The Asparagus Thread

[KASASpace]

So, I was making an Excel Spreadsheet. I had a two stage vehicle that put 500 of anything into orbit (all units were arbitrary until the D-v equation, but the gravitational constant was in its own cell, so you could change it easily)

When I added an Asparagus feature to the design, in the fashion of the Kerbal-X (smaller tanks around a bigger one) I managed to eradicate the need for a second stage. So, either I was really wrong in my equations (I checked thoroughly) or we should at least be trying to actually go and build something like this.

So, I have a question: What are your thoughts as to Asparagus Staging?

Is it a beautiful concept?

A pipe dream?

Or is it the craziest thing ever?

Explain why you have your views of the concept, please.

[N_las]

Do the smaller tanks around the bigger one have there own enginges? If yes, why do you think it would be better than just having a normal second stage? And even if they haven't there own engines, you will have around 4 seperation events, opposed to just one. If the outcome is the same, then a second stage seems better than more complex alternatives.

[rkman]

I managed to eradicate the need for a second stage.

I'd say the asparagus stages have replaced/are the first stage(s). The core stack being the final ascent stage.

I really like the concept, saves a significant amount of fuel by dropping as much 'dead weight' as possible. Theoretically it is a no-brainer.

Practically it is probably quite tricky.

I think that in ksp it is a bit cheaty, especially because it already is rather easy to get into orbit. Maybe there should be a part that is a special kind of (somewhat weighty and costly) fuel pump that allows fuel transfer from and to tanks that are also feeding engines.

If the outcome is the same

It is not, in terms of fuel requirements.

[N_las]

It is not, in terms of fuel requirements.

If two launchers have the same dV, the fuel requirements are irrelevant. Only the costs and the reliability are relevant. If your launcher only takes half the fuel but has more seperation events, it is an inferior launcher.

[KASASpace]

If two launchers have the same dV, the fuel requirements are irrelevant. Only the costs and the reliability are relevant. If your launcher only takes half the fuel but has more seperation events, it is an inferior launcher.

Who wants a really expensive rocket that ony throws about 10 tons in to LEO?

I would want a cheap one that's also reliable. So wait until a bunch of successes in a row.

[sgt_flyer]

There are key problems when going from KSP to real life (without talking about fuel transfers and drag)

An asparagus with no upper stages can be counted like this : core stage + number of booster drops. A core + 6 boosters would be a 4 stages to orbit rocket. (As the remaining stages are 'full' when the empty pairs are dropped.

The key advantage of the design, is to limit 'dead weight' as all stage engines burn all the time. This is particularly effective in KSP, because the engines and fuel tank dry weight are so heavy in regard to their thrust (so you want to shed this dead weight as you go)

Now, in real life, there is several problems with this : rocket engine nozzles of different lengths (like Merlin and merlin vacuum - same engine, different nozzles) are designed to have their peak ISP at different air pressures. (In KSP, all engines have their peak ISP in vacuum, which is not the case in real life)

So, if you keep your core stage all the way to space, the core needs to have engines tuned for these altitudes. (You could either use aerospike designs or a 'lip' like on the SSME to enhance the ISP at various pressures - yet, they were much more effective in near vacuum - once the SRB's carried the shuttle high enough.

An engine built for vacuum will have a much worse thrust than the same engine built for sea level - (unlike stock KSP, ISP don't change fuel consumption, but thrust - as the turbopumps run generally give a fixed fuel flow)

In these cases, you might want a dedicated upper stage with specific nozzles (so you can mass build the booster's engines - like Falcon Heavy)

In real life, true costs savings for rocketry comes when you have a lot of 'common' equipment - no need to redevellop new systems for each rocket.

In this spirit, Modular rockets are very interesting. (Angara, Falcon Heavy, Delta IV heavy) - it counts even more than the meager savings you would get from asparagus

Edited April 29, 2014 by sgt_flyer

[N_las]

Who wants a really expensive rocket that ony throws about 10 tons in to LEO?

I would want a cheap one that's also reliable. So wait until a bunch of successes in a row.

Nobody wants an expensive rocket. And simple rockets have low costs. Complex rockets are the expensive ones. The amount of fuel a rocket needs isn't a cost factor.

If you propose a small asparagus launcher that can lift 20 tons into orbit, I simply propose a big two-stage rocket that can lift the same. Mine will be cheaper and more reliable.

[R0cketC0der]

Who wants a really expensive rocket that ony throws about 10 tons in to LEO?

I would want a cheap one that's also reliable. So wait until a bunch of successes in a row.

Excactly - most launch failures are either because of engine failures or because of separations go badly.

While usually more engines often gives you even more reliability due to engine-out capabilities, engine failures would be much less forgiving on asparagus-staged vehicles. Imagine if an engine on the pair of boosters which gets decoupled lastly fails. You have to shut down the one on the opposite site to avoid asymmetric thrust, meaning that you have two useless engines attached to your vehicle which you can't get rid of, while having to drop other engines which work perfectly fine.

Also asparagus staging also introduces a lot more separation events you wouldn't need otherwise.

[KASASpace]

Excactly - most launch failures are either because of engine failures or because of separations go badly.

While usually more engines often gives you even more reliability due to engine-out capabilities, engine failures would be much less forgiving on asparagus-staged vehicles. Imagine if an engine on the pair of boosters which gets decoupled lastly fails. You have to shut down the one on the opposite site to avoid asymmetric thrust, meaning that you have two useless engines attached to your vehicle which you can't get rid of, while having to drop other engines which work perfectly fine.

Also asparagus staging also introduces a lot more separation events you wouldn't need otherwise.

The Soviet R-7 had a clustered engine on the individual booster rocket. So, perhaps a similar setup? So if one fails, you shut off the corresponding one on the opposite booster. Perhaps you could jettison the ones that failed? I mean using a modular system, like some sort of clamps? That can be undone if an engine fails?

And I know that the more events the more dangerous it is, but it's an efficient concept. Plus, you can resort to an infallible separation technology:

Explosive bolts. I'm sure they're used anyways, but when they are used you can detach and thrust away a parallel stage.

[KASASpace]

Nobody wants an expensive rocket. And simple rockets have low costs. Complex rockets are the expensive ones. The amount of fuel a rocket needs isn't a cost factor.

If you propose a small asparagus launcher that can lift 20 tons into orbit, I simply propose a big two-stage rocket that can lift the same. Mine will be cheaper and more reliable.

You could use the individual pumps for the engines on the boosters to pump the fuel into the neighboring stage. It's simple, and only more plumbing in the way of piping.

Oh, and:

BTW, the less fuel the smaller the tank, and thus a smaller rocket. And thus less thrust needed. And thus a smaller engine.

Less fuel is the best thing a rocket scientist can do.

[Redrobin]

Enough asparagus for all!!!

[Ralathon]

You could use the individual pumps for the engines on the boosters to pump the fuel into the neighboring stage. It's simple, and only more plumbing in the way of piping.

Oh, and:

BTW, the less fuel the smaller the tank, and thus a smaller rocket. And thus less thrust needed. And thus a smaller engine.

Less fuel is the best thing a rocket scientist can do.

Yea, and all you need to achieve fusion is to get the nuclei really close to one another. It's simple, and only some heating is required.

Things are always easy in theory. In practice asperagus staging is a hellish ordeal due to the amounts of fuel involved. This is a video inside the saturn V 1st stage:

See how quickly that monster drains the tank? That's a LOT of mass you have to pump around at ridiculous speeds. This means either enormous pipes or extremely high pressures, both giving you lots of problems.

Even something as simple as a bend becomes an engineering nightmare in those conditions. You get all sorts of vortices and oscillations inside the fluid that can completely destroy your vehicle. And you need to develop fast closing valves for that... Not to mention that the most expensive parts of a rocket are the engines. More engines = more expensive rocket. The fuel itself is dirt cheap compared to the hardware, nobody cares about a few extra barrels of LOX. So why would you want to build a vehicle that eats through so much engines?

If we had infinite resources and infinite manpower asperagus would be the way to go. But if you actually look at resources vs efficiency instead of wet mass vs efficiency our current tactics are way better. The only time asperagus is going to be viable is if you can recover the boosters somehow.

[R0cketC0der]

The Soviet R-7 had a clustered engine on the individual booster rocket. So, perhaps a similar setup? So if one fails, you shut off the corresponding one on the opposite booster. Perhaps you could jettison the ones that failed? I mean using a modular system, like some sort of clamps? That can be undone if an engine fails?

And I know that the more events the more dangerous it is, but it's an efficient concept. Plus, you can resort to an infallible separation technology:

Explosive bolts. I'm sure they're used anyways, but when they are used you can detach and thrust away a parallel stage.

I think the R7 was indeed able to continue a flight after an engine failed. You would just shut down the engine on the opposite side and let the affected boosters burn a little bit longer. I guess this would also work in asparagus, but if engines fail, you might not have the needed TWR directly after booster separations.

Explosive bolts are actually pretty unsafe as a decoupling technology. If the ignition of the explosive charge fails, you're flight is over. The same applies to all decoupling technologies, but ones that you can actually test before flight are generally safer.

[KASASpace]

Explosive bolts are actually pretty unsafe as a decoupling technology. If the ignition of the explosive charge fails, you're flight is over. The same applies to all decoupling technologies, but ones that you can actually test before flight are generally safer.

Explosive bolts are actually extremely reliable. The only known instance (that I remember) where it failed was on the second manned flight of the Mercury capsule. And even then, it's not confirmed.

[KASASpace]

Yea, and all you need to achieve fusion is to get the nuclei really close to one another. It's simple, and only some heating is required.

Things are always easy in theory. In practice asperagus staging is a hellish ordeal due to the amounts of fuel involved. This is a video inside the saturn V 1st stage:

See how quickly that monster drains the tank? That's a LOT of mass you have to pump around at ridiculous speeds. This means either enormous pipes or extremely high pressures, both giving you lots of problems.

Even something as simple as a bend becomes an engineering nightmare in those conditions. You get all sorts of vortices and oscillations inside the fluid that can completely destroy your vehicle. And you need to develop fast closing valves for that... Not to mention that the most expensive parts of a rocket are the engines. More engines = more expensive rocket. The fuel itself is dirt cheap compared to the hardware, nobody cares about a few extra barrels of LOX. So why would you want to build a vehicle that eats through so much engines?

If we had infinite resources and infinite manpower asperagus would be the way to go. But if you actually look at resources vs efficiency instead of wet mass vs efficiency our current tactics are way better. The only time asperagus is going to be viable is if you can recover the boosters somehow.

Simple does not equal easy. It means simple. It doesn't mean easy.

We could von Braun it. By that I mean design it, test it, fix it. He literally did that with his team on the A-4/V-2.

Now, we would first do testing on the ground, like all other rockets. And then test the components.

You actually can recover the engines, BTW. You could then take what is usable and melt down the rest.

Plus, you could design the engine to be ablative. Not aerogel, but like early heat shields.

Now, turbopumps..............

[N_las]

Oh, and:

BTW, the less fuel the smaller the tank, and thus a smaller rocket. And thus less thrust needed. And thus a smaller engine.

Less fuel is the best thing a rocket scientist can do.

"The size of the rocket is irrelevant. The thrust needed is irrelevant. Resistance is futile. You will be assimilated."

But seriously, if it's cheaper and more reliable, than the size and thrust doesn't matter.

How is an asparagus staged rocket more reliable?

How is an asparagus staged rocket cheaper? (Because one needs less fuel and smaller engines? puleeze...)

Edited April 30, 2014 by N_las

[Ralathon]

Simple does not equal easy. It means simple. It doesn't mean easy.

[h=2]¹sim·ple[/h] adjective \ˈsim-pÉ™l\: not hard to understand or do

: having few parts : not complex or fancy

: not special or unusual

Of those things I can only see the "Not hard to understand" applying. It is very hard to do, requires a lot of extra parts and it is certainly unusual in the current climate.

We could von Braun it. By that I mean design it, test it, fix it. He literally did that with his team on the A-4/V-2.

Now, we would first do testing on the ground, like all other rockets. And then test the components.

This is how practically every large engineering project works... Design, prototype, test, redesign till satisfied. This is standard procedure, it isn't going to magically make asperagus any easier or cheaper.

You actually can recover the engines, BTW. You could then take what is usable and melt down the rest.

refurbishing engines is a nasty job. Even the space shuttle engines, which where never exposed to salt water or hard landings, had to be taken out and completely rebuild after every flight. It is almost cheaper to just buy a new engine than it is to refurbish a flown engine. Think about it, engines aren't expensive because they're build out of unobtanium. They're expensive because they are complex machines with lots of parts. Stripping them for nuts and bolts isn't going to rake in the big cash.

Plus, you could design the engine to be ablative. Not aerogel, but like early heat shields.

Now, turbopumps..............

Are you just tossing around buzz words? How would an ablative engine solve anything? It becomes harder to refurbish and it'll only be slightly cheaper.

[KASASpace]

"The size of the rocket is irrelevant. The thrust needed is irrelevant. Resistance is futile. You will be assimilated."

But seriously, if it's cheaper and more reliable, than the size and thrust doesn't matter.

How is an asparagus staged rocket more reliable?

How is an asparagus staged rocket cheaper? (Because one needs less fuel and smaller engines?)

Did you even read it?

Having to use less fuel, and thus get a smaller rocket, and thus get less weight, and thus get less and less fuel needed is the best thing a rocket engineer could want. Heck, it's what half of them want for Christmas every year.

The thrust needed is decreased, thus less pressure needed in the combustion chamber, thus less everything.

The Curse of the Rocket has two sides:

The light side:

You shave off a bit of mass, you can shave off even more mass for quite a while.

The dark side:

The more mass added the more fuel needed.

It's more reliable because you would use many common components. The engines for the boosters would be the same, and so thus the engine is a little bit cheaper than normal, especially if mass produced. (it will happen eventually)

The boosters would all be the same. That means you simply build six of them at a time. More common components, the cheaper a rocket is. Just like everything else.

[KASASpace]

Of those things I can only see the "Not hard to understand" applying. It is very hard to do, requires a lot of extra parts and it is certainly unusual in the current climate.

Not hard does not imply easy, it implies easy OR intermediate.

Now, it isn't hard to understand. It's actually really simple. Like the game Risk .

This is how practically every large engineering project works... Design, prototype, test, redesign till satisfied. This is standard procedure, it isn't going to magically make asperagus any easier or cheaper.

Not how I'm thinking of how it will be done. It's not standard procedure. I'm talking even if it fails and the cause is not known.

refurbishing engines is a nasty job. Even the space shuttle engines, which where never exposed to salt water or hard landings, had to be taken out and completely rebuild after every flight. It is almost cheaper to just buy a new engine than it is to refurbish a flown engine. Think about it, engines aren't expensive because they're build out of unobtanium. They're expensive because they are complex machines with lots of parts. Stripping them for nuts and bolts isn't going to rake in the big cash.

Did I say "refurbish"?

No, I said recover them and then strip out what can be used. Melt or get rid of everything else.

Are you just tossing around buzz words? How would an ablative engine solve anything? It becomes harder to refurbish and it'll only be slightly cheaper.

What I just said applies here. You wouldn't refurbish the damn thing! You would take what you can. Salvaging the engine. If you can take the combustion chamber, or even some piping, or perhaps other things you get a cheaper second engine.

Plus, using ablative nozzles would remove much of that "complicated" piping and such.

[N_las]

Did you even read it?

Having to use less fuel, and thus get a smaller rocket, and thus get less weight, and thus get less and less fuel needed is the best thing a rocket engineer could want. Heck, it's what half of them want for Christmas every year.

The thrust needed is decreased, thus less pressure needed in the combustion chamber, thus less everything.

It's more reliable because you would use many common components. The engines for the boosters would be the same, and so thus the engine is a little bit cheaper than normal, especially if mass produced. (it will happen eventually)

The boosters would all be the same. That means you simply build six of them at a time. More common components, the cheaper a rocket is. Just like everything else.

If you could save half the fuel by using asparagus (and that's unreasonably optimistic), and that would translate to half the thrust (which is unreasonably optimistic), that could maybe translate to half the cost for the engines (which is unreasonably optimistic).

You now have to pay for all the extra pumps, plumbing, values, electronics, boosters, seperation mechanism, everything extra needed for asparagus staging (and everything redundant), for less than half the cost of your rocket engines. If you pay more, it isn't cheaper.

Reliable:

If one booster has a succes rate of 99.5%, then an asparagus configuration of 7 boosters (6 + center) will have a reliablility of approx. (99.5%)^7 = 96.6%. Using common components may be more reliable than using different components, but it can't be more reliable than using LESS components.

[Ralathon]

Not hard does not imply easy, it implies easy OR intermediate.

Now, it isn't hard to understand. It's actually really simple. Like the game Risk .

You're arguing semantics. And I totally agree that the concept is really easy. Just like the concept of nuclear fusion, antimatter torchships and alcubiere warp drives is very easy. Yet we don't see those in real life. The problem is that translating a concept into a working machine is a nontrivial challenge.

Not how I'm thinking of how it will be done.

What you think seems to only have a passing resemblance to how reality operates...

It's not standard procedure. I'm talking even if it fails and the cause is not known.

It is called a test. We do those in the engineering world. We use them to see what parts fail to meet expectations and figure out the cause. We don't go directly from napkin scribbles to functional product.

Did I say "refurbish"?

No, I said recover them and then strip out what can be used. Melt or get rid of everything else.

[h=2]re·fur·bish[/h] transitive verb \ri-ˈfər-bish\: to repair and make improvements to (something, such as a building)

I'm giving your engines the benefit of the doubt and say that most parts survived the flight intact, so you only need to repair a few parts for a working engine. Which is the definition of refurbish.

But again. Engines are expensive due to the complexity. The raw materials aren't worth anything. It's the same as with your car. If you take your car apart and individually sell the nuts and bolts I'd be surprised if you get back 1% of the price of the car. The money you pay for an engine goes to the designers and workers, almost nothing is used for the raw materials.

What I just said applies here. You wouldn't refurbish the damn thing! You would take what you can. Salvaging the engine. If you can take the combustion chamber, or even some piping, or perhaps other things you get a cheaper second engine.

Plus, using ablative nozzles would remove much of that "complicated" piping and such.

Congratulations, after ripping apart the remains of your engine you now have 3 washing machines worth of scrap metal, worth a mighty 40 bucks at the local scrapyard. I'm sure that'll compensate for the 200.000 engine somehow!

[KASASpace]

If you could save half the fuel by using asparagus (and that's unreasonably optimistic), and that would translate to half the thrust (which is unreasonably optimistic), that could maybe translate to half the cost for the engines (which is unreasonably optimistic).

You now have to pay for all the extra pumps, plumbing, values, electronics, boosters, seperation mechanism, everything extra needed for asparagus staging (and everything redundant), for less than half the cost of your rocket engines. If you pay more, it isn't cheaper.

Who would add extra pumps?

Use the pumps on the boosters. Or use the core's pump. (Notice how I said pump, not plural. That's right, one pump for multiple engines on one stage. It can be and has been done. And, as you said, less components = more reliable)

What in the heck are "values"?

Half the fuel, no. Let's say 3/4 of the fuel. You can lose 25% of the tank's length. That's quite a lot of weight!

Now, you can use a shorter tank. You can then use less outer material, less tankage, less structural weight, and less thrust needed. You can then either increase payload or lower the rocket's weight more.

Reliable:

If one booster has a succes rate of 99.5%, then an asparagus configuration of 7 boosters (6 + center) will have a reliablility of approx. (99.5%)^7 = 96.6%. Using common components may be more reliable than using different components, but it can't be more reliable than using LESS components.

As I said, you can use one turbopump for a whole cluster of engines, and thus no extra pumps.

And plus, you can then use the pump inside the core around halfway through the fuel pump.

The Saturn V had over a million components. It's reliability (Apollo 4 stats) was 99.999%. The whole thing. All three stages.

[KASASpace]

You're arguing semantics. And I totally agree that the concept is really easy. Just like the concept of nuclear fusion, antimatter torchships and alcubiere warp drives is very easy. Yet we don't see those in real life. The problem is that translating a concept into a working machine is a nontrivial challenge.

The final design will be as simple as possible.

Perhaps using a small amount of the highly pressurized combustion products to pressurize a canister of neutral gases?

What you think seems to only have a passing resemblance to how reality operates...

Wait, they proved that this is the actual reality!!!? When did that happen?

It is called a test. We do those in the engineering world. We use them to see what parts fail to meet expectations and figure out the cause. We don't go directly from napkin scribbles to functional product.

Let me reiterate:

If I build from a design, and then test and add as small an improvement as possible as quickly as possible (Soviet Style), than is that considered typical?

[h=2]re·fur·bish[/h] transitive verb \ri-ˈfər-bish\: to repair and make improvements to (something, such as a building)

I'm giving your engines the benefit of the doubt and say that most parts survived the flight intact, so you only need to repair a few parts for a working engine. Which is the definition of refurbish.

But again. Engines are expensive due to the complexity. The raw materials aren't worth anything. It's the same as with your car. If you take your car apart and individually sell the nuts and bolts I'd be surprised if you get back 1% of the price of the car. The money you pay for an engine goes to the designers and workers, almost nothing is used for the raw materials.

Wait, aren't turbopumps effectively compressors? Is it that hard to build a compressor? Once you have the molds you can do it easily...........

And this is not repairing, it's taking apart and putting back together using as much of the original as possible. (repairing is more like adding what's missing, so it would be finishing another engine)

Congratulations, after ripping apart the remains of your engine you now have 3 washing machines worth of scrap metal, worth a mighty 40 bucks at the local scrapyard. I'm sure that'll compensate for the 200.000 engine somehow!

I never said "take the tiniest of parts".

You clearly don't understand much of what I say.

Let me reiterate:

If you can take a turbopump, some piping, and only a portion of the combustion chamber, than that's the majority of the engine.

BTW: 40/200 = 1/5. So, that's actually quite a lot. (Sorry, I had to.)

I either use nothing: 200000

Or a comma: 200,000

[N_las]

BTW: 40/200 = 1/5. So, that's actually quite a lot. (Sorry, I had to.)

I either use nothing: 200000

Or a comma: 200,000

200.000,00

200,000.00

200 000,00

200 000.00

200000.00

200000,00

On an international forum, those are all common ways to write numbers.

[KASASpace]

200.000,00

200,000.00

200 000,00

200 000.00

200000.00

200000,00

On an international forum, those are all common ways to write numbers.

Yes I know. It gets confusing for me sometimes. And occasionally I have an urge to make a joke about it. Sorry, I'm not the greatest person in terms of morality. (Seriously guys, writing nothing is a good compromise.......)