Sleeping in space is weirdly difficult — and other lessons from Scott Kelly's year in orbit

By now, 543 humans have spent time orbiting the Earth. But almost no one has stayed up as long as NASA astronaut Scott Kelly.

Since March of 2015, Kelly has been living on the International Space Station as part of the One Year Mission. He and Russian cosmonaut Mikhail Kornienko spent nearly a year in orbit to see how the human body copes with extended periods of microgravity — research that could help agencies prepare for future missions to Mars. (Kelly's identical twin brother, Mark, is staying on Earth as a control.)

It's a grueling task. Most astronauts who go the space station come back after 180 days or so. Kelly and Kornienko have spent a full 340 days — and are coming back tonight, March 1:

#Countdown We're down to a wakeup. #Earth. I'm coming for you tomorrow! #GoodNight from @space_station! #YearInSpace pic.twitter.com/kLe2755XyG

— Scott Kelly (@StationCDRKelly) March 1, 2016

So what was it like up there? Back in January, Kelly did a Reddit AMA interview from the space station — he gets internet, though he said it's "like dial-up" — and shared some of the more unusual aspects of living in space. I've rounded up his most interesting answers below.

1) Microgravity does weird things to your feet

When asked what the oddest thing about living in microgravity was, Kelly pointed to … his feet.

"The calluses on your feet in space will eventually fall off," he noted. "So, the bottoms of your feet become very soft like newborn baby feet. But the top of my feet develop rough alligator skin because I use the top of my feet to get around here on space station when using foot rails."

2) Sleeping in space is more difficult than you think

Piers Sellers sleeps aboard Space Shuttle Atlantis. (NASA)

Many Earth-dwellers might assume it's entirely pleasant to sleep in space. You just float. But Kelly points out that this actually makes snoozing more difficult.

"Sleeping is harder here in space than on a bed," Kelly writes, "because the sleep position here is the same position throughout the day. You don't ever get that sense of gratifying relaxation here that you do on Earth after a long day at work. Yes, there are humming noises on station that affect my sleep, so I wear ear plugs to [bed]."

He's not the first to lodge this complaint. A 2014 study found that a large portion of astronauts on the space station suffer from sleep deprivation — with many resorting to sleeping pills. This is one problem NASA will have to solve before sending people to Mars, since that journey is likely to take years and it'd be no good if the astronauts are perpetually exhausted.

And what about dreams? "My dreams are sometimes space dreams and sometimes Earth dreams," Kelly wrote. "And they are crazy."

3) Figuring out what to do with your arms is a challenge

One perceptive Reddit reader noted that Kelly always has his arms folded in every photograph. Turns out there's a good reason for that:

"Your arms don't hang by your side in space like they do on Earth because there is no gravity," Kelly explains. "It feels awkward to have them floating in front of me. It is just more comfortable to have them folded. I don't even have them floating in my sleep, I put them in my sleeping bag."

4) Cleaning the toilet is … different

"What's the creepiest thing you've encountered while on the job?" asked one reader.

"Generally it has to do with the toilet," Kelly replied. "Recently I had to clean up a gallon-sized ball of urine mixed with acid." He clarified a bit further down: "The acid is added to the urine so the urine doesn't damage the machinery that moves it through the system. It keeps it from clogging up the system."

5) Microgravity is great for your joints. Coming back, not so much.

One of the biggest hurdles NASA has to tackle before sending anyone to Mars is the fact that bones and muscles tend to decay during long space missions, thanks to the lack of gravity.

To fight against that, Kelly says, he exercises for a full hour and a half each day. (Since it's not exactly practical to lift dumbbells, this exercise typically involves a treadmill, a stationary bike, and a resistance device that simulates weight training.) All the while, NASA is taking vital signs, including blood and saliva samples, and monitoring his progress.

"My muscles and joints are a whole lot better up here than with gravity," Kelly reports. "It's almost like you are in a bed rest. There is no pressure or pain. I do stretch before I exercise because my muscles aren't stretched out, they are somewhat dormant." And, he adds, "It seems blood pressure is lower because it doesn't have to fight against gravity."

But the ultimate test will be what happens when he returns to Earth and faces gravity again. Kelly expects this to be difficult. "It takes a while. Everyone is different. Dizzy, tired, sore muscles. … I'll have to wait until I return again after this flight to see what my adjustment will be after a year." NASA will be very interested to see how quickly Kelly can regain full strength — a crucial task for astronauts landing on Mars.

6) Liquid salt and pepper are indispensable

(NASA)

One reader asks what would happen if the astronauts tried to salt their food. That's a no-no.

"It would be a disaster to have something powder like that," Kelly points out. "Depending on how much it was, we would possibly consider shutting down the ventilation to stop it from spreading. For salt, we actually use liquid salt that we put on our food."

For that matter, astronauts have to be careful when they sneeze. "I just sneezed twice coming into my crew quarters," Kelly writes. "And I do what I do on Earth and cover my mouth with my hand. If I didn't do that, it's possible the sneeze could be found floating in another module."

7) Kelly's first food when he gets back? Probably a cucumber.

"What will be the first thing you eat once you're back on Earth?" one redditor asks.

"The first thing I will eat will probably be a piece of fruit (or a cucumber) the Russian nurse hands me as soon as I am pulled out of the space capsule and begin initial health checks," Kelly replies.

Another redditor asked: "What ONE thing will you forever do differently after your safe return home?"

Kelly's reply: "I will appreciate nature more."

For now, however, he's enjoying the sights (and taking incredible photos). Asked whether he ever finds the view unnerving, he replied: "When I look at the clouds over the Earth, and I know how high clouds are, I get a sense we are really, really far above those clouds. So, it does look like we are very high. I wouldn't call it scary, but I am aware I am in space. A spacewalk requires an incredible amount of mental concentration, so it's not something I think of when I am spacewalking."

Read more: Joseph Stromberg chatted with Kelly last year, shortly before he embarked on his current mission.

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