Moon orbit discrepancy upon load

[Person012345]

Hi. I have a game with a fairly-high-mass-compared-to-the-parent-"planet" moon orbiting pretty closely (1,200 km). Or at least I do so long as I don't close the game. However, every time I load the simulation (6 or 7 times so far), the game randomly gives said moon a highly eccentric orbit and changes it's distance to around 8,000 km. It did this once with another moon around another planet too. Both of these planets are very far away from the parent star. The simulation I'm loading is paused and has never been run, so it can't be any sort of natural drift, the game is just delliberately changing it for no reason as far as I can tell (when I do run it after correcting the settings it orbits perfectly well). It is not doing this with any of the other moons in the system (the planet with 20 moons is working just fine, as is the one with 18, and all the others with 1 or 2, there are a total of 10 planets and 52 moons in the system, plus 3 asteroid belts) apart from the one time I mentioned.

Anyone got any idea why it's doing this? It's highly annoying having to reset it each time, and check every single one of the 52 other moons just in case.

[FiahOwl]

How far is the planet from the star?

[vh]

Can you give the exact masses for the first moon planet
"Hi. I have a game with a fairly-high-mass-compared-to-the-parent-"planet" moon orbiting pretty closely (1,200 km). Or at least I do so long as I don't close the game. However, every time I load the simulation (6 or 7 times so far), the game randomly gives said moon a highly eccentric orbit and changes it's distance to around 8,000 km"

so that i can replicate it?

[Person012345]

How far is the planet from the star?

26,700,000,000 kilometres, 178 AU. Although it's not really a planet per se. The star has a mass of 0.63 suns.

Can you give the exact masses for the first moon planet
"Hi. I have a game with a fairly-high-mass-compared-to-the-parent-"planet" moon orbiting pretty closely (1,200 km). Or at least I do so long as I don't close the game. However, every time I load the simulation (6 or 7 times so far), the game randomly gives said moon a highly eccentric orbit and changes it's distance to around 8,000 km"

so that i can replicate it?

Uh... I've attatched the save game, will that do? The moon I'm having problems with is Rhyption-A XII Moon 1. It should have no eccentricity and have an orbital distance of 1,200km.  Also, having just loaded up the games, it appears to be altering some of the other moons of the outer planets. It has placed Rhyption-A XV Moon 1's orbit inside the diameter of the parent when it should actually be at 3,900km (and was set up correctly when I saved the game), which results in it's immediate destruction upon starting the simulation.

As I say, if I reset them before starting, they orbit just fine and I don't see how it could be anything to do with physics since the time elapsed in the savegame is 0.0 seconds, but it does only seem to be happening with those very close orbit ones.

[vh]

You said the orbits are messed up when you close out and open the game. Uploading the simulation would do much the same. No, i need the exact stats and try to replicate the simulation so that i can figure out what is causing.

How exactly did you create the sim?

what do you mean reset them.

[FiahOwl]

Oh yes, there is a bug when objects far away from the center of the simulation (0.0 0.0 0.0 coords) would disappear or orbit in the wrong way. This will be fixed in a future update.

[vh]

...ok i put a moon and earth in orbit around the sun at 200 AU
yeah i think rounding issues

[Person012345]

You said the orbits are messed up when you close out and open the game. Uploading the simulation would do much the same. No, i need the exact stats and try to replicate the simulation so that i can figure out what is causing.

Actually, it's just when I load the game. And it does it with ANY save I make with that simulation, even after I fix it and save, reloading the file causes problems.

As for your question, ok (although if you load up the simulation the stats are there for you to see).

The star:
Mass: 0.63 Suns
Diameter 1.11M km
Density: 1.75 g/cm^3
Temperature: 4211 K
Luminosity (I think you have to uncheck the box to get this to match up with the mass): 0.18L
I -think- the initial star I placed was Alpha Centauri B

The Parent Object:
Mass: 0.016 moons
Diameter: 1200 km
Density: 1.32 g/cm^3
SMA: 179 AU

Rotationary period is 4 hours

The Offending Moon:
Mass: 0.042 10^20 kg
Diameter: 180 km
Density: 1.38 g/cm^3
SMA (as I want it): 1,200km
It is tidally locked.

Hopefully this covers the information you need, if not let me know.

How exactly did you create the sim?

I opened the game, placed the star, placed planets that looked how I wanted them too in the correct place, adjusted them so they were the correct size and, in the cases of most of the moons, density.

what do you mean reset them.

Selecting the offending moon, clicking "auto orbit" then changing the SMA back to where I want it. If I then start the simulation the moon in question orbits just fine.

[vh]

ok the problem is rounding error which switch the position of your plants as shown here

just don't place planets with moons so far out or
if you must, make the orbit at least 10,000 km, i did that and my orbit was shifted about 1000km.

[Person012345]

>.>'

Well, thanks, at least I now know what's causing it. And that I only have to reset those two now (instead of checking all 52, lol).

[smjjames]

Oh yes, there is a bug when objects far away from the center of the simulation (0.0 0.0 0.0 coords) would disappear or orbit in the wrong way. This will be fixed in a future update.

We're gettimg a completely new engine for it anyway in a major update this year. If it doesn't get fixed in a minor update, it probably will get fixed in the major one.

[FiahOwl]

Oh yes, there is a bug when objects far away from the center of the simulation (0.0 0.0 0.0 coords) would disappear or orbit in the wrong way. This will be fixed in a future update.

We're gettimg a completely new engine for it anyway in a major update this ywar. If it doesn't get fixed in a minor update, it probably will get fixed in the major one.

this war? dammit, WWIII is still like 11 months away.

Other then that, he's right.

[Person012345]

Thanks, that's good to know.

[Dan Dixon]

Did the suggestion of not placing the moons so far out fix the problem?

[Person012345]

Well, put it this way, I haven't had any problems with any moons that aren't that far out and close to the main body.