NASA may have to temporarily abandon the International Space Station in November, as a recent Russian rocket crash has called into question the safety of the vehicle that ferries astronauts to and from the station. If astronauts have to board up and leave the orbiting science laboratory, how long could it last without human maintenance?
Several years. If NASA were to completely abandon the space station and make no attempt whatsoever to maintain it, the engines would eventually run out of fuel or suffer some kind of mechanical failure. Its orbit would decay—that's a space-y way of saying the station would get closer and closer to Earth—until it came crashing down. (NASA plans to aim the charred debris at the Indian Ocean if an emergency landing ever becomes necessary.) It's hard to predict exactly when the end would come. When NASA abandoned its low-Earth-orbit station called Skylab in 1974, they expected it would remain aloft until 1983. (The last crew left some food and clothing in case the space agency had a change of heart.) But intense solar radiation in the late 1970s expanded the Earth's upper atmosphere, which increased drag on Skylab and brought it down in 1979.
In reality, the current crimp in the astronaut supply chain is very unlikely to bring down the space station. Even if there's no crew onboard, mission control could steer the station around space debris and give it a little boost when necessary to keep it in orbit. Unmanned rockets would refuel the engines, and before the last crew left the station—if it ever came to that—they'd install redundant parts to make sure the critical cooling and power systems could survive a few unexpected failures. (The engines would stop working without coolant, as the temperature swings by 400 degrees Fahrenheit multiple times per day, depending on whether the ISS is exposed to the sun.)
Assuming the station didn't come careening out of orbit, its interior would stay in pretty good shape for quite some time. Rust is occasionally a problem up there—corroded wiring briefly disabled the orientation system in 2007—but that's only a risk when there is moisture emanating from the humans and animals onboard. NASA could easily dehumidify the station before withdrawing, preventing significant rust. Other factors that destroy objects on earth, like microbes and pests, aren't a problem. Fungi and bacterial spores can live for years in space, but they're not likely to thrive or damage any equipment. Aside from some brittleness from temperature cycling and some mechanical parts in need of a little lubricant, the astronauts could come back years later and find most of the station's innards to be in working order.
The biggest problem with temporary abandonment is that many of the science experiments on the station would be cut short. Space-based biology is a big field of interest, but some of those studies couldn't survive without people there to water the plants and feed the mice.
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Explainer thanks Stephanie Schierholz of NASA.