Asparagus staging overrated?

[OhioBob]

Not just you :-(

Squad have this view that they don't want to give newbies something so good they won't have to make their own designs. Nothing tells you that though so loads of people assume the stock ships are "the way" it should be done, struggle like mad to make them work and then complain that KSP is really hard. It annoys me that unless you read (or watch) a lot of tutorials and accidentally trip-over that nugget of information your early experience with KSP can be ruined, to the extent there may be no later experience with it.

I've never used the stock vehicles, except maybe once when I first started just to see what they looked like. I'm not a pro but I do have a good understanding of what makes a good rocket, so I just dove in from the start with my own designs. The only reason I used the stock Kerbal X this time was because it was the simplest way to test my theory, which was that SRBs are cheaper. Calling up an existing asparagus design and comparing it to a modified version seemed like the easiest way to go about it.

Basically, anyone who made launch-vehicles in one style rarely wanted to make them in another as well.

I'm somewhat guilty of that. I generally prefer a simple stack of multiple stages with, if necessary, SRBs for thrust augmentation at liftoff. I experimented a little bit with asparagus staging but found it too time consuming to set up. I abandoned it once I realized how much cheaper SRBs are.

I probably do more optimization that a lot of people. I'll custom design each mission, scripting all the maneuvers and computing a delta-v budget. I'll then design my payload and will add progressively larger stages beneath it, including SRBs if needed, until I reach my delta-v budget. Although I tend to follow a preferred design philosophy, each launch vehicle is customized design for the specific mission. I only repeat designs when I have a similar payload mass and delta-v budget.

[Kerbart]

Please enlighten me if there's something I'm not considering here.

In the Kerbal universe "cost" hasn't been around that long.

On the other hand, “getting it into orbit†has been a consideration of tremendous importance for a very, very, very long time in KSP. And Asparagus does excel at that.

Is it cost effective? Not in the current versions of KSP. But if you don't care about cost it's a great way of keeping your total launch mass down, which is a pretty big consideration in space flight.

[deepspacecreeper]

I kinda played with SRBs after accepting a suggestion of "using SRBs instead of asparagus" because "it was cheaper".

I tested that myself. I slapped 8 Kerbodyne SRBs (0.23.5) onto a liquid core, and also did an asparagus config without the SRBs. Currently I tested 2 payload ranges. Results were:

(Payload/With SRB cost/Asparagus cost)

30/50000/90000

60/157000/180000

From this experiment i conclude: SRBs save you a lot of money.

But I thought of the reliability of SRBs, especially when decoupled. There is a bug which will cause the boosters to crash back on the liquid core, even with seperatrons. Asparagus staging helps you keep the rocket small and structural issues minimal, and you dont have to slap 8x2=16 SRBs on a single 3.75m core stage. But it is more expensive compared to a SRB+LF rocket.

MOAR BOOSTERS!!!

--Jebediah Kerman

Edited November 13, 2014 by deepspacecreeper
(Payload/With SRB cost/Asparagus cost) incorrect value

[OhioBob]

There is a bug which will cause the boosters to crash back on the liquid core, even with seperatrons.

Yes, I've been having a problem with that since I installed the most recent update. My original installation (July this year) did not do that.

[LethalDose]

[...] if you don't care about cost it's a great way of keeping your total launch mass down, which is a pretty big consideration in space flight.

I don't really think "total launch mass" is a major concern IRL since we have purpose-built launchpads for standard launchers. The biggest issue is really payload mass, which is what needs to be kept down to a minimum.

But I thought of the reliability of SRBs, especially when decoupled. There is a bug which will cause the boosters to crash back on the liquid core, even with seperatrons. Asparagus staging helps you keep the rocket small and structural issues minimal.

Yes, I've been having a problem with that since I installed the most recent update. My original installation (July this year) did not do that.

Claw has posted an unofficial bug fix for the radial decoupler issue here.

[SRV Ron]

It has its advantages in launch efficiently in Sandbox especially when using mods.

With drop tanks on the fusion powered payload

[LethalDose]

It has its advantages in launch efficiently in Sandbox especially when using mods.

No one is debating how effective the method is on a payload:total mass basis. The crux of the original post is the cost efficiency of asparagus staging, which is irrelevant in sandbox...

[GoSlash27]

Whether or not it's overrated depends on how you rate launch vehicles. If you're looking for high mass ratios at the expense of everything else, it's awfully hard to beat. If you're looking to factor in cost, then it's not very good.

Suppose you want to design a mission to Eve. SSTO is impossible there without cheating or glitch exploits and jets don't work. You want the lightest possible return vehicle because you have to move it out there and place it on the surface.

You're gonna use an asparagus booster for that job because the mission dictates best mass ratio.

Kerbin surface to LKO, OTOH, is a different job and different priorities apply.

Best,

-Slashy

[OhioBob]

Suppose you want to design a mission to Eve. SSTO is impossible there without cheating or glitch exploits and jets don't work. You want the lightest possible return vehicle because you have to move it out there and place it on the surface.

You're gonna use an asparagus booster for that job because the mission dictates best mass ratio.

Excellent point. My principle argument was in regard to Kerbin surface to LKO. I agree with you that priorities need to adapt to the conditions.

[OhioBob]

Claw has posted an unofficial bug fix for the radial decoupler issue here.

Thanks for bringing this fix to my attention. That bug was really bugging me.

[GoSlash27]

Excellent point. My principle argument was in regard to Kerbin surface to LKO. I agree with you that priorities need to adapt to the conditions.

Grazi.

Kerbin is, IMO, the most unique environment in the system AFA mission priorities. It's the only place where you can build the rocket, wheel it out fully-fueled, and launch it. Everywhere else requires placing your launch vehicle on the surface from orbit intact after having (ultimately) launched it from Kerbin's surface and transported it there across deep space.

Prior to the last couple of updates, nobody cared about cost, so it wasn't a factor. Big mass ratios means big payloads so it was the way to go.

But now price is a huge deal. The buy- in is low for SRBs on a single- shot mission, while SSTOs are clearly the cheapest operating cost for sustained missions.

But out at the other end of the mission, the priority hasn't changed. The better your mass ratio, the lower your payload off of Kerbin and thus the cheaper and easier the mission overall.

So in that sense, asparagus staging isn't overrated at all. It's excellent for the jobs that suit it. But lifting payloads from LKO isn't a job that suits it very well.

Best,

-Slashy

[DerekL1963]

But I thought of the reliability of SRBs, especially when decoupled. There is a bug which will cause the boosters to crash back on the liquid core, even with seperatrons.

While there is a bug, if you're still having them crash back into the core with Sepratrons, then you've placed your Sepratrons wrong.

But, back to the topic at hand, I find the obsession with cost badly misplaced - because even without contract mods, I've never found costs to be a problem unless I'm flying a bunch of expensive non-contract missions. And even then, Strategies cure that handily. Tip: Spend rep like water since you can only have so much on hand. Once you've got most of the tree unlocked (enough to get probes headed out to the planets), consider spending some science.

[DrMonte]

I've came to conclusion that LF Asparagus lifter price is comparable with somewhat 70% recoverable SSTO. So saving my own time I ditched SSTO's. (Plane SSTO's is a different topic and they are for small payloads.)

Asparagus is a design. It does not refer to Liquid Fuel. Using SRB's can make you SRB Asparagus. It is very difficult to work with SRB's in upper stages and I doubt if they suit for the heavy lifters.

[Moonfrog]

Two types of asparagus staging, the bad way and the proper way. Biggest mistake with asparagus staging is that everyone copies the 6 fuel tanks of equal size and engine around one main body. They think this is aspargus, thats the bad way of doing it.

True asparagus is done like a pyramid. It is calculated per stage, not as a 6 barrel like a revolver.

Key advantages of doing proper aspargus is, use of small engines, since all engines can be fired to produce same thrust. Like many point out this is your greatest mass saving. It is not more fuel efficient. only engine mass efficient.

I'm tempted to make a proper asparagus design for u guys to see and post it here.

For most efficiency u should use hybrid design of Serial staging and aspargus, but the pyrimad style asparagus not the 6 barrels of fuel one. Pyrimad is also more aerodynamic.Less so than a standard serial staging rocket.

[GoSlash27]

Asparagus is a design. It does not refer to Liquid Fuel. Using SRB's can make you SRB Asparagus. It is very difficult to work with SRB's in upper stages and I doubt if they suit for the heavy lifters.

I disagree with this part. Asparagus staging is using the fuel in the early stages to feed all the active engines. It doesn't work if you can't transfer fuel between stages, and of course you can't transfer solid propellant.

Best,

-Slashy

[Starman4308]

I disagree with this part. Asparagus staging is using the fuel in the early stages to feed all the active engines. It doesn't work if you can't transfer fuel between stages, and of course you can't transfer solid propellant.

Best,

-Slashy

I've done some pseudo-asparagus off SRBs by slapping a fuel can or two onto the top of an SRB and using that to fuel the inner liquid stage. I am, however, also confused by what DrMonte means.

[John FX]

OK so here is my Mun orbiter craft. Total cost 11,585.5 payload mass 2T

Payload cost 7859.5 (includes some fuel for orbital insertion.

Stage 1 cost 3726 (SRB)

orbital insertion used 54.88 liquidfuel (and corresponding Ox) which cost approx 56.5 funds

Stage 1 recovery amount 75% dry cost 3216 (.75*3216=2412)

3216-2412=804 part costs

3726-3216=510 stage 1 fuel costs

510+56.5=566.5 total fuel costs for orbit

total launch costs=566+804=1370

With liquid fuel

craft cost 16,281.5

stage 1 costs 8422

orbital insertion used similar fuel

stage 1 recovery amount

8422-8054=368 fuel costs

368+57=425 total fuel costs for orbit

8054*.75=6040

8054-6040=2014

total launch costs=2014+368=2439

Like I say, the difference is not one I notice ingame. I just make the cheapest launcher I can.

[Red Iron Crown]

Asparagus is a design. It does not refer to Liquid Fuel. Using SRB's can make you SRB Asparagus. It is very difficult to work with SRB's in upper stages and I doubt if they suit for the heavy lifters.

Count me in the camp that is confused by this statement. The essential feature of asparagus staging is completely draining two tanks before drawing fuel from the next, it is this that lets asparagus shed its dry mass more quickly and thereby increasing its efficiency. AFAIK it's not possible to have multiple solid fuel engines draw from just two solid fuel containers.

[Jouni]

Two types of asparagus staging, the bad way and the proper way. Biggest mistake with asparagus staging is that everyone copies the 6 fuel tanks of equal size and engine around one main body. They think this is aspargus, thats the bad way of doing it.

True asparagus is done like a pyramid. It is calculated per stage, not as a 6 barrel like a revolver.

Key advantages of doing proper aspargus is, use of small engines, since all engines can be fired to produce same thrust. Like many point out this is your greatest mass saving. It is not more fuel efficient. only engine mass efficient.

I'm tempted to make a proper asparagus design for u guys to see and post it here.

For most efficiency u should use hybrid design of Serial staging and aspargus, but the pyrimad style asparagus not the 6 barrels of fuel one. Pyrimad is also more aerodynamic.Less so than a standard serial staging rocket.

There are two key ideas in asparagus staging:

1) Every engine should be used at launch. Unused engines are dead weight that reduce the efficiency of the rocket. It's better to run even nuclear engines at sea level than to keep them waiting for the upper atmosphere.

2) Staging approximates the ideal rocket by dropping unnecessary fuel tanks and engines.

Let's assume that all fuel tanks have the same mass fraction, all engines have the same TWR, and that all fuel tanks and engines are continuous. The ideal rocket maintains the optimal TWR by dropping engines (and fractions of engines), while maintaining a constant fuel tank mass fraction by dropping fuel tanks (and fractions of fuel tanks) as soon as they become empty. The optimal TWR depends on the stage of the ascent and the TWR of the engines. A high TWR leads to lower gravity losses, higher drag losses, and lower total delta-v.

Asparagus staging approximates that ideal rocket. The more staging events there are, the closer the rocket can approximate the ideal. On the other hand, every staging event reduces the efficiency, because the rocket needs more decouplers. As a result, big rockets should probably have more stages than small rockets.

Traditional asparagus staging uses three pairs of identical boosters, because it's easy to build, and having three pairs is a significant improvement over two pairs, while having four pairs does not improve that much over three pairs. The design has been optimized for a very specific scenario: lifting tens of tonnes to a low orbit from stock Kerbin using LV-T30 engines and LV-T45 engines, which were the most reasonable heavy lifting engines before 0.23.5. The size of the engines implies a granularity of 12-14 tonnes. The boosters can't be smaller than that, and if the rocket has boosters of different sizes, the size differences should be multiples of 12-14 tonnes. While having boosters of different sizes probably helps asymptotically, coarse granularity means that it's not relevant for most payloads. 48-7S engines would reduce the granularity to 1.5-2 tonnes, but the part count would be too high for most payloads.

[Laie]

The essential feature of asparagus staging is completely draining two tanks before drawing fuel from the next,

To me, the defining feature is that the "upper" stage isn't on top of a lower stage, but has a free field of fire and can be utilized from the very first moment. Under that view, the space shuttle was already asparaging (if that even is a word).

Put differently, an asparagus is a shriveling rocket that stages outside-in rather than bottom-up. Carry as few useless engines as possible.

Edited November 13, 2014 by Laie

[Red Iron Crown]

You're right, Laie, another essential feature of asparagus staging is all engines firing and discarding those engines as they are no longer needed. I don't consider that a defining feature of asparagus though as it is also present in other forms of staging.

Basically, there are three variants of the parallel staging idea, all of which feed fuel to the later stages, have all engines firing simultaneously, and drop engines with expended tanks:

Twisted candle - Drains and drops one expended tank per stage.

Asparagus - Drains and drops two expended tanks per stage.

Onion - Drains and drops three or more expended tanks per stage.

[The_Rocketeer]

I think people are getting a little too involved in this discussion.

Asparagus staging means empty tanks fall off the side.

Bamboo staging means empty tanks fall off the bottom.

Then engines you carry and use really have very little to do with it. It's all about the tanks.

[cicatrix]

Really, is there an alternative to Asparagus when it comes to lift something from Eve's sea level to orbit? Provided you have to land this thing first.

[Jouni]

I think people are getting a little too involved in this discussion.

Asparagus staging means empty tanks fall off the side.

Bamboo staging means empty tanks fall off the bottom.

Then engines you carry and use really have very little to do with it. It's all about the tanks.

Fuel tank placement has nothing to do with asparagus staging.

• If the rocket drops fuel tanks when they become empty, it's using drop tanks.
  
• If the rocket drops engines when they become unnecessary, it's using drop-away engines.
  
• If the rocket ignites engines in multiple stages simultaneuously, and then drops some of these stages, when their fuel tanks become empty, it's using (strap-on) boosters.
  
• If the rocket uses boosters and the rest of the stages use fuel from the boosters before their own fuel tanks, it's using fuel crossfeed.
  
• If the rocket uses fuel crossfeed with multiple layers of boosters, it's using onion staging.
  
• If the rocket uses onion staging with two boosters in each layer, it's using asparagus staging.
  

[The_Rocketeer]

Well done for being very precise, and also rather confusing. Nonetheless, for people who want to understand the basics of asparagus staging, what I said is accurate enough. FWIW it's also more cost efficient to use one large booster than drop lots of little ones.

I think sometimes people on this forum forget that not everybody is a rocket physicist or gives a crap about precise terms. People who ask questions like this aren't looking for a degree-level answer, they want the schoolroom version.

Edited November 13, 2014 by The_Rocketeer