International space station astronauts are aiming to finish repairing a faulty cooling system in a third spacewalk that will begin at 1155BST on Monday.

Astronauts Tracy Caldwell Dyson and Douglas Wheelock removed a faulty pump in two spacewalks, the first of which was complicated by an ammonia leak.

The spacewalkers must now replace the pump, which cools station equipment.

The space station has been working at reduced cooling capacity since the pump first failed on 31 July.

The enormous pumps circulate ammonia in heat exchangers outside the station, where water cannot be used because it would freeze.

A second pump has taken the place of the failed unit, and Nasa has stressed that the failure presents no risk to the crew.

Source : bbc.co.uk