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What happens to sweat in outer space (Hint: There's no gravity to help it drip away)

MARY LOUISE KELLY, HOST:

This summer, we have been examining sweat in a series of stories on all aspects of perspiration. Today we are leaving the planet to ponder sweating in space because, as NPR's Nell Greenfieldboyce reports, sweat is a big deal for space travelers.

NELL GREENFIELDBOYCE, BYLINE: Astronauts have to stay in shape both on the ground and once they're in orbit.

MIKE MASSIMINO: I was exercising all the time I was an astronaut, it seemed like. And, yeah, I sweat. I'm a big sweater.

GREENFIELDBOYCE: Mike Massimino is now a professor at Columbia University. He says in space, sweat won't drip off of you.

MASSIMINO: Sweat does not fall off of your body, like, because there's no gravity there.

GREENFIELDBOYCE: Instead, in microgravity, water tends to cling to whatever surface it's touching. So he says if you're on an exercise bike...

MASSIMINO: The water would just kind of form on your body and not go away necessarily unless you wiped it with a towel.

GREENFIELDBOYCE: A towel works fine if you're inside the International Space Station, but if you go outside on a spacewalk...

MASSIMINO: That's a real athletic event when you're spacewalking. They typically run about 6 1/2 hours, and you're moving that whole time typically. And so you can build up a heavy heat load.

GREENFIELDBOYCE: To deal with that heat, spacewalkers wear a special garment, basically long underwear that has tubes full of cooling water. Spacewalkers also wear sweat-absorbing fabrics like gloves and a sweat band around the head. Still, Massimino remembers one time when sweat got into the communications cap that's fitted out with headphones.

MASSIMINO: And we had some problems where sweat was getting - water was getting getting stuck in there and causing a problem with communication.

GREENFIELDBOYCE: Electronics and water just don't get along. So in the space station, any and all water in the air, like from sweat, has to get collected.

JILL WILLIAMSON: We have to reclaim that water. Otherwise, you know, you'll have a buildup of water condensing on all surfaces.

GREENFIELDBOYCE: Jill Williamson is NASA's water subsystems manager for the station. She says if you add up all the water that astronauts either sweat out or breathe out as moisture, it's about 1 1/2 liters per day per person.

WILLIAMSON: That is about 50% of our water that we do reclaim. Of course, the other 50% is coming from urine.

GREENFIELDBOYCE: All that reclaimed water is cleaned and recycled so that astronauts can drink it and sweat it out all over again. Nell Greenfieldboyce, NPR News.

(SOUNDBITE OF FLYING LOTUS' "FF4") Transcript provided by NPR, Copyright NPR.

Nell Greenfieldboyce
Nell Greenfieldboyce is a NPR science correspondent.