Since NASA rotates ISS crews every six months, the stranded astronauts, Suni Williams and Butch Wilmore, won't return to Earth until late February.

Boeing's first astronaut flight with the Starliner launched in June was only supposed to last a week, but multiple failures, including thruster troubles and helium leaks, led NASA officials to deem the spacecraft too dangerous for Williams and Wilmore. The crewless Starliner returned to Earth earlier this month, landing without a problem in New Mexico.

After Saturday's launch, NASA Deputy Administrator Pam Melroy said "human spaceflight" is very "complicated and dynamic."