The first step to living in space is getting there. All astronauts hitch a ride to the ISS on board a giant space shuttle that launches from Russia.
The shuttle takes astronauts all the way up to the ISS, which floats about 250 miles above the planet.
The station is a system of labs, living quarters, and control rooms, and it spans about the length of a football field. A rotating crew of six astronauts share the space.
The ISS is hurtling around the Earth at about 17,150 miles per hour. That extreme velocity puts the ISS in a constant free fall around the planet.
So everything on board experiences weightlessness, including the astronauts.
So they get around the station by floating. Which means sometimes it's too hard to resist the temptation to strike a Superman pose.
Weightlessness causes a lot of weird problems though — the kind of problems we never experience here on Earth thanks to gravity.
For example, sweat doesn't evaporate. Instead, it pools on astronauts' bodies, so they are constantly toweling off sweat. You can see sweat droplets escape from this astronaut's towel after he wipes his head.
If objects escape inside the ISS, they can float away, get lodged in equipment, and cause malfunctions.
For example, even small tasks like clipping your nails become a problem. Astronauts clip them near a vent, so that tiny pieces of nail don't end up floating all over the station.
Water is also difficult to manage. It likes to stick together in a big blob.
So washing and showering is a challenge. Astronauts squirt a few lines of water on their skin and hair and then use no-rinse soap and shampoo to clean themselves.
The station only gets resupplied every few months, so astronauts have to be mindful of their supplies. Luckily, over 90% of the water on board gets recycled and reused.
That includes everything from dirty wash water, water from astronauts' breath, and yes, even urine is recycled. It's all sent through this high-tech water filter on board.
The water is perfectly safe to drink after it's run through the filter (it's actually cleaner than the water we drink on Earth), but many astronauts say they try not to think about it too much when they refill their water pouches.
Getting back to that urine thing, "How do you go to the bathroom?" is one of the most common questions astronauts get.
If you're going number one, it gets sucked into this tube through the yellow nozzle.
Things are little more complicated when you need to go number two. There's a tiny seat, a container for the waste, and a suction pump.
Once you do your business and suction it away, you have to change out the "poop bag" for the next person.
Still, all the complications that come from weightlessness don't get in the way of what astronauts are really there for. They spend most of their time working on various research projects and repairing the station.
Sometimes that even involves venturing out into the dangerous vacuum of space. Trips outside the station are called "spacewalks," and they take a lot of preparation and safety training.
One wrong move and an astronaut could just float off into the vacuum of space (like George Clooney in "Gravity"). They also have to watch for leaks in the spacesuits that protect them from the bitterly cold temperatures and radiation in space.
When they aren't working, astronauts still have to stick to a pretty tight schedule. They have mandatory workouts so they don't lose too much muscle mass in the weightless environment. (Since they don't have to fight gravity, they get a lot less exercise while moving around.)
You can easily lift hundreds of pounds in a weightless environment, so astronauts have a cleverly designed machine for weight lifting.
After a good work out, you gonna eat. Space meals are stored in dehydrated packets. Once you add a little water, dinner is served.
And the menu isn't half bad. Here's an astronaut enjoying a milkshake.
After dinner it's time for bed. The middle section of the station is where most of the crew sleeps. Labs and work spaces make up the rest of the structure, and the giant yellow panels collect sunlight to help power everything.
Each astronaut has their own tiny room that includes a work space and a sleeping bag strapped to the wall. You can see on the screens that it appears astronaut Scott Kelly is chatting on Facebook.
Sleeping in space is hard to get used to since you don't feel the sensation of lying down. Astronauts zip themselves into a sleeping bag every night so they don't float around in their sleep.
And they have to keep careful track of their sleep schedule since days don't pass the same on the ISS as they do on Earth. The station is whizzing around the planet so quickly that the crew sees about 16 sunrises and sunsets during a 24-hour Earth day.
When it's time to return to Earth, a shuttle flies up to the station to pick up the astronauts. Then they parachute back down to Earth in a landing pod.
Astronauts are a little wobbly on their feet when they first land, but it doesn't take long to readjust to a weighted environment.
Living on the ISS is no picnic, but it's a once in a lifetime opportunity. Most astronauts say they wouldn't trade the experience for anything.
