rocket systems mounted in vertical sequence.
The lowest, or first, stage ignites and lifts the vehicle (sometimes assisted by attached booster rockets) at increasing speed until its propellants have been used up. The first stage then drops off, which makes the vehicle lighter, and the second stage ignites and accelerates the vehicle further. The use of additional stages generally follows the same pattern until the payload
the spacecraft
has reached the velocity needed to achieve orbit or leave the vicinity of Earth. The number of stages required depends on the details of the mission, the launch vehicle's characteristics, and other factors. Some early vehicles needed five stages to reach orbit; most current launch vehicles need only two.