Faint Object Spectrograph

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.

• 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. 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.