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2001 Mars Odyssey
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Guidance, Navigation, and Control

Using three redundant pairs of sensors, the guidance, navigation and control subsystem determines the spacecraft's orientation, or "attitude." A sun sensor is used to detect the position of the sun as a backup to the star camera. A star camera is used to look at star fields. Between star camera updates, a device called the inertial measurement unit collects information on spacecraft orientation.

This system also includes the reaction wheels, gyro-like devices used along with thrusters to control the spacecraft's orientation. Like most spacecraft, Odyssey's orientation is held fixed in relation to space ("three-axis stabilized") as opposed to being stabilized via spinning. There are a total of four reaction wheels, with three used for primary control and one as a backup.

The guidance, navigation and control subsystem weighs 23.4 kilograms (51.6 pounds).