The Infrared Astronomical Satellite (IRAS) was a mission with joint execution by the United States (NASA), the Netherlands, and the United Kingdom. The basic goal of this mission was to obtain a full-sky survey over the approximate wavelength range 8 to 120 micrometers with four broadband photometry channels. IRAS increased the number of cataloged astronomical sources by about 70%, detecting about 350,000 infrared sources, and its numerous discoveries included revealing for the first time the core of our Milky Way galaxy. The satellite design and survey strategy were optimized for maximally reliable detection of point sources. Pointed observations, known as Additional Observations or Aos, were interspersed with survey observations. IRAS contained a 0.6 m Ritchey-Chretien telescope cooled by helium to a temperature of near 10 K. An array of 62 detectors was used to detect the infrared flux in bands centered at 12, 25, 60, and 100 micrometers. The noise equivalent flux densities were, respectively, 0.1, 0.1, 0.1, and 0.3 Jy (1 Jansky = 1E-26 W/sq m-Hz) in the four survey bands. The positions of galactic and extragalactic sources were determined to an accuracy of 0.5 arc-min. In addition to the focal-plane detector array used for the all-sky survey, a low-resolution spectrometer and a 60-and 100-micrometer chopped photometric channel were included on IRAS. To scan the sky for the survey, the satellite was rotated at a constant angular velocity perpendicular to the satellite-sun vector. IRAS could be pointed also at a selected celestial object for up to 12 min. This pointing ability permitted observations of selected objects with up to a factor of 10 increase in sensitivity or spatial resolution compared to that of the survey. IRAS ceased operations on November 21, 1983. Further discussion of the IRAS mission can be found in G. Neugebauer et. al., Science, v. 224, pp. 14-21, 1984, and in the entire March 1, 1984 issue of Astrophysical Journal Letters (v. 278, pp. L1-L85).
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