GALEX

GALEX
Name	GALEX
Mission type	Space telescope
Operator	NASA
Launch date	28 April 2003
Launch vehicle	Space Shuttle Columbia
Launch site	Kennedy Space Center
Manufacturer	Jet Propulsion Laboratory; California Institute of Technology
Instruments	Ultraviolet imaging spectrograph
Wavelength	Far-ultraviolet; Near-ultraviolet
Orbit	Low Earth orbit

GALEX The Galaxy Evolution Explorer was a NASA ultraviolet space observatory that conducted a comprehensive sky survey in the far-ultraviolet and near-ultraviolet bands. Launched from Kennedy Space Center aboard Space Shuttle Columbia, the mission provided imaging and spectroscopic data that informed studies of galaxy formation, star formation rates, and cosmological evolution. GALEX operated alongside observatories such as Hubble Space Telescope, Spitzer Space Telescope, Chandra X-ray Observatory, XMM-Newton, and International Ultraviolet Explorer to create multiwavelength views used by research teams at institutions including California Institute of Technology, Jet Propulsion Laboratory, Massachusetts Institute of Technology, Harvard–Smithsonian Center for Astrophysics, and Space Telescope Science Institute.

Overview

GALEX was designed to map ultraviolet emission across large portions of the sky to probe stellar populations and galaxy evolution over cosmic time. Its survey strategy complemented deep-field programs of Hubble Deep Field, wide-area surveys like the Sloan Digital Sky Survey, and infrared campaigns such as the Two Micron All Sky Survey and Wide-field Infrared Survey Explorer. The mission fostered contributions from research groups at University of California, Berkeley, Johns Hopkins University, Max Planck Institute for Astronomy, and additional teams in Europe, Australia, and Japan. GALEX observations were pivotal for linking ultraviolet diagnostics to studies carried out with the Very Large Telescope, Keck Observatory, Subaru Telescope, and the Atacama Large Millimeter/submillimeter Array.

Mission and Instruments

The GALEX payload featured a 50-centimeter modified Ritchey–Chrétien telescope feeding a dichroic beam splitter and two photon-counting microchannel plate detectors covering the far-ultraviolet and near-ultraviolet bands. The instrument suite delivered imaging with a 1.2-degree diameter field of view and a slitless spectroscopic mode for low-resolution spectra. Instrument calibration and performance were benchmarked against standards observed by International Ultraviolet Explorer and reference stars catalogued by Hipparcos and Tycho. The payload was built and tested by teams at Jet Propulsion Laboratory and Caltech, with detector technology informed by prior work at NASA Goddard Space Flight Center and facilities at Ball Aerospace.

Science Goals and Discoveries

GALEX aimed to quantify the history of star formation from the local universe to redshifts where ultraviolet light shifted into the observed bands, addressing questions posed by projects such as the Hubble Ultra Deep Field and the Cosmic Evolution Survey. Major scientific outcomes included ultraviolet luminosity functions for galaxies, measurements of star-formation rate density evolution, and detection of extended ultraviolet disks in nearby spirals first highlighted in observations of systems like M101 and M83. GALEX contributed to studies of galaxy mergers observed by Arp Atlas of Peculiar Galaxies, provided ultraviolet counterparts to Sloan Digital Sky Survey sources, and enabled census work connecting ultraviolet emission to dust attenuation laws calibrated against IRAS and Spitzer infrared data. The mission also advanced knowledge of stellar populations in globular clusters such as Omega Centauri, ultraviolet-bright quasars catalogued in the Sloan Digital Sky Survey Quasar Catalog, and starburst galaxies examined in the context of the Kennicutt–Schmidt law.

Data Processing and Archive

Data reduction pipelines developed for GALEX transformed raw photon-counting events into calibrated images, source catalogs, and slitless spectra. The processing architecture borrowed algorithms from pipelines used by Hubble Space Telescope and the Sloan Digital Sky Survey, incorporating astrometric solutions tied to the Two Micron All Sky Survey and photometric cross-calibration with standards from International Ultraviolet Explorer. GALEX produced several major data releases, including source catalogs used extensively by teams at European Southern Observatory, National Optical-Infrared Astronomy Research Laboratory, and university groups. The mission archive interfaced with virtual observatory standards promoted by organizations such as the International Virtual Observatory Alliance and was accessed via data centers including the Mikulski Archive for Space Telescopes and NASA science archives.

Operations and Mission History

Following its deployment during STS-93, the observatory entered a near-circular low Earth orbit and commenced survey operations. The primary mission spanned several years with extensions approved by NASA, mirroring operational decision processes also seen in missions like Hubble Space Telescope servicing and Chandra operations. The observatory executed all-sky imaging, medium-deep surveys, and targeted deep fields coordinated with programs on Hubble and ground-based facilities. As detector sensitivity evolved and attitude-control issues arose later in the mission, operations teams at Jet Propulsion Laboratory and California Institute of Technology adjusted observing modes until mission termination. GALEX data continued to be reprocessed and used in legacy science long after data acquisition ceased.

Collaborations and Legacy

GALEX established a legacy of multiwavelength synergy with observatories including Hubble Space Telescope, Spitzer Space Telescope, Chandra X-ray Observatory, Sloan Digital Sky Survey, and facilities at European Southern Observatory. The mission trained generations of researchers at institutions such as California Institute of Technology, Harvard–Smithsonian Center for Astrophysics, University of California, Berkeley, and international partners in data analysis, survey design, and ultraviolet astrophysics. GALEX catalogs remain integrated into virtual observatory services and continue to support research on galaxy evolution, star formation laws, and transient ultraviolet phenomena studied in coordination with observatories like Swift and surveys such as the Zwicky Transient Facility. Its scientific outputs influenced proposals for future ultraviolet missions and instrumentation developed by groups at NASA Goddard Space Flight Center, ESA, and universities worldwide.

Category:Ultraviolet telescopes Category:NASA space telescopes Category:Spacecraft launched in 2003