Far Ultraviolet Spectroscopic Explorer

The Far Ultraviolet Spectroscopic Explorer (FUSE) is a space-based telescope operated by the Johns Hopkins University Applied Physics Laboratory. FUSE was launched on a Delta II rocket on 24 June 1999, as a part of NASA's Origins program. FUSE detected light in the far ultraviolet portion of the electromagnetic spectrum, between 90.5–119.5 nanometres, 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 (410 nmi) in altitude, with an inclination of 25 degrees and just less than a 100-minute orbital period. Its Explorer designation is Explorer 77.

Far Ultraviolet Spectroscopic Explorer

FUSE in a pre-launch cleanroom
Names	Explorer 77 MIDEX-0
Mission type	Ultraviolet astronomy
Operator	NASA / JHUAPL
COSPAR ID	1999-035A
SATCAT no.	25791
Website	http://fuse.pha.jhu.edu/
Mission duration	Planned: 3 years[1] Final: 8 years, 3 months, 23 days[2]
Spacecraft properties
Manufacturer	Orbital Sciences / JHUAPL[3]
Launch mass	1,360 kg (3,000 lb)[4]
Dimensions	5.3 × 1.9 m (17.4 × 6.2 ft)[4]
Power	Average: 520 watts Peak: 645 watts[4]
Start of mission
Launch date	24 June 1999, 15:44 UTC[5]
Rocket	Delta II 7320-10[5]
Launch site	Cape Canaveral AFS SLC-17A
End of mission
Disposal	Decommissioned
Deactivated	18 October 2007
Orbital parameters
Reference system	Geocentric
Regime	Low Earth
Semi-major axis	7,127.8 km (4,429.0 mi)
Eccentricity	0.0010062
Perigee altitude	742.5 km (461.4 mi)
Apogee altitude	756.8 km (470.3 mi)
Inclination	24.9836°
Period	99.8 minutes
RAAN	129.8201°
Argument of perigee	246.2689°
Mean anomaly	113.6763°
Mean motion	14.43 rev/day
Epoch	18 April 2016, 11:52:03 UTC[6]
Main
Wavelengths	90.5 to 119.5 nm (far ultraviolet)[1]
Medium Explorers

On 12 July 2007, FUSE's final reaction wheel, which is required for accurately pointing a spacecraft, failed and efforts to restart it were unsuccessful. An announcement was made on 6 September that because the fine control needed to perform its mission had been lost, the FUSE mission would be terminated.[7]

Optical design

Although the original specification was to have a Wolter-type grazing incidence telescope,[8] the final design of the FUSE telescope comprises four individual mirrors. Each of the four mirrors is a 39-by-35 cm (15.4-by-13.8 in) off-axis parabola. Two mirror segments are coated with silicon carbide for reflectivity at the shortest ultraviolet wavelengths, and two mirror segments are coated with lithium fluoride over aluminum that reflects better at longer wavelengths. This optimizes performance over the entire spectral range.[1]

Each mirror has a corresponding astigmatism-corrected, holographically-ruled diffraction grating, each one on a curved substrate so as to produce four 1.65 m (5.4 ft) Rowland circle spectrographs. The dispersed ultraviolet light is detected by two microchannel plate intensified double delay-line detectors, whose surfaces are curved to match the curvature of the focal plane.[9]

Science results

Over 400 scientific papers have been written using data from FUSE,[10] with subjects ranging from cool stars to the intergalactic medium. One of the primary science goals of FUSE was to study the abundance of deuterium, an isotope of hydrogen. Because of the large number of atomic absorption and emission lines in the far-ultraviolet, FUSE enabled many studies of galactic, extragalactic and intergalactic chemistry and chemical evolution.

Impacts

Canada credits work on the FUSE as helping them prepare for making the fine guidance sensors instrument on the James Webb Space Telescope.[11] Canada's contribution is called FGS/NIRISS and is a combined Fine Guidance Sensor, spectrograph, and camera.[11]

See also

• Cosmic Origins Spectrograph, instrument on the Hubble Space Telescope from 2009 which operates down to 90 nm

References

1. "FUSE". National Space Science Data Center. Retrieved 19 April 2016.
2. "Far Ultraviolet Spectroscopic Explorer". Space Telescope Science Institute. Retrieved 19 April 2016.
3. Venere, Emil (16 August 1995). "Hopkins Chooses Orbital Sciences Corp. To Build Spacecraft" (Press release). Johns Hopkins University. Retrieved 19 April 2016.
4. Miller, Michael W. (1998). Far Ultraviolet Spectroscopic Explorer spacecraft development. 1998 IEEE Aerospace Conference. 21–28 March 1998. Aspen, Colorado. doi:10.1109/AERO.1998.685851.
5. "NSSDC Master Catalog Display: Spacecraft Launch/Orbital Information". NASA.gov. Retrieved 1 January 2014.
6. "FUSE – Orbit". Heavens Above. 18 April 2016. Retrieved 19 April 2016.
7. NASA HQ (6 September 2007). "ROSES-07 Amendment 20: Cancel FUSE Legacy Science Program". Spaceref.com. Retrieved 7 September 2007.
8. Content, David A.; et al. (July 1990). Crawford, David L (ed.). "Optical design of Lyman/FUSE". Instrumentation in Astronomy VII. 1235: 943–952. Bibcode:1994SPIE.2011...34K. doi:10.1117/12.19157. S2CID 122644673.
9. Sahnow, David J.; et al. (3 July 1995). "The Far Ultraviolet Spectroscopic Explorer Mission". JHU.edu. Archived from the original on 23 July 2008. Retrieved 7 September 2007.
10. "FUSE Publications". JHU.edu. Archived from the original on 19 August 2007. Retrieved 7 September 2007.

External links

• FUSE website at Johns Hopkins University
• FUSE website at Institut d'Astrophysique de Paris
• FUSE archive at Multimission Archive at STScI (MAST)