Astronaut Christina Koch's busy Thursday

Astronaut Christina Koch returns to Earth after a record setting 328 days in space. She along with Russian cosmonaut Aleksandr Skvortsov, and Italian astronaut Luca Parmitano, will undock from the International Space Station (ISS) in their gumdrop shaped Soyuz-MS spacecraft at 12:50 am EST for the nearly 3.5 hour trip home.

The first 2.5 hours will be spent safely clearing the ISS. Mission controllers outside Moscow then upload updated commands to the spacecraft for autonomous descent. But the vehicle is still traveling more than 35,000 miles per hour.

Christina Koch's year of ISS science

A deorbit burn scheduled for 3:18 a.m. will slow the spacecraft down some allowing gravity to do the job of bringing the crew home. This 4 minute, 45 second burn is critical. Too short of a burn and the capsule could skip off the atmosphere like a stone on a pond. Too long of a burn and the capsule will reenter steep and fast risking burning up the capsule.

The crew will use this growing sense of gravity, something they've not felt for a few months, to help them settle into their seats and tighten their harnesses.

About 30 minutes later the Soyuz reaches Entry Interface, a point 75 miles above Earth, and the atmosphere takes over the job of slowing the vehicle down. Eight minutes later friction from the thickening atmosphere begins to heat the spacecraft to over 3600 degrees Fahrenheit, darkening covers on the windows as it streaks through the sky at 755 feet per second. Deceleration will push the crew into their seats with a force of about 4 g.

"You feel your hands are heavy, your watch weighs a ton, your head feels extremely heavy" described European Space Agency astronaut Paolo Nespoli following his return from the ISS in 2011.

A pair of drogue parachutes, each about the size of a backyard trampoline, are deployed fifteen minutes before landing. They slows the rate of descent to 262 feet per second. Next the main chute deploys with a surface area of 1000 square meters, nearly a quarter of an acre, slowing capsule to 24 feet per second. But this is still too fast for a safe landing.

The blackened window covers on the sides along with the heat shield on the capsule's bottom are jettisoned revealing six small solid propellant engines, a blinking light beacon and altimeter. Those engines fire just two feet above the ground, slowing the capsule for a "soft landing" on the flat grassy plains near Dzhezkazgan, Kazakhstan at 4:18 a.m. EST (3:18 p.m. local time). Veteran astronauts describe the landing more a car crash.

Christina and her crew mates will get their first taste of fresh air about five minutes after Russian recovery forces reach the capsule by helicopter and all-terrain vehicle. The recovery team opens the hatch and helps the crew from the capsule into folding chairs. They enjoy a few minutes to stretch out after the cramped ride through the atmosphere and make calls to loved ones, then it's off to the medical tent for some checks before boarding a helicopter to begin the journey home by more conventional vehicles.