MIAMI (AFP) - Two solid whacks to a stuck brake handle was all it took for a spacewalking American astronaut to fix a stalled rail car outside the International Space Station, Nasa said on Monday (Dec 21).

"That was pretty easy," Commander Scott Kelly said, according to a live broadcast of the spacewalk on Nasa television, after he hit the stuck brake handle and got the car moving again.

Kelly and his fellow spacewalker, US flight engineer Tim Kopra, made swift work of the job and accomplished their main mission in less than an hour.

The mobile transporter rail car carries the robotic arm from one location to another on the outside of the orbiting lab.

It was fully latched back into place at 8.35am (9.35pm Singapore time), just 50 minutes after the spacewalk began.

The rail car's brake was believed to have become stuck unexpectedly last week after it moved about 10cm from its starting point.

The car needed to be latched in place so as not to interfere with the arrival of the Russian Progress supply ship on Wednesday.

After Kelly and Kopra moved the rail car, they routed cables to prepare for a new docking adapter for commercial cargo ships.

The shorter-than-usual spacewalk ended after three hours and 16 minutes, about half the duration of a regular outing.

Kelly is spending a year in space, along with Russian cosmonaut Mikhail Kornienko, in order to study the effects of long-duration spaceflight on the human body and mind.

The duo will return to Earth in March.

Monday's spacewalk was Kelly's third for his career, and was Kopra's second.

It was the 191st spacewalk in the history of building and maintaining the ISS.