10:37 <GH> [Principia] zilti commented on issue #1272: I've tested it with RSS *only* now, the problem still persists. It's not a matter of propelled or unpropelled. I made a quick video: https://streamable.com/87tf0 https://git.io/vydsu

20:09 <Arrowstar> Hey there, quick question for someone who knows how principia works. Besides the Jool system, was the stock KSP solar system modified in any way by this mod?

20:10 <Arrowstar> I've been putting together an N-body simulation for KSPTOT and I seem to get different results than what Principia shows

20:12 <Arrowstar> Namely, around Kerbin, the Mun and Sun seem to have a huge perturbation on the orbit of a spacecraft, which isn't reflected in Principia

20:28 <egg|zzz|egg> hi Arrowstar

20:28 <egg|zzz|egg> we don't modify anything but the Jool system

20:28 <egg|zzz|egg> Arrowstar: but it is true that high Kerbin orbits get massively perturbed by the Mun

20:29 <egg|zzz|egg> Arrowstar: also, how is it going? I haven't seen you around IRC in a while

20:46 <Arrowstar> egg: one second :)

21:46 <GH> [Principia] pleroy opened pull request #1274: Try to fix the non-deterministic replay by making the ordering of maps and sets deterministic (master...Replay2) https://git.io/vyd91

21:50 <GH> [Principia] pleroy commented on issue #1274: retest this please https://git.io/vyd9b

22:09 <Arrowstar> Egg, you still here? Actually, I've been noticing low Kerbin orbits suffering huge perturbations. Something on the order of a 100 km altitude circular orbit getting deorbited in a few revs (say, ~10 or so) due to solar and lunar gravity.

22:10 <Arrowstar> Yet when I reduce the grav model down to just Kerbin, it matches the two body model perfectly.

22:11 <egg|zzz|egg> Arrowstar: uuh that seems inaccurate

22:12 <Arrowstar> I agree... which is why I'm a bit confused. :)

22:12 <egg|zzz|egg> a synchronous orbit will get significant perturbations I think, but 100 km is fine

22:12 <Arrowstar> Any idea what sort of accelerations I should be seeing from solar and munar sources around Kerbin?

22:12 <egg|zzz|egg> dunno, I haven't done the calculation but it should be doable by hand

22:14 <Arrowstar> Yup, I agree. Was just hoping to be lazy about it. ;)

22:14 <egg|zzz|egg> Arrowstar: so your integrator models the 2-body problem wells, so that's not the issue... are the masses and distances of the other celestials right?

22:14 <Arrowstar> Yes. This is all in KSPTOT, which has been demonstrated to have a nice accurate solar system model :)

22:14 <teabot> Demonstratead.

22:14 <egg|zzz|egg> hmm

22:15 <egg|zzz|egg> also right now principia has a bug where the rocket gets stuck skipping along the edge of the atmosphere at high speeds for a while then lobbed at 50 km/s into space if it exits on the trailing side of Earth's orbit >_>

22:15 <egg|zzz|egg> I blame crepuscular demons

22:16 <Arrowstar> Nice bug, that's a new one :)

22:16 <egg|zzz|egg> (it's probably KSP's rotating frame doing things to us)

22:17 <egg|zzz|egg> Arrowstar: the mechjeb plots are fun >_> http://i.imgur.com/uX344Mw.png

22:17 <Arrowstar> Here's an example of what I mean by the spacecraft being deorbited. This is 10 revs. The SMA is stable of I get some wicked eccentricity grown due to lunar and solar gravity: http://imgur.com/a/4f2hs

22:17 <kmath_> http://i.imgur.com/dqHTEWL.png

22:18 <Arrowstar> *Of -> but

22:18 <Arrowstar> *grown -> growth :)

22:18 <egg|zzz|egg> Arrowstar: uhm, in which reference frame are you doing the integration

22:19 <Arrowstar> Kerbin inertia

22:19 <Arrowstar> As is the plot shown

22:19 <egg|zzz|egg> Arrowstar: and you are applying the correction for that not being an inertial frame?

22:19 <egg|zzz|egg> because that looks *exactly* like the effect from not applying the correction

22:19 <Arrowstar> Hmm. So tell me a bit about this correction?

22:20 <egg|zzz|egg> (protip: integration not in the barycentric frame of the solar system will drive you mad)

22:20 <Arrowstar> Because I doubt I'm doing it.

22:20 <egg|zzz|egg> Arrowstar: well, Kerbin-centred is not an inertial frame

22:20 <Arrowstar> Ah, because it's translating around the Sun?

22:20 <egg|zzz|egg> it's accelerated, since it follows Kerbin, which doesn't move in a straight line

22:21 <Arrowstar> Okay, so I need to translate all accelerations, velocities, and positions to the sun-centered frame before integrating then, yes?

22:22 <egg|zzz|egg> Arrowstar: I advise barycentric frame of the solar system, which is truly inertial (the sun moves, too)

22:25 <Arrowstar> Sure, makes sense.