Randomly changing orbit during time warp

[king of nowhere]

I want to describe a glitch that's been pestering me a few times: spaceships changing orbits for no reason.

Today the latest instance: here's my spaceship, in low earth orbit, slowly raising apoapsis with nuclear engines over multiple passages. Here it just stopped the engines, and it's got a 37700 km apoapsis. I reset the manuever node, click a few minutes before the next periapsis and tell the game to time warp to there

When i enter time warp, the manuever suddenly rises to 8000 m/s.

Not only, but though the ship moved in front of the manuever node, the game thinks there's still a few minutes left.

You can see what happened: the orbit has been changed, the apoapsis lowered by 1000 km, which changed the orbital time and screwed up the manuever node.

It's the second time it happened today - good thing I'm saving after every manuever - but it's not the first time I see this bug. Previously in my A'Tuin mission, while the eponymous ship was orbiting Tekto (an OPM moon that's a Titan analogue), the orbit also changed, with the periapsis inexplicably becoming lower between different saves, despite the ship never using the engines. We're talking 50 m/s lower, not the small differences caused by docking manuevers.

While it happened occasionally in the past, though, it seems now it's happening every other save. Just as I write, I had to reload for the third time because it happened again. And again, it happens as soon as I activate time warp.

Do you also experience it? Is there any solution?

 

[Fraktal]

This appeared a couple versions ago, yes, and is caused by float rounding errors in the engine as far as I'm aware.

Only workaround I know of is to engage 5x time warp before you warp to the maneuver node. Kicking to high warp right away is what triggers this.

[king of nowhere]

1 hour ago, Fraktal said:

This appeared a couple versions ago, yes, and is caused by float rounding errors in the engine as far as I'm aware.

Only workaround I know of is to engage 5x time warp before you warp to the maneuver node. Kicking to high warp right away is what triggers this.

if i go 5x and then tell it to warp to manuever node, it tell me that it cannot because manual warp already active

EDIT: it doesn't seem to do that anymore, actually. it does prevent me from ordering time warp only if i use x4 time warp.

Edited May 6, 2022 by king of nowhere

[Vanamonde]

I have not seen this happen in the stock game. Is it perhaps modding-related? 

[king of nowhere]

11 minutes ago, Vanamonde said:

I have not seen this happen in the stock game. Is it perhaps modding-related? 

likely, because i've also only seen it with mods that change the planets. opm in the old mission, rss in this one

[DeadJohn]

Roundoff errors in the game frequently distort orbits. I've made it a habit to quicksave frequently. I also readily use the Hyperedit mod and alt-f12 orbit cheat to fix orbit bugs.

The roundoff is especially frustrating when doing aerobraking passes. For example, a Duna lander might want to sample the atmosphere from multiple biomes on the way down. I set a high apoapsis, place periapsis barely inside the atmosphere so I don't deorbit too quickly, then plan to do multiple passes in and out of the atmo to gather science. Warping past each apoapsis will eventually, randomly, raise periapsis above the atmosphere.

[jimmymcgoochie]

Engage the first level of time warp manually, and then click warp to node. I recently had a lunar flyby change to an apoapsis of just 11Mm (from over 350Mm!) by just clicking warp to node, so now I always quicksave before warping and bump the warp one notch manually before letting anything else take over.

MechJeb seems less prone to this error as it engages time warp one step at a time, resulting in relatively small trajectory changes (which can still be annoying, but manageable) whereas the stock warp to node button cranks it up as high as it can immediately and seems to make the problem much worse.

[Nazalassa]

On 5/7/2022 at 7:23 PM, Vanamonde said:

Is it perhaps modding-related? 

I'm afraid no, because I got the exact same issue today with an unmodded KSP.

[se5a]

I tend to suspect the root of the problem is not rounding errors, but something causing the game to not put the entity into a rails type Kepler orbit, which thing causes it to keep it in the physics loop which is where you're possibly getting the rounding errors, or a phantom force.

This could be caused by Kraken drive type physics bugs and or something very similar. ie the game thinks there's a force acting on the ship, so it says in the physics loop.

Last time this happened to me (yesterday) I solved it by switching away from the ship to KSC before enabling warp. this *should* force the ship out of the physics loop. (I use Kerbal alarm clock, which stopped warp and switched me back to the ship when it needed it)

[Nazalassa]

Got the problem four times today!

That's getting annoying.

In the ideal KSP, this wouldn't happen.

[se5a]

Does using the built in alarm clock or KAC and switching to the KSC (or switching to any other object out of physics range should work) fix it for you?

[king of nowhere]

I don't know about anyone else, but to me manually warping at 10x first, and then activating higher time warp, helps.

Saving often and reloading if needed is also the general panacea

[GigFiz]

The workaround I use that seems to work (along with always quicksaving before a warp) is never using the warpto button and instead just manually clicking a spot on the flight path close to it and warping there. Why that works better than the warpto button, idk (maybe it doesn't ramp up as quick?) but I have had a high success rate (I think it has always worked, but these things blur together sometimes, so can't say 100%)  

Edit: just tried it again, and of course it failed this time . Though it worked when I was focused on the craft, and it failed when focused on the body. May be just a coincidence, maybe not. I'll keep on eye on it in the future

Edited August 25, 2022 by GigFiz
Update

[Nazalassa]

On 8/25/2022 at 10:20 PM, GigFiz said:

it failed when focused on the body

it's probably part of the issue as the same thing happens with my game.