Space station wobble

[Khalani]

So I wanted to put some fuel tanks in space and thought I connect them very simple.
http://steamcommunity.com/sharedfiles/filedetails/?id=1179191940
Everything was fine, I was in high orbit, nothing happened and then I tried to decouple my engine at the back (right side). Everything went south and after a few second those tanks began to wobble more and more until I was doomed.
http://steamcommunity.com/sharedfiles/filedetails/?id=1179192143

So why does a simple decouple affect all those tanks? Decoupling my cockpit (left side of those tanks) works fine without any wobble.

[ray.mcdonough]

I'm guessing you're working without 'autostruts'. Good luck with something that big.

[GeneralVeers]

Originally posted by DaFG Khalani:

So why does a simple decouple affect all those tanks?

The SAS system is the most likely culprit. Decoupling almost always introduces a small force to the mothership. If the SAS is turned on, it will see the ship wobble off course a little, and try to correct it. If the ship is floppy, the correction will cause part of the ship to wobble too far in that direction, and the SAS will see that and try to correct in the opposite direction. If it has to correct with more force than the first time, a runaway seesaw kind of deal can result.

Try turning the SAS off and see if the problem goes away.

[RoofCat]

SAS isn't even on in that picture.

You can try to reduce decoupling force in VAB.
Sometimes ships don't like loosing the root or change "control from here" spots suddenly.
Why don't you attach struts to tanks instead of size adapters
Why don't you actually strut tanks to each other instead. Center is light, kind of irrelevant and those struts run with a lot of mass leverage at bad angles. You have "star" while "box" type struts would create much more sturdy construction.

Parasitic swinging starts in most cases when some part is experiencing forces above its limits.

You can only guess which part is it in your construction. It doesn't break immediatelly except you failed extreme, but it can't control the forces either. One good example is building too heavy plane on too small wheels (and too close together due to how mass leverage works). They will start to bounce just placing the craft on the runway until it explodes because wheels and springs get compressed beyond their limits. Add larger wheels with more kN in description and it won't.


You don't need those construction elements in the middle. Build one fat tanker instead with more tanks attached. You can still build it like a star of course with fat core, while it is not too smart anyway - star makes mass move outwards, which introduces more leverage for any inertia. It looks cool in space movies, but rather won't be used for anything ever. Because it makes the construction worse. Design has purpose, intent, function. Art not so much.

[Khalani]

I'll test that autostrut thing when I get home.
I know that it isn't the most stable design, I made it for the looks like that. I wouldn't complain if that wobble would have happened right away but simply because decoupling the end causes it was the reason that made me sigh. I've already tried to stabilize it with time-warp or decouple the front and back together but I think I just wasted money there and have to redesign it.

[Jupiter3927]

You may have summoned the Kracken.
http://steamcommunity.com/sharedfiles/filedetails/?id=1179176411
Shake some autostruts at it and it should go away.

Autostrut is an advanced tweakable option and you'll have to go into the main menu game settings to enable them.
They're unlocked in the career and science sandbox modes when you get regular struts and always enabled in sandbox mode.

[RoofCat]

btw best tanking solution for Kerbin orbit may be heavy SSTO planes. It is rather easy to build one for 50..100t orbital fuel left. Which is quite a lot for all transfers imaginable. Somewhere above 150t payload on orbit is the limit for planes. They just break apart themselves on runway or during turns in atmosphere due to heavy mass. You may try, but it will be hard and not very comfortable. My heaviest MK3 SSTO delivers around those 150t. While the other one with half that is 3 times better to fly and easier to design safe. A plane can deliver up to half of it's launch weight as payload to LKO.

Or just park some mining asteroid there.

The thing is, you have fuel volumes onboard which would be needed for launch (~600t tanks). While upper stages need just 1/10 of that or less. And the cheapest way to get extra fuel on orbit is RAPIER plane.

You can actually build Kerbin-Laythe or Kerbin-Duna orbital express with permanent inflatable heatshields on. And just tank them on both ends with landable miners/ssto's while also transfering crew. Very cheap and efficient solution with easy capture.
Except there is not so much to do on those planets to build one and it would require docking on both ends.

[doum]

i activate sas and deactivate it many time. i try to do that at the right time so the station get more and more stable. not the best. after that i didnt built big station. didnt see the point of doing so. So, doing that might work but it aint easy. you will have to do that each time. :(

[Khalani]

Autostrut solved it but I think I'll build a new one anyway since I don't wanna get a surprise later on. So what should I try to avoid?
You said low mass of at the centre is bad, what about girder in general? Are they bad to connect different parts of a station?
Should I also reduce docking ports to a minimum? For example, I could shoot every single part of a station seperated and just plug it together with docking ports or I can build one huge thing and try to get it in space. What's better?

[Jupiter3927]

I played with multiple docking ports to make my stuff more stable.
It's possible to connect the same 2 ships together with more than 1 docking port.
More connections = more stability.
Bigger docking ports = more stability too...

Good luck docking all your ports together at once though.

About girders and stuff...
I only ever had the Kraken attack when I was using girders and I-beams.
They connect 2 parts together but it's a very small connection.
Use struts with your girders and it should work.

[Chibbity]

As far as autostrut goes; be sure not to use "heaviest part" or "root part"as that can change in flight and cause issues. I usually consider "grandparent part" to be the safest.

In general low part count and fewest number of docking ports you can get away with is best, if for no other reason than performance. Try to avoid putting very heavy things way out on the end of a noodle, even in space this is a problem. (Although autostrut properly used should negate it.)

A single piece station will be sturdier, but harder to launch. Neither way is "right" it's really up to you to decide which is better.

[Astronaut]

Use struts and wider docking ports.

[A Terrible Modder]

Originally posted by Astronaut:

Use struts and wider docking ports.

or use 3 small docking ports

[Astronaut]

That's hard to dock and could be glitchy

[A Terrible Modder]

Originally posted by Astronaut:

That's hard to dock and could be glitchy

or strong

[Jupiter3927]

Originally posted by BOOMH34D$HOT:

Originally posted by Astronaut:

That's hard to dock and could be glitchy

or strong

Or both.