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Far Ultraviolet Spectroscopic Explorer


Designation 25791 / 99035A
Launch date 24 Jun 1999
Country of origin United States
Mission Scientific: Astronomy
Perigee/Apogee 800 km
Inclination 25°
Launch vehicle Delta 2 #271

FUSE will access the wavelength below 1180 Angstroms (the HST STIS cutoff) with high resolution astronomical spectroscopy in the far-ultraviolet spectral region. No long-term observatory since Copernicus (1972) has possessed this capability.

Total project cost: $171 million including $120 million for the satellite. Funded by NASA. French and Canadian space agency share observation time. French CNES paid 6 million EUR.

On 10 Dec 2001 the satellite went into safe mode when the second of 4 reaction wheels stopped. In Feb 2002, partial usability was restored with the use of the magnetic torquer. Full operations were restored in March 2002.

In July 2003 we learn that the gyroscopes are ageing and that software to operate in gyroless mode was uploaded in April 2003. In this mode, the science data is to remain the same quality.

On 27 Dec 2004 the third reaction wheel stopped. The satellite went into safe mode. Observations resumed in November 2005 and were back to original quality in Jan 2006. The control system has been modified again to use magnetic control on two axes, which provides a tenuous but acceptable level of control.

End of life

Out of service Jul 2007
Cause Last reaction wheel failed

External resources


sat-index articles

Technical data


Prime contractor OSC
Mass at launch 1360 kg
Mass in orbit  
Dimension 1.2 x 1.8 x 5.5 m
Solar array  
DC power  
Design lifetime 3 years

Carries a telescope with 4 mirrors. It explores in the 912 to 1187 angstrom range. The instrument is provided by the John Hopkins University.

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