UmbralRaptop changed the topic of #principia to: READ THE FAQ: http://goo.gl/gMZF9H; The current version is Fano. We currently target 1.3.1, 1.4.x, 1.5.1, and 1.6.1. <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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<discord-> A​very. — With principia could you deorbit a moon theoretically
<UmbralRaptop> I bet KSP (or Unity) would break in a weird way if you had parts scaled to make that possible
<discord-> A​very. — But like are planets affected by spacecraft
<UmbralRaptop> Ramming, maybe. Craft don't pull on planets. Ask œuf about the performance concerns.
<UmbralRaptop> … actually I'm not sure about ramming either
<discord-> E​vanR. — You could do an asteroid redirect mission by just sticking a probe next to it early enough
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<discord-> l​amont. — precompiled C++ libraries for the IPOPT NLP solver: https://www.coin-or.org/download/binary/Ipopt/
<discord-> S​ir Mortimer. — ```
<discord-> S​ir Mortimer. — /* "Do not try and tilt the planet, that's impossible.
<discord-> S​ir Mortimer. — * Instead, only try to realize the truth...there is no tilt.
<discord-> S​ir Mortimer. — * Then you'll see that it is not the planet that tilts, it is
<discord-> S​ir Mortimer. — * the rest of the universe."
<discord-> S​ir Mortimer. — ```
<discord-> E​vanR. — :morpheus:
<discord-> S​ir Mortimer. — damnit i need kopernicus + rss to actually do this.
<discord-> S​ir Mortimer. — and there is no kopernikus for 171.
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<discord-> e​gg. — @Sir Mortimer where is that comment from?
<discord-> S​ir Mortimer. — my new kerbalism branch that tilts magnetic fields 😃
<discord-> e​gg. — hah
<discord-> e​gg. — by the way
<discord-> e​gg. — @Sir Mortimer another reason why you want to use the scaled space thingy (which gives you the full orientation, tilt + rotation) is that the belts rotate with the planet https://en.wikipedia.org/wiki/South_Atlantic_Anomaly
<discord-> S​ir Mortimer. — yes we had that discussion in a different channel (forgot which, guess it was the kerbalism server)
<discord-> S​ir Mortimer. — it rotates around the magnetic pole, not the north pole.
<discord-> S​ir Mortimer. — this will be one wobbly field in time warp
<discord-> e​gg. — it doesn't *rotate* around the magnetic pole
<discord-> S​ir Mortimer. — yeah i know
<discord-> S​ir Mortimer. — i#M in a hurry 😛
<discord-> e​gg. — the axis of symmetry is the magnetic pole
<discord-> e​gg. — and that pole is (in first approximation) unmoving in ECEF
<discord-> e​gg. — and ECEF you can get by the scaledBody orientation
<discord-> S​ir Mortimer. — thing is, i need something that tells me the axis of the magnetic field
<discord-> e​gg. — yeah that needs a separate config
<discord-> S​ir Mortimer. — i just could add a config that defines lat/lon of the magnetic pole and work from that
<discord-> e​gg. — yeah
<discord-> e​gg. — @Sir Mortimer OK you want the *geomagnetic* poles, not the *magnetic* poles https://en.wikipedia.org/wiki/Geomagnetic_pole#Movement
<discord-> e​gg. — conveniently those don't move very much, contrary to the magnetic poles which dance all over the place
<UmbralRaptop> Implement magnetic fields as spherical harmonics?
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<discord-> e​gg. — aaaaaaaaaaaaaaaa
<discord-> E​vanR. — um geomagnetic pole vs magnetic pole?
<discord-> E​vanR. — ok
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<discord-> S​ir Mortimer. — so there are 2 of those, didn't know that
<discord-> S​ir Mortimer. — i only knew that there's a geomagnetic pole, and that you have to watch out for where you are on the world if you want to rely on a magnetic compass
<discord-> 王​小谦同学. — @egg I was talking to the founder of KerbCat today, and he recommends me to restructure my guide by split the chapters, so this way, it's easier to read, and, I could get more awards given by the robot of KerbCat
<discord-> D​amien. — @Sir Mortimer you'll learn pretty quick that egg doesn't accept approximately correct, he only accepts precisely correct
<discord-> D​amien. — as most computers do
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<discord-> G​ordon Dry. — Is adding zeros increasing precision?
<discord-> D​amien. — when the last digit is so small that KSP's floating point errors can make it anything from 1-9 probably not 😄
<discord-> G​ordon Dry. — One of the RP-1 auto-contracts (miulestones) is such a thing, like "90.000001 km crewed altitude milestone achieved"
<discord-> G​ordon Dry. — One of the RP-1 auto-contracts (milestones) is such a thing, like "90.000001 km crewed altitude milestone achieved" (edited)
<discord-> e​gg. — @Sir Mortimer @Damien nah, I'm fine with approximations (e.g. here considering the Earth as a dipole is probably the right thing to do, the spherical harmonics UmbralRaptop suggests would be madness), as long as we are eggsplicit and correct when describing what we are doing :-p
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<discord-> D​amien. — I know but you do love to get all wordy and specific when someone makes a simplification for the sake of ease of discussion 😄
<discord-> D​amien. — but we expect nothing more from our resident EggAI
<discord-> D​amien. — but we expect nothing less from our resident EggAI (edited)
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<discord-> S​ir Mortimer. — i'm tempted to put the magnetic pole of some planet near the equator once this works. with a killer radiation.
<egg|cell|egg> Hahahaha
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<discord-> S​ir Mortimer. — getting there https://imgur.com/a/cWpFH3J
<discord-> S​ir Mortimer. — i know what egg is typing 😛
<discord-> e​gg. — It's not aligned with the planet though, only with the orbit, right?
<discord-> e​gg. — (i.e. the red thing points to the sun)
<discord-> S​ir Mortimer. — exactly 😃
<discord-> e​gg. — eggsactly
<discord-> e​gg. — can you tilt it in the red-green plane
<discord-> S​ir Mortimer. — i'll just tilt the belts according to where the geomagnetic pole is. but i won't change their shape. the deformation won't be accurate. but i'll keep the magnetopause fixed on the sun axis. so the belts will wobble in 2 degrees of freedom within a magnetopause that wobbles in just one.
<discord-> e​gg. — In that case you should keep the belts rotationally symmetric around the geomagnetic axis
<discord-> e​gg. — otherwise it will be very weird
<discord-> e​gg. — (and the magnetopause can happily keep its current shape)
<discord-> S​ir Mortimer. — dimensions and effect of solar winds are config values, luckily 😃
<discord-> e​gg. — my point is, once the belts are fixed in ECEF, they'll revolve once a day
<discord-> e​gg. — so any deformation "due to the sun" will be absurdly oriented
<discord-> S​ir Mortimer. — yeah that must not happen.
<discord-> D​amien. — inb4 a bug whereby the belts rotate around the planet when the craft changes attitude
<discord-> S​ir Mortimer. — yeah. well. finding orbits that stay OUT of these will be fun.
<discord-> S​ir Mortimer. — or munar transits for crew.
<discord-> S​ir Mortimer. — "bill, let's go!" - "wait for 3 hours, jeb, otherwise you're not going to have kids"
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<discord-> e​gg. — @Sir Mortimer it's also going to be interesting for misc. mission design (can't do space telescope stuff in the belts generally)
<discord-> e​gg. — umbralraptor had found this out about IRAS: https://lambda.gsfc.nasa.gov/product/iras/docs/exp.sup/ch3/B.html#6
<discord-> e​gg. — '''
<discord-> e​gg. — Another constraint was the depression in the Van Allen belts known as the South Atlantic Anomaly (SAA). Proton hits in the detectors when passing through the SAA increased the noise to such an extent that it was impossible to continue observations. Data were not taken whenever the satellite entered a geographically fixed flux/energy contour. As a result of analysis of the effects of radiation on the d
<discord-> e​gg. —
<UmbralRaptop> Please do not irradiate your telescopes
<discord-> e​gg. — A second effect of a passage through the SAA was a long term enhancement, by as much as factors of ten, in the responsivity and noise caused by the large radiation dosage. As described in Section II.C.5, these large changes could be erased by increasing the bias voltage on the detectors, a technique referred to as bias boosting".
<discord-> e​gg. — '''
<discord-> e​gg. — '''
<discord-> e​gg. — Blue areas along the southern ecliptic are less covered due to the South
<discord-> e​gg. — Atlantic Anomaly. The partial second coverage allowed by a 9 month survey
<discord-> e​gg. — cuts out half of this undercovered portion of the sky.
<discord-> e​gg. — '''
<UmbralRaptop> How about the ISS, specifically AMS-02?
<discord-> e​gg. — South Atlantic Anomaly Detector (SAAD)
<discord-> e​gg. — > SAA image from the South Atlantic Anomaly Detector (SAAD) on board the ROSAT [43] satellite
<discord-> e​gg. — interesting
<UmbralRaptop> figures
* UmbralRaptop eyes Chandra's orbit, and vaguely wonders about XMM Newton, Fermi, NuSTAR, and Compton
<UmbralRaptop> Er, and Uhuru?
<discord-> e​gg. — I think CXO or XMM don't observe in the belts
<discord-> e​gg. — > The perigee of ISO's orbit lay well inside the Van Allen radiation belt, forcing the science instruments to be shut down for seven hours during each pass through the radiation belt. Thus, 17 hours in each orbit remained for scientific observation.
<discord-> S​ir Mortimer. — so, basically, a lot of instruments don't work if radiation is too high.
<discord-> e​gg. — yeah
<discord-> e​gg. — especially detectors
<discord-> e​gg. — unless your goal is to observe the belts
<discord-> S​ir Mortimer. — `RadiationMax` - known restriction for kerbalism. just not used. at all.
<discord-> S​ir Mortimer. — guess that's gonna change 😃
<discord-> S​ir Mortimer. — but ohmygod this is going to be so tricky
<discord-> e​gg. — flight computers you can make radhard, CCDs perhaps less so
<discord-> T​heRealWiwaxia. — Yes radiation is known to mess with electronics
<discord-> S​ir Mortimer. — what was the ratiation on this specific orbit during the last 5 hours? don't forget, the belts wobble
<discord-> e​gg. — for all things telescope ask umbralraptor
<UmbralRaptop> chirp?
<discord-> e​gg. — @Sir Mortimer yeah with the weird shape of the belts it might be best to just compute that numerically
<discord-> e​gg. — interpolate the orbit (this needs to be done in a way that's singularity-resistant), and numerically integrate that
<UmbralRaptop> Incidentally, CCDs degrade over time. Like, there are notable degradations in HST
* discord- e​gg. — pets HST_
<discord-> S​ir Mortimer. — yep. i had a solution like that in mind. take a couple of samples and interpolate the rest.
<discord-> e​gg. — @Sir Mortimer yes but you need to be very very careful how you do that
<UmbralRaptop> singularity resistant - good thing that the schwarzschild solution doesn't eggsist in Principia?
<discord-> e​gg. — especially interpolating orbital elements can get weird
<discord-> S​ir Mortimer. — ugh. this is going to be such a mess.
<discord-> e​gg. — e.g. take a near-circular orbit, the argument of periapsis will basically be random noise
<discord-> S​ir Mortimer. — well. approximation could work. take the stock orbit for interpolation, surely it won't be off by THAT much... and even if, nobody would notice 😃
<discord-> e​gg. — nope, as I just said
<discord-> e​gg. — the stock orbit can insanely vary because singularities in the elements
<discord-> e​gg. — even if you have a reasonably near-keplerian orbit
<discord-> S​ir Mortimer. — do those variations affect the position of the vessel on that orbit?
<discord-> e​gg. — ... yes, the elements define that
<discord-> S​ir Mortimer. — so you're saying a near circular orbit is haywire in KSP?
<discord-> e​gg. — absolutely
<discord-> S​ir Mortimer. — in a way that it cannot be used to determine my position on that orbit 5 hours ago?
<discord-> e​gg. — not unless you're careful
<discord-> e​gg. — if you're careful you're just fine
<discord-> S​ir Mortimer. — *...forgo all hope ye who enter here...*
<discord-> e​gg. — genau
<discord-> S​ir Mortimer. — man this is messy.
<discord-> S​ir Mortimer. — careful how?
<discord-> e​gg. — @Sir Mortimer consider this orbit https://imgur.com/8AqBSQU
<discord-> e​gg. — note that you have two perigees and two apogees per obrit
<discord-> e​gg. — note that you have two perigees and two apogees per orbit/ (edited)
<discord-> e​gg. — @Sir Mortimer now, if you are at apogee, your mean anomaly is π, if you are at perigee, it's 0; so your *osculating* mean anomaly makes 2 turns per orbit here (but on a Kepler orbit it obviously does one turn), so it's garbage
<discord-> e​gg. — but your mean anomaly is the thing that tells you how far along the orbit you are
<discord-> e​gg. — on that orbit, the thing that behaves usably is the argument of latitude
<discord-> S​ir Mortimer. — i see.
<discord-> e​gg. — the four-apsis thing is caused by J2; in stock KSP the perigee might just wander around aimlessly when out of timewarp
<discord-> S​ir Mortimer. — so numerically, you would jump any place on that orbit because of floating point errors.
<discord-> e​gg. — no don't blame that on floating-point
<discord-> e​gg. — you'll jump anywhere on that orbit, because the anomalies and the argument of perigee are singular there
<discord-> e​gg. — and since Kepler orbits are but an approximation of the real trajectory, these elements are essentially randomized on an orbit that puts them near their singularity
<discord-> S​ir Mortimer. — so... `FlightGlobals.ActiveVessel.orbit.getObtAtUT` is worthless?
<discord-> e​gg. — well, that's slightly different
<discord-> e​gg. — that's very bad in the presence of Principia, because there you can't account for precessions
<discord-> S​ir Mortimer. — or rather, `getPositionAtUT`
<discord-> e​gg. — yeahyeah I get it
<discord-> e​gg. — this will work in stock, but it will be abysmal around an oblate earth during timewarp
<discord-> e​gg. — we need to interpolate the precessing elements
<discord-> S​ir Mortimer. — it will require 2 implementations, then. unless principia is a hard dependency.
<discord-> e​gg. — no that's the thing
<discord-> e​gg. — you can easily do something that's principia-agnostic
<discord-> e​gg. — but it cannot be getPositionAtUT
<discord-> e​gg. — it has to look at the orbit before, the orbit after, and interpolate the orbit in a robust way
<discord-> e​gg. — assuming constant nodal and apsidal precession, this will be good enough at any sane timewarp
<discord-> S​ir Mortimer. — i think i get the picture
<discord-> e​gg. — ultimately it's just (fancyInterpolation(oldOrbit,newOrbit,t).getPositionAtUT(t)
<discord-> e​gg. — ultimately it's just FancyInterpolation(oldOrbit,newOrbit,t).getPositionAtUT(t) (edited)
<discord-> S​ir Mortimer. — I know someone who *won't* code FancyInterpolation 😃
<discord-> e​gg. — oh it's not that hard
<discord-> S​ir Mortimer. — lol. of course not 😛
<discord-> e​gg. — linearly interpolate longitude of ascending node; linearly interpolate longitude of periapsis; linearly interpolate mean longitude, re-extract the elements KSP wants
<discord-> e​gg. — It needs test cases based on Principia trajectories so we can check that it actually works
<discord-> e​gg. — I'll try to provide test cases for things in https://github.com/Kerbalism/Kerbalism/wiki/Satellite-Contracts#implementation in general
<discord-> e​gg. — and orbit interpolation will definitely be in there
<discord-> S​ir Mortimer. — 😅
<discord-> e​gg. — in fact there's a section title for it :D
<discord-> e​gg. — @Sir Mortimer basically the FancyInterpolation is very obvious away from the singularities, and then you need a trick to handle singularities
<discord-> e​gg. — The underlying assumption is that you are on an orbit where Ω, ω, and M change at a constant rate, and a, i, e basically don't change
<discord-> e​gg. — so naively you could linearly interpolate Ω, ω, and M; but you then get bitten by the singularities; instead you linearly interpolate Ω, Ω+ω, and Ω+ω+M, which behave better
<discord-> e​gg. — @Sir Mortimer for orbits that are close to parabolic it's a bit messier but we can probably find something clever there too
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<UmbralRaptop> ☄️❓
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<discord-> e​gg. — @Sir Mortimer hm, thinking about it, this approach works well for LEO, but for say things at Lagrange points it probably falls on its face; perhaps it would be easier to have an API by which you ask Principia "where was this vessel at this time"
<discord-> e​gg. — @Sir Mortimer but anyway, that's something to think about at some later point, there are a lot of empty sections in that document before we get there :D
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<discord-> S​ir Mortimer. — Lol yeah
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<discord-> S​ir Mortimer. — There’s a lot of work to be done before that
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<discord-> e​gg. — @Sir Mortimer also, mocks
<discord-> S​ir Mortimer. — You’re egging on 😉
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