Astronauts Wait, as Space Station Fix Fails

Astronauts aboard the broken International Space Station are keeping busy, as the spaceship awaits critical repairs.

Following a failed attempt to repair a broken ammonia pump through one of the longest spacewalks in history on Saturday, science experiments and computer systems remain off on the International Space Station. The pump was part of a knocked-out half of the space station's cooling system, which won't be fixed until Sunday at the earliest.

But U.S. astronauts Douglas Wheelock and Tracy Caldwell Dyson aren't twiddling their thumbs.

According to a NASA spokeswoman, the astronauts have a number of things to do before Wednesday's spacewalk, the first of two required to finally replace the failed pump. Wheelock and Dyson will be reviewing procedures for the spacewalk, updating inventory systems on board, and prepping spacesuits, helmets and gloves for the extra-vehicular activity.

To prevent muscles from atrophying in the zero-gravity environment, they continue to exercise for 2 hours per day as well.

In the daily mission update, which contained live footage from the International Space Station, cool heads appeared to prevail. NASA has said that while the situation is serious, it poses no immediate danger for the astronauts.

While the crew in orbit focuses its attention on Wednesday's spacewalk, NASA's ground crew continues assessing issues associated with Saturday's walk and the plans to complete the task of removing the problematic pump module.

A mission control team will meet tomorrow to give the final go-ahead for Wednesday's spacewalk, scheduled to begin at 7 a.m. eastern time.

Stubborn ammonia hoses

The problems for Wheelock and Caldwell Dyson cropped up about four hours into Saturday's spacewalk, when one of four ammonia hoses they needed to disconnect stuck fast.

"Wow, that is not budging," Wheelock said as they spacewalkers fell behind schedule. The delays ultimately prevented the astronauts from disconnecting the stricken pump and installing its replacement.

The astronauts began their spacewalk outside the International Space Station at 7:19 a.m. EDT (1119 GMT) as the outpost flew 220 miles (354 km) above Earth.

The astronauts managed to disconnect the other hoses, some of which released frozen bits of ammonia coolant, which the astronauts said resembled tiny snowflakes. Any ammonia that attached to their spacesuits was expected to bake off in the sunlight.

Aside from the ammonia leaks, those hoses were disconnected swiftly.

"Don't you wish they were all that easy?" Mission Control radioed the spacewalkers.

Finally, Wheelock returned to the stuck hose. He banged on it with a lever tool and managed to free it, only to see a large amount of ammonia leak out.

"You can see, it's got a pretty good snowstorm there," Wheelock said. "Boy that's a lot of pressure in there."

The astronauts waited while Mission Control decided what to do and described the ammonia flakes leaking out.

"That one looked like a giraffe," Wheelock said.

Ultimately, the astronauts left the hose connected to the faulty pump as time ran out.

At one point, the carbon dioxide sensor inside Wheelock's spacesuit failed. As a precaution, Mission Control told him to make sure to report any symptoms related to elevated carbon dioxide levels – though none were reported.

Pump failure in space

The ammonia pump failed July 31, knocking out half of the space station's cooling system and forcing astronauts to turn off some experiments and systems, as well as leave others without backups, in order to prevent the station from overheating. A tripped circuit breaker, likely caused by a power spike, caused the malfunction, station managers have said.

Space station managers have said the pump malfunction is a major failure for the 12-year-old orbiting lab, enough so that engineers had already drawn up repair plans on the off chance it occurred.

The International Space Station uses liquid ammonia to cool its onboard systems by transporting waste heat to a network of radiators mounted to its main truss. There are two main cooling system loops -- Loop A and Loop B. The failed pump is in Loop A, while the other cooling loop remains operational.

The failed ammonia pump is located on the station's right side truss and will be replaced with one of four spare pumps stored at the orbiting lab.

Each pump weighs 780 pounds (353 kg) and is 5 1/2 feet long (1.6 meters) by 4 feet wide (1.2 meters). They are about 3 feet tall (almost 1 meter). Dyson has said the pumps are about the size of a laundry dryer.

Saturday's spacewalk marked the first for Dyson and the fourth for Wheelock.

Space.com contributed to this report.