[1.8.1] Superheavy lifter design randomly plagued by phantom forces on atmosphere exit

[Starseeker]

I feel like I'm losing my mind, so apologies in advance for any rambling or excessively-frustrated wording.

So, to the gist of it: the upper stage of the test vehicle I have for a >100 tons-to-LKO lifter will, most of the time, start spinning out of control (frequently on multiple axes) as soon as it leaves the atmosphere. It's not the ascent guidance or SAS bugging out, since the RCS thrusters are firing as hard as they can to counter the motion; the only explanation is some sort of phantom force.

However, it's maddeningly inconsistent; I've launched the vessel completely successfully, reverted back to launch, and flown it again with no tweaks, and it's struck by the issue the second time around. I've tried using rigid attachment, shifting around the autostruts, etc; the only thing I could do is completely remove autostruts, but the vehicle is so large that it's dangerously wobbly if I do so.

And perplexingly, everything is fine until the moment I hit 85km (I'm using the JNSQ planet pack); in atmosphere, there's nothing amiss.

Anyone have any idea what might be happening? (The only modded part on the upper stage is the ReStock+ three-nozzle RCS block)

[jimmymcgoochie]

Pictures/video would help here, without actually seeing the rocket in question it’s hard to guess at possible causes. Have you tried a brief burst of time warp when you leave the atmosphere to kill the spin? It would also help to know all the mods you’re using and what version of KSP/DLCs if you have those.

Are there any errors in the logs? Might help narrow it down if there are.

[Starseeker]

12 minutes ago, jimmymcgoochie said:

Pictures/video would help here, without actually seeing the rocket in question it’s hard to guess at possible causes. Have you tried a brief burst of time warp when you leave the atmosphere to kill the spin? It would also help to know all the mods you’re using and what version of KSP/DLCs if you have those.

Are there any errors in the logs? Might help narrow it down if there are.

I'll grab some video in the morning (it's very late for me rn). I'd do the timewarp thing, but I have Persistent Rotation installed, so that's not exactly an option for me ^^;
Here's a list of all mods I'd think could be relevant (mods that affect game physics and/or do more than add parts I'm not using here):

Spoiler

• ReStock
• ReStock+
• MechJeb
• Persistent Rotation
• Kerbalism
• JNSQ planet pack

If you want, I can type out a full modlist alongside the video when I upload that.

As for errors in the logs: which logs should I be checking?

[jimmymcgoochie]

Player.log/Player.txt will have the most information, on windows it’s under C:/users/your user/AppData/LocalLow/Squad/Kerbal Space Program. The KSP.txt log file inside the KSP directory might help but it doesn’t have nearly as much information.

You could also try removing persistent rotation (unless you really need it) and launching the rocket a few times, which might help identify what part(s) are causing the spinning or prove PR’s involvement (or not) in the problem itself; disabling all auto struts to see if that helps; hitting F3 when the ship starts tumbling to see if something broke; quick saving and loading again when you reach space, if possible, to see if the problem persists if you come back to the ship; or unclipping all the parts on your rocket to make sure they can’t ‘collide’ with each other in weird ways that induce a spin.

You should also check that no parts have zero or negative mass, but that tends to have the opposite effect and make ships stay still when they should be moving. Try rebuilding the rocket from scratch and see if that has the same issue, it might just be a corrupted craft file.

A full list of mods would be useful, but check that you have the correct versions of them all.

[Starseeker]

Hmmm, I think I might have found the source of the problem. The 5m engine plate likes to tilt & clip into the fuel tank beneath it for some reason - I'll try remaking the rocket's upper stage, see if that helps

[Starseeker]

Well, removing persistent rotation, keeping physics timewarp to 2x or lower, and messing around with some struts on the engine plate all seem to have worked together to solve the issue. I suspect it's something to do with ReStock or ReStock+, tbh; asked if anyone was having the same issue on that thread.