(CNN) -- NASA scaled back operations on the International Space Station on Wednesday after discovering a problem with a cooling system, but officials aren't sure yet what's causing it.
One of two cooling pumps has failed, NASA spokesman Josh Byerly said.
Authorities are troubleshooting the problem. The station's crew is not in danger, he said.
Officials discovered the malfunctioning cooling loop was producing too much ammonia, he said.
They've shut down some non-critical systems on the station as a result, Byerly said, but the space station's life support system is still up and running.
Officials could determine that an emergency spacewalk is the best way to fix the failed pump -- something they've done in the past.
But it's too soon to tell whether that's the best option.
The current mission of the space station, officially called Expedition 38, is scheduled to fly until March 2014.
The six-person crew consists of NASA astronauts Mike Hopkins and Rick Mastracchio of the United States; Russians Mikhail Tyurin, Sergey Ryazanskiy and Oleg Kotov; and Koichi Wakata of Japan.