US astronauts creating parking spots outside the International Space Station

Two US astronauts have begun rigging parking spots outside the International Space Station for commercial space taxis to dock there in the future.

The work will prepare docking ports for upcoming flights by Boeing and privately owned Space Exploration Technologies, or SpaceX, which are developing capsules to ferry crew to and from the station, which flies about 418km above the earth. The United States has been dependent on Russia for station crew transportation since the space shuttle was retired in 2011.

The first test flight of a new US crew craft isn't expected until late next year, but the station, a US$100 billion laboratory owned by 15 nations, needs to undergo a significant transformation to prepare for the new vehicles, Nasa has said.

That work began on Saturday with station commander Barry Wilmore, 52, and flight engineer Terry Virts expected to install six cables to a docking port on the station's Harmony module, the same site where space shuttles used to berth.

"This will be the most complicated cable-routing task that we have performed (by spacewalkers) to date," Karina Eversly, lead spacewalk official, said.

After two more spacewalks scheduled for Wednesday and next Sunday, the station will be outfitted with a total of 233 metres of new cabling, as well as a communications system to support Boeing's CST-100 and SpaceX's upgraded Dragon capsules.