> I can't see any efficiency problem though, electrical spin-up and spin-down with regenerative braking should reclaim the energy. A lot of uses of reaction wh

> I can't see any efficiency problem though, electrical spin-up and spin-down with regenerative braking should reclaim the energy. A lot of uses of reaction wheels requires them to constantly spin because there's been an outside force applied. The wheel mass also tends to be low because it's divided between multiple axes and so speeds of wheels need to be pretty high.