Decouplers, girders and struts = funky

[ShunterAlhena]

Hi guys,

I created a rocket where I wanted the innermost ring to contain 8 boosters. However (using Rockomax parts) the most I could fit on would have been 6.

So instead of attaching radial decouplers to the main rocket and attaching the boosters to the decouplers (the normal way), I've attached decouplers to the main rocket, girders to the decouplers (to get some extra spacing) and the boosters to the girders.

However the rocket is unstable and so I also had to use struts to connect the boosters to the main rocket to make them less wobbly.

The problem: normally when a decoupler between strutted-together parts is fired, the struts disconnect (disappear) and the affected stage falls apart beautifully. In this case, however, the girders between the decouplers and the boosters apparently prevent KSP from noticing that the struts should disconnect, and so they stay put - they are broken apart a split second later as the booster tries to fall away, but this puts a spin on the booster and it crashes into its brother boosters, making the entire ship tear itself apart in a magnificent display of fireworks.

I've put hours of work into this project (3-ring Asparagus staged ship containing 32 boosters) and I'd really hate to abandon it.

Did anyone else encounter this issue? Any thoughts or recommendations on solving it?

Thanks!

[Kasuha]

It is not really caused by girders or anything. The game first explodes the decoupler, simulates one physics frame while struts are still in place, then removes struts. And what exactly happens with the decoupled part depends on how flexible the decoupled part is, and on the way how struts are drawn between the decoupled part and the rest.

In 0.23.5, part connections got a significant boost. That means you can have a lot of space between the decoupler and the place where you need to put a strut. That allows at least part of the decoupler's explosive force to be utilized in pushing the stage away from the rocket.

If you want to get rid of struts effect completely, you need to use another set of decouplers as anchors for struts.

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Edited May 1, 2014 by Kasuha

[NecroBones]

I've never run into this problem. I routinely use struts to stabilize booster sections that are mounted radially.

I had to do something similar, with girders etc, with the launcher shown below (it was an Eve ship), in which most of the center rocket is the interplanetary stage. I mounted 8 booster stages radially (as asparagus pairs), using girders on decouplers, and struts at various positions to keep it stable. There were struts connecting the boosters to each other, as well as to the main central body. Everything disconnected as expected.

I've also done asparagus lifters with 18+ radial boosters before, and had no problems.

Question: In your design, are you using the new 3.75m vertical decoupler in multiple places? There's currently a bug with that, where only the first one will disconnect properly in staging, and sometimes struts stay connected across those.

[mellojoe]

The problem: normally when a decoupler between strutted-together parts is fired, the struts disconnect (disappear) and the affected stage falls apart beautifully. In this case, however, the girders between the decouplers and the boosters apparently prevent KSP from noticing that the struts should disconnect, and so they stay put - they are broken apart a split second later as the booster tries to fall away, but this puts a spin on the booster and it crashes into its brother boosters, making the entire ship tear itself apart in a magnificent display of fireworks.

Did anyone else encounter this issue? Any thoughts or recommendations on solving it?

Holy smokes! I've been experiencing this EXACT SAME BUG. My struts are not auto-splitting when the decouplers fire, causing major explosions.

The solution I've found that temporarily works:

Just before staging, cut your engines. Then right click on the engine fairings and manually jettison them. Then stage. Then throttle up. This seems to help.

[Vanamonde]

Some pics of the ship might help diagnose the problem. (Also, moved to gameplay questions.)

[NecroBones]

I've never run into this problem. I routinely use struts to stabilize booster sections that are mounted radially.

BTW, don't take the above the wrong way. What I meant by that, is that since I do it routinely, it's definitely possible under the current version. And I'm curious as to why its breaking for you.

One possibility that has occurred to me:

Can you verify whether you still have control of the engines, right before you decouple the stage? I haven't seen this so much in 0.23.5, but frequently with larger designs in 0.23, I would see joints break in the center stack, and it wouldn't be immediately obvious. The struts would still be there, and since I wasn't throttling back the engine anyway (until it ran out of fuel on its own), I wouldn't notice that I could no longer control current stage.

If you're using gimbal-engines, you should still be able to see it wiggle when you tap the controls, even after it's spent.

I'm just wondering if a joint is breaking, but as far as the struts are concerned, it's still part of the vessel?