Difference between revisions of "Asparagus staging"

From Kerbal Space Program Wiki
Jump to: navigation, search
(Future Disadvantages: still no change in 0.20.2)
(Drag)
(45 intermediate revisions by 27 users not shown)
Line 1: Line 1:
 
[[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.
+
'''Asparagus staging''' was a method to build very efficient [[rocket]]s in early versions of Kerbal Space Program. 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.
+
Over various version updates the drag model of the game has been made more realistic and larger, higher-efficiency engines added to the game, this has caused asparagus staging to become much less viable as a rocket constructing technique in modern versions of the game as usually it is better to simply use a single large engine per stage.
  
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.
+
The technique is still useful for building exceptionally large rockets when no larger engines are available.
  
The stock vessel "Kerbal X" demonstrates this technique.
+
== Function ==
 +
[[File:Asparagus staging sequence.png|thumb|left|upright|Kerbal X's seq.]]
 +
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.
  
== Current Disadvantages ==
+
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 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)
+
The main use of Asparagus Staging is to lift heavy payloads with higher mass to thrust ratio, mainly in the form of fuel, to orbit for the purpose of missions to the [[Mun]] and beyond. It can also be used effectively for the purpose of Space Station launch.
  
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).
+
== Disadvantages ==
 +
[[File:AsparagusStaging-6x3.png|right|300px|thumb|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.
  
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.
+
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.
  
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.
+
Another disadvantage is that rockets utilizing this design may be unrealistic, because in the real world it is impractical or impossible to move fuel as quickly as would be needed. It also might look not aesthetic especially with multiple layers, because there are then many small rockets bundled together.
  
== Future Disadvantages ==
+
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 loses 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.
  
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.
+
As of [[0.24]] when a lot of parts have their cost modified, some rocket designs which use solid fuel boosters may be cheaper than those which use asparagus staging, when both rockets' payload mass to low Kerbin orbit is the same.
  
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.
+
=== Drag ===
 +
With the the release of [[1.0|version 1.0]],a more realistic drag and aerodynamics model was introduced, making very wide asparagus staged craft far more challenging or even less efficient than more conventional staging. However, more limited asparagus staging as seen in the [[Kerbal X]] is still very effective.
  
== References ==
+
In [[1.2|version 1.2]] trans and supersonic drag was made more severe this causes rockets with a larger cross-section to experience much more drag and is a large blow to the effectiveness of asparagus staging.
  
<references/>
+
The DLC Making History adds R-7 styled fuel tanks which have superior aerodynamic qualities. Their low drag makes them the most viable option for an asparagus type rocket.
 +
 
 +
== Real world application ==
 +
Asparagus staging, properly known as propellant crossfeed system, is currently only a feature of Kerbal Space Program. It originates from a proposed booster design in a book on orbital mechanics by Tom Logsdon. According to the book, an engineer named Ed Keith coined the term "asparagus-stalk booster" for launch vehicles using propellant crossfeed.<ref>{{cite book|last= Logsdon |first= Tom |title= Orbital Mechanics - Theory and Applications |publisher= [[Wiley-Interscience]] |location= New York |year=1998|isbn=978-0-471-14636-0 |page= [https://books.google.com/books?id=C70gQI5ayEAC&pg=PA143&lpg=PA143&dq=asparagus-stalk+booster&source=bl&ots=eXLhW_FLSQ&sig=WVZJZM1kpAzAXXCZRVVa_fwtYAI&hl=en&sa=X&ei=72rtUfybI8aayQHkhoHwCA&ved=0CH8Q6AEwDQ#v=onepage&q=asparagus-stalk%20booster&f=false 143]}}</ref> While [[w:Falcon Heavy|Falcon Heavy]]  was originally going to feature this staging, although only with one level, Elon Musk eventually stated that crossfeed is not currently planned to be implemented, at least in the first Falcon Heavy version. 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. Another — very important — reason is pressure losses that occur because of additional piping and further valves. This can call for added propellant pumps, which negatively impacts the efficiency of asparagus staging.
 +
 
 +
In 1947, [[w:Mikhail Tikhonravov|Mikhail Tikhonravov]] developed this kind of staging which he called “packet rockets”. This led 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 none of those rockets ever used the original “packet rockets”/asparagus staging.
 +
 
 +
== Name ==
 +
The application of the term "asparagus" to a form of rocket staging predates Kerbal Space Program and is not a creation of the players.  The "Asparagus-Stalk Booster" was described by aerospace engineer Ed Keith on page 144 of Tom Logsdon's "''Orbital Mechanics: Theory and Applications''" in 1997.
 +
 
 +
[[Category:Tutorials|{{PAGENAME}}]]

Revision as of 07:40, 20 March 2018

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

Asparagus staging was a method to build very efficient rockets in early versions of Kerbal Space Program. The stock vessel Kerbal X demonstrates this technique.

Over various version updates the drag model of the game has been made more realistic and larger, higher-efficiency engines added to the game, this has caused asparagus staging to become much less viable as a rocket constructing technique in modern versions of the game as usually it is better to simply use a single large engine per stage.

The technique is still useful for building exceptionally large rockets when no larger engines are available.

Function

Kerbal X's seq.

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.

The main use of Asparagus Staging is to lift heavy payloads with higher mass to thrust ratio, mainly in the form of fuel, to orbit for the purpose of missions to the Mun and beyond. It can also be used effectively for the purpose of Space Station launch.

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 in the real world it is impractical or impossible to move fuel as quickly as would be needed. 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 loses 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.

As of 0.24 when a lot of parts have their cost modified, some rocket designs which use solid fuel boosters may be cheaper than those which use asparagus staging, when both rockets' payload mass to low Kerbin orbit is the same.

Drag

With the the release of version 1.0,a more realistic drag and aerodynamics model was introduced, making very wide asparagus staged craft far more challenging or even less efficient than more conventional staging. However, more limited asparagus staging as seen in the Kerbal X is still very effective.

In version 1.2 trans and supersonic drag was made more severe this causes rockets with a larger cross-section to experience much more drag and is a large blow to the effectiveness of asparagus staging.

The DLC Making History adds R-7 styled fuel tanks which have superior aerodynamic qualities. Their low drag makes them the most viable option for an asparagus type rocket.

Real world application

Asparagus staging, properly known as propellant crossfeed system, is currently only a feature of Kerbal Space Program. It originates from a proposed booster design in a book on orbital mechanics by Tom Logsdon. According to the book, an engineer named Ed Keith coined the term "asparagus-stalk booster" for launch vehicles using propellant crossfeed.[1] While Falcon Heavy was originally going to feature this staging, although only with one level, Elon Musk eventually stated that crossfeed is not currently planned to be implemented, at least in the first Falcon Heavy version. 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. Another — very important — reason is pressure losses that occur because of additional piping and further valves. This can call for added propellant pumps, which negatively impacts the efficiency of asparagus staging.

In 1947, Mikhail Tikhonravov developed this kind of staging which he called “packet rockets”. This led to the development of the R-7 Semyorka. Later developments of this rocket became then the R-7 rocket family. But none of those rockets ever used the original “packet rockets”/asparagus staging.

Name

The application of the term "asparagus" to a form of rocket staging predates Kerbal Space Program and is not a creation of the players. The "Asparagus-Stalk Booster" was described by aerospace engineer Ed Keith on page 144 of Tom Logsdon's "Orbital Mechanics: Theory and Applications" in 1997.
  1. Template:Cite book