It’s a refrain echoed every summer by parents sitting in the car about to launch on another road trip: “If you need to go, go before we leave.” Apparently, space shuttle trips are no different, which is why NASA built a last-minute bathroom for departing astronauts.

Almost 200 feet above the sands of Cape Canaveral, nestled in the steel crossbeams of the twin launch pads of Launch Complex 39, are two bathrooms, one for each pad. Unlike its multimillion-dollar counterpart on the space station, this bathroom is rudimentary: a stainless steel bowl mounted to the wall and a small sink.

The facility has been used by nearly every astronaut since STS-1. In fact, graffiti on one wall boasts, in language unfit for publication, that John Glenn himself blessed this outpost before his 1998 flight on STS-95.

Some might wonder why astronauts would need a toilet on the launch pad, given that a perfectly good facility awaits them on the space shuttle. Says Mike Foreman, a veteran of two shuttle missions, “You’re looking at at least two and a half hours on the pad. Then it’s eight and a half minutes to orbit. And then you have to activate the shuttle bathroom. It’s about an hour after we get to orbit that the Waste Containment System is activated, all the circuit breakers are put in, all the hoses connected. I have a small bladder I guess. So I was always motivated to get that thing activated quickly.”

Astronauts do have another option: diapers. “The only problem there,” says Foreman, “is that it’s hard to pee when you’re lying on your back. You’ve got to psyche yourself up. It’s something psychological. I challenge you. Lie on your back sometime and try using a diaper. It’s not easy.”

So, three hours before launch, shuttle astronauts line up at the last-minute bathroom. “The spacesuits zip up the back, so the zipper starts at the back of your neck and comes down around your crotch. That’s where the zipper ends. So you can’t reach,” says Foreman. “I mean, I’m not a contortionist. Someone else gets the zipper started for you, and you go in there. They don’t like you to take the suit off, so all you can do is sort of unzip the thing and kind of work your way out of the suit a little and get through your undergarments and use the facilities and try to tuck everything back in.”

Shimmying out of bulky spacesuits, lying on their backs for hours at a time…astronauts could certainly be forgiven for thinking that this had all been designed to make them look foolish. And maybe they’d be right.

As a former shuttle engineer, I know the tension that sometimes exists between engineers and astronauts. A sort of sibling rivalry develops as we watch our brothers and sisters do something many of us have always dreamed of doing. It’s jealousy, plain and simple. They fly into space, we sit in cubicles. They sign autographs, we write computer code. They wear snazzy blue flightsuits, we wear orthopedic footwear and pocket protectors.

When you take the time to look at it, it all makes sense. Who decided to put the zippers on the back of the spacesuits? Engineers. Who suggested that the astronauts wear diapers? Engineers. Who built a cramped, rustic toilet 200 feet in the air? Engineers. If you’re still not convinced, just look at the final moments of a shuttle launch sequence (a system designed by engineers). Just before the main engines light, two hours after the astronauts first strapped in, 16 nozzles spew 300,000 gallons of water on the launch pad. Engineers swear that it’s a “sound suppression system,” but it might just be the final touch on the world’s greatest practical joke.