After more than nine months on the International Space Station, two astronauts are a step closer to returning home following the launch of a crew swap mission on Friday.

Nasa decided that it would not take even a small risk in bringing back Butch and Suni on Starliner, when they had the option of returning them on SpaceX's Dragon capsule. Nasa decided the best option was to do this during a scheduled crew rotation, even though it would mean keeping the astronauts on the space station for several months.