|MadSci Network: Engineering|
Gyroscopes are used for attitude control (roll, pitch and yaw) in satellites. The gyroscopes are an economical means of keeping the satellite oriented correctly for many months or even years. For example, several gyroscopes acting together are used to adjust the Hubble Space Telescope. To maintain the proper orbital height, though, small station keeping rockets are used.
For the space shuttle and other craft requiring significant, rapid adjustments not only to attitude but speed, the gyroscopes probably would not have sufficient acceleration for attitude adjustment. The space shuttle's on obit mass is approxi mately 100,000 kg, and it is almost 40 meters long. Compare that to a typical satellite that is less than 500 kg and only a few meters in length. Gyroscopes for large atitude adjustments with performance equivalent to the maneuvering rockets the could easily weigh thousands of kilograms.
The other problem is gyroscopes cannot affect the velocity of the shuttle. To go up or down in orbit, the velocity of the shuttle must be changed. Without this ability docking and other maneuvers become impossible. The use of the Orbital Maneuvering System and the Reaction Control Systems can allow significant adjustements in the orbit height. Since the rockets are already required and weight is absolutely critical, the use of redundent gyroscopes does not make sense for this application.
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