UmbralRaptop changed the topic of #principia to: READ THE FAQ: http://goo.gl/gMZF9H; The current version is Fano. We currently target 1.3.1, 1.4.x, 1.5.1, and 1.6.1. <scott_manley> anyone that doubts the wisdom of retrograde bop needs to get the hell out | https://xkcd.com/323/ | <egg> calculating the influence of lamont on Pluto is a bit silly…
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<Gregrox>
howdy
<UmbralRaptop>
\o
<Gregrox>
I haven't checked that Principia works with Whirligig World in a while!
<Gregrox>
damn this thing. It started as a perfect analogue of the Pluto/Charon system and now *this*
<Gregrox>
it's even missing a moon
<Gregrox>
speaking of missing a moon, another planet seems to have lost a perfectly stable moon due to integrator issues
<egg|zz|egg>
Gregrox: tweaking the integrator settings only helps if your system is stable but is faster than we expect
<egg|zz|egg>
if it's actually unstable, you will just simulate its breakdown better
<Gregrox>
right
<Gregrox>
but a few bodies I know ought to be astable
<Gregrox>
Statmun around Mesbin for instance, should be stable according to some (modified, realistic) US2 sims, and Lowel and Ollym are a tight binary pair around a red dwarf. Both cases you have objects which should be in stable orbits but are very close and have short periods
<Gregrox>
which as I understand it is the main cause for buggy breakdowns
<Gregrox>
Once I get the definitely stable stuff definitely stable, then I'd like to talk to you about trying to fix the Mandrake/Rutherford system (which should be identical to Pluto/Charon, just at a different scale)
<Gregrox>
even with a 30 second step size, Statmun likes to escape
<Gregrox>
it orbits about 2 or 3 kerbin diameters away from an object with 75 kerbin masses, with a period of 1701 seconds.
<Gregrox>
and statmun definitely should not immediately escape
<Gregrox>
there's no flybys or anything that cause this
<Gregrox>
it just starts wobbling back and forth and flies out into deep space
<Gregrox>
Drastic problems caLL FOR DRASTIC MEASURES. :|
<Gregrox>
is there perhaps a better default integrator to use?
<Gregrox>
I see reference to uh
<egg|zz|egg>
Gregrox even with a 30 second step size, Statmun likes to escape << that sounds like actual instability
<egg|zz|egg>
oh yeah use a blanes SPRK, not the quinlan slms
<Gregrox>
US2 should have produced that instability if it was actually unstable
<Gregrox>
oh ok
<Gregrox>
one of these? BLANES_MOAN_2002_SRKN_6B BLANES_MOAN_2002_SRKN_11B BLANES_MOAN_2002_SRKN_14A
<Gregrox>
which one?
<egg|zzz|egg>
BLANES_MOAN_2002_SRKN_14A
<Gregrox>
ok
<Gregrox>
that's the one I randomly chose so good
<Gregrox>
I'm using 30 seconds with that
<Gregrox>
for the moment
<Gregrox>
so that was interestion
<Gregrox>
so that was interesting
<Gregrox>
within five minutes, statmun slows down to almost an orbital halt, falls into Mesbin's center, and gets flung out at a few dozen kilometers per second
<Gregrox>
I'm now finding a piece of what is probably genuine instability, but I want to make sure everything that definitely should be stable is definitely stable first.
<egg|zzz|egg>
hm yeah 0.11 might still be OK given that shape
<egg|zzz|egg>
Gregrox: the orbit plots don't mean much
<Gregrox>
the inclination gets pumped up and I'm wondering if this really is an instability thing--Lowel and Ollym's binary orbit is over 60 degrees inclined to the orbit around their star, and it *is* a red dwarf.
<Gregrox>
(and close to it)
<egg|zzz|egg>
Gregrox: but be careful with "is actually 0", we use the initial elements under some interpretation, but they are very approximative to describe the true orbit esp. if J2 is significant
<egg|zzz|egg>
(the true orbit is obviously not at all the plotted ellipse, but you are probably familiar with that by now)
<Gregrox>
It's not exactly zero, sorry, what I meant is that it's not as eccentric as it appears, which we both understand by this point)
<Gregrox>
damn it, it looks like Lowel and Ollym really *are* unstable.
<egg|zzz|egg>
what are the perturbing bodies?
<Gregrox>
Should just be Lowel, Ollym, and the star Gememma.
<Gregrox>
I don't think any of the other gememma-orbiting planets should have any meaningful effect, but the only two that would are Gannovar and the combined mass of Mandrake/Rutherford.
<Gregrox>
Lowel and Ollym have no defined J2 btw, to be cleare
<Gregrox>
(Statmun is fine with the current integrator settings)
<Gregrox>
which is wrong, those moons should all be in nearly circular orbits
<Gregrox>
hmm... maybe it is right, since it's the only body on the same side as Rutherford
<Gregrox>
and thus the orbit prediction would be wrong
<Gregrox>
need to put this in US2 where I can have orbit lines that mean something
<Gregrox>
Beagrid (moon2) and Lozon (moon1) eventually have a close approach that knocks Lozon into a higher orbit. The whole thing is also scattered a bit out of the plane, so I'm thinking this is also a problem of the high axial tilt (which yes, Pluto does have, but Gememma exerts more tides than the Sun does by quite a lot). However, I believe this system
<Gregrox>
was still unstable when it orbited Kaywell with no axial tilt, so I don't think that's all there is to it.
<Gregrox>
God I'm really beating myself up about having waited this long to verify my system's stability.
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