Two NASA astronauts have failed to replace a faulty cooling pump module aboard the International Space Station (ISS) after a lengthy effort, Press TV reported.
Doug Wheelock and Tracy Caldwell Dyson, two US astronauts, spent over eight hours outside the space station, but were unable to completely disconnect and remove the 780-pound pump module, NASA announced on Saturday.
It was the longest spacewalk in the floating observatory's history.
The orbiting lab's ammonia pump failed last Saturday, disabling half of the station's cooling system.
"It was a tough one as spacewalks go," a spokesman for NASA's mission control in Houston, Texas, said during a live video feed.
NASA says that each pump is about as large as a laundry dryer and maneuvering such a large objects is difficult in the weightless conditions of space.
The failed attempt left NASA engineers rushing to come up with a new repair plan.
The astronauts will once again attempt to repair the system during a second spacewalk which is now planned for Wednesday.