NASA officials announced on Friday that astronauts onboard the International Space Station (ISS) are set to conduct an unscheduled spacewalk next week to fix a railcar used by the orbital facility's robotic arm.

ISS crewmembers Tim Kopra and Scott Kelly will carry out the spacewalk as early as Monday, Dec, 21, to try and free up the space station's Mobile Transporter that has stopped operating last Wednesday while being controlled via remote by flight controllers on Earth.

The astronauts have to complete the maintenance work on the railcar before an unmanned Russian Progress supply ship arrives on Dec. 23.

Kenny Todd, manager of the ISS's Mission Integration and Operations, said that engineers from NASA believe the railcar stalled because of a brake handle that has gotten stuck.

The Mobile Transporter railcar is a rail-based platform that makes up a majority of the orbital facility's primary truss. It was designed to allow the robotic arm of the ISS to reach different areas of the space station.

The railcar is currently only 4 inches from the latch point it was intended to reach where controllers can secure it into place and have it powered before the arrival of the Progress spacecraft.

The unmanned Progress 62 supply ship is making its launch from Kazakhstan's Baikonur Cosmodrome on Monday, Dec. 21. It is expected to dock at the International Space Station two days later.

Todd said that they will assess the situation of the stalled Mobile Transporter and develop a plan to have it freed over the weekend. ISS management team members will meet on Sunday to find out whether they will push through with the astronauts' spacewalk on Monday or schedule it on Tuesday.

The spacewalk, which will take up to three and a half hours to finish, will be televised live by NASA.