NASA flight controllers were monitoring an ammonia coolant leak on one of the International Space Station's solar panel arrays, NASA officials said late Thursday. The space agency said the crew of the ISS was not in any danger due to the leak on the station's left-side power truss.

The leak was reported by the station crew around 11:30 a.m. Eastern on Thursday. Video, sources said, showed a stream of white flakes dissipating into the vacuum of space.

The leak is in the system used to cool electronics associated with solar array power channel 2B, one of eight fed by the station's huge solar panels. Ammonia flowing through a large radiator is used to carry away heat generated by the array's batteries and electrical systems.

The coolant system requires at least 40 pounds of ammonia to operate normally. Based on the observed leak rate, NASA said in a web update, the channel 2B coolant loop could drop below that level and shut down within 48 hours if nothing is done to resolve it.

In that case, the station's six-man crew would be forced to reconfigure the station's cooling systems. While the crew would lose redundancy in the cooling system, flight controllers do not believe any major systems would have to be shut down to reduce cooling requirements.

The space station can operate without the full complement of cooling channels, but the total loss of a coolant loop would require a significant reconfiguration to prevent electrical systems on the affected loop from overheating.

The station is equipped with spare parts for the coolant system and the U.S. astronauts are trained for possible spacewalk repair jobs. But as of this writing, it is not known whether a spacewalk might be required at some point or whether some other repair option might be implemented.

A spacewalk would require two U.S. astronauts. At present, two U.S. astronauts, a Canadian flier and three Russians are aboard the outpost. But NASA astronaut Thomas Marshburn, Canadian space station commander Chris Hadfield and cosmonaut Roman Romanenko are scheduled to return to Earth early Tuesday aboard a Russian Soyuz spacecraft.

NASA astronaut Sunita Williams during a speacewalk outside the International Space Station, Nov. 1, 2012, to perform work and to support ground-based troubleshooting of an ammonia leak.

"We don't see anything technically that we can't overcome," astronaut Doug Wheelock radioed the crew from Houston. "But we are still getting our arms fully around that issue."

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NASA: Coolant leak on ISS no threat to crew