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View Full Version : FUSE mission comes to an end



ngc3314
2007-Aug-17, 08:22 PM
The management of the Far-Ultraviolet Spectroscopic Explorer (FUSE) mission, consulting with NASA headquarters, has decided that the science mission is over. This follows what appears to be an irrecoverable failure in one of the reaction wheels needed to point the spacecraft. The team had shown extraordinary originality in working around a string of less serious gyroscope failures, keeping the telescope operating while using a combination of star tackers and the Earth's magnetic field for pointing meaurement and control. FUSE was launched in 2000, and designed to probe the wavelength region in the far-UV between about 912 and 1150 Angstroms. This is a region where Hubble's mirrors are not highly reflective, for example, since it is difficult to find a substance which works well both in the far-UV and at long wavelengths. In fact, no mirror coating is all that good in this range, so far-UV instruemnt designers always jump through hoops to reduce the number of reflections to a minimum no matter how much difficulty that causes... Despite its spectral narrowness, this piece of the spectrum is uniquely rich in atomic spectral lines. FUSE made huge strides in studying the cosmic ratio of deuterium to hydrogen (important for cosmology as well as study of how stars and the ISM interact), and provided most of what we know so far about the rarefied, hot gas between the galaxies. This was most easily seen through absorption of O VI (5-times ionized oxygen) against the light of background quasars. FUSE was also used to make major contributions to the study of hot stars and the history of chemical enrichment of galaxies (OK, so I made up the "major" part for that last one).

Rats. It would have been cool to have FUSE and COS working at the same time.

Nereid
2007-Aug-18, 02:04 PM
How much of an overlap was there between FUSE's far UV range and GALEX? between FUSE and Swift's UVOT? How much better - in whatever sense - was FUSE than EUVE?

antoniseb
2007-Aug-18, 02:49 PM
How much of an overlap was there between FUSE's far UV range and GALEX? between FUSE and Swift's UVOT? How much better - in whatever sense - was FUSE than EUVE?

It appears that there was not much overlap.

FUSE covered 90.5-119.5nm with a spectral resolution of about 0.003nm
GALEX covered 135-280nm with a spectral resolution of about 1nm
SWIFT covers 170-650nm with a spectral resolution of about 1nm
EUVE covered 70-760nm.

FUSE was specifically designed to distinguish Hydrogen from Deuterium, looking at the Lyman series. the others could never do this.

ngc3314
2007-Aug-18, 03:47 PM
It appears that there was not much overlap.

FUSE covered 90.5-119.5nm with a spectral resolution of about 0.003nm

GALEX covered 135-280nm with a spectral resolution of about 1nm
SWIFT covers 170-650nm with a spectral resolution of about 1nm
EUVE covered 70-760nm.

FUSE was specifically designed to distinguish Hydrogen from Deuterium, looking at the Lyman series. the others could never do this.

Slight correction: EUVE worked from 70-760 Angstroms (rather than nm), so there was no overlap there. The only overlap in instrumental capability was at the extreme short-wavelength end of STIS (not operating at the moment either, but with some hope) and the old Copernicus spectral scans of very bright stars. COS should be able to pick up at 1150 Angstroms, but at low redshifts that still misses some of the things FUSE keyed on - O VI and molecular hydrogen absorption come to mind. There have been shuttle or SPAS-borne far-UV experiments, but so far they have had either much less sensitivity or much less spectral resolution.

Other slight ciorrection: even with high-voltage supply flakiness in the far-UV channel, GALEX still deserves the present tense!

Hmm. I keep thinking there must be a handy graphical way to compare sensitivity, spectral resolution, and spectral range all at once.

antoniseb
2007-Aug-18, 03:58 PM
I keep thinking there must be a handy graphical way to compare sensitivity, spectral resolution, and spectral range all at once.
Thanks for the corrections. I knew about the EUVE A not nm thing, but spaced it as I keyed it in, and also about the present tense for GALEX.

Concerning the graphical representation, I suspect that a 2D graph with axes showing wavelength sensitivity and lamda/d-lamda would do the trick. You could use line thickness or color as a third dimension showing spatial resolution or something if you needed to. Each instrument (FUSE had two for example) would show up as a line (or shallow curve) on this graph.