I need stability help.

[sneezedr424]

Hello all!

I use mechjeb to get things into orbit, and I've been recently been trying to get communications sattelites at about 100 kilometers. My issue is, that once I get in the air, my ship tends to slip sideways. I tried adding extra rockets to maintain stability, but to no use. Can anyone help me out>

Thanks,

Sneeze

[Serratus]

Do You have SAS and ASAS on board? If that's not enough, add winglets, replace some engines with gimbaling ones, add more power (or indeed take some power out), etc. Not much useful can be said without at least a picture...

[sneezedr424]

Gimbaling engines? I've never heard of those. Sorry I'm still kind of a noob >_<

[Serratus]

Look to parts description in VAB. You will see its statistics. There should be "Thrust vectoring: Yes" and under that "Gimbaling range: [something]" That means that this engine can change the direction of the burn to steer the rocket. With that, the ASAS has WAY easier time keeping the ship on course.

EDIT: What @EndlessWaves wrote beneath.

Edited August 26, 2012 by Serratus

[djnekkid]

if you have novapunch, try makeing something small, instead of big

Im currently launching the following into a 7150km orbit:

1m nosecone

remote control with attached mechjab and 5000km antenna

the small white fueltank with KSP written on it

some tiny engine, 35newton thrust

the gridded decoupler

1x2m fueltank

aerospike engine

the onboard sas is more then sufficient

[EndlessWaves]

Look to parts description in VAB. You will see its statistics. There should be "Thrust vectoring: Yes" and under that "Gimbaling range: [something]" That means that this engine can change the direction of the burn to steer the rocket. With that, the ASAS has WAY easier time keeping the ship on course.

Only when those engines are burning though, they'll do nothing when another set of engines is firing.

[sneezedr424]

Thanks guys! I really appriciate this. I'm gonna go download NovaPunch.

>_< nove punch is unavailable to download

Edited August 27, 2012 by Navy4422
merged

[Serratus]

Hehe. Don't listen to those old cynics. You DON'T need to DL anything. Stock parts have everything You need, to stabilize Your rocket.

Ps. Just a friendly remainder that mods asked that ppl don't double post, instead editing their previous post.

[Nori]

One of the easiest ways to add some stability is to make sure you have a AdvSAS module and then to put on control surfaces (Canard or Winglets).

Here is a rocket I made recently that was able to do a Mun/Minmus landing and still make it back to Kerbin with fuel left:

http://kerbalspaceprogram.com/forum/showthread.php/18278-First-Mun-Minmus-landings-Mostly-stock-rocket

Notice the excessive amount of Winglets I use. I don't really need that many, but what the heck..

Here is another design worth looking at:

http://kerbalspaceprogram.com/forum/showthread.php/18062-First-multi-moon-landing?p=246499#post246499

Notice the Pyramid sort of shape? You want the rocket to be smallest at the top and largest at the bottom, unless you add a lot of control pieces. I would post a pic of a crazy satellite I somehow managed to get into space, which was top heavy, but I'm not at my home computer.

It is important to realize where the center of gravity is, and that it will change as you use fuel. Also like people said, a thrust vectoring (gimbaling) engine is rather important, especially early. You can get around it with a lot of control surfaces and SAS, but usually thrust vectoring engines are easiest.

There are other great designs in the spacecraft exchange. You don't need to copy them, just look to get some ideas on general design concepts.

Edited August 27, 2012 by Nori

[sneezedr424]

I always figured that the stock engine with thrust vectoring wasn't strong enough to lift my rockets. What do you think?

[Serratus]

The difference in thrust is negligible. TBH I only use the big engine on heavy cargo rockets... Aside from those cases, it's always the small ones.

[Markus Reese]

I use a combination of engines to create the initial lift on stock parts. All 2m engines have thrust vectoring. On the small engines, I used for initial stage a tricoupled stack of tanks with the -30 thrust vectoring. On those, I mounted another set of the same with a radial decoupler. Crossfeed the -30s outside to the inside.

I also mount to each of the tri coupled two stacks of the -45 non thrust vectoring engines. Initial launch has the outer engines firing. Fuel lines crossfeed from the -45 engines to the -30 booster stack. Use solid boosters as well depending on your satellite weight. With enough tanks, stack of 5 I find works well, the -30s will get you into a thinner atmosphere. When they jettison, ignite the inner ring of engines.

It should be able to get you into orbit if my calculations are correct in my mind. It is similar to the booster staging I use on my munar ones, but mostly I have used the 2m in combination with the 1m parts to lift my heavy and overly complex designs.