NASA Delays Commercial Crew Launch To Assess ISS Air Leak

NASA and Axiom Space have indefinitely delayed the Axiom-4 launch to the International Space Station due to concerns about a persistent air leak in the Russian PrK vestibule of the aging Zvezda module. 'The PrK serves as a passageway between the station's Zvezda module and spacecraft docked at its aft port,' notes CBS News. From the report: In a blog post, NASA said cosmonauts aboard the station 'recently performed inspections of the pressurized module's interior surfaces, sealed some additional areas of interest, and measured the current leak rate. Following this effort, the segment now is holding pressure.' The post went on to say the Axiom-4 delay will provide 'additional time for NASA and (the Russian space agency) Roscosmos to evaluate the situation and determine whether any additional troubleshooting is necessary.'

Launched in July 2000 atop a Russian Proton rocket, Zvezda was the third module to join the growing space station, providing a command center for Russian cosmonauts, crew quarters, the aft docking port and two additional ports now occupied by airlock and research modules. The leakage was first noticed in 2019, and has been openly discussed ever since by NASA during periodic reviews and space station news briefings. The leak rate has varied, but has stayed in the neighborhood of around 1-to-2 pounds per day. 'The station is not young,' astronaut Mike Barratt said last November during a post flight news conference. 'It's been up there for quite a while, and you expect some wear and tear, and we're seeing that in the form of some cracks that have formed.' The Russians have made a variety of attempts to patch a suspect crack and other possible sources of leakage, but air has continued to escape into space.

In November, Bob Cabana, a former astronaut and NASA manager who chaired the agency's ISS Advisory Committee, said U.S. and Russian engineers 'don't have a common understanding of what the likely root cause is, or the severity of the consequences of these leaks.' 'The Russian position is that the most probable cause of the PrK cracks is high cyclic fatigue caused by micro vibrations,' Cabana said. 'NASA believes the PrK cracks are likely multi-causal including pressure and mechanical stress, residual stress, material properties and environmental exposures. 'The Russians believe that continued operations are safe, but they can't prove to our satisfaction that they are, and the US believes that it's not safe, but we can't prove that to the Russian satisfaction that that's the case.'

As an interim step, the hatch leading to the PrK and the station's aft docking compartment is closed during daily operations and only opened when the Russians need to unload a visiting Progress cargo ship. And as an added precaution on NASA's part, whenever the hatch to the PrK and docking compartment is open, a hatch between the Russian and U.S. segments of the station is closed. 'We've taken a very conservative approach to close a hatch between the US side and the Russian side during those time periods,' Barratt said. 'It's not a comfortable thing, but it is the best agreement between all the smart people on both sides. And it's something that we crew live with and enact.' Cabana said last year that the Russians do not believe 'catastrophic disintegration of the PrK is realistic (but) NASA has expressed concerns about the structural integrity of the PrK and the possibility of a catastrophic failure.'

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