Drag and wacky wobble in space during transit

[daffy]

If this is an old topic, forgive me, and I'd be happy to read the discussions on it if there is a direction or link available.

It seems to me that there should be no drag in space, which would cause a craft to wobble or twist in transit. I'm trying to move a large object, (station) from Kerbin orbit to the Mun. It's got large engines which should be more than enough for the delta v, and a ton of fuel. The problem is, I think, that it has some appendages or docked sections that protrude non-symmetrical along the main core. Anyway, when I begin the maneuver, and reach about 1/4 throttle on the burn, the craft begins to wobble, eventually into a slow out of control twist which takes it off course, and impossible to correct. The only way I've been able to make any progress on the trip is to literally, hold the throttle below a quarter thrust and maintain constant counter force on the RCS.

I know it's not symmetrical, and it's not completely balanced...but would that have a real effect in space? I honestly don't know the answer, and am by no means complaining or griping about the game...at all. I love it. I'm just curious if I am missing something? Or is this somewhat appropriate behavior for a very large craft like space station size? Or is it an aspect of the game that I have to just play around?

Thanks!

Edited September 8, 2013 by daffy

[Yibbachester]

it torques due to the trust. even though there is no resistance, the parts will still flex badly when the main thrusted section moves. my suggestion is to undock all the parts and send each to the mun orbit via rockets sent into space to take them there

[Johnno]

That's not from drag, as soon as you're out of the atmosphere (slightly over 69km on Kerbin) your craft won't experience any drag. It's due to an imbalance between your center of mass and your center of thrust. And if your ship is unbalanced enough then gimbal and reaction wheels (or even RCS) won't be enough to hold it steady.

It's not just an "aspect of the game" but real physics.

[lumpman2]

If you're using normal-sized docking ports, then yes, it will wobble even on 1/4 throttle, especially if your have a particularly strong engine. Space stations aren't really designed to move around a lot (unless you design it that way, of course ) Usually if you want a space station around the mun, you take another core to the mun and construct it there. Like I said before, you really can't move them around all that much if you don't make it that way.

[daffy]

Makes a lot of sense. Thanks for the response.

The 'Station' I guess, if I call it that, wasn't really intended to move anywhere. I just kept adding stuff to it over the past couple of weeks, and then today thought..."Hey, there's a big engine there. Wonder if I can push it to the Mun."

[Captain Sierra]

The trick for movable space stations is easy reconfiguration. You'll want to place it in a giant line (or balance it if you have multiple of the same module to reduce length). In said giant line, it is more stable to pull rather than push. To do that, you'll need to disable gimballing on the puller engines since KSP does not yet reverse control on engines in front of the center of mass.

[SRV Ron]

Gimbals and reaction wheels can cause shake as they attempt to counter imbalance. You want to see a real bad example of this, undock an MK-1 capsule for reentry and watch how bad it shakes when the SAS is turned on.

[Awaras]

If off-center thrust DIDN'T cause stuff to pitch off course, then RCS thrusters wouldn't work at all.

[daffy]

Well, I took the whole thing apart and reassembled it into a giant toothpick, about 100 meters long!! Fortunately, I've gotten accurate enough with docking, that I have had plenty of RCS to work with and remaining in order to reconstruct it. After the information, and discussions, I've decided to pull it to Duna and reassemble it there. Maybe I'll try to set up some sort of a relay network for my RemoteTech, and use it as a big hub. It was actually too long to push, so I thankfully had a large tug already built that was able to launch and hook up with it. There's four LV-N 60's on the tug. I know it's going to be a slow and long trip, but I think it should work. We'll see. Thanks a ton for the comments.