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…
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<queqiao->
⟨haida⟩ Is principia good enough to be used for planning trajectories of real life missions? If for whatever reason you couldn't use GMAT or smth
<queqiao->
⟨Joshua Wood⟩ Stock physics is close enough for most real missions to be close enough
<queqiao->
⟨clayel⟩ anything with mercury might be a bit off without principia (and perhaps even without general relativity if its a really long mission?)
<queqiao->
⟨clayel⟩ anything with mercury might be a bit off without principia (and perhaps even without general relativity if its a really long mission?)
<queqiao->
⟨ezsnack⟩ what are the most stable inclinations at venus? :V
<queqiao->
⟨egg⟩ The absence of solar radiation pressure is probably going to be the most obvious problem (and in LEO the lack of atmospheric drag, of course).
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⟨raptop | ²³⁹Pu powered⟩ I'd be hesitant with small bodies where things like outgassing and the yarkovsky effect matter
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⟨vlood⟩ Proposal to add Vulcan to RSS
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⟨egg⟩ Venus is not like the moon, it is a spherical cow. And it doesn’t even have a moon to perturb you. Do whatever you want there.
<queqiao->
⟨raptop | ²³⁹Pu powered⟩ … I'm pretty sure that Venus doesn't have lunar-scale masscons?
<queqiao->
⟨egg⟩ It doesn’t even have Earth-scale ones iirc
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⟨test_account9540⟩ Highly elliptical orbits still change their periapsis over time
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⟨egg⟩ Well yes, the Sun is still around.
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⟨egg⟩ I think our Лидов–古在 test is on Butcher’s Mercury orbiter rather than a Venus orbiter, but it is the same story.
<queqiao->
⟨ezsnack⟩ so another question, why does my periapsis decrease with time if i capture retrograde and increases if i capture prograde. venus is barely rotating no?
<queqiao->
⟨ezsnack⟩ * decreases
<queqiao->
⟨ezsnack⟩ * decrease
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⟨ezsnack⟩ * increase
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⟨egg⟩ Where are you reading the periapsis?
<queqiao->
⟨ezsnack⟩ orbit analysis tool, lowest altitude, its a higly elliptical orbit
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⟨ezsnack⟩ * highly
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⟨egg⟩ Well, as just noted, you have the Лидов–古在 mechanism
<queqiao->
⟨egg⟩ There is an exchange between eccentricity and inclination, preserving the quantity (1−𝑒²) cos² 𝑖.
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⟨egg⟩ (At least we don’t have to worry about the direction of longitudes…)
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⟨Damien⟩ Obviously this isn't a simple question to answer (aside from 'no go away') but if principia was going to model atmospheric drag, how would it work?
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⟨Damien⟩ As a _if I had to hack something together right now_ kind of thing
<queqiao->
⟨Damien⟩ Some potential interplay with the FAR mod perhaps?
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⟨siimav⟩ > As a if I had to hack something together right now kind of thing*AHAHAHAAAA*
<queqiao->
⟨egg⟩ I discussed that with ferram4 some years ago. If I recall correctly, you can get away with a pretty simple model, though you still need to know something about the shape and size of the spacecraft (same for solar radiation pressure btw). But more pressingly, it would be a serious problem for gameplay unless you can have a more systematic way of dealing with stationkeeping, and now you’re dealing with a hard problem.
<queqiao->
⟨Damien⟩ Yeah I figured that re: stationkeeping. I'm not suggesting it's in any way feasible right now but just wondered how plausible it would be
<queqiao->
⟨Damien⟩ And as for SC, I'd file that under 'deal with it' similar to unstable L-point orbits
<queqiao->
⟨Damien⟩ "Here's your deorbit date, fix it or dont"
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⟨patrikcath⟩ Keep in mind I have no idea how principia's or KSP's code works lmao, but this was such an interesting problem to me I wanted to think about it and share something in case it ends up being even vaguely useful
<queqiao->
To me the most obvious way to implement atmospheric drag in space is to just calculate a craft's drag coefficient when it's active, and save it so once it's unloaded Principia can just keep applying a retrograde force depending on its altitude
<queqiao->
This would assume you always have some way of keeping the craft pointed prograde (or in whatever other orientation you chose), but that's not an unreasonable assumption anyway
<queqiao->
I have no idea how resource intensive it would be compared to the simulations principia already does though. You could obviously just not do the calculation if the craft is high enough or doesn't orbit a body with an atmosphere, but I suspect with a few LEO satellites it could become a performance hog with all the extra calculations
<queqiao->
⟨Joshua Wood⟩ could you make trajectories a dependency and steal it's values for drag? xd
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⟨egg⟩ (Note that this has been discussed every now and then already.)
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<queqiao->
⟨Damien⟩ I imagine trajectories uses an extremely simplified drag model or approximation and that's the antithesis of eggdev
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⟨Joshua Wood⟩ I have heard it uses FAR nowadays and it's pretty accurate
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⟨GoForPDI (less drag=more faster)⟩ iirc it integrates with FAR if you have it installed
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⟨GoForPDI (less drag=more faster)⟩ but the one thing I always wish it or any mod that does drag predictions had is support for a staging event before entry, even though that would probably be a nightmare