Inertia wheel
In the technique, a spacecraft is inertia wheel ( English momentum wheel ), momentum wheel , stabilizing flywheel , sometimes gyroscope , a massive gyro , the stabilized orientation of a missile . The early satellites received their spatial stabilization by rotating the entire satellite.
An inertia wheel runs constantly at high speed and high angular momentum and thereby generates a stabilizing twist , i.e. That is, the reaction to disturbing torques transverse to the axis of rotation of the wheel is minimized. Therefore there is typically only one spin wheel (possibly two redundant ones ) per satellite. Inertia wheels are z. B. used in classic twist-stabilized GEO satellites.
If the cage of the inertia wheel can be rotated, the satellite can be aligned as required ( moment gyro / CMG ); the inertia wheel then takes over the function of several reaction wheels (see below).
Difference to reaction wheels
Inertia wheels are not to be confused with reaction wheels , which are not used to stabilize the position of a satellite, but to change it . A reaction wheel is normally at a standstill and is only brought to a corresponding speed to realign the satellite or to compensate for external disturbing torques. Such changes in the speed of the reaction wheel rotate the satellite along the axis of rotation of the wheel, but in the opposite direction ( conservation of angular momentum )
Typically there are several reaction wheels per satellite, which are aligned in different spatial directions. Reaction wheels are subject to high mechanical loads, which is why failure safety through redundancy also plays a major role here. So are z. For example, four reaction wheels are installed in the international space station and six in the Hubble space telescope .