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Similar to ancient mariners,
the MESSENGER spacecraft will keep track of its position by checking
the location of stars and the Sun. On September 12 the MESSENGER
team re-installed the spacecraft's two Star Tracker Cameras, after
removing them for testing and to work on the spacecraft below
the cameras' location. The devices sit on MESSENGER's top deck
- the portion of the spacecraft facing the windows at left in
this Webcam view - and work in conjunction with six Sun Sensors
and the Inertial Measurement Unit.
The cameras are amazing instruments; each
compact device weighs about 3.1 kilograms (about 7 pounds) and
stores a complete map of the heavens. Every second, one of the
cameras takes a wide-angle picture of space, compares the locations
of stars to its onboard map, and then calculates the spacecraft's
orientation. Accurate spacecraft orientation is critical not only
for obtaining the best science data, but also for keeping the
spacecraft steady and moving in the right direction during course-correction
maneuvers.
Last updated: September
17, 2003
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