The infrared space observatory (ISO)

ISO is an astronomical satellite which will operate at wavelengths from 2.5-240 microns. ISO will provide astronomers with a unique facility of unprecedented sensitivity for a detailed exploration of the universe ranging from objects in the solar system right out to distant extragalactic sources. The satellite essentially consists of a large cryostat containing at launch over 2000 liters of superfluid helium to maintain the Ritchey-Chretien telescope, the scientific instruments, and the optical baffles at temperatures between 2 and 8 K. The telescope has a 60-cm diameter primary mirror and is diffraction-limited at a wavelength of 5 microns. A pointing accuracy of a few arcsec is provided by a three-axis-stabilization system consisting of reaction wheels, gyros, and optical sensors. ISO's instrument complement consists of four instruments, namely, an imaging photo-polarimeter, a camera, a short wavelength spectrometer, and a long wavelength spectrometer. (Author)