Orbital Fluctuations During Timewarp

[Jodo42]

I've got a *very* close to circular LKO (70,038 by 69,836), and as my probe has been flying around, my apo/periapsis have been rising/falling whenever I time warp. It's somewhat annoying and I'd like to know if there's a way to fix it. The only thing that I can think of is that my probe's rotation causes it to become taller/shorter which shifts them, but it's only 2 gigantor panels tall/wide.

Edited September 25, 2013 by Jodo42

[Mr.Rocket]

Is it possible that you have SAS on with RCS, I've noticed that in a delicate orbit, like a probes, sometimes RSC changes my orbit. If not, make sure you have a high enough orbit

.

[Jodo42]

Is it possible that you have SAS on with RCS, I've noticed that in a delicate orbit, like a probes, sometimes RSC changes my orbit. If not, make sure you have a high enough orbit

.

Sadly, no, there's no RCS onboard. My periapsis is also several hundred meters above the upper limit of Kerbin's atmosphere, which ends at 69,077m. It's not that the orbit degrades like what you'd see if you were entering the atmosphere, where your periapsis and apoapsis both drop. It's this constant small fluctuation of both apoapsis and periapsis, where they oscillate up and down by <+-100m. It's very weird, and I'm thinking it's possibly just a bug.

[shrx]

Same happened to me. Noticeable on high time-warp (at least 5 triangles). SAS was turned off and I didn't have any RCS.

Edit: I read the thread more carefully and it seems I have a different problem. At high time warp the Pe can change dramatically, for hundreds of thousands km.

The problem you described seems to be just physics calculations rounding errors.

Edited September 25, 2013 by shrx

[Jodo42]

Did you happen to be in a very low Kerbol (Solar) orbit? My *guess* is that if you were, the extremely high velocities exemplified the rounding problem significantly, or possibly just a Kraken attack. In any event, I'll chock this one up to physics errors. Does anyone know; if I edited the persistance file and set my ship's peri/apoapsis to what I want, would it stay that way?

[M5000]

Nope, I have this same issue, and I have NO idea what causes it. Just came here to express my "I know that feel bro."

Let me guess, you're doing multiple probe missions to mark off significant altitudes in the Kerbin system, and this one happens to be the "Safe orbit" probe.

Because that's what I was doing and, sure enough, my AP/PE lower whenever I timewarp. Like, as soon as you un-warp and physics enable again, the PE/AP jump a tiny bit ahead...Really annoying..

[Kurtvw]

I certainly don't know exactly how KSP does its math, but generally, with any simulation, you're going to lose resolution as you increase time compression, because you are asking the program to skip the calculations it would be doing in real time in favor of doing a calculation every X times the normal interval. Thus things can get a little wonky.

Since you are so very close to the 69077 magical top of atmosphere, perhaps at high simulation rates, it just goofs by tiny margin and you 'drag a toe in the water' as it were, and this causes a tiny variation in your numbers?

[Vector]

I have noticed large variations in the orbit when a craft rotates, as it seems the velocity of the command module (or whichever is 'control from here') is extrapolated to calculate the orbit. Then when physics is switched off, whatever orbit your command module happened to have at that moment is locked in, and that becomes your rails orbit. This can be used to cheat... er... to change your orbit without using any fuel.

When physics is turned on, I have the feeling nothing is really stationary. Everything "vibrates" perhaps due to roundoff or perhaps on purpose to give a seed for dynamic instabilities. I believe SAS can even contribute to the vibrations if it is trying to counteract the small perturbations and creating perturbations of its own. I'm sure you have seen the AP/PE markers wobble when very nearly circular, and AN/DN nodes wobble with very low inclinations. These are the vibrations I am talking about.

I would say try building a craft with the command module or remote guidance unit as close to the center of mass as you can possibly manage. See if that helps.

Edit: I tried this myself, with the center of mass very close to the control, and I still saw apoapsis/periapsis jump when I left time-warp, so it's not that.

Edited September 25, 2013 by Vector

[Garek]

There is a 'bug' in KSP where objects jump around a bit when entering/exiting non-physical timewarp. Even if the jumping itself is to little to be noticeable on a specific vessel, it could still affect its orbit. I remember seeing some video on youtube where Scott Manley was doing stuff with a modded-in Asteroid (which worked as a vessel) and on close approach in solar orbit, that asteroid and his probe would jump like 2 or 3 km relative to each other whenever he turned timewarp on/off.

[Capt_Reynolds]

I notice this a lot while rendezvousing. I'll enter time warp to get my two vessels closer together and my finely tuned ap/pe fluctuate.