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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]
Also changed out was one of four Reaction Wheel Assembly units that use spin momentum to move telescope toward a target and maintain it in a stable position. After this EVA, mission managers decided to add EVA 5 to repair the thermal insulation on HST. [2] EVA 4 began at 10:45 pm, February 16, and lasted six hours, 34 minutes.
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]
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 ...
The ADACS consists of the Earth Sensor Assembly (ESA), the Sun Sensor Assembly (SSA), four Reaction Wheel Assemblies (RWA), two roll/yaw coils (RYC), two pitch torqueing coils (PTC), four gyros, and computer software for data processing.
The attitude determination and control subsystem featured a 3-axis zero-momentum-bias reaction wheel assembly with a Sun sensor, a star tracker and inertial measurement units, delivering an attitude jitter of 15.7 arcsec/sec, and pointing accuracy and knowledge of 648 and 540 arcsec, respectively.
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Fuel and oxidizer tanks were shipped out to assembly in September 2015. [33] In 2015, the communications subsystems, star trackers, reaction wheels, fine Sun sensors, deployment electronics Unit, command telemetry processors, and wire harnesses were delivered for construction. [34]