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Explorers

The mission of the Explorers Program is to provide frequent flight opportunities for world-class scientific investigations from space utilizing innovative, streamlined and efficient management approaches within the heliophysics and astrophysics science areas. This program is managed by the Heliophysics Division and solicits missions for both Heliophysics and Astrophysics. Explorers are opportunities for innovative science and fill the scientific gaps between the larger missions.

The program seeks to enhance public awareness of, and appreciation for, space science and to incorporate educational and public outreach activities as integral parts of space science investigations.

The Explorer program enables the definition, development and implementation of mission concepts through a variety of modes to meet the need of the scientific community and the NASA space science enterprise.

The Explorer Program Office at Goddard Space Flight Center in Greenbelt, MD, 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.

Missions listed below were competitively selected under the Explorers Program.  A mission is assigned to another SMD once the mission launches and throughout the operating phase of the mission.

*Sort missions by clicking the column headers.

DivisionNameLaunch DatePhase
Heliophysics ACE
Advanced Composition Explorer (ACE) observes particles of solar, interplanetary, interstellar, and galactic origins, spanning the energy range from solar wind ions to galactic cosmic ray nuclei. This mission is part of SMD's Explorers Program. This mission is part of SMD's ...
19970825 August 25, 1997 3Operating
Heliophysics AIM
Aeronomy of Ice in the Mesosphere (AIM) is a mission to determine the causes of the highest altitude clouds in the Earth's atmosphere. The number of clouds in the middle atmosphere (mesosphere) over the Earth's poles has been increasing over ...
20070425 April 25, 2007 3Operating
Astrophysics ASTRO-H
ASTRO-H is a powerful orbiting observatory being developed by the Japan Aerospace Exploration Agency (JAXA) for studying extremely energetic processes in the universe. NASA and the JAXA/Institute of Space and Astronautical Science have teamed up to develop a high resolution ...
20150215 2015 2Development
Heliophysics CINDI/CNOFS
The Coupled Ion-Neutral Dynamics Investigations (CINDI) is a mission to understand the dynamics of the Earth's ionosphere. CINDI will provide two instruments for the Communication/Navigation Outage Forecast System (C/NOFS) satellite, a project of the United States Air Force. This mission ...
20080416 April 16, 2008 3Operating
Heliophysics FAST
Fast Auroral Snapshot Explorer (FAST) studies the detailed plasma physics of the Earth's auroral regions. Ground support campaigns coordinate satellite measurements with ground observations of the Aurora Borealis, commonly referred to as the Northern Lights. The science instruments on board ...
19960821 August 21, 1996 4Past
Astrophysics FUSE
Far Ultraviolet Spectroscopic Explorer (FUSE) studied the far ultraviolet portion of the electromagnetic spectrum from high orbit. This range provided an opportunity to answer important questions about many types of astrophysical objects, such as the nuclear regions of active galaxies ...
19990624 June 24, 1999 4Past
Astrophysics GALEX
GALEX explored the origin and evolution of galaxies and the origins of stars and heavy elements. It also conducted an all-sky ultraviolet survey.
20030428 April 28, 2003 4Past
Astrophysics GEMS
GEMS was not confirmed to move into development. GEMS would have used an X-ray telescope to measure the polarization of the X-rays coming from the vicinity of compact objects in the universe.
14Studied
Astrophysics HETE-1
The prime objective of the HETE spacecraft was to carry out the first multiwavelength study of gamma-ray bursts with Ultraviolet, X-ray and gamma ray instruments. A unique feature of the mission was its capability to localize bursts with several arc-second ...
19961104 November 04, 1996 4Past
Astrophysics HETE-2
HETE-2 was a small scientific satellite designed to detect and localize gamma-ray bursts.
20001009 October 09, 2000 4Past
Heliophysics IBEX
IBEX will be the first mission designed to detect the edge of the Solar System. As the solar wind from the sun flows out beyond Pluto, it collides with the material between the stars, forming a shock front. This mission ...
20081019 October 19, 2008 3Operating
Heliophysics IRIS
The primary goal of the Interface Region Imaging Spectrograph (IRIS) explorer is to understand how the solar atmosphere is energized. The IRIS investigation combines advanced numerical modeling with a high resolution UV imaging spectrograph.
20130401 April 2013 2Development
Astrophysics NuSTAR
The Nuclear Spectroscopic Telescope Array is a pathfinder mission that will open the high energy X-ray sky for sensitive study for the first time. This mission is part of SMD's Astrophysics Explorers program.
20120613 June 13, 2012 3Operating
Heliophysics RHESSI
Reuven Ramaty High Energy Solar Spectroscope Imager (RHESSI) studies solar flares in X-rays and gamma-rays. It explores the basic physics of particle acceleration and explosive energy release in these energetic events in the Sun's atmosphere. This is accomplished by imaging ...
20020205 February 05, 2002 3Operating
Astrophysics RXTE
Rossi X-ray Timing Explorer studied variability over time in the emission of X-ray sources, with moderate spectral resolution. This time behavior is a source of important information about processes and structures in white-dwarf stars, X-ray binaries, neutron stars, pulsars and ...
19951230 December 30, 1995 4Past
Astrophysics Suzaku (Astro-E2)
Suzaku (formerly Astro-E2) provides powerful tools to use the Universe as a laboratory for unraveling complex, high-energy processes and the behavior of matter under extreme conditions. This mission is part of SMD's Astrophysics Explorers program. This mission was awarded via ...
20050710 July 10, 2005 3Operating
Astrophysics SWAS
The Submillimeter Wave Astronomy Satellite (SWAS) instrument was a submillimeter wave telescope that incorporated dual heterodyne radiometers and an acousto-optical spectrometer to investigate the composition of dense interstellar clouds.
19981206 December 06, 1998 4Past
Astrophysics Swift
Swift Gamma Ray Burst Explorer is a three-telescope space observatory for studying the position, brightness, and physical properties of gamma ray bursts. Although gamma ray bursts are the largest known explosions in the Universe, outshining the rest of the Universe ...
20041120 November 20, 2004 3Operating
Heliophysics THEMIS
Time History of Events and Macroscale Interactions during Substorms (THEMIS) is a study of the onset of magnetic storms within the tail of the Earth's magnetosphere. THEMIS will fly five microsatellite probes through different regions of the magnetosphere and observe ...
20070217 February 17, 2007 3Operating
Heliophysics TRACE
Transition Region and Coronal Explorer (TRACE) observed the effects of the emergence of magnetic flux from deep inside the Sun to the outer corona with high spatial and temporal resolution. This mission was part of SMD's Heliophysics Explorers program. This ...
19980401 April 01, 1998 4Past
Heliophysics TWINS A & B
TWINS will provide stereo imaging of the Earth's magnetosphere, the region surrounding the planet controlled by its magnetic field and containing the Van Allen radiation belts and other energetic charged particles. This mission is part of SMD's Explorers Program. This ...
20080313 March 13, 2008 3Operating
Astrophysics WISE
WISE spent over a year imaging the entire sky in the infrared. The NEOWISE Survey surveyed small bodies, asteroids, and comets in our solar system.
20091214 December 14, 2009 4Past
Astrophysics WMAP
WMAP addressed fundamental questions in cosmology: What is the geometry of the Universe? How did structures, such as galaxies and galaxy clusters, that we see in today’s sky come about? How old is the Universe, and what are its constituents?
20010630 June 30, 2001 4Past