NASA has confirmed on May 21st that the PrK module, a small transfer tunnel connected to the Zvezda service module, has resumed losing air after several months where the pressure appeared to have stabilized. This issue affects an area that has experienced air leaks and undergone repairs and checks since 2019.
The PrK module, also known as the Service Module Transfer Tunnel, is located between the Zvezda module and an docking port used by Russian spacecraft. In recent years, the leak has been attributed to structural micro-cracks that are difficult to locate and seal precisely in orbit. By January 2026, after various inspections and sealant applications, NASA had indicated that the segment had reached a stable configuration with no measurable leaks.
The situation changed on May 1st, following the undocking of the Progress-95 cargo capsule. Roscosmos detected a slow decrease in pressure within the PrK. According to NASA’s report, data analysis indicated a loss of approximately 450 grams of air per day. Roscosmos subsequently allowed the pressure in the tunnel to decrease gradually while continuing to monitor the leak’s progression.
Currently, NASA states that there are no impacts on ISS operations and no immediate risks to the crew. The area is being maintained at a lower pressure than the rest of the station, with minor repressurizations as needed. This procedure has been applied in previous years: when the module is not in use, the hatch is kept closed to limit the leakage.
A Problem of “Wear and Tear”?
However, the renewed leak confirms that the problem cannot yet be considered definitively resolved. In 2024, the leak in the PrK had reached much higher levels, with peaks of about 1.7 kg of air per day. At that time, NASA had classified the risk as the highest level for both probability and severity within the ISS’s internal risk management system.
The primary challenge remains precisely identifying the origin of the micro-cracks. Repairs performed so far have reduced or temporarily halted the leak but have not eliminated the uncertainty about the structural cause. Therefore, NASA and Roscosmos continue to coordinate to define the next steps and assess whether new inspections of the module will be necessary.
The return of the leak occurs at a delicate phase for ISS management. The station is expected to remain operational until at least 2030, but discussions are ongoing in the United States about the possibility of extending its use until 2032 or beyond. A new anomaly in the Russian segment does not, in itself, necessitate an immediate change in plans, but it adds a significant technical factor to the assessments of safety and maintenance for an orbital structure that has been in service for over twenty-five years.
English Translation and Paraphrasing:
NASA confirmed on May 21st that the PrK module, a small connecting tunnel to the Zvezda service module, has started leaking air again. This comes after a period of several months where the pressure inside the module seemed stable. The issue is related to an area that has been experiencing air loss and undergoing repairs and checks since 2019.
The PrK module, also referred to as the Service Module Transfer Tunnel, is situated between the Zvezda module and a docking port used by Russian spacecraft. For years, the leak has been linked to microscopic structural cracks, which are challenging to pinpoint and seal accurately while in orbit. By January 2026, following multiple inspections and sealant applications, NASA had reported that the segment was in a stable condition with no detectable leaks.
The situation shifted on May 1st, shortly after the Progress-95 cargo capsule completed its mission. Roscosmos observed a gradual pressure drop within the PrK. NASA’s analysis of the data indicates a daily air loss of approximately 450 grams. In response, Roscosmos has been gradually reducing the pressure in the tunnel while continuously monitoring the leak rate.
According to NASA, the current situation does not affect ISS operations and poses no immediate danger to the crew. The affected area is being kept at a lower pressure than the rest of the station, with minor repressurizations performed as needed. This strategy has been employed in prior years: when the module is not in use, its hatch is kept closed to minimize air loss.
An “Aging” Problem?
The reappearance of the leak, however, underscores that the problem is far from being permanently resolved. In 2024, the leak in the PrK module had escalated significantly, reaching daily losses of up to approximately 1.7 kg of air. During that period, NASA had categorized the risk as extremely high in terms of both likelihood and severity within the ISS’s internal risk management framework.
The main difficulty persists in accurately identifying the root cause of these micro-cracks. While past repair efforts have managed to reduce or temporarily stop the leakage, they haven’t resolved the underlying structural uncertainty. Consequently, NASA and Roscosmos are continuing their collaboration to determine the next course of action and to evaluate the necessity of further inspections within the module.
This renewed leak occurs at a critical juncture for the management of the ISS. The station is scheduled to remain operational until at least 2030, with ongoing discussions in the United States about potentially extending its service life to 2032 or even longer. While a new issue in the Russian segment doesn’t automatically alter these plans, it introduces a crucial technical consideration for evaluating the safety and maintenance of an orbital facility that has been in operation for over a quarter of a century.
