NASA and Roscosmos are managing an ongoing atmospheric leak within the PrK transfer tunnel of the International Space Station’s Zvezda service module. While the issue has persisted since 2019, recent cargo operations involving the Progress 95 spacecraft prompted a temporary increase in leak rates, leading to precautionary safety measures for the crew on board.
Why the PrK Module Leak Rate Increased
The leak rate in the Zvezda module’s transfer tunnel rose to approximately two pounds per day during the week of June 1, 2026, according to NASA. This uptick occurred during cargo operations with the Progress 95 spacecraft. Engineers subsequently identified new suspected leak areas within the PrK, a structure that has been the focus of long-term mitigation efforts by Roscosmos, including the application of temporary and permanent sealants.
The PrK module functions as a critical transfer tunnel, connecting the Zvezda Service Module to the rest of the Russian segment. Keeping this pressure vessel sealed is vital for station operations.
What Happens During a “Safe Haven” Procedure
On June 5, 2026, NASA directed four SpaceX Crew-12 members and NASA astronaut Chris Williams to enter a “safe haven” posture. This precautionary step was taken while Roscosmos evaluated a potential structural repair plan that involved cutting a bracket to access suspected leak sites. NASA noted that this specific repair method carried potential risks to the surrounding station structure. During this time, the crew sheltered inside the SpaceX Dragon spacecraft as a safety measure.
Status of Repair and Future Monitoring
Roscosmos opted to pause the structural repair work on the morning of June 5 to gather more data and perform additional measurements, according to NASA. Following this decision, the crew ended their safe haven activities and resumed normal operations. NASA continues to coordinate with Roscosmos and international partners to ensure the leak is addressed and station operations remain stable.
Comparison of Leak Management Strategies
| Period | Status |
|---|---|
| January 2026 | NASA reported the PrK module had reached a “stable configuration” after sealant applications. |
| May 2026 | A leak was detected again, with a loss of about one pound per day. |
| June 2026 | Leak rate increased to two pounds per day during cargo operations, prompting an evaluation of structural repairs. |
Frequently Asked Questions
Is the International Space Station crew in danger?
No. NASA has stated that there are no impacts to station operations and that the current leak rates are being managed through monitoring and repressurization.
What is the PrK module?
The PrK is a transfer tunnel attached to the Zvezda Service Module on the Russian segment of the space station, which has been the site of microscopic structural cracks since 2019.
How is the leak being fixed?
Roscosmos has used both temporary and permanent sealants. Recent efforts to perform structural repairs were paused to allow for further data collection and analysis.
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