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[0.1.1.0] Wrong trajectory prediction through SOI changes for many bodies (affects planetary return missions)


Draradech
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KSP2 0.1.1.0.21572   -   Windows 10 Home 21H2   -   Ryzen 9 3950X   -   RTX 2080 Ti (Driver 531.18)

 

Summary:
Predicted trajectories leaving the SOI of most bodies are incorrect. This affects the manuever plan trajectory as well as the trajectory displayed after burn. The trajectory flips to the correct one after leaving the SOI.

 

I noticed that the map view camera rotates by the same amount as the perceived wrong angle of the trajectory relative to the bodies affected when switching focus between the vessel and Kerbol (or the parent body for moons). The following are the approximate rotations relative to the parent body, these match my experiences for Kerbin, Mun, Minmus and Duna, as well as the screenshots of others I have seen in this thread:

Spoiler
Moho -85
Eve -15
Gilly -90
Kerbin 0
Mun 0
Minmus -115
Duna -135
Ike 0
Dres -10
Jool -50
Laythe 0
Vall 0
Tylo 0
Bop -35
Pol -15
Eelo 50

(Note that I had the Lazy Orbit mod installed to get to all the bodies easily. The observed behaviour matches an unmodded installation for all bodies I have been to so far.)

 

Original report:

KSP2 0.1.0.0.20892   -   Windows 10 Home 21H2   -   Ryzen 9 3950X   -   RTX 2080 Ti (Driver 528.49)

(Save file link removed, this affects all craft).

History: This craft launched from Kerbin, landed on Duna, picked up a stranded Kerbal, and launched from Duna to the east. Now in 200km Duna Orbit.

Problem: As can be seen in the video, a maneuver node set up to leave Duna retrograde leads to a planned trajectory of a Kerbol orbit with an AP further out than Duna and PE at Duna (this is wrong). This will also be the case for the displayed trajectory after the burn, right until the craft exits Duna SOI. At Duna SOI exit the trajectory flips to the correct one, with a Kerbol AP at Duna and PE further in (see images - images from a different run than video).

oC55Zi3.jpg

clDLtTc.jpg

 

Edited by Draradech
Added additional information, changed title
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Got the same problem on Duna.

  • KSP Version :
  • 0.1.0.0.20892
  • Operating System and version :
  • Windows 10 Pro
  • CPU and GPU models, any other system information which could be relevant :
  • I7 8700K, RTX 3070, 32Go RAM DDR4
  • Description of the bug.  
  • The map tell me to go into retrograde of Duna to increase around Kerbol and go prograde of Duna to descrease around Kerbol. It's just visual, the physics is good and if I go retrograde of Duna, I decrease my orbit around Kerbol
    • Expected Behavior
    • Going into retrograde of Duna decrease the orbit around Kerbol in the map view
    • Observed Behavior
    • Going into retrograde of Duna increase the orbit around Kerbol in the map view
  • Steps to Replicate
  • In orbit around Duna, going to retrograde of Duna
  • Fixes / Workarounds (if known..)
  • I don't know
  • A list of ALL mods.  If the list is long, please consider using a spoiler window.
  • BepInEx
  • Sticky Orbit Markers
  • Other Notes / Screenshots / Log Files (if possible..)


I tried to create a maneuver node to come back on Kerbin, I go in the retrograde of Duna but my AP round Kerbin increase.

KSP2_x64_QbkpLGjJDC.jpg?width=1618&heigh

KSP2_x64_vApd3ks7CD.jpg?width=1618&heigh

 

I seen this problem around Minmus yesterday, I've deleted the node and tried by myself and the game tell me that my AP increase like the node said before.

image.png?width=1618&height=910

image.png?width=1618&height=910

 

I tried to escape the SOI of Duna and finally, I got my PE decreasing like I wanted.

image.png?width=1618&height=910

Edited by Niko_Dragovich
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Ah, I'm not the only one who can't return. But yes, planned maneuver and resulting trajectory led me thinking that I will intercept Kerbin, but as soon as I left Duna SOI it was nowhere near what it said a second earlier. I previously thought it was because of timewarp but no.

Transfer trajectory in Duna SOI, exactly as it was showed in the maneuver

WtEvVSw.jpg

After leaving SOI:

FOF6W9C.jpg

Edited by The Aziz
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Instance on wrong velocity prediction during a returning trip from Laythe is also available on Bilibili (language: Chinese):

https://www.bilibili.com/video/BV1nv4y1a7yH (by ReachStar)

At 11'56'':
-- "最终,在利用引力弹弓返回时,出现了弹射后显示轨迹和实际轨迹不一致的 bug,飞船 dv 耗尽"
-- Finally, when trying to return by utilizing gravitational slinghost, a bug emerged, where the predicted trace does not match the actual orbit after the slingshot. The spacecraft runs out of its dv (thus the returning attempt failed).

Though the returning trip is not shown with its full details, it seems that this issue is happening on exiting Jool's SOI.

Edited by sunnyssk
Checked the video again and it seems to be only related to Jool rather than its satallites.
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  • 2 weeks later...

I spent a LOT of time last night and tonight trying to get as close to the canonical "optimum" dV transfer from Jool back to Kerbin. This was the projected trajectory AFTER I had completed the Jool departure burn. Note the periapsis very close to Kerbin's orbital plane.

0aaqeku.png

However, immediately after leaving Jool's SOI, having made no maneuvers or any kind of trajectory adjustment, my vessel was tremendously far off the trajectory projected after the departure burn:

PL2IFLD.png

The orbit after leaving Jool's SOI required almost 1,000 m/s to get anything close to a Kerbin encounter, and then a final mid-course burn of about 140 m/s to ensure it. And then once inside Kerbin's SOI, due to the inability to see the trajectory projections through the SOI, I was so far off I needed almost 2,400 m/s radially to get a Pe close enough to guarantee an atmospheric entry.

Nearly all of the remediation efforts set forth above, however, can be attributed to the utterly WRONG trajectory that resulted at the exit from Jool's SOI. I was only able to salvage this return because I had a massively over-powered SWERV powered transfer stage with a good amount of dV left for the return, and a completely full Laythe methalox powered lander with 3,400 m/s dV available. (*)

 

(*) I vastly mis-guesstimated the T/W ratio for Laythe so I just gave up on the lander and came home with full tanks. Had I not done so, these four Kerbals would be stranded in digital hell forever. 

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Unfortunately, this does not appear to have been corrected in Patch 1.

I loaded up the save I made prior to executing this Jool escape burn and once again, after completing the burn showing a nice near-Kerbin approach at the completion of the burn, once outside Jool's SOI the actual solar orbit trajectory was wildly different than predicted. Once again, it took nearly 1,000 m/s to get a proper Kerbin close approach and intercept. Fortunately, with the fixes patched conics inside SOI's, I was at least able to make some nice small mid-course burns to get a good close approach and not have to spend thousands more meters per second to achieve an entry and recovery, unlike the other night's attempt. 

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So I planned a maneuver to lower my orbit from minmus to mun, and the trajectory it had me take to escape minmus seemed fishy, but it showed I would get a mun intercept for it, so i gave it a try. instead, I got sent on a kerbin escape trajectory that didn't lower my orbit anywhere, but only showed this after I left minmus' SOI. I went back to replicate the problem and got basicly the same result. This is all after the first patch.

https://imgur.com/gallery/fvvYX7U

My pc:

OS: Windows 10 Home, version 22H2

CPU: 12th Gen Intel(R) Core(TM) i5-12400F   2.50 GHz

GPU: AMD Radeon RX 6600

RAM: 16GB

Mods: none

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Yes this happens for Minmus, Duna, and apparently Jool.  You can eyeball just putting your trajectory on a retrograde heading to get around it, but it really sucks interplanetary.

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I can also confirm incorrect conic-patching at Duna. My craft entered Duna SOI from a wildly different direction than the predicted orbit, although the predicted periapsis and inclination at least seemed to be accurate. And now trying to leave Duna again I seem to be unable to plot a return to Kerbin, with any escape orbit resulting in an increase of Kerbol SMa, as though I had left Duna prograde, regardless of what direction I align my escape orbit. 

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This has been occurring since launch and not fixed in Patch 1. See my bug report related to my Joel return trajectory the other evening. 

Last night, I loaded a save from before that burn, recreated it, and the same bug persists with v0.1.1

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When in Duna' SOI and attempting to create a maneuver node for an interplanetary transfer back to Kerbin something goes wrong in the orbit calculations. Because if I make a maneuver node that should make the orbit bigger (burning along Duna's prograde), the orbit line appears to be a smaller orbit (around the sun). This stops happening once you leave Duna's SOI, so you can create a maneuver which appears to give an encounter with Kerbin, but only from Duna's broken calculations, so once you leave the SOI the orbit has gotten bigger instead of smaller. This also works the other way, if you make a maneuver to burn Duna's retrograde, which should make the orbit smaller, it appears bigger until you leave Duna's SOI.

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So it's still not fixed. Bummer.

Well honestly the current workaround is to not trust the shown trajectory, but rather focus and setting up the maneuver node in the right place, in front of the planet for lowering orbit, behind for raising. Any errors you can fix after leaving SOI.

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1 hour ago, The Aziz said:

So it's still not fixed. Bummer.

Well honestly the current workaround is to not trust the shown trajectory, but rather focus and setting up the maneuver node in the right place, in front of the planet for lowering orbit, behind for raising. Any errors you can fix after leaving SOI.

Yep.  Basically, just use one of the online phase-angle calculators to get yourself into the correct position for the transfer burn, then burn just enough to exit the current SOI. Once outside the current SOI, make the rest of the burn necessary for an intercept. 

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Can confirm. Just saw this behavior while trying to leave Minimus on way back to Kerbin. Following the maneuver actually resulted in elevating my orbit and leaving the kerbin SOI.

 

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Maybe it has something to do with mission time versus actual time. Since what time it is in the simulation is very important to this game, could it be confused and think it's in a different time frame? This could be a consequence of multiplayer maybe needing to have different frames of reference for what time it is and where planet SOIs would be at that given time. 

When this happened to my duna-ike mission, re-docking my lander after the duna ascent caused the mission timer to reset and give me some kind of "vessel launched" pop-up. Re-setting the timer would make the game think it's on the wrong side of the kerbolar system when I tried to burn back to Kerbin.

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  • KSP Version
    • 0.1.1.0
  • Operating System and version  (Windows 10, Windows 11)
    • Windows 10
  • CPU and GPU models, any other system information which could be relevant
    • i9-9900k
    • ASUS TUF 3080
  • Description of the bug.  
    • Expected Behavior
      • When I try to return from a moon to Kerbin or when I try to return from Duna, I expect to do an escape burn on the inside of an orbit (the side of the mun facing Kerbin or the side of duna facing Kerbol) that results in a smaller orbit than that of the body I am leaving, as if I had done a retrograde burn from that orbit.  
    • Observed Behavior
      • I get a larger projected orbit as if I had done a prograde burn.  The bug is consistent in that if I do an escape burn on the other side, I get a projected orbit that's smaller than the moon's/planet's orbit.
      • Once I leave the moon or planet's SOI, I get the correct orbit based on my angle of departure, i.e. the incorrect orbit disappears and the correct one takes its place. 
      • This makes it very difficult to plan a reentry maneuver.
  • Steps to Replicate
    • From a circular orbit around the mun, minmus, or duna, create maneuver node that leads to a retrograde escape trajectory.
    • Executing the burn still results in the wrong orbit
    • Exiting the SOI leads to the correct orbit
    • Bug doesn't always manifest but seems to recur with the same saves
  • Fixes / Workarounds (if known..)
    • Using an external calculator to determine angle and delta_v of maneuver.
  • A list of ALL mods.  If the list is long, please consider using a spoiler window.
    • None
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