Unexpected ammonia leaks and a jammed quick-disconnect fitting derailed a marathon eight-hour spacewalk Saturday to replace a coolant system pump aboard the International Space Station, forcing the astronauts to delay the repairs until a second excursion Wednesday.

Michael T. Suffredini, manager of the space station program at the Johnson Space Center in Houston, said he was “disappointed” the astronauts ran into the unexpected snag, saying a third spacewalk likely will be needed to resolve the leak and bring a replacement pump on line.

“Ammonia QDs are known to be sensitive systems,” he said referring to the quick-disconnect fittings. “They’re very complicated; it’s very high-pressure ammonia you have to try to be able to disconnect and reconnect on a regular basis.”

“We will get thorugh this problem,” he said. “The challenge is to get through this problem before the next problem hits the other cooling system.”