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Trajectory above surface on Phobos ends in Collision #2237

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fat-lobyte opened this issue Jul 7, 2019 · 7 comments
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Trajectory above surface on Phobos ends in Collision #2237

fat-lobyte opened this issue Jul 7, 2019 · 7 comments
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@fat-lobyte
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Some trajectories around Phobos end up by Principia detecting collisions.

In this case, when the vessel goes below 2685m "sea level" and 738 m above ground while time warping, it freezes in place. If the timewarp is stopped, the vessel continues moving away but the camera stays in place. The Warning log file reads:

W0707 14:14:08.615089  9604 plugin.cpp:778] Vessel Mars 4 - Phobos Lander (4f6db824-027f-47e7-9413-d05abba21700) collided with a celestial: OUT_OF_RANGE: Collision detected

Here is a screenshot of the trajectory:
screenshot218

Here is a quicksave file to reacreate the situation: phobos-plunge-logs.zip
Logs: phobos-plunge-logs.zip

@fat-lobyte fat-lobyte changed the title Subsurface trajectory on Phobos ends in Collision Trajectory above surface on Phobos ends in Collision Jul 7, 2019
@pleroy
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pleroy commented Jul 13, 2019

I think that you linked to the logs twice but didn't link to the save. It would be useful to get it because from the logs everything is as expected, ie the vessel seems to be killed (which is what we are trying to do after the collision).

Now it's a bit embarrassing that we incorrectly detect the collision in this case, but it's not easy to fix: on the one hand we cannot trust KSP to do the right thing, on the other hand we cannot afford to take the body shape into account in the middle of the force computation.

@fat-lobyte
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I think that you linked to the logs twice but didn't link to the save

Oops, my bad. Here's the save: phobos-plunge.zip

but it's not easy to fix: on the one hand we cannot trust KSP to do the right thing, on the other hand we cannot afford to take the body shape into account in the middle of the force computation.

Fair enough. This is not really much of an issue for me, I just wanted to visit Phobos and Deimos once. I'll keep away from space potatoes for now.

As a workaround , are there any rules where I can and can't safely fly?

@pleroy
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pleroy commented Jul 13, 2019

We detect a collision at 90% of the mean radius (this is working fine for just about everything, except the Mars satellites). The mean radius of Deimos is 6.2 km and that of Phobos is 11.08 km. So around 10 km you should be fine.

@pleroy
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pleroy commented Jul 31, 2019

We should obtain the min radius from the game and use that instead of our mean radius (a margin like 90%, 95% or 99% would probably be good for safety).

@pleroy
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pleroy commented Aug 24, 2019

#2298 obtains the min radius from the game and uses that (with some tolerance) to detect collisions. With that change we were able to land on Phobos. The trajectories will still be missing in some areas close to Phobos (as seen on the picture for the bottom part of the prediction) but that's much harder to fix.

@pleroy pleroy added the bug label Aug 24, 2019
@pleroy pleroy added this to the del Ferro milestone Aug 24, 2019
@eggrobin
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Tested by fooling around in the lowlands of Phobos in del Ferro:

@pleroy
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pleroy commented Apr 21, 2022

Closing as trajectories are hidden by mountains after #3035.

@pleroy pleroy closed this as completed Apr 21, 2022
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