The Infrared Space Observatory (ISO) satellite being checked by European Space Agency engineers before its launch in November 1995. The main body of the satellite is a huge flask which surrounds the telescope itself, a 60cm Ritchey-Chretien optical system. The flask contains about 2150 litres of liquid helium, which cools the infrared detectors to just 1. ISO will have an observing lifetime of two or three years before its cooling helium runs out. It will carry out observations in the 2.
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