...keep my radial rockets from colliding with the core stage during staging.

[EndOfTheEarth]

I've been working on a new vehicle for the sake of preparing myself for interplanetary flyby missions, but I noticed that with the present vehicles, like several other vehicles I've had in the past, my radial boosters seem to collide with the lower end of my core stage during flight, which either blows up my rocket or forces a mission abort.

Here's the rocket:

Here's the detail of the lower part of the staging, showing the positions of the rockets and decouplers:

Have I been doing something wrong in my design? The ship file is attached.

Additional information:

1) I use MechJeb as a tool, not as a crutch. I got myself all the way through targeted manual Minmus landings before I downloaded it for the first time. I'm used to MechJeb not acting smart during staging, and as such, when the accident happened for the first two times, I shut off MechJeb and attempted to fly the entire launch manually. Same thing happened.

2) In both manual and mechjeb-guided flights, the rocket was flying vertically during staging. It was NOT turning or rotating.

3) The staging is set up so that two of the radial rockets drop off first, then the other two. Staging occurs after the cutoff of the first pair of radials. When this is occurring, the core and two remaining radial rockets are at full throttle, and the two empty radials are not firing at all (as they are empty).

4) The ship is flying in .16. The only mod or plugin I have is MechJeb, which is one piece up near the command module. The rest of the rocket is stock parts with stock settings.

[ForumHelper]

I had simillar issues with my rockets. Replace your radial decouplers with the other ones and add struts(a lot of them). This usually allows you to drop used parts without blowing your rocket up. This particular radial decoupler works for boosters but is really bad when you use it to detach huge used stages.

If you have enough dV in this stage you can go full kerbal and add 2 boosters that'd be perpendicular to your rocket part(s) which you want to drop in such a way that the smoke goes inside your ship and fire them seconds before detaching;) Works pretty well but creates a LOT of smoke.

Edited September 8, 2012 by ForumHelper

[Xenotheos]

If I understand correctly, one of the outside tank stacks is colliding with the main body. What is likely happening is that the outer tanks are being released mid or late into the gravity turn and the main body is between the outer tank and kerbin so when gravity acts on it they collide. I had this problem as well, and what I did was rotate the rocket 45 degrees when it gets to that stage of the rocket, and I was using mechjeb at the time but was still able to get it rotated there easily.

[Equidox]

I had this problem in the last few day more than enough. I have no idea why it didn't happen before o.O

The main problem seems to be that the "big" decouplers (the one that you are using) are too weak to push the Boosters away, the boosters will turn to the core and "eat" the middle stage.

To solve that i used the decouplers for the smaller parts, works the same but they are a little further away from the middle stage. If that doesnt work, there is also a mod with 5 sec boosters to mount horizontal on the boosters. they will push them away from your middle stage. i use them quite often for bigger rockets, hate it to get hit by my own debris xD

hope i could help you

[Vanamonde]

There are several things you can do. Add a little more weight or drag to the outside surface of the discarded boosters, toward the bottom, so that they rotate away from the ship when discarded. Or place additional decouplers to throw them away with more force. Some players have advised rolling the ship to throw the boosters away with centrifugal force. You can put spacer pieces so that the outer boosters start a little further from the inner rocket to begin with. Or my most effective response, which would be to move the outer boosters down further so that they just don't overlap as much. Or some combination of these.

Incidentally, are you piping fuel from the inner rockets to the outer ones? That would keep them running longer, but diminishes the benefit of discarding the booster when its own tanks are empty.

Edited September 8, 2012 by Vanamonde

[2008dragon]

Do you mean that when you're in orbit, the bottom part of the rocket crashes into the command pod? I tested your design and that is what had happened. I think the problem is that the ASAS, decouple, and mechjeb unit are smaller parts, and cannot handle the 1200 thrust of the largest rocket.

Try putting the ASAS where the parachute is and put the parachute(s) on the side of the pod. Also, use the larger decoupler if you want (it dousn't have much better stats than the smaller, but it looks better ). One more thing, you might want to put a MechJeb Ar202 Case on the side of the rocket instead of the 1m unit like you have there. It is smaller and weighs less, so more delta-v

Edit: 3 other people just posted lol

[Vanamonde]

I think the problem is that the ASAS, decouple, and mechjeb unit are smaller parts, and cannot handle the 1200 thrust of the largest rocket.

I don't know about mechjeb, but I use this configuration on all my landers, without a problem. Large or small decouplers, ASAS, and RCS tanks all stand up to the load, with the help of a few struts.

[EndOfTheEarth]

@Xenotheos, 2008dragon: To reiterate. The ship was flying vertically relative to the surface of kerbin (Heading 000deg). No gravity turn or orbital mechanics; I hadn't even gotten into orbit yet. Thanks for bringing the capsule bit to my attention though.

@Vanamonde: The setup is designed (I'm pretty sure) so that the fuel is drained from the first booster pair into the second booster pair, and from the second booster pair to the core rocket. Otherwise all my rockets would have shut off at the first radial-rocket burnout. Thank you for the suggestions though, I'll try some of those first before I redesign.

@ForumHelper: About how many struts and radial decouplers would you recommend per radial rocket?

[ForumHelper]

This works pretty well. Looks like it shouldn't though;)

I use 3 or 4 rows of struts per stage and one row of decouplers. Sometimes more but that depends on how much weight a stage has to carry.

Edited September 8, 2012 by ForumHelper

[EndlessWaves]

I tried your test machine but on three flights it worked perfectly each time.

However, observing it's behaviour it does seem to flex a bit around that smaller engine so that may be causing the collisions. Unfortunately there are no large stock non-vectoring rockets so you can't stop it entirely but a couple of sets of canards placed along the central column may reduce the flexing enough to allow the boosters to drop clear with more reliability.

[TheProdigy]

Put decouplers on your decouplers

Gives it some more space from your main ship lol.

[Pirate]

I think the problem may be that the 'boosters' are miss weighted and is causing them to spin once being ejected and colliding with the main core, what you could do is add stabilizers to the top of the boosters and that may help...

[Zephram Kerman]

This will sound really weird. Sometimes loading a .craft file changes something, so that a previously perfect design starts wobbling and exploding all over the place. If it happens to you, try this:

• pick the first part in order to remove the entire rocket from the command pod,

• release that assembly so that it becomes translucent and floats in the VAB,

• pick it up again,

• reattach it to the command pod,

• return to the launch pad...

• Stability!

[Punk]

I use a similar first stage to yours for heavy lifting, the only difference is that i use nine liquid boosters mounted in a 3x3 square configuration. My four corner boosters were impacting the others when i dropped them (burnt out, vertical and stable). I didn't want to move them down for stability and asthetic reasons so instead i used parachute modules mounted out from the base of the boosters on the long wing part to pull the spent parts away from the live ones. With a bit of tweaking i managed to get it working nicely, you have to fire the parachutes and let them drag for just an instant before firing the seperation charge things. Also had some more parachutes closer in near the top of the stack. Im away from my comp at the moment so i cant post a craft file for my rocket. I also like to think that the parachutes also stop the dropped parts falling onto some green engineer at KSC too.

[Vanamonde]

I tried using chutes that way, but they just ripped off. There's some limit to how much speed or force they can handle.

[Punk]

Could also try placing more seperation charges lower down? Not sure if it actually works but it seems like even if they arent connected properly they can still impart some force to clear parts. If your rocket is still travelling straight up the trick is moving it away without kicking the bottom back in.