Russia Seals Leaking International Space Station Chamber, Complicating Cargo and Orbit Boosts

A docking port can remain mechanically useful even when astronauts can no longer pass through the chamber behind it. That is now the operational problem on the International Space Station, where Russia has reportedly permanently isolated a leaking transfer chamber in the Zvezda service module from the station’s pressurized interior.

The closure removes normal pressurized access through the chamber, known as PrK, but does not eliminate the value of its external docking interface. Progress cargo spacecraft can still dock there and use their engines to raise the station’s orbit. Crews, however, must use another port to unload supplies or load waste, separating jobs that a single docked vehicle could previously support from one location.

That distinction turns a pressure-boundary repair problem into a logistics and scheduling constraint. Progress MS-36 is scheduled to unload through Russia’s Poisk module, move to the PrK-associated port for an orbit correction, and then return to Poisk to take on trash, according to Russian Space Web. It described the flight as “the first cargo mission scheduled to unload its cargo and perform orbit corrections of the ISS at different docking ports.”

Each relocation adds another planned spacecraft movement to a station schedule in which docking locations must be assigned well in advance. The sequence also separates cargo access from the port preferred for some reboost operations. Soyuz crew spacecraft had occasionally used the affected location as well, further reducing flexibility within the Russian segment’s available docking arrangement.

Reboosts are routine but essential station maintenance. Residual atmospheric drag gradually lowers the ISS orbit, so docked spacecraft periodically supply thrust to restore altitude and position the station for future visiting vehicles. In April 2026, for example, NASA reported that Progress 93 fired its engines for just over five minutes, placing the station at the correct altitude for the approaching Progress 95 cargo mission.

The PrK problem therefore does not remove the station’s ability to conduct orbit corrections. It makes operators preserve the useful thrust geometry of that docking location while working around the loss of its interior passage. The cost is operational complexity rather than the immediate loss of the port’s every function.

Cracks reportedly began appearing in the transfer chamber in 2019 and produced minor air leakage. Russian crews attempted multiple repairs, including applications of a sealant identified as Germetall-1. During a June repair episode, NASA reportedly directed its astronauts to shelter temporarily inside a Crew Dragon because officials were concerned that the proposed work could lead to a depressurization event. The available reporting does not provide an official finding on what originally caused the cracks.

Permanent isolation is a substantial change because PrK formed part of the pressure envelope around a crewed spacecraft interface. Closing it protects the rest of the station from the persistent leak, but the measure also concedes that crews will no longer use that passage for routine transfers.

The affected hardware sits within one of the station’s foundational modules. Zvezda docked with the orbital complex in July 2000 and provides living quarters, life support, power distribution, data processing, flight control, propulsion and communications functions. It also supports docking by Russian Soyuz and Progress spacecraft.

That broad role explains why operators can isolate one chamber without abandoning Zvezda or its other station functions. The ISS is assembled from compartments that can be closed off from one another, allowing a localized pressure problem to be contained. Isolation, however, cannot recreate the lost route through the module or recover the scheduling flexibility that came with it.

Progress MS-36 will provide the first clear operational demonstration of the new arrangement: cargo and waste handling at Poisk, with a separate visit to the sealed chamber’s docking position for the orbit boost. The port still has work to do, but one spacecraft will now have to move between two locations to complete the jobs previously associated with one.

By David Whitaker — Associate editor for AMI’s aerospace and drone systems desk, translating flight systems, aircraft programs, spaceflight, and UAV developments into accessible technical stories.