Control Moment Gyroscope
Experiments conducted in space must be accomplished under stable conditions.
In America's first space station, Skylab, the experiments involved
viewing three basic targets: the Sun, the Earth, and celestial space.
Instruments for these experiments were located at places providing proper
viewing directions with a minimum of maneuvering. Active and continuous
control of Skylab attitude (direction) assured that instruments were pointed in
the desired directions while they were in operation.
Changes in Skylab attitude were accomplished by the control moment gyro system
(CMG) or the nitrogen thruster attitude control system (TACS). The CMG control
system, consisting of three large gyroscopes with mutually perpendicular axes,
represents the chief method of Skylab control
Each of the three CMGs in the Skylab control system weighs 400 pounds (181
kilograms); consists of a rotor 22 inches (0.55 meters) in diameter, spinning
at 9,000 RPM; and an inner and outer gimbal ring. The control moment gyro
system is currently used in the International Space Station.