Commercial crew launch delayed while ISS air leak assessed

Concern about a small but persistent air leak in a Russian compartment of the International Space Station has prompted NASA and Axiom Space to indefinitely delay this week's launch of a commercial flight to the orbiting outpost, officials said Thursday.

The privately-financed Axiom-4 crew — commander Peggy Whitson, Indian pilot Shubhanshu Shukla, Polish researcher Sławosz Uznański-Wiśniewski and Hungarian engineer Tibor Kapu — originally planned to take off Tuesday.

But the flight was delayed to the end of the week, first by high winds in the off-shore emergency splashdown zone and then by an oxygen leak in their Falcon 9 rocket's first stage. SpaceX tentatively targeted Thursday and then Friday for launch, with Saturday and Sunday available if needed.

But during SpaceX troubleshooting to find and fix the rocket's propellant leak, NASA engineers decided they needed more time to assess recent efforts to plug an air leak aboard the International Space Station in a Russian vestibule known as the PrK. The PrK serves as a passageway between the station's Zvezda module and spacecraft docked at its aft port.

"Teams met today and we will not be launching Axiom-4 tomorrow," flight controllers in Houston radioed the ISS. "We are assessing a new launch date. This is due to the ongoing PrK investigation. So I don't have a new launch date right now, but we will not be launching tomorrow and docking Saturday."

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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