The International Space Station (ISS) has been in orbit for decades, providing humanity with a key research outpost during a transitional time for space exploration. The multinational effort to assemble the station was a huge success, and the ISS has avoided any major incidents thanks to careful management and maintenance. But it is getting old, and the cracks are beginning to show -- literally.

NASA and Russia's Roscosmos cannot agree on how dangerous the leaks in the Zvezda module may be to the station. While Russia believes the risk is low, NASA is reportedly concerned the leaks could lead to a catastrophic structural failure.

The leaky module is not new -- cosmonauts first detected the leak in 2019. The tiny cracks formed in a tunnel known as PrK that connects Zvezda to the Russian docking module where Progress cargo vehicles attach to the station. The leaks were initially almost undetectable, but the severity has increased over time. Earlier this year, the leak had grown from less than one pound of atmosphere per day to 3.7 pounds.

NASA recently claimed efforts to address the leak have successfully lowered atmosphere loss by a third. In that September briefing, NASA downplayed the severity of the leak, but NASA's discomfort with the escalating leak was on display at a Nov. 13 ISS Advisory Committee meeting.

Roscosmos apparently thinks the leaks are the result of "high cyclic fatigue" from consistent micro-vibrations Zvezda has experienced since its installation in 2000. However, NASA takes a dimmer view, calling out several possible causes, including pressure stress, material properties, and long-term environmental exposure. Roscosmos continues to search for and patch the cracks in PrK and does not believe catastrophic disintegration of the module is realistic. However, NASA continues to push for more action based upon the belief inside the agency that the leaks could lead to structural failure.

The Russian Zvezda module and its Progress docking ports. Credit: NASA

This is backed up by a recent Office of the Inspector General (OIG) report (PDF), which explored the disconnect between NASA and Roscosmos. The agencies apparently cannot agree at what point the leaks could present a clear and present danger to the station, but the OIG report calls it a "top safety risk."

Bob Cabana, chair of the ISS Advisory Committee, believes the two agencies still need to come to a common understanding of ISS structural integrity. "The Russians believe that continued operations are safe but they can't prove to our satisfaction that they are, and the U.S. believes that it's not safe but we can't prove to the Russians' satisfaction that that's the case," Cabana tells SpaceNews.

For now, NASA is having American astronauts close the hatch to the Russian side of the ISS whenever the PrK tunnel is in use. If NASA is proven correct and the leaks escalate, the crew is prepared to seal the PrK hatch permanently.

NASA currently expects to maintain the ISS through 2030, at which time it will have a SpaceX tug deorbit the station. However, this plan is dependent on the launch of commercial space stations, none of which have moved beyond the design stage.