Mun orbit apogee and perigee

[Ty Tan Tu]

I have a space station orbiting Mun and it orbit is rock solid, But I launched a simple  MK2-Lander from Mun and the apogee and perigee jump all over the place. It will go up and down by as much as 5 km. It makes a transfer a bit more complicated. I had a MechJeb, but it was not activated. It seems like whatever ship has focus is unstable. I turned off SAS to see if that was causing it, but it still happens. What is going on with that? Is Kerbin affecting the orbit? The orbit was only at about 70 km. I thought that would be low enough.

[Superfluous J]

Quick note on terms: "Apogee" and "Perigee" are relative to Earth, which doesn't exist in Kerbal Space Program. We use Apoapsis and Periapsis, which are the general terms.

You are experiencing a bug. With no thrust active, your orbit should not move at all. Practically speaking, it could waver a few meters back and forth but nowhere near a Km or more.

This bug may not be worth reporting, unless you can recreate it not only in a stock game, but in the new 1.2 prerelease. They've done a lot of work on orbits over the past few versions and any bugs you're seeing in 1.1.3 could easily have been fixed already.

Edited September 25, 2016 by 5thHorseman

[Ty Tan Tu]

Thanks. I was hoping that 1.2 might fix that. I was still able to dock, but it was a bit of a surprise to see my Periapsis suddenly lower than it had been on the last pass - when I was trying to slow down. The encounter nodes were jumping around. At about 2.8 km I just stopped looking at them and did my maneuver to close on the Mun station. 

I actually did know I was using the wrong word and thought about saying 'apocynthion' and 'pericynthion', but those words have always seemed so awkward to me. :-) I think from now on I will just use APO and PER...

[Snark]

1 hour ago, Ty Tan Tu said:

I actually did know I was using the wrong word and thought about saying 'apocynthion' and 'pericynthion', but those words have always seemed so awkward to me. :-) I think from now on I will just use APO and PER...

Well, if you're talking to KSPers, your best bet is to use the common terms that all KSP folks use on the forums.

So, call them "periapsis" and "apoapsis".  Or if you want to abbreviate, "Ap" and "Pe".

[Gaarst]

3 hours ago, Ty Tan Tu said:

I actually did know I was using the wrong word and thought about saying 'apocynthion' and 'pericynthion', but those words have always seemed so awkward to me. :-) I think from now on I will just use APO and PER...

Now I'm thinking we really need apoapsis and periapsis names for bodies in KSP. There's one for every object in the solar system and none for the Kerbal system... I'm going to fix it, gimme a bit of time!

 

Also yes, bug. There is a setting that enables or disables the correction for a known orbit wobbling/decaying bug; check that it is on. If that doesn't work and your game is stock then do submit a bug report.

Edited September 26, 2016 by Gaarst

[Superfluous J]

1 hour ago, Gaarst said:

Now I'm thinking we really need apoapsis and periapsis names for bodies in KSP. There's one for every object in the solar system and none for the Kerbal system... I'm going to fix it, gimme a bit of time!

If you do this, in my head Mun's Latin name is "Loona." Someone on these forums suggested it years ago and I think it's PERFECT. So it'd be Periloon and Apiloon. The other 13 are up to you

[Guest]

Apimoe/Perimoe
Apoeev/Perieev
Apokee/Perikee
Apiloon/Periloon
Apimine/Perimine Apimint/Perimint
Apidoon/Peridoon
Apidree/Peridree
Apijule/Perijule
Apoeel/Perieel

?

Edited September 26, 2016 by Guest
Updated Minmus terms.

[Superfluous J]

31 minutes ago, Brikoleur said:

Apimine/Perimine

Apimint/Perimint? Ancient Kerbals thought Minmus was made of mint, but modern ones realized it wasn't. Probably. But they better check just to make sure.

[Guest]

Definitely. Updated the list!

[Rodhern]

I agree that -kee, -loon and -mint are spot on. And they are the most important ones. Both -dree and -jule make (Kerbal) sense. Even "perieel" has a nice ring to it. The one that seems a bit off to me is -doon; maybe -dune; but that might not be Kerbal enough (which of course is a major concern for any would be astronomer).

I am getting the feeling that maybe I am missing something. Would someone explain the -doon word? Is it close to some English word that I can't think of right now?

edit: btw. off topic bonus question, how do you decide whether Apoeel or Apieel is correct/best. There must be some rule, not just the one with the greatest appeal right?

Edited September 26, 2016 by Rodhern
off topic question about apo vs api

[Superfluous J]

34 minutes ago, Rodhern said:

I am getting the feeling that maybe I am missing something. Would someone explain the -doon word? Is it close to some English word that I can't think of right now?

I don't think it's anything other than "looks funny" coupled with "duna -> dune -> doon"

Oh and...

[Guest]

I was thinking of Mun -> Loon, Dune -> Doon, for a kind of phonetic symmetry. I also thought it sounded amusing. No logic beyond that.

[Gaarst]

3 hours ago, Rodhern said:

edit: btw. off topic bonus question, how do you decide whether Apoeel or Apieel is correct/best. There must be some rule, not just the one with the greatest appeal right?

Apo- is technically a bit more correct than api- but just choose the one which is more apieel-ing to you (had to do it, forgive me).

[Rodhern]

2 minutes ago, Gaarst said:

Apo- is technically a bit more correct than api- but just choose the one which is more apieel-ing to you (had to do it, forgive me).

You are forgiven for taking the bait. Thank you for the apo- explanation. I did wonder why all this api-stuff have come up recently. So it is a sound thing, kind of.

[Gaarst]

2 minutes ago, Rodhern said:

You are forgiven for taking the bait. Thank you for the apo- explanation. I did wonder why all this api-stuff have come up recently. So it is a sound thing, kind of.

The "official" prefix is apo- or ap- (we say aphelion and not apohelion); so while apiloon is not wrong, it means ap-iloon more than api-loon

[Warzouz]

17 hours ago, Ty Tan Tu said:

I have a space station orbiting Mun and it orbit is rock solid, But I launched a simple  MK2-Lander from Mun and the apogee and perigee jump all over the place. It will go up and down by as much as 5 km. It makes a transfer a bit more complicated. I had a MechJeb, but it was not activated. It seems like whatever ship has focus is unstable. I turned off SAS to see if that was causing it, but it still happens. What is going on with that? Is Kerbin affecting the orbit? The orbit was only at about 70 km. I thought that would be low enough.

I had this bug in 1.0.2, 1.0.5 and 1.1.x. It was very significant in 1.1, causing the ship to move quite fast, making docking very hard. I called that my own "munar malediction"  In 1.0.x it showed on polar orbit. On 1.1, it showed on vehicles with landing struts.

In 1.2, I hope that's finally fixed.

[FleshJeb]

15 hours ago, Brikoleur said:

Apimoe/Perimoe
Apoeev/Perieev
Apokee/Perikee
Apiloon/Periloon
Apimine/Perimine Apimint/Perimint
Apidoon/Peridoon
Apidree/Peridree
Apijule/Perijule
Apoeel/Perieel

?

Apiho/Periho

[Hupf]

On 26.9.2016 at 1:47 PM, Gaarst said:

Apo- is technically a bit more correct than api- but just choose the one which is more apieel-ing to you (had to do it, forgive me).

 

On 27.9.2016 at 0:11 AM, FleshJeb said:

Apiho/Periho

Apoho/Periho then.