Mun station crashing into the mun

[Simen]

I had a mun space station in an 10k orbit around The Mun and after some days it disappeared. I assuming it crashed into the mun, but I don't believe there is any terrain around the mun which is in anyway near being 10k tall. So how did my space station crash into the mun orbiting 10k over it? 

[Zhetaan]

30 minutes ago, Simen said:

I had a mun space station in an 10k orbit around The Mun and after some days it disappeared. I assuming it crashed into the mun, but I don't believe there is any terrain around the mun which is in anyway near being 10k tall. So how did my space station crash into the mun orbiting 10k over it? 

Welcome to the forum!

The highest point on the Mun is about 7100 metres.  It's also in the southern polar region; if your station was in an equatorial orbit, then the terrain was never very close to it.  However, there is a point of closest approach where objects in low orbit will be deleted because the game assumes that they crashed regardless of the reality.  You see this when you separate lower stages while launching from Kerbin; anything more than 25 kilometres away that is not landed (or splashed) is deleted.  I don't know what the limit of approach for the Mun is, but it's possible that the game decided you were too close.  This only happens when you're not controlling it or in physics range (about 2.5 km)--and that's good because otherwise landings would be very frustrating--but it also means that things in too-low orbits are deleted only when you're not paying attention to them.  For reference, I typically keep my Mun orbiters to 15 kilometres and don't have any problems at that altitude, so I cannot say definitively that this is what happened.  Perhaps @bewing would know better.

Another possibility is that your station was not in the orbit you thought it was and it really did crash.  Or it was ejected into Kerbin or even solar orbit.  The easy way to check that is in the Tracking Station.

Yet another possibility is that you modded your game and deleted a part; that would throw an error when you tried to load, though, so you would know.

Lastly, it's possible that you activated a filter in your map view (or in the Tracking Station) that would keep you from seeing your station.  At the top of the screen in map view or in the Tracking Station is a pop-out menu that shows what classes of object you have set to visible.  Perhaps you shut off stations for some reason.  On the other hand, perhaps your station became something else accidentally; if it doesn't have power, then it may be classed as debris.  If you undocked from it, then it may be classed as a probe.  There are a few ways it could have gone.

Edited August 7, 2019 by Zhetaan

[bewing]

As Zhetaan said, there is a hidden thing in KSP called an "autodeletion altitude". Each celestial body has one. The game does not keep the terrain loaded for any celestial body except the one you are orbiting. So there is no way for the game to really tell when a non-focused craft crashes into the terrain of some CB. This autodeletion altitude is a simple replacement for checking if things crash. On the Mun, I think the autodeletion altitude is 8km. So if the Pe of your station was below 8km at the Mun, then that's almost certainly what happened to it. You can hit your F3 key to get a report of all events that occurred recently. If your craft was autodeleted, it will say "station crashed into terrain".

If that's not what caused it, then Zhetaan gave you a lot of other very good possibilities.

 

[Simen]

2 hours ago, Zhetaan said:

Welcome to the forum!

The highest point on the Mun is about 7100 metres.  It's also in the southern polar region; if your station was in an equatorial orbit, then the terrain was never very close to it.  However, there is a point of closest approach where objects in low orbit will be deleted because the game assumes that they crashed regardless of the reality.  You see this when you separate lower stages while launching from Kerbin; anything more than 25 kilometres away that is not landed (or splashed) is deleted.  I don't know what the limit of approach for the Mun is, but it's possible that the game decided you were too close.  This only happens when you're not controlling it or in physics range (about 2.5 km)--and that's good because otherwise landings would be very frustrating--but it also means that things in too-low orbits are deleted only when you're not paying attention to them.  For reference, I typically keep my Mun orbiters to 15 kilometres and don't have any problems at that altitude, so I cannot say definitively that this is what happened.  Perhaps @bewing would know better.

Another possibility is that your station was not in the orbit you thought it was and it really did crash.  Or it was ejected into Kerbin or even solar orbit.  The easy way to check that is in the Tracking Station.

Yet another possibility is that you modded your game and deleted a part; that would throw an error when you tried to load, though, so you would know.

Lastly, it's possible that you activated a filter in your map view (or in the Tracking Station) that would keep you from seeing your station.  At the top of the screen in map view or in the Tracking Station is a pop-out menu that shows what classes of object you have set to visible.  Perhaps you shut off stations for some reason.  On the other hand, perhaps your station became something else accidentally; if it doesn't have power, then it may be classed as debris.  If you undocked from it, then it may be classed as a probe.  There are a few ways it could have gone.

I went back to a quick save and it seems like I changed the orbit without noticing by EVAing to many times, which I didn't know was possible tbh. The periapsis had went down to 6k and propably got auto-deleted for being to low as you have mentioned. Thanks for answer! 

[Snark]

33 minutes ago, Simen said:

I went back to a quick save and it seems like I changed the orbit without noticing by EVAing to many times, which I didn't know was possible tbh. The periapsis had went down to 6k and propably got auto-deleted for being to low as you have mentioned. Thanks for answer! 

Depending on how you're EVAing and getting back in... it can make a difference.  Each time a kerbal bumps your vessel, it alters the orbit slightly.  In particular, if your kerbal has a significant orbital or component relative to the ship, it'll raise or lower the opposite side of the orbit very slightly.

Usually it's not something that matters much, but if you're in a very low orbit to start with, even just a kilometer or two of difference can be critical.

1 hour ago, bewing said:

On the Mun, I think the autodeletion altitude is 8km.

Unless they've changed it recently, I'm pretty sure it's lower than that-- I'm just about positive that I've managed to create stable circular Mun orbits at altitudes a fair bit lower than that.  I think you can get down to about 6K if you're careful.  But yes, there's certainly a limit. 

[VoidSquid]

35 minutes ago, Snark said:

Unless they've changed it recently, I'm pretty sure it's lower than that

Depends on your orbit inclination, afair the highest elevation is about 7k... and yes, my Kerbals did have that painful lithobreaking experience once  

I was trying to recreate this landing

 

... the rest of the story is up for imagination  

Edited August 7, 2019 by VoidSquid

[Geschosskopf]

1 hour ago, Simen said:

I went back to a quick save and it seems like I changed the orbit without noticing by EVAing to many times, which I didn't know was possible tbh. The periapsis had went down to 6k and propably got auto-deleted for being to low as you have mentioned. Thanks for answer! 

Welcome aboard!

Another possibility is if you warped at high rate.  AFAIK, the game only moves 1 object at a time and the faster you're warping, the more each object moves during its "turn".  So, Mun might move and then your orbiting ship, or vice versa.  Either way, if you warp fast enough, this sequential moving can cause the orbit of a very low ship to move inside the autoleletion altitude or even into the terrain.

[Snark]

1 hour ago, VoidSquid said:

Depends on your orbit inclination, afair the highest elevation is about 7k... and yes, my Kerbals did have that painful lithobreaking experience once  

https://wiki.kerbalspaceprogram.com/wiki/Mun#Terrain

If you're equatorial, then the highest point is just under 6 km.  It's the cliffs flanking the big equatorial canyon that extends from the eastern edge of East Farside Crater.

The reason I remember the minimum possible orbital height being lower than 10 km was that one time (quite a while ago) I wanted to see how low I could put something in a stable long-term orbit.  So I got it perfectly equatorial and threaded the needle on that canyon.  I don't remember exactly (it's been a few years), but I believe I had my orbital height down so that it was about at the level of those cliff tops.

[Espatie]

How fast were you going when you threaded that needle, @Snark?

 

With relevance to the question: Science Labs are, in my experience, the absolute worst modules for knocking your spacecraft about on exit. It's so bad that I habitually block the exists when building stations. I don't know why this is.