Two astronauts from the U.S. space agency have completed the first stage of an effort to repair a faulty pump that shut down part of the International Space Station's critical cooling system several days ago.
NASA says astronauts Rick Mastracchio and Mike Hopkins disconnected the faulty ammonia pump while working outside the space station for more than five hours on Saturday.
The agency says the two men will try to install a spare pump module during their next spacewalk on Monday, with a final session outside the spacecraft on Wednesday.
The station has since been using a backup system for cooling internal and external equipment. The problem has forced the astronauts to turn off all non-essential equipment, including some science experiments.
Until Saturday, the station's crew members had not ventured out into space since July, when a still-unexplained problem nearly drowned an Italian astronaut whose helmet filled with water during a spacewalk.
NASA said Mastracchio and Hopkins attached snorkels to their spacesuits to use for breathing in case of a helmet water leak.