Washington: Two US astronauts transformed into spacewalking mechanics on Wednesday as they floated outside the International Space Station to grease a robotic arm and help prepare parking docks for commercial crew capsules.
Commander Barry "Butch" Wilmore and flight engineer Terry Virts began their six-and-a-half hour spacewalk at 6:51 am (12:51 GMT) when they placed their suits on internal battery power before emerging from the airlock, NASA said.
The astronauts are both wearing helmet cameras that allow viewers on Earth to see the spacewalkers` perspective, as part of a live broadcast on NASA television and on its website.
The team`s goal for the spacewalk is to route two bundles of cable, lubricate latching parts of the space station`s robotic arm and prepare for another operation later this year to move modules around the orbiting outpost.
Virts began greasing screws and bearings at the end of the 17-meter-long (56-foot) Canadian robotic arm, called Canadarm 2, about halfway through the spacewalk.
The whole robotic arm process will take about three hours, said NASA commentator Rob Navias.
Launched in 2001, the robotic arm is regularly used to move equipment and astronauts around the exterior of the space station.
It also reaches out to grab the arriving unmanned space capsules bringing supplies and science experiments to the space station.
Navias described the robotic arm as "the workhorse for the assembly of the space station," and said parts of it have "grown a bit arthritic."A key part of the spacewalkers` mission is to set up additional docking ports -- which are essentially parking spots for space taxis -- at the ISS for the arrival of more crew-carrying spacecraft.
Boeing plans to send its first astronaut to space aboard the CST-100 spaceship in late 2017, followed by SpaceX soon after.
During the first outing by Wilmore and Virts on Saturday, the pair routed 364 feet (110 meters) of cable, with goal of setting up 700 feet by the end of the final spacewalk of this series on Sunday.
Several more spacewalks in the coming months will help the station get ready for the arrival of a pair of international docking adapters that will be delivered later this year.
Traffic to the ISS is expected to increase once private industries like SpaceX and Boeing get their crew capsules up and running.
The flights will restore US access to the orbiting lab where global crews of astronauts live together for six months at a time.
California-based SpaceX, with the creation of its Dragon cargo craft, became the first US commercial spaceship to begin supply missions to the ISS in 2012.
However, Boeing is expected to be the first to send astronauts to space when its CST-100 is ready for a crew flight in December 2017.
The retirement of the 30-year space shuttle program in 2011 left the United States without a spaceship that could send astronauts to low-Earth orbit.
In the meantime, the world`s astronauts are riding aboard Russian Soyuz capsules at a price of $70 million per seat.