The Asparagus Thread

[xcorps]

They haven't considered because they're satisfied with its current performance.

"If it ain't broke, don't fix it."

An intellectually lazy quip.

In 1947, Mikhail Tikhonravov developed a theory of parallel stages, which he called "packet rockets". In his scheme, three parallel stages were fired from lift-off, but all three engines were fueled from the outer two stages, until they are empty and could be ejected. This is more efficient than sequential staging, because the second stage engine is never just dead weight. In 1951, Dmitry Okhotsimsky carried out a pioneering engineering study of general sequential and parallel staging, with and without the pumping of fuel between stages. The design of the R-7 Semyorka emerged from that study. The trio of rocket engines used in the first stage of the American Atlas I and Atlas II launch vehicles, arranged in a "row", used parallel staging in a similar way: the outer pair of engines existed as a jettisonable pair which would, after they shut down, drop away with the lowermost outer "skirt" structure of the booster, leaving the central "sustainer" engine to complete the first stage's engine burn towards apogee or orbit.

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

[KASASpace]

An intellectually lazy quip.

In 1947, Mikhail Tikhonravov developed a theory of parallel stages, which he called "packet rockets". In his scheme, three parallel stages were fired from lift-off, but all three engines were fueled from the outer two stages, until they are empty and could be ejected. This is more efficient than sequential staging, because the second stage engine is never just dead weight. In 1951, Dmitry Okhotsimsky carried out a pioneering engineering study of general sequential and parallel staging, with and without the pumping of fuel between stages. The design of the R-7 Semyorka emerged from that study. The trio of rocket engines used in the first stage of the American Atlas I and Atlas II launch vehicles, arranged in a "row", used parallel staging in a similar way: the outer pair of engines existed as a jettisonable pair which would, after they shut down, drop away with the lowermost outer "skirt" structure of the booster, leaving the central "sustainer" engine to complete the first stage's engine burn towards apogee or orbit.

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

I know very well the history of the R-7. I also know very well how the Atlas was developed and the techniques it used.

You seem to have managed to barely address my comment yet at the same time quote it.

If you're satisfied with a launch vehicle, than you don't have to improve performance. Heck, even making it an Onion stage system is advantageous.

The concept was that all engines fire, so less "useless" weight of the engines. They all fired. Now, with the R-7, they made it so it used fuel in the core and gained TWR of the core, which was actually quite heavy alone (thus the need for boosters).

Now, if you could improve a rocket further (there is a limit to what you can do without going into advanced staging) than you can actually get a better cost per unit payload. That gives you a better rocket.

[Red Iron Crown]

They haven't considered because they're satisfied with its current performance.

"If it ain't broke, don't fix it."

So if not the Russians, who, exactly, does this apply to:

You can use all of the present pumps, you just need extra piping. That adds at most a few hundred kilograms. But the payload increase would be very worthwhile.

Very worthwhile to whom?

[xcorps]

I know very well the history of the R-7. I also know very well how the Atlas was developed and the techniques it used.

Now, if you could improve a rocket further (there is a limit to what you can do without going into advanced staging) than you can actually get a better cost per unit payload. That gives you a better rocket.

I think it's a bit of a stretch to assume that the two major superpowers haven't conducted a cost benefit analysis of a staging system that's been around since the 30's, having spent billions on research. I think it's intellectually lazy to conclude that because asparagus staging works very well in KSP the only reason it isn't being used IRL is because "it ain't broke don't fix it."

Clearly there is a reason, and I have some serious doubt that those reasons match any of the conclusions in this thread.

[DaveofDefeat]

I don't understand why people think asparagus would be better in some way, a lot of very smart people work on designing rockets and they all seem to have thought it wasn't the way to go.

[shynung]

I don't understand why people think asparagus would be better in some way, a lot of very smart people work on designing rockets and they all seem to have thought it wasn't the way to go.

This is KSP people. They observed that asparagus staging works in KSP, and assumed it would also work IRL. The problem is, KSP handwaves some laws of physics to be able to be run on a typical computer, one of them being conservation of momentum. Also, there is no such things as turbopumps in KSP, so people here often overlook that critical component.

[sgt_flyer]

In my eyes, the most simple onion staging concept thought about in real life was the one for the UR-700 rocket.

(The lower stages were a composite of tanks / engine) 3 in the middle, each with one engine, and 6 around them, each also with one engine)

Basically, on the 6 outer boosters, 3 of them had an additional oxydizer tank on top, three of them had an additional fuel tank on top - each of the boosters making the central core received fuel from one of the three fuel tanks, and oxy from one of the three oxy tanks. Those additional tanks were only meant to fed the central core, they were not feeding the outer boosters tanks.

The position of those additional tanks (above the central core) meant that they just needed wide enough pipes to support the flow - gravity / rocket thrust would take care of the rest. - they only needed reliable separation system and valves for the separation.

So, no need of extra turbopumps in this case, the additiobal fuel/oxy on top of the outer boosters would naturally top-off the central core tanks.

The downside is additional structure fitted on top of the outer boosters, making their dry mass higher.

Sadly, the UR-700 concept never left the drawing board - N1 concept was used instead. (I built in KSP a recreation of this, in my sig, but i did not tested it in 0.23.5 (worked in 0.23 though) - on this recreation, the additional tanks are isolated from the boosters tanks, and only feed the core stack.

No wonder i dubbed this rocket the soviet's most kerbal design direct moon ascent, onion staging, and somehow pancake rocket

[Red Iron Crown]

This is KSP people. They observed that asparagus staging works in KSP, and assumed it would also work IRL. The problem is, KSP handwaves some laws of physics to be able to be run on a typical computer, one of them being conservation of momentum. Also, there is no such things as turbopumps in KSP, so people here often overlook that critical component.

There are definitely problems with asparagus staging in real life, but conservation of momentum isn't one of them.

[KASASpace]

This is KSP people. They observed that asparagus staging works in KSP, and assumed it would also work IRL. The problem is, KSP handwaves some laws of physics to be able to be run on a typical computer, one of them being conservation of momentum. Also, there is no such things as turbopumps in KSP, so people here often overlook that critical component.

You do realize that you can use a turbopump to pump fuel/LOX down more than ONE pipe, right?

[KASASpace]

I think it's a bit of a stretch to assume that the two major superpowers haven't conducted a cost benefit analysis of a staging system that's been around since the 30's, having spent billions on research. I think it's intellectually lazy to conclude that because asparagus staging works very well in KSP the only reason it isn't being used IRL is because "it ain't broke don't fix it."

Clearly there is a reason, and I have some serious doubt that those reasons match any of the conclusions in this thread.

I didn't say that was the reason. They don't do it because they're afraid it will cost them. Heck, NASA is supposed to be "stirring competition" but they're still using the same brand SRBs.

The only reason is more that they are either afraid of change, or that they think it might just not go well, and then set them back. But that's why they invented testing. If anything, NASA could do some PHYSICAL research involving crossfeed, like how to pump the fuel around, and also how to separate the stages quickly. It doesn't even need to be a launch vehicle, you can do it on the ground!

[N_las]

You do realize that you can use a turbopump to pump fuel/LOX down more than ONE pipe, right?

If you pump it down two pipes instead of one, you need twice the flow rate. If your pumps are already used at their limit, then you need two pumps. Or you have to build a pump twice as big.

"Just put two pipes there and pump the liquid anywere for free" dosen't work.

Edited May 1, 2014 by N_las

[sgt_flyer]

I didn't say that was the reason. They don't do it because they're afraid it will cost them. Heck, NASA is supposed to be "stirring competition" but they're still using the same brand SRBs.

The only reason is more that they are either afraid of change, or that they think it might just not go well, and then set them back. But that's why they invented testing. If anything, NASA could do some PHYSICAL research involving crossfeed, like how to pump the fuel around, and also how to separate the stages quickly. It doesn't even need to be a launch vehicle, you can do it on the ground!

And who tell you they don't already do researches in these domains ?

They don't have to make big announcements each time they make experiments.

Nasa made a Swamp Works research center (the name is taken after lockheed martin skunk works)

http://www.nasa.gov/centers/kennedy/news/masters-swampworks.html

They built it specifically to devellop and experiment new technologies on small scales - so they could 'fail' a lot for cheap with experiments, and learn a lot from it. "Fast fail forward".

Maybe they are working on it, but they don't have a cheap, efficient and reliable enough results to share for now.

Edited May 1, 2014 by sgt_flyer

[KASASpace]

If you pump it down two pipes instead of one, you need twice the flow rate. If your pumps are already used at their limit, then you need two pumps. Or you have to build a pump twice as big.

"Just put two pipes there and pump the liquid anywere for free" dosen't work.

That's why you design the engines in such a way so that the pumps WOULDN'T be at their limit.

[KASASpace]

And who tell you they don't already do researches in these domains ?

They don't have to make big announcements each time they make experiments.

Nasa made a Swamp Works research center (the name is taken after lockheed martin skunk works)

http://www.nasa.gov/centers/kennedy/news/masters-swampworks.html

They built it specifically to devellop and experiment new technologies on small scales - so they could 'fail' a lot for cheap with experiments, and learn a lot from it. "Fast fail forward".

Maybe they are working on it, but they don't have a cheap, efficient and reliable enough results to share for now.

Because NASA can't exactly just slap rockets together. It's not KSP, not at all. But they may be tied up their as well. I mean, come on, there's a lot of technologies that are experimental that haven't even touched the surface there.

[architeuthis]

I don't think the size of the turbopumps is the problem. Propellant crossfeed isn't pumping from tank to tank, just engine feedline to feedline. Its problems are not dissimilar to those of the SM-65 Atlas stage an a half approach. There may be weird shutdown transients associated with jettisoning the side boosters for one thing. While propellant crossfeed is technically feasible (the principle was demonstrated on the Space Shuttle for instance), the main problem is just the surprisingly high amount of development and cost risk associated with making the feed and separation systems doubly or triply redundant with very high reliability. Unfortunately this is not trivial and we should recognize that Space X is taking a risk here. Obviously KSP handwaves away all the engineering difficulty that goes into this. It will be really cool if propellant cross feed pans out for the falcon heavy.

[sgt_flyer]

Because NASA can't exactly just slap rockets together. It's not KSP, not at all. But they may be tied up their as well. I mean, come on, there's a lot of technologies that are experimental that haven't even touched the surface there.

Well, in your previous post, you specifically said :

If anything, NASA could do some PHYSICAL research involving crossfeed, like how to pump the fuel around, and also how to separate the stages quickly. It doesn't even need to be a launch vehicle, you can do it on the ground!

So why wouldn't they be able to experiment those things in a research center like swamp works ?

If we are no rocket scientists and we thought about that, there's surely people somewhere in the world already working on that... (Oh wait, there's already SpaceX working on this technology...) so if they work on that, rest assured that the other rocket building companies have at least one research team doing at least theoritical research on that - if only to be able to evaluate the potentials, to be able to keep an edge in the long run.

Rocket technology improvements don't start and end with Nasa you know... Nasa just the ones doing the space Science no industrial want to make, and the ones able to decide how to attribute the fundings for contractors to answer nasa's specific needs.

It's the contractors who create the new rocket techs, not Nasa.

But seriously KasaSpace - you should really try to learn a bit of the engineering ideas, costs and problems behind real life rocketry, instead of coming with preconceived ideas which seems to come straight from Stock KSP.

Then, it will be all the more interesting to be able to debate with you and others on those subjects with an open mind - instead of listening to people trying to try to enforce preconceived ideas.

I'm no rocket scientist, but there's largely enough information material on the subject on the net to be able to understand the various concepts behind rocketry - and keeping in mind the probabilities math used around those rocket concepts. you can't have something 100% reliable in real life - this put a lot of things in perspective when dealing with those from different point of views (from economic side to engineering side and r&d, even P.R, etc)

Today's Real life Rocketry can't be reduced to only an engineering viewpoint

Edited May 2, 2014 by sgt_flyer

[KASASpace]

I am a rocket scientist, well, a protégé rocket scientist. Okay, fine, rocket engineer.

(I misspelled over there <--- as a joke)

I understand and know many of the engineering ideas, problems, cost, etc. Notice how I actually know of the handling cost of the fuel, and that the entire rocket is pretty much just accommodations for the fuel, and thus the fuel is the most expensive part via its respective requirements.

I know what NASA does and I know it's not the only LV/rocket development organization. I personally believe NASA is doing the wrong thing. They should have done what NACA did: Make it so that the criteria of rocket engines are easily available, so it takes a year or less to develop engines. Then its all about the design of the LV itself.

Does liquid propane come from KSP? No.

It comes from reality. It has a similar bulk density as RP-1, has better Isp, and needs the same amount of insulation as LOX. So, thinner common bulkhead, the same wall material, and thus it's cheaper (more common components).

NASA should be the pioneering cross feed, not SpaceX. Sure, its great that someone is doing it, but it should be the guys who have more experience with the technologies required for rocket science.

The contractors build the equipment, this I know. But NASA has been known to sometimes build their own things for testing. (it is rare, but it has happened previously)

Plus, when people like Lockheed are only building for NASA, then they have no incentive to develop new rocket tech. They aren't SpaceX, being led by a guy who wants space.

They are more focused on finishing their job, not actual want and desire for space-related equipment.

[shynung]

There are definitely problems with asparagus staging in real life, but conservation of momentum isn't one of them.

What I meant was, in a typical asparagus staging, fuel is pumped from one side booster to another, in a circular pattern. This implies that a lot of mass (fuel) is being rotated, which means the rocket should rotate while there are more than 2 side boosters remaining. We're not seeing this in KSP.

Also, having a spinning rocket that was not designed for spin-stabilization might not be a good idea.

[sgt_flyer]

@Kasaspace - if you're a rocket engineer, i would be interested in reading some papers giving infos that would indicate that the propane which makes it a viable rocket fuel ?

Currently, all researches on alternative fuels in commercial rocket industry seems to be going towards liquid Methane -

Liquid propane being seemingly only used in amateur rocketry when doing researches over the web.

If you're a rocket engineer, you seem to have a very specific point of view on rocketry - which is somewhat different from what we would expect when considering real life.

I'll let you with a xkcd post which could seemingly resume your situation : http://xkcd.com/1356/

Edited May 2, 2014 by sgt_flyer

[Red Iron Crown]

What I meant was, in a typical asparagus staging, fuel is pumped from one side booster to another, in a circular pattern. This implies that a lot of mass (fuel) is being rotated, which means the rocket should rotate while there are more than 2 side boosters remaining. We're not seeing this in KSP.

Also, having a spinning rocket that was not designed for spin-stabilization might not be a good idea.

The fuel stops rotating when it gets to the destination tank, exactly offsetting the impulse from pumping it. The idea that an asparagus rocket will spin faster and faster because of fuel pumping is inaccurate.

There is a slight net rotational impulse from the changing CoM in the asparagus ring, but it is at most 180 degrees over the entire burn of the ring, stops of its own accord when it gets to two radial boosters, and is easily counteracted by vectored thrust or aerodynamic controls if desired.

[Red Iron Crown]

I am a rocket scientist, well, a protégé rocket scientist. Okay, fine, rocket engineer.

What kind of degree(s) do you have? Are you working in the field?

I ask because you make some statements that I have a hard time believing a rocket scientist would make. Like "oxygen can burn itself" and "liquid propane needs the same amount of insulation as LOX", for example. I'm not a trained rocket scientist or engineer, but even my fairly basic science education tells me that these statements are just plain wrong.

[shynung]

There is a slight net rotational impulse from the changing CoM in the asparagus ring, but it is at most 180 degrees over the entire burn of the ring, stops of its own accord when it gets to two radial boosters, and is easily counteracted by vectored thrust or aerodynamic controls if desired.

This particular effect is what I meant. Yes, the rocket would rotate, but only until 2 boosters remain, not continuously accelerating its rotation. From there, the configuration becomes a crossfeed, similar to the Falcon Heavy. At this point, no rotational impulse should occur, since the mass flow exactly counteract each other. When the asparagus ring is still present, the same mass flow, while opposite of each other, happened at opposite sides of the rocket, creating the rotational impulse.

[Red Iron Crown]

This particular effect is what I meant. Yes, the rocket would rotate, but only until 2 boosters remain, not continuously accelerating its rotation. From there, the configuration becomes a crossfeed, similar to the Falcon Heavy. At this point, no rotational impulse should occur, since the mass flow exactly counteract each other. When the asparagus ring is still present, the same mass flow, while opposite of each other, happened at opposite sides of the rocket, creating the rotational impulse.

I really don't think it's a big deal. If left unchecked, the rocket does at most a slow half roll (or significantly less, a six booster arrangement would roll 60 degrees at most), and it takes the burn of all boosters in the ring to do it. It should be well within the control authority of a well-designed rocket to counteract if desired, especially if the rocket is designed for asparagus in the first place.

[shynung]

I really don't think it's a big deal. If left unchecked, the rocket does at most a slow half roll (or significantly less, a six booster arrangement would roll 60 degrees at most), and it takes the burn of all boosters in the ring to do it. It should be well within the control authority of a well-designed rocket to counteract if desired, especially if the rocket is designed for asparagus in the first place.

I suppose a good design could render an asparagus stable enough to fly predictably. Though, I still have some doubt.

Most of the rocket's mass at launch is fuel, often more than 4/5 of the total mass. Assuming a six-booster asparagus with one core booster, this means 4 out of 7 boosters are not connected directly to the core, having to pump fuel via the asparagus-ring fuel line. That's a lot of mass to move around, so I'm not really sure the rotational impulse from pumping 4 tanks of fuel around the ring would rotate the rocket no more than 60 degrees.

Then again, I never see a 6-booster asparagus-staged rocket launching IRL as of yet, so I may be surprised.

[Red Iron Crown]

I suppose a good design could render an asparagus stable enough to fly predictably. Though, I still have some doubt.

Most of the rocket's mass at launch is fuel, often more than 4/5 of the total mass. Assuming a six-booster asparagus with one core booster, this means 4 out of 7 boosters are not connected directly to the core, having to pump fuel via the asparagus-ring fuel line. That's a lot of mass to move around, so I'm not really sure the rotational impulse from pumping 4 tanks of fuel around the ring would rotate the rocket no more than 60 degrees.

Then again, I never see a 6-booster asparagus-staged rocket launching IRL as of yet, so I may be surprised.

Let me illustrate with some diagrams. Apologies for their crudeness, I'm not very good at image manipulation. Red dots indicate the centers of mass for each side of the asparagus ring.

Starting:

When down to the last boosters:

If left unchecked, the rocket will rotate clockwise to keep those red dots in line with each other, and no more.