Since there's no drag the thermal system isn't as constrained in space as it would be for a car or aircraft. If you assemble the final spacecraft in orbit, all

Since there's no drag the thermal system isn't as constrained in space as it would be for a car or aircraft. If you assemble the final spacecraft in orbit, all that matters is mass so you can create very high surface area radiators that are extremely efficient as long as they're a few AU from the nearest star (or pointed in different direction). It'd probably be as big or bigger than a solar sail but it would use the sails to emit photons instead of absorbing them and itd work far from any star.