I don't understand why bigger isn't better

[Pecan]

Uh, no.

Parallel triples the amount of drag you get; three towers instead of one. You can get away with that with enough power. going from 2 symmetry to 4 symmetry does not give you a doubling of dV, but it does double the drag.

Who mentioned 4 symmetry? If you have 2 boosters with fuel lines to the core they are asparagus, since all asparagus means is onion with symmetry-2.

[-Velocity-]

Asparagus is just onion with symmetry-2 so if you can't use asparagus you can't use onion.

Onion is just side-boosters with fuel-lines so if you can't use onion you can't use radial/parallel.

If you can't use radial/parallel you must build in a single stack - which is very odd.

IF, on the other hand, you CAN use radial/parallel boosters then you can use onion.

If you can use onion you can use asparagus.

So the argument does not hold.

What doesn't hold? ANYTHING that gives you more than one stack drastically increases drag. I don't care if you call it asparagus, onion, broccoli, cauliflower, tomato... WHATEVER. If you're pushing more than one rocket body cross-section through the air, it's going to drastically increase your drag. You want to make your rockets tall and thin, not short and fat.

[Pecan]

What doesn't hold? ANYTHING that gives you more than one stack drastically increases drag. I don't care if you call it asparagus, onion, broccoli, cauliflower, tomato... WHATEVER. If you're pushing more than one rocket body cross-section through the air, it's going to drastically increase your drag. You want to make your rockets tall and thin, not short and fat.

Right, so you ARE saying you can only launch things in a single stack - that's what I was asking and what I find very odd.

It was blaming 'asparagus' throughout the exchange that I didn't understand and that doesn't hold, since it's any staging or other building requirement that causes you to use more than one stack in the first place. Look at the ship I showed back in post 32 - it's a SSTO but still 5 stacks, because a) I needed 4 engines, piling all those orange tubes into a single stack wouldn't be structually sound.

Were I not specifically designing that as a recoverable SSTO it would make sense to asparagus-stage those, especially the short pair that is designed to burn-out early anyway and probably even adding a fifth engine on the core stack to ditch the other two as well. Just don't blame asparagus for the drag; it's the engine and structural requirements that causes that and are equally applicable to any staging strategy, including SSTO.

Where I totally agree with you though is that when using side-stacks for any reason, I never go beyond one ring - usually core+6 but core+8 1.5m around a 2.5m core. Again that's mainly for structural reasons though as I use stock aerodynamics (it's also partly for personal aesthetic reasons, but obviously that has no objective justification). I've also noted though that I hardly ever launch anything over 40t, preferring to assemble anything bigger in space, so I can't really understand the problems you're having nor the solutions you've found.

[Red Iron Crown]

It's not the number of stacks that are important drag wise, but the total frontal area (in FAR/NEAR, not stock aero obviously). A 2.5m stack has exactly the same frontal area as four 1.25m stacks, so the drag should be roughly equivalent. So if you're lifting a 1.25m payload that is heavy enough to justify a 2.5m lower stage, you're probably better off going with a 1.25m core stage with three crossfed 1.25m boosters. Such a setup will have about the same drag at liftoff and less once the boosters are jettisoned.

Similarly, a 3.75m stack has the same frontal area as nine 1.25m stacks or a 2.5m stack with five radial 1.25m boosters, so the same logic applies to them. Radial staging is definitely possible and worthwhile, even under FAR/NEAR.

[DrMonte]

In stock (without FAR mod) drag is calculated for each part and it does not matter where you put it. You can build flat asparagus or a needle tower the drag will stay the same. A nice example lies in wiki http://wiki.kerbalspaceprogram.com/wiki/Aerodynamic_Nose_Cone

Sorry if I repeat some words of those six pages.

[Pecan]

The wiki is wrong. While the nosecone adds mass its lower drag coefficient helps stabilise the ship.

[Red Iron Crown]

...with the stipulation that the nosecone is placed ahead of the center of mass.

(They almost always are, but sometimes on radial boosters they are not.)

[Dat_Spacewaffle]

*obligatory non serious answer* because MOAR BOOSTERS!

[Aedile]

To the OP question - because of reasons.

Everything, is about having the optimal tool for the job, and your definition of efficiency, dead weight etc.

A grand example of smaller is better is a lander. There is no reason to land all that fuel you need for the return trip/multiple landings. (Same reason why we don't drive fuel truck)

On the other hand bigger is often better, due to square-cube law. Generally speaking, tank with double the volume, will not have twice the dry mass. (other great example for this are ships). On the other hand, agility, dynamic forces(momentum), drag, become problematic as size increases (though it's much easier to keep one big tank together, than 10). In addition (mainly due KSP weird physics, aminly tanks and engines great weight), having small tanks give you the possibility to stage and shed weight easier.

KSP has several major differences with RL.

The stock drag model is BS, dependent on mass as well - directly violating square-cube law!

Dry mass of tanks linearly dependent on volume - again same problem. (orange tank will weigh the same as 8 FL-T800).

Heavy engines/tanks - pretty light structural elements (decouplers etc)

Engines you can throttle, no structural failures due G forces etc (other than lateral)...

Auto throttling of LF engines - ISP change changes consumption rather than thrust.

SRBs which have constant trust. Most of RL SRBs actually lose thrust, and some are build in such a way that they provide almost constant TWR. Unlike most LF engines, which gain thrust due ISP increase...

etc, etc..

Many mods change lots of these...

[magnemoe]

What doesn't hold? ANYTHING that gives you more than one stack drastically increases drag. I don't care if you call it asparagus, onion, broccoli, cauliflower, tomato... WHATEVER. If you're pushing more than one rocket body cross-section through the air, it's going to drastically increase your drag. You want to make your rockets tall and thin, not short and fat.

Yes as using multiple stacks is very unpractical and never used in real world.

http://fr.wikipedia.org/wiki/Ariane_(fusée)#mediaviewer/File:Ariane_5_Le_Bourget_FRA_001.jpg

Even worse, this implausible spacecraft

http://en.wikipedia.org/wiki/Space_Shuttle_program#mediaviewer/File:Space_Shuttle_Columbia_launching.jpg

4 stacks, two of them fat, off center trust, wings on rockets they do it all wrong.

Granted much of the idiot aspargus staging from earlier KSP is gone, it was used not only as the mainsail was the most powerful engine but also as the physic did not allow long and thin rocket, you had to build something wide. With 0.235 its seldom need for more than three 3.75 meter stacks with crossfeed, that lift 200 ton anyway.

[Jouni]

Granted much of the idiot aspargus staging from earlier KSP is gone, it was used not only as the mainsail was the most powerful engine but also as the physic did not allow long and thin rocket, you had to build something wide. With 0.235 its seldom need for more than three 3.75 meter stacks with crossfeed, that lift 200 ton anyway.

Tall rockets were entirely feasible before 0.23.5. For example, this was my standard fuel tanker back in 0.23:

This was in 0.23.5, but it should have been possible before that with a few more struts:

There were other reasons that made asparagus staging so popular back then. The first was that you get what you measure. When people were measuring payload fractions, asparagus staging was the obvious solution, as it maximized the chosen measure. Another reason was that it took a lot of work to ensure that big rockets didn't break apart during launch. Small, efficient rockets took often less time to build than big, inefficient ones, which again favored asparagus staging.

In FAR, just like on other reasonable aerodynamic models, drag losses are roughly proportional to the inverse of the average height of the rocket. This means that as long as the rocket is tall enough, it doesn't really matter how wide you make it. At least as far as drag is concerned – there's obviously more to aerodynamics than just drag.

[Aedile]

Tall rockets were entirely feasible before 0.23.5. For example, this was my standard fuel tanker back in 0.23:

http://jltsiren.kapsi.fi/ksp/0.23/tanker_launch.jpg

This was in 0.23.5, but it should have been possible before that with a few more struts:

http://jltsiren.kapsi.fi/ksp/0.23.5/moho-apollo/screenshot6.jpeg

There were other reasons that made asparagus staging so popular back then. The first was that you get what you measure. When people were measuring payload fractions, asparagus staging was the obvious solution, as it maximized the chosen measure. Another reason was that it took a lot of work to ensure that big rockets didn't break apart during launch. Small, efficient rockets took often less time to build than big, inefficient ones, which again favored asparagus staging.

In FAR, just like on other reasonable aerodynamic models, drag losses are roughly proportional to the inverse of the average height of the rocket. This means that as long as the rocket is tall enough, it doesn't really matter how wide you make it. At least as far as drag is concerned – there's obviously more to aerodynamics than just drag.

Stock drag model is based on mass. Not on surface area, not on surface area exposed to airflow.

The tall/vs fat is balancing act.

Long and tall is not particularly good for structural integrity and stability.

Also IRL diameter vs height of cylinder will change your tank volume/surface ratio, weight etc.

You need to remember, doubling the cylinder's diameter will give you 4 times the volume. With other words, if you went for height instead, you'd need to make it 4 times taller.

Edited September 17, 2014 by Aedile