Infrared Space Observatory


Infrared Space Observatory:

see infrared astronomyinfrared astronomy,
study of celestial objects by means of the infrared radiation they emit, in the wavelength range from about 1 micrometer to about 1 millimeter. All objects, from trees and buildings on the earth to distant galaxies, emit infrared (IR) radiation.
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Infrared Space Observatory

(ISO) A satellite project funded by ESA. The spacecraft was launched in Nov. 1995, on an Ariane–4 rocket, and injected into a highly elliptical 24-hour orbit. Its telescope plus instruments were used to make photometric and spectroscopic studies of galactic, extragalactic, and Solar-System objects emitting in the infrared in the waveband 2–200 μm.

The payload consisted of a Ritchey–Chrétien telescope with a 60-cm diameter primary mirror, and experiments mounted behind this at the Cassegrain focus. This equipment was all housed in a toroidal liquid-helium cryostat, which is insulated and Sun-shielded, the telescope looking out from one end of the enclosure. The tank of superfluid liquid helium, at a temperature below 2.17 K, provides the temperatures of 2–3 K that are necessary for the detectors to become sensitive. The telescope structure and mirrors were cooled to about 8 K by the gas boiling off from the helium.

Four cryogenically cooled instruments made up the scientific payload. ISOCAM is an infrared camera system that uses two infrared detector arrays (32 by 32 pixels) to view selected parts of the sky through the ISO telescope. The first array operates over 2.5–5.5 μm and the second over 4–17 μm, bandpass filters being used to limit the spectral coverage. The total field of view can be as large as 3 arc minutes. ISOPHOT is a multiband imaging photometer-polarimeter operating over 2–200 μm. Its 23 infrared filters can be used to limit the radiation reaching different detectors in the system. Some of these filters are common to those used on ISOCAM, and to those flown on the earlier satellite IRAS, thus providing overlap with both. The short-wavelength and long-wavelength spectrometers, SWS and LWS, are high-resolution spectrometers operating over 2–45 μm and 45–180 μm respectively. A variety of infrared detectors can be used with both instruments, and Fabry–Perot interferometers provide the highest resolutions.

Two ground stations were used to control and receive the data from ISO. One was provided by ESA and the second was provided by a Japanese/US collaboration.