The European Space Agency offered me a seat on their zero-g plane: it's an Airbus A310 that flies parabolic maneuvers, pulling up into the sky and then arcing back down, giving its passengers about 20 seconds of weightlessness (or "microgravity") at a time. Here's how it works. Some people would have filmed their script on the ground, and just messed about while floating. I decided to go for something a bit more challenging.