Any time the shuttle hits the Factory, Depot, Space Station, or debris it will be damaged and leak fuel. The greater the number of hits, the greater the rate of fuel loss.
Any time the Challenger hits an object there is at least a 25% chance you will damage your cargo. Due to packing constraints, if you are carrying two sections and hit an object, you will definitely damage one section – possibly both. You can only examine the sections at the Factory or Space Station. If the section has no prongs on the right-hand side, it is damaged and cannot be used. If one of the two sections being carried is damaged, the good section will be brought out first by the astronaut.
The shuttle consumes more fuel carrying two sections (damaged or not) than carrying one section, and more fuel carrying one section than with no cargo.
Only one refueling should be necessary for the truly proficient pilot.