I must admit that you've surprised me with the numbers on solar vs RTG. (I've learned something today!) But of course you can always strap multiple RTGs togethe

I must admit that you've surprised me with the numbers on solar vs RTG. (I've learned something today!) But of course you can always strap multiple RTGs together. According to wikipedia's article on RTGs the most efficient ones produce about 4 watts per kilogram, so you'd need a couple of tons of 'em to equal Dawn's 10 kW at Earth, well in excess of Dawn's mass. Solar panels still rapidly become useless (like the square of the distance from the sun) as you get further out, of course.