Space station repairs 'only partial success'
Two astronauts have carried out an eight-hour spacewalk to try to repair a cooling system on the International Space Station but were only partially successful.
Douglas Wheelock and Tracy Caldwell Dyson hammered away and finally removed the unit's hoses but could not replace the bulky item as scheduled.
Two walks were always planned but Nasa says a third will now also be needed.
The faulty unit is one of two that cool the station's systems.
The ISS has to cope with temperatures that can range from 121C (250F) to minus 157C (-250F).
Nasa has said the three Russian cosmonauts and three Nasa astronauts aboard the station are not at any risk but the functioning coolant system is having to do all the work.
The right-hand side system failed dramatically last week, forcing crew to reduce power on the space station and halt experiments.
The walk was the longest at the ISS and the sixth longest ever. The astronauts found the task "tough".
"Wow! That thing is not budging," Wheelock told Mission Control at one point.
Nasa said: "Because of difficulties with the disconnect on the ammonia lines that feed that pump, they were unable to remove the pump."
The astronauts worked so closely their helmets bumped. Wheelock finally unjammed the fourth of four hoses to loud applause from Mission Control.
The pair were also sprayed with ammonia and had to clean off their suits.
"It's got a pretty good snowstorm there," Wheelock said.
Next time the two astronauts will have to remove the failed unit and move a 355kg (780lbs) spare unit about 10m (30ft) in order to insert it into the gap.
The ammonia fluid lines will then have to be connected.
If the second of the two cooling units were to fail - said to be a highly unlikely scenario - then the astronauts would no longer be able to cool most of the components.
The crew would not be in immediate danger, however, as they could move to the Russian segment of the ISS, which has its own cooling system.