A manoeuvre to remove the excess momentum that builds up in a spacecraft's momentum wheels. Frequent desats are usually required. The manoeuvre applies torque (force causing rotation) to the spacecraft by using its thrusters. The Hubble Space Telescope, which would be contaminated by thruster exhaust, achieves desat by using on-board magnets that interact with the Earth's magnetic field to produce torque.
Subjects: Astronomy and Astrophysics.