NASA has postponed a scheduled crew launch due to a significant leak on the International Space Station (ISS). NASA has withheld details about the incident but insiders report that officials are deeply worried about the situation.

And with good reason: The ISS has exhibited signs of strain before despite its more than twenty-year orbit around Earth. The gradual progression of time along with increasing pressure has begun to reveal its effects.

A Leak That Won’t Quit

Leaks on the ISS aren’t new. Since 2019 the ISS has dealt with a continuous air leak that primarily affects the Russian Zvezda service module. As one of the most ancient modules in the ISS complex launched during the early 2000s this component remains a vital part of the station’s infrastructure. The air leak problem originates from the PrK transfer tunnel which connects Zvezda with the docking ports for Soyuz crew capsules and Progress resupply ships.

Russian cosmonauts have conducted multiple repair attempts throughout the years. They have successfully reduced air loss with each repair attempt but have yet to achieve total cessation. The station loses an average of a couple of pounds of air daily because of the leak. The situation remains manageable but presents undesirable challenges while operating 250 miles above Earth.

The workaround? Always keep the PrK hatch shut unless there’s a critical reason to open it.

So, What Changed?

Russia’s space agency Roscosmos announced this month that it had achieved full sealing of the PrK module. NASA confirmed the statement by observing that the recent repairs had produced successful results. The two agencies confirmed that the leak rate inside the module had ceased completely.

That should’ve been good news.

The total air pressure at the station unexpectedly continued its downward trend. If the PrK module leak was sealed, the location of the disappearing air remains unclear.

The Mystery Deepens

Two sources told Ars Technica that the likeliest explanation isn’t comforting: The seals on the hatch of the PrK module appear to be developing leaks. These defective seals could allow air to enter the PrK module which would account for the station’s stable internal pressure while its air supply diminishes.

The situation remains uncertain because nobody can fully understand what’s taking place. NASA remains vigilant in tracking the leak while developing contingency plans for all potential scenarios.

A senior industry source informed Ars that the situation presents genuine concerns. NASA space station program leaders express their concern about the situation.

A Launch Delay—and Growing Risk

NASA delayed the launch of Axiom Mission 4 which involved sending four astronauts to the station during its Thursday commercial flight. NASA asked for additional time to analyze the leak issue.

NASA announced that delaying Axiom Mission 4 allows both NASA and Roscosmos more time to assess the current situation and identify any further troubleshooting steps that may be needed.

NASA announced June 18 as the new tentative launch date. The tentative launch date depends entirely on developments in the emerging leak situation.

Worst-Case Scenario? Let’s Talk Fatigue

The leak itself is worrying. But what really has experts on edge is what it might represent: a sign of high cycle fatigue. Metal structures commonly experience this phenomenon. Imagine bending a paperclip—once, it flexes. Bending it repeatedly will lead to its eventual breakage. That’s fatigue.

The ISS consists primarily of aluminum which is susceptible to fatigue stress. Parts of the station have spent nearly three decades in orbit since 1998. The space station has endured about thirty years of micro-vibrations while docking and experiencing thermal cycles.

Metal fatigue might lead to instantaneous and disastrous failures of some parts of the space station. It’s not just a theory. On Aloha Airlines Flight 243 the cabin tore apart because of metal fatigue in 1988.

NASA knows the risks. NASA’s internal evaluations position ISS structural cracking as the top risk category in their 5v5 risk matrix which assesses hazard likelihood and severity.

And Yet—Silence

NASA has made few other public statements at this time. Reporters and concerned observers have repeatedly asked questions yet no press conference has been set up. The only official word so far?

NASA reports that the International Space Station crew is performing regular operations safely.

And that’s reassuring—to a point. The visible signs of aging on the space station mean that metal cracks are not the sole emerging issue.