NASA astronauts have successfully completed their third spacewalk in just over a week to complete an extensive cable job at the International Space Station.
The work - involving nearly 244 metres of cable over three spacewalks - is needed for new crew capsules commissioned by NASA. A pair of docking ports will fly up later this year, followed by the capsules themselves, with astronauts aboard, in 2017.
American astronauts Terry Virts and Butch Wilmore had 122 more metres of power and data cable, as well as two antennas, to install today. They successfully routed 111 metres on their first two excursions, on February 21 and last Wednesday.
NASA hasn't conducted such a quick succession of spacewalks since its former shuttle days, and the amount of cable work is unprecedented. Even more spacewalks will be needed once the new docking ports start arriving in June.
"Good luck, guys," Italian astronaut Samantha Cristoforetti said from inside the station as the spacewalk got under way.
Within the first hour, the astronauts had hooked up both antenna booms and got started on the cable work. There were wires everywhere, and the men had to move their bodies in different positions to access one especially cramped work site.
This month, meanwhile, marks the 50th anniversary of the world's first spacewalk. Soviet cosmonaut Alexei Leonov floated out into the vacuum of space on March 18, 1965, beating America's first space walker, Gemini 4's Edward White II, by just 2.5 months.
Before approving today's spacewalk, engineers spent two days analysing a water leak in Virts' helmet that occurred on Wednesday when he was back in the air lock and the chamber was being repressurised.
Engineers concluded it was the result of condensation, and a safe and well understood circumstance that had occurred several times before with the same spacesuit. Virts was never in danger, according to NASA.
Wilmore's suit functioned perfectly during the first two spacewalks, but today a pressure sensor briefly malfunctioned before he floated out. A mechanical gauge, however, was operating fine. Mission Control told Wilmore that he would need to pay extra attention to how his suit was feeling throughout the seven-hour excursion.
Wilmore is due to return to Earth next week following a five and a hald month mission. Virts is midway through his expedition. Russian Soyuz spacecraft carried them both up, with NASA paying for their multimillion-dollar tickets.
To save money and to stop being so reliant on the Russian Space Agency, NASA has hired Boeing and SpaceX to develop spacecraft capable of transporting astronauts to the space station. The two contracts are worth nearly $7 billion.