by 
NASA TV
A Russian spacewalk was called off at the last minute Wednesday night when a spacecraft attached to the International Space Station unexpectedly caused a major breach.
Cosmonauts Sergey Prokopyev and Dmitri Petelin were wearing spacesuits, with the airlock depressurized, when flight controllers told them to stand by while a leak in a Soyuz spacecraft was investigated. The spacewalk was later canceled just before 10pm ET (03am UTC on Thursday).
The leak appears to have originated in an external cooling loop located at the aft end of the Soyuz MS-22 spacecraft. Public affairs officer Rob Navias, who was commenting on the spacewalk for NASA Television, called the spacecraft a “pretty substantial” loss. Video of the leak showed particles streaming continuously from the Soyuz, quite a remarkable sight. It was likely ammonia, which is used as a coolant for spacecraft, although Russian officials have not confirmed this.
At no time were any of the space station crew members in danger, including Prokopyev and Petelin, their fellow cosmonaut Anna Kikina; NASA astronauts Frank Rubio, Nicole Mann and Josh Cassada; and Japanese astronaut Koichi Wakata. The leak was outside the station, not inside the orbiting laboratory.
However, the leak raises questions about the viability of the Soyuz spacecraft, which is the return journey to Earth for NASA’s Prokopyev, Petelin and Frank Rubio. They were launched to the space station in September aboard this Soyuz vehicle and are expected to return to Earth next spring. After three hours on Monday evening the leak remained ongoing, showing no signs of abating.
The Soyuz is a rugged spacecraft, so it is plausible that there could be no impact on its ability to undock from the space station and return to Earth. However, if Russian engineers — and those at NASA, considering Rubio will be on board — determine there’s a problem, a replacement Soyuz would have to be flown to the station. Soyuz vehicles have the ability to autonomously launch and dock. However, it would mean that, until the replacement spacecraft arrived, the three crew members would not have an emergency escape vehicle.
NASA TV
The other four astronauts aboard the station flew on a SpaceX Crew Dragon spacecraft in October. That vehicle can’t accommodate seven people for a return to Earth.
Given the long duration of the leak, NASA is also likely to have concerns about the impact of all that ammonia on the surfaces of the space station and those of other docked vehicles. Much of the ammonia would likely evaporate from the surface of the hardware over time, but it will certainly complicate matters as the US space agency works to conduct its own spacewalk on Dec. 19 to install new solar panels.
