Astronauts help move stalled rail car during spacewalk at the International

NASA astronaut Scott Kelly is seen during his first spacewalk outside the International Space Station on October 28, 2015. The vehicle is not in its usual spot and hence Mike Hopkins, another astronaut at the Mission Control warned Kelly and Kopra from accidentally contacting the MT.

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.

The green light for the unplanned spacewalk to take place Monday came three days after the Mobile Transporter stalled just four inches away from its embarkation point at worksite 4 near the center of the station’s truss as it began to move to another worksite to support robotic payload operations with its attached Canadarm2 robotic arm and the Special Purpose Dexterous Manipulator (Dextre).

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. Kelly and Kopra’s spacewalk optimized the station for receipt of the cargo, CBS News reported.

With their primary task completed, Kelly and Kopra split up to work on separate tasks of routing cables along the space station.

The robotic cargo ship, called Progress 62, is scheduled to launch toward the space station from Baikonur Cosmodrome in Kazakhstan on Monday at 3:44 a.m. EST (0833 GMT).

The outing by Scott Kelly and Tim Kopra began at 7:45 am (1245 GMT), the U.S. space agency said. Kopra, Peake and cosmonaut Yuri Malenchenko arrived at the space station on Tuesday (Dec. 15).

Kelly and Kornienko are flying a one-year mission to the space station and due to return to Earth in March with Volkov, who is on a six-month trip.