The cooling system of the International Space System has suffered from a debilitating malfunction, leading to an emergency situation for the six-person crew which NASA has described as “urgent.”

One of the main cooling coils of the International Space System (ISS), a habitable, low orbit satellite which is the product of collaboration between the US and Russian space agencies, has suffered from a failure which has compelled the station's six-person crew to shut down inessential systems in order to remain safely on board.

The ISS is equipped with two cooling loops - Loop-A and Loop-B, which under regular circumstances must operate simultaneously in order to ensure that the complex technical systems of the station stay at a reasonable temperature.

Loop-A suffered from the suspected mechanical failure last week, leaving the ISS with only a single functioning loop to cool down its extensive panoply of laboratories and equipment.

In order to conserve energy, ISS crew members have shut down non-essential systems and science experiments, including Japan's Kibo science module and Europe's Columbus lab. Only systems of critical importance, such as life support equipment and storage freezers, have been kept operating.

The failure of the space station's cooling system is on the list of 14 major malfunctions (the "Big 14") compiled by NASA, for which the agency prescribes a two-week repair period in the absence of a pre-scheduled space walk. The list includes problems involving electrical and cooling equipment, but not those which could impact life-support systems, for which NASA has drawn up a separate set of contingency plans.

NASA has characterized the situation on the ISS as "urgent" but not life-threatening, and is now making haste to work out the reason for Loop-A's failure and find a fix for the malfunction. Engineers speculate that one of the flow control valves for the station's ammonia coolant suffered from a malfunction, leading to a temperature imbalance which caused the system to shut down automatically. If this supposition is correct, remedying the problem could be as easy as uploading a fresh set of management software for the valve.

While observers expect the international team of astronauts on board the ISS to quickly resolve the dilemma, even under a worst-case scenario they should remain safe from peril as the result of thorough back-up plans. Were Loop-B to also shut down, the astronauts would still have sufficient air for several days - hopefully buying them enough time to fix the problem.

And even if the failure of the cooling system proved to be intractable, the astronauts can always duck back to earth via the multiple Soyuz capsules rigged to the station.

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