Saber Instrument Design Update

This paper describes the design of a 10-channel infrared (1.27 to 16.9 micrometers ) radiometer instrument known as SABER (sounding of the atmosphere using broadband emission radiometry) that will measure earth-limb emissions from the TIMED (thermosphere- ionosphere-mesosphere energetics and dynamics) satellite. The instrument telescope, designed to reject stray light from the earth and the atmosphere, is an on-axis Cassegrain design with a clam shell reimager and a one-axis scan mirror. The telescope is cooled below 210 K by a dedicated radiator. The focal plane assembly (consisting of a filter array, a detector array, a Lyot stop, and a window) is cooled to 75 K by a miniature cryogenic refrigerator. The conductive heat load on the refrigerator is minimized by a Kevlar support system that thermally isolates the focal plane assembly from the telescope. Kevlar is also used to thermally isolate the telescope from the spacecraft. Instrument responsivity drifts due to changes in telescope and focal plane temperatures as well as other causes are neutralized by an in-flight calibration system. The detector array consists of discrete HgCdTe, InSb, and InGaAs detectors. Two InGaAs detectors are a new long wavelength type, made by EG&G, that have a long wavelength cutoff of 2.33 micrometers at 77 K.