![Pointing X-ray Eyes at our Resident Supermassive Black Hole](https://upload.wikimedia.org/wikipedia/commons/6/63/Pointing_X-ray_Eyes_at_our_Resident_Supermassive_Black_Hole.jpg)
The Explorers program is a
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
exploration program that provides flight opportunities for physics,
geophysics
Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ''geophysics'' som ...
,
heliophysics
Heliophysics (from the prefix " helio", from Attic Greek ''hḗlios'', meaning Sun, and the noun "physics": the science of matter and energy and their interactions) is the physics of the Sun and its connection with the Solar System. NASA define ...
, and
astrophysics
Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. As one of the founders of the discipline said, Astrophysics "seeks to ascertain the nature of the h ...
investigations from space. Launched in 1958,
Explorer 1
Explorer 1 was the first satellite launched by the United States in 1958 and was part of the U.S. participation in the International Geophysical Year (IGY). The mission followed the first two satellites the previous year; the Soviet Union's ...
was the first spacecraft of the United States to achieve orbit. Over 90 space missions have been launched since. Starting with
Explorer 6
Explorer 6, or S-2, was a NASA satellite, launched on 7 August 1959, at 14:24:20 GMT. It was a small, spheroidal satellite designed to study trapped radiation of various energies, galactic cosmic rays, geomagnetism, radio propagation in the ...
, it has been operated by NASA, with regular collaboration with a variety of other institutions, including many international partners.
Launchers for the Explorer program have included
Juno I
The Juno I was a four-stage American space launch vehicle, used to launch lightweight payloads into low Earth orbit. The launch vehicle was used between January 1958 to December 1959. The launch vehicle was a member of the Redstone launch veh ...
,
Juno II, various
Thor
Thor (; from non, Þórr ) is a prominent god in Germanic paganism. In Norse mythology, he is a hammer-wielding æsir, god associated with lightning, thunder, storms, sacred trees and groves in Germanic paganism and mythology, sacred groves ...
,
Scout
Scout may refer to:
Youth movement
*Scout (Scouting), a child, usually 10–18 years of age, participating in the worldwide Scouting movement
**Scouts (The Scout Association), section for 10-14 year olds in the United Kingdom
**Scouts BSA, sectio ...
,
Delta
Delta commonly refers to:
* Delta (letter) (Δ or δ), a letter of the Greek alphabet
* River delta, at a river mouth
* D ( NATO phonetic alphabet: "Delta")
* Delta Air Lines, US
* Delta variant of SARS-CoV-2 that causes COVID-19
Delta may also ...
and
Pegasus
Pegasus ( grc-gre, Πήγασος, Pḗgasos; la, Pegasus, Pegasos) is one of the best known creatures in Greek mythology. He is a winged divine stallion usually depicted as pure white in color. He was sired by Poseidon, in his role as hor ...
launch vehicles, and
Falcon 9
Falcon 9 is a partially reusable medium lift launch vehicle that can carry cargo and crew into Earth orbit, produced by American aerospace company SpaceX.
The rocket has two stages. The first (booster) stage carries the second stage and payl ...
.
The program has three classes: Medium-Class Explorers (MIDEX), Small Explorers (SMEX), and University-Class Explorers (UNEX), with select Missions of Opportunity operated with other agencies.
History
Early Explorer satellites
![Explorer1](https://upload.wikimedia.org/wikipedia/commons/7/73/Explorer1.jpg)
The Explorer program began as a
U.S. Army
The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, cl ...
proposal (
Project Orbiter) to place a "civilian"
artificial satellite
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisoto ...
into orbit during the
International Geophysical Year
The International Geophysical Year (IGY; french: Année géophysique internationale) was an international scientific project that lasted from 1 July 1957 to 31 December 1958. It marked the end of a long period during the Cold War when scientific ...
(IGY). Although that proposal was rejected in favor of the
U.S. Navy
The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage o ...
's
Project Vanguard
Project Vanguard was a program managed by the United States Navy Naval Research Laboratory (NRL), which intended to launch the first artificial satellite into low Earth orbit using a Vanguard rocket. as the launch vehicle from Cape Canaveral ...
, which made the first sub-orbital flight
Vanguard TV0
Vanguard TV-0, also called Vanguard Test Vehicle-Zero, was the first sub-orbital test flight of a Vanguard rocket as part of the Project Vanguard.
Project Vanguard was a program managed by the United States Naval Research Laboratory (NRL), and ...
in December 1956, the
Soviet Union
The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...
's launch of
Sputnik 1
Sputnik 1 (; see § Etymology) was the first artificial Earth satellite. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957 as part of the Soviet space program. It sent a radio signal back to Earth for t ...
on 4 October 1957 (and the resulting "
Sputnik crisis
The Sputnik crisis was a period of public fear and anxiety in Western nations about the perceived technological gap between the United States and Soviet Union caused by the Soviets' launch of ''Sputnik 1'', the world's first artificial satelli ...
") and the failure of the
Vanguard 1
Vanguard 1 (Harvard designation: 1958-Beta 2, COSPAR ID: 1958-005B ) is an American satellite that was the fourth artificial Earth-orbiting satellite to be successfully launched, following Sputnik 1, Sputnik 2, and Explorer 1. It was launched ...
launch attempt resulted in the Army program being funded to match the Soviet space achievements.
Explorer 1
Explorer 1 was the first satellite launched by the United States in 1958 and was part of the U.S. participation in the International Geophysical Year (IGY). The mission followed the first two satellites the previous year; the Soviet Union's ...
was launched on the Juno I on 1 February 1958, becoming the first U.S. satellite, as well as discovering the
Van Allen radiation belt.
Four follow-up satellites of the Explorer series were launched by the Juno I launch vehicle in 1958, of which
Explorer 3 and
Explorer 4 were successful, while
Explorer 2 and
Explorer 5
Explorer 5 was a United States satellite with a mass of . It was the last of the original series of Explorer satellites built, designed, and operated by the Jet Propulsion Laboratory.
Background
Explorer 5 was similar in all respects to Ex ...
failed to reach orbit.
The Juno I vehicle was replaced by the
Juno II in 1959.
Continuation of the Explorer program
![M101 combined low](https://upload.wikimedia.org/wikipedia/commons/f/f0/M101_combined_low.jpg)
With the establishment of NASA in 1958, the Explorer program was transferred to NASA from the
U.S. Army
The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, cl ...
. NASA continued to use the name for an ongoing series of relatively small space missions, typically an artificial satellite with a specific science focus.
Explorer 6
Explorer 6, or S-2, was a NASA satellite, launched on 7 August 1959, at 14:24:20 GMT. It was a small, spheroidal satellite designed to study trapped radiation of various energies, galactic cosmic rays, geomagnetism, radio propagation in the ...
in 1959 was the first scientific satellite under the project direction of NASA's
Goddard Space Flight Center
The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC empl ...
(GSFC) in
Greenbelt, Maryland
Greenbelt is a city in Prince George's County, Maryland, United States, and a suburb of Washington, D.C. At the 2020 census, the population was 24,921.
Greenbelt is the first and the largest of the three experimental and controversial New Deal ...
.
The
Interplanetary Monitoring Platform Interplanetary Monitoring Platform was a program managed by the NASA Goddard Space Flight Center in Greenbelt, Maryland, as part of the Explorers program, with the primary objectives of investigation of interplanetary plasma and the interplaneta ...
(IMP) was launched in 1963, and involved a network of eleven Explorer satellites designed to collect data on space radiation in support of the
Apollo program. The IMP program was a major step forward in spacecraft
electronics
The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...
design, as it was the first space program to use
integrated circuit
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
(IC) chips and
MOSFET
The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...
s (MOS transistors).
The IMP-A (
Explorer 18) in 1963 was the first spacecraft to use IC chips, and the IMP-D (
Explorer 33
Explorer 33, also known as IMP-D and AIMP-1, was a spacecraft in the Explorer program launched by NASA on 1 July 1966 on a mission of scientific exploration. It was the fourth satellite launched as part of the Interplanetary Monitoring Platform ...
) in 1966 was the first to use MOSFETs.
Over the following two decades, NASA has launched over 50 Explorer missions,
some in conjunction to military programs, usually of an exploratory or survey nature or had specific objectives not requiring the capabilities of a major space observatory. Explorer satellites have made many important discoveries on: Earth's
magnetosphere
In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynam ...
and the shape of its
gravity field
In physics, a gravitational field is a model used to explain the influences that a massive body extends into the space around itself, producing a force on another massive body. Thus, a gravitational field is used to explain gravitational phenome ...
; the
solar wind
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...
; properties of
micrometeoroids
A micrometeoroid is a tiny meteoroid: a small particle of rock in space, usually weighing less than a gram. A micrometeorite is such a particle that survives passage through Earth's atmosphere and reaches Earth's surface.
The term "micrometeoroid ...
raining down on the
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
; ultraviolet, cosmic and X-rays from the
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
and beyond;
ionospheric physics;
Solar plasma;
solar energetic particles
Solar energetic particles (SEP), formerly known as solar cosmic rays, are high-energy, charged particles originating in the solar atmosphere and solar wind. They consist of protons, electrons and heavy ions with energies ranging from a few ten ...
; and
atmospheric physics
Within the atmospheric sciences, atmospheric physics is the application of physics to the study of the atmosphere. Atmospheric physicists attempt to model Earth's atmosphere and the atmospheres of the other planets using fluid flow equations, che ...
. These missions have also investigated air density, radio astronomy,
geodesy
Geodesy ( ) is the Earth science of accurately measuring and understanding Earth's figure (geometric shape and size), orientation in space, and gravity. The field also incorporates studies of how these properties change over time and equivale ...
, and
gamma-ray astronomy
Gamma-ray astronomy is the astronomical observation of gamma rays,Astronomical literature generally hyphenates "gamma-ray" when used as an adjective, but uses "gamma ray" without a hyphen for the noun. the most energetic form of electromagneti ...
.
With drops in NASA's budget, Explorer missions became infrequent in the early 1980s.
SMEX, MIDEX, and Student Explorer programs
In 1988, the Small Explorer (SMEX) class was established with a focus on frequent flight opportunities for highly focused and relatively inexpensive space science missions in the disciplines of astrophysics and space physics.
The first three SMEX missions were chosen in April 1989 out of 51 candidates, and launched in 1992, 1996 and 1998
The second set of two missions were announced in September 1994 and launched in 1998 and 1999.
[
In the mid 1990s, NASA initiated the Medium-class Explorer (MIDEX) to enable more frequent flights. These are larger than SMEX missions and were to be launched aboard a new kind of medium-light class launch vehicle.][ This new launch vehicle was not developed and instead, these missions were flown on a modified ]Delta II
Delta II was an expendable launch system, originally designed and built by McDonnell Douglas. Delta II was part of the Delta rocket family and entered service in 1989. Delta II vehicles included the Delta 6000, and the two later Delta 7000 va ...
rocket. The first announcement opportunity for MIDEX was issued in March 1995, and the first launch under this new class was FUSE
Fuse or FUSE may refer to:
Devices
* Fuse (electrical), a device used in electrical systems to protect against excessive current
** Fuse (automotive), a class of fuses for vehicles
* Fuse (hydraulic), a device used in hydraulic systems to protect ...
in 1999.[
In May 1994, NASA started the Student Explorer Demonstration Initiative (STEDI) pilot program, to demonstrate that high-quality space science can be carried out with small, low-cost missions. Of the three selected missions, SNOE was launched in 1998 and TERRIERS in 1999, but the latter failed after launch. The STEDI program was terminated in 2001.][ Later, NASA established the University-Class Explorer (UNEX) program for much cheaper missions, which is regarded as a successor to STEDI.
The Explorer missions were at first managed by the Small Explorer Project Office at NASA's Goddard Space Flight Center (GSFC). In early 1999, that office was closed and with the announcement of opportunity for the third set of SMEX missions NASA converted the SMEX class so that each mission was managed by its ]principal investigator
In many countries, the term principal investigator (PI) refers to the holder of an independent grant and the lead researcher for the grant project, usually in the sciences, such as a laboratory study or a clinical trial. The phrase is also often us ...
, with oversight by the GSFC Explorer Project. The Explorer program Office at Goddard Space Flight Center, provides management of the many operational scientific exploration missions that are characterized by relatively moderate costs and small to medium-sized missions that are capable of being built, tested, and launched in a short time interval compared to larger observatories like NASA's Great Observatories
NASA's series of Great Observatories satellites are four large, powerful space-based astronomical telescopes launched between 1990 and 2003. They were built with different technology to examine specific wavelength/energy regions of the electrom ...
.
Excluding the launches, the MIDEX class has a current mission cap cost of US$250 million in 2018, with future MIDEX missions being capped at US$350 million. The cost cap for SMEX missions in 2017 was US$165 million. UNEX missions are capped at US$15 million. A sub-project called Missions of Opportunity (MO) has funded science instruments or hardware components of onboard non-NASA space missions, and have a total NASA cost cap of US$70 million.[
]
Classes
Medium-Class Explorers (MIDEX)
Small Explorers (SMEX)
The Small Explorers class was implemented in 1989 specifically to fund space exploration missions that cost no more than . The missions are managed by the Explorers Project at the Goddard Space Flight Center
The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC empl ...
(GSFC).
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 Explorer 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, with oversight by the GSFC Explorers Project.
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). In June 2019 NASA selected TRACERS and PUNCH for flight.
File:SAMPEX 3.jpg, SAMPEX
File:RHESSI.jpg, RHESSI
File:IBEX spacecraft.jpg, IBEX
File:IXPE-artist-rendition.jpg, IXPE
University-Class Explorers (UNEX)
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.
Beacon Explorers
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 #REDIRECT GEOS
{{redirect category shell, {{R from other capitalisation{{R from ambiguous page ...
.
Launched spacecraft
Explorer name numbers can be found in the NSSDC master catalog, typically assigned to each spacecraft in a mission. These numbers were not officially assigned until after 1975.
Cancelled missions
Many missions are proposed, but not selected. For example, in 2011, the Explorers Program received 22 full missions solicitations, 20 Missions of Opportunity, and 8 USPI. Sometimes mission are only partially developed but must be stopped for financial, technological, or bureaucratic reasons. Some missions failed upon reaching orbit including WIRE and TERRIERS.
Examples of missions that were not developed or cancelled were:[
*Owl 1 and 2 (cost, 1965)
*MSS A (Magnetic Storm Satellite, Explorer-A, 1970)
*CATSAT (STEDI 3) (cost)]
*IMEX (UNEX 2) (cost)
* FAME (MIDEX 4)
*SPIDR (SMEX 8) (technical, 2003)
*GEMS
Gems, or gemstones, are polished, cut stones or minerals.
Gems or GEMS may also refer to:
Arts, entertainment and media
*Gems (Aerosmith album), ''Gems'' (Aerosmith album), 1988
*Gems (Patti LaBelle album), ''Gems'' (Patti LaBelle album), 1994
*G ...
(SMEX 13)
Recent examples of conclusions of launched missions, cancelled due to budgetary constraints:
* FAST - 2009
*TRACE
Trace may refer to:
Arts and entertainment Music
* ''Trace'' (Son Volt album), 1995
* ''Trace'' (Died Pretty album), 1993
* Trace (band), a Dutch progressive rock band
* ''The Trace'' (album)
Other uses in arts and entertainment
* ''Trace'' ...
- 2010 (Solar observatory, see Solar Dynamics Observatory
The Solar Dynamics Observatory (SDO) is a NASA mission which has been observing the Sun since 2010. Launched on 11 February 2010, the observatory is part of the Living With a Star (LWS) program.
The goal of the LWS program is to develop the ...
)
* Wilkinson MAP - 2010
* WISE - 2011 (extended in 2013 as NEOWISE mission)
*RXTE
The Rossi X-ray Timing Explorer (RXTE) was a NASA satellite that observed the time variation of astronomical X-ray sources, named after physicist Bruno Rossi. The RXTE had three instruments — an All Sky Monitor, the High-Energy X-ray Timing E ...
- 2012
*Galaxy Evolution Explorer
Galaxy Evolution Explorer (GALEX or Explorer 83 or SMEX-7) was a NASA orbiting space telescope designed to observe the universe in ultraviolet wavelengths to measure the history of star formation in the universe. In addition to paving the way ...
- 2013
Launch statistics
Number of launches per decade:
See also
* Cosmic Vision
Cosmic Vision is the third campaign of space science and space exploration missions in the Science Programme of the European Space Agency (ESA). Formulated in 2005 as ''Cosmic Vision: Space Science for Europe 2015–2025'', the campaign succee ...
, a European Space Agency
, owners =
, headquarters = Paris, Île-de-France, France
, coordinates =
, spaceport = Guiana Space Centre
, seal = File:ESA emblem seal.png
, seal_size = 130px
, image = Views in the Main Control Room (1205 ...
(ESA) programme
* Cosmic Vision S-class missions, the European Space Agency equivalent to the Small Explorer program
* Discovery program
* New Frontiers program
The New Frontiers program is a series of space exploration missions being conducted by NASA with the purpose of furthering the understanding of the Solar System. The program selects medium-class missions which can provide high science returns.
...
References
External links
*
NASA Explorers Program missions page
Explorers Program Profile
b
NASA's Solar System Exploration
by Goddard Space Flight Center
The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC empl ...
SMEX-series satellites
by Colorado State University
{{DEFAULTSORT:Explorers Program
NASA programs