egg changed the topic of #principia to: READ THE FAQ: http://goo.gl/gMZF9H; The current version is Germain. We currently target 1.8.1, 1.9.1, 1.10.1, and 1.11.0. <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… | <egg> also 4e16 m * 2^-52 is uncomfortably large
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<nilof> what is lamont and how does it influence Pluto
<discord-> Z​eusbeer. — haven't been here in a while, how is 2400 coming along?
<discord-> S​tandecco. — lamont is a person, but I don't think he has enough mass to influence pluto significantly
<discord-> S​tandecco. — he'd have to be as dense as a black hole possibly
<nilof> does Principia still use the same fifth order SPRK method? I remember some talk about hybrid integrators when I was trying this out a few years ago, not sure how practical they ended up being
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<discord-> e​gg. — nilof: For the ephemeris, we use a 12th order symmetric linear multistep method for the real solar system, and a 6th order, 14-stage symplectic Runge–Kutta–Nyström method by default otherwise.
<discord-> e​gg. — For the vessels, we use an 8th order symmetric linear multistep method.
<discord-> e​gg. — Lamont is https://github.com/lamont-granquist but also https://en.wikipedia.org/wiki/Lamont_(lunar_crater); neither significantly affects the motion of Pluto.
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<nilof> OK wow, reading through the changelog over the past few years since I played the mod around 2016 theres a lot of cool stuff including the vessel rotation, the planetary orbit plotting, etc etc. Does it also support low thrust burns/ion engine burns or not?
<discord-> e​gg. — nope
<nilof> I see. Stationkeeping burns are also still 100% manual operations then?
<discord-> e​gg. — yup
<discord-> e​gg. — and now with rotation, you have the question of attitude-keeping, though I might realistically address that at some point (but for now spin-stabilization is the way to go)
<nilof> ah, SAS & reaction wheels don't work during time warp?
<discord-> s​cimas. — Nope
<discord-> e​gg. — @sarbian @dkavolis OK poking at this aerodynamics/timing thing a bit more, it looks like with old MFI, Principia JaiFailliAttendre (which picks up the drag vector) runs *before* MFI-mediated UpdaetAerodynamics
<discord-> e​gg. — I wonder whether this is correct
<discord-> e​gg. — but if it is incorrect, it has to be incorrect in a subtle way, since we have a behaviour which is very similar to stock FAR
<discord-> s​arbian. — It may have run in the required order just because they loaded in a specific order before
<discord-> s​arbian. — (I mean when they used the same timming)
<discord-> e​gg. — yeah it is definitely not carefully thought through
<discord-> e​gg. — I am more wondering whether that might explain some bugs like https://github.com/mockingbirdnest/Principia/issues/2808
<discord-> e​gg. — if UpdateAerodynamics sets the drag vector and we are reading it beforehand, are we picking up the drag vector one frame late?
<discord-> e​gg. — but also, we end up completely screwing up if we run after MFI so something is going on there too
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<discord-> d​kavolis. — FAR uses the same `dragVectorDir` code as stock + wind
<discord-> e​gg. — I am very confused, I thought FAR zeroed out those stock things? or am I missing some multiplier somewhere
<discord-> e​gg. — or it uses the drag and zeros out the lift?
<discord-> e​gg. — it applies its own forces in FixedUpdat, and we pick that up
<discord-> e​gg. — so if it sets the stock channels, why do we not always end up with doubled forces ? ?
<discord-> d​kavolis. — Hmm, FAR zeroes out `dragScalar` in fixed update
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<discord-> Z​eusbeer. — 12 order meaning 12 derivatives ?
<discord-> Z​eusbeer. — scary
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<discord-> m​oar ssto. — Seems like under stock aero aero forces are calculated using the frame before the frame they are applied.
<discord-> e​gg. — right so that is how we end up ignoring it, we count a 0 force
<discord-> e​gg. — but what happens to the lifts the
<discord-> e​gg. — but what happens to the lifts then (edited)
<discord-> e​gg. — does FAR apply them through stock or directly with AddForce[AtPosition]?
<discord-> d​kavolis. — Only `AddForce` but sets `bodyLiftScalar` like `dragScalar`
<discord-> d​kavolis. — FAR doesn't touch body lift vectors
<discord-> d​kavolis. — And stock sets body lift vector in `UpdateAerodynamics`
<discord-> e​gg. — right so with FAR, dragScalar is 0 from standard FixedUpdate to MFI FixedUpdate, and Principia needs to see that 0, which is why MFI 1.2.9 breaks things.
<discord-> e​gg. — But now I wonder whether we have silly things going on with the bodyLiftVector, because there our code will happily swallow that with no intervening scalars <https://github.com/mockingbirdnest/Principia/blob/1a05724811b95fb8b1af925eebe88ef782ef5ab4/ksp_plugin_adapter/ksp_plugin_adapter.cs#L1634-L1641>
<discord-> d​kavolis. — Body lift vectors may always be 0 with FAR
<discord-> e​gg. — oh yeah, they already factor in the scalar I suppose
<discord-> e​gg. — (and anyway since stock FI does not run they would not be set to start with)
<discord-> e​gg. — OK, so we now fully understand the MFI 1.2.9-mediated FAR–Principia interaction
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<discord-> l​amont. — honestly my head is large enough that principia probably should worry about its effect on pluto, is is likely to not be negligible. had to bump up to an XXL scuba diving hood.
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