The crew of the International Space Station will have to wait for new supplies a while longer, while mission specialists on Earth continue to investigate the latest failure of the orbiter's external cooling system.

The next cargo launch to the station commercial transport company Orbital Sciences Corp. has been delayed at least one day, to Thursday, Dec. 19, giving the National Aeronautics and Space Administration added time to figure out and fix the frozen pump in question.

Orbital Sciences Corp. on Saturday said the launch of its Antares rocket and unmanned Cygnus cargo spacecraft from Virginia's Eastern Shore was expected no earlier than 9:19 p.m. EST Thursday, the opening of a five-minute launch window.

The company indicated it would learn sometime Sunday if NASA wanted it to go ahead and load time-sensitive material in preparation for the rocket to roll onto the launch pad Tuesday, for a Thursday lift-off.

NASA had said it would update the launch schedule after mission managers met Monday morning.

Ultimately, the launch window for Orbital's resupply mission, the first of eight under a $1.9 billion contract, extends until next weekend.

One of the station's two cooling loops shut down earlier this week. Flight controllers think a faulty valve inside an external pump was to blame. The shutdown is considered serious and needs to be fixed soon, NASA said.

The space station's cooling system uses ammonia to dissipate the heat generated by the on-board machinery.

Mission engineers in Houston have been working through the issue, hoping to solve the problem remotely -- before the station crew needs to conduct any spacewalks to replace the pump, as astronauts did in 2010, when they had to go outside three times to complete the job.

After the cooling system froze Dec. 11, the six astronauts turned off all nonessential equipment -- including some science experiments -- to reduce the heat load.

Flight controllers are researching ways to fix the valve, with a software repair the easiest option, a spacewalk being the most complicated.

Kenny Todd, one of NASA's space station managers, told the Associated Press the station is left "somewhat vulnerable" with only one good cooling line, making the possibility of additional failures higher than usual -- which is why the problem needs to be fixed as soon as possible.

"At this point, for lack of a better term, we're going to kick the can for a little bit and go let the team work a little bit more," Todd said.

U.S. spacewalks have been on hold since July, after an Italian astronaut nearly drowned because of a water leak in his helmet.