Science & Environment

Second spacewalk under way to fix ISS cooling units

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Media captionWatch part of the second spacewalk carried out by the NASA astronauts

A second spacewalk to repair vital cooling units on the International Space Station is under way.

The ISS has been operating with half its cooling capability, crucial for keeping electronics from overheating, since a coolant pump failed in July.

An attempt to fix the cooling units on Saturday was aborted after astronauts struggled to detach hoses connected to them, causing ammonia to leak out.

A third spacewalk will still be required to replace the coolant pump.

The unit, approximately the size of a bathtub, is one of two that cools the station.

Nasa said the three Russian cosmonauts and three US astronauts aboard the ISS were not at any risk, but that the sole functioning coolant system was having to do all the work.

Difficulties

Astronauts Douglas Wheelock and Tracy Caldwell Dyson had hoped to remove the faulty pump on their first spacewalk, but it took longer than anticipated to remove hoses connected to the unit.

They were working on the hoses for over eight hours, one of the longest spacewalks in history.

When the astronauts wrestled one of the hoses free they were sprayed with ammonia, forcing them to call off the spacewalk and return inside to clean their suits.

The difficulties meant Nasa mission control had to add a third spacewalk to their itinerary in order to replace the pump, which failed one-and-a-half weeks ago. That is not expected to happen until Sunday.

The cooling units allow the station to cope with external temperatures ranging from 121C (250F) to -157C (-250F).

If the second of the two cooling units were to fail - said to be a highly unlikely scenario - the crew would not be in immediate danger as they could move to the Russian segment of the station, which has its own cooling system.

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