Air Leak from Zvezda Module on ISS Successfully Sealed by Roscosmos

On June 13, 2025, it was reported by Roscosmos that the air leak from the «Zvezda» module on the International Space Station (ISS) has been resolved. The Russian segment of the station comprises six modules: «Zvezda,» «Zarya,» «Rassvet,» «Poisk,» «Nauka,» and the docking module «Prichal.»

«Roscosmos continues its daily monitoring and maintenance of all systems within the Russian segment of the International Space Station. The latest stage of sealing the transition chamber of the service module ‘Zvezda’ has been completed. According to experts from the Mission Control Center, there are no leaks in the Russian segment of the ISS. The issue of air leaking from the intermediate chamber of the ‘Zvezda’ module has persisted for over five years, first becoming known in September 2019. Multiple attempts have been made in recent years to fix the leak, but these efforts yielded only partial results. After the sealing process in June 2025, tests indicate that the air leak in the transition chamber has completely ceased for the first time since it was detected,» explained Roscosmos.

On June 12, 2025, NASA and Axiom Space postponed the launch of the commercial mission «Ax-4» to the ISS aboard a SpaceX Falcon 9 rocket due to an unexpected drop in pressure within the Russian «Zvezda» module after the completion of repair work on sealing elements in the module’s aft section.

A year earlier, NASA reported that the air leak from the Russian «Zvezda» module had doubled and was (according to unconfirmed information from Roscosmos) occurring at a rate of 1 kilogram per day. The transition chamber (TC) of the Russian segment of the ISS is currently sealed. Roscosmos confirmed the presence of a leak and stated that this incident does not pose a threat to the crew and that the station’s operation continues normally.

«Specialists have been monitoring the air leak aboard the ISS. The crew regularly carries out work to locate and eliminate potential leak sites, and data from the station is sent for analysis to specialists as part of routine operations. There is no danger to the crew or the station,» a representative from Roscosmos explained to the media.

Previously, air leaks had been detected in the «Zvezda» module. At that time, the rate of atmospheric pressure drop aboard the station was 0.3 to 0.4 mmHg per day, while a critical emergency threshold on the ISS is considered to be 0.5 to 1 mmHg per hour. Such values were recorded in late 2020, but after sealing the suspected leak area, the loss of air aboard the ISS stabilized and decreased.

In mid-January 2021, while searching for a second leak site in the «Zvezda» module, the air leak rate on the ISS was approximately 0.9 to 1.4 kg per day (the normal rate is 0.7 kg per day). During that time, a patch applied by the cosmonauts near the crack reduced the leak rate but did not eliminate it entirely.

Roscosmos had previously sent a powerful microscope to the ISS to help locate the leak, along with a repair kit to seal the elements of the transition chamber and additional oxygen to compensate for the leak.

The main module of the Russian segment, «Zvezda» (17KSM factory no. 12 801), with the transition chamber, was manufactured in 1986. The first cracks in the module appeared in 2020, and leaks have been consistently recorded since then.

In October 2020, Russian cosmonauts informed Mission Control that they had finally located the exact source of the air leak in the transition section of the «Zvezda» module of the ISS. A teabag was instrumental in detecting the leak. Previously, Roscosmos had instructed the cosmonauts to reduce the volume of the transition chamber using film and to attempt to localize the leak’s source.