4 ms·
As long as their axes have some orthogonal component, three allow for a torque-cancelling solution in three dimensions. It may not be as easy an equation as th
by mapt 13y ago
As long as their axes have some orthogonal component, three allow for a torque-cancelling solution in three dimensions. It may not be as easy an equation as three pairs of cancelled-moment wheels, but it's more weight-efficient.
However...
What little I can puzzle out about systems like this suggests that six active wheels (plus spares) would allow for desaturation of spin (cutting back when one flywheel approaches its maximum RPM) without either additional spacecraft rotation or thrusters.
- lutusp 13y ago> What little I can puzzle out about systems like this suggests that six active wheels (plus spares) would allow for desaturation of spin (cutting back when one flywheel approaches its maximum RPM) without either additional spacecraft rotation or thrusters. But in the absence of thrusters or another method, to stop one reaction wheel from spinning, you have to start another one spinning -- in other words you have to transfer the conserved momentum to another wheel. So wheels acting by themselves cannot cancel their own momentum, they can only transfer it from one wheel to another. Another approach is to stop a wheel spinning with a brake pad, which would convert the momentum into heat. But this has obvious drawbacks, among which the energy is irretrievable.