Is it normal for trajectory values to be rapidly fluctuating while your craft is completely stationary?

[starship747]

Is it normal for the values of things such as time to periapsis, vert. speed, horizontal speed, periapsis height, etc to be rapidly going up and down? And the mechjeb atmosphere info tab is telling me the pressures and density keeps going up and down as if i was actually flying real fast or something even though im stationary. Does anyone know if this is a normal part of the game's orbital workings and stuff? 

https://imgur.com/a/pls-help-QKqwZO5

[arbsoup]

Information on your orbit and such is all meaningless when you're parked on the surface, so in the first place you can probably close these windows.

It's calculated based on the tiny, tiny differences in part positions between frames due to game physics (each part experiences forces from gravity and other parts separately, so over time your craft very subtly jitters around in random directions); if, for one frame, your craft's root part happens to be moving very slightly east, then Mechjeb's displays (which are extremely sensitive and can report tiny numbers) will calculate atmospheric drag and an "orbit" (that intersects the ground) and such as if you were moving very slightly east.

Once you start moving you'll appear to get "constant" or "smoothly"-changing values, merely because the craft's bulk motion is simply many times bigger than these random physics jitters. (For example, Mechjeb reports a dynamic pressure in micropascals for the parked plane here, but a vehicle in typical atmospheric flight is experiencing kilopascals — billions of times more. So the micropascals of randomness just disappear behind about nine decimal places.)

You can also use (rails) timewarp and see that all the numbers lock down, because physics no longer gets calculated for your parts.

Edited Sunday at 11:40 PM by arbsoup

[starship747]

37 minutes ago, arbsoup said:

Information on your orbit and such is all meaningless when you're parked on the surface, so in the first place you can probably close these windows.

It's calculated based on the tiny, tiny differences in part positions between frames due to game physics (each part experiences forces from gravity and other parts separately, so over time your craft very subtly jitters around in random directions); if, for one frame, your craft's root part happens to be moving very slightly east, then Mechjeb's displays (which are extremely sensitive and can report tiny numbers) will calculate atmospheric drag and an "orbit" (that intersects the ground) and such as if you were moving very slightly east.

Once you start moving you'll appear to get "constant" or "smoothly"-changing values, merely because the craft's bulk motion is simply many times bigger than these random physics jitters. (For example, Mechjeb reports a dynamic pressure in micropascals for the parked plane here, but a vehicle in typical atmospheric flight is experiencing kilopascals — billions of times more. So the micropascals of randomness just disappear behind about nine decimal places.)

You can also use (rails) timewarp and see that all the numbers lock down, because physics no longer gets calculated for your parts.

Thank you for your reply.. ok so it is normal, it must be something else giving me lag. I was getting console error messages with mechjeb so I uninstalled the plugin. Is it normal to get lag spikes when other (non error) console messages come up? and how about "warning" messages? I seem to be getting lots of lag spikes even with this new computer i got which is decent. I used to play KSP on a 2011 iMac which wasn't great, but I had much higher expectations for performance with ksp with this new pc. If I have like 3 or 4 small crafts all next to each other it'll get somewhat choppy. Even if its one single ship with 300 parts or so itll get choppy too. thank you again for explaining

[arbsoup]

Any computer will run the game slower with a 300-part craft than with a 30-part craft because part physics is (IIRC) mostly bottlenecked by single-threaded CPU performance, and a single CPU core can only get so good.

The question is just whether the slowness you experience is primarily from that, or primarily from other stuff. And I don't know. You have EVE and Parallax installed, which are notably heavy on GPU usage and might be causing slowdown. In the extreme case, lag spikes might be caused if you are close to full usage on RAM, as a result of having a ton of mods installed in general.

Errors or exceptions in the game log are not necessarily caused by or related to lag. Right now it looks like you've highlighted some Parallax-related grass bugs (known problem with Parallax 2 but shouldn't really affect performance; no longer a problem in Parallax Continued). Other than that the random snippets of log you posted don't reveal anything much. Most likely it's just that you're running a combination of really heavy mods and getting up to a modestly high part count.

Edited Monday at 12:40 AM by arbsoup

[starship747]

58 minutes ago, arbsoup said:

Information on your orbit and such is all meaningless when you're parked on the surface, so in the first place you can probably close these windows.

It's calculated based on the tiny, tiny differences in part positions between frames due to game physics (each part experiences forces from gravity and other parts separately, so over time your craft very subtly jitters around in random directions); if, for one frame, your craft's root part happens to be moving very slightly east, then Mechjeb's displays (which are extremely sensitive and can report tiny numbers) will calculate atmospheric drag and an "orbit" (that intersects the ground) and such as if you were moving very slightly east.

Once you start moving you'll appear to get "constant" or "smoothly"-changing values, merely because the craft's bulk motion is simply many times bigger than these random physics jitters. (For example, Mechjeb reports a dynamic pressure in micropascals for the parked plane here, but a vehicle in typical atmospheric flight is experiencing kilopascals — billions of times more. So the micropascals of randomness just disappear behind about nine decimal places.)

You can also use (rails) timewarp and see that all the numbers lock down, because physics no longer gets calculated for your parts.

The console keeps repeating this over and over, would this be volumetric clouds causing the error? 

[EXC 20:36:48.110] ArgumentNullException: Value cannot be null.
Parameter name: _unity_self
    ParallaxGrass.ScatterCompute.AwaitDistributeReadback (UnityEngine.Rendering.AsyncGPUReadbackRequest req) (at <f8c4be58fd694d77865148b1dd7ab67c>:0)
    UnityEngine.DebugLogHandler:LogException(Exception, Object)
    ModuleManager.UnityLogHandle.InterceptLogHandler:LogException(Exception, Object)
    UnityEngine.Debug:CallOverridenDebugHandler(Exception, Object)

[starship747]

1 minute ago, arbsoup said:

Any computer will run the game slower with a 300-part craft than with a 30-part craft because part physics is (IIRC) mostly bottlenecked by single-threaded CPU performance, and a single CPU core can only get so good.

The question is just whether the slowness you experience is primarily from that, or primarily from other stuff. And I don't know. You have EVE and Parallax installed, which are notably heavy on GPU usage and might be causing slowdown. In the extreme case, lag spikes might be caused if you are close to full usage on RAM, as a result of having a ton of mods installed in general.

Errors or exceptions in the game log are not necessarily caused by or related to lag. Right now it looks like you've highlighted some Parallax-related grass bugs (known problem with Parallax 2 but shouldn't really affect performance; no longer a problem in Parallax Continued). Other than that the random snippets of log you posted don't reveal anything much. Most likely it's just that you're running a combination of really heavy mods and getting up to a modestly high part count.

Oh I see, so, if my computer has quite a few cores then the single-core performance is not so good, right? KSP is just very performance limited reguardless?. So at that point it doesn't matter how your computer specs are. Also I have volumetric clouds installed on top of the other visual mods.

As for ram this computer has 32gb but could that still overflow with all these? Since that screenshot I have removed a dozen or more ish mods and I think it helped a bit. But there are still lag spikes from normal console messages. And a few errors. When I have my ship in orbit ofthe moon Pandor for example, any time I pan the camera and the gas giant Novin comes into view i'll get a lag spike with a console message for example.

I thought I remember reading you can go to your pc settings and allocate more ram to a certain thing like ksp, I'm not sure if that is true. I will try removing more of these mods. Thank you again for explaining this to me

 

[arbsoup]

3 minutes ago, starship747 said:

But there are still lag spikes from normal console messages. And a few errors. When I have my ship in orbit ofthe moon Pandor for example, any time I pan the camera and the gas giant Novin comes into view i'll get a lag spike with a console message for example.

Errors generally are not causing the lag, nor are the messages about the lag. Likely the loading of a planet with various visual effects prompts all these visual mods to do something, they log what they do (as always) with or without anything going wrong internally, but processing the visualization of a planet is simply what causes a bit of slowdown in the meantime.

If you do notice that a specific mod is giving you a specific error whenever a planet is loaded, you might want to contact the mod authors on the forum or Github or whatever with a full KSP.log and mention what's going on in the console. Again, that is not necessarily what is causing lag, so you have to be a little cautious; you can say "I get an error and a lag spike when this planet enters the screen", but not "there's a lag spike from the console" because you don't know that.

[starship747]

5 minutes ago, arbsoup said:

Errors generally are not causing the lag, nor are the messages about the lag. Likely the loading of a planet with various visual effects prompts all these visual mods to do something, they log what they do (as always) with or without anything going wrong internally, but processing the visualization of a planet is simply what causes a bit of slowdown in the meantime.

If you do notice that a specific mod is giving you a specific error whenever a planet is loaded, you might want to contact the mod authors on the forum or Github or whatever with a full KSP.log and mention what's going on in the console. Again, that is not necessarily what is causing lag, so you have to be a little cautious; you can say "I get an error and a lag spike when this planet enters the screen", but not "there's a lag spike from the console" because you don't know that.

Okay I gotcha so an error message and lag are not necessarily related? That one from the gas giant is probably a visual thing. Mostly I'll get like a hundred error messages when loading a craft with extraplanetary launchpads. But the lag could just be the vessel loading I guess even if excessive. 

[Vanamonde]

How big are the fluctuations? The game has to use numbers to simulate smooth curves and there are things like rounding off decimal places which can cause the readings to change. 

[starship747]

On 3/31/2025 at 1:42 AM, Vanamonde said:

How big are the fluctuations? The game has to use numbers to simulate smooth curves and there are things like rounding off decimal places which can cause the readings to change. 

Quite a lot actually. The "time to apoapsis" will go from 0min to 10 and back several times every second. Horizontal and vert speed will go from 0m/s to 50, then into the hundreds, and back down into negative values, and back up into hundreds. All in less than a second. 

 

Under atmosphere info, dynamic pressure, aero drag, and atmo density are all going crazy too as if I was teleporting between different altitudes. Dynamic pressure will go from 50 nPa to 300 and back.

On 3/31/2025 at 1:42 AM, Vanamonde said:

How big are the fluctuations? The game has to use numbers to simulate smooth curves and there are things like rounding off decimal places which can cause the readings to change. 

https://imgur.com/a/ksp-problem-QKqwZO5

[Bej Kerman]

43 minutes ago, starship747 said:

Quite a lot actually. The "time to apoapsis" will go from 0min to 10 and back several times every second. Horizontal and vert speed will go from 0m/s to 50, then into the hundreds, and back down into negative values, and back up into hundreds. All in less than a second. 

 

Under atmosphere info, dynamic pressure, aero drag, and atmo density are all going crazy too as if I was teleporting between different altitudes. Dynamic pressure will go from 50 nPa to 300 and back.

You can ignore orbital properties. The orbital values fluctuate because the math used to figure out your orbit isn't supposed to be applied to an object at rest on the surface.

Atmo density and pressure don't fluctuate in the video you shared. Dynamic pressure fluctuates because it's based on your airspeed, and your airspeed is very close to 0.

TL;DR: This is not an issue or a bug, all of this is very normal.