Why NASA Ordered the ISS Crew to Shelter in a SpaceX Capsule

For about six years, a small vestibule on the International Space Station has been quietly leaking air. On Friday, June 5, 2026, that persistent problem suddenly became a pressing safety concern when NASA ordered five of its astronauts to take refuge in their docked SpaceX Crew Dragon capsule. The reason: Russian cosmonauts had initiated previously unannounced repair work on newly discovered cracks and leaks in the station's aging Russian segment .

The directive, described by NASA as an “abundance of caution,” required all four members of the agency's SpaceX Crew-12 mission, along with NASA astronaut Chris Williams, to assume an elevated safety posture inside the Dragon spacecraft Freedom while the two Russian cosmonauts onboard worked to address the leaks . The crew returned to the station after the repair work paused, but the incident highlights a deeper, unresolved problem: a leak in the PrK transfer tunnel of the Zvezda service module that has defied permanent repair since 2019 .

What Triggered the Shelter-in-Place Order

On June 5, Roscosmos discovered new cracks and leaks within the Russian segment and proceeded with what NASA described as a “more extensive repair operation” without prior notification to the U.S. agency . Russian officials had not informed NASA of the planned work, a fact confirmed by NASA spokesperson Bethany Stevens in a post on X .

To protect the U.S. segment crew from the risk of depressurization or toxic fumes during the repairs, NASA ordered five astronauts into the docked Crew Dragon. The five who sheltered were:

• All four members of NASA's SpaceX Crew-12 mission
• NASA astronaut Chris Williams

The two Russian cosmonauts who remained outside the capsule to conduct the repairs were not named in initial reports .

The shelter-in-place order was temporary. The astronauts returned to the station after the repair work was paused. The event is the most dramatic safety precaution taken to date in response to the long-running leak saga .

Timeline of a Leak That Won't Stay Fixed

The persistent leak originates in the PrK transfer tunnel, a small connecting vestibule in the Russian Zvezda service module that leads to an aft docking port. First detected in 2019, it has followed a troubling trajectory of temporary fixes and renewed leakage .

• September 2019: The leak is first detected. Initially minimal—less than one pound (0.45 kg) per day—it is deemed manageable .
• February 2024: The leak rate escalates to approximately 1.7 kg (3.7 lbs) of air per day .
• April 2024: The leak reaches its highest recorded rate of 3.7 kg per day (~8.2 lbs), more than six times the ISS's normal planned leak rate. NASA elevates the issue to its highest risk level .
• June 2025: Roscosmos applies sealant and patches, announcing the leak as “eliminated.” NASA delays the Axiom-4 private astronaut mission to verify the repair holds .
• May 22, 2026: Gizmodo reports that new pressure signals indicate the leak has returned, despite the previous repairs .
• June 5, 2026: Discovery of new cracks triggers the unannounced repair work and the NASA shelter-in-place order .

The June 2025 repairs appeared momentarily successful, but by May 2026, the familiar pressure drops had resumed, confirming that the underlying structural issue remains unresolved .

How the Cosmonauts Are Attempting Repairs

On June 5, the two Russian cosmonauts aboard the station conducted emergency repair work targeting newly found cracks. The precise method used during this latest operation was not detailed in immediate reports, but historical repair attempts provide context .

Past efforts have involved applying epoxy-based sealants to the interior surfaces of the PrK tunnel and covering visible cracks with specialized tape and polymer compounds. These techniques temporarily reduced the leak rate by roughly one-third during earlier operations . The reactive and unannounced nature of the June 2026 work suggests that cosmonauts were responding to a sudden and concerning detection of new leakage .

The NASA–Roscosmos Disagreement

Beneath the technical challenge of patching an aging module lies a fundamental rift between the two space agencies over the leak's severity and cause.

NASA's position has hardened significantly. In June 2024, the ISS program elevated the PrK leak to “the highest level of risk in its risk management system”—a 5 out of 5 score on its risk matrix for both likelihood and consequence . Internal NASA documents have discussed the potential for “catastrophic failure,” and the agency's Office of Inspector General warned in September 2024 that the cracks and leaks had become a primary safety risk for sustaining station operations through 2030 .

Roscosmos' position has consistently been more sanguine. Russian officials have described the leaks as minor and argued they pose no immediate threat to the crew or station . The agencies also disagree on the root cause: Roscosmos attributes the cracks to micrometeoroid impacts and material fatigue, while NASA suspects deeper structural degradation and welding flaws that could worsen unpredictably .

Former NASA astronaut Bob Cabana, who chaired the ISS Advisory Committee, publicly noted that “U.S. and Russian officials do not have a common understanding of the most probable root cause or the severity of the consequences of these leaks” . The lack of advance notice for Friday's repair work further illustrates the ongoing communication gap between the two agencies .

What's at Stake: The Risk of Catastrophic Failure

NASA's 5×5 risk classification means the agency judges that further structural degradation is very likely and that the consequences could be severe—potentially including a rapid depressurization event or a loss of the Zvezda module's structural integrity .

To put this in perspective, the April 2024 peak leak rate of 3.7 kg per day was more than six times the ISS's normally expected atmospheric loss . While the station carries reserves of nitrogen and oxygen to compensate for routine leakage, a sudden acceleration or cascading structural failure would far exceed the system's capacity to maintain a livable atmosphere.

The 2026 shelter-in-place order, while brief, was the most tangible evidence to date that the six-year-old leak is more than an engineering nuisance. It is a chronic safety problem on an aging station where two international partners still do not agree on the severity of the threat.

Note: This article synthesizes reporting through June 5, 2026. Check back for updates as the ISS partners continue to assess and address the repair effort.