For 16 years, the International Space Station has been staffed by different crews of astronauts. So what does it take to shift crews in and out of orbit?
First, a new crew has to arrive on the ISS. In this recent case, the flight from Earth to the station took two days.
The astronauts have to position their craft at just the right place in orbit so the ISS actually catches it.
Bringing a crew back to Earth has its own challenges.
When a capsule returns to Earth it gets so hot that it's basically covered in a ball of fire. A special coating protects the capsule, but outside layers are still burned off.
When the capsule is about six miles above ground, it's still traveling at 500 miles per hour. The parachute opening is unsurprisingly violent.
Right before it hits the ground, the craft slows to less than five miles per hour, but astronauts have said the landing still isn't that soft.
Dizziness is expected. Astronauts report feeling five times heavier the moment they stand up. And it can take more than a week to get back to feeling normal.
The Expedition 49 crew spent 115 days in space –– completing hundreds of experiments in bio-tech, biology and physical science.
Expedition 50 crew members will have just over four months before they too feel what it's like to come out of orbit.