Asteroid tutorial mission #1: engine imbalance?

[ROXunreal]

The tutorial mission where you have to intercept the asteroid. After your lower stage with the nuke engines runs out of fuel, the upper stage with the four Rockomax Mk55 engines spins around like crazy when you increase thrust, making any intercept impossible. I double checked that all the engines are active and thrust limiters set to 100%

[Anquietas314]

I think you've found a "bug" with the tutorial; the design you're given has the engines placed in a way that their exhaust hits the solar panels, causing the (slight) tendency to make the craft spin. If you enable SAS it seems to be enough to counteract it, though the severity will depend on the exact orientation of the panels and so on.

Possibly related: http://bugs.kerbalspaceprogram.com/issues/3887

Edited January 2, 2015 by armagheddonsgw

[ROXunreal]

For me SAS intensifies the rotation, weird. Without SAS it leans slightly, with SAS it literally spins like crazy, at first I thought I might have collided with the lower stage and destroyed an engine, but nope. In any case it's not a crucial thing for me as I already know how to do things in those two tutorials, it's just that I wanted to finish them because they're the only tutorial missions I never completed.

[Anquietas314]

For me SAS intensifies the rotation, weird. Without SAS it leans slightly, with SAS it literally spins like crazy

Which SAS mode are you using? The hold maneuver/prograde/... modes are a little buggy in 0.90; hopefully they'll be fixed soon. In the meantime, the old "stabilize" mode (the default, top left button) works just as well (or badly) as it ever did

[ROXunreal]

No hold nothing mode, just the stabilize thing. Never had even the tiniest issue with it in vacuum.

[Cerberus738]

Could the engine gimbal be making the problem worse?

[Anquietas314]

Could the engine gimbal be making the problem worse?

That seems to be the gist of the bug report I linked (it also specifically mentions that tutorial). Since the gimbal doesn't seem to be an issue on my end I guess it must be either platform specific somehow, or a result of some particular sequence of actions I can't replicate

OP: have you tried manually disabling engine gimbal in the tutorial? You can do it using the right click menu for the engines, but it needs to be done for each engine.

[ROXunreal]

Just tried it now, and apparently that does the trick! Weird.

[cantab]

I've not checked the ship, but SAS doesn't understand gimballed engines forward of the Centre of Mass and will gimbal them the wrong way. So you need to either lock the gimbals or fly without SAS.

[Anquietas314]

I've not checked the ship, but SAS doesn't understand gimballed engines forward of the Centre of Mass and will gimbal them the wrong way. So you need to either lock the gimbals or fly without SAS.

The engines are forward of CoM, but for me SAS behaves correctly. Weird.