It may only represent a smidgen of the multi-trillion dollar annual federal budget, but funding for NASA never fails to stir up debate, and that looks like it'll be the case more than ever with the Obama administration's just-announced 2011 budget. While NASA's budget will actually increase slightly to $19 billion, the big news is that Constellation moon program started by the Bush administration in 2006 (with the goal of returning by 2020) is being shelved amid what amounts to a fairly big change in priorities for NASA. That includes the first phase of more than $9 billion in spending on robotic exploration and heavy-lift rockets and, perhaps most notably, $6 billion in spending to promote the development of commercial rockets and spacecraft -- which NASA hopes will eventually be able to transport astronauts into orbit. Turning around a space agency isn't exactly easy though, and it'll apparently cost $3 billion over two years simply to end what's already been started on the Constellation program.Feeling a little wistful? Then head on past the break for a brief history of NASA's recent lunar ambitions.