egg changed the topic of #principia to: Logs: https://esper.irclog.whitequark.org/principia | <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…
<queqiao->
⟨Just...Shoo⟩ Is there a calculator toll that can be used to calculate the transfer window in RSS?
<queqiao->
⟨Just...Shoo⟩ one that also works in Principia*
<queqiao->
⟨Farrier⟩ ⟪Just...Shoo⟫ Is there a calculator toll that can be […] ⮪ TWP fork, same as usual RSS
<queqiao->
⟨RyanRising⟩ can I ask why celestials’ positions aren’t on-rails in principa? It’s not obvious to me that n-body gravitation can’t work just as well if the attracting bodies are positioned arbitrarily, and while it’s more accurate for our real solar system to act like that, we all know the problems it can cause with the stock system.
<queqiao->
⟨RyanRising⟩ * arbitrarily rather than with the integrator,
<queqiao->
⟨Quadrupole⟩ Basically having planets on-rail is harder than you thought
<queqiao->
⟨egg⟩ they are on « rails » in the sense that nothing you do will influence where they go. They really shouldn’t be on conics because you will violate all sorts of nice properties of the physical system.
<raptop>
In this channel we follow the law of conservation of energy
<queqiao->
⟨egg⟩ Yes, this one in particular would become very sad.
<queqiao->
⟨RyanRising⟩ I probably should have figured as much
<queqiao->
⟨egg⟩ (Also, it would probably not help with performance, and in a reasonably sized solar system, it may well hurt, if they were on conics; it would certainly make the code a lot more unwieldy.)
<queqiao->
⟨RyanRising⟩ I was gonna ask that specifically
<queqiao->
⟨RyanRising⟩ it’s computationally simpler if the rules are consistent, huh?
<queqiao->
⟨egg⟩ Yeah. Anyway, besides conservation of energy, if you just bolt the planets onto conics but have vessels move as if attracted by all those planets, literally nothing will work. You’d have to do some sort of SoI-like thing to even begin to get things that don’t just fall out of orbit.
<queqiao->
⟨RyanRising⟩ ⟪egg⟫ Yeah. Anyway, besides conservation of […] ⮪ ah, I see, and then there’s not really any point to making them not on conics
<queqiao->
⟨RyanRising⟩ lastly, are any of you (to you knowledge) an iteration of the function that created John Carmack?
<queqiao->
⟨egg⟩ Yeah. Anyway, besides conservation of […] ⮪ if the Earth moves as if it were pulled upon only by the Sun, but the ISS moves as if it were also pulled by Pluto, the ISS behaves, wrt the Earth, as if it had a small thruster always pointing in the same direction as it orbits. It will pretty quickly become sad.
<queqiao->
⟨RyanRising⟩ 👍
<queqiao->
⟨RyanRising⟩ sorry, that should have been a reaction
<queqiao->
⟨RyanRising⟩ I forget myself sometimes
<raptop>
RyanRising: no, as an astronomer I'm an iteration of a fast sin(x), not a fast 1/sqrt(x)
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<queqiao->
⟨lamont⟩ principia uses interpolants right? so it isn't like it runge-kutta's up a single fixed step size in the integrator, it takes appropriately sized steps for the accuracy necessary and then interpolates based on whatever the KSP tick size is.
<queqiao->
⟨egg⟩ ⟪lamont⟫ principia uses interpolants right? so […] ⮪ both the ephemeris and the vessel histories are fixed-step (because adaptive stepsize and symplecticity don’t mix), but yes, the ephemeris has a much larger step and the result is interpolated to compute the gravitational field wherein the vessels move.
<queqiao->
⟨egg⟩ (the KSP game step is completely irrelevant to any calculations we make, of course.)
<queqiao->
⟨Butcher⟩ Cone of shame cat went to the vet today, healing up nicely. £2000 of surgery. 😬