NASA astronauts to take space walk to fix International Space Station rail car

NASA astronauts will take a previously unscheduled space walk as early as Monday to fix stalled equipment outside the International Space Station.

Tim Kopra

A PAIR of NASA astronauts will step out on a previously unscheduled space walk as early as Monday to fix a piece of motorised equipment that stalled outside the International Space Station.

The mobile transporter rail car — used to position the station’s robotic arm — stalled on Wednesday just 10cm from where it began its move, said the US space agency in a statement.

The Canadian-made robotic arm is used to reach out and grab approaching US cargo ships and was most recently used for the arrival of Orbital ATK’s Cygnus spacecraft on December 9.

Efforts to correct the problem robotically from mission control in Houston failed.

Prepare for landing ... the Cygnus spacecraft approaching the International Space Station. At right is the station's robot arm. Picture: Scott Kelly/NASA

Astronauts Scott Kelly and Tim Kopra will float outside the orbiting lab to move the rail car “so it can be latched in place ahead of the Wednesday, December 23 docking of a Russian cargo resupply spacecraft,” NASA said.

The Progress spacecraft docks automatically so it doesn’t need the robotic arm, but a NASA spokeswoman said it is important for the mobile transporter to be latched in place prior to Progress’ arrival.

Joining the scheduled space walk ... NASA astronaut Scott Kelly. Picture: NASA/Scott Kelly

Set to take a space walk ... US astronaut Tim Kopra.

“It’s currently not latched since it stalled while they were trying to move it,” she told AFP.

The cause of the stall remains unclear, but “experts believe it may be related to a stuck brake handle,” according to ISS mission integration and operations manager Kenny Todd.

.@Space_Station Ops Mgr Kenny Todd talks about a likely #spacewalk for us next week https://t.co/YMyJh2eBhI pic.twitter.com/HWummAoMJe

— Scott Kelly (@StationCDRKelly) December 18, 2015

A time for the space walk has not been announced, but NASA said it will happen no earlier than Monday, or perhaps Tuesday.

A final decision will be made after a mission management meeting on Sunday.