Self-balancing cube - GIF

[mklotz]

Um, why? Because you can I guess.

A satellite in orbit that needs to point in various directions (e.g. a telescope) can use reaction jets powered by a stored compressed gas supply. The problem is that once the gas is exhausted, the satellite is no longer useful; refueling is seldom mechanically or economically possible.

Reaction wheels, being electromechanical devices, can replace the reaction jets. Since they consume only electricity they will continue working as long as the solar cells on the satellite are viable.