Help with current rocket problems

[DucharmeHD]

I'm using the RSS, FAR, Real fuels, & real engines mods (the only ones i find relevant), and I've been trying to get off earth for 3 weeks and cant seem to do it. I want to go to the mun & do some science while exploring different biomes, so I need around 15k delta V.

I built this rocket the past few days & i'm trying to improve it so it will carry out the mission:

http://imgur.com/a/UWCT3#0

I started off with two boosters using procedual parts, they were using LOx/Ker, and the middle tank was using UDMH/N202. Then I switched to 3 LOx/Ker tanks in the middle, along with on the outside boosters. Then I tried to put two solid boosters on the side of that. The problem with all of them is they don't have enough Delta V, & they are way too big which causes it to start wobbling mid-flight regardless if i try to gravity turn or not. I'm scared to make my rocket any bigger (which would increase my delta V), but would suffer a harder to control rocket.

My first stage (the lander) has 4730 m/s Delta V for when I get to the mun. It will burn to circularize my mun orbit, & de orbit.

My second stage has 4000 delta V, it will be used to get an encounter from low earth orbit with the mun, nothing more.

This leaves me with getting the remaining delta V from my 3rd or 4th stage.

My 1st stage has 4,619 m/s Delta V combined w/ boosters. I need to get to 8600 delta V for my 1st stage. Maybe a 5th if necessary. That leaves me with an extra 3,981 delta V that needs to be added.

Well, if my rocket already has aerodynamic failures, it doesn't make sense to make it any bigger. When I just send my rocket straight up, without any controlling, it will start bending at the joint of the 2 & 3rd stage & break off. \

Also, i'm using this map for my delta v calculations: http://i.imgur.com/AAGJvD1.png

How do I go about getting the extra 3,981 delta V, all while maintaing a controllable rocket? Any help is greatly appreciated!

Edited July 3, 2014 by DucharmeHD
changed 3rd & 4th stage to 1st stage, which is now correct

[Taki117]

I will say this: That small connection between your payload and the rest of your rocket isn't doing you any favors. Also, if you can, mimic the Saturn V rocket (There's a reason Apollo did it that way) Unless this is a career mode ship, in which case, Explore Kerbin/Kearth/Earth to get as much science as you can to unlock more/better engines. You might also want to take a look at Novapunch or KW Rocketry for more engine designs. FASA is another one to look at for engine and rocket parts.

[DucharmeHD]

I currently have NovaPunch2, KW, & AIES engines installed. Primarily just engines from NovaPunch, and engines from KW & AIES but with various parts from both of them.

Yes, this is a career mode.

[Jimbimbibble]

You really need kerbal joint reinforcement for RSS to be playable or it will wobble to pieces as you have seen. Also, you probably need to reduce your TWR. 1.2 off the launch pad works pretty well and your second stage should be around 0.6-0.8. Your first and second stages should each have about 4500m/s.

[DucharmeHD]

Well as of right now my second stage is used to get an encounter with the Mun, which requires 3,267 (something like that) delta V. So i need 9,400 delta V in addition to the 3,267. I could increase my second stage to 4500 delta V, which would require 8167 delta V from my first stage. I already have 4619 delta V for my first stage, so that would then require me to get an additional 3548 delta V. Do I just increase the size of my rocket? But how do I make it aerodynamically stable? I read something about CoL & CoM.

Edit: I'm downloading Kerbal Joint Reinforcement & will test that out. Also, I realized that in realism overhaul I needed kw_gimbal, I also am downloading that. That explains why some engines would go whacko when lifting off the launch pad, thus having to disable the gimbal totally.

Edited July 3, 2014 by DucharmeHD

[Jimbimbibble]

I think we are confusing terms. When I say 1st stage, I mean the bottom stage (first to light). So what a moon lander looks like it 1st stage=4500m/s, 2nd stage=4500m/s, 3rd and 4th stage do the rest. What I do is have a service module with enough to get from Leo to low moon orbit with the lander and return without it. The lander has about 4700m/s.

[Hodo]

You really need kerbal joint reinforcement for RSS to be playable or it will wobble to pieces as you have seen. Also, you probably need to reduce your TWR. 1.2 off the launch pad works pretty well and your second stage should be around 0.6-0.8. Your first and second stages should each have about 4500m/s.

This is the best answer.

You will need KJR to make larger rockets actually work. And your TWR is to high on launch. Most of the best launches I have had have been with a TWR around 1.2-1.4 on launch. Much higher then that and it will push through the rocket.

[Tortoise]

Just add an SAS to each stage and u should be able to control it well.

Add some more big boosters, maybe 2x 1 in the front and 1 in the back. And keep the ones on the left and right.

[lammatt]

generally, if you want >10Gm/s of dV at launch,

you want to have a very light payload so that it's easier to build.

see... dV is a log function of mass(wet)/mass(dry), it's exponentially harder to get more dV w.r.t the rise in dry mass

----------------------

secondly, how about refuelling in a low parking orbit before going elsewhere?

if you manage to push your 1st stage lifter into orbit to begin with, you ditch it.

refuel it, and boom, off you go, here's about 4km/s worth of fuel.

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but if you insist on have an extra 4km/s at launch with the same payload,

you'll probably want to use those crazily efficient propulsion methods, like the ion engines, or nukes in your upperstages in expense of the thrust.

thrust doesnt mean much in space anyways... unless your encounter is very short or your relative velocity is very fast (say for example you are going to moho)

Edited July 3, 2014 by lammatt

[Vigelius]

I agree with Jimbimbibble and Hodo with regard to your TWR. Having any more than you absolutely need in any given situation is just making life hard for yourself.

Your design is rather spindly. Don't be afraid of a shorter, fatter rocket. That will help structural integrity of the stack, and also makes it easier to cluster engines.

For aerodynamic stability, I like to put tiny fins at the base of my second stage, and then at the base of the first stage I put whatever size fins are neccessary to put the CoL very close below the Com. Early on you get nice control to start your gravity turn, then as your first stage depletes the rocket becomes more and more stable.

Only use SAS in the first two stages if you're not going to touch the controls! For example, launch with it on, turn it off to begin the gravity turn, and then use it very sparingly on the way up. Turn it off before you make course corrections. It has a habit of overcompensating for wobbles when it straightens up after a manoeuvre, which builds into a positive feedback cycle and shakes rockets to pieces! If you see an oscillation beginning, knock off SAS pronto.

You might get some design inspiration from this challenge.

[DucharmeHD]

Okay, thank you for the input. So i'll work on getting my first stage to 4500, second stage 4500, and third stage will have around 4000 to get into a munar orbit. Then my 4th stage will be my lander.

[DucharmeHD]

The problem with refueling is I don't have any fuel tanks up in LEO. Nor do I care to go through the process of doing that, at least not right now.

Unfortunately I don't have ion or nuclear engines right now due to my tech tree

I'm going to try what jimbimbibble was describing earlier about how the stages should be set up.

[DucharmeHD]

If it helps with any designing of the rocket, here is what my lander looks like: It has 5,666 m/s delta V in vaccum.

http://imgur.com/a/2TRW3#1

Equipped with landing legs, science experiments, communitron, 2x3 solar panels, A ladder, and procedural parts to attach the legs to that will help them extend further than the engine.

[DucharmeHD]

Also, is AIES' "gravimeter" the same thing as squad's Negative Gravioli Detector?

[DucharmeHD]

You really need kerbal joint reinforcement for RSS to be playable or it will wobble to pieces as you have seen. Also, you probably need to reduce your TWR. 1.2 off the launch pad works pretty well and your second stage should be around 0.6-0.8. Your first and second stages should each have about 4500m/s.

The best I can get with all my engines on hand, is either a TWR (for my second stage) of 1.01, or .57/.58ish. Which one do I take?

Edited July 3, 2014 by DucharmeHD