Russia’s space agency is preparing to launch a mission on Friday to provide a ride for two cosmonauts and one U.S. astronaut who are on the International Space Station without a designated ship to get home.
The spacecraft that brought the three crew members to the ISS in the fall later experienced a leak in its radiator cooling loop, and officials from both countries had to develop a new plan to get the trio back to Earth.
Here’s a brief overview of what’s happened so far:
A Russian spacecraft suffered a coolant leak in December
NASA astronaut Frank Rubio and Roscosmos cosmonauts Sergey Prokopyev and Dmitri Petelin arrived at the International Space Station in September aboard the Russian spacecraft Soyuz MS-22, which remained docked at the space station.
On Dec. 14, as Prokopyev and Petelin were preparing to embark on a planned spacewalk, an external coolant leak was discovered on the MS-22, NASA said.
Following an investigation into the leak, Roscosmos engineers determined that the craft wouldn’t be viable for a normal return mission to Earth. It would still be available in the case of an emergency evacuation from the space station.
A Roscosmos official suggested the leak probably occurred when a small meteoroid collided with the ship’s radiator, The Guardian reported.
Russian and U.S. space officials began working on an alternate scheme to return the three crew members to Earth.
A separate leak stymied the first attempt
The new plan was to launch an uncrewed Soyuz MS-23 spacecraft to the ISS on Feb. 19, giving the astronaut and two cosmonauts a functional vessel to fly home in.
But that plan was soon paused after another coolant leak was discovered in a separate vessel on the ISS.
An unpiloted Russian cargo ship called Progress 82 that was docked at the space station suffered an unexplained depressurization of its coolant loop on Feb. 11.
The leak on Progress 82 was not connected to the planned rescue mission, but it prompted engineers at the Russian Mission Control Center near Moscow to investigate why the cargo vessel lost coolant and postpone the launch of the MS-23.
Russian officials have approved the mission for this week
The Soyuz MS-23 is now scheduled to launch on Friday.
Roscosmos announced on Monday that a state commission had issued a permit approving the launch of the replacement ship, the Russian state news agency TASS reported.
The spacecraft will carry roughly 948 pounds of cargo to the space station, including food and equipment for experiments. Rubio, Prokopyev and Petelin will then fly home in the MS-23 in several months. They were originally scheduled to leave by late March but NASA said in January that their missions would now last until September.
Russia’s state commission also decided to return the damaged MS-22 vessel to Earth without a crew, TASS said.