In this Saturday, May 11, 2013 photo made available by NASA, astronaut Chris Cassidy and Tom Marshburn, not pictured, perform a space walk to inspect and replace a pump controller box on the International Space Station after an ammonia coolant leak was discovered. (AP) - An impromptu spacewalk over the weekend seems to have fixed a big ammonia leak at the International Space Station, NASA said Thursday. The "gusher" erupted a week ago, prompting the hastiest repair job ever by residents of the orbiting lab. Spacewalking astronauts replaced a suspect ammonia pump on Saturday, just two days after the trouble arose. NASA is now calling the old, removed pump "Mr. Leaky," said flight controller Anthony Vareha. Right now, we're feeling pretty good. We definitely got the big leak," Vareha said in a NASA broadcast from Mission Control in Houston. Vareha said engineers don't know whether the pump replacement also took care of a smaller leak that has plagued the system for years. It will take at least a couple months of monitoring to know the full status. Ammonia is used as a coolant in the space station's radiator system. The leak forced one of the station's seven power channels to go offline. NASA hopes to resume normal operations early next week, following computer software updates. One of the spacewalkers, NASA astronaut Thomas Marshburn, is now back on Earth. He returned this week aboard a Russian Soyuz capsule, ending a five-month mission. The other spacewalker, Christopher Cassidy, a recent arrival, spent Thursday chatting with three of the actors and a writer-producer of the newest Star Trek movie, "Star Trek into Darkness." The film was beamed up to the space station a few days before its U.S. opening in theaters Thursday. Cassidy watched the first half-hour of the movie while he was exercising Thursday morning and offered a stellar review. "I was riveted as you're racing through the woods and jumping off cliffs," he told the actors. I won't spoil the rest of the movie for anybody who hasn't seen it. But pretty cool scenes.