Two NASA astronauts have ventured out of the International Space Station in their third spacewalk in just over a week.
Terry Virts and Butch Wilmore went into space on Sunday morning with 122 metres of cable and two antennas to install. Once that's complete, the spacewalkers will have routed nearly 244 metres of power and data lines, all of it needed for future American crew capsules.
NASA is paying Boeing and SpaceX nearly $US7 billion ($A8.98 billion) to develop spacecraft capable of transporting astronauts to the space station.
The first manned flight is targeted for 2017. New docking ports will fly up later this year.
Virts and Wilmore's first spacewalk was on February 21 and their second was on Wednesday. NASA hasn't conducted such quick spacewalks since its former shuttle days.
