WASHINGTON — While leaks in a Russian section of the International Space Station have stopped, engineers still don’t understand how the cracks formed or how to deal with them for the rest of the station’s life.
At an April 29 meeting of the International Space Station Advisory Council, Bob Cabana, the chairman of the committee, said the cause of cracking in PrK, a vestibule in the Zvezda service module that links a docking port with the rest of the station, remains under investigation.
Cabana, a former astronaut and NASA associate administrator, said his committee met with its Russian space agency counterparts, the Roscosmos Advisory Expert Council, in Houston in March as a “joint commission” to discuss the status of the station, with an emphasis on the cracking in PrK.
“The joint commission noted that NASA and Roscosmos technical teams have made significant progress in understanding the root cause and mitigations of cracking in the PrK,” he said, but had failed to identify a single root cause.
He said those technical teams had identified two potential causes: very high cycle fatigue from pump vibrations or environmental-assisted cracking. Testing and analysis continue, he said, with a goal of identifying the cause the next time the joint commission meets, the date of which he did not disclose.
The cracks have been the source of small but persistent air leaks in the station for several years, resulting in PrK being sealed off from the rest of the station when not in use. Recent efforts by Russian cosmonauts on the ISS to apply sealant to the cracks, though, appear to have stopped the leaks.
“The current position right now is there are no leaks,” Joel Montalbano, acting associate administrator for space operations and a former ISS program manager, said at a March 25 House Science Committee hearing. “They’ve put some sealant over it and we’re not leaking.”
That did not mean, though, that the problem with the cracking in PrK was solved. “We’re still worried about the structure there,” he said. When the vestibule is being used, NASA and other non-Russian ISS crew members stay on the U.S. segment of the station, with a hatch between the U.S. and Russian segments closed.
Montalbano said they also minimize the time that the PrK is pressurized, and that NASA was working with Russia to assess using other ports for visiting vehicles, like the Progress cargo spacecraft, “so we can save that port for the lifetime of the International Space Station.”
Cabana said at the council meeting that the joint commission recommended a “conservative approach” to continued use of PrK until the root cause is found, including using it at reduced pressure and closing the hatch between the Russian and U.S. segments when the PrK hatch is open.
However, while he said the agencies have made progress on the PrK cracking, “the teams have not yet agreed on the severity of the consequences of the cracks,” he said. That lack of consensus has been a long-running issue, one Cabana noted at a November 2024 meeting of the council.
He added that while station officials agree to minimize the time the PrK is pressurized, “the NASA team continues to have concerns over the length of time that the PrK remains at pressure.”
He added that NASA and Roscosmos signed a protocol in August 2025 about lowering the pressure in PrK when not in use. “This lower pressure is not always being adhered to, and teams are comparing analysis.”
The joint commission also reviewed other ISS issues, including the effects on the station from delayed Progress launches caused by damage to a Baikonur launch pad last November, as well as the early return of the Crew-11 mission because of a medical issue with one of the astronauts.
They also got an update on Boeing’s CST-100 Starliner, which has yet to return to flight after experiencing thruster problems on its mid-2024 crewed flight test mission to the ISS. Uncertainty about when Starliner will be certified, Cabana said, “creates challenges for crew training, crew rotations and flight plans,” and the joint commission recommended that NASA provide Roscosmos with updated safety hazard reports before Starliner’s next mission to the ISS.
The joint commission also reviewed planning for the deorbiting of the ISS, including backup options should the United States Deorbit Vehicle not be available. NASA is still officially planning for a 2030 retirement of the ISS, but a Senate bill would extend NASA’s authorization to operate the ISS to 2032.
The space station’s multilateral control board, he said, has an “expressed desire that the decision by the partner agencies for ISS deorbit or extension be made by the end of 2026 to allow for the initiation of coordination of government approvals and procurement of necessary vehicles.”
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