NASA investigating small air leak on International Space Station

NASA is tracking down the source of a minor air leak on the International Space Station.

Crewmembers of the station’s current Expedition 63 are in no immediate danger and will spend the weekend in the orbiting laboratory’s Russian segment, inside the Zvezda service module, NASA officials said in an update today (Aug. 20).

Astronauts can work in a shirtsleeve environment inside the station, but the orbiting lab is never completely airtight; a little bit of air always leaks over time, requiring routine repressurization from nitrogen and oxygen tanks that are sent up during cargo missions, NASA added in the update. 

The leak was first spotted in September 2019, but it did not interfere with normal operations. Nor was the rate of air loss accelerating or high enough to cause alarm; as such, NASA monitored the situation and focused on other station priorities before addressing the leak, agency spokesman Dan Huot said in an email to

The last few months were very busy at the station. NASA and SpaceX completed the first crewed commercial mission to the orbiting lab, known as Demo-2, and agency astronauts finished several complex spacewalks to repair a broken dark-matter detector and to upgrade batteries for the station. The batteries will be needed to power the station through its planned end of life in 2024, which could be extended to 2028 or later if all partners agree.

“Now that we have a relatively quiet period in the operations — spacewalks, vehicle traffic, additional crew members can all result in fluctuations — the crew will be shutting the hatches to every single module so the ground can monitor each module’s pressure to further isolate the source” of the leak, Huot said.

“It’s the most effective means we have of finding the leak, as it is so small,” he added. “We don’t know definitively if the leak is in the U.S. or Russian segment, and won’t until we’re able to review the data from this weekend’s tests.”

While the leak rate is higher than usual, it is still within specifications for the station and poses no immediate danger to the crew, NASA officials emphasized. (Agency representatives did not answer questions about the rate of the current air leak, the normal leak rate, how much air the pressurized compartment usually holds, and what nitrogen and oxygen supplies are like right now on the space station.)

Astronauts deal with leak simulations during training for their stays on the space station, which typically are about six months long. In terms of crew time and disruption, NASA said there should be minimal changes to their schedule. Only NASA astronaut Chris Cassidy has personal items outside of the Russian segment, as his sleeping quarters are housed in the Harmony module of the orbiting lab.

“All the crew is doing is shutting the hatches between the different modules and isolating themselves in the Zvezda service module in the Russian segment,” Huot said. “There are some associated cargo ops [operations] for Chris Cassidy to move some of his supplies over for the weekend, but that’s the extent. All of the pressure monitoring is done on the ground by flight controllers.”

Cassidy and his Russian crewmate cosmonauts, Ivan Vagner and Anatoly Ivanishin, will stay in the Russian Zvezda service module from Friday night to Monday morning (Aug. 21 to Aug. 24). 

The three astronauts will have “plenty of room,” NASA officials said in today’s update, noting that Zvezda was where crews first stayed when the ISS was under construction in the early 2000s. Further, the Expedition 63 crew will have access to the Poisk mini-research module and their Soyuz MS-16 crew ship while staying in Zvezda.

The current leak investigation is not the first that space station team members have performed. And NASA officials emphasized that this leak is smaller than the one that astronauts encountered in 2018.

In August 2018, a small air leak was discovered in a Russian Soyuz spacecraft attached to the station, and Expedition 56 crewmembers eventually found an 0.08-inch-wide (2 millimeters) hole in the Soyuz hull. Russian officials investigated the cause of the leak, although as of September 2019 media reports indicated they were not prepared to publicly share what happened.

“The main point we want to get across is, this is not a leak in the same neighborhood as the one detected in the Soyuz spacecraft back in August 2018, or one that poses any immediate or even long-term risk to the safety of the crew,” Huot said. “The station is fully capable of maintaining normal operations with the current leak rate, but we now have an opportunity to try and isolate it.”

There have been other minor air leak events over the long history of the station, whose first modules were sent into space in 1998. For example, in November 2004, NASA astronaut Michael Foale found a small air leak that had been puzzling controllers for three weeks, according to a report from NBC. He found the leak at a main window at the U.S.-built Destiny laboratory, in a flexible cable called a vacuum jumper. The cable normally was used to assist with equalizing air pressure in the window, which had several panes. But Foale spotted signs of a leak in the area where the hose connected with a steel harness at the window’s edge.

NASA also briefly troubleshot another small air leak in 2007, shortly after the station’s then-new NASA-managed Harmony module was installed.


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