Design of a superfluid helium dewar for the IRAS telescope

The Infrared Astronomy Satellite (IRAS) is planned for launch in 1981, and is a joint project of the Netherlands, the United Kingdom and the United States. The instrument will consist of a superfluid helium-cooled 60 cm telescope with a large array of infrared detectors at the focal plane. The primary purpose of the mission is to perform an all-sky survey in the infrared region from 8 to 120 micrometers. The dewar contains 70 kg of superfluid helium which will maintain the telescope and detectors at 2K for one year. The dewar contains a supercritical helium cover tank which will be ejected after the experiment has been in orbit for two weeks.