It occurs to me that "Asparagus Staging" has become a common term here...

[Ryu Gemini]

While that is not surprising, as it has arisen from the community for KSP, I have to wonder if it will eventually become a sort of "standard nickname" for this particular type of fuel crossfeeding.

Specifically, where the "outermost" boosters feed fuel into both their engines and the more "inner" boosters and main rocket, such that when they run out of fuel and are detached the remaining rocket is effectively fully fueled despite having been using its rockets the entire time as well.

The Falcon Heavy is an upcoming rocket that uses this basic concept in real life, and already one of the Falcon Heavy's footnotes in Wikipedia mentions the technique is nicknamed "asparagus staging" (though this isn't in the main article).

I am almost tempted to suggest that an Asparagus Staging article be created on wikipedia detailing what asparagus staging means, with examples like the Falcon Heavy. And maybe a brief sentence or two telling where the term originated. Because I could see it becoming the go-to term for this particular method of fuel crossfeeding in rocket design as the Falcon Heavy becomes more well known (and as other real-life rockets begin using the concept).

.

[sal_vager]

The term does actually predate KSP, there's a document somewhere that shows a booster design we know as asparagus and it's called that by its creator, If I can find it I'll post the link

Edit:

Aha! Here it is!

Edited December 4, 2013 by sal_vager

[Sternface]

With real aerodynamics in play, I am skeptical that the weight-shedding benefits of asparagus staging would offset the loses in drag. Except maybe in limited use, such as in the Falcon Heavy. Seems much more efficient just to use series staging rather than parallel.

I haven't done the maths, so I could be wrong.

[Deathsoul097]

Actually, the fuel lines wouldn't create much in the way of drag, so you would gain Delta V from using asparagus. The problems are primarily:

1- Getting a fuel pump powerful enough to pump the fuel as fast as or faster than the engines are consuming it.

2- Getting a fuel pump light enough so as to not significantly affect the mass of the craft.

3- Though the losses due to drag would be minimal, the fuel lines would have to be strong enough to withstand several Gs of aerodynamic drag without warping or breaking.

4- It isn't exactly safe to dump a fuel line during ascent, as the fuel line would have to be closed and detached within less than a second, and would have to be dropped in such a way that it moves as far away from the craft as possible, as fast as possible, because there may be some residual fuel left in the line, and it could very well explode and damage the rocket.

5- These fuel lines could act as fins due to aerodynamic drag, and put the craft into a spin. (Never fun on a real rocket)

The best thing I could advise you to do if you want to test this out (Assuming you don't have billions of dollars to go and start developing and testing this in the real world) would be to play the Realism overhaul mods (RSS, FAR, MF etc, you can easily find the thread in the add-ons section), and try this out there. (I personally play RO more than stock KSP nowadays, but I haven't attempted Asparagus yet.)

[magnemoe]

With real aerodynamics in play, I am skeptical that the weight-shedding benefits of asparagus staging would offset the loses in drag. Except maybe in limited use, such as in the Falcon Heavy. Seems much more efficient just to use series staging rather than parallel.

I haven't done the maths, so I could be wrong.

Well both delta heavy and the upcoming falcon heavy uses two main stage sized boosters, using four large boosters would increase drag but not far more than the extra trust.

Main issue would be the complicated pumping arrangement for having booster one feed both the main stage and booster 2.

As other will point out, real world engines have far higher TWR and real tanks are lighter.

Asparagus is so popular in KSP as our engines and tanks are very heavy, you want to get rid of them as fast as possible, stage separation is also much more dangerous in real world.

[Sternface]

Actually, the fuel lines wouldn't create much in the way of drag, so you would gain Delta V from using asparagus.

I meant the parasitic drag from the extra fuel tanks set up in parallel, each of which would add considerably to the rocket's cross-sectional area - increasing form drag by a non-trivial amount. Not to mention interference drag and boundary layer-vorticity mayhem.

Fuel line drag would be trivial in comparison to that caused by parallel fuel tanks, which would probably increase the rockets cross-sectional area by at least double.

Then once you factor in aerodynamic stresses, the structure would need to be incredibly strong to hold the thing together.

Seems much more practical to use series staging, barring the heaviest of rockets (heavier than the Saturn V).

P.S. I've been using FAR, RSS, and modular fuels since they came out (Came here from Orbiter2010). I can't imagine going back to stock.

Edited December 5, 2013 by Sternface

[Kerbin Dallas Multipass]

I consider asparagus staging in KSP a clever "exploit". I don't see why it would make sense in RL other than increased flexibility.

I mean, seriously. Why drop the tank AND the engine?

[Sternface]

^

The only practical application I can see, other than very limited use, is if the rocket was so heavy that series staging would snap even the strongest of materials due to it's length. That would be quite a heavy rocket.

[kujuman]

I consider asparagus staging in KSP a clever "exploit". I don't see why it would make sense in RL other than increased flexibility.

I mean, seriously. Why drop the tank AND the engine?

I could envision just having ETs that feed the core and then dropping those ETs a la the Space Shuttle. Of course then you might get issues with ever climbing TWRs which could put your payload in jeopardy. And there might be bigger difficulties in keeping the fuel flow from opposite tanks equal enough to not get too off center mass. And then your engines in the first stage core are going to have to be stronger at launch in order to lift the spare fuel + structure of ETs.

So it makes sense to have the extra strap-on tanks have engines.

WRT to asparagus being a KSP exploit, it's not that it is an exploit so much as an issue which isn't as punishing as it would be IRL. To repeat people above, the added mass and complexity of the plumbing needed to pull this off is not taken into account when you add a simple fuel line. Of course, the developers could eliminate fuel lines, but this would make Space Shuttle like lifters and small landers with fuel tanks arranged in a way other than a stack (both things which are done in real life) impossible to build in KSP.

[Superfluous J]

I consider asparagus staging in KSP a clever "exploit". I don't see why it would make sense in RL other than increased flexibility.

I mean, seriously. Why drop the tank AND the engine?

What do you think they do with the tanks and engines in non-asparagus lifters?

They drop them.

[Kerbin Dallas Multipass]

So it makes sense to have the extra strap-on tanks have engines.

Those are called boosters and I do not dispute their use in spaceflight:)

On earth something like "reverse asparagus" makes more sense. Hey the Space Shuttle used it, thanks for supporting my point

[Kerbin Dallas Multipass]

What do you think they do with the tanks and engines in non-asparagus lifters?

They drop them.

Well. Yea, you need staging to get anywhere in space. I understand that.

Asparagus staging requires multiple boosters and multiple tanks. The concept is to feed the fuel inwards and drop outward boosters as quickly as possible.

But why would you drop an engine in the thickest atmosphere? It's exactly where you need the fat first stage engines. Why not drop tanks instead?

Tanks are much lighter in RL but they do have enormous drag (if stacked sideways) RL. Not so in KSP.

Basically.. if you want a more powerful rocket IRL you just make it taller and a bit wider and you add some boosters. Going lateral like we do in KSP would make no sense at all.

[Kryten]

If you're 'in the thickest atmosphere' and already dropping stuff, you've got more fundamental problems than the kind of staging you're doing.

[Superfluous J]

Well. Yea, you need staging to get anywhere in space. I understand that.

Asparagus staging requires multiple boosters and multiple tanks. The concept is to feed the fuel inwards and drop outward boosters as quickly as possible.

But why would you drop an engine in the thickest atmosphere? It's exactly where you need the fat first stage engines. Why not drop tanks instead?

Actually they could do this IRL but it's hard to do it in KSP due to design constraints. I did make a pretty successful lifter where I had a central column of rockets and then hooked fuel tanks around the outside and dropped them as they were used up. It wouldn't work in real life due to drag, but in real life if you build a rocket really tall it doesn't wag around like a dog's tail so I figure we and reality are even on that one

[Idobox]

You can do reasonable asparagus, like Space X, which makes sense, and you can make Whackjob asparagus, and forfeit all claim of realism.

A relatively simple game mechanic to limit asparagus would be to have fuel lines with limited throughput that also cost a lot. You know, like real turbopomps. That way, you couldn't build gigantic asparagus monstrosities until you unlocked end-game tech, while still allowing landers and stuff, and once money is implemented, you would have a good reason to stack stages.

[DonLorenzo]

In my 'Mission a Day' series I play with money constraint and I've actually found asparagus to be prohibitively expensive. I've used it once, with two of the four boosters using small and cheap engines instead of the larger, more expensive ones.

[TheBedla]

But why would you drop an engine in the thickest atmosphere? It's exactly where you need the fat first stage engines. Why not drop tanks instead?

1. I believe the real atmosphere is far less soupy than that of Kerbin (though I might be wrong on that), so getting through the dense layer is less of a pain IRL.

2. Most of the weight you push up is fuel - and once you use some of the fuel, you do not need that much thrust to maintain velocity (and surpassing terminal velocity by much is inefficient).

3. You can think of asparagus staging as an upgrade to a setup when you have outer boosters in first stage and the core engine in second stage (igniting when the boosters run out of fuel). But with asparagus, you get to use that central engine all the way up, which increases your TWR, which increases your payload capability.

3b. Or you can think of it as an alternative to the setup with the boosters and the core firing at the same time, boosters separating when empty, but with asparagus you now have a full core stage with more dV than it would have had it consumed its own fuel.

Asparagus staging has real benefits IRL, but so far, the fuel crossfeed technology has not allowed us to use them without risks or high cost. That might change with Delta Heavy (note that the basic variant of Delta Heavy is non-asparagus; they only plan to use the fuel crossfeed for heavier payloads. This already tells us that if the same rocket is able to get more mass into orbit if you add asparagus staging).

[nhnifong]

You don't really need an additional pump right? Every engine already has it's own turbopump. You just need to have the propellant supply from the center tank come through a closable valve, which you don't open until stage separation. You also have one-way valves that allow fuel in from the side tanks, and the turbopumps will suck it in.

[K^2]

You do have to have a pump on each tank. In order to drop a tank, you need to have a valve you can shut off. That puts some limitations on feasible diameter. At the same time, you have to have a huge mass flow to the engine. That means you have to take the fuel/oxidizer and accelerate them to very high speed before they even pass through the tank separation valve. There is no way to do that without a turbopump.

[FenrirWolf]

Not to mention that the more boosters you have chained to each other, the more work the pumps in the outermost boosters would have to do. Like if you have a 3-stage asparagus rocket like is so common in KSP, the outermost boosters would have to be pumping fuel fast enough to keep its own engines running, plus also keeping the next two boosters in the chain along with the central stack fully fueled or at least nearly so.

[K^2]

We only chain tanks in KSP because of the way that the fuel logic works. With a real rocket, you are much better off having a manifold sitting atop the engine's main pump, and running a fuel line from manifold to each tank. Then simply switch which of these lines are feeding the manifold, and drop tanks as they are expended. There is no need to move fuel/oxidizer from tank to tank.

[magnemoe]

We only chain tanks in KSP because of the way that the fuel logic works. With a real rocket, you are much better off having a manifold sitting atop the engine's main pump, and running a fuel line from manifold to each tank. Then simply switch which of these lines are feeding the manifold, and drop tanks as they are expended. There is no need to move fuel/oxidizer from tank to tank.

True, not unheard to have multiple drop tanks on fighter planes for an ferry or long distance strike mission.

If you do this in KSP you would pipe from tank one to tank 2 then to plane. As this is simpler to code than having an switch to select fuel source.

[thescientist]

Actually, the fuel lines wouldn't create much in the way of drag, so you would gain Delta V from using asparagus. The problems are primarily:

1- Getting a fuel pump powerful enough to pump the fuel as fast as or faster than the engines are consuming it.

2- Getting a fuel pump light enough so as to not significantly affect the mass of the craft.

3- Though the losses due to drag would be minimal, the fuel lines would have to be strong enough to withstand several Gs of aerodynamic drag without warping or breaking.

4- It isn't exactly safe to dump a fuel line during ascent, as the fuel line would have to be closed and detached within less than a second, and would have to be dropped in such a way that it moves as far away from the craft as possible, as fast as possible, because there may be some residual fuel left in the line, and it could very well explode and damage the rocket.

5- These fuel lines could act as fins due to aerodynamic drag, and put the craft into a spin. (Never fun on a real rocket)

The best thing I could advise you to do if you want to test this out (Assuming you don't have billions of dollars to go and start developing and testing this in the real world) would be to play the Realism overhaul mods (RSS, FAR, MF etc, you can easily find the thread in the add-ons section), and try this out there. (I personally play RO more than stock KSP nowadays, but I haven't attempted Asparagus yet.)

In other words, the magic yellow fuel line doesn't exist in RL.

[Soda Popinski]

I consider asparagus staging in KSP a clever "exploit". I don't see why it would make sense in RL other than increased flexibility.

I mean, seriously. Why drop the tank AND the engine?

That already happens with serial staging. Otherwise the Saturn V would bring the entire stack to Lunar orbit.

As to the issue KSP currently leading to unrealistic asparagi builds, it must be fixable, since FAM + Ferram's Kerbal Joint Reinforcement mod (specifically so FAM works better with realistic vertical builds) does a pretty good job.

Squad has stated they want to put in a more realistic drag model. If they do something similar to FAM and RL, where cross-section matters, we may see the end of asparagus over use.

Edited December 6, 2013 by Soda Popinski

[Thiel]

I consider asparagus staging in KSP a clever "exploit". I don't see why it would make sense in RL other than increased flexibility.

I mean, seriously. Why drop the tank AND the engine?

For the same reason that upper stage engines tend to have less thrust than the main stage, you simply don't need as much of it once you've cleared the denser parts of the atmosphere.