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Aaaargh, what am I doing wrong? (Spacecraft shaking itself to pieces)


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Okay, so I'm no greenhorn. I have at least three successful Mun landings, plus a bunch of landings that were close enough that the crew could at least get out and take a good look around the desolate wasteland where they would starve to death.

But since 0.16 came out, I've been trying and trying to get rockets to work, to no avail!

Now, as long as I stick to the old parts, we've got no trouble. But once I try to use the new range of parts, the big ones, suddenly I'm in a world of hurt. Even though I use struts liberally, the spacecraft shakes itself to bits, often at insanely low g forces!

WHAT AM I DOING WRONG?

Looking around at other parts of the forum, I have seen some gobbledegook about the stack decouplers being too weak. Is that correct? If so, how do I fix it? Assume that you're talking to someone who hasn't the faintest idea how to edit a config file or whatever (I'm willing to do so, but I'll need step-by-step instructions!).

Edited by Johno
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Go to "KSP directory/parts/decoupler1-2/part.cfg"

search for "crashTolerance" and change it's value to ~200

EDIT: On second note - If You have more than 2 decouplers along the main body of the rocket, don't be surprised to have control problems...

Edited by Serratus
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Well, this isn't RL. Anyway, so far I've managed to get into orbit by having all 5 main lower stage engine burn at the same time, and then decoupling the whole thing. Just keep an eye on Your g's. If You keep them in green zone, it works fine.

EDIT: So I just finished a successful mission to the Mun, and I'd say it's a good rocket. The orbital stage is underpowered so I supplemented with landing stage for orbiting and transfer as well as landing. The return stage was OK. So my only problem is staging of lift-off stage, and possibility of maybe exchanging orbital stage engines with something more robust.

EDIT2: Modified version.

[ATTACH]32431[/ATTACH]

Apart from those changes, just keep the g-force in green and You're golden :) Good luck!

Edited by Serratus
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When your craft shakes itself to pieces, look at the event log to find out which part broke first. Then strengthen that part with struts.

If you can't use struts, try a lower throttle setting at the time of the failure, and don't use SAS.

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>_< The Space Kraken strikes again...

I would say the Kraken has nothing to do with this.

This is very much an issue involved with the large stack decouplers. The small ones are fairly robust, for the weight they are made to hold, but the large ones seem to be made to hold the same as the small ones (strength and impact tolerances are identical). The only real difference is how much they weigh and their ejection force. As it is now, you could literally use a small stack decoupler wherever you use a large one and you would be saving yourself .45 tons per. Not only are struts your friend, but their placement really matters (don't attatch struts to decouplers).

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I've looked at the rocket and there seem to be three things causing problems.

1. The large decouplers won't take as much weight as they look like they should.

2. Long thin rockets tend to amplify forces which is why the capsule simply snaps off without the struts. Try building horizontally as well - there's nothing stopping you attaching stages with radial decouplers higher up the rocket.

3. The thrust is a little on the high side at times. It's not too bad, but keeping the speed down would help with the above two problems.

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Two give you the exactg answer that allows you to maintain your rocket design and know the mechanics, it comes down to the removal of internal collisions. At current, the structural connections on the large parts are a little weak, but the actual structure of the rocket itself outside of the mounting point react different. This is why you might find large rockets running alot smoother. The large decoupler itself is also a bit weak for the output of the engines. Much similar to what henge says.

My common re-inforcement to this is to use the small structural hardpoints (the non jettisoned ones) around the lower fuel stage. Use this to attach structural members to link past the coupler to the upper stage. Another thing to consider is the more complex fuel and thrust mechanics. The 2m high thrust engines often can be too much acceleration for a heavy rocket entering orbit. It sometimes helps to reduce your thrust to prevent wobble and structural collapse. You can do this by simply reducing throttle, or what I have done is fuel line link my outer ring of engines to my inner one. As I gain higher altitude, the outer tanks and engines run out and are jettisoned, the inner stage still has full tanks. Once in space, use the efficent small engines for your travelling. It might not be as quick, but you won't overpower your structure, and the increased fuel efficiency allows you to cut out some weight.

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I've looked at the rocket and there seem to be three things causing problems.

3. The thrust is a little on the high side at times. It's not too bad, but keeping the speed down would help with the above two problems.

Yes indeed. I've also noticed that keeping speed down helps alot.

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build a frame to hold parts of your rocket together during launch

<a href="http://imgur.com/hv4me"><img src="http://i.imgur.com/hv4me.png" alt="" title="Hosted by imgur.com" /></a>

Wow that station looks pretty awesome. Did you launch that using normal rockets? Could you be persuaded to upload a craft file? :P

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