That dreaded air leak on the ISS’s Russian segment is back

At a glance:

• Air leak in ISS Russian Zvezda module returning, losing ~1 lb of air per day
• Leak first detected 2019, rate rose to >2 lb/day in 2024, recent measurements show drop again in May 2025
• NASA and Roscosmos monitoring the transfer tunnel, no immediate crew risk, station slated for retirement in 2030

What happened

The International Space Station’s Russian segment has begun leaking air again, a problem that first surfaced in September 2019. At that time Roscosmos traced the loss to the vestibule (PrK) that links a docking port to the Zvezda Service Module. Initial measurements showed a loss of about one pound of air per day, but a 2024 report indicated the rate had doubled to a little over two pounds per day, prompting NASA to elevate the issue to its highest risk level.

Efforts to seal the breach appeared promising in June 2025 when NASA recorded a new pressure signal that suggested the leak had been patched. However, on May 1 2025, cosmonauts unloading cargo from Progress 95 observed a slow pressure drop in the same Zvezda module. NASA spokesperson Josh Finch confirmed that the transfer tunnel’s pressure was deliberately allowed to fall while the crew performed small repressurizations as needed, indicating the leak had re‑emerged or never fully closed.

Why it matters

Even though the leak does not pose an immediate danger to the crew, the persistent loss of roughly one pound of air per day underscores the aging hardware of the orbiting laboratory. The ISS has been in low‑Earth orbit for nearly three decades, and the cumulative wear from micrometeoroids, thermal cycling, and radiation is now manifesting as microscopic cracks that are difficult to locate and seal.

The situation also has policy implications. Earlier this year the U.S. Congress urged NASA to postpone the station’s planned retirement in 2030 until a commercial replacement is operational, fearing a gap in human presence in Earth orbit. A safety advisory panel has warned that the air leak, combined with other degrading systems, raises the overall risk profile as the station approaches the end of its service life.

Future outlook

NASA and Roscosmos are continuing joint investigations to pinpoint the exact source of the leak and evaluate repair options, which may include temporary sealing patches or more invasive hardware replacement during a future EVA. Both agencies stress that crew safety remains the top priority, and any corrective actions will be scheduled around existing mission timelines.

Long‑term, the leak highlights the urgency of developing a commercial successor to the ISS. Stakeholders in the emerging low‑Earth‑orbit market are watching the situation closely, as a reliable hand‑over could mitigate the operational risks that the current station is beginning to exhibit.