First off, I really like the story! However, I can't seem to get a different ending. [SPOILERS]
The doctor never seems to believe me and always rips up my notes when I try to convince him of the supernova, and it seems the only thing that I can change is whether or not Sam knows that the world is going to end. I might have missed a combination of choices, but I've done about 5 or 6 run throughs now and it seems that nothing really changes in the end. Am I missing something?