AIRS

Scan Head Assembly

The AIRS Scan Head Assembly consists of the primary scan mirror, the rotating baffle which surrounds the scan mirror and protects it from contamination and stray light, the scan Motor Encoder Assembly (MEA), the and the scan head housing. The Scan Head Assembly also contains the sunshields, the VIS/NIR Sensor Assembly and the On-Board Calibrators.

A 360-degree rotation of the scan mirror generates a scan line of IR data every 2.667 seconds. The scan mirror motor has two speeds:

1. During the first two seconds, the mirror rotates at 49.5 degrees/second, generating a scan line with 90 footprints of the Earth Scene, each with a 1.1-degree diameter Instantaneous Field of View (IFOV).

2. During the remaining 0.667 seconds, the scan mirror completes one complete revolution, with four independent views of cold space, one view into a 310 K radiometric calibrator (the On-Board Calibrator [OBC] blackbody), one view into a spectral reference source (Parylene), and one view into a photometric calibrator.

The VIS/NIR photometer, which contains four spectral bands, each with nine pixels along track, with a 0.185-degree IFOV, is bore sighted to the IR spectrometer to allow simultaneous visible and infrared scene measurements.

The scan head support system consists of a three point interface to the base ring of the instrument support truss. Its primary function is to support scan head and maintain boresight. It is comprised of beryllium.

The MEA consists of a two phase 24 pole brushless DC torquer motor with redundant windings. It was developed by BEI Motion System Co. It contains an optical encoder with redundant read heads and motor commutation using a master code disks. The Bearings are an angular contact duplex pair mounted back-to-back.