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In this image American astronaut Megan McArthur posted on Twitter, astronauts are performing their duties at the International Space Station. (Twitter screenshot)

What do astronauts do with the clothes they’ve been wearing all day? Here’s the answer: they wear it again the next day.

Since you can’t just run the laundry in space, astronauts keep wearing their clothes until they’re filthy and then put them in the receptacle.

Clothing does stay clean a little longer in space than it would on earth. Less energy is expended in zero gravity, which means that astronauts don’t sweat as much.

The length of time that astronauts wear clothing depends on the category: underwear, socks, gym clothes and work clothes.

According to NASA, astronauts need 150 pounds of clothing for each year in space. Astronauts would need three times that much for a round trip to Mars, which would take three years. The old clothing is stored in cargo ships that burn up during atmospheric reentry.

But wearing clothes until they get grubby is one of the downers about spending time in space. The length and frequency of space travel will keep increasing in the future, and a permanent base may be built on the moon someday – two reasons why the current approach to space duds isn’t sustainable.

Inner garments astronauts put on underneath their spacesuits are shared among astronauts. (provided by the European Space Agency)

NASA wants to rectify this costly and inefficient practice, so it has partnered with Procter & Gamble, the manufacturer of lifestyle goods, to find a way to wash clothing in space and enable continued wear.

The organization was looking into special antimicrobial clothing, but eventually concluded that that wasn’t a long-term solution.

Astronauts on the space station currently need to exercise two hours a day in zero gravity so they don’t lose bone and muscle mass. This exercise leaves underwear drenched in sweat – and smelly, too.

Former NASA astronaut Leland Melvin, spokesperson for the project, told the Associated Press that “t-shirts, shorts, and socks end up so foul that they run through a pair every week.”

“After that, they’re deemed toxic,” Melvin said. “They’re so stiff from all that sweat.”

This December, Procter & Gamble plans to send up Tide powder detergent it has developed for use in space and see whether the detergent functions properly in zero gravity over six months. Then in May 2022, the company will also send up stain remover pens and wet wipes for astronauts to try out.

Procter & Gamble plans to run an equivalent and simultaneous experiment on the same ingredients back on earth to see whether the detergent functions differently in the two environments.

Astronauts on the space station currently need to exercise two hours a day in zero gravity so they don’t lose bone and muscle mass. (Wikimedia Commons)

Finding a way to wash clothes in space would reduce garbage and save money by cutting down on the cost of purchasing and transporting clothing. The cost of clothing a single astronaut for one year is about US$1.6 million.

Procter & Gamble is also developing a combo washer dryer that will operate on detergent and a minimal amount of water. If successful, the technology could also be put to good use in dry parts of the planet.

But there’s one obstacle to developing a washer dryer for space: the laundry water would have to be recycled, just as astronauts’ sweat and urine is.

By Kwak No-pil, senior staff writer

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