Pesky leaks on the International Space Station aren't the most serious issue facing U.S. human spaceflight
In the hostile conditions beyond Earth, a spacecraft is all that stands between an astronaut and certain death. So having yearslong seemingly unfixable leaks on the International Space Station (ISS) sounds like a nightmare scenario. It's also a reality, one that a recent agency report calls "a top safety risk." Amid months of headlines about astronauts stranded by Boeing's Starliner vehicle and NASA's announcement of a contract with Elon Musk's SpaceX to destroy the ISS early next decade, the ongoing concerns about the leaks come as another reminder that supporting a long-term population in space is a challenge that's quite literally out of this world.
Simultaneously, the station's leaks are mundane -- perhaps shockingly so for those of us who are neither engineers nor astronauts. "When you're on the space station, it's like your life here," says Sandra Magnus, an engineer at the Georgia Institute of Technology and a former NASA astronaut who previously served on NASA's Aerospace Safety Advisory Panel, an independent panel that monitors safety concerns. "You don't run around in your daily life and wonder if you're going to get hit by a car when you cross the street, right? It's your life -- you just live your life."
The disconcerting truth is that the ISS leaks some air every day -- and it always has. "All spacecraft leak," says David Klaus, an aerospace engineering professor at the University of Colorado Boulder. The space station is just the most high-profile spacecraft there is, and it's leaking more now than it used to.
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It's indeed leaking more but still not all that much, says Michael Kezirian, an adjunct professor of astronautical engineering at the University of Southern California. The current leak is "bigger than a pinhole, maybe two pinholes," he says. "You're talking about something relatively small." The worst rate of leakage shared publicly comes from April, when the station was losing 3.7 pounds of atmosphere per day. (For context, all the air above any given square inch of Earth's surface at sea level stretching to the end of the atmosphere weighs, on average, a bit shy of 15 pounds.)
It's not even particularly surprising to experts that NASA and the international partners who run the space station have had so much trouble tracking down and fixing the leaks. "Leaks are hard to sort out," Magnus says. "The station is huge; there's a large volume of air. So trying to isolate a teeny tiny leak or anything that's not leaking a lot, it's hard." (Much of the station's hull is also difficult to access from inside because of the sheer amount of equipment, cargo and general stuff cluttering its corridors.)
The troublesome leaks, which were first detected in September 2019, were traced to a tunnel in the Russian Zvezda service module, which launched in July 2000. The tunnel connects a docking port to the main part of the module -- and to the rest of the space station. Magnus describes the tunnel as "the back porch," mainly used to store trash scheduled for incineration in Earth's atmosphere.
Astronauts have had some luck over the years tracking down precise locations where the station is losing air and have even tried to patch the tunnel up. In theory, spacecraft leaks are straightforward to seal from the inside. "All you have to do is get something up against that leak with some sort of adhesive, and it becomes self-forcing up against the leak," Klaus says. "The pressure in the spacecraft helps to hold the seal against the leak." But these patch efforts have only reduced the flow of the leaks rather than eliminating them entirely.
While astronauts and ground control continue their troubleshooting, NASA and its Russian counterpart, Roscosmos, have decided to keep the leaky tunnel's hatch closed when possible. It's an elementary solution but a reasonable one, Magnus says, given the back porch's relatively low importance. As long as the leaks stay steady, Klaus says, the only real issue is that astronauts may need more frequent or larger deliveries of air, which is one of the many so-called consumables, such as food and water, that cargo vehicles supply to the station.
In the long term, should the leaks worsen, the stopgap strategy can become a permanent one without serious impact, all three experts say. Losing access to the port on the tunnel's far end would be inconvenient, requiring tighter coordination of the crew and cargo vehicles that visit the orbiting laboratory and the material they deliver. "They'll have to sharpen their pencils in the logistics community and figure out how to compensate," Magnus says of this scenario. "Is it going to be a disaster? No. Is it going to be a little more challenging? Perhaps."
Even that approach comes with its own complications: according to the September report, NASA and Roscosmos disagree on the threshold at which the leaks will become serious enough to necessitate shutting the hatch permanently.
Still, the leaks themselves, while far from ideal, are essentially under control. "No one should be panicking," Magnus says. "It's a serious problem, and they're taking it seriously, that's really the bottom line."
The leaks, however, are also a nagging reminder of how long the ISS has spent in orbit. The oldest segments launched in 1998; since then they have endured a host of stressors. Spacecraft arrive and depart, rockets push the ever sinking laboratory higher above Earth, and materials degrade from exposure to cosmic radiation. And the sun's heat comes and goes 16 times every single day as the station swoops over Earth's nightside and dayside, causing its components to expand and shrink each time.
Sooner or later -- hopefully later -- the toll of all that mechanical stress will manifest in something more serious than pinprick leaks. "We know that the space station cannot be up there forever," Kezirian says. "It's a little bit easier with an old house to paint and replace components that fail." Home repair on a space outpost is both more expensive and more finnicky, and at some point, entropy will win out.
NASA hopes that won't happen this decade and aims to keep the space station operational through 2030. (Russia has so far only committed to the orbiting laboratory through 2028.) But the leak challenges give additional urgency to a concern that the Aerospace Safety Advisory Panel has been raising for years: that the orbital laboratory will fail before it can be safely destroyed -- and will fall uncontrolled through Earth's atmosphere, with its debris potentially doing serious damage to people and buildings. Earlier this year NASA commissioned SpaceX to develop a vehicle to safely deorbit the space station in 2031, targeting a 2029 launch. That's a very tight timeline for a program of this scale, so the anxiety continues.
A second ticking clock looms over the agency: in whatever condition the space station meets its fiery doom, it will leave the U.S. with no viable long-term orbital habitats. NASA officials have spent years promoting the idea that companies will take over low-Earth orbit by launching and maintaining space stations to continue the ISS's 24-year streak of continuous human occupation.
In 2020 the agency contracted Texas-based Axiom Space to construct the first habitable, commercially built module on the station, which the company is hoping to launch in 2026 and to then undock to fly free when the space station retires. In 2021 NASA also awarded funding to companies, including Washington State-based Blue Origin (owned by Amazon's Jeff Bezos) and Texas-based Nanoracks, to develop additional commercial destinations in space. NASA has said that Axiom's module is under construction and that components of Blue Origin's station have undergone testing, but progress remains slow. Company representatives for each station that were contacted for this article did not provide additional details on their current status to Scientific American. Meanwhile Axiom is reportedly facing serious financial troubles.
These proposed commercial stations may be able to learn from the ISS's leak troubles, Klaus says. "Once you've identified this as a potential concern, you can be smarter about future designs," he says. "If you're clever, you don't have the same failures twice. It happens once; you fix it and move on."
But fears are mounting that these stations won't be operational by the time the ISS needs to be retired or becomes uninhabitable, leaving the U.S. capable of only brief excursions into Earth orbit.
For NASA, the prospect bears uncomfortable similarity to the 2011 retirement of the space shuttle fleet with no active replacement. For nearly a decade afterward, the agency purchased its astronauts seats on Russian spacecraft to reach the ISS -- an expensive strategy in the financial sense but also in terms of lost knowledge and expertise in the U.S. space industry.
"You really don't want to see that whole thing happen again," Magnus says. "If we're going to be a nation that explores space, then we need to do so in an intelligent, cost-effective and maximal way. [An approach in] fits and starts is just nonoptimal, and it's wasteful."