The Faint Object Spectrograph (FOS) was a

spectrograph An optical spectrometer (spectrophotometer, spectrograph or spectroscope) is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify mate ...

installed on the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

. It was replaced by the

Space Telescope Imaging Spectrograph The Space Telescope Imaging Spectrograph (STIS) is a spectrograph, also with a camera mode, installed on the Hubble Space Telescope. Aerospace engineer Bruce Woodgate of the Goddard Space Flight Center was the principal investigator and cre ...

in 1997, and is now on display in the

National Air and Space Museum The National Air and Space Museum of the Smithsonian Institution, also called the Air and Space Museum, is a museum in Washington, D.C., in the United States. Established in 1946 as the National Air Museum, it opened its main building on the N ...

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., page 55. A 40 MB PDF file. The instrument used two

digicon A digicon detector is a spatially resolved light detector using the photoelectric effect directly. It uses magnetic and electric fields operating in a vacuum to focus the electrons released from a photocathode by incoming light onto a collectio ...

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 The Lyman-alpha line, typically denoted by Ly-α, is a spectral line of hydrogen (or, more generally, of any one-electron atom) in the Lyman series. It is emitted when the atomic electron transitions from an ''n'' = 2 orbital to the ...

line at 121.6 nm inaccessible.

References

External links

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The Faint Object Spectrograph (FOS)
Hubble Space Telescope instruments Space science experiments Spectrographs Space hardware returned to Earth intact {{observatory-stub