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A small reaction wheel viewed in profile A momentum/reaction wheel comprising part of a high-accuracy Conical Earth Sensor to maintain a satellite's precise attitude. A reaction wheel (RW) is an electric motor attached to a flywheel, which, when its rotation speed is changed, causes a counter-rotation proportionately through conservation of angular momentum. [1]
Another method for achieving three-axis stabilization is to use electrically powered reaction wheels, also called momentum wheels, which are mounted on three orthogonal axes aboard the spacecraft. They provide a means to trade angular momentum back and forth between spacecraft and wheels. To rotate the vehicle on a given axis, the reaction ...
Spacecraft rotational operations, such as turning to point in a new direction, are usually performed by angular momentum storage devices such as reaction wheels or control moment gyroscopes. It is generally preferable to use these devices instead of traditional thrusters , as they are powered by renewable electricity instead of by propellant ...
Four reaction wheels (arranged so that any three can provide complete three-axis control) were used for normal attitude control. The thrusters were used to dump angular momentum from the reaction wheels, as well as for rapid slew and propulsive maneuvers. Attitude control was to 0.1 degree, line-of-sight pointing stability is within 50 ...
The CMGs will eventually saturate (accumulating angular momentum to the point where they can accumulate no more), resulting in loss of effectiveness of the CMG array for control. Some kind of angular momentum management scheme (MMS) is necessary to allow the CMGs to hold a desired attitude and at the same time prevent CMG saturation.
Alternatively, reaction wheels can be used for attitude control. Use of diverted engine thrust to provide stable attitude control of a short-or-vertical takeoff and landing aircraft below conventional winged flight speeds, such as with the Harrier "jump jet", may also be referred to as a reaction control system. [1]
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There are also eight Monopropellant Rocket Engines (MRE-1), so called because they use only hydrazine as fuel. They are used for attitude control and momentum unloading of the reaction wheels. [2] [16] JWST has six reaction wheels for attitude control, spinning wheels that allow the orientation to be changed without using propellant to change ...