| A multistage (or multi-stage) rocket is, like | | | | lightens itself. The thrust of the future |
| any rocket, propelled by the recoil pressure | | | | stages is able to provide more acceleration |
| of the gases it emits as it burns fuel. What | | | | than if the earlier stages were still |
| characterizes it as "multi-stage" is that it | | | | attached, or than a single, large rocket |
| successively jettisons one or more stages as | | | | would be capable of. When a stage drops off, |
| they become empty. It is effectively one or | | | | the rest of the rocket is still travelling |
| more rockets (stages) stacked on top of or | | | | near to the speed that the whole assembly |
| attached next to each other ("parallel | | | | reached at burn-out time. This means that it |
| staging"); in order to reduce the total | | | | needs less total fuel to reach a given |
| amount of mass which needs to be accelerated | | | | velocity and/or altitude. |
| to the final speed/height. Generally each | | | | |
| stage consists of one or more motors, plus | | | | A further advantage is that each stage can |
| fuel and oxidiser tanks for a liquid rocket | | | | use a different type of rocket motor, with |
| or the casing for a solid rocket. In | | | | each stage/motor tuned for the conditions in |
| rocketry, this concept is known as staging. | | | | which it will operate. Thus the lower stage |
| | | | motors are designed for use at atmospheric |
| Solid or liquid rocket Boosters are often | | | | pressure, while the upper stages can use |
| used for parallel staging schemes and all | | | | motors suited to near vacuum conditions. |
| motors are ignited at launch. These are | | | | Lower stages tend to require more structure |
| sometimes referred to as 'stage 0'. The first | | | | than upper as they need to bear their own |
| stage is at the bottom and is usually the | | | | weight plus that of the stages above them, |
| largest, the second stage above it and is | | | | optimizing the structure of each stage |
| usually the next largest, etc. In the typical | | | | decreases the weight of the total vehicle and |
| case, the first stage's motor(s) fire and | | | | provides further advantage. |
| then any fitted boosters, and the entire | | | | |
| rocket is propelled upwards. When the | | | | Disadvantages |
| boosters run out of fuel, they detached from | | | | |
| the rest of the rocket (usually with some | | | | On the downside, staging requires the vehicle |
| kind of small explosive charge) and fall | | | | to lift motors which are not being used until |
| away. The first stage then burns to | | | | later, as well as making the entire rocket |
| completion and falls off. This leaves a | | | | more complex and harder to build. |
| smaller rocket, with the second stage on the | | | | Nevertheless the savings are so great that |
| bottom, which then fires. This process is | | | | every rocket currently used to deliver a |
| repeated until the final stage's motor burns | | | | payload into orbit uses staging. |
| out. | | | | |
| | | | In more recent times the usefulness of the |
| The Space shuttle has two large boosters and | | | | technique has come into question due to |
| is not Single-stage-to-orbit (SSTO). | | | | developments in technology. In the case of |
| | | | the Space Shuttle the costs of space launches |
| Advantages | | | | appear to mostly composed of the operational |
| | | | costs of the people involved (as opposed to |
| The main reason for multi-stage rockets and | | | | fuel or equipment), reducing these costs |
| boosters is that once the fuel is burnt, the | | | | appears to be the best way to lower the |
| space and structure which contained it and | | | | overall launch costs. New technology that is |
| the motors themselves (in the case of | | | | mainly in the theoretical and developmental |
| liquid-fuelled rockets) are useless and only | | | | stages is being looked at to lower the costs |
| add weight to the vehicle which slows down | | | | of launch vehicles. More information can be |
| its future acceleration. By dropping the | | | | found on single stage to orbit designs that |
| stages which are no longer useful, the rocket | | | | do not have separate stages. |