Personally if I were designing a satellite I would be wary of putting
something spinning at high revs in my delicate assembly. If anything
went wrong and it broke free it could wreak havoc. I assume satellites
have gyros for navigational / orientation purposes, but with heavy
armour around them... (don't really know enough about this). Similarly
an aircraft won't want something equivalent to a small bomb inside it.
Imagine the safety certification issues. I do know that gyro storage of
energy is generally best for big pulses of power, it's not too efficient
for a high energy density torage device. That's what batteries or, if
cost is no object, fuel cells are for.
--
Nemo