(CNN) -- Engineers are reviewing data after astronauts completed a spacewalk to start fixing a part of the International Space Station's cooling system, NASA said.
Saturday's spacewalk lasted 8 hours, 3 minutes -- the sixth longest in human spaceflight history, NASA said. But despite its long duration, the two astronauts participating in the spacewalk were unable to complete all they hoped to accomplish.
Astronauts could start another spacewalk Wednesday to resume efforts to remove and replace a failed ammonia pump, NASA said.
The pump failed July 31, setting off warning alarms and shutting down part of the space station's cooling system.
NASA says that without controls, the temperature of the orbiting station's sun-facing side would soar to 250 degrees (121 degrees Celsius), while thermometers on the dark side would plunge to minus 250 degrees Fahrenheit (-157 degrees Celsius).
But a backup system on the space station is keeping it cool, even with the failed ammonia pump, NASA said.
Six people -- three Americans and three Russians -- are on the International Space Station.
The station's crew members are conducting more than 100 ongoing experiments in biology, physical sciences, technology development, and Earth and space sciences, according to NASA.