INFRARED TELESCOPE ON SPACELAB 2.

The infrared telescope (IRT) on Spacelab 2 will be the first cryogenically cooled telescope operated from the Orbiter. The principal objectives, consistent with those of the second Spacelab mission, are to measure the induced environment about the Orbiter and to demonstrate the ability to manage a large volume of superfluid helium in space. The prime astrophysical objectives are to map extended sources of low surface brightness infrared emission, including the zodiacal light, the galactic plane, and extragalactic regions. The IRT consists of a 250 liter helium dewar and an articulated cryostat containing the telescope, which scans plus or minus 45 degrees about a single axis orthogonal to both the local vertical and the Orbiter pitch axis. The telescope is an f/4 15. 2 cm highly baffled Herschelian telescope cooled to 8K, which may scan to within 35 degrees of the sun. The focal plane cooled to 3K consists of nine discrete photoconductors covering a wavelength interval of 4. 5 to 120 microns in five bands. Each detector has a 0. 6 multiplied by 1. 0 degree field of view. A single 2 micron stellar detector is used for aspect determination. A cold shutter provides a zero flux reference. Overlapping scans, contiguous orbits, and a six degree per second scan rate permit rapid redundant coverage of 60% of the sky.