Two US astronauts floated outside the International Space Station on Monday in a hastily planned spacewalk to move a stuck rail car before a Russian cargo ship reaches the outpost on Wednesday, NASA said. Station commander Scott Kelly and newly arrived flight engineer Timothy Kopra were due to spend about 3.5 hours on an abbreviated spacewalk to latch the stalled car into a parking spot along the station’s exterior truss.

The car serves as a mobile base for a Canadian-built robotic crane to move rails outside the station, a $100 billion research laboratory that files about 250 miles (400 km) above Earth. The rail car jammed about 4 inches (10 cm) short of its intended latching point last Wednesday, blocked by a crew equipment cart that was left with its brake on.

Kelly and Kopra fixed the stuck rail car in 15 minutes, leaving them time to tackle work to prepare the station for new modules, said mission commentator Rob Navias from NASA’s Johnson Space Center in Houston.

Russia, one of 15 nations that own and operate the station, plans to launch a new research laboratory, while the US National Aeronautics and Space Administration is preparing to install docking ports for new commercial space taxis that are slated to begin flying in 2017.

NASA usually spends months planning spacewalks, but the one that began shortly before 8 a.m. EST (1300 GMT) was just arranged over the weekend.

Kopra arrived at the station six days ago with Britain’s first professional astronaut, Timothy Peake, and Russia’s Yuri Malenchenko. Kopra and Kelly released the brake handle during the spacewalk, freeing up the mobile transporter, Navias said.

A Russian Soyuz rocket carrying a Progress cargo ship blasted off from the Baikonur Cosmodrome in Kazakhstan at 3:44 a.m. EST (0844 GMT) and is due to reach the station on Wednesday.