Ever wonder what it’s like inside the ISS Cupola — that iconic, windowed module that lets Astronauts peer into space as our planet zooms by? In his latest video, science YouTuber Destin of Smarter Everyday set off to find out. Unexpectedly, what caught his attention amidst the wires and buttons were the module’s window shutters.

Space windows have a lot to contend with: there’s micro-meteorites, radiation, extreme temperatures (you get the idea), so each window on the Cupola has been fitted with a protective shutter that can be opened or closed by an astronaut inside. It seems pretty simple at first, but in order to mechanically open something on the outside of a space station by manipulating something on the inside, wouldn’t there have to be a hole going straight through? And wouldn’t that be problematic for anyone who might want to oh, you know, breathe?

After some digging, Destin discovered that there isn’t a hole in the Cupola. There are seven holes.

Perhaps no one has spent more time floating inside the Cupola than Don Pettit. An engineer, scientist, NASA astronaut, and the ISS’s resident didgeridoo player (no, really), Pettit is the photographer behind the incredible ISS timelapses. He explains that the windows’ shafts are surrounded by a system of rubber O-Rings to keep the airtight seal. “It’s called really good engineering,” he says with a laugh. So Destin did was any good science enthusiast would do: he found the man who invented it.

The man-with-the-plan is Charlie Vanvalkenburgh, an accomplished engineer with a humility you can’t help but smile at. Back in 1988, Vanvalkenburgh was commissioned to design for “Space Station Freedom,” the concept station that eventually morphed into the ISS. When the change happened, Vanvalkenburgh left astro-engineering, but not before handing his shaft design over to Italy, who went on to build the Cupola.  Over two decades later, he had no idea they had ever used it.

The inner shaft relies on a system of special grooves that compress the O-Rings with more, or less pressure as the windows open and close. When pressure is applied, the O-ring will move toward the low pressure side of the groove, filling any holes that might be dangerous. At its core, this is the same concept used to seal a DSLR camera in an underwater housing.

Of course, the O-Ring grooves on the ISS can be held with extreme precision, but this is a great example of using simple physics to solve complicated problems. “You’ve got your air you breathe as an astronaut, and it’s really held back from the vacuum of space by two little bitty O-Rings,” says Destin. “It’s just incredible.”

Images: NASA Marshall Space Flight Center, Smarter Everyday