Heavy lifter Issues

[AtomicRocketBooster]

So, I\'ve been working furiously on my Kitan Series of Rockets. There\'s the Kitan 3, which is a simple crew ferry, there\'s the Kitan 1, which is a simple midsize cargo ferry, and then there\'s the Kitan 2, the heavy lifter. For the first 200,000 m of altitude, everything works perfectly. However, once I fire up the second stage, no matter what I do, the nose invariably creeps up. I\'ve tried everything. IT just doesn\'t go down. I\'m well out of the atmosphere, so it can\'t be that CoG/CoP stuff- what is going on?

[tofof]

I think what you\'re not realizing is that as you push away from the earth (orthogonally to a radius to it) the horizon gets lower and lower, resulting in the appearance of the nose creeping up but what\'s actually happening is that the horizon is falling down. The normal SAS modules will do this to you (throw SAS on and sit back for an orbit and watch your attitude relative to the earth go through the entire 360, since it\'s holding your attitude fixed relative to an infinitely distant point).

[Ivan Ivanovich]

I have noticed the same effect on very long rockets, and I can reassure you it\'s not SAS trying to point somewhere. Either that or SAS chooses a lot of points during this procedure, since the rocket does spin a full circle... and not just one. Actually, the issue is a more intriguing one. I try to align my rocket with a certain plane so it only spins left/right or up/down, and I try to correct it, with no success whatsoever. Turning SAS on actually remedies the problem eventually... but only as long as I keep SAS on, else the rocket resumes its spinning. For no good reason, I might add, since I have long left the atmosphere and every kind of propulsion is turned off.

[shadowfax]

Because stopping all spin means that you will spin relative to the planet, whereas SAS tries (I think) to keep your orientation constant relative to the planet. Say you\'re in a polar orbit, and you start at the equator at an exact tangent to the planet. As your orbit carries you over the pole, if your rocket isn\'t spinning, you\'ll still be oriented the same direction you were when you were at the equatorial tangent, but because you\'re over the pole, your rocket is now facing either directly toward or directly away from the planet. You appear to have spun 90 degrees, but you really didn\'t.

[AtomicRocketBooster]

See, I recognize it when that happens. But this is far more extreme than that. If I take SAS off, often times I\'ll just start tumbling and end up pointing back towards the planet. The velocity vector is what creeps up when I shoot off into deep space, the nose should be more or less in line with that. But it doesn\'t work that way, and it\'s only my really big, long rockets that do this.

[shadowfax]

I wonder if it\'s a timing issue. If you disengage SAS when it\'s applying a force, then it can\'t apply an opposing force to compensate for the fact that the force it was applying when you disengaged it was too high. Put in terrestrial terms, if you swerve your car violently to the left, and then take your hands off the wheel, you won\'t end up going the direction you wanted to go because you stopped applying inputs before the necessary counter-steer.