Orbital Decay Bug

[Grenartia]

So, I first noticed this a few weeks ago in a modded copy of 1.12.3 I have. Essentially, anything I have in orbit has its Pe decrease and its Ap increase, with no discernable reason why. These were basic craft with no RCS at all, and I am absolutely certain the throttle was at 0. So I deleted that save file, made a new one, and tried again. I noticed the problem again. So then I nuked that copy, took my clean steam copy, and replaced it (and reinstalled all my mods). The problem persisted. I nuked the steam copy, and redownloaded it, and waited, then copied it and modded it, and tried again. Still the same issue. On a lark, I just tried playing from the clean copy, and noticed the issue is present, thus ruling out any mod causing it. I revalidated the game files, retried it, and its still acting up.

If there's any specific files I need to include, let me know and I'll provide them.

[Scarecrow71]

What body are you in orbit around?  And what are your starting Ap/Pe?  Can you share images of the craft you are seeing this with?

[Grenartia]

11 minutes ago, Scarecrow71 said:

What body are you in orbit around?  And what are your starting Ap/Pe?  Can you share images of the craft you are seeing this with?

1. Kerbin. I had been playing a 10% science career when I first noticed it, and I had no opportunity to try any other body.
2. Starting Ap was always ~100km in a circular orbit. I never let the craft long enough to get more than about 1km deviation above and below that figure, because by that point, it was already obvious that something weird was happening (though I did end up having something like a 150 x 69 km orbit in the first game I noticed the issue in, but that was after several hours of IRL play time).
3. I don't currently have any screenshots, but I'll try to recreate it for some screenshots later on.

[jimmymcgoochie]

Is this happening slowly over time or all at once? If it’s a gradual thing then it might be phantom forces acting on your vessel (a.k.a. Kraken) but if larger jumps them it’s probably the time warp bug.

Try rebuilding the vessel and avoid part clipping wherever possible to minimise the chances of a phantom force occurrence. You can also usually quicksave/quickload to get rid of them.

There’s a bug in KSP 1.12 where activating time warp can shift your orbit a bit; the bigger the jump, the worse the orbit shift. Try pressing ./> to speed time warp up one notch before clicking any “warp to” buttons and see if that helps, it will lessen but not eliminate the problem and you’ll likely need to do course corrections on longer journeys to fully counter it.

[Grenartia]

12 hours ago, jimmymcgoochie said:

Is this happening slowly over time or all at once? If it’s a gradual thing then it might be phantom forces acting on your vessel (a.k.a. Kraken) but if larger jumps them it’s probably the time warp bug.

Try rebuilding the vessel and avoid part clipping wherever possible to minimise the chances of a phantom force occurrence. You can also usually quicksave/quickload to get rid of them.

There’s a bug in KSP 1.12 where activating time warp can shift your orbit a bit; the bigger the jump, the worse the orbit shift. Try pressing ./> to speed time warp up one notch before clicking any “warp to” buttons and see if that helps, it will lessen but not eliminate the problem and you’ll likely need to do course corrections on longer journeys to fully counter it.

That's the thing. Literally none of that applies here. I didn't use time warp at all, it happens to basically any vessel, and there's no part clipping at all.  When I first noticed the problem, it was gradual, a constant (slow, but still noticeable over a few seconds) change in Ap and Pe. But somewhere along the way, between nuking and reinstalling, it shifted to more discrete jumps (I never noticed when it changed, because it would always be significant fractions of an orbit, and would only happen when my attention got directed elsewhere, but I did notice a change in numbers), but again, not due to time warp, because I wasn't using it. 

I'll try to get a video up tomorrow or the day after.

 

[Grenartia]

I was unable to do a video, unfortunately. But, I did run a mission for an hour, and recorded the Ap and Pe every 2 minutes. 

 

Spoiler

MET 6 min:
-Ap: 118.974km
-Pe: 85.2505km

MET 8 min:
-Ap: 118.974km
-Pe: 85.2503km

MET 10 min:
-Ap: 118.974km
-Pe: 85.2498km

MET 12 min:
-Ap: 118.974km
-Pe: 85.2495km

MET 14 min:
-Ap: 118.975km
-Pe: 85.2490km

MET 16 min:
-Ap: 118.975km
-Pe: 85.2486km

MET 18 min:
-Ap: 118.975km
-Pe: 85.2481km

MET 20 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 22 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 24 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 26 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 28 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 30 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 32 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 34 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 36 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 38 min:
-Ap: 118.990km
-Pe: 85.2324km

MET 40 min:
-Ap: 118.990km
-Pe: 85.2319km

MET 42 min:
-Ap: 118.990km
-Pe: 85.2312km

MET 44 min:
-Ap: 118.990km
-Pe: 85.2307km

MET 46 min:
-Ap: 118.990km
-Pe: 85.2299km

MET 48 min:
-Ap: 118.991km
-Pe: 85.2290km

MET 50 min:
-Ap: 118.991km
-Pe: 85.2285km

MET 52 min:
-Ap: 118.998km
-Pe: 85.2204km

MET 54 min:
-Ap: 118.998km
-Pe: 85.2204km

MET 56 min:
-Ap: 118.998km
-Pe: 85.2204km

MET 58 min:
-Ap: 118.998km
-Pe: 85.2204km

MET 1 hr:
-Ap: 118.998km
-Pe: 85.2204km

 

[Superfluous J]

Your ship may be pushing on itself in an odd way. Could you post a pic of the ship in orbit, to imgur or wheverever and share a link?

Also there was an old bug where this happened, and they added a setting for it. I don't recall the name but it's defaulted to on. If it's off turn it on. If it's on turn it off and see if that helps.

And if this sounds like "turn it off and then on again" yeah that's about where I am on this one

[Grenartia]

9 hours ago, Superfluous J said:

Your ship may be pushing on itself in an odd way. Could you post a pic of the ship in orbit, to imgur or wheverever and share a link?

Also there was an old bug where this happened, and they added a setting for it. I don't recall the name but it's defaulted to on. If it's off turn it on. If it's on turn it off and see if that helps.

And if this sounds like "turn it off and then on again" yeah that's about where I am on this one

Yeah, doing that now. I had hoped the video would show everything that's needed (craft construction, initial orbit, where in the orbit the changes happen, etc.), but youtube wouldn't accept it because its "too big" (???), despite 'only' being an hour long and at medium quality.

 

Spoiler

 

As you can see, there is no part clipping, and the craft is as barebones as it gets.

Also, I've never heard of this setting you're talking about, and I've been playing since before 1.0

Edited October 26, 2022 by Grenartia

[Nazalassa]

I got the same problem during my "atmospheric orbit" thing a few days ago (don't ask). The craft spent 9 hours at least under full physics, without time warp, no drag, and that was enough to significantly move the ap and the pe. However, during half the orbit the ap increased and the pe decreased, but during the other half it was the opposite...

KSP's physics are the best.

[Grenartia]

27 minutes ago, Nazalassa said:

I got the same problem during my "atmospheric orbit" thing a few days ago (don't ask). The craft spent 9 hours at least under full physics, without time warp, no drag, and that was enough to significantly move the ap and the pe. However, during half the orbit the ap increased and the pe decreased, but during the other half it was the opposite...

KSP's physics are the best.

I swear there used to be some kind of telemetry mod that would graph stuff like this for you. That would be really great to have purely for diagnostic reasons like this.

[Grenartia]

Also, I just tried my test craft again, and used time warp. I noticed no change whatsoever in Ap or Pe, even at max time warp. So, I feel confident in ruling out the time warp bug.

Edited October 27, 2022 by Grenartia

[Grenartia]

So, I've noticed this issue persists in 1.12.4. I've also finally figured out how to do the log file thing (previous attempts resulted in pastebin yelling at me for going over the file size limits).

Log file: https://pastebin.com/QRNenryR

[markinturamb]

I've noticed a similar problem and found this topic.

Seems like the problem only happens when the ship is near a planet. I tested in Kerbin, and it only happens between 70k and 100k, minmus up to 100k, and in Jool it happened between 200k and 220k. So if your ship is in low orbit, or even just passing through a low periapsis, the Ap/Pe fluctuation happens. After it's above that it seems to stop, with a slight jump to the Ap and Pe (a couple of meters) when going through that altitude threshold.

If you have Kerbal Engineer, it's easily noticeable both on the Ap/Pe indicators, and to be even more precise you can see that the Arg. of Periapsis keeps moving around as well.

Things I tested:

• Turned "Orbital Drift Compensation" in the main menu options off and on again
• On my current 1.12.3 heavily modded carrer
• Same install on a new save
• New fresh 1.12.4 install
• With a complex ship
• With a very simple ship
• Just a probe core, cheated to orbit

The result seemed to be the same in all cases. If the vessel in under timewarp or unloaded, the orbit stays stable.

I noticed this bug when trying to create a maneuver node for a planetary transfer, and while fidgeting with it, the encounter kept moving around for no apparent reason. For now seems like the solution is to have my ship parked in a higher orbit and hope for the best

 

[Grenartia]

6 hours ago, markinturamb said:

I've noticed a similar problem and found this topic.

Seems like the problem only happens when the ship is near a planet. I tested in Kerbin, and it only happens between 70k and 100k, minmus up to 100k, and in Jool it happened between 200k and 220k. So if your ship is in low orbit, or even just passing through a low periapsis, the Ap/Pe fluctuation happens. After it's above that it seems to stop, with a slight jump to the Ap and Pe (a couple of meters) when going through that altitude threshold.

If you have Kerbal Engineer, it's easily noticeable both on the Ap/Pe indicators, and to be even more precise you can see that the Arg. of Periapsis keeps moving around as well.

Things I tested:

• Turned "Orbital Drift Compensation" in the main menu options off and on again
• On my current 1.12.3 heavily modded carrer
• Same install on a new save
• New fresh 1.12.4 install
• With a complex ship
• With a very simple ship
• Just a probe core, cheated to orbit

The result seemed to be the same in all cases. If the vessel in under timewarp or unloaded, the orbit stays stable.

I noticed this bug when trying to create a maneuver node for a planetary transfer, and while fidgeting with it, the encounter kept moving around for no apparent reason. For now seems like the solution is to have my ship parked in a higher orbit and hope for the best

 

I only tested near 100k over Kerbin, but generally with enough margin of error that my Pe was below (something like 98-99km). 

So, I took a cue from you, and cheated a probe core into orbit. At the 86.750km circular orbit the cheat defaults to, orbital decay is constant and noticeable. Oddly, the orbital period remained fixed at a constant 31m, 42s. At 150km, I continued to observe decay behavior, again with a constant orbital period (in this case, 36m, 11s).

I also did manage to find the "Orbital Drift Compensation" option. At best, it only reduces the issue, rather than correcting it. At worst, it does nothing at all. My testing on that front seems inconclusive.

Edited November 12, 2022 by Grenartia
Providing additional context

[Nazalassa]

Seems to do that whenever the ship is under physics. Recently got a chain of three slingshot maneuvers. The orbit after the third changed like crazy while the ship was under physics (ap dropped from 1,600,000 m to 230,000 m, which is not good) before I engaged time warp.

Seems to be related to physics time steps...

[Grenartia]

1 hour ago, Nazalassa said:

Seems to do that whenever the ship is under physics. Recently got a chain of three slingshot maneuvers. The orbit after the third changed like crazy while the ship was under physics (ap dropped from 1,600,000 m to 230,000 m, which is not good) before I engaged time warp.

Seems to be related to physics time steps...

I haven't touched the settings for that in any way.

[Nazalassa]

19 minutes ago, Grenartia said:

I haven't touched the settings for that in any way.

That's not the settings, that's just the way KSP simulates physics and it's horribly unprecise.

[JonnyOThan]

On 11/11/2022 at 10:03 AM, markinturamb said:

Seems like the problem only happens when the ship is near a planet. I tested in Kerbin, and it only happens between 70k and 100k, minmus up to 100k, and in Jool it happened between 200k and 220k

This is vital info: these are the altitudes where the simulation switches from a rotating reference frame to a fixed one.  There must be some kind of error in the math.

[Grenartia]

1 hour ago, JonnyOThan said:

This is vital info: these are the altitudes where the simulation switches from a rotating reference frame to a fixed one.  There must be some kind of error in the math.

I'm noticing that at altitudes above 150km over Kerbin, the location of Ap and Pe along the orbit rapidly and randomly shift. Perhaps related?

[JonnyOThan]

3 hours ago, Grenartia said:

I'm noticing that at altitudes above 150km over Kerbin, the location of Ap and Pe along the orbit rapidly and randomly shift. Perhaps related?

Did you cheat it into a circular orbit?  That’s kind of expected, because there *is* no pe and AP in a perfectly circular orbit.

[Grenartia]

2 minutes ago, JonnyOThan said:

Did you cheat it into a circular orbit?  That’s kind of expected, because there *is* no pe and AP in a perfectly circular orbit.

Yeah, I did. And yeah, that makes sense.

[yagiziskirik]

On 10/26/2022 at 11:26 PM, Grenartia said:

I swear there used to be some kind of telemetry mod that would graph stuff like this for you. That would be really great to have purely for diagnostic reasons like this.

I can modify mine for precise orbital telemetry data to showcase the situation if you want to

[Grenartia]

On 12/17/2022 at 9:34 AM, yagiziskirik said:

I can modify mine for precise orbital telemetry data to showcase the situation if you want to

That would be great, yes. Thank you!

[Grenartia]

Has anyone fixed this? At this point, I'll take a modfix. 

[Bej Kerman]

On 10/26/2022 at 7:07 AM, Grenartia said:

I was unable to do a video, unfortunately. But, I did run a mission for an hour, and recorded the Ap and Pe every 2 minutes. 

  Hide contents

MET 6 min:
-Ap: 118.974km
-Pe: 85.2505km

MET 8 min:
-Ap: 118.974km
-Pe: 85.2503km

MET 10 min:
-Ap: 118.974km
-Pe: 85.2498km

MET 12 min:
-Ap: 118.974km
-Pe: 85.2495km

MET 14 min:
-Ap: 118.975km
-Pe: 85.2490km

MET 16 min:
-Ap: 118.975km
-Pe: 85.2486km

MET 18 min:
-Ap: 118.975km
-Pe: 85.2481km

MET 20 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 22 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 24 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 26 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 28 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 30 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 32 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 34 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 36 min:
-Ap: 118.982km
-Pe: 85.2403km

MET 38 min:
-Ap: 118.990km
-Pe: 85.2324km

MET 40 min:
-Ap: 118.990km
-Pe: 85.2319km

MET 42 min:
-Ap: 118.990km
-Pe: 85.2312km

MET 44 min:
-Ap: 118.990km
-Pe: 85.2307km

MET 46 min:
-Ap: 118.990km
-Pe: 85.2299km

MET 48 min:
-Ap: 118.991km
-Pe: 85.2290km

MET 50 min:
-Ap: 118.991km
-Pe: 85.2285km

MET 52 min:
-Ap: 118.998km
-Pe: 85.2204km

MET 54 min:
-Ap: 118.998km
-Pe: 85.2204km

MET 56 min:
-Ap: 118.998km
-Pe: 85.2204km

MET 58 min:
-Ap: 118.998km
-Pe: 85.2204km

MET 1 hr:
-Ap: 118.998km
-Pe: 85.2204km

Probably just floating point imprecision