WASHINGTON \u2014 While leaks in a Russian section of the International Space Station have stopped, engineers still don\u2019t understand how the cracks formed or how to deal with them for the rest of the station\u2019s life.<\/p>\n
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.<\/p>\n
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 \u201cjoint commission\u201d to discuss the status of the station, with an emphasis on the cracking in PrK.<\/p>\n
\u201cThe 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,\u201d he said, but had failed to identify a single root cause.<\/p>\n
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.<\/p>\n
The cracks have been the source of small but persistent air leaks in the station for several years<\/a>, 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.<\/p>\n \u201cThe current position right now is there are no leaks,\u201d Joel Montalbano, acting associate administrator for space operations and a former ISS program manager, said at a March 25 House Science Committee hearing. \u201cThey\u2019ve put some sealant over it and we\u2019re not leaking.\u201d<\/p>\n That did not mean, though, that the problem with the cracking in PrK was solved. \u201cWe\u2019re still worried about the structure there,\u201d 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.<\/p>\n 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, \u201cso we can save that port for the lifetime of the International Space Station.\u201d<\/p>\n Cabana said at the council meeting that the joint commission recommended a \u201cconservative approach\u201d 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.<\/p>\n However, while he said the agencies have made progress on the PrK cracking, \u201cthe teams have not yet agreed on the severity of the consequences of the cracks,\u201d he said. That lack of consensus has been a long-running issue, one Cabana noted at a November 2024 meeting of the council<\/a>.<\/p>\n He added that while station officials agree to minimize the time the PrK is pressurized, \u201cthe NASA team continues to have concerns over the length of time that the PrK remains at pressure.\u201d<\/p>\n He added that NASA and Roscosmos signed a protocol in August 2025 about lowering the pressure in PrK when not in use. \u201cThis lower pressure is not always being adhered to, and teams are comparing analysis.\u201d<\/p>\n 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<\/a>, as well as the early return of the Crew-11 mission<\/a> because of a medical issue with one of the astronauts.<\/p>\n They also got an update on Boeing\u2019s 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, \u201ccreates challenges for crew training, crew rotations and flight plans,\u201d and the joint commission recommended that NASA provide Roscosmos with updated safety hazard reports before Starliner\u2019s next mission to the ISS.<\/p>\n