GALEX

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Galaxy Evolution Explorer
GALEX spacecraft model.png
GALEX spacecraft
NamesExplorer-83
SMEX-7
Mission type Ultraviolet astronomy
Operator NASA  / JPL (2003-2012)
Caltech (2012-2013)
COSPAR ID 2003-017A OOjs UI icon edit-ltr-progressive.svg
SATCAT no. 27783
Website https://www.galex.caltech.edu/
Mission duration29 months (planned) [1]
10 years, 2 months (achieved) [2] [3]
Spacecraft properties
SpacecraftExplorer LXXXIII
Spacecraft typeGalaxy Evolution Explorer
Bus Orbview 4
Manufacturer Orbital Sciences Corporation
Launch mass280 kg (620 lb)
Dimensions1 × 2.5 m (3 ft 3 in × 8 ft 2 in)
Power290 watts
Start of mission
Launch date28 April 2003, 11:59:57 UTC [1]
Rocket Pegasus XL (F33)
Launch site Cape Canaveral, Stargazer
Contractor Orbital Sciences Corporation
Entered service28 May 2003 [2]
End of mission
Deactivated28 June 2013, 19:09 UTC [3]
Last contact28 June 2013
Decay date2068 (planned)
Orbital parameters
Reference system Geocentric orbit [4]
Regime Low Earth orbit
Perigee altitude 691 km (429 mi)
Apogee altitude 697 km (433 mi)
Inclination 29.00°
Period 98.60 minutes
Revolution no.85423
Main telescope
Type Ritchey–Chrétien [1]
Diameter50 cm (20 in)
Focal lengthf/6.0
Wavelengths135–280 nm (Ultraviolet)
Instruments
Ultraviolet telescope
Explorer program
  CHIPS (Explorer 82)
Neil Gehrels Swift Observatory (Explorer 84) 
 

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 for future ultraviolet missions, the space telescope allowed astronomers to uncover mysteries about the early universe and how it evolved, as well as better characterize phenomena like black holes and dark matter. The mission was extended three times over a period of 10 years before it was decommissioned in June 2013. GALEX was launched on 28 April 2003 and decommissioned in June 2013. [1]

Contents

Spacecraft

The spacecraft was three-axis stabilized, with power coming from four fixed solar panels. The satellite bus is from Orbital Sciences Corporation based on OrbView 4. The telescope was a 50 cm (20 in) Modified Ritchey–Chrétien with a rotating grism. GALEX used the first ever UV light dichroic beam-splitter flown in space to direct photons to the Near UV (175–280 nanometers) and Far UV (135–174 nanometers) microchannel plate detectors. Each of the two detectors has a 65 mm (2.6 in) diameter. The target orbit is 670 km (420 mi) circular and inclined at 29.00° to the equator.

Launch

An air launched Pegasus launch vehicle, launched on 28 April 2003 at 11:59:57 UTC, placed the craft into a nearly circular orbit at an altitude of 697 km (433 mi) and an orbital inclination to the Earth's equator of 29.00°. [4]

Mission

The Galaxy Evolution Explorer (GALEX) which explored the origin and evolution of galaxies, and the origins of stars and heavy elements over the redshift range of Z between 0 and 2. GALEX conducted an all-sky imaging survey, a deep imaging survey, and a survey of 200 galaxies nearest to the Milky Way galaxy. As well, GALEX performed three spectroscopic surveys over the 135–300 nanometre band. GALEX had a planned 29-month mission, and is a part of the Small Explorer (SMEX) program.

The first observation was dedicated to the crew of the Space Shuttle Columbia, and was images in the constellation of Hercules taken on 21 May 2003. This region was selected because it had been directly overhead the shuttle at the time of its last contact with the NASA Mission Control Center, Houston, Texas.

After its primary mission of 29 months, observation operations were extended. In 2009, one of its detectors, which observed in far-ultraviolet light, stopped functioning. [5] Late in the mission, observations of more intense UV sources were allowed, including the Kepler field. [5]

Observation operations were extended to almost 9 years, with NASA placing it into standby mode on 7 February 2012. [6] NASA cut off financial support for operations of GALEX in early February 2011 as it was ranked lower than other projects which were seeking a limited supply of funding. The mission's life-cycle cost to NASA was US$150.6 million. The California Institute of Technology (Caltech) negotiated to transfer control of GALEX and its associated ground control equipment to the California Institute of Technology in keeping with the Stevenson-Wydler Technology Innovation Act. Under this Act, excess research equipment owned by the U.S. government can be transferred to educational institutions and non-profit organizations. [5] On 17 May 2012, GALEX operations were transferred to Caltech. [7]

On 28 June 2013, NASA decommissioned GALEX. It is expected that the spacecraft will remain in orbit until at least 2068 before it will re-enter the atmosphere. [3] [2]

Science mission

GALEX field of view compared to a full Moon GALEX Field of View.jpg
GALEX field of view compared to a full Moon

The telescope made observations in ultraviolet wavelengths to measure the history of star formation in the universe 80% of the way back to the Big Bang. Since scientists believe the Universe to be about 13.8 billion years old, the mission studied galaxies and stars across about 10 billion years of cosmic history. [8]

The spacecraft's mission was to observe hundreds of thousands of galaxies, with the goal of determining the distance of each galaxy from Earth and the rate of star formation in each galaxy. Near-UV (NUV) and Far-UV (FUV) emissions as measured by GALEX can indicate the presence of young stars, but may also originate from old stellar populations (e.g. sdB stars).

Partnering with the NASA Jet Propulsion Laboratory (JPL) on the mission were the California Institute of Technology, Orbital Sciences Corporation, University of California, Berkeley, Yonsei University, Johns Hopkins University, Columbia University, and Laboratoire d'Astrophysique de Marseille, France.

The observatory participated in GOALS with Spitzer Space Telescope, Chandra X-ray Observatory, and Hubble Space Telescope. [9] GOALS stands for Great Observatories All-sky LIRG Survey, and Luminous Infrared Galaxies were studied at the multiple wavelengths allowed by the telescopes. [9]

Science objectives

The primary objective of the Galaxy Evolution Explorer was to learn what factors trigger star formation inside galaxies; how quickly stars form, evolve and die; and how heavy chemical elements form in stars. Additional goals include: [10]

To accomplish its objectives, the Galaxy Evolution Explorer will conduct eight surveys, grouped into two broad categories – a local universe investigation and a star formation history investigation. The local universe investigation includes the following four surveys: [10]

The star formation history investigation will take information gathered by the local universe investigation and apply it to more distant galaxies by looking further back in time. It includes the following four surveys: [10]

Telescope specifications

The telescope had a 50 cm (20 in) diameter aperture primary, in a Ritchey–Chrétien telescope f/6.0 configuration. It can see light wavelengths from 135 nanometres to 280-nm, with a field of view of 1.2° wide (larger than a full Moon). It had gallium arsenide (GaAs) solar cells which supply nearly 300 watts to the spacecraft. [11]

Experiment

Ultraviolet telescope

GALEX carries a single f/6.0, Ritchey–Chrétien telescope, with a 50 cm (20 in) diameter primary, and a 22 cm (8.7 in) secondary mirror. Beam-splitters direct the Near UV (NUV) and Far UV (FUV) components to separate photoelectric detectors of diameter 6.5 cm (2.6 in). In each, the photoelectrons are multiplied by a microchannel plate, and detected by the anode grid. The grid enables determination of the exact position of electron impact, by the time delay of each pulse at the two ends. The telescope has a field of view (FoV) of 1.2°, and a resolution of five arcseconds, and enables either imaging or spectral composition of a single star/galaxy, by a rotatable wheel containing a clear window and a grism (a cross between a grating and a prism). [12]

Pre-launch images

See also

Related Research Articles

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<span class="mw-page-title-main">Hubble Deep Field</span> Multiple exposure image of deep space in the constellation Ursa Major

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<span class="mw-page-title-main">IRAS</span> Infrared space observatory

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<span class="mw-page-title-main">Spitzer Space Telescope</span> Infrared space telescope (2003–2020)

The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), is an infrared space telescope launched in 2003, that was deactivated when operations ended on 30 January 2020. Spitzer was the third space telescope dedicated to infrared astronomy, following IRAS (1983) and ISO (1995–1998). It was the first spacecraft to use an Earth-trailing orbit, later used by the Kepler planet-finder.

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<span class="mw-page-title-main">Far Ultraviolet Spectroscopic Explorer</span> NASA satellite of the Explorer program

Far Ultraviolet Spectroscopic Explorer represented the next generation, high-orbit, ultraviolet space observatory covering the wavelength range of 90.5–119.5 nanometre (nm) of the NASA operated by the Johns Hopkins University Applied Physics Laboratory. FUSE was launched on a Delta II launch vehicle on 24 June 1999, at 15:44:00 UTC, as a part of NASA's Origins Program. FUSE detected light in the far ultraviolet portion of the electromagnetic spectrum, which is mostly unobservable by other telescopes. Its primary mission was to characterize universal deuterium in an effort to learn about the stellar processing times of deuterium left over from the Big Bang. FUSE resides in a low Earth orbit, approximately 760 km (470 mi) in altitude, with an inclination of 24.98° and a 99.80 minutes orbital period. Its Explorer program designation is Explorer 77.

<span class="mw-page-title-main">International Ultraviolet Explorer</span> Astronomical observatory satellite

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<span class="mw-page-title-main">Wide-field Infrared Survey Explorer</span> NASA satellite of the Explorer program

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<span class="mw-page-title-main">Extreme Ultraviolet Explorer</span> NASA satellite of the Explorer program

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<i>Euclid</i> (spacecraft) European visible and near-infrared space observatory

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<span class="mw-page-title-main">Large Ultraviolet Optical Infrared Surveyor</span> Proposed NASA space telescope

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<span class="mw-page-title-main">Origins Space Telescope</span> Proposed far-infrared space observatory to study the early Universe

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Transient High-Energy Sky and Early Universe Surveyor (THESEUS) is a space telescope mission proposal by the European Space Agency that would study gamma-ray bursts and X-rays for investigating the early universe. If developed, the mission would investigate star formation rates and metallicity evolution, as well as studying the sources and physics of reionization.

<span class="mw-page-title-main">UVEX</span> NASA satellite of the Explorer program

The Ultraviolet Explorer (UVEX) is an upcoming wide-field ultraviolet space telescope from NASA scheduled to launch in 2030. UVEX will build off of previous ultraviolet space telescopes, specifically GALEX, conducting surveys of the entire sky in both near- and far-ultraviolet light. UVEX will study the evolution of low-metallicity stars and how they affect the evolution of low-metallicity and low-mass galaxies. The probe can also be used for quick-turnaround observation of cosmic events, such as merging stars. UVEX's data will be able to complement other all-sky survey programs in different wavelengths of light, notably those by the Vera C. Rubin Observatory, the Roman Space Telescope, and the Euclid telescope. Compared to earlier ultraviolet space telescopes, UVEX will feature more capable instrumentation and a larger mirror, enabling it to obtain higher-resolution data and observe fainter objects.

References

  1. 1 2 3 4 "Display: GALEX (Explorer 83) 2003-017A". NASA. 28 October 2021. Retrieved 3 December 2021.PD-icon.svg This article incorporates text from this source, which is in the public domain .
  2. 1 2 3 "Mission to Universe: Galaxy Evolution Explorer". NASA. Retrieved 3 December 2021.PD-icon.svg This article incorporates text from this source, which is in the public domain .
  3. 1 2 3 "NASA Decommissions Its Galaxy Hunter Spacecraft". CalTech. 28 June 2013. Retrieved 3 December 2021.
  4. 1 2 "Trajectory: GALEX (Explorer 83) 2003-017A". NASA. 28 October 2021. Retrieved 3 December 2021.PD-icon.svg This article incorporates text from this source, which is in the public domain .
  5. 1 2 3 Stephen Clark (10 February 2012). "NASA, Caltech mull over unique satellite donation". Spaceflight Now. Retrieved 8 June 2021.
  6. GALEX Mission Comes to an End 7 February 2012 Universe Today
  7. "NASA lends ultraviolet space telescope to Caltech". Phys.org. 17 June 2012. Retrieved 3 December 2021.
  8. "Cosmic Detectives". European Space Agency (ESA). 2 April 2013. Retrieved 26 April 2013.
  9. 1 2 GOALS: The Great Observatories All-Sky LIRG Survey
  10. 1 2 3 "Galaxy Evolution Explorer Launch" (PDF). NASA. April 2003. Retrieved 3 December 2021.PD-icon.svg This article incorporates text from this source, which is in the public domain .
  11. Encyclopedia Astronautica – GALEX Archived 2008-07-06 at the Wayback Machine
  12. "Experiment: Ultraviolet Telescope". NASA. 28 October 2021. Retrieved 3 December 2021.PD-icon.svg This article incorporates text from this source, which is in the public domain .