Asperagus Staging?

[The Man Myth and Legend]

I have heard people discussing asparagus staging but I don't know what it is or how to do it. How do I do it and is it important?

 

 

[klesh]

Its less important nowadays with the changes that have been made to fuel flow and the tank priority that you can set using advanced tweakables.

 

In essence, its a method of construction that see's you dropping booster stages, while having your remaining tanks be full at the point of staging rather than half empty. 

https://wiki.kerbalspaceprogram.com/wiki/Asparagus_staging

 

 

In the above pics, the last booster in the chain (S4) is actually feeding its own engines and all the other engines.   It will burn out much quicker than a usual setup, but when it gets staged the remaining booster stages will all be full because they've been running off S4's fuel.

The concept still works, to be sure.  

Edited November 27, 2017 by klesh
added link and pics.

[Deddly]

Looks like you have a great answer already, but I moved this gameplay question to Gameplay Questions

[The Man Myth and Legend]

11 minutes ago, Deddly said:

Looks like you have a great answer already, but I moved this gameplay question to Gameplay Questions

My apologies for that.

 

32 minutes ago, klesh said:

Its less important nowadays with the changes that have been made to fuel flow and the tank priority that you can set using advanced tweakables.

 

In essence, its a method of construction that see's you dropping booster stages, while having your remaining tanks be full at the point of staging rather than half empty. 

https://wiki.kerbalspaceprogram.com/wiki/Asparagus_staging

 

 

In the above pics, the last booster in the chain (S4) is actually feeding its own engines and all the other engines.   It will burn out much quicker than a usual setup, but when it gets staged the remaining booster stages will all be full because they've been running off S4's fuel.

The concept still works, to be sure.  

 

Thanks! that helps a lot.

[Deddly]

Just now, The Man Myth and Legend said:

My apologies for that.

No problem! I would never argue with The Man, The Myth, The Legend himself! :))

[klesh]

You're welcome.  Try it out, see how far you can go, then remove the asparagus fuel pipes and see how far your traditionally setup rocket will go.  Note the difference. 

[The Man Myth and Legend]

Just now, klesh said:

You're welcome.  Try it out, see how far you can go, then remove the asparagus fuel pipes and see how far your traditionally setup rocket will go.  Note the difference. 

I always went with just add a bigger stage below. always was unstable. This should help.

[klesh]

2 minutes ago, The Man Myth and Legend said:

I always went with just add a bigger stage below. always was unstable. This should help.

You can alternate between more powerful LVT-30 engines and stability-improving LVT-45 engines for the boosters as well, depending on where you're losing stability.

[OhioBob]

Another technique that works well but is not as complex to set up is onion staging.  In onion staging all the engines run off the propellant in the outboard stages first.  When that propellant is gone, the outboard tanks and engines are jettisoned, and the rocket continues running on the center engine with a full fuel tank.  This works really well when you set it up with three identical stages side-by-side.  It looks similar to the Delta IV Heavy but with fuel lines feeding from the outer tanks to the inner tank.

 

Edited November 27, 2017 by OhioBob

[The Man Myth and Legend]

5 minutes ago, OhioBob said:

Another technique that works well but is not as complex to set up is onion staging.  In onion staging all the engines run off the propellant in the outboard stages first.  When that propellant is gone, the outboard tanks and engines are jettisoned, and the rocket continues running on the center engine with a full fuel tank.  This works really well when you set it up with three identical stages side-by-side.  It looks similar to the Delta IV Heavy but with fuel lines feeding from the outer tanks to the inner tank.

 

Isn't that the same thing???

[GoSlash27]

Best,
-Slashy

[GoSlash27]

On the second part of the original question, no it's not very important.

 If you need to squeeze more payload from a limited pad, asparagus staging can help boost your payload fraction at the expense of part count. "Quasi- asparagus" staging (where the outer stages feed the inner stages like asparagus, but are drop tanks propelled by SRBs) can dramatically reduce the cost to orbit for large payloads, but aren't cost- effective for smaller payloads.

Generally speaking, using this technique won't have a big impact on your career.

Best,
-Slashy

[The Man Myth and Legend]

2 hours ago, GoSlash27 said:

On the second part of the original question, no it's not very important.

 If you need to squeeze more payload from a limited pad, asparagus staging can help boost your payload fraction at the expense of part count. "Quasi- asparagus" staging (where the outer stages feed the inner stages like asparagus, but are drop tanks propelled by SRBs) can dramatically reduce the cost to orbit for large payloads, but aren't cost- effective for smaller payloads.

Generally speaking, using this technique won't have a big impact on your career.

Best,
-Slashy

Ok

[Aegolius13]

4 hours ago, The Man Myth and Legend said:

Isn't that the same thing???

On a 3 engine setup, yes,  there's no difference between asparagus and onion.   The distinction cones when you add more after that,  as in Slashy's diagram. 

[Norcalplanner]

5 hours ago, OhioBob said:

Another technique that works well but is not as complex to set up is onion staging.  In onion staging all the engines run off the propellant in the outboard stages first.  When that propellant is gone, the outboard tanks and engines are jettisoned, and the rocket continues running on the center engine with a full fuel tank.  This works really well when you set it up with three identical stages side-by-side.  It looks similar to the Delta IV Heavy but with fuel lines feeding from the outer tanks to the inner tank.

That's actually one of my self-imposed role-playing rules.  On those rare occasions when I use fuel crossfeed, it can only be from two side boosters into the central core, as was originally proposed (but since abandoned) in the Falcon Heavy.

[Snark]

18 hours ago, The Man Myth and Legend said:

Isn't that the same thing???

As @Aegolius13 points out, they're the same thing on a 3-engine setup.  Different for when there are more engines.  Slashy's diagram above best captures the difference:

18 hours ago, GoSlash27 said:

...Also, note the really critical difference between "asparagus or onion" on the one hand, and "simple" on the other:  all engines fire all the time until they're staged away.  (By "simple" I mean "the default behavior you get if you just slap everything together in the VAB and don't tinker with fuel ducts or crossfeed options or anything").

For example:  Let's say you have a central stack with two radial boosters, all of them liquid-fueled.  Let's consider a few possible options:

• Option 1:  "Simple" staging, radial boosters first.
  • The ship lifts off on the radial boosters alone (central stack is not yet activated).  When the booster fuel is exhausted, jettison the boosters and activate the central-stack engine.
  • Advantage:  Simple to build.  Saves the central stack's fuel for the 2nd stage, which is mathematically nice for the rocket equation (it's why staged rockets are a thing).
  • Disadvantage:  The central stack's engine is just dead weight, until the radial boosters run out, so there's a dV hit there.  Also, since the central stack doesn't contribute to your TWR when lifting off the pad, it means your radial boosters need bigger engines, which means more dead weight, which means another dV hit.
• Option 2:  "Simple" staging, all engines together.
  • The ship lifts off on all three engines.  The radial engines burn the radial boosters' fuel; the central-stack engine burns the central-stack fuel.  If the radial boosters happen to run out of fuel first, jettison them when they do.  Or if all three engines run out of fuel simultaneously, jettison them all together when they run out.
  • Advantage:  Simple to build.  All engines participate in launchpad TWR, so you're not lugging any more engine than you need, which saves dV.
  • Disadvantage:  Now you only have 1 stage instead of 2.  (Or, if the radial boosters happen to run out first, one-and-a-fraction stages).  Which is less friendly to the rocket equation, which costs you dV.
• Option 3:  Radial/onion staging.
  • The ship lifts off on all three engines (same as in option 2 above)... but, crucially, the central stack engine isn't using the central stack fuel.  It's draining the radial boosters' fuel.  As soon as the radial boosters run dry (which will be quicker than in the above options, since 3 engines are sharing 2 boosters' worth of fuel), then jettison the radial boosters and the central engine continues burning, now using its own fuel.
  • Advantage:  Combines the best features of both of the above, and then some.  Like Option 1, it has the advantage of being two stages rather than one, which is very friendly to the rocket equation.  Like Option 2, all engines are firing all the time, which minimizes dead weight and saves dV.  And a third advantage is that it burns through the radial boosters' fuel quickly, which allows you to jettison them sooner and save the dead weight of the booster engines & fuel tanks.
  • Disadvantage:  Requires slightly more understanding of the fiddly bits in the vehicle editor, and about how fuel-flow works.  Other than that, basically no disadvantage in this scenario.

Bear in mind that all of the above three options share the common disadvantage that you have radial boosters and therefore somewhat more drag than if you just had one big central stack with a giant engine under it.  This is the reason why asparagus staging became somewhat less common after KSP 1.0, which introduced a new aerodynamic model.  (For the curious:  That's because the old, pre-1.0 aero was simplistic and didn't care at all how parts were arranged on a ship-- it was based purely on mass.  Therefore, having radial boosters was zero extra drag compared with having the fuel-and-engine components inline with the central stack, which gave asparagus a big competitive advantage.)

Asparagus still has its uses (I use it fairly frequently myself)-- it's just not the magical unambiguously-better-than-any-other-option silver bullet that it used to be in the old days. 

Also note that since 1.2, the improved fuel-flow options in the vehicle editor allow you to build asparagus ships without using any fuel ducts at all, by proper attention to decouplers' fuel crossfeed status, and/or individual fuel tanks' flow priorities.  It leads to a slightly less convenient piloting style (you have to watch the tank contents and jettison, since you can't just wait for the radial engines to go dead), but saves you from having to place fuel ducts (thus saving cost, weight, drag, and some editor inconvenience).  YMMV, some folks prefer one, some folks prefer the other.

[wumpus]

[TL:DR forget about aspargus and onion staging and just use drop tanks.]

First, "pure asparagus" has a lot of hype thanks to fitting well with KSP's pre-1.0 broken aero-model.  I'd expect drop tanks to make more sense for modern usage.

Note that "onion staging" is strictly inferior to using drop tanks, assuming you can upgrade/spam engines on the last 'stage'.  Changing from 6 tanks dropped at once to 3 stages dropping two tanks each (you will need to put 3 times the engine on the last stage, but the Poodle/terrier ratio is close enough) will always work better (assuming you can hit the space bar remotely fast enough).

Don't expect to use "pure asparagus" outside of Eve.  Drop tanks nearly always are a great idea (KSP uses unrealistically heavy tanks to compensate for the scale of Kerbal), but asparagus only makes sense when you need to carefully manage TWR (which was a thing in the souposphere, now likely confined to Eve).  It shouldn't be hard to make a better "onion" with pairs of droptanks and vertical staging (presumably putting a large central engine that could then be vertically staged)  than a "pure onion", so I'd recommend thinking in terms of drop tanks than any type of classical KSP staging tricks.

[in the pre-1.0 game it made sense to maintain TWR=2.0 from 0-10km elevation than hard right as fast as you could.  You should only consider throttling down if you velocity is approaching terminal velocity (this should be nearly impossible for KSP>=1.0, before that you hit it if your TWR>2.0).  Asparagus was useful for maintaining exactly TWR=2.0].

Edited November 28, 2017 by wumpus

[OhioBob]

3 hours ago, Snark said:

• Option 3:  Radial/onion staging.
  • The ship lifts off on all three engines (same as in option 2 above)... but, crucially, the central stack engine isn't using the central stack fuel.  It's draining the radial boosters' fuel.  As soon as the radial boosters run dry (which will be quicker than in the above options, since 3 engines are sharing 2 boosters' worth of fuel), then jettison the radial boosters and the central engine continues burning, now using its own fuel.
  • Advantage:  Combines the best features of both of the above, and then some.  Like Option 1, it has the advantage of being two stages rather than one, which is very friendly to the rocket equation.  Like Option 2, all engines are firing all the time, which minimizes dead weight and saves dV.  And a third advantage is that it burns through the radial boosters' fuel quickly, which allows you to jettison them sooner and save the dead weight of the booster engines & fuel tanks.
  • Disadvantage:  Requires slightly more understanding of the fiddly bits in the vehicle editor, and about how fuel-flow works.  Other than that, basically no disadvantage in this scenario.

The only other disadvantage that I can think of with this type of arrangement is that the center engine burns from liftoff all the way to orbit.  The engine can be adapted to perform best under only one of those conditions - sea level or vacuum.  We're most likely to use one of the booster engines designed for best performance at or near sea level.  Therefore when we get to near vacuum conditions, we're using an engine that will deliver a lower specific impulse than we would typically like to have.  That's going to cost some delta-v.  However, I think some of the other advantages of this type of launch vehicle, i.e. all engines being used all the time (no dead weight), makes it worth using.  The advantage of a vertically stacked two-stage design is that the engines can be optimized for the particular environment in which they'll operated, providing better overall specific impulse.

[OhioBob]

1 hour ago, wumpus said:

I'd expect drop tanks to make more sense for modern usage.

I problem I see with drop tanks is that decouplers and nosecones in KSP and ridiculously overpriced.  I haven't done the math, but I wouldn't be surprised if in some cases it might actually be cheaper to lug the empty tank along with you and just pay for some extra fuel.

[Deddly]

42 minutes ago, OhioBob said:

I problem I see with drop tanks is that decouplers and nosecones in KSP and ridiculously overpriced.  I haven't done the math, but I wouldn't be surprised if in some cases it might actually be cheaper to lug the empty tank along with you and just pay for some extra fuel.

I'd love to see some attempts to test that theory

[DoctorDavinci]

48 minutes ago, OhioBob said:

I problem I see with drop tanks is that decouplers and nosecones in KSP and ridiculously overpriced.

This is why you use small hardpoints or structural pylons which do the same job and look much sleeker IMO

[wumpus]

1 hour ago, OhioBob said:

I problem I see with drop tanks is that decouplers and nosecones in KSP and ridiculously overpriced.  I haven't done the math, but I wouldn't be surprised if in some cases it might actually be cheaper to lug the empty tank along with you and just pay for some extra fuel.

I've done worse: hauling spent SRBs until dropping a larger stage (typically thumpers attached to kickers).  I try to limit side decouplers to two and attaching as many SRBs as possible to a single decoupler (and don't bother sticking nosecones on anything smaller than a kicker [assuming I bother to add decouplers.  Presumably decoupling it would make more sense than a nosecone and no decoupler].

One favorite trick is attaching fuel tanks to SRBs and filling the tanks to run out along with the SRB (and detached together).  Current KSP doesn't even require the fuel pipe (although you might attach it to let KE compute the right amount of fuel then delete it before launch).

[GoSlash27]

3 hours ago, OhioBob said:

The only other disadvantage that I can think of with this type of arrangement is that the center engine burns from liftoff all the way to orbit.  The engine can be adapted to perform best under only one of those conditions - sea level or vacuum.

OB,

 Actually, I've found (at least in the stock game) that the improved Isp of a pure vacuum engine doesn't quite overcome it's mass in fuel savings in the 1,700 m/sec or so flight requirement. As a result, a parallel staged lifter with a generic core can outperform a serial staged lifter with a dedicated vacuum upper stage, even without resorting to complicated plumbing techniques.

Best,
-Slashy

[Vanamonde]

 

[Starman4308]

19 hours ago, wumpus said:

[TL:DR forget about aspargus and onion staging and just use drop tanks.]

First, "pure asparagus" has a lot of hype thanks to fitting well with KSP's pre-1.0 broken aero-model.  I'd expect drop tanks to make more sense for modern usage.

Note that "onion staging" is strictly inferior to using drop tanks, assuming you can upgrade/spam engines on the last 'stage'.  Changing from 6 tanks dropped at once to 3 stages dropping two tanks each (you will need to put 3 times the engine on the last stage, but the Poodle/terrier ratio is close enough) will always work better (assuming you can hit the space bar remotely fast enough).

Not strictly correct. Onion/asparagus stages not only remove empty fuel tank mass, they also remove unnecessary engines. Especially for something like Eve: you're going to start off needing far more thrust than you need at the end. If you put all your engine mass on the central stage, by the end of your staging, you have a lot of thoroughly unnecessary engine mass on a ridiculously overpowered core stage; if you spread out the engines and drop them every so often, you can keep your vessel more trim and avoid losing delta-V to having more engine than you actually need.

Also, one note for the OP since I haven't seen it mentioned yet: these sorts of staging setups (onion, asparagus, droptank) etc are generally considered a bit unrealistic because of the mass and mechanical complexity that would be required to pump fuel very, very rapidly from the radial tanks to the core stage. That's why real-world rockets tend to stick towards simpler staging setups.