Two American astronauts will step out on a short spacewalk Monday to move a stalled rail car that is stuck outside the International Space Station, NASA said.

Commander Scott Kelly and Flight Engineer Tim Kopra will float out of the orbiting lab to move the mobile transporter rail car "a few inches," NASA said in a statement on Sunday.

Once they coax it to its new position on the station's truss, it will be "latched in place and electrically mated to the complex."

NASA television coverage of the outing begins at 6:30 am (1130 GMT) and the spacewalk should start by 8:10 am (1310 GMT).

The spacewalk should last three hours, about half as long as a typical spacewalk.

The problem began last week when the mobile transporter rail car, a piece of moveable equipment that is attached to the Canadarm2 robotic arm, began to move to another work site.

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.

Engineers at mission control in Houston have been unable to robotically move it back into place.

If the brake was somehow inadvertently engaged, it may be an easy task to unstick it. The astronauts may then turn to a few other get-ahead tasks as part of their ongoing maintenance and upgrades of the ISS.

NASA described the job as a "cautionary measure" that needs to be done ahead of the arrival of the Russian Progress supply ship on Wednesday.

The US space agency announced last week that an unplanned spacewalk would likely be necessary, and mission managers decided after meeting Sunday to go ahead with the outing on Monday.