The Infrared Space Observatory (ISO) mission.

ESA's Infrared Space Observatory (ISO) is an astronomical satellite, operating at wavelengths from 2.5-240 μm. Essentially, ISO consists of a large cryostat which contained at launch about 2300 litres of superfluid helium to maintain the Ritchey-Chretien telescope, the scientific instruments and the optical baffles at temperatures of 2-8 K. The telescope has a 60-cm diameter primary mirror. A three-axis-stabilisation system provides a pointing accuracy of a few arc seconds. ISO's instrument complement, built by international consortia of scientific institutes and industries, consists of an imaging photo-polarimeter (ISOPHOT), a camera (ISOCAM), a short wavelength spectrometer (SWS) and a long wavelength spectrometer (LWS). ISO was placed into a highly-elliptical orbit in November 1995 by an Ariane 4 launcher. All systems are performing very well and ISO is expected to have an in-orbit lifetime of around 24 months. In keeping with its rôle as an observatory, the majority of ISO's observing time is being made available to the astronomical community in ESA member states, Japan and the USA via "calls for observing proposals".