Spacewalker Alvin Drew quickly headed to a broken pump and vented the last bit of ammonia left to make it safe for handling in case it's returned to Earth on the last shuttle mission this summer.
The toxic ammonia coolant -- about 10 pounds' worth -- was vented through a hose, away from the two spacewalkers. It took two minutes to empty the pump.
A few pieces of frozen ammonia appeared to float away. Mission Control asked if spacewalker Stephen Bowen encountered any of the bits of ice, and he replied that he had not. Controllers wanted to keep any ammonia residue from getting into the space station.
Drew was invigorated and working so fast that Mission Control cautioned him, barely an hour into the spacewalk, to slow down. He promised he would.
Also on Wednesday's to-do list for Drew and Bowen: installing a camera, light and equipment covers, and removing some insulation. It was a hodgepodge of relatively minor jobs that will leave the orbiting lab in the best possible condition once space shuttles stop flying.
A leak in Bowen's suit had to be fixed before they could venture out.
Overseeing the action from Mission Control was astronaut Timothy Kopra. He was supposed to be the lead spacewalker, but was hurt in a bicycle accident last month. Bowen replaced him.
"Tim, it is great to hear your voice," shuttle astronaut Michael Barratt called down.
"Likewise," replied Kopra, who hobbled into Mission Control on crutches.
Discovery will remain at the space station until Sunday. The shuttle astronauts are staying an extra day to help outfit the new storage room installed Tuesday.
A humanoid robot -- the first one in space -- was carried up in the storage unit. It will remain boxed up until May, then put through a series of tests to see if it might help the space station crew with simple chores.
Once Discovery's 12-day flight ends Tuesday, the shuttle will be decommissioned and sent to the Smithsonian Institution for display.