Well, I wrote a Babylon 5 crossover AU. I don't know if it REALLY counts, but it's definitely IN SPACE. (Okay, it starts out on a space station, but by the end there's a space battle. And space piracy. Promise.)

http://aris-writing.livejournal.com/2982.html and http://aris-writing.livejournal.com/6390.html have links to all the parts.