Star tracker for the infrared

A computer-controlled star tracker has been built for use in the IR. A small dedicated computer is the active element in a servo loop that moves two small mirrors located in the light path and keeps the light beam centered in the input aperture of an IR heterodyne spectrometer. It does this without reducing the amount of light available to the spectrometer. The system has been used at the coude focus of the IRTF at Mauna Kea and can track a -1m (5 micron) star at frequencies up to 10 Hz while holding the output beam to within a few tenths of a second of arc on the sky.