raptop changed the topic of #principia to: READ THE FAQ: http://goo.gl/gMZF9H; The current version is Fréchet. We currently target 1.5.1, 1.6.1, and 1.7.x. <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
<discord-_> M​yshiko. — Sort of stupid question: how many asteroids in practice gets spawned total, is nothing is touched?
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<discord-_> M​yshiko. — Sort of stupid question: how many asteroids in practice gets spawned total, is nothing if touched? May be it’s ok just to leave them be. (edited)
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<_whitenotifier-d13c> [Principia] DRVeyl commented on issue #2530: Principia crash when decoupling with msg Check failed: 0 <= r (0 vs. -1) - https://git.io/JfOFf
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<discord-_> e​gg. — Yeah I saw your comment but I’m not completely sure that is it : we are the ones crashing here, not KSP
<discord-_> D​RVeyl. — I think you just crashed first, is all.
<discord-_> D​RVeyl. — I CTD'd my stock environment.
<discord-_> e​gg. — It might well be that our fix then lets the game crash itself :D
<discord-_> e​gg. — but then it is no longer our fault
<discord-_> D​RVeyl. — Yep!
<discord-_> e​gg. — otoh it means we have poorer error reporting, because when we crash we are pretty explicit about what went on...
<discord-_> e​gg. — anyway, we will see if someone comes back with another crash :-p
<discord-_> e​gg. — > I think you just crashed first, is all.
<discord-_> e​gg. — We love crashing, so we do so very eagerly :-p
<discord-_> D​RVeyl. — Don't get accused of being -faster- than stock often, do you? 😉
<discord-_> e​gg. — hahaha
<discord-_> e​gg. — We do get accused of being easier than stock on one specific aspect, that of rendez-vous, which I find quite satisfying
<discord-_> e​gg. — the target-centred frame is good
<discord-_> e​gg. — turns out there is a reason they use that in aerospace I suppose
<discord-_> D​RVeyl. — Weird. Who knew.
<discord-_> D​RVeyl. — In general: your more advanced tools make a finite task easier once you understand them? ie a hard part of using Principia is keeping things in stable orbit, because, well, that is hard. With rendezvous your task ends when you get there?
<discord-_> D​amien. — with rendezvous it's because the principia implementation gives you more information regarding future orbit phases
<discord-_> D​amien. — stock only gives you the next two intercepts
<discord-_> l​pg. — the target frame also makes it much easier to focus on the pass that matters
<discord-_> D​amien. — ^
<discord-_> D​amien. — another principia feature I love is the navball midline changing so in situations like trying to launch into plane of a target you can use the navball midline as a guide and launch when your prograde indicator hits it
<discord-_> e​gg. — been a while since I’ve glanced at reddit Principia chatter, I should do that
<_whitenotifier-d13c> [Principia] garnet420 commented on issue #2519: Spin-up on reentry under physics warp with FAR - https://git.io/JfObS
<discord-_> e​gg. — more people happy with the tooling : https://www.reddit.com/r/KerbalSpaceProgram/comments/fkrl6s/principia/
<discord-_> D​amien. — that's where that Calvin_Maclure guy heard about it
<discord-_> e​gg. — > If you want to though you can make KSP render in seconds per frame.
<discord-_> e​gg. — :D
<discord-_> D​amien. — hehe
<discord-_> D​amien. — hey I'm not lying
<discord-_> e​gg. — indeed; the predictions should be better than they used to be now that they are asynchronous, but you can definitely stop the world with the flight plan
<discord-_> l​pg. — surface-fixed with a moderately long prediction length (i.e. what you get when going straight from launchpad to map view) is a bit painful
<discord-_> l​pg. — this, I mean
<discord-_> e​gg. — ah yeah the planets can be a bit silly in that configuration
<discord-_> D​amien. — ^ when the earth wears fishnets to look sexy
<discord-_> S​tandecco. — @egg @Gregrox I wanted to play whirlgig world with principia, does it work?
<discord-_> S​tandecco. — and mostly, does mesbin have the correct J2?
<discord-_> G​regrox. — Kind of, and No
<discord-_> G​regrox. — Mesbin used to have... *a* J2. Who knows if it was even close to the proper J2. But it was removed as it caused Statmun to fall out of the sky.
<discord-_> G​regrox. — As for orbital stability, it should *mostly* work, except for two cases which ought to be possible in the real world but which are hard to define in a way principia will put in motion properly, that being the trojan moon of Kerbmun, and the close-in moons of the binary Mandrake & Rutherford
<discord-_> G​regrox. — so i make patches to fix those, by inclining Troymin's orbit and cutting Rutherford's semimajoraxis in half
<discord-_> G​regrox. — Mandrake & Rutherford are based on the Pluto system, which is stable, so in principle this system should work, just not in princi*pia*
<discord-_> e​gg. — well if it works in principle it ought to work in principia if you give it a correct initial state
<discord-_> e​gg. — doing that is left as an exercise to the reader
<discord-_> G​regrox. — Various simulations in Universe Sandbox 2 show that troymin is stable (and just common sense looking at the thing), but the initial state is wrong there too
<discord-_> G​regrox. — frankly I have *no clue* how to get the initial state right :v
<discord-_> e​gg. — just because you think you are feeding Universe Sandbox 2 the same thing (and running it at settings that will yield a correct simulation for your purposes) does not mean you do
<discord-_> e​gg. — the same holds for common sense  :-p
<discord-_> G​regrox. — i know
<discord-_> G​regrox. — the initial state is different between principia and US2 despite all the kepler elements appearing the same
<discord-_> G​regrox. — principia and us2 interpret them in different ways
<discord-_> e​gg. — we interpret the Keplerian elements as hierarchical Jacobi elements
<discord-_> e​gg. — i.e., each thing orbiting the barycentre of the inner ones
<discord-_> e​gg. — (still osculating, mind you)
<discord-_> e​gg. — since that generally better replicates stock behaviour
<discord-_> G​regrox. — that's the key difference, it must be
<discord-_> G​regrox. — us2 targets the most massive central body, not the barycenter
<discord-_> G​regrox. — so unless you do some tricks, circumbinary orbits aren't even possible
<discord-_> e​gg. — but tbh if you are doing something even slightly nontrivial I strongly recommend providing us with a Cartesian initial state
<discord-_> G​regrox. — so unless you do some tricks, circumbinary orbits (around sufficiently equal partners) aren't even possible (edited)
<discord-_> G​regrox. — how
<discord-_> G​regrox. — that's like, velocities and positions, right?
<discord-_> e​gg. — yes
<discord-_> e​gg. — > how
<discord-_> e​gg. — by reading the documentation
<discord-_> e​gg. — how to compute those? depends what you are trying to do
<discord-_> G​regrox. — to be clear i mean how do i *get* them
<discord-_> G​regrox. — not how do I *use* them
<discord-_> e​gg. — for something simple you might be able to compute them from first principle
<discord-_> e​gg. — for something simples you might be able to compute them from first principle (edited)
<discord-_> e​gg. — for something simple you might be able to compute them from first principle (edited)
<discord-_> e​gg. — for something simple you might be able to compute them from first principles (edited)
<discord-_> e​gg. — for things where some empirical properties must be verified, run an optimization as we did with TRAPPIST-1
<discord-_> G​regrox. — is it possible to use cartesian initial state with regular orbits as well? Like define everything easy with kepler and then for the moons that don't work have the initial state
<discord-_> e​gg. — but that is a lot of work and a fairly expensive computation
<discord-_> G​regrox. — is it possible to use cartesian initial state with regular orbits as well? Like define everything easy with kepler and then for the moons that don't work have the cartesian initial state (edited)
<discord-_> e​gg. — No, you provide us with the entire system or nothing
<discord-_> G​regrox. — tragic
<discord-_> e​gg. — it would not make any sense to mix the two, with the Jacobi elements being based on all other bodies
<discord-_> G​regrox. — is there any tool that will just convert a system to cartesian initial state
<discord-_> G​regrox. — because anything more mathematically complex is just straight up a no-go for me
<discord-_> e​gg. — not that I know of, but you can learn, or make one
<discord-_> G​regrox. — aeg i dropped out of college precalc trig because i couldn't keep up with the workload
<discord-_> e​gg. — how is that relevant
<discord-_> G​regrox. — it is meant to show that learning is not really a thing i feel capable of doing
<discord-_> G​regrox. — it is meant to show that learning something like this is not really a thing i feel capable of doing (edited)
<discord-_> e​gg. — it is not very effective at showing much
<discord-_> e​gg. — anyway
<discord-_> e​gg. — you will have far more direct control over what you are doing with the cartesian config; our system to handle Keplerian elements (via hierarchical Jacobi coordinates) exists primarily to deal with simple enough stockish systems that « just work », but if you design with fancy things in mind its assumptions will fail and you will end up fighting it
<discord-_> e​gg. — I am not even sure you can express every possible initial state using Keplerian elements via Principia’s interpretation of them, because as you lower the semimajor axis you can change the ordering of the bodies, which changes the interpretation of them
<discord-_> G​regrox. — i wonder
<discord-_> G​regrox. — US2 has velocities and positions listed for all its objects
<discord-_> G​regrox. — maybe if i built the system in US2 i could copy over all those values
<discord-_> e​gg. — Assuming the US2 simulation is accurate, and the other data is the same (masses, oblateness, etc.), that could work
<discord-_> e​gg. — (does US2 even handle oblateness?)
<discord-_> G​regrox. — it does not
<discord-_> G​regrox. — but a nearly circular equatorial orbit should be more or less the same, right?
<discord-_> G​regrox. — between oblate and spherical planet
<discord-_> G​regrox. — between oblate and spherical versions of a planet (edited)
<discord-_> G​regrox. — like, same orbital velocity and in the same direction, right?
<discord-_> G​regrox. — like, it'd have same orbital velocity and in the same direction, right? (edited)
<discord-_> e​gg. — no
<discord-_> e​gg. — and your *nearly* is doing a lot of work here
<discord-_> e​gg. — but even without that concern, no
<discord-_> G​regrox. — damn
<discord-_> S​tandecco. — > Mesbin used to have... a J2. Who knows if it was even close to the proper J2. But it was removed as it caused Statmun to fall out of the sky.
<discord-_> S​tandecco. — so if I removed Statmun...
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<discord-_> G​regrox. — don't you fucking dare
<discord-_> G​regrox. — :v
<discord-_> A​cer_Saccharum. — land tides on mesbin would remove statmun anyway
<discord-_> A​cer_Saccharum. — or launch it into a higher orbit
<discord-_> A​cer_Saccharum. — it's a coin flip
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<discord-_> S​tandecco. — I just wanted to see what orbits you'd actually get around a body of that kind
<discord-_> e​gg. — @Standecco note that you can eggsperiment with J2 even in stock using a Principia config
<discord-_> S​tandecco. — but that system is cooler
<discord-_> e​gg. — true
<discord-_> S​tandecco. — what would a reasonable J2 value for mesbin?
<discord-_> S​tandecco. — what would be a reasonable J2 value for mesbin? (edited)
<discord-_> A​cer_Saccharum. — you'd also need a reasonable reference radius
<discord-_> A​cer_Saccharum. — I'm not sure if you should use the equatorial radius, polar radius, or the geometric mean radius (abc)^(1/3)
<discord-_> e​gg. — usually you use the equatorial radius as a reference
<discord-_> e​gg. — this is merely a matter of convention, you would simply get different coefficients for the same field with a different reference radius
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