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[[Image:Foslarge sm.jpg|thumb|The Faint Object Spectrograph (FOS). This picture was taken after FOS was brought back to the Earth again. Credit: [[NASA]]/[[ESA]].]]

The '''Faint Object Spectrograph''' (FOS) was a [[spectrograph]] installed on the [[Hubble Space Telescope]]. It was replaced by the [[Space Telescope Imaging Spectrograph]] in 1997, and is now on display in the [[National Air and Space Museum]] in Washington DC.

==FOS facts==
*'''Instrument type''': Spectrograph
*'''Wavelength range''': 115 to 850 nm

A technical description of the construction and operation of the FOS can be found in NASA technical report CP-2244.<ref name="CP-2244">{{cite tech report |title=The Space Telescope Observatory |number=CP-2244 |institution=NASA |url=http://hdl.handle.net/2060/19820025420 |date=1982}}, page 55. A 40 MB PDF file.</ref> The instrument used two [[digicon]] detectors, 'blue' and 'red', and had a spectral resolution of about 1300 over the 115 nm to 850 nm range. It had a number of apertures of varying size, but the aberration of the HST mirror meant that, until COSTAR was installed, the smallest apertures suffered very serious loss of light; even the largest 4.3-arcsecond aperture collected only 70% of the light from a point source.

The digicons suffered from inadequate magnetic shielding, which meant that a static image was smeared over several pixels; the red digicon suffered most from this. Also, either the blue detector or one of the mirrors in the system was contaminated in such a way as to remove sensitivity below 150 nm; this was a serious problem since it makes the [[Lyman-alpha]] line at 121.6 nm inaccessible.

==References==
{{reflist}}

==External links==
*{{Commonscatinline}}
*[https://archive.today/20121214233815/http://www.stsci.edu/hst/fos The Faint Object Spectrograph (FOS)]
*[http://www.spacetelescope.org/news/html/heic0112.html ESA/Hubble Release about FOS]
*[http://www.spacetelescope.org/about/general/instruments/fos.html FOS at ESA/Hubble]

{{Hubble Space Telescope}}

[[Category:Hubble Space Telescope instruments]]
[[Category:Space science experiments]]
[[Category:Spectrographs]]
[[Category:Space hardware returned to Earth intact]]

{{observatory-stub}}

Faint Object Spectrograph - Revision history

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