[Solarsail]

Just a couple of asides, since I was reading about these very subjects (Am-241 RTGs and outer solar system photovoltaics) a few weeks ago;

The UK's NNL prototyped out a process for volume manufacture of Am-241 in 2013. http://www.nnl.co.uk/news-media-centre/news-archive/space-ba... And a few notes about the Americium-RTG effort more generally: http://www.planetary.org/blogs/guest-blogs/2015/0423-can-a-n...

NASA has also studied use of solar power beyond Jupiter's orbit: (PDF link) https://www.lpi.usra.edu/opag/nov_2007_meeting/presentations...

(Edit: Fixed a link)