Spacewalkers Barry "Butch" Wilmore and Terry Virts work at the front of the International Space Station, installing cables needed for new docking mechanisms that will be launched later this year. NASA TV

Astronauts Barry "Butch" Wilmore and Terry Virts floated back outside the International Space Station Wednesday for the second of three spacewalks to help ready the lab complex for dockings by commercial crew capsules being built by Boeing and SpaceX.

Floating in the Quest airlock module, Wilmore and Virts switched their spacesuits to battery power at 6:51 a.m. EST (GMT-5) to officially kick off a planned six-and-a-half-hour spacewalk, the second of three outings planned by the Expedition 42 crew.

For identification, station commander Wilmore, call sign EV-1, is wearing a suit with red stripes and will be using helmet camera No. 18. Virts, EV-2, is wearing an unmarked suit and will use helmetcam 20. The mission control communicator, or CAPCOM, for the spacewalk is veteran astronaut Joe Acaba.

During a six-hour 41 minute EVA Saturday, the astronauts laid out eight bundles of cables near the front of the space station that will supply power and data to new docking port mechanisms that will be launched and installed later this year.

During Wednesday's outing, they first removed a protective cover from a docking port extension on the front end of the space station that was once used by visiting space shuttles. The cover turned out to be fairly stiff, but the astronauts managed to stuff it in a stowage bag as planned.

"Hey Joe, please don't ask us how we did it," Virts joked with Acaba.

"I tell you what, I wish I had a video of it," Wilmore said.

"That was the 'stuff your sleeping bag in the bag in the morning' technique," Virts quipped.

The spacewalkers then stowed no-longer-needed shuttle power cables that were disconnected Saturday before installing two final sets of power and data cables needed by the docking mechanisms.

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Second spacewalk advances space station upgrades