Far Ultraviolet Spectroscopic Explorer

From Wikipedia, the free encyclopedia

**FUSE**
Physical characteristics
FUSE
Organization	Johns Hopkins University APL, NASA
Wavelength regime	90–120 nm
Orbit height	773 km
Orbit period	100.06 minutes
Launch	June 24, 1999 on a Delta II
Launch site	Cape Canaveral
Deorbit date
Mission duration	3 years [1]
Mass	1360 kg (launch), 580 kg (dry)
Webpage	http://fuse.pha.jhu.edu/
Telescope style
Diameter
Collecting area
Focal length

FUSE, the Far Ultraviolet Spectroscopic Explorer, is a space-based telescope run by the Johns Hopkins University. FUSE was launched on a Delta II rocket on June 24, 1999, as a part of NASA's Origins project, and as of October 2006 is still functioning [2]. Its Explorer designation is Explorer 77.

FUSE looks at light in the far ultraviolet portion of the electromagnetic spectrum, between 90 to 120 nanometers, which is unobservable with other telescopes. Its primary mission is to characterize universal deuterium, in an effort to learn about the stellar processing times of the deuterium left over from the Big Bang.

[edit] Optical Design

Although the original specification was to have a Wolter type grazing incidence telescope, the final design of the FUSE telescope comprises four individual mirrors. Each of the four mirrors is a 39 cm by 35 cm 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 the performance over the entire spectral range.

Each mirror has a corresponding astigmatism-corrected, holographically-ruled diffraction grating, each one on a curved substrate so as to produce four 1.65 meter 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.