The research in the Polaris program, planned to be three flights, is particularly focused on human health and the effects of spaceflight on the body. The current mission will be studied by Baylor College of Medicine, with the astronauts giving blood and going through extensive biomedical testing both before and after the flight.

SpaceX's Polaris Dawn mission was a spaceflight for the ages. Here's what the historic mission was like from launch to landing.

The first-of-its-kind Polaris Dawn space mission concluded Sunday with the return to Earth of four private sector astronauts in a Crew Dragon capsule that had lifted off five days earlier atop a SpaceX Falcon 9 rocket.