This is a electric motor that drove a component of the Voyager 2 attitude/control system. It is a flight-qualified piece of spare hardware, which was used in laboratory simulations to resolve in-flight problems encountered by the Voyager spacecraft. Voyager 2 was an unmanned space probe which, in 1986, passed close to the planet Uranus to transmit images of its surface.
NASA's Jet Propulsion Laboratory transferred this object to the Smithsonian in 1998.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.