The space station is leaking. Why it hasn't imperiled the mission.

Some of the main modules of the International Space Station are nearly a quarter-century old. "That's considered classic for a car," said Bennett Maruca, an astronomer and physicist at the University of Delaware.

So it's little surprise one of the earliest chambers, attached in 2000, has sprung a problematic leak. The leak is in Russia's Zvezda service module, an area connecting the module to a docking port, and it was first detected five years ago. But the rate of leakage has increased in 2024, and in April, NASA revealed it had reached the highest level yet, at three times the leakage observed in 2019. In a recent Inspector General's report, the space agency labeled these cracks and leaks a "top safety risk."

The leaking hull has earned understandable scrutiny from both NASA and the Russian space agency. "NASA and Roscosmos continue to evaluate onboard and ground test data with the primary goal of identifying the root cause, gaining a better understanding of the risk to station operations, and implementing repairs," a spokesperson from Johnson Space Center told Mashable.

The problem exemplifies how NASA is contending with aging but critical space infrastructure: The orbiting laboratory, with a living area larger than a six-bedroom house, is the agency's only way to learn about health impacts to astronauts, develop or test life support systems for future missions, and advance a plethora of space technologies. NASA wants to keep it running until 2030 — but doing so will require constant surveillance and, literally, patching.

"It's an old station, and it has done some amazing things," Don Platt, an associate professor of space systems at Florida Tech, told Mashable.

Contending with the space station's leak

The space station is actually designed to leak — a little.

That's because it has eight ports for spacecraft, meaning eight hatches that must open and close. So a negligible level of leaking was always expected, because no seal, however tight, is perfect. The only way to eliminate any leakage and preserve finite air would be to weld the openings shut. "But that would be a pretty useless space station," Maruca told Mashable.

The increased leakage rate, however, could be coming from cracks in different parts of the Zvezda service module. Space station personnel are sleuthing for potential culprits. "Cosmonauts aboard the space station have performed inspections of the module’s interior surfaces with an instrument that can detect even the most minor surface blemishes," NASA's spokesperson said, adding "There are several areas of interest identified subject to future Roscosmos inspections." Already, the Russian agency has applied sealant to some cracks, leading to some leak reduction, and for years a Zvezda tunnel hatch has been kept closed as much as possible between dockings, sealing off that section to reduce leakage. (The space agencies do not currently agree on the potential causes of the leak, according to NASA’s ISS Advisory Committee.)

These present leaks are microscopic, which is why NASA has concluded they're not an immediate risk to the structural integrity of the station, nor to astronauts. Unlike in some Hollywood depictions, a small hole in a space station or airplane wall won't result in a rapid and dramatic depressurization event. The air pressure aboard the station is 14.7 psia (pounds per square inch absolute), which is not nearly enough pressure on a small hole (even as wide as an inch across) to, for example, suck a person out of the station and into the vacuum of space.

But valuable, finite air is still being lost. Fortunately, the station orbits Earth, so it's regularly resupplied with oxygen, water, food, clothing, and beyond. The space station's current air loss is similar to the stubborn, but fixable, slow leak we've all experienced in our car tires. "It's a slow leak that allows you to get to the gas station in time," Platt said. "It's not the big hole you get when you run over a sharp piece of metal on a highway."

(Though a crewed deep space mission wouldn't have the luxury of resupply. "If this was a vehicle on its way to Mars, that would be a real problem," he noted.)

The space station isn't just resupplied with oxygen tanks, it also makes oxygen. Using the station's Urine Processor Assembly, astronauts reclaim 87 percent of the water in urine, which in turn is used to create oxygen and drinking water. As astronauts like to say, "Yesterday's coffee becomes tomorrow's coffee." A process called "electrolysis" — which uses an electric current to separate oxygen and hydrogen in water — then recycles oxygen aboard the station. (What's more, space station oxygen is even produced from exhaled carbon dioxide.)

What if, however, the current leaks in the Zvezda module grow dangerous, and cannot be repaired? The station is composed of different capsules that can be isolated. "Much like a submarine, you can close off sections of it," Platt said.

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We'll see how these problematic leaks play out in the coming year, and beyond. The aging space station is vulnerable to a host of potential issues, such as orbital debris (which has previously forced the station to move), 1.5 million lines of software code operating on 44 computers, and generally old parts. NASA, Roscosmos, and the astronauts aboard all have good reason to fix this known problem — and ensure it doesn't become worse.

"You always need to have a high level of vigilance when you're flying in space," Platt said.