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
<egg|laptop|egg> bofh: meow
<egg|laptop|egg> bofh: hm, TLE-to-cartesian then integrate might not be ideal for finely synchronized satellites, apparently the uncertainties on TLEs are km-level
<egg|laptop|egg> bofh: e.g. for FormoSat-2, I can get it nearly-phased if I multiply the velocity by (1 - 0.00014) from what I get out of the TLEs
<egg|laptop|egg> (that's a bit below 1 m/s)
<egg|laptop|egg> (it was probably phased since the TLE is before decommissioning)
<egg|laptop|egg> bofh: meow
<bofh> egg|laptop|egg: like the TLEs just before decommissioning are prolly complicated but also largely irrelevant, since they're prolly for when it's shifting into a graveyard/disposal orbit
<bofh> as for book idées, uh
<egg|laptop|egg> bofh: before you ask I have both Muller books
<egg|laptop|egg> though probably first editions whereas they're on 2nd and 3rd apparently?
<egg|laptop|egg> bofh: anything in numerics?
<bofh> I get the feeling you have all the essentials? Like if you *don't* have a copy of Golub & van Loan and can get it cheaply, do so, but I swear you already do.
<bofh> Otherwise, hm.
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<bofh> Gautschi's Orthogonal Polynomials book is on the top of my to-purchase list, I use it a *lot* and I really want a physical copy (libgen has a very nice pdf or http://138.68.64.246/Walter_Gautschi_-_Orthogonal_Polynomials_-_Computation_and_Approximation_%282004%29.pdf ), not sure if it's useful to you but I actually do think so (it goes into a lot of depth on integration, quadrature and a lot of really
<bofh> fun things like that).
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<egg|laptop|egg> bofh: hm, I'm not sure I have Golub and van Loan
<egg|laptop|egg> I have higham
<egg|laptop|egg> bofh: have you tweeted your Golub and van Loan picture on main, I forget
<egg|laptop|egg> bofh: there are some hairer books on geometric numerical integration
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<egg|laptop|egg> bofh: do you know how much difference there is between the third and first editions of Muller's Elementary Functions?
<bofh> I very highly doubt there's mich of a difference.
<bofh> 00:35:08 < egg|laptop|egg> bofh: have you tweeted your Golub and van Loan picture on main, I forget
<bofh> I don't think so.
<bofh> I prolly should at some point.
<egg|laptop|egg> bofh: do eeeeeeet
<egg|laptop|egg> bofh: also should I get Ignition! in hardcover or paperback
<bofh> Either, but if you can afford the hardcover, why not?
<egg|laptop|egg> yeah probably
<egg|laptop|egg> bofh: the paperback is "Publisher: RUTGERS UNIV PR; None edition (30 April 2018)" whereas the hardcover is "Publisher: Rutgers University Press; None edition (23 May 2018)"
<egg|laptop|egg> None edition! :-p
<bofh> rofl None Edition
<bofh> None Book with Left Edition
<egg|laptop|egg> bofh: unfortunately the Capderou book only eggsists in paperback
<egg|laptop|egg> even though it's 862 pages (whereas Ignition! is 302)
* egg|laptop|egg stares in confusion
<egg|laptop|egg> it does exist in hardcover in english on springer's website
<egg|laptop|egg> ... but not in french
<egg|laptop|egg> the translator binds the book i guess
<egg|laptop|egg> "Sorry, this item can't be sent to your selected address" fuuuuck
<bofh> In Zürich?
<egg|laptop|egg> wait they can't even send it to normandy?
<egg|laptop|egg> they're a french bookstore O_o
<egg|laptop|egg> "No sellers are currently delivering this item to Switzerland"
<egg|laptop|egg> "No sellers are currently delivering this item to France - Mainland"
<egg|laptop|egg> um
<egg|laptop|egg> bofh: okay so for this book (in french!) there's one bookstore in france that ships to neither france nor switzerland, and the other that does ship to switzerland but sells it > twice the price of the other
<egg|laptop|egg> bofh: I guess it's cheaper if you can't buy it
<UmbralRaptop> None to mainland France, so corsica?
<egg|laptop|egg> Hah
<bofh> 01:09:35 < egg|laptop|egg> "No sellers are currently delivering this item to France - Mainland"
<bofh> what on *earth*?
<egg|laptop|egg> bofh: no but the one that sells it for double the price does work, it's just amazon being bad at aggregating on the page for the book
<egg|laptop|egg> but the fact that one of the sellers ships nowhere is weird
<bofh> which is the other seller, out of curiosity?
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<egg|laptop|egg> wait but the one that does ship is Arrives between February 21-28, so it won't ship in a while....
<egg|laptop|egg> okay so on the delivery option page it says "get it on Thursday, Feb 21 - Thursday, Feb 28"
<egg|laptop|egg> I'm flying on the 23rd
<egg|laptop|egg> lol and for Ignition! Wednesday, Feb 20 - Saturday, Mar 9
<egg|laptop|egg> then again these estimates tend to be long
<bofh> Yeah, I think those are particularly pessimistic estimates, tbqh.
<egg|laptop|egg> bofh: by the way speaking of shipping woes
<egg|laptop|egg> (one of them from IL!)
<bofh> I should get that and bring it with me.
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<egg|laptop|egg> bofh: yes :-p
<egg|laptop|egg> bofh: well, it's a couple months before decommissioning
<egg|laptop|egg> (re. the TLEs)
<egg|laptop|egg> bofh: but also TLE-to-cartesian-then-integrate probably has more errors than TLE-evolved-by-SGP-4, because TLE-to-cartesian has large errors even at epoch
<egg|laptop|egg> I'll request TLEs from 2010 to see what those look like
<bofh> I wonder how much you can simplify SGP4 and still get reasonable results, particularly for systems we care about (since I know there are certain terms there that effectively are zero for most sats).
<egg|laptop|egg> bofh: well I'm largely not interested in SGP4 anyway for principia porpoises
<egg|laptop|egg> the only reason I'm touching TLEs is to use real satellites as test cases
<egg|laptop|egg> the only thing principia does is numerical integration, no cheesy analytic models
<bofh> I mean Principia *should* start using analytic models when numerical integration itsself stops sufficing, that would improve long-term accuracy :p
<egg|laptop|egg> bofh: O_o
<egg|laptop|egg> bofh: the analytic models (at least for artificial satellites) are eggstremely *short-term* in their validity
<bofh> I can't see them being *worse* than just integrating the Keplerian elements, since the whole point is they're corrections *to* the integration of the Keplerian elements.
<egg|laptop|egg> ..... wat
<egg|laptop|egg> bofh: when I say principia does numerical integration, I mean in the full-potential problem
<egg|laptop|egg> bofh: which (ignoring atmospheric effects) is what SGP-4 and the like tries to analytically approximate
<bofh> OH, right, in the full-potential problem, not the simple case I was thinking of.
<bofh> Right.
<bofh> Disregard. Yeah, that has questionable utility for Principia, then.
<egg|laptop|egg> bofh: evolving a Kepler orbit hardly counts as integrating
<egg|laptop|egg> I mean, you could do it by integration
<egg|laptop|egg> also twitter informs me that i have had an account for five years
<bofh> not bad
<bofh> how old is mine I wonder
<egg|laptop|egg> gah, Rosetta was 5 years ago?!
<bofh> 6 years this May, apparently.
<egg|laptop|egg> wait, 6? I'm confused
<egg|laptop|egg> ah you mean your twitter account not Rosetta
<egg|laptop|egg> also I'm confused as to why I created this account
<egg|laptop|egg> I thought it was to follow the rosetta coverage from elakdawalla, but the encounter was august
<egg|laptop|egg> i should sleep
* egg|laptop|egg meows at bofh
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<bofh> https://twitter.com/jamesheathers/status/1093529958960586755 just implemented this as a cloud2butt ext, lol.
<kmath> <jamesheathers> I'm going to write a browser extension that replaces "wellness guru" with "hammering twat" to make things like this… https://t.co/3X4DqSP8Gu
<bofh> I created mine b/c following Oona Räisänen and Chris Hadfield by hand was getting annoying.
<bofh> Don't know why I started posting on it tho.
<egg|zzz|egg> bofh: it took me ages to actually follow people (and I still don't use the timeline), I just created the account to not get the reminder to do so :-p
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<egg|cell|egg> Zzz
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* UmbralRaptop >_<
<UmbralRaptop> So, apparently 1) a 46 was almost passing my QM qual (cutoff was 50ish), and 2) only ~25% of students taking the QM qual this semester passed.
<SnoopJeDi> jeez
<UmbralRaptop> After additional searching (with my advisor), we determined that Sakurai does go over parity operators. But my edition carefully avoids showing this in the table of contents or the index. >_<
<bofh> bloody hell, I have that exact edition, I think it was fixed in a later one.
<bofh> (or had, rather)
<bofh> also jfc
<bofh> like, my hot take is a qual so difficult only a quarter of people pass is garbage.
<SnoopJeDi> the very existence of quals tells me that a department is insecure about the coursework's ability to teach students what they're expected to know
<SnoopJeDi> (insecurity in academia? why, I never!)
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<UmbralRaptop> If anything, the flaw is in *newer* editions (advisor's copy is fine)
<SnoopJeDi> i.e. the not-Sakurai ones?
<bofh> Huh, that might make sense, I think mine was a 2nd-ed. I should check what's in the library copy of Sakurai.
<bofh> (or just libgen all the editions and compare).
<SnoopJeDi> bofh, that'd be a good for-nerds startup idea.
<SnoopJeDi> some kind of system that kludges multiple versions together so you get a map of the text over time
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<SnoopJeDi> bofh, Science Friday has started a second run of their etymology series, and TIL that "chocolate" is an indigenous word that for some reason never really got Anglicized
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<egg|zzz|egg> meow
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<SnoopJeDi> what the heck, 2014 MU69 is a pancake?!
<UmbralRaptop> wat
<kmath> <✔Alex_Parker> So if you already thought that 2014 MU69 looked a little ... odd? You haven't seen anything yet. Our latest data si… https://t.co/rYBdvXrkTC
<SnoopJeDi> take the mental model you have and squish it perpendicular to the binary-contact axis o.O
<kmath> <✔Alex_Parker> And @AscendingNode has been working on a full 3D shape model based on all the data in hand. WEIRD. https://t.co/KYX5RG1Jws
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<egg|laptop|egg> bofh: paris-brest came out nice
<egg|laptop|egg> easy to make too
<egg|laptop|egg> 1 28254U 04018A 10001.06515326 .00000104 00000-0 10000-3 0 3571
<egg|laptop|egg> 2 28254 99.1103 64.2419 0002824 109.6874 2.6228 14.00732798287225
<bofh> egg|laptop|egg: ooh excellent, I need to try now.
<egg|laptop|egg> bofh: you need piping bags to extrude the dough and filling, other than that no fancy equipment required
<egg|laptop|egg> ok from those 2010 TLEs ιξιων computes κ = 14.000110
<egg|laptop|egg> let's see what I get
<bofh> egg|laptop|egg: yeah I think I even have some piping bags here somewhere; if not they're easy to acquire.
<UmbralRaptop> Today in colloquia: Professor Nikolic (BSc from Belgrade) introduces Professor Nikolic (BSc from Belgrade).
<egg|laptop|egg> UmbralRaptop: not Nikolić?
<UmbralRaptop> yes that. Unicode is hard
<egg|laptop|egg> hm, I get κ = +14.002761(89)
<SnoopJeDi> UmbralRaptop, that professor appears to be degenerate
<egg|laptop|egg> in both cases (2010 and 2016) ιξιων in much closer to the nominal κ
<egg|laptop|egg> bofh: how are TLEs actually computed
<egg|laptop|egg> as in, from what kind of observations
<bofh> I'm not actually sure, I think it might strongly depend on the sat in question.
<bofh> But their main purpose from what I gather is satellite ground tracking from ground stations.
<egg|laptop|egg> bofh: what I'm seeing suggests that you get a much better estimate of, say, the anomalistic period from the TLEs than of the state vectors
<egg|laptop|egg> so that if you compute the state vectors, integrate and determine the anomalistic period from that, you'll get higher errors
<bofh> what do you mean by "state vectors" here?
<bofh> TLEs are basically just Keplerian Elements
<egg|laptop|egg> bofh: by state vectors I mean instantaneous position and velocity
<egg|laptop|egg> bofh: "basically just Keplerian Elements" << yes, but *mean* elements following some theory
<egg|laptop|egg> (Brouwer-Lyddane I think)
<bofh> I mean yes, are there any other *sensible* types other than mean elements?
<egg|laptop|egg> osculating
<egg|laptop|egg> and there is an infinite supply of mean element theories, so "mean elements" covers many things
<bofh> I mean yes, but I'm pretty sure just about any mean element theory still gives more useful Keplerian elements than using the osculating ones.
<bofh> :p
<egg|laptop|egg> depends what you want
<egg|laptop|egg> mean elements are utterly useless if you want an instantaneous state, which is precisely the issue here
<bofh> I mean yes, but you very rarely want an instantaneous state, you're usually concerned with a state propagating over some time interval of at the least, a few hours.
<egg|laptop|egg> bofh: unless of course you're trying to have something interchangeable from one model to another
<egg|laptop|egg> bofh: but my question is, since it seems that the actual periods (as in node-to-node times, or perigee-to-perigee times) can be recovered more accurately from the TLEs than by TLEs->instantaneous state vectors->numerical integration and period measurement, are the TLEs computed directly from such period measurements (rather than say, instantaneous ranging observations)?
<bofh> (Also yes, it appears TLEs usually use Brouwer-Lyddane)
<bofh> Generally, IME, yes.
<bofh> Again, their principal use is ground station tracking of LEO sats. Most of those can't even really do instantaneous RF ranging b/c there's not really a use for it, your beamwidths are large enough you can tolerate a few arcseconds of pointing error.
<egg|laptop|egg> bofh: OK, so the correct TLE-to-instantaneous-state transformation would be fitting the actually-observed quantities (which of course are undocumented and probably obscured somewhat in the Brouwer-Lyddane elements), rather than SGP4?
<bofh> I *believe* so. Not 100% sure, but I'm fairly certain that is the correct approach.
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<egg|laptop|egg> bofh: um when was this FAQ updated, https://celestrak.com/columns/v04n03/#FAQ04
<egg|laptop|egg> https://arxiv.org/pdf/1002.2277.pdf "Our method is essentially to use TLE data as “pseudo-observations” and to fit an orbit to these pseudo-observations using a high-precision special perturbations propagator and traditional batch least-squares differential correction."
<bofh> rofl Constrained Least Squares Strikes Again
<egg|laptop|egg> bofh: B787_300: UmbralRaptop: what is a typical order of magnitude for velocity corrections in stationkeeing
<egg|laptop|egg> s/ee/eep/
<galois> egg|laptop|egg meant to say: bofh: B787_300: UmbralRaptop: what is a typical order of magnitude for velocity corrections in stationkeeping
<B787_300> we talking GEO or LEO
<egg|laptop|egg> recurrent ground track LEO, but I'm interested in all of them
<egg|laptop|egg> to clarify I mean the amplitude of a single correction, i.e. the precision to which the velocity is kept, rather than the cost over time
<B787_300> oh dV for a single correction?
<B787_300> a couple m/s
<B787_300> for GEOs to a 10s of m/s for LEOs
<B787_300> drag is a bitch
<bofh> GEO corrections often aren't required too often due to the nature of GEO
<bofh> and yeah, 10s of m/s for LEO
<egg|laptop|egg> wait, even for repeat ground track applications? don't you want a fairly precise velocity there?
<B787_300> depends
<B787_300> how precise do you need your repeats?