A Russian spacecraft started leaking uncontrollably on Wednesday night

A Russian spacewalk was called off at the last minute on Wednesday night due to a large leak.

When flight controllers told Sergey Prokopyev and Dmitri Petelin to take a break, they were wearing space suits with the airlock depressurized. Shortly before 10pm, the spacewalk was stopped.

The leak appears to have come from an external cooling loop located at the rear of the spaceship. Rob Navias, who was commentary on the spacewalk for NASA Television, characterized the leak as fairly substantial. Particles were streaming from the Soyuz in the video. Russian officials have not confirmed the use of ammonia, but it is likely.

All of the crew members on the space station were safe. There was a leak outside the station.

The ride back to Earth for Prokopyev, Petelin, and NASA's Frank Rubio is questionable due to the leak. They were on the space station in September and will return to Earth in the spring. The leak continued after 3 hours Monday night.

It is possible that the ability to undock from the space station won't be affected by the Soyuz. If Russian engineers determine there is an issue, a replacement Soyuz would need to be flown up to the station. The vehicles have the ability to autonomously dock. The crew members wouldn't have an emergency escape vehicle until the replacement spaceship arrived.

The crew on the station flew up on a Crew Dragon in October. Seven people can't fit in that vehicle.

NASA is likely to have concerns about the impact of ammonia on the surface of the space station and other docked vehicles, given the length of the leak. It will be difficult for the US space agency to conduct a spacewalk on December 19 due to the ammonia on the hardware.