Difference between revisions of "Asparagus staging"

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m (Added a link to my video version of this tutorial)
(*rewritten most of the article; -part count isn't really an issue here; *summarized about the drag (but is not unique to AS); +names;)
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[[File:Asparagus-staging.svg|right|thumb|All engines uses first S4's fuel, then S3's fuel and so on]]
 
[[File:Asparagus-staging.svg|right|thumb|All engines uses first S4's fuel, then S3's fuel and so on]]
[[File:AsparagusStaging-6x3.png|right|300px|thumb|Overhead view of a vessel using asparagus staging]]
 
  
Asparagus staging is a method to build very efficient rockets.
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'''Asparagus staging''' is a method to build very efficient [[rocket]]s. The stock vessel [[Kerbal X]] demonstrates this technique.
  
The idea is that you create a rocket with a lot of parallel rocket engines with fuel tanks on top of them. All engines ignite at the same time. The trick, however, is that each rocket engine isn't depleting its own tank, but they are all draining their fuel from the two outmost tanks. When these are depleted, the outmost tanks with their engines are decoupled and the next fuel tank takes over which is still completely full. The result is that the rocket always flies with the minimum number of tanks required to transport the fuel it has left while also constantly using all engines it has on board.
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== Function ==
 +
The idea is to create a rocket with a lot of parallel [[rocket engine]]s with fuel tanks on top of them. All engines ignite at the same time. The trick, however, is that each rocket engine isn't depleting its own tank, but they are all draining their fuel from the outermost tanks. When these are depleted, the outmost tanks with their engines are decoupled and the next fuel tank takes over which is still completely full. The result is that the rocket always flies with the minimum number of tanks required to transport the fuel it has left while also constantly using all engines it has on board.
  
This concept can be realized through fuel ducts which connect the stages in the order they will be dropped. It exploits the fact that engines will always take their fuel from the most distant fuel tank available.
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This concept can be realized through [[fuel line]]s which connect the stages in the order they will be dropped. It uses the fact that engines will always take their fuel from the most distant fuel tank available.
  
The stock vessel "Kerbal X" demonstrates this technique.
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== Disadvantages ==
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[[File:AsparagusStaging-6x3.png|right|300px|thumb|Overhead view of a vessel using massive asparagus staging]]
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The biggest disadvantage of this technique is the complexity of building it. Usually the symmetry modes can only be used partially. One way is to only mirror each separate stage allowing to use symmetry for the complete setup. One drawback is, that the engines then are not always at the same height which may induce torque. Another way is to build everything except the fuel lines with the symmetry mode, but there each fuel line needs to be placed manually.
  
To learn how to set up and use asparagus staging in the form of a video, click [http://www.youtube.com/watch?v=rKGfwr2vrew here].
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With more massive payloads it may require more layers of fuel stacks and struts, making the technique challenging due to the high part count. Although a rocket without asparagus staging has a higher part count because it is more inefficient. The part count can be reduced by installing rocket part mods that provide fuel tanks and engines of larger sizes, allowing to achieve equal performance with less parts, more stability and better looks.
  
== Current Disadvantages ==
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Another disadvantage is that rockets utilizing this design may be unrealistic, because there is no real world application yet. It also might look not aesthetic especially with multiple layers, because there are then many small rockets bundled together.
  
The biggest disadvantage of this technique is the complexity of building it. While building one layer of 6 fuel stacks connected to the central stack by asparagus is relatively easy, higher payloads will require more layers of fuel stacks and struts, and this overall makes the technique challenging and laggy(due to the high part count)
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The rocket tends to start to [[roll]] when using this type of staging which might result in a loss in control of the craft. It also looses thrust with each staging event but only a lower mass compared to other staging methods. This can cause a serious drop of velocity reducing the efficiency.
  
Another disadvantage is that rockets utilizing this design are generally unaesthetic and unrealistic, which also results from attaching many SAS modules, the lack of nosecones(due to their negative impact on performance).
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=== Drag ===
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As rockets with asparagus staging may be wider than usual vertical stacked their real world [[drag]] would be higher. But as the drag depends on the mass instead of the cross-sectional area, there is no disadvantage of using asparagus staging when comparing the drag with other methods.
  
These disadvantages can be solved by installing rocket part mods that provide fuel tanks and engines of larger sizes, allowing you to achieve equal performance with less parts, more stability and better looks.
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Although this might change in the future — [[Planned features#Physics & Dynamics|the developers have already announced that the aerodynamic model will be made more realistic in future versions]]{{cn}}<sup>[''not cited in the link'']</sup> — this will most likely not a big issue, as the advantages outweigh this. But it will likely make it a lot more challenging to create aerodynamic crafts which use this technique excessively.
  
The rocket tends to start to rotate when using this type of Staging. The rotating will result in a loss in control of your craft so this is something to be remembered when trying Asparagus Staging.
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== Real world application ==
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This system is currently only a feature of Kerbal Space Program. In the real world there might be one craft, the [[w:Falcon Heavy|Falcon Heavy]] by 2014/2015 which uses this type of staging, although only with one level. The problem with asparagus staging is, that transferring fuel to an engine is already complicated. With additional pumps transferring between tanks the rocket becomes more complicated which may reduce the reliability.
  
== Future Disadvantages ==
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In 1947, [[w:Mikhail Tikhonravov|Mikhail Tikhonravov]] developed this kind of staging which he called “packet rockets”. This lead to the development of the [[w:R-7 Semyorka|R-7 Semyorka]]. Later developments of this rocket became then the [[w:R-7 (rocket family)|R-7 rocket family]]. But all those rockets never used the original “packet rockets”/asparagus staging.
  
Asparagus staging benefits a lot from the inaccurate way KSP is modeling atmospheric drag in the current version (0.20.2). Currently, each part of a vessel generates drag proportional to its mass, regardless of how it is placed and how much of its surface area is exposed to the direction of the airflow (yes, that means all the [[Aerodynamic Nose Cone]]s you put on your rockets just slowed them down even more). [[Planned features#Physics / Dynamics|The developers have already announced that the aerodynamic model will be made more realistic in future versions]], which will likely mean that the wide, flat designs of asparagus-staged crafts will generate a lot more atmospheric drag than slimmer designs with vertical staging.
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== Name ==
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Because there is no real world application of the asparagus staging, the name itself is a creation by the players of KSP and not an official word used in rocket science. Because of the design it is also called “onion staging”.
  
The new atmospheric drag model is unlikely to make asparagus staging completely obsolete as there is a planned real-life rocket which uses this method with one stage <ref>http://en.wikipedia.org/wiki/Falcon_Heavy#First_stage</ref>, but it will likely make it a lot more challenging to create aerodynamic crafts which use this technique excessively.
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== See also ==
 
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* [http://www.youtube.com/watch?v=rKGfwr2vrew Asparagus Staging Tutorial] by Rureglathon
== References ==
 
 
 
<references/>
 

Revision as of 12:05, 5 December 2013

All engines uses first S4's fuel, then S3's fuel and so on

Asparagus staging is a method to build very efficient rockets. The stock vessel Kerbal X demonstrates this technique.

Function

The idea is to create a rocket with a lot of parallel rocket engines with fuel tanks on top of them. All engines ignite at the same time. The trick, however, is that each rocket engine isn't depleting its own tank, but they are all draining their fuel from the outermost tanks. When these are depleted, the outmost tanks with their engines are decoupled and the next fuel tank takes over which is still completely full. The result is that the rocket always flies with the minimum number of tanks required to transport the fuel it has left while also constantly using all engines it has on board.

This concept can be realized through fuel lines which connect the stages in the order they will be dropped. It uses the fact that engines will always take their fuel from the most distant fuel tank available.

Disadvantages

Overhead view of a vessel using massive asparagus staging

The biggest disadvantage of this technique is the complexity of building it. Usually the symmetry modes can only be used partially. One way is to only mirror each separate stage allowing to use symmetry for the complete setup. One drawback is, that the engines then are not always at the same height which may induce torque. Another way is to build everything except the fuel lines with the symmetry mode, but there each fuel line needs to be placed manually.

With more massive payloads it may require more layers of fuel stacks and struts, making the technique challenging due to the high part count. Although a rocket without asparagus staging has a higher part count because it is more inefficient. The part count can be reduced by installing rocket part mods that provide fuel tanks and engines of larger sizes, allowing to achieve equal performance with less parts, more stability and better looks.

Another disadvantage is that rockets utilizing this design may be unrealistic, because there is no real world application yet. It also might look not aesthetic especially with multiple layers, because there are then many small rockets bundled together.

The rocket tends to start to roll when using this type of staging which might result in a loss in control of the craft. It also looses thrust with each staging event but only a lower mass compared to other staging methods. This can cause a serious drop of velocity reducing the efficiency.

Drag

As rockets with asparagus staging may be wider than usual vertical stacked their real world drag would be higher. But as the drag depends on the mass instead of the cross-sectional area, there is no disadvantage of using asparagus staging when comparing the drag with other methods.

Although this might change in the future — the developers have already announced that the aerodynamic model will be made more realistic in future versions[citation needed][not cited in the link] — this will most likely not a big issue, as the advantages outweigh this. But it will likely make it a lot more challenging to create aerodynamic crafts which use this technique excessively.

Real world application

This system is currently only a feature of Kerbal Space Program. In the real world there might be one craft, the Falcon Heavy by 2014/2015 which uses this type of staging, although only with one level. The problem with asparagus staging is, that transferring fuel to an engine is already complicated. With additional pumps transferring between tanks the rocket becomes more complicated which may reduce the reliability.

In 1947, Mikhail Tikhonravov developed this kind of staging which he called “packet rockets”. This lead to the development of the R-7 Semyorka. Later developments of this rocket became then the R-7 rocket family. But all those rockets never used the original “packet rockets”/asparagus staging.

Name

Because there is no real world application of the asparagus staging, the name itself is a creation by the players of KSP and not an official word used in rocket science. Because of the design it is also called “onion staging”.

See also