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[[Image:BasicRocket.png|thumb|right|100px|Simplified drawing of a rocket]]
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[[Image:BasicRocket.png|thumb|right|200px|Simplified drawing of a rocket]]
[[Image:Multistage.png|thumb|right|100px|Simplified drawing of a two-stage rocket]]
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[[Image:Multistage.png|thumb|right|200px|Simplified drawing of a two-stage rocket]]
  
A '''rocket''' is a machine which ejects mass for generating [[velocity]]. Typical elements of a rocket are propulsion systems, propellant utilization systems, structures, guidance and control and tanks. A rocket does not need to be its own spacecraft. It can be made for space or as part of a larger spacecraft system.
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A '''rocket''' is a machine which ejects mass for generating [[velocity]].  
 
 
==Propulsion systems==
 
  
 
A rocket gains velocity by ejecting mass through a [[rocket engine]]. The concept is plain conservation of impulse (or Newtons third law). Every second, the rocket ejects propellant mass through the nozzle of the rocket engine. The impulse of this mass is compensated with the remaining rocket accelerating. The more mass getting ejected (This property is called [[mass flow]]) or the faster this mass gets ejected (called average [[exhaust velocity]] or [[specific impulse]]), the more velocity the rocket gains.  
 
A rocket gains velocity by ejecting mass through a [[rocket engine]]. The concept is plain conservation of impulse (or Newtons third law). Every second, the rocket ejects propellant mass through the nozzle of the rocket engine. The impulse of this mass is compensated with the remaining rocket accelerating. The more mass getting ejected (This property is called [[mass flow]]) or the faster this mass gets ejected (called average [[exhaust velocity]] or [[specific impulse]]), the more velocity the rocket gains.  
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* The higher the chamber pressure a rocket engine, the smaller can be the nozzle for the same thrust.  
 
* The higher the chamber pressure a rocket engine, the smaller can be the nozzle for the same thrust.  
 
* The ratio of the throat area and the exit area of the nozzle (the so called expansion ratio) depends on the ambient pressure (for example sea level or vacuum). The smaller the expansion ratio, the lower is the effect of ambient pressure, meaning the rocket engine is more effective on lower altitudes. That's why boosters usually have short nozzles and upper stages which operate in vacuum, even get moving extensions to make the nozzles longer.
 
* The ratio of the throat area and the exit area of the nozzle (the so called expansion ratio) depends on the ambient pressure (for example sea level or vacuum). The smaller the expansion ratio, the lower is the effect of ambient pressure, meaning the rocket engine is more effective on lower altitudes. That's why boosters usually have short nozzles and upper stages which operate in vacuum, even get moving extensions to make the nozzles longer.
 
===Bipropellant rockets===
 
[[Image:BipropellantRocket.png|thumb|left|100px|Bipropellant rocket]]
 
 
A bipropellant rocket is a rocket, which uses two liquid or gasous chemicals for propulsion. One component is called typically fuel, the other oxidizer (even when it, in the case of Flour, does not contain oxygen). The propellant combinations of bipropellant rockets are further classified by the storage temperatures, toxicity and  ignition behavior. Propellants which require cooling below -50°C to stay liquid are called cryogen. They can only get filled into the rocket tanks shortly before launch and can't stay liquid for long once inside the tanks. The amount of propellants, which turn to gaseous form and need to be vented outside the tanks is called ''boil-off''.
 
 
A common problem of all liquid fueled rockets are the movements of the liquid propellants inside the tanks, called sloshing. It requires careful design of the tank walls to increase the resistance and also has to be considered inside the control loop design.
 
 
Typical fuel combinations are liquid hydrogen and oxygen (called hydrolox) and kerosine plus liquid oxygen (kerolox).
 
 
===Solid rocket===
 
[[Image:SolidRocket.png|thumb|left|100px|Solid rocket]]
 
 
A solid rocket or solid rocket motor stores all the propellants in solid form inside the [[Combustion chamber|combustion chamber]]. Their advantage is, that, once ignited, they don't shutdown. They are also very simple in design and construction and can deliver very high thrust. Their main disadvantage are their low [[specific impulse]].
 
 
 
Once ignited, thrust can only be terminated by thrust termination devices, which for example lower the chamber pressure below the threshold required for sustaining combustion. This is usually destructive.
 
 
[[Category: Articles]]
 
[[Category:Glossary]]
 

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