star tracker

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A system used as part of a space shuttle's navigation system. Its two units are located outside the crew compartment, forward and to the left of the commander's window. It is normally mounted in the aft crew station, and only moved to near the commander's station for ascent and deorbit thrusting periods. The star tracker aligns the inertia measurement unit (IMU) approximately every 12 hours by measuring the line-of-sight vector to at least two stars. If the IMU alignment error is more than 1.4°, the star tracker is not able to correct it until the crewman optical alignment sight corrects it to within 1.4°.

The star tracker system also provides angular data from the shuttle to a target, as for close or rendezvous operations with a target.

Each of the units has a door that protects it during the shuttle's ascent and re-entry but is open when the shuttle is in orbit.

Subjects: Astronomy and Astrophysics.

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