Somewhere above your head right now, a person with a doctorate is deciding whether a pair of underpants has one more day in them.
There is no washing machine on the International Space Station. No laundry, no clothesline, no sneaky rinse in the sink, because every drop of water up there is recycled from sweat, breath and urine, and none of it can be spared for a wash cycle. Clothes go up clean, get worn until they are unpleasant, then get thrown out.
How long one shirt has to last
The allowances are oddly specific. European Space Agency astronaut Samantha Cristoforetti laid hers out in a crew diary published through ESA’s Moon Camp Challenge: one pair of trousers a month, one T-shirt a week, fresh underwear every two days, socks every four. Japan’s space agency works to a similar rhythm, telling the public that its crews pack roughly one polo shirt for every 15 days and one pair of underwear for every three.
Retired NASA astronaut Leland Melvin gave Fortune the American version: about a week out of a pair of shorts, five days out of a shirt, a week out of socks.
Exercise gear wears out faster, and it earns that. Crew members spend up to two hours a day on a treadmill or a resistance machine to keep their bones from thinning, and sweat in microgravity does not drip off you. It clings.
Roughly 75 kilograms a person, a year
Add it up and each crew member needs around 72.5 kilograms, or 160 pounds, of clean clothing flown up every year. NASA and Procter & Gamble published that figure when they announced their Space Act Agreement on space laundry, and it is the reason anyone is working on the problem at all.
Every kilogram launched costs money and pushes something else off the manifest. Food, oxygen, spare parts, science.
Where the dirty clothes go
Used garments get packed into a departing cargo freighter with the rest of the station’s rubbish. The freighter undocks, drops into the atmosphere and burns.
Which means a bright streak crossing the sky at night might be several months of somebody’s socks.
Bringing them home is not an option either, because return capacity is scarcer than launch capacity and a bag of worn T-shirts will never win that argument.
Why nobody has simply installed a washing machine
Two things make it hard. Water in a sealed habitat has to come back out of the wash clean enough to drink, so any detergent has to be compatible with a life support system that will eventually serve it to a human. Microgravity handles the rest, because water will not pour, drain or spin out of fabric. It wraps itself around whatever it touches and stays put.
Tide has been chipping away at the first half of that since a prototype detergent called Tide Infinity launched to the station in December 2021, followed by stain wipes and pens for the messier realities of eating in orbit.
Clothes that stay wearable longer
The other approach is to stop garments getting foul in the first place. In 2009, JAXA astronaut Koichi Wakata tested a line of antibacterial, odour-suppressing clothing called J-Wear, and took the experiment to its logical conclusion by keeping one pair of silver-coated underwear on for a month. As reported by Space.com, his verdict was diplomatic: his crewmates never complained.
NASA has put the same question through fabric science. Its Advanced Clothing Study ran wool, modacrylic, polyester blends and treated cottons through extended wear trials, with daily questionnaires logging how each garment felt and why the wearer finally retired it.
Mist, ozone and the break-even point
A team at the China Astronaut Research and Training Center has costed out an alternative. Writing in the Chinese Journal of Space Science, the researchers describe a laundry platform that uses ultrasonic arrays to atomise water into a fog, so it soaks into fabric that would otherwise float free of it, and ultraviolet lamps to generate ozone as the disinfectant.
Their modelling puts the cost of running it for a year at 15.7 percent of conventional laundry technology, and finds a 61.9 percent saving in equivalent system mass compared with throwing clothes away. On those figures the platform earns back its own launch weight after roughly two and a half months.
That is one paper, built on simulation rather than hardware in orbit, so nobody is folding towels above the Kármán line yet.
Still, the arithmetic is what keeps the idea moving. A round trip to Mars runs two to three years with no resupply, and at station rates a crew of four would get through the better part of a tonne of clothing. Solve laundry and you win back cargo mass for something that actually does science.