egg|zzz|egg changed the topic of #principia to: READ THE FAQ: http://goo.gl/gMZF9H; The current version is Clifford. We currently target 1.2.2, and 1.3.1. <scott_manley> anyone that doubts the wisdom of retrograde bop needs to get the hell out | https://xkcd.com/323/
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<GregroxMun>
o/
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<GregroxMun>
what property of a planetary system mod would cause principia to crash?
<GregroxMun>
would an object with a negative sma do it?
<GregroxMun>
I have a hyperbolic asteroid called Fasteroid in a planet pack
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<UmbralRaptor>
Hrm, not sure with "planets", but that *should* be fine. If not, it's a bug.
<UmbralRaptor>
More likely a collision?
<GregroxMun>
it works fine when I remove fasteroid
<GregroxMun>
well not fine
<GregroxMun>
and to be clear it crashed the moment the save starts
<GregroxMun>
for some reason after a certain point one moon just starts spazzing out moonlet bop style despite being further out than a moon that did fine. It is possible there was a near collision with another moon that got ejected though.
<GregroxMun>
the step size is 1 minute
<GregroxMun>
and i'm using the default integrator
<GregroxMun>
the system in question *is* weird
<GregroxMun>
let me see if I can get a screenshot.
<GregroxMun>
Mesbin is 6 Mkerbin and spinning rapidly (portmanteau of Mesklin and Kerbin of course)
<GregroxMun>
5 gee poles and 1.2 gee equator
<GregroxMun>
I do forsee a problem calculating oblatenss on Mesbin: I want the equatorial gravity to remain 1.2 gee, but adding oblateness to the gravity model would make the gravity at that distance from the center higher.
<GregroxMun>
So then I'd need to spin Mesbin up more, screwing up any calculation of the flattening.
<awang>
GregroxMun: See if a fixed point can be found?
<awang>
Set up the equations and have at it
<GregroxMun>
what are the equations though
<GregroxMun>
I have zero chance of figuring out how to do it if I don't have the equations
<awang>
Well
<awang>
One equation for the force of gravity
<awang>
One equation relating oblateness with rotation speed
<awang>
One equation for the centri(fugal|pital) force
<GregroxMun>
It's not actually the oblateness I need
<GregroxMun>
I don't remember what it is
<GregroxMun>
J2?
<awang>
That works too
<GregroxMun>
it's the flattening of the gravitational field
<awang>
idk what the equation for that would be though
<awang>
Yeah, something like that
<awang>
I mean, you can always claim that whatever material your planet is made of has really really high tensile/compressive strength
<awang>
So it can rotate fast without deforming as much
<awang>
So just pick some arbitrary J2 and see if the rest can be found
<GregroxMun>
No it needs to deform
<GregroxMun>
it's gotta be meskliny
<GregroxMun>
that's the whole point
<GregroxMun>
of the entire planet pack
<awang>
Yeah, I know it needs to deform
<awang>
But if you mess with material properties, you can fine-tune how much it deforms
<awang>
Actually, now that I think about it
<awang>
I wonder if the oblateness depends on compressive/tensile strength of rock
<awang>
Tensile near the equator, compressive at the poles
<awang>
I think?
<awang>
Well
<GregroxMun>
I don't know for sure
<awang>
brb
<awang>
Sorry
<GregroxMun>
I'm going to find the density of Mesbin as it is now
<GregroxMun>
actually I really should use the flattening equations to figure out how much to deform Mesbin in the first place, I know where to find that one.
<GregroxMun>
the flattening equation considers the density of the material, but it's specifically for fluid planets with the same density everywhere
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<GregroxMun>
that's actually better than I thought
<GregroxMun>
in real scale, 5.221 g/cm^3, is around the density of Venus and Earth
<GregroxMun>
I was afraid I had concocted some unphysically dense world
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<awang>
Uh
<awang>
That *is* unphysically dense
<awang>
Osmium is ~22.5 g/cm^3
<awang>
And that's the densest element
<bees>
awang: it is made of Kerbium
<awang>
I wonder how much the assumption of constant density affects the calculations
<awang>
Compared to a more realistic model, i.e. dense core and less dense crust/mantle
<awang>
bees: ....That is true
<GregroxMun>
52.21 is unphysical
<GregroxMun>
but not by kerbal standards
<GregroxMun>
5.221 is its real scale density
<GregroxMun>
and that's how I build planets
<GregroxMun>
kerbin is made of iron and silicates, but gravity is 10 times higher
<GregroxMun>
so even though its density is 58 g/cm^3 according to its measured mass and radius, the materials it's made of are really averaging out to 5.8 g/cm^3
<awang>
Pretty sure those are mutually exclusive statements
<awang>
You can't get 58 g/cm^3 only using things that are 5.8 g/cm^3
<awang>
You can compress the latter down to the former, but then you're not at 5.8 g/cm^3 any more
<awang>
Unless you're talking about STP
<awang>
Higher gravity either means more mass or smaller radius
<awang>
Which means increased density either way
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<UmbralRaptor>
Incidentally, something like a planet has 0 tensile strength.
<UmbralRaptor>
A liquid approximation is basically accurate.
<awang>
I stand corrected
<UmbralRaptor>
If it passes the hydrostatic equilibrium test for being a planet, it has negligible tensile strength.
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<GH>
[Principia] pleroy commented on issue #1737: There is no "pesky limit" or anything like that. However what you are seeing is an interesting effect. We never tried to go beyond Eeloo so we never saw it, but now that we tried we've encountered the problem. Here is what we think is happening:... https://git.io/vASkC
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