Kerbal, OTRAG Style

[RocketBlam]

Some of you may be familiar with the OTRAG rocket. It was a system designed by a German entrepreneur, you can read about it here:

https://en.wikipedia.org/wiki/OTRAG

OTRAG was a system for massively parallel rockets. The idea was, you built a rocket out of many individual rocket lifting units, and instead of stacking them on top of each other, you stacked them side by side. That way, the same rocket would be used, just in different quantities, thus (hopefully) resulting in economies of scale. They would ideally only ever have one rocket design, and would just add more rockets for heavier payloads.

The system never got off the ground for various reasons, but I've always found it interesting.

Now, massively parallel rockets are nothing new in Kerbal Space Program - people have been using them for a long time to lift heavier payloads than they probably should have. But I decided to check out making an OTRAG-style launch system, using only one rocket engine type, and with all engines having their own fuel supply.

My system, however, is a little different. In OTRAG, they did regular staging, it was just with parallel rockets. In my attempt, I wanted to create a launch system that used no staging whatsoever. It should all be a single stage. My thinking was, "if 4 rocket units can achieve orbit with no staging, carrying X payload, then 16 rocket units should be able to do the same, but with a heavier payload."

So my two rules are:

1. All rockets must be the same type, and have the same amount of fuel. No cross-feed allowed.

2. The system should deliver a payload to LKO in one stage.

So here's what I have so far:

OKRAG 16

This vehicle can deliver a 16-ton payload to a 100km orbit.

OKRAG 32

This vehicle can deliver a 32-ton payload to a 100km orbit (actually somewhat more).

Is this a good idea, from an economics standpoint? Nope! These rockets will cost you quite a lot more than a vertical, normal staged rocket - assuming you have access to those engines. And of course the economies of scale never enter the equation, because in KSP, no matter how many rockets you build, they all cost the same amount. The one big advantage it has, though, is the ability to launch very heavy payloads into orbit from pretty early on in the tech tree. And if you wanted to make an OTRAG-style launcher with bigger engines and tanks, you could put huge payloads into orbit.

You pretty much need to get to struts in the tech tree, though. These things do not fly well without some stabilization. Also, in the OKRAG 32, I had to put fins on the bottom, as it had a tendency to flip over at about 15km.

Edited July 6, 2015 by RocketBlam

[RyanRising]

When I read the first bit of this thread I was thinking "...Great. You invented boosters.".

But as it tuned out, you made a rocket SSTO, and without the NASA parts. Fantastic!

[Dangerous_Beans]

When I read the first bit of this thread I was thinking "...Great. You invented boosters.".

But as it tuned out, you made a rocket SSTO, and without the NASA parts. Fantastic!

OTRAG is not quite boosters, it's using a cheap, simple rocket design as both the core stage and boosters.

i did something similar a while back. there was the Tiny Cat 1 that could get about 5t into orbit, using a long 1.5m tank (from a mod) and engine. then the TC2, which was a TC1 rocket with 2 other TC1 cores setup as an asparagus staged boosters. next one (Tiny Cat 3) had 3 TC1 rockets as a central stage, with 3 asparagus TC1 boosters.

i think the TC4 might have had a TC3 core with 6 asparagus boosters, in two stages.

from memory there were also heavy versions that used SRBs on the initial launch.

they were cool to design, but not practical in Kerbal logic.

@RocketBlam it would be cool to see what your rockets could do if you had them staged, either asparagus or sequential.

[RocketBlam]

@RocketBlam it would be cool to see what your rockets could do if you had them staged, either asparagus or sequential.

Well, yes and no.

I have no doubt that I could make a more cost-efficient launch system using staging... as I said, lower costs are not a feature of this get-up. But staged, massively-parallel rockets have been done in KSP, and frankly, they've been done to death. In beta, everyone was making these rockets, that were sometimes wider than they were tall.

[Sharpy]

The problem with this idea is that it doesn't scale all that well due to growing structural concerns.

The strutting for a 64-rocket system is heavier than sum of struts for four 16-rocket systems, and each of these is heavier than strutting of four rocket systems. The lift grows linearly while the structural costs grow exponentially. It's not a very fast growth and until a point it's not much of a pain. I'm fairly sure OKRAG-128 would be a total pain to hold together, and OKRAG-256 would simply not be doable because it would rip itself apart on the landing pad - or fail to lift off due to the total strut weight.

[Gaarst]

That sounds like a very Kerbal way to build rockets ^^

But, anyway, this type of design might be interesting, though not for larger payloads...

And, btw, due to the natural logarithm in the rocket equation, twice as much rockets do not mean twice the payload to orbit, unfortunately. So this might not be a very efficient design.

[problemecium]

...why is the diagram scale in nanometers?

[Laie]

...why is the diagram scale in nanometers?

because it's in nautical miles.

[Frank_G]

Can it be more kerbal, than adding boosters until it lifts? Cool

[jkool702]

That sounds like a very Kerbal way to build rockets ^^

But, anyway, this type of design might be interesting, though not for larger payloads...

And, btw, due to the natural logarithm in the rocket equation, twice as much rockets do not mean twice the payload to orbit, unfortunately. So this might not be a very efficient design.

I could be wrong, but I think thats exactly what it means...

Rocket eq:

delta_v = ve*ln(m_initial / m_final)

EDIT: I think what you may be thinking of is that doubling the rockets and leaving the payload the same will not double delta_v, due to the natural logarithm in the rocket equation.

doubling the amount of rockets and the payload:

m_initial --> 2*m_initial

m_final --> 2*m_final

new rocket equation:

delta_v = ve*ln(2*m_initial / 2*m_final) = ve*ln(m_initial / m_final)

Hense, double the rockets equals double the payload. Alternately you could think of shooting up two individual identical rockets with identical payloads, and then just strutting them together. Double the rockets and double the payload.

Note the above logic ignores strut weight, so doubling the rockets does result in just under double the payload, unless you use certain mods (such as KJR).

Edited July 6, 2015 by jkool702

[SAI Peregrinus]

because it's in nautical miles.

Which raises the question of why the altitude is indicated in nautical miles, which are only really useful for navigation along the surface of the Earth.

[martinborgen]

The soviet N1 was supposed to work in a kind of similar way. The same small engines would power all stages - though tuned for the altitude they were supposed to work in.

[Gaarst]

The soviet N1 was supposed to work in a kind of similar way. The same small engines would power all stages - though tuned for the altitude they were supposed to work in.

And we all know how the N1 turned out...

- - - Updated - - -

I could be wrong, but I think thats exactly what it means...

[snip]

Note the above logic ignores strut weight, so doubling the rockets does result in just under double the payload, unless you use certain mods (such as KJR).

Yep, you're totally right, my bad ^^

[RocketBlam]

It's actually quite interesting how little the TWR changes when you double the rockets, or increase the payload. I actually don't quite understand it. I guess it's because the payload is such a small percent of the total weight.

[Sharpy]

Yes, and becoming diminishinghly smaller too. Also adding more fuel causes that effect as initial TWR drops and dry mass rises, I once happened to make a rocket with four Rhinos that started with 1.00 TWR due to far too much fuel for the engine power. It was really cool to watch it hover over the launchpad after releasing the clamps, then after a good while it began rising really slowly and accelerated as it kept burning through the fuel.

[martinborgen]

And we all know how the N1 turned out

Well, to be fair, they did not get the resources to test the thing in a test stand first. I suspect it would have helped.

[Michaelo90]

It may not be an economical design if you just get it to space and leave it there, but if you save some of the fuel and slap on some parachutes you could deorbit and land it to get most of your money back.

[Laie]

It may not be an economical design if you just get it to space and leave it there, but if you save some of the fuel and slap on some parachutes you could deorbit and land it to get most of your money back.

How very Kerbal. In all seriousness, these boosters were quite simple and meant to be mass-produced. That was the key idea behind the whole design. The projected price was so low that recovery seemed barely worthwhile -- something to be considered "maybe later" if at all.

[RocketBlam]

It may not be an economical design if you just get it to space and leave it there, but if you save some of the fuel and slap on some parachutes you could deorbit and land it to get most of your money back.

The thought has occurred to me.