Kerbal Space Program

One interesting thing I found in the player.log file was this:

[OrbitDriver]: On-Rails SOI Transition from Tylo to Tylo.
Transition UT Range: 5900013.4 - 5910013.4.
Transition UT: 5909861.118. Iterations: 20.

Prior to that, Jool was the dominant body. Not sure if this is a normal message or not, but the statement 'SOI transition from Tylo to Tylo.' indicates to me that perhaps the game already thought it was within Tylo's SOI, and therefore would not need to plot encounter information?

The above section of the player log appeared shortly before the collision with Tylo.

The quicksave is result of determined effort to get undetected intercept which ends up in a crash. "surprise slingshots" from Tylo happen to me regularly whenever I visit Jool, however "surprise crash" only happens rarely.

Probable reason is that solver or a branch of one used for this particular set of orbital parameters contains an error and does not find a solution which exists. Since I have no idea how these solvers are organized, I also have no idea what properties must orbital parameters have for this to occur. I can, however, replicate such undetected intercept anytime e.g. on Mun SOI from low Kerbin orbit. The situation has three modes:

1/ the intercept is completely undetected
2/ the intercept randomly flickers on and off, even on time warp when the orbital parameters are fixed
3/ there is partial intercept with no SOI entry point and no periapsis, just a small part of trajectory inside the SOI and exit point.

These three situations happen on closely grouped sets of orbital parameters so they may be result of the same solver bug, but it is not certain

I believe the "transition from Tylo to Tylo" is caused by the fact that the game suddenly realized the ship is inside Tylo SOI although it did not expect that to happen. Initially, Jool was the dominant body, and conic patches were drawn relative to it, not to Tylo. Also in the save file, the initial dominant body of the ship is Jool.

First, thanks Kasuha for the information. This bug has been forwarded to the experimental, QA, and developers.

Of the three modes you listed above, I've seen all three while attempting to transfer to Duna from a Kerbol orbit, originating from Kerbin.

If you find additional information that may be helpful, this would be a good place to report it.

Note to the last update: some of notes to uploaded files are mixed up - I put some observations next to wrong files. Sorry about that.

Another possible explanation (at lest for some related cases):
If the current fragment of patched conics intersects SOI of several moons only intersection with the first (closest to the planet) moon not the first intersection (the actual SOI switch that may occur with higher moons) is detected. Seems that the patched conics system is checking moon SOI intersects starting with the closest to the planet and stopping at the first intersection found without checking if the other moons SOI intersection occurs first.

As example let's take LKO-Minmus transfer trajectory:
0) no actual intersection occurs - elliptic trajectory displayed
1) Mun encounter happens first - Mun encounter displayed properly, if the trajectory after Munar slingshot intersects Minmus SOI, second intersect is displayed
2) only Minmus encounter found - Minmus encounter displayed properly (other bugs might be present), if the trajectory after Minmus flyby then encounters the Mun, the second encounter will be displayed as well
3) the trajectory intersects Minmus SOI, but if there wasn't Minmus it would have Mun encounter on the way back down (after Minmus encounter!) - only the (hypothetical!) Mun encounter displayed, but Minmus encounter is ignored! until you suddenly find yourself in Minmus SOI.

The same seems to be true in cases when predicted Laythe encounter ignores Tylo and Vall encounters that happen before that.

Alchemist wrote:

If the current fragment of patched conics intersects SOI of several moons only intersection with the first (closest to the planet) moon not the first intersection (the actual SOI switch that may occur with higher moons) is detected. Seems that the patched conics system is checking moon SOI intersects starting with the closest to the planet and stopping at the first intersection found without checking if the other moons SOI intersection occurs first.

If that was the case, it would still be a bug. But this is certainly not the case.

First, when I was setting up the example, I was in parameter space where the intercept did not show up regardless whether there was or was not Laythe intercept. The Laythe intercept just randomly popped up as I was trying to tweak the trajectory to crash into Tylo.

Second, it is possible to set up similar situation in Kerbin SOI where the ship will crash into Mun without the Mun intercept showing up until the ship enters the Mun SOI. Mun is the closest moon in Kerbin SOI and the orbit does not even have to intersect orbit of Minmus.

Second, it is possible to set up similar situation in Kerbin SOI where the ship will crash into Mun without the Mun intercept showing up until the ship enters the Mun SOI

Yes, I can confirm that this also happens sometimes (depending on orbital parameters?). We are likely having at least 2 different bugs at once here.