What if we use a really strong tow-cable?

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"What you think you thought you saw you did not see." Agent J, MiB - Manhatten Bureau

Clearly you want the envelope of the biggest 'successful rocket " of which it is easy to errect without collasping of it's own weight at rest or under acceleration.
Just what can we do with 75 SRB's (A la shuttle) for the 1 ST stage .
Can we go that large??
I feel confident that someone has looked at the profile effeciencies of
many designs already certified has wondered....."Gee, if we strap the srb's..
that is 'enough SRB's" , and that there are some interesting links .
And of course, no cargo or facilities are boosted, just it's own weight.

I'll bet Dr VonBraun would have marveled at the question. What are the practical limits of constructing a rocket for launch to a successful orbit in LEO?
Can you imagine the thunder coming out of 75 SRB's on a pad at KSC ?

Mind you, once you have a design to lift itself, then you have to add the weight of everything else to adjust the design.....shrinkage.
Best regards,
Dan

You apparently have not designed many rockets.

Hi, No, we used to fire them, not build and design them.
It get's exciting though.

Best regards,
Dan

LoL, good point! Wrong thread, though...

Actually, he agonized over it. The initial calculations of the proposed Moon shots indicated anything like the Apollo program was impossible.

Hi, I should think he was concerned over the details of the structure of tankage and indeed the whole system under vibration . And probably a few
thousand minor details.
And who taught them rocket science? Robert Goddard .

" "We shall stand on the shoulders of giants."


Best regards,
Dan

Funny, but I do mean a puller-rocket instead of a pusher-rocket.

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"What you think you thought you saw you did not see." Agent J, MiB - Manhatten Bureau

That is in line with what I thought. That is why test engineering is a separate discipline and department from design engineering.
First we designed and only much later did we fire them. Lots of analysis proceeds the first live test, and it is during that design and analysis period that the structural issues are addressed. Thrust loads tend to be only a small part of the overall structural design process.

Yep, I suppose that a designer would have the whole thing built out of titanium and assembled underwater to support it and perhaps have the occupied portion of the ship above water(fresh would be nice..salt is trouble). Then, of course, the design is submitted to "The committee" .
And the first thing they say is...."But do you realize what this will cost?"
But they did say "The biggest chemical rocket". Hmmmm.....

Best regards

Dan

Nope.

The designer would probably use a lot of graphite-epoxy composite, analyzed in detail using a finite element code tailored for orthotropic materials, with lamina and laminate properties determined from an exhaustive series of tests. Other components receive similar structural analysis based on the technologies involved. The "committee" would review the analysis and make certain that the methods were appropriate and the margins adequate.

Depending on the propulsion technology there would also be reviews of the , interior ballistics and aerodynamic and thermo-structural analysis to make certain that the structure was adequate under operational conditions, and that the control system was compatible with the dynamics of the structure. Performance analysis would be run and coupled with aerodynamics to determine flight loads and those loads in turn re-analyzed from a structural perspective.

It is an overal iterative procedure, and it takes a broad spectrum of people from an equally broad spectrum of disciplines. It also takes a group of experts to review the design and assure that it is adequate and ready for flight. Several major reviews occur during the development period.

And then prior to laiunch the actual hardware and the data from both static tests and analysis are reviewed again in detail before a "go" is given for launch.

Been there. Done that.

One of the Apollo proposals before the Saturn was decided on was called Nova. It was going to be bigger than the Saturn V, but was never built.

Would an insanely huge solid rocket (say 400 feet tall, 100 feet diameter) work, assuming you could get the propellant?

Hi Dr, Interesting rocket. I like your description of the process. It smacks of experience and reality.
I wonder what the all up weight limit would be on .... well.... the largest
practical rocket we could launch into orbit or even beyond? As an academic question it remains tantalizing.
Best regards,
Dan

I dare say we have the technology to build one 1,000 ft tall and 200 ft wide.

We simply have no need of such a large rocket, and we're not going to build it on a whim as it would be ridiculously expensive.

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I am as yet amazed that one of those mathematics experts has not come striding through here wreaking havoc upon this idea and demon straighting the reasons why...
Weight / strength / lift potential. I would suggest a graph as most of us would understand the whole picture.

How Big could a Rocket Be ? Dependant on the ability to build such strengths as required are all calculable.

Finding sufficient quantities of fuels required would not be impossible, just costly.

The graph would show that as the advantage of massive size might be tolerant of massive engines and thrust. The limiting factions of strengths of materials. The lifting by point of thrust... Its not safe.

Unfortunately the whole idea of violent chemical burning rockets is very inefficient.

and its a whole new subject of how we could best get heavy things off this planet.

As I said earlier I don't see a limit imposed by physics on the size of a chemical rocket for launch from the Earth.

What I do see is a limit imposed by manufacturing and safety considerations. I don't know quite what the limit might be, but with the current infrastructure (manufacturing, launch and transportation) anything larger than Saturn V and Shuttle sizes strikes me as problematic.

The infrastructure in place to manufacture, assemble and launch the Shuttle is already pretty impressive. I suppose that one could design equipment for a larger rocket and locate the launch site in a more remote location, but it would take a lot of resources to do that.

As size goes up the demands on the manufacturing capabilities grow rapidly. Shuttle already is the driver for many of the existing facilities. For instance, larger cases for the solids could be made but would require much additional infrastructure to manufacture and handle them. If they were to be made of steel, like the current ones, I think that there would need to be quite a bit done to make them and to design fixtures and tooling to force them into roundness so that they could be stacked. If they were to be made graphite epoxy composite, then new facilities would be probably be need to accommodate much larger winding mandrels and machines and cure ovens. That is just a tiny piece of the puzzle of course, but it serves to illustrate the depth to which infrastructure changes would be driven by much larger scale than what we currently have.

It is not any single thing that imposes barriers, but the combination of everything that needs to be considered in order to increase the scale significantly. It is all doable. But it would be costly. What is needed is sufficient payback to expend the necessary time and resources.

Right. As I pointed out in the other thread, the only physical limitations are for rockets with simple, monolithic tanks, single large engines, etc. It's quite simple: if you can build a rocket of a certain size, you can attach two of them side by side and get a bigger rocket with roughly double the payload.

In reality, there's other considerations like aerodynamics, vibration modes, staging large numbers of parallel units, structural issues in distributing the load across them, etc...it's not a matter of duct taping rockets together. But this does show why there isn't a hard physical limit on the size of a rocket...at least, up to the point where you run into issues with fitting the rocket on the planet.

Hi, I expect that building such a rocket would require building in situ....
construct it exactly where it will be launched, no moving it via crawler to
the launch pad. It means building a VAB around the rocket and disassembling the Vab for launch. Peculiar,yes, but when you push the envelope, things often work a little different.
Best regards,
Dan

That sort of thing has been considered, and will probably be considered again.

Hi, It's just an academic point. But... like you said, not improbable.
I think good, solid and prudent designs fall more in line with what has worked
for us already. It's hard to argue with success.
Best regards,
Dan

Non-engineer here,

I was just wondering, some of you guys suggested wiring 75 conventional rockets together and forming some kind of "rocket carpet". While this would be a hell of a thing to see, I have to wonder...

During all those launches I've seen the exhaust billows around and away from the rocket right at lift-off. If the rockets are all next to one another, isn't there a risk that right at take-off the exhaust would bounce back and damage the surrounding rockets? I'm wondering what are the chances of some of them being damaged to the point of the fuel catching and burning out of control. Which would basically cause the damaged rocket to explode, I'm thinking.

I guess it would have to do with how closely they are spaced, but... you know, it's bound to be very risky business.

I'd be happy just to see Sea Dragon in action.

Hi Phil, Rocket science is an inherently risky business, that being attenuated by good solid research, experiment, observation, repeated testing and some of the brightest minds ever assembled for a common goal.
As per your question.... launch pads have extraordinary provisions for directed exhausts for just this purpose. The arresting gear must needs retain the rocket untill it's FULL thrust authority has been achieved before release.
Untill that happens, exhaust is directed lateraly .

Best regards,
Dan

As danscope noted there is quite a bit of engineering involved in the design of the "flame bucket" for launch pads. Rockets on the pad do not exhaust directly to the ground, but rather into a large duct that carries the exhaust gasses away from the pad. That duct often includes water injection systems that protect the structure and also serve to dampen acoustics.

As the size of the rocket increases the complexity of design of the flame bucket also increases. Once must not only keep the exhaust gasses from overheating the aft end of the rocket structure, but also one must control the magnitude of the reflecting pressure waves, which can overload the nozzles and the thrust vector actuation hardware.

It is unlikely that the exhaust gasses would create an immediate explosion, except in some outlandish case. The aft end of rockets is heavily insulated, and when they are burnning the exhaust velocity at the nozzle throat is the local speed of sound. That sonic throat velocity prevents not only gas flow but in fact even pressure waves from propagating through the throat into the combustion chamber.

However, if there were a lot of hot gas impinging on the rockets themselves, as opposed to flowing away through the flame bucket, there could be structural issues related to external hardware that might result in a failure.

75 rockets strapped together in a "rocket carpet" would be a very difficult thing to make work. There would be the issues that you mentioned with regard to controlling the plumes associated with each of the individual rockets at ignition. There would also be issues related to making sure that all 75 rockets ignited uniformly and consistently, since unbalances in the thrust from so many separate rockets could be a problem.

A more likely approach would be fewer but larger rockets.

Rocket science isn't risky at all. Sitting behind a desk, punching buttons on a keyboard, moving a mouse... Might get mouse elbow or carpal tunnel once in a while, but it's pretty safe.

Riding atop what rocket science designs, however, well that's a different story.

Sorry, Dan, but deflecting the exhaust laterally has nothing to do with keeping the rocket on the launch pad until "full thrust authority" has been achieved.

The sequence is that all three SSME's are lit. If they're fully functioning, including proper gymballing, and assuming all other systems are also a go, the SSRBs are lit. When both SSRBs are functioning properly, explosive bolts are fired and the entire stack leaves the Earth.

The ONLY reason exhaust thrust is diverted is to protect the assembly from the exhaust. Even if the system were designed to fire all engines at once, with no retaining bolts, the launch pad would still have an exhaust diversion structure to protect the assembley.

There is of course the small matter of actually manufacturing the rockets and handling the fuel ingredients in their raw form. There are tests to be run, and data to be obtained. There is laboratory work that accompanies the computer analysis. That entails quite a bit of work with explosives and knowledge of explosive handling. People have died doing that. It is not just sitting behind an desk and punching buttons.



Actually the sequence for the shuttle is that the "main engines" are lit, and because of the geometry of the package they exert a bending moment, which causes the rocket to flex. As the rocket rebounds and comes back to upright, the solids are lit and launch the package. The retaining explosive bolts are fires as part of the release, but if they don't fire the solids have quite enough thrust to break the bolts. Some bolts have failed to fire in the past, with little impact on the launch.

The retaining bolts do keep the shuttle on the ground while the liquids are firing.

You are correct that a flame bucket would be need even if there were no retaining bolts. It is necessary to control the exhaust plume in any case. There is a LOT of very hot exhaust gas being generated once the rockets are burning. The stagnation temperature of the gas from the solids is in the 5500 deg F range. If not manage that gas would damage not only the assembly but also the aft end of the rocket assembly during the initial stages of liftoff. Once up and away from structure the gas is exhausted sufficiently far behind the rocket that only radiant heating is important and there is adequate insulation for that.

Ok. I'd class this as "rocket design and development," but if you want to encapsulate it into rocket science, I'll grant some leeway.

Hmmm... Didn't know the solids had enough thrust to break the bolts. Stands to reason, though I wonder what would happen if one solid fired and the other failed...

I should think that they have employed redundant firing mechanisms for that
posibility. However, the history of solid rocket firing seems to be quite
excellent.

What difference is there, in principle, between turning the Moon into a rocket and turning the Earth into a rocket?

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If logic doesn't work, then surely it does.

A bigger nozzle...