Sorry to bump Julianne's fun post further down the page, but lots of news today. This particular piece of news is not fun: NASA is abandoning LISA, the planned Laser Interferometer Space Antenna, as well as IXO, an X-ray satellite observatory (formerly "Constellation X"). Steinn has some of the ugly details. Short story: money is tight, and the James Webb Space Telescope is taking all of it. (Not that JWST is completely immune from danger itself...) LISA is not completely dead: the European Space Agency will keep the planning alive. But this is a serious step, not just a feint in a budget negotiation; the LISA International Science Team is being disbanded, told to pack up and go home. Hopefully the ESA will continue to push forward, and individual researchers in the US can somehow find money to still think about gravitational-wave astrophysics from space. It's possible that a smaller mission could be put forward, but it's not as if NASA has extra money they're looking to spend right now.
Of all the concepts for big astrophysics missions in space, LISA is my favorite. Unlike LIGO, which strains as hard as possible and hopefully will detect something once its upgraded, LISA would be bombarded with gravitational waves, and the trick will be picking out the interesting signals from above the ambient noise. (That's a problem we don't mind having.) I was part of the original Beyond Einstein roadmap team (pdf) that packaged LISA and Constellation-X together with a dark energy mission to create an ambitious but realistic plan for NASA cosmology that Congress and the OMB could get behind. That was in 2002, before wars and tax cuts and financial catastrophes sapped the government of its ability to pay for anything. The best-laid plans of mice and men and NASA panels, as the saying goes. LISA's science is not just achievable, it's incredibly interesting. It would detect thousands of binary systems within our galaxy, as well as numerous inspirals of middleweight black holes into supermassive ones in other galaxies, giving us incredibly detailed access to the spacetime metric near a black hole. As a side benefit, the wavelength is just right for looking at gravitational waves that might be produced in the early universe if the electroweak phase transition is especially violent. I remember giving a talk to particle physicists planning the International Linear Collider (another possibly doomed endeavor) back in 2003. It was great to see their eyes light up when I told them about this connection between satellite observatories and particle accelerators -- at a meeting dominated by budget worries, it was a tiny oasis of actual science. Hopefully things will somehow work out, but there's not a lot of reason for optimism at the moment. We'll see how things go.