For instance, and this would be very, very bad: a puncture wound.
In the vacuum of space, the amount of debris—spent rocket stages, splintered satellites, micrometeoroids—numbers in the millions, all zooming about, often at 17,000 mph speeds. They’re also constantly hitting each other in a tsuris of exponential littering. Most of these pieces are tiny, and many are not anywhere near the altitude of the ISS. But the area isn’t completely clean.
Debris actually pelts the ISS all the time, and noticeable dents and cracks line the exteriors. But should something fully breach the station, cabin atmosphere will seep into the vacuum of space and alarms will go off. Pressure gauges will confirm to astronauts that the station has, almost certainly, been hit, and the speed of the seepages may indicate how much time the crew has to respond. According to one NASA estimate, a 0.6-centimeter-wide hole leaves 14 hours to plug the leak. A 20-centimeter hole leaves less than a minute.
There is a plan to prevent such a strike—the Space Surveillance Network, a bevy of sensors that the military uses to track space debris. NASA monitors what’s unofficially known as the “pizza box,” a sort of no-fly zone around the ISS. When pieces of debris are predicted to enter the box—if there’s at least a 1 in 100,000 chance of collision—mission controllers order avoidance maneuvers, firing thrusters that move the ISS and dodge the trash. The technique has been used dozens of times since the first ISS module launched in 1998. But the system only tracks about 45,000 larger pieces, and all sensors have noise. Plus, risk thresholds can miss stuff, sometimes badly. In 2025, Chinese astronauts were briefly stranded at their station after debris hit their return vehicle.
The ISS does have its own defenses, of course. Fabric-y buffers envelope some of the systems, and a bumper called the Whipple Shield helps blunt impact. That shield is only built to stop debris up to about 1 cubic centimeter, though, and the debris tracker is only designed to catch pieces 10 cubic centimeters and larger. In other words, there’s a gap in defenses.
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