Gravity and Extreme Magnetism Small Explorer (GEMS or SMEX-13) mission was 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 ...
space observatory mission.
The main scientific goal of GEMS was to be the first mission to systematically measure the
polarization of
X-ray sources. GEMS would have provided data to help scientists study the shape of
spacetime
In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why differen ...
that has been distorted by a spinning
black hole
A black hole is a region of spacetime where gravitation, gravity is so strong that nothing, including light or other Electromagnetic radiation, electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts t ...
's gravity and the structure and effects of the
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
s around
neutron star
A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. white ...
s. It was cancelled by NASA in June 2012 for potential cost overruns due to delays in developing the technology and never moved into the development phase.
GEMS was managed by the NASA
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 project was an
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 ...
program reporting to NASA's
Science Mission Directorate
The Science Mission Directorate (SMD) of the National Aeronautics and Space Administration (NASA) engages the United States’ science community, sponsors scientific research, and develops and deploys satellites and probes in collaboration with NAS ...
(SMD) in
Washington, D.C.
)
, image_skyline =
, image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan, ...
[ ]
Cancelled missions can be reinstated - for example,
NuSTAR
NuSTAR (Nuclear Spectroscopic Telescope Array, also named Explorer 93 and SMEX-11) is a NASA space-based X-ray telescope that uses a conical approximation to a Wolter telescope to focus high energy X-rays from astrophysical sources, especiall ...
was cancelled in 2006, but reinstated a year later and launched in June 2012.
However, NuSTAR was not cancelled due to project overruns, but rather due to changes in the overall NASA budget, so the circumstances for cancellation were very different. Small missions of the Explorer program offer much flexibility and launch opportunities, and the lessons learned can be applied to the same missions goals, but on a different mission (compare, for instance,
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 ...
to
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 ...
). Several years later two new X-ray polarimetry missions won a NASA award to develop X-ray polarimetry missions.
[ ] NASA's
IXPE
Imaging X-ray Polarimetry Explorer, commonly known as IXPE or SMEX-14, is a space observatory with three identical telescopes designed to measure the polarization of cosmic X-rays of black holes, neutron stars, and pulsars. The observatory ...
X-ray polarimetry telescope was launched in 2021; its X-ray observational capabilities and mission objectives are very similar to those (proposed) of the GEMS.
Launch
The spacecraft would have been launched in July 2014 on a nine-month mission with a possible 15-month extension for a guest observer phase;
but the mission was terminated at the Confirmation Review stage on 10 May 2012 due to expected cost overruns.
Mission
![GEMS MoviePoster](https://upload.wikimedia.org/wikipedia/commons/7/70/GEMS_MoviePoster.jpg)
The GEMS
X-ray telescope
An X-ray telescope (XRT) is a telescope that is designed to observe remote objects in the X-ray spectrum. In order to get above the Earth's atmosphere, which is opaque to X-rays, X-ray telescopes must be mounted on high altitude rockets, balloon ...
was designed to indirectly measure the regions of distorted space around spinning black holes through a measurement of the polarization of X-rays emitted. It would have also probed the structure and effects of the
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
s around
magnetar
A magnetar is a type of neutron star with an extremely powerful magnetic field (∼109 to 1011 T, ∼1013 to 1015 G). The magnetic-field decay powers the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays.War ...
s and other star remnants with magnetic fields trillions of times stronger than Earth's.
GEMS could reveal:
* How spinning black holes affect space-time and matter as it is drawn in and compressed by strong gravitational fields
* What happens in the very strong magnetic fields near pulsars and magnetars
* How cosmic rays are accelerated by shocks in supernova remnants
[ ]
Current missions cannot do this because the required
angular resolution
Angular resolution describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object, thereby making it a major determinant of image resolution. ...
is limited and magnetic fields are invisible.
The detector in GEMS would have been a small chamber filled with gas. When an X-ray is absorbed in the gas, an
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no kn ...
carries off most of the energy, and starts out in a direction related to the polarization direction of the X-ray. This electron loses energy by ionizing the gas; the instrument measures the direction of the ionization track, and thereby the polarization of the X-ray. The GEMS detector readout was to employ a time projection chamber to image the track. The GEMS instrument was planned to be about 100 times more sensitive than previous X-ray polarization experiments.
Cancellation
Mission costs were capped at US$105 million (in Fiscal Year 2008 dollars), excluding the launch vehicle,
but an independent confirmation review board at NASA claimed it would grow to an estimated US$150 million, leading to cancellation of the mission. The cancellation of GEMS marked the end of a multi-year-long binge of cancellations and attempted cancellations of current and future missions: it was at the time the last funded future U.S. space telescope besides
James Webb Space Telescope
The James Webb Space Telescope (JWST) is a space telescope which conducts infrared astronomy. As the largest optical telescope in space, its high resolution and sensitivity allow it to view objects too old, distant, or faint for the Hubble Spa ...
(JWST). The cancellation of GEMS may have jeopardized the
Pegasus XL
Pegasus is an air-launched launch vehicle developed by Orbital Sciences Corporation (OSC) and now built and launched by Northrop Grumman. Capable of carrying small payloads of up to into low Earth orbit, Pegasus first flew in 1990 and remai ...
launcher. (The Pegasus XL has successfully launched other small explorer missions)
Project status
GEMS was one of six Small Explorer missions selected in May 2008 for the
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 ...
Small Explorer
The Explorers program is a NASA exploration program that provides flight opportunities for physics, geophysics, heliophysics, and astrophysics investigations from space. Launched in 1958, Explorer 1 was the first spacecraft of the United Stat ...
(SMEX) Program Phase A study.
[ ] In June 2009, GEMS was chosen to be the second of these missions to go forward into Phase B, starting in October 2010 for a launch in April 2014.
[ ]
The project completed and successfully passed the
Systems Requirements Review (SRR) in December 2010.
GEMS did not pass a confirmation review conducted on 10 May 2012, which effectively cancelled the project. The project team intended to appeal the cancellation.
On 7 June 2012, NASA officially announced the cancellation of the GEMS project. The mission was supposed to launch in July 2014 to study black holes and neutron stars, but external reviews found the project would likely exceed its budget. GEMS was supposed to hold at US$119 million, not counting the launch vehicle. NASA's astrophysics director, Paul Hertz, says the technology needed for the instrument took longer to develop than expected, and that drove up the price.
NASA continued studying X-ray polarimetry missions in 2015 for future Explorer program observatories.
Project and Science Team
![376203main_GEMS_labeled](https://upload.wikimedia.org/wikipedia/commons/b/b7/376203main_GEMS_labeled.jpg)
The GEMS
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 ...
was Dr
Jean H. Swank, 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 ...
,
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 ...
.
Project Team
* GSFC was responsible for the GEMS instrument, system engineering, spacecraft contract, and the overall program management.
*
Ames Research Center
The Ames Research Center (ARC), also known as NASA Ames, is a major NASA research center at Moffett Federal Airfield in California's Silicon Valley. It was founded in 1939 as the second National Advisory Committee for Aeronautics (NACA) laborat ...
would have provided co-investigators and performed the Education and Public Outreach (EPO) support.
* The satellite would have been built by
Orbital Sciences Corporation
Orbital Sciences Corporation (commonly referred to as Orbital) was an American company specializing in the design, manufacture, and launch of small- and medium- class space and launch vehicle systems for commercial, military and other governmen ...
using its
LEOStar-2 satellite bus
A satellite bus (or spacecraft bus) is the main body and structural component of a satellite or spacecraft, in which the payload and all scientific instruments are held.
Bus-derived satellites are opposed to specially produced satellites. Bus-d ...
design, and would also conduct mission operations, under a
US$
The United States dollar (symbol: $; code: USD; also abbreviated US$ or U.S. Dollar, to distinguish it from other dollar-denominated currencies; referred to as the dollar, U.S. dollar, American dollar, or colloquially buck) is the official ...
40 million contract.
*
Alliant Techsystems
Alliant Techsystems Inc. (ATK) was an American aerospace, defense, and sporting goods company with its headquarters in Arlington County, Virginia, in the United States. The company operated in 22 states, Puerto Rico, and other countries. ATK's ...
(ATK) would build a deployable boom to place the X-ray mirrors at the proper distance from the detectors or polarimeters.
*
University of Iowa
The University of Iowa (UI, U of I, UIowa, or simply Iowa) is a public university, public research university in Iowa City, Iowa, United States. Founded in 1847, it is the oldest and largest university in the state. The University of Iowa is org ...
would have provided instrument calibration assistance and would have had students prepare a small instrument that could be part of the mission.
Science Team
Co-investigators
*
NASA 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 ...
*
NASA Ames Research Center
The Ames Research Center (ARC), also known as NASA Ames, is a major NASA research center at Moffett Federal Airfield in California's Silicon Valley. It was founded in 1939 as the second National Advisory Committee for Aeronautics (NACA) laborat ...
*
University of Iowa
The University of Iowa (UI, U of I, UIowa, or simply Iowa) is a public university, public research university in Iowa City, Iowa, United States. Founded in 1847, it is the oldest and largest university in the state. The University of Iowa is org ...
*
Massachusetts Institute of Technology
The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the ...
(MIT)
Science collaborators
Other GEMS collaborators are from universities include:
[ ][GEMS home page, accessed 2009-08-14 ]
*
Johns Hopkins University
Johns Hopkins University (Johns Hopkins, Hopkins, or JHU) is a private university, private research university in Baltimore, Maryland. Founded in 1876, Johns Hopkins is the oldest research university in the United States and in the western hem ...
*
Cornell University
Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to teach an ...
*
Rice University
William Marsh Rice University (Rice University) is a Private university, private research university in Houston, Houston, Texas. It is on a 300-acre campus near the Houston Museum District and adjacent to the Texas Medical Center. Rice is ranke ...
*
University of Oulu
The University of Oulu ( fi, Oulun yliopisto) is one of the largest universities in Finland, located in the city of Oulu. It was founded on July 8, 1958. The university has around 13,000 students and 2,900 staff. 21 International Master's P ...
(
Finland
Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...
)
*
North Carolina State University
North Carolina State University (NC State) is a public land-grant research university in Raleigh, North Carolina. Founded in 1887 and part of the University of North Carolina system, it is the largest university in the Carolinas. The universit ...
*
Washington University
Washington University in St. Louis (WashU or WUSTL) is a private research university with its main campus in St. Louis County, and Clayton, Missouri. Founded in 1853, the university is named after George Washington. Washington University is r ...
See also
*
Explorer program
The Explorers program is a NASA exploration program that provides flight opportunities for physics, geophysics, heliophysics, and astrophysics investigations from space. Launched in 1958, Explorer 1 was the first spacecraft of the United Stat ...
References
External links
NASA Project HomepageNASA Science HomepageGEMS Homepage at Orbital Sciences
{{Space observatories
NASA programs
Explorers Program
Space telescopes
X-ray telescopes
Proposed NASA space probes