I love building asparagus rockets in KSP but don't see them much in real life.

[Gus]

What's up with that. Is it the air resistance? Is it "unrealistic" to use it? Does the FAR mod make asparagus staging less "powerful"? Thanks.

[Moar Boosters]

The main problem is pumping the fuel. We've not invented those miraculous yellow pipes yet.

After that you've got aerodynamic issues, and the fact that IRL they want to minimize staging events because there's more chance of something going wrong during the staging event than regular flight.

So yeah.... it's pretty unrealistic to have a rocket that drops boosters every few seconds.

[DisarmingBaton5]

It's inefficient due to the extreme air resistance caused by, well, extra rockets. Think about how much a rocket drags alone, now what about 3? 5? 7? IIRC the only proper asparagus rocket to be used is the Falcon Heavy built by SpaceX.

EDIT: Ninja'd! Listen to what the guy above me said.

[Kerbart]

Add reliability to the list. If your engines are clustered tight together you can compensate for one of the engine failing and simply burn longer. With asparagus setups you will need every engine to burn, doubling, tripling or even quadrupling the chances of failure. And RL engines are fare less reliable than the KSP ones...

[Eric S]

Moar Boosters is right. Turbo fuel pumps are one of the most frequent non-human causes of rocket failures, and asparagus staging would make a rocket even more dependent on them.

On the other hand, even basic cross-feeding between two fuel stacks, both with an engine, took 60 years from the time someone pictured it to the time someone thinks they'll actually fly something like that. SpaceX's Falcon 9 Heavy will be doing that, and there's a proposed variant on the Delta IV Heavy that will do it as well, despite the idea first being proposed in 1947. So it's too early to say that we'll never see asparagus staging in real life, but yes, there are some technical issues that need to be resolved before the launchers would be considered reliable.

[Stankleberry]

Is it possible to turn on random engine failures?

[tavert]

Don't forget that the space shuttle had fully functional fuel cross-feed, just without engines on the tank from which the fuel was being pumped.

Another reason asparagus staging is so attractive in KSP is the characteristics of the engines and fuel tanks. In KSP, the engines have thrust-to-weight ratios of 30 or less. Real rocket engines are more like 50-150. The KSP fuel tanks have dry mass equal to 1/9th of their wet mass, real rockets have structural mass ratios of 2-3 times better than that (depending on fuel type, cryogenic vs not). So shedding the mass of engines and fuel tanks as soon as you don't need them anymore is more important in KSP than in reality.

[Apophis775]

Is it possible to turn on random engine failures?

I hope this is in the game at release. It would put more of a emphesis on escape system planning, which, I always setup (Engines cut and detach, parachutes on crew compartments deploy). I mean hell, I spent time building, launching, and docking an escape pod for my Space Station, just in case.

[LameLefty]

SpaceX's Falcon 9 Heavy will be doing that, and there's a proposed variant on the Delta IV Heavy that will do it as well, despite the idea first being proposed in 1947.

Nits: It was specifically proposed for the D4H a long time ago, during the design phase, but no customers needed enough lift to justify the development cost or risk. For that matter, other than NSA and DoD payloads, nothing needs even the payload that the stock D4H provides without cross-feed. Don't count on the first version of the Falcon 9 Heavy to utilize it either, although SpaceX needs the extra performance for a number of reasons - first, Musk wants to be able to recover and re-use his cores; that eats into performance. If cross-feed can eventually be made to work, he'll use it to buy back the perfomance reserves required to recover the cores. Second, SpaceX still lacks a high-ISP upper stage engine; the Merlin 1D Vac has excellent performance for kerolox but still comes nowhere close to the efficiency of a hydrolox stage. That doesn't matter much for LEO payloads but it kills performance to GTO and beyond (planetary missions and Musk's eventual Mars dreams).

[lammatt]

fluid dynamics is not as easy as a yellow duct

[numerobis]

Yet another reason: in-game, we use the same engine at all altitudes and just pay for more fuel use at low altitude. IRL, nozzle design is much more complicated. A nozzle that burns well at all altitudes is less efficient than a nozzle that is only usable in a smaller range of conditions and melts or otherwise fails in the wrong conditions.

[Gus]

I guess one way to penalize players a bit for asparagus staging would be to give the radial decouplers very high drag.

[Eric S]

I guess one way to penalize players a bit for asparagus staging would be to give the radial decouplers very high drag.

Of the things that could seriously impact the use of asparagus staging in career mode, the most likely possibility may be that asparagus launchers will just be more expensive due to more engines. If 6 engines that combined have the same thrust as one big engine, but the one big engine works out cheaper, then the big engine could be more cost effective.

The other possibilities:

Kill fuel lines: Not likely.

Rebalance engine TWR, ISP, and fuel tank dry weight so that engines aren't so much dead weight. Not likely.

A better aerodynamics model: This really depends on how realistic they make it. RL aerodynamic drag losses (as a % of total delta-v) are more than an order of magnitude less than they are in KSP, so unless they go semi-realistic, asparagus can afford higher drag losses than normal stacks.

As for making radial decouplers very high drag, we'd need the better aerodynamics model to make that practial, otherwise, the numbers would have to be stupidly high because of the low mass of the radial decouplers. Not to mention the fact that you'd be doing the same amount of damage to very traditional boosters.

[Vector]

In real life engines are expensive. In KSP everything is free, so who cares if you throw away extra engines. Liquid engines can be treated like SRBs.

[Hodo]

There are 3 mods currently that will pretty much kill the "asparagus" launch technique.

Modular Fuel Systems - http://forum.kerbalspaceprogram.com/threads/52780-Modular-Fuel-System-Continued-v2-TECH-LEVELS

Ferram Aerospace Research - http://forum.kerbalspaceprogram.com/threads/20451-0-22-Ferram-Aerospace-Research-v0-9-6-3-Aerodynamics-Fixes-For-Planes-Rockets

Kerbal ISP difficulty Scaler - http://forum.kerbalspaceprogram.com/threads/52882-0-22-Kerbal-Isp-Difficulty-Scaler-v1-2

Those three mods will kill a great many of the "asparagus" monsters we see out there. Not to say that you can't do it with in them, you can, but there are more efficient ways in game to do something with those mods.

[Gus]

Of the things that could seriously impact the use of asparagus staging in career mode, the most likely possibility may be that asparagus launchers will just be more expensive due to more engines. If 6 engines that combined have the same thrust as one big engine, but the one big engine works out cheaper, then the big engine could be more cost effective.

The other possibilities:

Kill fuel lines: Not likely.

Rebalance engine TWR, ISP, and fuel tank dry weight so that engines aren't so much dead weight. Not likely.

A better aerodynamics model: This really depends on how realistic they make it. RL aerodynamic drag losses (as a % of total delta-v) are more than an order of magnitude less than they are in KSP, so unless they go semi-realistic, asparagus can afford higher drag losses than normal stacks.

As for making radial decouplers very high drag, we'd need the better aerodynamics model to make that practial, otherwise, the numbers would have to be stupidly high because of the low mass of the radial decouplers. Not to mention the fact that you'd be doing the same amount of damage to very traditional boosters.

First off, I enjoying building asparagus rockets. I just don't want them overpowered.

Yes, money will add a lot of the decision process.

Any time I use a radial decoupler it is to add a fuel tank or solid rocket booster. These produce a new cross section of air to be pushed through by the rocket. Setting radial decoupler drag high would represent the new cross section's "raw" drag.

[FlamedSteak]

I can't wait for money to be added into the game. Dealing with the restrictions imposed by the tech tree has been the most fun I've had with this game since I first put a Kerb on the Mun.

Adding that next level of complexity to manage is going to make this game go from awesome to something better than that...like super-awesome or something.

[Jarnis]

What's up with that. Is it the air resistance? Is it "unrealistic" to use it? Does the FAR mod make asparagus staging less "powerful"? Thanks.

* In real life, your crossfeed pumps do not weigh 0 grams.

* In real life, your crossfeed fuel lines do not weigh 0 grams.

* In real life, pumping around cryogenic propellants between rocket stages at rates eaten by the engines is Hard - you need big fat pipes, you need heavy plumbing and you need a lot of careful design to avoid that plumbing from failing in flight. You also need to close those pipes very quickly and securely without spewing stuff all over the place (any leaks potentially causing a Rapid and Unplanned Disassembly Event as the propellant cloud goes boom) when staging the side boosters.

But SpaceX is actually going to try it (with two side cores) with Falcon Heavy. It has a crossfeed-enabled version planned that would use side core fuel to run all the engines (27 of them!) at liftoff and when the two side cores are nearly empty, they are ditched (and they will return to land for reuse! using the remaining fuel to slow down the fall back & steer for propulsive landing) while the central core continues on at almost full fuel load. Gives a substantial payload boost, but it remains to be seen how much they lose to the added weight of the crossfeed lines and pumps. It Should Work® - on paper - but it hasn't been tested yet.

Russians also have plans for a design like this but they have never built one. I believe their version had four side cores.

Edited October 22, 2013 by Jarnis

[trekkie_]

Asparagus rocketry is basically why the Russians failed to beat the US to the moon.

Pogo oscillation is a potentially dangerous type of self-excited combustion oscillation in liquid fuel rocket engines. This oscillation results in variations of thrust from the engines, causing variations of acceleration on the rocket's structure, giving variations in fuel pressure and flow rate. That's why the N1 rocket wasn't successful. It had over 30 engines. It would literally bounce up and down like a pogo stick in a runaway effect until it matched the vibration frequency and shaked itself apart and exploded in what is still the biggest non nuclear explosion in history I think. of course these engines weren't meant to detach in an asparagus manner, but the principle is the same. A rocket can literally have a million different parts. The more engines, the more parts. In comparison the US only used 5 larger engines for the first stage launch. Reliability is sometimes more important than using the least amount of fuel in the real world. Better to spend a little more in fuel than to potentially lose the whole ship at launch and waste untold amounts of money.

Edited October 22, 2013 by trekkie_

[ferram4]

A proper way to penalize asparagus staging in KSP, though one that would probably be somewhat complicated to model, would be to conserve the momentum of the fuel as it drains. As the fuel drains counterclockwise out of each liquid booster, the rocket will pick up clockwise spin to conserve momentum in the system. Then the primary issue with an asparagus monster isn't drag (though it is a fairly big factor), but the fact that your rocket is spinning like mad as you try to pilot it into orbit; this would make gravity turns particularly nasty, since it could lead to the rocket's roll combining with the pitch-over movement to send it off course.

Of course, this is one of the larger problems in real life.

[p1t1o]

Long story short:

1. pretend air is made of jelly.

2. is it easier to push a long pencil through it or a bunch of asparagus?

3. trick question, the asparagus has been steamed and is too floppy.

4. steamed asparagus smashed in jelly sounds like something a Kerbal would eat.

[Sean Mirrsen]

Most of the issues mentioned here are easily avoided with a simple crossfeed system that just uses two liquid fuel boosters. No excessive drag, no rotational control issues, no excessive staging either.

Also, I was mulling over an idea at one point, that might seem a little silly at first. Basically, rocket propelled drop tanks. Asparagus staging is already that, in a way, but it could be made less infrastructure-intensive. Instead of feeding fuel out of two live boosters, and potentially endangering the ship when staging as the crossfeed needs time to separate, why not fit the ship with simple, dumb drop tanks? Plus boosters. The fuel in the drop tanks would be carefully measured to last nearly exactly to the point where the ship sheds the LFBs, and the inert(ish) tanks are decoupled and parachuted off on their own, without delaying the separation of boosters.

The net effect is still the same. Extra fuel for the main stack, plus booster rockets to push the ship and that extra fuel along. Except they're separated instead of being the same potentially dangerous thing. Of course, setting the system up for more than two boosters would be a challenge, but it's not, ultimately, impossible.

[RSwordsman]

^^I've used the drop tank method on a few designs. It's not quite as efficient as asparagus because you lose thrust-mass ratio, but it seemed to work alright.

[damny]

I think there are two aspects to why we're not seeing this much in real life.

One is, we're simply not going very far. We've sent people to Low Earth Orbit, and a few of them to the moon. We've sent unmanned landers to Venus and Mars. We've sent out some probes doing flybys of some other bodies. That's it. None of these things require asparagus staging in KSP, either.

The other is, we're more efficient and much better at rocket science in the real world. The delta v to get to a Low Earth Orbit is around 9.5 km/s. In KSP that kind of budget puts you in orbit around a *different* planet. The payloads we send up in the real world aren't tiny, either. The Apollo landers were quite heavy compared to what you'd send up in KSP.

It's true that the Falcon Heavy that has been mentioned in this thread will use some basic variant of asparagus staging (two side stages that pump their fuel into the center one). But it will not actually beat the payload capacity the Saturn V had 50 years ago! So we still don't need asparagus staging ... we're kind of only seeing it at all because SpaceX is trying new things to make their rocket safer than other rockets.

[allmappedout]

I think there are two aspects to why we're not seeing this much in real life.

One is, we're simply not going very far. We've sent people to Low Earth Orbit, and a few of them to the moon. We've sent unmanned landers to Venus and Mars. We've sent out some probes doing flybys of some other bodies. That's it. None of these things require asparagus staging in KSP, either.

The other is, we're more efficient and much better at rocket science in the real world. The delta v to get to a Low Earth Orbit is around 9.5 km/s. In KSP that kind of budget puts you in orbit around a *different* planet. The payloads we send up in the real world aren't tiny, either. The Apollo landers were quite heavy compared to what you'd send up in KSP.

It's true that the Falcon Heavy that has been mentioned in this thread will use some basic variant of asparagus staging (two side stages that pump their fuel into the center one). But it will not actually beat the payload capacity the Saturn V had 50 years ago! So we still don't need asparagus staging ... we're kind of only seeing it at all because SpaceX is trying new things to make their rocket safer than other rockets.

But bear in mind the reason it won't beat the payload capacity is the reusability function. The Falcon Heavy could give the Sat V a run for its money if it didn't need 15% of its fuel for landing its boosters. It mightn't beat it (I can't remember if the exact lift capacity was greater or not), but it definitely comes close, and is a much smaller rocket for its troubles.

Edit: Sorry I'm wrong.

http://en.wikipedia.org/wiki/Falcon_Heavy

http://en.wikipedia.org/wiki/Saturn_V

FH can lift 53tons, SV is 120tons. Still, FH is 'only 1.4m kg' vs 'only 2.3m kg', so you're getting just under half the lift for half the mass, but at much less than half the cost.

Edited October 22, 2013 by allmappedout