Before NASAshot astronaut Scott Kelly into orbit for the first time in 1999,??? ? ?? he had an important order from his commander: Take one of these diapers, and go practice at home. 

So there he was, wearing a government-issued spacediaper, lying down in his bathtub with his legs propped up. He was trying to simulate the way he'd be sitting in the Space Shuttle. 

After living his whole life trying to avoid peeing his pants, Kelly found it took some unlearning to be able to relax and let the good times, er, flow. But he eventually figured out how to open the floodgates. When it was his turn as commander on his next mission, he gave the same instructions to his crew: Go practice. That order, however, didn't go over so well with one male astronaut.

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"I actually had a crew member that wouldn't practice, refused to, and then almost had to be catheterized in space," Kelly told Mashable, adding empathetically that being an astronaut is a lot of pressure. 

That's why when his agent called him with a promotional opportunity to work with Goodnites, a maker of children's disposable bedtime underwear, he wanted to help reduce the stigma of bedwetting. It wasn't just the shared experience of needing to wear a diaper-like undergarment he identified with, it was the incredible pressure he realized children also must feel. Nighttime incontinence affects one in four 5-year-olds, one in five 7-year-olds, and one in 20 10-year-olds, according to the American Academy of Pediatrics. 

"Kids have a lot of stuff on their plate," said Kelly, who has two adult children, "so if this could help some kids feel less embarrassed about wetting the bed, I was all in."

SEE ALSO: Yes, NASA astronauts will still pee in their new spacesuits NASA astronaut Scott Kelly prepares for the Expedition 43 launch inside the Soyuz TMA-16M spacecraft at the Baikonur Cosmodrome in Kazakhstan. Credit: NASA / Victor Zelentsov

It's common knowledge that astronauts wear diapers. Perhaps no one brought that to the fore more than former astronaut Lisa Nowak— but that's a 900-mile story for another time. 

The shuttle and International Space Station have toilets, but sometimes the crew don't have access to them. During launches and landings, astronauts must stay strapped into their seats, and spacewalks — when astronauts venture outside for experiments or maintenance tasks — often require being sealed in a spacesuit for up to eight hours. 

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Not many people can hold it for that long while continuously hydrating, so diapers have become a necessity— especially after the astronaut corps expanded to include women. The original urine collection contraptions designed for male astronauts couldn't be easily adapted for female anatomy. 

A sample of an adjustable Maximum Absorbency Garment, or "MAG." Credit: NASA / Center for the Advancement of Science in Space NASA donated unused MAG samples to the National Air and Space Museum. Credit: NASA / National Air and Space Museum

In 1988, NASA started making MAGs — Maximum Absorbency Garments — for all its astronauts, said Kiona N. Smith, author of Peeing and Pooping in Space. The MAG uses a highly absorbent polymer compoundbetween layers of material to remove moisture, which turns the pee into a solid gel.

Perhaps deep down we're all snickering 12-year-olds, a fact that may have inspired Smith's book, but that curiosity is as innate as nature's call. 

"As silly as the questions and answers sometimes sound," Smith told Mashable, "it's that human urge to go, 'OK, but how does this work?'"

Goodnites' new "Mission Dry" ad campaign, which launched last month, includes a commercial featuring Kelly. The video opens with the astronaut and a young crewmate doing a spacewalk and basking in the once-in-a-lifetime view of the stars. But the child can't enjoy the experience because he's distracted. He accidentally peed in his spacesuit and fears mission control will make fun of him. 

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Child: Houston's probably laughing. 

Kelly: They're not laughing. 

Child: How do you know?

Kelly: Because I just peed.

Child: Just now? 

Kelly: Just now. 

Kelly, who is now retired after spending 520 days in space, was paid for the gig. As a public space agency, NASA doesn't usually endorse companies or their products. But he's not the only astronaut who liked the campaign's message. Cady Coleman, also retired from NASA, and a handful of other people who have flown on parabolic and short commercial flights, are also lending their voices. 

"On one of my missions, I did need to pee while I was wearing my spacesuit, and it went just fine," Coleman said in a reel on Instagram. "My suit was clean and dry, ready to go, and so was I."

Retired NASA astronaut Scott Kelly and others have joined a Goodnites disposable nighttime underwear ad campaign. Credit: Goodnites

For four decades, NASA has used the same spacesuit technology for astronauts. Axiom Space is designing a new one for the Artemis III crew, who will be the first people to walk on the moon since 1972. Though engineers have made several improvements, including dust-resistant materials, a compact life support system, and an HD video camera attachment, some things won't change, like wearing a MAG, said Russell Ralston, Axiom Space's deputy program manager for extravehicular activity.

"If it's not broken, don't fix it," Ralston told Mashable during the news conference in 2023. "They're just honestly a very effective solution. Sometimes simplicity is best."

That means a long and illustrious legacy of pants-peeing on the moon will continue, following in the boot prints of Apollo 11's Buzz Aldrin, the self-proclaimed first.

"He stepped off the bottom step of the lunar lander and realized he had to go," Smith said. "So you've got this picture of him standing there on the lunar surface, and what you don't realize is he is 100 percent peeing into his urine collection device at that moment."