Russia has agreed to permanently seal off the PrK module on the International Space Station, bringing an end to a six-year dispute between NASA and Roscosmos over persistent air leaks that NASA considered a “highest risk” safety issue.
The PrK module is a narrow transfer tunnel attached to the aft end of the Zvezda service module on the Russian segment of the ISS, used as a passageway to a docking port for Progress cargo spacecraft. Since September 2019, microscopic structural cracks in the module have been causing slow but persistent atmosphere leaks into space. By early June 2026, the crack count had reached approximately 16.
A long-simmering dispute
The cracks became a major point of tension between NASA and Roscosmos. American officials considered the PrK module’s structural integrity a critical risk, with some NASA engineers warning that the module could “unzip and fail completely” in a catastrophic rapid-depressurization event. Russian officials repeatedly played down the severity, insisting the leaks were manageable.
Previous repair attempts, including the application of sealants and patches, provided only temporary relief. The cracks would reopen and the leak rate would return, sometimes worse than before. The behind-the-scenes dispute dragged on for years as NASA pushed for permanent sealing and Russia resisted, unwilling to lose a docking port.
The breaking point
The situation came to a head on June 5, 2026, when the leak rate doubled to approximately 2 pounds of air per day during cargo operations with the Progress 95 spacecraft. NASA ordered five astronauts to take emergency shelter inside a docked SpaceX Crew Dragon while two Russian cosmonauts performed emergency repairs on the module.
This highly visible shelter-in-place order, described by sources at Ars Technica as a “spectacle in space,” appears to have forced Roscosmos to finally back down from its position. Within days, Russian officials agreed to permanently decommission the PrK module.
What the sealing means
Under the agreement, the hatch connecting the PrK module to the rest of the station will remain permanently closed. Cosmonauts will no longer enter the module, and no further attempts will be made to repressurize it. Russia will reroute Progress resupply and refueling missions to other available docking ports, reducing its docking capacity from four ports to three.
For NASA, the decision eliminates the single highest-risk structural threat on the station, substantially reducing the likelihood of a catastrophic depressurization. For Roscosmos, it means the loss of a docking port and a blow to its claims that the aging Russian segment was in good condition.
Broader implications for the ISS
The ISS is now over 25 years old, and the PrK incident is the most dramatic example yet of the challenges posed by its aging infrastructure. As modules age, structural fatigue, micro-meteoroid impacts, and material degradation become increasingly difficult to manage.
The agreement sets a potential precedent for how future module problems will be handled: rather than endless patching, problematic sections may be retired. This could inform planning for the station’s eventual transition, currently targeted for around 2030-2031, when both NASA and Roscosmos have expressed interest in shifting to commercial space station platforms.
The resolution of the PrK crack dispute also marks a rare moment of cooperation between U.S. and Russian space agencies amid broader geopolitical tensions over the war in Ukraine. The ISS partnership has long been one of the few areas where the two countries continue to work together directly.