CAPE CANAVERAL, Fla. - Two US astronauts floated outside the International Space Station on Wednesday for the second of three spacewalks to begin preparing parking spots for new commercial space taxis.
Station commander Barry "Butch" Wilmore, 52, and flight engineer Terry Virts, 47, left the station's Quest airlock just after 7 a.m. EST (1200 GMT) and headed to the space shuttle's old docking port, a NASA Television broadcast showed.
The spacewalkers struggled a bit to remove a cover protecting the berthing slip, one of two sites being reconfigured for new spaceships under development by Boeing and Space Exploration Technologies, or SpaceX.
"This thing has rigidified out here," Wilmore radioed to flight controllers in Houston.
"That's as expected, so good luck with that," replied astronaut Joe Acaba at Mission Control.
The cover's removal was another step to prepare the station for new international docking port adapters that are due to arrive later this year. The adapters will be installed during four more spacewalks NASA plans in 2015.
On Saturday, Wilmore and Virts installed about 340 feet (104 meters) of power and data cables to support the new docking systems. During Wednesday's spacewalk, scheduled to last about 6.5 hours, they planned to attach two more cables and lubricate the grapple fixture at the end of the station's robot arm.
The spacewalkers also will prepare the Tranquility connecting node for the September arrival of an experimental inflatable habitat built by privately owned Bigelow Aerospace.
Las Vegas-based Bigelow is developing free-flying expandable habitats for lease by agencies, researchers and businesses. NASA is looking at the technology for future human expeditions beyond the station's 260-mile (418-km) high orbit.
The station, a partnership of 15 nations, is a collection of laboratories and platforms for materials and life science experiments, Earth studies, physics and other investigations that take advantage of the microgravity environment and unique vantage point of space.
The Russian space agency Roscosmos said on Tuesday it would remain part of the international outpost until 2024, a four-year extension proposed by the United States.