unexpected rotation prevents docking

[ainamogel]

Hi all,

I wonder if anyone else has seen this. I am trying to dock to a very simple spacecraft, but it is super hard because it keeps randomly rotating without any cause that I can determine. The target ship consists of just a few parts: a clamp-o-tron Jr., a mk1 command pod (no occupant), two parachutes symmetrically mounted, a small fuel tank, and a spark engine. Whenever I accelerate time warp, the rotation stops, of course, but as soon as I return to x1 speed the ship starts spinning in some random direction at perhaps one rotation per 15 seconds, which makes docking to it very very difficult as the alignment of the docking port is constantly changing.

Does anyone have any thoughts as to what might be causing this? For what it is worth, the docking attempt is taking place in orbit around the Mun. I have scads of mods installed, but not Persistent Rotation or anything else that I naively would expect to cause this behavior.

Thanks very much for your help,

Ainamogel

[The_Rocketeer]

SAS off? You might have accidentally adjusted your trim setting slightly. Try pressing alt-x to reset all trim to neutral.

[Corw]

It might have something to do with part clipping. Those can do funny things, especially in conjunction with cargo bays.

[ForScience6686]

Do you by chance have a joy stick connected. I frequently run into inputs from a miss calibrated joy stick. Turn off SAS and see if the control indicators are showing any sign of input.

[capi3101]

I've encountered this kind of behavior before; it's a bug, and a really annoying one because it forces you to use SAS (as opposed to it being merely an option). Assuming all things are equal, you need to make sure you've got SAS turned on on both craft. If the target craft is spinning, switch control over to it momentarily and set SAS, then switch back. Unfortunately, in my experience if you've got one craft doing this, they'll all do it. The only permanent workaround I've encountered is to begin a whole new save game.

Other possibilities - since you've got mods, I'll recommend try Docking Port Alignment Indicator and RCS Build Aid as two to add. Both make the docking process far easier, one by helping with port alignment, the other by helping to better balance RCS thrusters (that one is also surprisingly helpful if you ever want to journey into the realm of spaceplane design).

[Hagen von Tronje]

Shot in the dark but FAR flight assistance can do this to you as well.

[ainamogel]

Thanks for the help so far, all.

The target craft has no probe core or Kerbalnaut on board, so I have no easy way to adjust the controls, such as turning SAS on or off or resetting the trim.

I don't have FAR installed.

I don't have a joystick installed.

Is there an easy way to tell if part clipping is happening? I did not intentionally clip any parts or enable part clipping, but I don't know for a fact that it isn't happening.

Finally, I already use DPAI (love it!) and have never felt the need for RCS aid; I just plonk the RCS thrusters down symmetrically around the CG and things work acceptably. I'm not having trouble controlling the active ship; it's the (nominally completely uncontrolled but nonetheless spinning) target ship that is causing the problems.

Thanks very much; maybe this additional info will help debug the problem. I am afraid that capi3101 is correct, though, and it is just a random game bug.

Thanks,

Ainamogel

[David104]

Heyho!

I only have the spinning problem when I have a craft which CoM is not right in the middle. If you dont have SAS control, it wont be controlable then because there is nothing to stabalize it..

Also what I also have from time to time, especially with docking ports, is that I forget to turn off symetry mode, so basically it attaches e.g. 2 docking ports on only one slot. Maybe that causes the CoM to shift...

Do you have enough electricity on it or solar panels?

[ainamogel]

Oh ho... I will look in the craft file to see how many C-o-T Jr.s are on there. Only one is visible, of course, on the nose of the command pod.

The only electricity on it is the 50 stored in the command pod; nothing is using it at the time I am trying to dock, since everything is turned off. No solar panels.

Thanks,

Ainamogel

[SpeedDaemon]

Another shot in the dark here... My last save (1.0.2) had a similar problem. One of my science stations - which I always tried to keep with the docking port pointed anti-normal to make it easier, would always drift, even crewed and SASed. Nothing like the one turn per 15 seconds you have (it was more like ~5 degrees every 60 seconds).

This save (1.0.4), a similar station is staying bang on where I left it.

This save, I have Kerbal Joint Reinforcement, though... Wonder if you try adding that temporarily and see if it makes any difference if the craft is stiffer.

EDIT: Does the rotation stay a constant speed, or continually get faster?

[Stoney3K]

I *do* notice the rotation as well, even though there is nothing you can do about it with the craft you have now.

That's because the target craft is an inert, "non-cooperative" target which has no means of controlling it, since there are no Kerbals or probe cores on board. There are two options: Try circling around the craft with your chaser until you catch up with the port (I dock with debris-parts often like this to construct a station) or try and get a Kerbal to sit in the command chair of your target and hit the SAS.

The cause of the rotation is probably physics inaccuracy, if either one of the 'rotation' forces is not exactly zero it will induce spin sooner or later.

Strangely enough, this is pretty consistent with real-world space missions where two craft that are *supposed* to dock both have active attitude keeping mechanisms to keep them pointed the right way. Docking with a powered-down or damaged satellite in real spaceflight is very challenging because the satellite can spin randomly in any direction due to atmospheric drag, solar winds or micrometeorite strikes.

[Kerbart]

Also make sure it's your craft that's doing the spinning, and not the craft you're docking with. Stations tend to have non-symmetrical layouts, and if they're pieced together you might have SAS units everywhere that (theoretically) should work in unison but due to flex at the docking ports don't always do that. Turning off SAS at the station might help in that case.

[ainamogel]

Another shot in the dark here... My last save (1.0.2) had a similar problem. One of my science stations - which I always tried to keep with the docking port pointed anti-normal to make it easier, would always drift, even crewed and SASed. Nothing like the one turn per 15 seconds you have (it was more like ~5 degrees every 60 seconds).

This save (1.0.4), a similar station is staying bang on where I left it.

This save, I have Kerbal Joint Reinforcement, though... Wonder if you try adding that temporarily and see if it makes any difference if the craft is stiffer.

EDIT: Does the rotation stay a constant speed, or continually get faster?

I have KJR installed. I will try _disabling_ it. (Remember this is a very very light craft... might drift faster than a multi-ton station, naively.)

I am not sure about the acceleration. I had the impression it was a constant angular velocity.

Thanks,

Ainamogel

[Vanamonde]

Does the target ship move as if responding to the control inputs of the ship you are piloting? That is a bug that comes up sometimes.

[Aegeas]

Out of curiosity does the target craft have a science module?

I noticed a bug with a space station the other day where it was doing a weird oscillation. After some detective work checking my other stations and then sending it back up each time deleting some parts I narrowed it down to the science module.

Been meaning to report this or check forums if this is a known bug?

Has anyone else encountered this?

If you use the science module as the core of a station oscillations can be amplified as you start adding mass and leverage, I was noticing some flickering with my apoapsis and periapsis - is how it first became apparent that something was up.

Launched just the science module to fully check this out and the oscillation was still there, it was too small to be seen on the orbital map but the heads up from Kerbal Engineer gives finer detail and I could see an oscillation there.

Not sure if this is causing your problem?

The only solution I could give you would be to make a 3rd craft with a Grabbing Unit (the thing you grab asteroids with) and Sufficient RCS/Reaction Torque to hold the spinning craft still while you dock the other one to it.

[ainamogel]

Does the target ship move as if responding to the control inputs of the ship you are piloting? That is a bug that comes up sometimes.

Interesting! It is hard to say, but it could be true.

Ainamogel

- - - Updated - - -

Out of curiosity does the target craft have a science module?

Not in this case. A really minimal craft: clampotron jr, chutes, command pod, fuel tank, spark engine.

Ainamogel

[Warzouz]

I had that on a old Mun space station. The station was starting to rotate in mostly random direction, even with SAS on. Sometime, rotation could be explosive. Never found what it was I replaced the station and crashed the buged one to the Mun ground...

[Friend Bear]

Hi all,

I wonder if anyone else has seen this. I am trying to dock to a very simple spacecraft, but it is super hard because it keeps randomly rotating without any cause that I can determine. The target ship consists of just a few parts: a clamp-o-tron Jr., a mk1 command pod (no occupant), two parachutes symmetrically mounted, a small fuel tank, and a spark engine. Whenever I accelerate time warp, the rotation stops, of course, but as soon as I return to x1 speed the ship starts spinning in some random direction at perhaps one rotation per 15 seconds, which makes docking to it very very difficult as the alignment of the docking port is constantly changing.

Does anyone have any thoughts as to what might be causing this? For what it is worth, the docking attempt is taking place in orbit around the Mun. I have scads of mods installed, but not Persistent Rotation or anything else that I naively would expect to cause this behavior.

Thanks very much for your help,

Ainamogel

There are two possibilities:

1) Above is right, it is likely a bug. I ended up having to delete the ship and try again when it happened to me.

2) BUT I have also seen this...Since I assume the ship you are trying to dock to is the one rotating, do you have a pilot in that vessel or an advanced enough radio controlled unit to engage SAS? If no, once the pilot leaves, SAS cannot be engaged. The smallest burst can cause the rotation.

It could even be a combo and I have seen that...where I had no pilot and after timewarping it decided to rotate even without an initial force (unless thrusters now interact with nearby objects as standard engines do).

[Damon]

On 21-9-2015 at 6:02 PM, The_Rocketeer said:

SAS off? You might have accidentally adjusted your trim setting slightly. Try pressing alt-x to reset all trim to neutral.

When you think it's and old post but yet this one saved my station from turning around while nothing should happen

[Climber Rat]

I’ve seen the target ship start to rotate annoyingly, making docking impossible (used up all my MP futilely trying once), due to a botched docking attempt were my ship knocked into target ship. I’ve learned in those cases to abort the attempt and leave that ship - go to Tracking Station or choose another ship to fly.  Then go back to the original and reattempt. This seems to reset to target ships stability.  I’m not sure if a certain amount of time has to pass though.