GEOS 3]].