Two astronauts have completed a six-hour spacewalk to install a parking spot on the International Space Station (ISS).

Jeff Williams and Kate Rubins stepped outside the orbiting lab to fit an adapter, which will be used by private spacecraft to dock at the station in the coming years.

The adapter launched aboard a SpaceX Dragon cargo ship last month, and NASA has called the equipment "a metaphorical gateway to a future".

ISS operations manager Kenneth Todd said it is a "very significant milestone on the path to establishing commercial crew capability."

Image: Don't look down ... one of the astronauts on the spacewalk

The adapter is one metre tall and 1.6 metres wide.


It will work with Boeing's CST-100 Starliner and SpaceX's Crew Dragon - both are currently under construction and will eventually be used to ferry astronauts to the space station.

It is more sophisticated than previous equipment because it will allow automatic parking instead of the current grapple and berthing process managed by astronauts.

Lead spacewalk officer Glenda Brown said: "In space, it has got a lot of capability, but on the ground it can barely support its own weight."

NASA is planning a second spacewalk on 1 September for a separate operation to retract one of the thermal radiators outside the space station.