Orbiting Kerbin Out of it's SOI!

[JK_Kerbineer]

So I recently returned from a Duna Trip, and Kerbin greeted me with this,

I looked at the KSP wiki, and it turns out,that I was 7 million meters aove Kerbin's SOI, and was still orbiting it.

Does anyone know how this could happen.

Edited October 15, 2017 by JK_Kerbineer

[NSEP]

Maybe because the trajectory is tight enough for orbiting?

[OhioBob]

2 hours ago, JK_Kerbineer said:

Does anyone know how this could happen.

A glitch.  Weird things happen sometimes.  I wouldn't worry about a one time freak occurrence.

[Jas0n]

Maybe the wiki data isn't accurate? or maybe you have mods that affect it?

[NateisKerbal]

It's most likely a glitch, ignore it.

[Zeiss Ikon]

I see a second AP marker in that plot (trying to view the full size image doesn't work, there seems to be a glitch in the imgur embed).  It looks like you're on a capture trajectory, and the game is displaying the pre-capture AP as well as the post-capture marker.  This is probably because you have a Munar encounter on that orbit.

[G'th]

^ That.  Its just showing your trajectory path but it uses the blue orbit lines. 

[MoarBoostersRUS]

Magic definitely magic

[OhioBob]

6 hours ago, Zeiss Ikon said:

I see a second AP marker in that plot (trying to view the full size image doesn't work, there seems to be a glitch in the imgur embed).  It looks like you're on a capture trajectory, and the game is displaying the pre-capture AP as well as the post-capture marker.  This is probably because you have a Munar encounter on that orbit.

It looks to me like we have a vessel currently at an altitude (above terrain) of 83,413.2 km moving toward an apoapsis of 90,887.7 km.  The blue orbit line passes through apoapsis and then moves toward periapsis (-450 km), where the vessel will impact Kerbin.  Despite the inevitable encounter with Kerbin, the orbit line continues on the other side and moves toward an encounter with one of the moons (hard to tell which one).  The vessel passes through the moon's sphere-of-influence (brown orbit line), and exists to have a new orbit (purple line) with a second apoapsis.

The problem, however, is that the vessel is currently just inside Kerbin SOI, while the apoapsis is outside the SOI.  The blue orbit line should show the vessel leaving Kerbin's SOI just past the its current position.  We should not be able to see an elliptical orbit around Kerbin having an apoapsis higher than Kerbin's SOI.  Also the indicated speeds are all messed up (82.74 m/s vertical and 24,483.56 m/s vertical).  I did a quick calculation of what the vessel's speed should be and came up with 83.6 m/s total.  Something is definitely glitchy here.

[samstarman5]

From when maneuver nodes were first introduced, I've seen plenty of instances where a vehicle on an escape trajectory would show an orbit like this when it was viewed from another vehicle.  It never bothered me as it seemed to merely show "this is what would be if the vehicle was not on an escape trajectory."  In fact it was rather fascinating to see such things. Nothing was changed about the vehicle's trajectory and it progressed as I saw it would when I last left it.  It was just an odd anomaly in the maneuver node as seen by a third party.

If it happens as you saw it in the image again, from the own vehicle's perspective, it might be worth doing a test run with mods off as a bit of troubleshooting, and if things do perform differently then, check to make sure your mods are up to date. (Make backups of your saves so you can go back to your original save with nothing lost if everything goes ok)

Edited October 17, 2017 by samstarman5

[Snark]

On 10/15/2017 at 9:57 PM, OhioBob said:

The blue orbit line should show the vessel leaving Kerbin's SOI just past the its current position.  We should not be able to see an elliptical orbit around Kerbin having an apoapsis higher than Kerbin's SOI.

Technically, yes.  My guess is that this isn't quite a "bug" per se, in the sense of being a "glitch".  My guess is that what it really is, is that the orbit-drawing code uses some very simple logic and you've discovered an unusual edge case that doesn't come up often.

Of course, since I don't work at Squad, I can't see inside their code, but I can guess what might be happening here.  My guess is that someone probably wrote some logic that looks something like this (paraphrased):

1. Okay, I need to draw the trajectory.  Do I draw a closed orbit, or do I draw an escape path?
2. Check whether the vessel is going faster than escape velocity.
   • If it is:  Draw an escape path.
   • If it isn't:  Draw a closed orbit

I have seen orbits drawn in the game that clearly would be closed ellipses, were it not for the SoI boundary, so it's likely somewhat more complicated than that, perhaps some complexity that's introduced by the fact that you've got a future Mun encounter.

The current vessel is in a literal edge case:  It's right out at the very very edge of the SoI.  Out there, escape velocity is practically nothing-- so it's pretty hard to be going fast enough to push your Ap outside the SoI without actually escaping entirely.  But this particular ship has managed that.

I expect the reason this hasn't been found and fixed before this, is that it's a very rare situation that almost no one ever runs into.  Most folks don't really have much reason to spend a lot of time in Kerbin's SoI out past Minmus, and the margin for "orbit just past the edge of the SoI without escaping entirely" is going to be razor-thin, which means the chance of bumping into it accidentally seems low.

On 10/15/2017 at 9:57 PM, OhioBob said:

Also the indicated speeds are all messed up (82.74 m/s vertical and 24,483.56 m/s vertical).  I did a quick calculation of what the vessel's speed should be and came up with 83.6 m/s total.  Something is definitely glitchy here.

I think that's a red herring.  I believe the reason you're seeing those wonky numbers is likely an issue with whatever mod is displaying them, not with the stock game.  What I think is going on there is that it's displaying the surface speed, not orbital speed.  I did a quick calculation.  The vessel is 83.4M meters above surface, meaning an orbital radius of 84M meters.  Kerbin rotates every 6 hours.  Let's do a quick calculation of "how fast would you be going if you were moving around Kerbin in a circle of radius 84M meters, once every six hours."

84,000,000m * 2π / (6 * 3600s) = 24,434 m/s

Sounds kinda familiar.

[JK_Kerbineer]

@Snark

Well, at least Jeb's happy for not being flung out into interplanetary space.

[severedsolo]

It's worth mentioning that the SOI is not a hard line either. It changes depending on whether you are entering/exiting it etc.

I've only noticed this at Kerbin, but it probably happens elsewhere. You have to be closer to the SOI to enter it than you do to escape. I presume this is to stop you "flip-flopping" over the line when you are on the edge.

In earlier versions of the game, if I had just escaped, and went to timewarp, I would "jump" back into Kerbins SOI.

I'm curious as to what actually happened to that ship, as I wonder if it was really escaping, but the Mun encounter messed up the patch conics rendering.