ISS Air Leak Forces Astronauts to Shelter in SpaceX Dragon Capsule

At 9:04 a.m. Eastern Time on Friday, June 5, 2026, mission control at NASA's Johnson Space Center in Houston issued an order that no astronaut wants to hear: get into your spacecraft and prepare to leave [1]. The four members of the Crew-12 mission — NASA astronauts Jessica Meir and Jack Hathaway, ESA astronaut Sophie Adenot, and Roscosmos cosmonaut Andrey Fedyaev — along with a fifth U.S. astronaut, entered the SpaceX Crew Dragon "Freedom" capsule, sealed the hatch, and donned their spacesuits [2][3].

The reason: a persistent air leak in the Russian segment of the International Space Station had doubled in severity, and two Russian cosmonauts were about to attempt a repair method that NASA considered too risky to proceed without precautions [4].

Two hours later, after Roscosmos paused the repair work, NASA lifted the safe-haven order and the crew returned to normal operations [5]. But the brevity of the shelter-in-place belies the scale of the underlying problem. The leak that triggered it has been growing for nearly seven years, has resisted every repair attempt, and has been rated by NASA's own inspectors as the single greatest safety risk to the station's plan to operate until 2030 [6].

The Leak: Seven Years and Counting

The trouble began in September 2019, when ISS ground teams noticed an anomalous increase in the station's atmosphere leakage rate — a metric that had been stable for years [7]. By August 2020, engineers had traced the source to the PrK transfer tunnel, a narrow cylindrical vestibule attached to the aft end of the Zvezda service module [8]. The PrK connects Zvezda's main pressurized working area to the rear docking port where Progress cargo ships dock.

Zvezda, which launched in July 2000, is one of the oldest modules on the station. At 26 years in orbit, it has endured tens of thousands of thermal cycles — each 90-minute orbit subjects the station's exterior to temperature swings from roughly -250°F in shadow to +250°F in sunlight — as well as the cumulative stress of hundreds of spacecraft dockings and undockings [9].

The leak rate has followed a jagged upward trajectory. It started below 0.5 pounds of air per day in 2019, climbed past 1 pound per day by 2020, and reached 2 pounds per day by 2023 [8][10]. In February 2024, it hit 2.4 pounds per day, then spiked to an unprecedented 3.7 pounds per day by April 2024 [10][11].

Source: NASA, Roscosmos reports (compiled)

Data as of Jun 6, 2026CSV

Both NASA and Roscosmos suspect the cause is metal fatigue manifesting as microscopic cracks in the tunnel's welds, but the exact root cause has never been definitively established [8]. Repair campaigns using sealants and patches have provided temporary relief — a round of patching in early 2025 brought the rate back down near zero — but the underlying structural degradation has consistently reasserted itself [4]. By early May 2026, the rate had climbed back to approximately one pound per day, then doubled during Progress 95 cargo operations in the week of June 1 [4].

NASA and Roscosmos have identified at least 50 "areas of concern" related to the leak, and after meetings in mid-2024, the ISS program elevated the air leak to the highest level of risk in its management system [6][12].

What Happened on June 5

The June 5 shelter order was not triggered by a sudden catastrophic breach. Rather, it was a precautionary response to a planned repair that NASA judged carried unacceptable structural risk [4].

Station commander Sergey Kud-Sverchkov and flight engineer Sergei Mikayev, the two Russian cosmonauts aboard, had prepared to use a saw to cut through a bracket inside the PrK tunnel in order to access and directly repair a crack that had been identified as a possible leak source [13][4]. The method — described by one source as a "dramatic saw repair" — would have involved cutting into the structure of the tunnel itself, a step beyond the sealant-and-patch approach used in previous repair attempts [13].

NASA officials assessed that this approach "could have resulted in elevated risk to the structure in the area," according to the agency's official blog post on the incident [4]. Mission control in Houston directed the five astronauts to enter the Dragon capsule as a precaution before the cosmonauts began work.

After Roscosmos paused the repair to gather additional measurements, NASA determined there was no immediate danger and lifted the safe-haven order [5][4]. The cosmonauts did not proceed with the cut.

The Dragon as Lifeboat

The SpaceX Crew Dragon serves as the designated emergency return vehicle — essentially a lifeboat — for the astronauts who arrived aboard it [14]. Since the first permanent crew arrived on the ISS in 2000, this emergency return role has been filled by Soyuz spacecraft and, more recently, by Crew Dragon capsules, which are rotated every six months [14].

Under safe-haven protocol, the crew enters the spacecraft, seals it, and keeps it powered and ready to undock within minutes [14][15]. NASA has not publicly disclosed the specific pressure threshold at which a full evacuation would be ordered, nor has it detailed how close the station has come to that threshold [15]. The decision to initiate safe-haven procedures rests with mission control in Houston, in coordination with the ISS program manager [15].

One open question is how long a Dragon capsule can sustain a crew in shelter mode. The capsule is designed for transit — typically a matter of hours between the ISS and Earth — not for extended habitation [16]. Its life support, power, and consumables are sized accordingly. If a shelter scenario extended to days rather than hours, the capsule's systems would face conditions outside their intended operational envelope. NASA has not publicly addressed this contingency in detail.

A Pattern of Escalation

The June 5 incident is the most dramatic in a long series of leak-related events, but it is far from the only one. The ISS has a documented history of pressurization incidents:

• January 2004: A leak traced to a vacuum jumper hose in the U.S. segment's window caused pressure to drop from the nominal 14.7 psi to 14.0 psi, with air loss reaching five pounds per day before the source was found and fixed [17].
• September 2019: The Zvezda PrK leak is first detected [7].
• December 2022: The Soyuz MS-22 spacecraft suffered an external cooling loop leak caused by a micrometeoroid impact — not a structural air leak, but an indication of the debris environment the station faces [17].
• February 2023: The Progress MS-21 cargo ship experienced a similar cooling loop leak from micrometeoroid impact [17].
• October 2025: A leak was observed from a radiator on the Nauka Multipurpose Laboratory Module, the newest Russian module, launched in 2021 [17].
• June 2026: The shelter-in-place event [1].

The Zvezda leak stands apart because it is structural, chronic, and has resisted resolution for seven years. Other incidents were acute — caused by impacts or equipment failures — and were resolved or isolated relatively quickly.

"The Riskiest Period of Its Existence"

NASA's Aerospace Safety Advisory Panel (ASAP), an independent body that reports to the NASA administrator and Congress, has issued increasingly blunt warnings. At an April 2025 public meeting, panel member Rich Williams stated that "the ISS has entered the riskiest period of its existence" [18]. He was not referring to any single new problem, but to the accumulation of technical issues and budget shortfalls that collectively threaten safe operations [18].

ASAP's 2024 annual report flagged the Zvezda leak specifically and expressed "grave concerns" that funding the ISS deorbit vehicle — the $843 million SpaceX contract to build a spacecraft that will push the station into the atmosphere around 2030 — could divert money from day-to-day maintenance and contingency operations [18][19].

Source: NASA ISS Program

Data as of Jun 6, 2026CSV

The station's oldest modules, Zarya and Unity, have been in orbit since 1998 — 28 years. Zvezda has been in orbit for 26 years. Boeing has certified the U.S. structural components through 2028 and NASA is "optimistic" the station can last until 2030, but that assessment depends on continued structural integrity in modules that Boeing did not build and does not control [9][20].

The U.S.-Russia Disagreement

The June 5 incident exposed a tension that has simmered for years: the United States and Russia do not fully agree on the cause or severity of the Zvezda leaks, nor on how to address them [12].

U.S. and Russian engineers have conducted joint investigations, but they have reached different conclusions about the root cause and the appropriate urgency of repairs [12]. The decision by Roscosmos to attempt a saw-based structural repair — and NASA's decision to put its crew in a safe haven before that repair began — suggests a gap between the two agencies' risk tolerances [4][13].

This dynamic is complicated by the broader geopolitical context. Russia has committed to ISS operations only through 2028, two years short of the U.S. target of 2030 [20]. Russia has also announced plans for its own orbital station, the Russian Orbital Service Station (ROSS), which would reduce its dependence on the ISS partnership [20].

Critics have argued that the operational partnership, once a symbol of post-Cold War cooperation, is now a source of risk. When the module experiencing structural failure is under one partner's jurisdiction, but the crew breathing the leaking air includes astronauts from the other partner's space program, the question of accountability becomes urgent. NASA has consistently maintained that the partnership remains functional and that crew safety is the top priority for both agencies [4][12].

The 2030 Question

The ISS was originally designed for a 15-year operational life. It has now exceeded that by more than a decade. The U.S., Japan, Canada, and ESA member states have committed to operations through 2030, and NASA has selected SpaceX to build the U.S. Deorbit Vehicle (USDV) under an $843 million contract [19][20].

The USDV is a modified Dragon capsule with six times the standard propellant load and up to four times the thrust, designed to guide the station through a controlled reentry into a remote area of the Pacific Ocean [19].

But the 2030 date is not purely a technical judgment. It is also driven by the timeline for commercial successor stations. NASA has agreements with Axiom Space, Blue Origin, Nanoracks, and Northrop Grumman for commercial low-Earth orbit platforms intended to replace the ISS [20]. Axiom plans to attach its first module to the station as early as 2026, eventually detaching its modules to form an independent station [20].

A NASA Office of Inspector General report from September 2024 (IG-24-020) identified the Zvezda leak as the top safety risk to the 2030 plan and raised concerns that the ISS program was managing too many concurrent risks with insufficient budget [6][21]. The report noted that NASA's ability to perform "normal and contingency ISS on-orbit operations" could be compromised if deorbit vehicle costs consumed ISS operational funds [18].

Some independent analysts have been more direct. The argument, as critics frame it, is that NASA is normalizing risk — accepting incremental increases in danger — to buy time for commercial stations that are not yet ready to replace the ISS [18][22]. By extending operations past the station's design life, this line of reasoning goes, NASA gains political and contractual runway but shifts the risk onto the crew.

NASA's counterargument is that the station's primary structure has been continuously monitored and that structural lifetime analyses, updated regularly by Boeing for the U.S. segment, show that the hardware can safely operate through 2030 with proper maintenance [9][20]. The agency points to its multilayered risk management system, the availability of emergency return vehicles, and its willingness to take protective action — as demonstrated on June 5 — as evidence that safety has not been compromised.

How Does This Compare?

The ISS is not the first long-duration space station to face structural aging. The Soviet/Russian Mir station, which operated from 1986 to 2001, experienced a catastrophic collision in June 1997 when the Progress M-34 cargo ship struck the Spektr module during a manual docking test, puncturing the hull and causing rapid depressurization [23]. The crew sealed the module within minutes, but Spektr was permanently lost as a habitable space [23]. Mir also experienced a fire in February 1997 and multiple systems failures in its final years [23].

China's Tiangong station, which began operations in 2021 with the Tianhe core module, is too new to offer a meaningful aging comparison — its oldest module is approximately five years old [24]. Tiangong's modules are self-contained and pre-assembled, a design approach that avoids some of the on-orbit assembly complexity of the ISS but also limits the station's size and flexibility [24].

The Mir comparison is instructive: Mir's most serious incident was caused by an operational error (a botched docking maneuver), not by structural aging. The ISS's Zvezda leaks, by contrast, appear to be the result of long-term material fatigue — a fundamentally different and in some ways more concerning failure mode, because it is progressive and cannot be fixed by a single corrective action.

Source: OpenAlex

Data as of Jan 1, 2026CSV

Academic interest in space station structural integrity has surged in recent years, with over 8,500 papers published on the topic in 2025 alone — more than triple the output from a decade earlier — reflecting growing concern in the engineering community about the challenges of maintaining aging orbital infrastructure [25].

What Comes Next

The PrK tunnel leak is not fixed. Roscosmos paused the June 5 repair attempt and has not announced when or how it will resume [4]. The hatch between the U.S. and Russian segments can be closed to isolate the leak if it worsens, but that would significantly constrain station operations [12].

NASA continues to operate the ISS with the PrK tunnel hatch closed as a default when cosmonauts are not actively accessing the area, a mitigation measure that limits but does not eliminate the risk [12]. The station's air supply is replenished by periodic deliveries of nitrogen and oxygen from cargo vehicles, which can compensate for the ongoing loss — but this is a workaround, not a solution [8].

The June 5 shelter-in-place lasted two hours. The next one may last longer. And eventually, the question may shift from whether the crew can safely return to the station to whether they should.