The Falcon 9 rocket is carrying four astronauts who will replace Wilmore and Williams, both of whom are veteran NASA astronauts and retired U.S. Navy test pilots and were the first to fly Boeing's faulty Starliner capsule to the ISS in June.

Once it does happen, the flight will kick off a series of events culminating in NASA astronauts Suni Williams and Butch Wilmore’s long-awaited trip back to Earth.