If successful, the landing will be the first major step toward one of the holy grails of the space industry: reusable rockets. Up until now, all rocket launches have been something of a one-and-done stunt. After a rocket blasts off, the first stage of the vehicle – which comprises the bulk of the rocket and contains most of the engines and fuel – burns up and falls away into the ocean, never to be used again. This rocket design is known as a disposable launch system, and it makes launching rockets extremely expensive. The only exception has been the Space Shuttle, which was considered a partially reusable launch system; although the shuttle itself and its solid rocket boosters were recovered after each launch, its large external tank, which carried most of the shuttle's fuel, broke apart and was never re-used. This made launching shuttles quite costly, as well, since a new external tank had to be built for each flight.