NASA announced Friday that air leaks had led the agency to instruct five astronauts on the International Space Station to prepare for possible evacuation. The leaks were found in the transfer tunnel of the Zvezda Service Module. This Russian-built module measures about 43 feet long and houses living quarters along with life support, communications, power distribution, data processing, flight control and propulsion systems. It was the first complete Russian addition to the ISS and features a docking port for Soyuz and Progress spacecraft.
The station orbits roughly 250 miles above Earth and is run by five agencies: NASA, the Canadian Space Agency, the European Space Agency, the Japan Aerospace Exploration Agency and Roscosmos. Crews from these partners carry out microgravity research, and humans have lived aboard continuously for 25 years, a milestone marked in November 2025.
The ISS is split into the Russian Orbital Segment managed by Roscosmos and the US Orbital Segment operated by NASA and its partners. A fifth US astronaut, currently on a 190-day stay with two Roscosmos cosmonauts, joined the four members of NASA’s SpaceX Crew-12 in sheltering for potential departure.
The leaks in the Zvezda transfer tunnel, known as PrK, have been monitored for some time. Roscosmos chose to begin more extensive repairs on Friday after fresh leaks appeared. NASA issued the shelter order as a precaution while both agencies continue investigating the cause and applying mitigation steps.
