A
multistage (or
multi-stage)
rocket is a
rocket that uses two or more
stages, each of which contains its own
engines and
propellant. A
tandem or
serial stage is mounted on top of another stage; a
parallel stage is attached alongside another stage. The result is effectively two or more rockets stacked on top of or attached next to each other. Taken together these are sometimes called a
launch vehicle. Two-stage rockets are quite common, but rockets with as many as five separate stages have been successfully launched. By jettisoning stages when they run out of propellant, the mass of the remaining rocket is decreased. This
staging allows the thrust of the remaining stages to
more easily accelerate the rocket to its final speed and height.