Space shuttles work by utilizing three major components to reach their destination. There are two rocket boosters that are critical for the launch itself and the external fuel tank that carries enough fuel for the launch. The orbiter is the component that carries the astronauts and payload. The boosters are ignited to launch the shuttle and separate shortly after launch. When the orbiter reaches its optimum height, the external fuel tanks separate. The orbiter is then set for the orbital path it will follow around the earth. When the orbiter is ready to return to the earth it will use an engine retrofire to leave its orbit and descend to re-enter the earth's atmosphere where it will land.