Two astronauts are undertaking a crucial spacewalk to make urgent repairs to a cooling system on the International Space Station.
Douglas Wheelock and Tracy Caldwell Dyson are carrying out the first of two walks that will be needed to repair a broken ammonia coolant pump.
There are two cooling units on the ISS needed to deal with temperatures that can range from 121C (250F) to minus 157C (-250F).
The second unit is so far unaffected.
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. BBC News
