raptop changed the topic of #kspacademia to: https://gist.github.com/pdn4kd/164b9b85435d87afbec0c3a7e69d3e6d | Dogs are cats. Spiders are cat interferometers. | Космизм сегодня! | Document well, for tomorrow you may get mauled by a ネコバス. | <UmbralRaptor> egg|nomz|egg: generally if your eyes are dewing over, that's not the weather. | <ferram4> I shall beat my problems to death with an engineer. | We can haz pdf
<_whitenotifier-5dfc> [Principia] eggrobin synchronize pull request #2293: Add error matchers - https://git.io/fjFEN
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<_whitenotifier-5dfc> [Principia] eggrobin synchronize pull request #2293: Add error matchers - https://git.io/fjFEN
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<_whitenotifier-5dfc> [Principia] eggrobin synchronize pull request #2293: Add error matchers - https://git.io/fjFEN
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<egg|work|egg> !wpn roysmeding
* galois gives roysmeding a friendly Einstein ray
<roysmeding> huh
<roysmeding> just as i was about to type something!
<egg|work|egg> clearly the Einstein ray is to blame
<UmbralRaptop> !wpn roysmeding
* galois gives roysmeding a function
<roysmeding> see, mofh suggested i go here for help with some orbital mechanics stuff. i've been trying to wrap my head around some old code for predicting tides
<roysmeding> although that might have to wait now that i've learned about this interesting KSP mod...
<egg|work|egg> yeah mofh pointed me to your tweets on the matter
<egg|work|egg> mean elements are Fun
<egg|work|egg> the best eggspression of that Fun might be that for very circular LEO, mean e is smaller than all osculating e
<roysmeding> yeah, the main thing i'm trying to figure out at this point is whether there's any elegant way i can get from the osculating elements to the mean orbit + corrections as defined in the old fortran
<egg|work|egg> "the" mean orbit
<roysmeding> egg|work|egg: yes, as defined in the fortran :)
<egg|work|egg> there are as many mean element theories as there are papers on mean element theories
<roysmeding> although a lot of the expressions i've come across in almanacs and such seem to match up pretty well
<egg|work|egg> yeah
<egg|work|egg> for the moon I'd really want to go with a numerical approach
<roysmeding> but yeah, they start with a mean orbit and then do a lot of hardcoded math to correct it for nodal precession and such, and i feel like it should be possible to just work with data pulled from HORIZONS
<egg|work|egg> an analytic theory just sounds like a pain
<roysmeding> let HORIZONS do the numerical stuff for me :)
<egg|work|egg> well
<egg|work|egg> the numerical stuff that HORIZONS does is the easy part, turning that into mean elements is Interesting
<egg|work|egg> (but there are things that work)
<egg|work|egg> what are you trying to do to start with
<roysmeding> well, the end goal is to predict the tides for arbitrary places based on models that people have generated
<egg|work|egg> topography sounds like it's going to be a lot trickier than the moon here
<UmbralRaptop> Won't that also require rheology models?
<egg|work|egg> rheology of cats
<roysmeding> well, that's already accounted for in the model
<UmbralRaptop> Cats need an eggsessive number of spherical harmonics
* UmbralRaptop chirps at mofh
<egg|work|egg> anyway, "just work with data pulled from HORIZONS" only works if you can live with the instantaneous state of the system
<roysmeding> the model just consists of complex coefficients for the various frequency components of the tides for each lon/lat
<egg|work|egg> otherwise, you're doing the integration, and at that point you're just redoing what HORIZONS does
<egg|work|egg> which is pretty easy at the level of precision that you care about mind you
<egg|work|egg> but a bit of a yak shave
<roysmeding> yeah, i'm wondering at this point if it's not just easier to use their models instead of trying to make external data sync up with their models
<roysmeding> this entire business is a bit weird anyway
<egg|work|egg> osculating elements are pretty much maximally useless
<egg|work|egg> they can be turned into mean elements, but you need a perturbation theory (which kind of defeats the point, you need to model the perturbations to the moon's orbit...)
<egg|work|egg> or you can turn a time series of osculating elements into some kind of mean elements by numerical averaging
<egg|work|egg> the numerical averaging needs to be clever, you should do it in equinoctial elements
<egg|work|egg> see https://imgur.com/Rn86qMD
<roysmeding> well, for context, since the end goal is basically to get the correct sine-ish wave
<roysmeding> (or waves, rather)
<roysmeding> i think i'm just going to try plotting the error between the osculating data and the numbers from the code tonight
<roysmeding> since the code applies a bunch of corrections, i suspect the difference might just basically be a phase offset
<egg|work|egg> which elements are you using?
<roysmeding> in what sense?
<egg|work|egg> of the osculating elements
<egg|work|egg> some elements are better behaved than others
<egg|work|egg> if you use the mean longitude, it's generally OK
<roysmeding> the numbers i need are the longitude of ascending node, the longitude of periapsis, and the mean longitude
<roysmeding> and then i need one parameter from the earth's orbit around the sun
<roysmeding> (also mean longitude)
<egg|work|egg> the mean longitude is OK, the others are going to be very yikes from osculating data
<egg|work|egg> again, if you sample one revolution and do suitable averaging, you can get decent elements for them
<egg|work|egg> but otherwise, it can get wild
<egg|work|egg> see these imgur plots for an eggstreme eggsample
<egg|work|egg> (TOPEX/Poseidon)
* UmbralRaptop swears that that sounds like a warhead rather than a satellite
<roysmeding> but yeah, so, in case it wasn't clear, basically tidal height in a given location is modeled as a sum of cosine waves of various frequencies
<roysmeding> the arguments of the cosine waves are all defined as linear combinations (with integer coefficients) of these astronomical numbers
<egg|work|egg> yeah
<roysmeding> they're not quite fixed frequencies, because they decided to take perturbations into account
<egg|work|egg> roysmeding: you really ought not use osculating elements as a substitute here; they will, in the best case, oscillate about the right value (but that oscillation matters little if you take the osculating elements at a single point in time)
<egg|work|egg> oscillate on timescales of a month in your case
<egg|work|egg> in the best case, because obviously they can just as well oscillate far away from the right value (see eccentricity in those plots)
<roysmeding> yeah.
<roysmeding> well, basically, what i'm wondering is
<roysmeding> the code starts with very simple expressions for the mean orbit (those four numbers are written as linear functions of time)
<egg|work|egg> yeah
<roysmeding> and then applies corrections as further phase shifts and such
<egg|work|egg> a precessing ellipse is a classic, but that's in mean elements
<egg|work|egg> in osculating elements you have a precessing ellipse + wildly oscillatory nonsense
<roysmeding> so that's basically what motivated me to look at osculating elements in the first place, to see whether i could sidestep all these hardcoded corrections
<egg|work|egg> you *can* get a pretty good idea of what those linear functions are even without an analytic perturbation theory, but you need to sample the osculating elements along at least one revolution
<egg|work|egg> what do the hardcoded corrections look like
<egg|work|egg> what are their frequencies
<egg|work|egg> if they're slow, then they definitely are not trying to get the osculating elements (otoh maybe you could numerically compute mean elements for the relevant time that would be better)
* UmbralRaptop chirps at mofh again. is https://photos.app.goo.gl/cqCCoMBJY38JLPQx5 a good approach to 2?
* egg|work|egg bites mofh
<roysmeding> well so uh. there's a lot of steps they take, but basically, they define a separate scale factor and phase offset for each constituent
<roysmeding> the biggest constituent is M2, defined here to have an argument of 2*<mean solar time> - 2*<mean longitude of the mean moon> + 2*<mean longitude of the mean sun>
<roysmeding> then on top of that argument, the phase "correction" they apply (they call it a "nodal correction", FWIW, so presumably this is about nodal precession) is atan((-.03731*sin(n)+.00052*sin(2*n)) / (1. - .03731 * cos(n)+.00052*cos(2*n)))
<roysmeding> with n being the longitude of the ascending node of the mean lunar orbit
<egg|work|egg> The nodal precession part is already in > those four numbers are written as linear functions of time
<egg|work|egg> Ω being a non-constant linear function of time is nodal precession
<roysmeding> yeah, but that omega doesn't show up in the definition of the argument
<egg|work|egg> > with n being the longitude of the ascending node of the mean lunar orbit
<egg|work|egg> It's just that Ω is denoted n which is vile
<roysmeding> yeah, that's what i mean, it shows up in the *correction*
<egg|work|egg> yeah
<egg|work|egg> but nodal precession itself is in the value of Ω, this is a term that does something with the orientation of the plane
<egg|work|egg> I guess those magic numbers have something to do with the inclination of the lunar orbit, among other things
<roysmeding> but yeah so basically what i was hoping originally was that i could grab the mean longitudes from the orbital data, and do away with the "corrections" that way
<egg|work|egg> that doesn't look like a correction to the mean longitude
<egg|work|egg> that's a correction to account for non-coplanarity of the orbits of the earth and moon
<egg|work|egg> but the nice thing with magic constants is they're googlable
<egg|work|egg> so maybe there's a way to figure out what's going on
<egg|work|egg> or maybe not
<egg|work|egg> these constants are too magical :-p
<roysmeding> yeah, i'd tried that trick already
<egg|work|egg> roysmeding: anyway, whatever this is, it has a period which is the period of Ω or Ω/2
<egg|work|egg> that is *not* a short period
<egg|work|egg> so that's not the short-period variation you would get from osculating elements; it's something which varies with the cycle of nodes (I forget whether that's the 8 or the 20 year one)
<egg|work|egg> it's the 18.6 year one apparently
<roysmeding> i did some more googling and found this, which refers to the same corrections i was talking about https://github.com/stephankramer/uptide/wiki/Tidal-signal-reconstruction
<mofh> UmbralRaptop: moment
<roysmeding> the bit at the end of the page about nodal corrections
<egg|work|egg> > The nodal corrections are contributions associated with the periodic movement of the lunar nodes with a period of 18.6 years.
<roysmeding> yeah
<roysmeding> bbl, i gotta make my way home
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<roysmeding> i live
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<_whitenotifier-5dfc> [Principia] pleroy reviewed pull request #2293 commit - https://git.io/fjFyj
<_whitenotifier-5dfc> [Principia] pleroy reviewed pull request #2293 commit - https://git.io/fjFSe
<_whitenotifier-5dfc> [Principia] pleroy reviewed pull request #2293 commit - https://git.io/fjFSv
<_whitenotifier-5dfc> [Principia] pleroy reviewed pull request #2293 commit - https://git.io/fjFSf
<_whitenotifier-5dfc> [Principia] pleroy reviewed pull request #2293 commit - https://git.io/fjFSJ
<_whitenotifier-5dfc> [Principia] eggrobin reviewed pull request #2293 commit - https://git.io/fjFS4
<_whitenotifier-5dfc> [Principia] eggrobin reviewed pull request #2293 commit - https://git.io/fjFS2
<_whitenotifier-5dfc> [Principia] eggrobin reviewed pull request #2293 commit - https://git.io/fjFSa
<_whitenotifier-5dfc> [Principia] eggrobin reviewed pull request #2293 commit - https://git.io/fjFSK
<_whitenotifier-5dfc> [Principia] eggrobin synchronize pull request #2293: Add error matchers - https://git.io/fjFEN
<egg> !wpn roysmeding
* galois gives roysmeding a krypton rubber chicken
<SnoopJeDi> !or the rubber is from Krypton or the rubber chicken is from Krypton
<galois> SnoopJeDi: the rubber is from Krypton
<_whitenotifier-5dfc> [Principia] pleroy reviewed pull request #2293 commit - https://git.io/fjFSj
<_whitenotifier-5dfc> [Principia] pleroy reviewed pull request #2293 commit - https://git.io/fjF9e
<_whitenotifier-5dfc> [Principia] pleroy reviewed pull request #2293 commit - https://git.io/fjF9v
<_whitenotifier-5dfc> [Principia] eggrobin synchronize pull request #2293: Add error matchers - https://git.io/fjFEN
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<_whitenotifier-5dfc> [Principia] pleroy labeled pull request #2293: Add error matchers - https://git.io/fjFEN
<egg> !wpn UmbralRaptop
* galois gives UmbralRaptop a killing icosohedron
<UmbralRaptop> The ambiguity in the adjective is intentional
<UmbralRaptop> !wpn egg
* galois gives egg a comulant woomera
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<UmbralRaptor> mofh: anyway, I'm stuck on the 3rd part of 3 and need to poke at the textbooks for question 4 https://photos.app.goo.gl/NHRS3p46FSPVkTx5A
* egg bites mofh
<egg> mofh: meow
<egg> mofh: meow
<egg> mofh: MEOW
<egg> mofh: MEOW MEOW MEOW MEOW MEOW MEOW MEOW MEOW
* UmbralRaptor pokes mofh with a stick
<_whitenotifier-5dfc> [Principia] eggrobin closed pull request #2293: Add error matchers - https://git.io/fjFEN
<_whitenotifier-5dfc> [Principia] eggrobin pushed 12 commits to master [+6/-2/±31] https://git.io/fjFHp
<_whitenotifier-5dfc> [Principia] eggrobin 8f08d42 - new matchers
<_whitenotifier-5dfc> [Principia] eggrobin cc780ea - use the matchers
<_whitenotifier-5dfc> [Principia] eggrobin 2ce91ad - fix the expectations
<_whitenotifier-5dfc> [Principia] ... and 9 more commits.
* UmbralRaptor caws at mofh
<UmbralRaptor> fully degenerate electron gases have convenient integrals, apparently?
<UmbralRaptor> It's weird overhearing new undergrads playing poker
<B787_300> so is KSP2 using some devs who might have worked on KSP1 and left?
<UmbralRaptor> ¯\_(ツ)_/¯
<UmbralRaptor> mofh: or not. Apparently I need to get Ω for 4b?
<mofh> UmbralRaptor: egg: okay, finally sitting down and looking at this.
* mofh grabs the problem sets
<UmbralRaptor> yay
* egg mewos at mofh
<mofh> UmbralRaptor: there's a bunch of ways to do 4b, the most common would be kinetic theory of gases (p = Force/Area, use the average particle velocity for v, and assume homogeneity giving you the factor of 3 outfront). The other easy approach is using degrees of freedom, average energy & equipartition thm.
* UmbralRaptor stares at Greiner because somehow we never went over the kinetic theory of gases >_<
<mofh> *blink* *blink* uhh
<mofh> hm, actually yeah I think Greiner would be your best ref there (I think Schroeder's Thermal Physics might cover it in enough detail actually, but if it doesn't, Greiner is 100% the text to use).
<UmbralRaptor> Oh, Schroeder, not Schroedinger
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<egg> !wpn mofh
* galois gives mofh a mistake
<egg> !wpn roysmeding
* galois gives roysmeding a adjoint parabolic moment
<egg> !wpn UmbralRaptop
* galois gives UmbralRaptop a Hermitian pastry with a eoraptor attachment
<mlbaker> !wpn
* galois gives mlbaker a boosted astatine mongoose
<UmbralRaptop> hrm. integrate over a velocity sphere, ish
<UmbralRaptop> Also, getting food since I'm drifting towards "too hungry to think straight"
<egg> UmbralRaptop: is coffee food
<UmbralRaptop> caffeine is a vitamin, but there are very few calories