NASA managers say they're still troubleshooting a problem with a coolant pump aboard the International Space Station — and although the crew is not in any danger, a commercial cargo flight might have to be postponed.
A decision on the Dec. 18 launch of Orbital Sciences Corp.'s Cygnus cargo ship atop an Antares rocket will be deferred until Monday, said Kenny Todd, NASA's space station mission integration and operations manager.
The cargo capsule is due to deliver about 3,200 pounds (1,400 kilograms) of supplies, spare parts and scientific experiment to the station, but during a televised update on Thursday, Todd indicated that the Cygnus flight could be put on hold if need be. This month's launch window runs until Dec. 21 or 22 at the latest.
The coolant system problem centers on a flow control valve within a pump for one of the ammonia coolant loops that shed excess heat from the station. A valve malfunction caused the loop to shut down on Wednesday. There are two such loops, and NASA was able to shift most of the station's equipment over to the other loop as a backup.
Some non-critical systems have been turned off as a precaution — but the reduced cooling capability means there's less of a safety margin on the station. Todd said mission managers don't want to risk having the Cygnus come in for a hookup under such conditions. "While we're sitting at one loop, we're somewhat vulnerable," he said.
Engineers are currently troubleshooting the valve problem, and Todd said NASA would "kick the can a little bit" to see if the situation can be resolved remotely, using the software that operates the coolant system. If it can't, astronauts would have to take on a spacewalk to inspect the pump and probably replace it. "We have spare pump modules on orbit," he said.
Spacewalk under consideration
Todd didn't mention the potential time frame for such a spacewalk, other than to say "our intention would be to try to get recovered as quickly as possible." In July, Italian astronaut Luca Parmitano experienced a frightening problem with water welling up in his U.S.-made spacesuit, which led NASA to suspend spacewalks. Russian spacewalks, however, continued unhindered.
On Thursday, Todd voiced confidence that the flooded-spacesuit issue would not reoccur. "We're a lot smarter now," he said. New measures were being put in place to inspect the U.S. spacesuits and make sure that the spacewalkers wearing them will stay safe, he said.
Six spacefliers — three Russians, two Americans and a Japanese astronaut — are living aboard the $100 billion-plus orbital outpost, which has been occupied continuously since 2000 and is due to stay in operation until at least 2020. Repairs to the coolant system are among a set of "Big 14" maintenance issues that NASA and its space station partners expect to deal with regularly.
Spacewalks to address coolant issues have been conducted on almost a yearly basis. The most recent repair operation, which involved the replacement of a coolant pump in May, was performed after only 48 hours of planning. But Todd indicated that there was no need to rush this time around.
More about the space station:
Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding +Alan Boyle to your Google+ circles. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.
First published December 12 2013, 6:06 PM