Solar panels have only been practical out to missions to Mars or the asteroid belt at farthest. For any more distant mission, nuclear power has been the only fe

Solar panels have only been practical out to missions to Mars or the asteroid belt at farthest. For any more distant mission, nuclear power has been the only feasible power source, in the form of RTGs at least. Spaceborne nuclear reactors have long been contemplated for providing much higher levels of power.