The troublesome toilet aboard the International Space Station appears to be working again, thanks to a replacement pump taken to the station by the shuttle Discovery. “The toilet appears to have been repaired,” said Rob Navias, the commentator for the National Aeronautics and Space Administration’s video channel on the Web, NASA TV (www.nasa.gov/multimedia/nasatv/). The single toilet aboard the station has separate systems for dealing with solid and liquid waste, and the systems are designed to work without the help of gravity. The solid waste system was operating properly, but the liquid system, which uses air flow to direct urine and store it in a receptacle, began malfunctioning more than a week before the shuttle’s arrival on Monday. A pump that separates urine from air and directs the urine into a tank failed; two spare pumps aboard the station were installed and failed as well.