Star tracker
Optical attitude sensor using stars
On display
Gyroscopes drift and solar sensors are useless in the Earth's shadow — only the stars gave precise attitude. The instrument pointed at a chosen star, held it in the photodetector field and fed an error signal to the control system.
The main difficulty was stray light from the Earth and Sun: the baffle and shutter system took up more volume than the optics themselves. Star trackers were used on interplanetary stations, where a fraction of a degree of attitude error meant missing a planet by thousands of kilometres.
On display is the instrument with its baffle and an alignment stand.
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