the.com/reaction wheel
a spinning disk that turns a spacecraft by refusing to spin itself
means A reaction wheel is a flywheel mounted inside a spacecraft that, by spinning faster or slower, lets the craft rotate or hold its orientation without firing any thrusters or expending fuel.
from A literal pairing of "reaction" and "wheel," both honest engineering words. "Reaction" comes from Latin re- ("back") plus actio ("a doing")—it nods straight to Newton's third law, where every action meets an equal and opposite reaction. "Wheel" is old Germanic stock, traceable through Old English hwēol back to a root meaning "to turn," a cousin of Greek kuklos (circle) and Sanskrit cakra. So the name simply describes the physics: a wheel that does its job through the reaction it provokes—spin the disk one way, and the spacecraft, obligingly, turns the other.
- Newton's revenge
- Spins one way so the satellite turns the other
- No fuel
- Steers using electricity, no propellant burned
- Kepler killer
- Failed wheels ended NASA's planet-hunting telescope mission
- Trio or quad
- Three needed for full 3D control, four for backup
- Saturation
- Spin too fast and they need thrusters to reset
skylab attitude control system — nasa's 1973 space station used reaction wheels to maintain orientation in orbit