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Upper Stage spinning


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Hi fellow KSP players,

Im a bit at a loss here. My upper stage starts to spin.

Here is my setup:

Orbiteter

Decoupler

1x FT A (Fuel Tank)

1x FT B

1x FT C

1x Engine,

I think the problem is that Fuel is sucked out of tank A so it is with the payload and orbiter that tank A gets lighter and becomes a pinpoint so to speak etc. How could i fix that ?

http://imgur.com/DC0rrRk

The Tank with the Info is tank A.

Thanks for hints :-)

ManuxKerb

Edited by ManuxKerb
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I think the main problem is that all the atmospheric drag is happening on the upper stages. That's where most of your mass is, and remember the game calculates drag as a function of mass. So especially when the lower stage tank is near empty, the drag vector is like a string pulling the top part of your ship towards the ground.

In other words it's like you built an arrow and put all the feathers on the tip.

You may be able to fix this by putting some fins on the bottom of the rocket... that will give you more drag on the back end and help to keep the ship pointed in the right direction. But ultimately I think you will have to redesign the upper stage so that the drag from all those hanging bits is managed. Moving everything closer to centerline may work... if it were me, though, I would launch those big rovers separately and assemble the thing in orbit. Good luck!

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Ah! Well, in that case you may have a center of mass/center of thrust problem. Try this: in the VAB, pull all the lower stage parts off until you are left with the ship that spins at 70-100km. Right-click on your tanks and adjust the fuel to whatever levels you have when the problem occurs. Also right-click on any engines that do not get used when the problem occurs, and reduce their thrust to 0%. Now when you click the icons in lower left of the window to display center of thrust and center of mass, you will see how the vectors line up at the critical moment in your flight. If they are not aligned, then that will explain your spinning and you can move things around to avoid the problem.

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Wow super expained and i learnd a lot, i did not know many of those things! Thanks very much, i will see what i can do. At the moment i try to pump fuel into the tanks to balance them but rocket still in flight, so dont know if this could work.

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Hi

Actually not :-( I just tried it. And i could not see anything not alligned. I was to fast with the solving :-)

See new pics. Any other ideas ? I try to disable crossfeed and pump the fuel around... We will see if it works

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On that picture is this the craft in exact configuration causing you problems? If so, why stage 5 has 5 engines? Are you sure you dont have 6th engine misplaced in later stage? Also are these engines above your center of mass? If so, they are gimbaling wrong way. KSP always assumes engines are bellow COM. Lock up their gimbals and try again. Impressive stack of equipment. Good luck.

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Yes thats the config. Yeah these rovers are basicly build out of tracks and science enquitment :-) Stage 5 has only 5 engines. I think this is enough. If staged the engines are not above COM only when the last booster stage is active but then the engines are off. Thanks

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Ok my solution with fuel punping did not work, but i found out, that the problem is that the COM goes to much to the front and ifi do not stage and one fueltank stays full as weight it works quite good. Now im going to try TAC Fuel Balancer and i will put one tank as weight. Also adding some boosters for a bit of a kick in orbit but i think they will not be so efficient.

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