Some kind of warning when orbit path intersects celestial

[PlutonianPassenger]

I already get "The integrator encountered a singularity" when an orbit I've made passes through the exact center of a planet.

But there are a lot of times where I think I have found a great trajectory for gravity assists, only to find that my plan goes -300000 m beneath the surface of a planet. It is kind of annoying to have to repeatedly zoom in to make sure that the orbit will stay outside of both the celestial and its atmosphere.

Is there a way to implement an on-screen warning whenever the periapsis goes beneath the surface (as measured by the indicators?)

[pleroy]

Note to self:

A collision with a celestial detected here (it's not exact as it doesn't take the terrain into account, but good enough for this issue) and is propagated as an OutOfRangeError. The error then bubbles up through BurnSegment and CoastSegment and is handled in various places (for instance here) to make the segment anomalous. The anomaly is observed here on the C# side, and it should cause the next burn editors (if any) to be disabled here. I suspect that we could use the status here to inform the user somehow. How we do that exactly remains to be determined.

This is from reading the code, I didn't try in game, so all of this should be taken with a grain of salt.

[eggrobin]

it's not exact as it doesn't take the terrain into account, but good enough for this issue

It might not be good enough: We detect the collision only where we evaluate the forces, but depending on where the steps of the variable-step method land, there might not be an evaluation within the planet.

[PlutonianPassenger]

I suppose it wouldn't be hard to query the coordinates/position of a celestial, then query the distance of a spacecraft to that position, then get the magnitude of the position difference; if it is less than the radius of the planet, then an error appears on screen?

[pleroy]

@eggrobin I would assume/hope that the integrator would use smaller steps near the periapsis. At any rate, this would have to be best-effort: we would not take terrain or atmosphere, and we might not detect if you just graze the planet. I don't see that we have alternatives that are not prohibitively expensive anyway. Note that this assumption would be easy to test in game.

@PlutonianPassenger You are missing the point. Yes, we know how to compute the distance. But at what time do we compute it? For most of the duration of the flight plan nothing interesting happens, but we don't know magically when something interesting happens.