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Galaxy Evolution Explorer, also called SMEX 7


Designation 27783 / 03017A
Launch date 28 Apr 2003
Country of origin United States
Mission Scientific: UV astronomy
Perigee/Apogee 690 km
Inclination 28.5°
Period 98.6 min
Launch vehicle Pegasus XL #34
Launch site Cape Canaveral

Cost: $16.5 million. Program managed by Caltech

Galex was a Space Ultraviolet Small Explorer mission that mapped the global history and probed the causes of star formation over the redshift range 0<z<2, 80% of the life of the Universe, the period over which galaxies have evolved dramatically, and the time that most stars, elements, and galaxy disks had their origins.

The mission's science highlights include the discovery of a gigantic comet-like tail behind a speeding star, rings of new stars around old galaxies, and "teenager" galaxies, which help to explain how galaxies evolve. The observatory also helped confirm the existence of the mysterious substance or force known as dark energy, and even caught a black hole devouring a star.

End of life

Out of service 28 Jun 2013
Cause Decommissionned by NASA

External resources

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Technical data


Prime contractor OSC
Platform Leostar-2
Mass at launch 313 kg
Mass in orbit  
Solar array  
Stabilization 3-axis
DC power 290 W
Design lifetime 28 months

GALEX uses the space ultraviolet to simultaneously measure redshift (using metal lines and the Lyman break), extinction (using the UV spectral slope), and star formation rate (using the UV luminosity which is proportional to the instantaneous star formation rate). Slitless grism spectroscopy is highly efficient, providing 100,000 galaxy spectra in one year. The 50 cm telescope, operating from 1300-3000 Å, is simple, cost-effective, efficient, and exploits MCP detectors and optical coatings which are flight-proven and cutting-edge to attain the deep, broad-band imaging and spectroscopy required.

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