Question

How is the space craft proppeled when external tank are depleted?

Answer 1

A space craft is inbuilt to cross counter the propulsion system issues , it has many chambers and components inbuilt , First chamber of PROPULSION system maybe of solid propellant or liquid , or a composite propulsion system may occur , when external propulsion tanks are depleted , internal inbuilt propulsion chambers are present there to propell them accordingly , Rest of the work is operated by gravity alone by any defined trajectory velocity given by pre installed propellant earlier

Answer 2

external fuel is only used to gain a certain velocity after that space craft followed a definite trajectory. space craft also had internal fuel to change direction.