the.com/reaction wheel
a spinning disk that turns a spacecraft by refusing to spin itself
Newton's revengeSpins one way so the satellite turns the other
No fuelSteers using electricity, no propellant burned
Kepler killerFailed wheels ended NASA's planet-hunting telescope mission
Trio or quadThree needed for full 3D control, four for backup
SaturationSpin too fast and they need thrusters to reset