Why Is This Rocket MisBehaving?

[Diche Bach]

Before installing mods, I was doing pretty well with getting in to orbit, doing fly-bys, etc. Now I seem to be having problems of the most basic sort.

For example, any idea why the throttle on this ship "Sputnik I Rocket." would just cut to zero after a 20 or so seconds in flight and then be unresponseive. It is designed to be able to complete the "Beta" mission in "NT Space Program" mission pack for Mission Controller, and also to be able to do the "Sputnik II" mission in the Stock mission pack for that plugin. These missions both require attaining a stable low orbit while carrying 3 communotron antennae plus one each of the science instruments and then safely returning to Kerbin (thus the parachute and the lander legs to break the fall a bit).

Also once I get up to about 10km it becomes uncontrollable. I don't get it. It seems like this (except the RT and lander stuff on top) is largely the same type of rocket I've launched dozens of times no problemo.

Mods that are installed (though I'm not trying to "use" any of the autopilot or flight computer features on anything):

B9 Aerospace Pack R3

Chatterer

HOME 1.03

Ioncross Crew Support Plugin

Kerbal Alarm Clock

Kerbal Engineer Redux

Kethane

Lazor Docking Cam

Mechjeb 2.09

Mission Controller

NovaPunch 2.02

NT Space Program

Orbital Construction

Procedural Fairings 2.2

Protractor

RemoteTech

Sub-Assembly Manager

TAC Fuel Balancer

Appreciate any ideas on why my ship won't fly and/or any general helpful advice on ship design.

Here is a short clip that shows what keeps happening when I try to get this into orbit.

1. At about about ~20 seconds in, the throttle just cuts out and then won't respond.

2. Once I jettison the solid boosters about about 35 seconds, the throttle becomes responsive again.

3. From about 45 seconds onward you can see me struggling to keep it under control, it is unresponse to pitch commands using the keyboard and wants to roll west and south.

4. Finally at about 1:00 I try to get it under control with the RemoteTech Flight Computer but even that does not work.

Is it just that it is top heavy? But then why the weird thing with the throttle cutting and and staying unresponsive for a while?

ADDIT: also of note, it has two command pods on it: one at the top for the final probe vehicle, and one about midway (nearer the starting center of gravity). In the video I launch it without transferring control to the lower command pod, but in repeated tests, this doesn't make any difference. Even if I change to "Control From Here" at the lower command pod that is closer to the center of gravity, it still exhibits the same uncontrollable wobble westn southwesterly after it gets about a minute up.

Edited August 6, 2013 by Diche Bach

[Johnno]

Pictures and/or a list of mods that specific craft file uses would be helpful.

[Xiphos]

I'm going out on a limb here but I'd say your probe is running out of power. Stick an RTG on there and you should be good to go.

[Diche Bach]

Pictures and/or a list of mods that specific craft file uses would be helpful.

Mod list is included in first post now, and a Youtube clip too.

I'm going out on a limb here but I'd say your probe is running out of power. Stick an RTG on there and you should be good to go.

Hmm, don't think so. Its got some solar panels and a 200 battery which should last it for a good 10 minutes or so.

[crparris]

if you hit F3 to see the status report after you lose control, you will most likely see that there was a structural failure decoupling your rocket stages (causing you to lose control of the rockets below that stage.)

i get this issue with taller rockets

[Vanamonde]

1) At launch, most of your thrust is coming from SRBs, which do not gimbal to aid in steering. 2) You hit physics warp while under thrust, which causes forces to be enacted in chunks rather than smoothly, which is when your rocket starts to get squirrelly. 3) After the SRBs run out, your remaining rocket engine is much to small for that ship (notice how your speed starts dropping?), so although it is a gimballing engine, it's not applying enough force to hold you straight. 4) Using RCS in atmosphere is relatively ineffectual, and a big waste of RCS fuel because control surfaces are more effective and require no fuel. So, replace the central engine with a more powerful version, don't use warp during a launch, and leave the RCS off until you get to space.

[Diche Bach]

Thanks guys!

[BubbaWilkins]

You have mechjeb's limit acceleration toggled which is passively active even when you are manually flying the craft. That's why you can't adjust your throttle while the boosters are active. Your main engine also appears to have too little thrust and/or gimble to keep you going straight up and you're going too slow at 50m/s for your fins to to control the craft.

Open mechjeb's ascension guidance and disable "limit acceleration". Then try launching again. This time, you should have full throttle for the entire first stage and enough velocity for your fins to work correctly.

Edited August 6, 2013 by BubbaWilkins

[Diche Bach]

Thanks Bubba!

[rpayne88]

Are the communitrons extended? That may be causing remote tech to cut off spacecraft control.