Astronaut Scott Kelly is in for a wild ride back to Earth inside Russia's Soyuz spacecraft.
The American astronaut, who is returning tonight after a year in space, will say his goodbyes to his co-workers at the International Space Station before the Soyuz hatch closes around 4:15 p.m. ET. He'll then be in for a roller coaster ride back to Earth as he sits inside the cramped Soyuz with two Russian cosmonauts.
Doug Wheelock, an astronaut who has traveled in both the Discovery Space Shuttle and the Soyuz, said the two experiences are notably different.
"It's incredibly bumpy and hot and cramped," Wheelock told ABC News last year. "It's kind of like going over Niagara Falls in a barrel but the barrel is on fire."
NASA has been purchasing seats for American astronauts on board the Soyuz since the 2011 retirement of the shuttle program. The agreement helps the United States maintain its presence in space as Boeing and SpaceX work on vehicles expected to be ready near the end of 2017.
The roughly 249 mile freefall back to Earth inside the Soyuz takes about 45 minutes, and the process for making sure the trio arrive at their destination will be very complex.
The Soyuz will stay with the ISS for about two revolutions of the Earth as it fires its engines to align with the landing site. The crew members on board the spacecraft will then turn their de-orbit engines in the direction of travel and fire them for four to five minutes before falling back to Earth.
"You have a lot of G-forces pushing you down. You're watching parts of your spaceship burn up outside of your window. It’s a little alarming visually," Wheelock said. "And then, of course, the heat shield on the Soyuz is ablative. It melts off and chunks roll off as you're coming through the atmosphere so, consequently, [it] gets thinner and thinner."
The atmosphere helps slow the Soyuz down until parachutes open and the spacecraft glides to a landing in Kazakhstan. Wheelock said the astronauts may be bracing themselves for what has the potential to be a jolting return to Earth.
"They train you to keep your hands and arms inside of your body enclosure to make sure you don’t break anything," Wheelock said. "You get as small as you can. When you hit, some people stick the landing. We bounced. We hit again and rolled over. It depends on the winds and things like that."
After that, a recovery team, which will include Wheelock, will locate the Soyuz capsule and help pull Kelly and his Russian counterparts out one by one.
The astronauts will then be taken to a medical tent, Wheelock said, where under professional supervision they can try standing up for the first time in months, a feat that isn't always easy after living in a micro-gravity environment.
"A lot of people feel a tingling in the bottoms of their feet," he said. "The nerve endings in your feet are feeling your body weight for first time in months."