NASA Astronaut Hands Over Command of International Space Station

— -- American astronaut Barry Wilmore has checked mostly everything off his to-do list in space.

With his bags packed and his crew quarters cleaned, Wilmore has officially handed over command of the International Space Station to American Terry Virts, who will oversee Expedition 43.

Wilmore is spending his final hours in space before he hitches a ride with his co-workers, cosmonauts Alexander Samokutyaev and Elena Serova, as they travel back to Earth in Russia's Soyuz spacecraft.

The group will begin undocking the Soyuz from the International Space Station today at 6:44 p.m. ET and land in Kazakhstan at 10:07 p.m. While the approximately 249 mile free-fall back to Earth takes about 45 minutes, the process for making sure they arrive at their destination is far more complex.

The Soyuz will stay close to the ISS for about two revolutions of the Earth as it fires its engines to align with the landing site. The crew on board the spacecraft will then turn its de-orbit engines in the direction of travel and fire them for four to five minutes before falling back to Earth.

The atmosphere helps slow the Soyuz down until parachutes open and help the spacecraft glide toward a landing.