The Infrared Astronomical Satellite (IRAS) is the first space telescope to perform observations in the far infrared from orbit. IRAS was launched from Vandenberg Air Force Base on January 25, 1983 into a 900 km orbit. The satellite is surveying the entire sky in four bands covering the wavelengths from 8 to 120 micrometers. The satellite performance is excellent. With 25% of the data reduced, 262,000 point sources and 80,000 extended sources have been detected.1 IRAS has the first large superfluid helium dewar in space and is expected to last approximately 345 days.

IRAS Cryogenic System Flight Performance Report

Performance of the relativity mission superfluid helium flight dewar

The long term storage of cryogens in space will be required for future space missions. These missions include the long life version of the Shuttle Infrared Telescope Facility (SIRTF), the Large Deployable Reflector (LDR), Gravity Probe B (GPB), Orbital Transfer Vehicles (OTVs), and the Space Station. We have studied the feasibility of building a long lifetime helium Dewar for space applications.1 The object of this study was to develop a feasible concept for a shuttle-launchable 3-yr lifetime Dewar, and to use this concept to identify key technology development areas. A 3-yr lifetime is a considerable improvement over the current flight Dewars as represented by the Infrared Astronomical Satellite (IRAS).2 For the purpose of comparison we chose an IRAS-type telescope and instrument for this study. The system requirements are given in Table 1. The specifications of the extensively analyzed final design are also given in this table where they differ from the requirements. A finite element structural analysis was done to determine resonant frequencies and buckling modes. A thermal analysis was done using a lumped node model with 77 nodes. The designed Dewar incorporates several novel features.

Long Term Cryogen Storage in Space: A Feasibility Study

The main cryogen tank is sized to hold 70 kg of superfluid helium with 12 percent ullage at a temperature of 1.8 K. The insulation system surrounds the main cryogen tank with four blankets of multilayer insulation spaced by means of three vapor-cooled shields. It is noted that the multilayer insulation is 6.4 micron double-aluminized Mylar separated by polyester net. The main shell provides the primary structural integrity of the system. In orbit the main shell is cooled to 170 K using insulation blankets on one side and second surface paint on the opposite side. The aperture cover subassembly is the vacuum seal for the main shell during operation on the ground. It is also a gas condensation trap before and during cooldown of the main cryogen tank during launch hold. It contains 6 kg of supercritical helium, which permits 14 days on orbit with a 48-hour launch pad hold.

P. V. Mason

Papers

Progress report on the infrared astronomical satellite cryogenic system