Russia Plans to Seal Off ISS Transfer Tunnel After Persistent Air Leak
Roscosmos intends to permanently close the PrK tunnel connecting the Zvezda module after years of unsuccessful repairs, shifting cargo unloading to the Poisk module.
Russia’s space agency, Roscosmos, is set to permanently seal the hatch between the Zvezda module and the PrK transfer tunnel on the International Space Station, aiming to isolate a long-standing air leak that has resisted multiple repair attempts since its discovery in 2019. The closure will redirect cargo deliveries from the upcoming Progress MS-36 resupply mission to the Poisk module instead of Zvezda.
The leak, first identified in the tunnel linking a docking port to Zvezda, has progressively worsened, with NASA reporting the loss rate rising from about one pound of air per day to 3.7 pounds per day in early 2024. Although a brief improvement was noted in mid-2025, a subsequent pressure drop confirmed the leak remained active.
Roscosmos and NASA have disagreed over both the cause and the remediation methods. Russian engineers proposed using a saw to access a suspected leak area, a plan NASA officials warned "could have resulted in elevated risk to the structure in the area."
With the hatch closed, Russian cosmonauts will lose direct access to the tunnel and will rely on alternative docking ports for future transfers. The move marks the latest step in addressing the aging station’s maintenance challenges.
"could have resulted in elevated risk to the structure in the area."