Next cargo mission to space station up in the air

NASA engineers are evaluating whether a spacewalk might be necessary to replace ammonia pump that cools the station.

APE CANAVERAL, Fla. — NASA delayed a decision Thursday on when to launch the next cargo resupply mission to the International Space Station while investigating a valve problem that has shut down half the outpost's coolant system.

Orbital Sciences Corp.'s Antares rocket and unmanned Cygnus spacecraft had been preparing to launch Wednesday from Virginia.

STORY: Space station suffers cooling problem
A decision was deferred until Monday. NASA said the mission could fly as late as Dec. 21 or 22 in this launch window.

Ground controllers Thursday were sending commands to a flow control valve inside an ammonia coolant pump that is believed responsible for Tuesday's shutdown of one of the station's two coolant loops, called Loop A.

Without that loop working, various noncritical systems had to be powered down to limit the heat generated by station systems, which has cut the amount of research that can be performed.

The crew is in no danger, but the station is more vulnerable to a failure with the other coolant loop or some other critical system.

NASA is evaluating whether a spacewalk might be necessary to replace the ammonia coolant pump housing the valve if early troubleshooting efforts are unsuccessful.

The pump module in question was replaced during spacewalks in 2010 after another pump failed.
NASA says it has enough spares to do the job, but any plan for spacewalks must take into account lessons learned from the most recent U.S. spacewalk, which was aborted when an astronaut's helmet began filling with water.