Spinning jenny

[Daveroski]

What causes a larger vessel, balanced and symmetrical, to rotate while in orbit?

RCS is off SAS is off. No force = No reaction.

Blue Danube should have been playing during my last docking around Duna.

[capi3101]

How exactly is it spinning? Is it a rapid spin, or just kind of a lazy drift where your ship doesn't hold a straight course unless you're turned normal/anti-normal to your orbit? If it's the former, there's an issue. If it's the latter, what you're seeing is your craft's orientation changing relative to the planet below, a simple side effect of being in an orbital path; your craft isn't actually changing its orientation at all, it just looks that way.

Like I said, if it's the former, there's an issue. Let us know - post some screenies if possible - and we can try to diagnose the problem.

[Padishar]

Are you sure it is actually rotating? A vessel in orbit will appear to do one complete rotation each time it goes around the planet. E.g. if you start with your ship pointing away from the planet then when you get around the other side of the planet you will be pointing at the ground...

[Norpo]

I've had this annoying problem as well.

I think it's the trim, which happens when you hold down Alt + (whatever direction). It makes your ship tend to go in that direction, and it's useful for things in atmosphere, but it's a heckuvalot annoying in orbit.

To reset the trim, hold down Alt (or whatever your modifier key is, should be Alt in windows), and X.

[Streetwind]

Once, back in .23, I had an issue with phantom forces from clipping issues that would make a my spacecraft constantly try to spin unless countered by SAS. It was really weird.

Unfortunately I don't recall details, but it involved a girder segment of some description.

[Daveroski]

Once, back in .23, I had an issue with phantom forces from clipping issues that would make a my spacecraft constantly try to spin unless countered by SAS. It was really weird.

Unfortunately I don't recall details, but it involved a girder segment of some description.

My ship does indeed have 4 lateral girder segments. placed with quad symmetry in the VAB. I'm aware that some parts values are not always symmetrical even though, by appearance the craft be completely symmetrical.

I've had this annoying problem as well.

I think it's the trim, which happens when you hold down Alt + (whatever direction). It makes your ship tend to go in that direction, and it's useful for things in atmosphere, but it's a heckuvalot annoying in orbit.

To reset the trim, hold down Alt (or whatever your modifier key is, should be Alt in windows), and X.

Curious. But something I can check out.

[Daveroski]

Images

As requested.

Unfortunately these don't show it slowly rotating.

@Norpo Alt X didn't help

[capi3101]

Taking a guess I'd say it's those big solar panels imparting forces on the craft when they rotate to keep focused on Kerbol. Other that the only thing I can think of is that it isn't 100% balanced - I had a space station that had a tendency to rotate due to a mass imbalance while it was under construction. On the other hand, you said it was balanced, so I'll take your word for it.

Come to think of it, that station did have a tendency to rotate even after construction was complete, and it too used several of the big solar panels...

[Daveroski]

Taking a guess I'd say it's those big solar panels imparting forces on the craft when they rotate to keep focused on Kerbol. Other that the only thing I can think of is that it isn't 100% balanced - I had a space station that had a tendency to rotate due to a mass imbalance while it was under construction. On the other hand, you said it was balanced, so I'll take your word for it.

Come to think of it, that station did have a tendency to rotate even after construction was complete, and it too used several of the big solar panels...

I thought that might be the problem too but it still does it even when the panels are folded up.

I was so OCD about making it balanced. I didn't even put a twig er.. Comms Antennae on it.

[Redshift OTF]

Maybe there's a bit of wobble in your craft that then gets translated into craft roll. Not sure if that's possible though.

[Cerberus738]

Do you have a joystick? Sometimes recalibrate it fixes that. Or you need to set dead zone higher. My joystick constantly caused roll in all my craft. Sometimes just moving the stick would be enough to fix the random roll.

[The_Rocketeer]

On which axis is it turning?

If you don't understand x/y/z explanations (no offense intended) use the question below instead.

Imagining the craft is a ball, look straight at the command module from in front. Does it turn like a ball rolling towards/away from you, a ball rolling past you, or a ball spinning on the spot?

[Daveroski]

Do you have a joystick? Sometimes recalibrate it fixes that. Or you need to set dead zone higher. My joystick constantly caused roll in all my craft. Sometimes just moving the stick would be enough to fix the random roll.

No, I don't have any other controller connected other than my Microsoft Trackball (mouse).

On which axis is it turning?

If you don't understand x/y/z explanations (no offense intended) use the question below instead.

Imagining the craft is a ball, look straight at the command module from in front. Does it turn like a ball rolling towards/away from you, a ball rolling past you, or a ball spinning on the spot?

On the Y axis.

The same happens in the vanilla game with no mods and the same ship.

It seems to be weighted at the COM as it isn't a perfect Y axis spin. The nose of the capsule has a small but noticeable circular motion.

The large central tank, the capsule and the RCS fuel tanks all serve to move the COM nosewards.

However, I believe the the COM placement on the Y Axis would only affect the circular motion of the nose. Not the spinning in itself. ie. closer to the nose smaller circles at the nose end.

D.

[GoSlash27]

It's not rotating, it just seems like it is.

Best,

-Slashy

[KerbMav]

Even the most imbalanced craft SHOULD not rotate at all if no force (thrust, reckless EVA-kerbonauts, etc.) is applied to it.

Does the rotation stop if you engage timewarp for a moment or does it start to rotate again? Is it getting faster?

There was a time many players reportet space stations dancing themselves to death - but I see nothing in your design that was mentioned as a cause back then, like crossing struts or part clipping.

[Daveroski]

It's not rotating, it just seems like it is.

Best,

-Slashy

Perhaps you should explain that to Bill. That it only seemed to rotate into him and only seemed to knock him flying.

Even the most imbalanced craft SHOULD not rotate at all if no force (thrust, reckless EVA-kerbonauts, etc.) is applied to it.

Does the rotation stop if you engage timewarp for a moment or does it start to rotate again? Is it getting faster?

There was a time many players reportet space stations dancing themselves to death - but I see nothing in your design that was mentioned as a cause back then, like crossing struts or part clipping.

I agree, it shouldn't be rotating. Hence my post.

Yes indeed, the rotation does stop if I time warp a little but then it starts, very slowly at first, slowly picks up speed until it looks like I'm playing Elite again.

No parts clipping, no crossing struts. Even my fuel lines are symmetrical.

[sal_vager]

Floating point inaccuracies, basically the son of Kraken, cause craft to start rotating slowly.

If you find it is a problem you can use SAS to hold your ship

[GoSlash27]

Perhaps you should explain that to Bill. That it only seemed to rotate into him and only seemed to knock him flying.

From everything you've described and posted, it's not rotating. Everything you ever put in orbit is going to seem to slowly "rotate", but it's just an illusion because you're confusing the planetary horizon with your inertial reference.

Sorry if you don't like the answer, but reality is sometimes inconvenient that way.

Regards,

-Slashy

[Kryxal]

I was thinking it was the issue where, even using physicless warp, you'll shift your heading relative to a maneuver node's marker. It's really annoying, line up half an orbit early, find you're a fair bit off when you come out of warp...

[Daveroski]

I was thinking it was the issue where, even using physicless warp, you'll shift your heading relative to a maneuver node's marker. It's really annoying, line up half an orbit early, find you're a fair bit off when you come out of warp...

I have that problem sometimes too. I have to keep an eye on my node during warp.

I have been playing without MechJeb for a few months, I stopped using it because i thought it might have been causing problems (so far none of my suspicions hold up) but I noticed that MechJeb allows for this drift by warping for a while, stopping the warp, reacquiring, and then continuing to warp to the node. So it must be in the code.

From everything you've described and posted, it's not rotating. Everything you ever put in orbit is going to seem to slowly "rotate", but it's just an illusion because you're confusing the planetary horizon with your inertial reference.

Sorry if you don't like the answer, but reality is sometimes inconvenient that way.

Regards,

-Slashy

Tenacious aren't you. Ok let's look at a few facts.

Fact 1. In my OP, only 3 lines of text but you missed it. I said on the bottom line that docking with it was a problem. Anyone who knows anything about space and space ships would have gotten the 'Blue Danube' reference.

Fact 2. It stops when I go to warp. (my post to KerbMav)

Fact 3. I already told you it hit bill and sent him flying. Physical evidence of motion.

Fact 4. I have sat and watched it get up to 4 revolutions a minute before stopping it with warp and watching it slowly start up again.

So to you Slashy, I say Get Facts!

[MarvinKitFox]

How exactly is it spinning?

How about the case where its orientation drifts by about 5-10 degrees per orbit, while orbiting *under timewarp* (not physics timespeed, actual 10* + timewarp)

[psyper]

Okay I'm gonna appologise right off the bat on this as I'm flying blind - my work don't allow Imgur through our gateway so I dont see any imgur pictures (not even a gap where they would be) think about how vanilla the forums are for me at this precise moment.

Anyway - therefore, I haven't seen the photo of your craft so I'm having to guess here. And yes I understand that your craft isn't rotating in relation to space and I got the blue danube reference too - smacking a kerbal away gave the game away somewhat too!!

Do you have any parts connected by docking ports? - I've had this problem a few versions ago and it was because I had a large space station with several docked elements - it shouldve been resolved since the update but i don't think it has. If you undock all of your parts do you still get a rotation - and if so does it remain on one part or several. IIRC it was phantom forces due to SAS being on while a part docks. It might be worth redocking everything together but switch SAS off just as you're about to dock.

Also is it stock? is there anywhere you can upload your persistence file so I can see if it spins on my game setup too - at least we can rule that out.

[capi3101]

How about the case where its orientation drifts by about 5-10 degrees per orbit, while orbiting *under timewarp* (not physics timespeed, actual 10* + timewarp)

Yeah, I still don't know why that happens...

[Daveroski]

Okay I'm gonna appologise right off the bat on this as I'm flying blind - my work don't allow Imgur through our gateway so I dont see any imgur pictures (not even a gap where they would be) think about how vanilla the forums are for me at this precise moment.

Anyway - therefore, I haven't seen the photo of your craft so I'm having to guess here. And yes I understand that your craft isn't rotating in relation to space and I got the blue danube reference too - smacking a kerbal away gave the game away somewhat too!!

Do you have any parts connected by docking ports? - I've had this problem a few versions ago and it was because I had a large space station with several docked elements - it shouldve been resolved since the update but i don't think it has. If you undock all of your parts do you still get a rotation - and if so does it remain on one part or several. IIRC it was phantom forces due to SAS being on while a part docks. It might be worth redocking everything together but switch SAS off just as you're about to dock.

Also is it stock? is there anywhere you can upload your persistence file so I can see if it spins on my game setup too - at least we can rule that out.

Ok

From the top.

Shielded docking port. For Resupply when payload installed.

2.5 command pod

Big battery

Big 2.5 reaction wheel.

2.5 to 3.25 adapter

Smallest new big tank 3.5m (Used as heavy COM)

Base of tank has a standard docking port. Connects to payload (currently empty)

From 3.5 tank 4 symetrical girders at 90 degrees (horizontal)

On the end of each girder an orange 2.5 tank. (vertical same orientation as main tank)

Each 2.5 orange tank has a large mollyprop (mono-propellant) tank at the top and a 2.5 nosecone.

Base of tank Poodle engine.

RCS thrusters on orange tanks for directional assist.

Fuel lines in line with girders from main tank to orange tanks.

Struts balanced equally balanced (not crossing each other) from one orange tank to it's neighbour.

A basic vanilla ship.

Had mods installed which made the bits prettier and Duna look more like a planet and less like a Malteaser with the ends nibbled.

No roll was obvious until I got out to Duna. I had docked with it to refuel in Kerbin orbit and Sent up a payload which docked with it without a hitch.

I had KAS installed and used KAS struts to secure the payload. Once in Duna orbit, I unlinked the struts and removed all the strut components.

These were discarded and deleted from the scene via kerbin Tracking station. So as to not have KSP tracking stuff that wasn't needed.

The payload. A lander with an reusable rover was taken down to duna. Did Science. Deployed rover. Roved for about 50K Round Trip - Did Science.

Returned rover to Lander. Launched for Rendezvous with Mothership.

On final approach, noticed the spin.

Swore

Then swore some more.

Wondered if I should have a go at docking 2001 style. Thought of Blue Danube.

Quickly considered the probability of catastrophe. Swore some more. and tried the warp.

Seemed to stop it long enough for me to dock and refuel for Ike.

Already spinning again by the end of the refuelling.

Swore a bit more.

Undocked and set off for Ike.

Seen this kind of roll many times before. Had the idea to see if mods were causing it. Removed all mods. Re installed KSP loaded the game. My ship loaded just fine. No errors on the bug-screen.

Ship rolled in exactly the same way.

Have since made similar ships in a vanilla KSP and the results are the same.

I'd like someone to make a similar ship and just watch it in Duna orbit

I hope my description is of help as you can't see the pictures.

D.

[Kryxal]

As a workaround, can you effectively control the mothership via RCS? If so, you can probably get your other ship on approach and just do fine adjustment from there ... and even if not, you can at least hold the ship steady with SAS.