Almost every orbital rocket is built from several stages that are dropped one after the other during the flight. Staging is one of the basic ideas of rocketry. It explains why rockets look the way they do and why reaching orbit with a single stage is so difficult.
Why staging works
A rocket has to carry its own propellant, tanks and engines. As the propellant is burned, empty tanks and heavy engines become dead weight. By dropping a stage once its propellant is used up, the rocket no longer has to accelerate that mass. The following stage starts lighter and can reach a higher final speed with less propellant.
How separation works
At the end of a stage's burn, its engines shut down, the connection to the next stage is released and the stages move apart. The upper stage then ignites its own engine. Some designs fire the upper stage engine while the stages are still close together, which is called hot staging.
Typical configurations
- Two stage rockets: many modern launchers, such as Falcon 9 and Ariane 6, use two main stages, sometimes with additional boosters.
- Three stage rockets: the Saturn V used three stages to send Apollo crews towards the Moon.
- Boosters: strap on boosters burn in parallel with the core stage at lift off and are dropped early in the flight.
Single stage to orbit
A rocket that reaches orbit without dropping any stages would be simpler to reuse, but the required ratio between propellant and structure is extremely demanding with current technology. Instead, the industry focuses on recovering and reflying stages.
Where the stages go
Lower stages usually fall back into the ocean or return for landing if they are reusable. Upper stages reach orbit and must be deorbited or moved to disposal orbits to meet debris rules. The drop zones of lower stages also shape the possible launch directions from each spaceport.
Related reading
- Upper Stages and Kick Stages: How Rockets Deliver Satellites to Their Final Orbit
- Liquid vs Solid Rocket Engines: How Launch Vehicles Are Powered
- Falcon Heavy Explained: How SpaceX Launches Heavy Payloads
Sources
- NASA: Basics of Space Flight
- ESA: Launch vehicles
- NASA: The Two-Stage SpaceX Falcon 9
- ESA: Ariane 6 overview
Cover image: Launch of Apollo 11 on a three stage Saturn V rocket, 16 July 1969. Credit: NASA (S69-39961), public domain.