Project Orion, the "abandoned" NASA-D.o'D. project to fly to different planets using the propulsive power of mini-nuclear explosions, was always kept Top Secret.
Although abandoned, you couldn't get the uncensored plans for it.
Unless, as Xeni Jardin's uncovered over at Boing Boing, you speak Arabic.
What are friends for?
[Thanks to Defense Tech for the tip. And if you're an offended Saudi Prince, well, that's life. I guess there are some things money can't buy.]