UmbralRaptop changed the topic of #principia to: READ THE FAQ: http://goo.gl/gMZF9H; The current version is Fuchs. We currently target 1.5.1, 1.6.1, 1.7.x, 1.8.1, and 1.9.1. <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… | <egg> also 4e16 m * 2^-52 is uncomfortably large
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<UmbralRaptor>
urgh, matricies
<UmbralRaptor>
… I guess Sakurai isn't *worse* than Jackson per se
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<discord->
egg. — I wonder whether we should have an "active vessel LVLH" frame in the same way we have a "target vessel LVLH" frame
<discord->
egg. — i.e., a reference frame centred on the vessel, where the reference plane is the orbital plane of the vessel and the reference direction is the primary
<discord->
Standecco. — orbital plane of the vessel relative to what?
<discord->
egg. — the chosen primary
<discord->
egg. — just like the target frame, but instead of the target, yourself
<discord->
Standecco. — oh and how do you chose the primary?
<discord->
egg. — just like the target frame
<discord->
egg. — in the list
<discord->
Standecco. — does it show that I don't actually play and I don't know how any of the interfaces for principia work?
<discord->
egg. — that's no excuse, I don't play either and I vaguely know how it works
<discord->
egg. — :-p
<discord->
Standecco. — so this would be a 5th reference frame in that list
<discord->
egg. — I should drop the barycentric rotating one though
<discord->
Standecco. — in that list that I vaguely recall containing the frames
<discord->
egg. — I suppose; though remember that the target frame is special and is not selectable from there
<discord->
Standecco. — oh one of those 2 barycentric frames is useless then
<discord->
Standecco. — it's not just me being clueless on how it works and how it differs from the other
<discord->
egg. — well, the barycentric one is useless, and the other should be renamed
<discord->
Standecco. — what is supposed to be the difference?
<discord->
egg. — centred on the barycentre vs. on the body
<discord->
egg. — you can read it all in the concepts page
<discord->
lpg. — There are no useless frames, since they all draw different arrangements of purple lines. pretty purple patterns are the reason we're all here, no?
<discord->
egg. — hah
<discord->
Damien. — @egg What would be the usage case of the frame you mentioned?
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<discord->
egg. — @Damien e.g. from a space station, seeing the trajectories of approaching vessels
<discord->
egg. — and for an observation satellite, a way to look at map view in a more "orbit-centric" fashion
<discord->
egg. — (the horizontal in map view would be your orbital plane)
<discord->
egg. — also, attitude-kept vehicles tend to have a fixed attitude in that frame
<discord->
egg. — you can sort of see what this would look like if you have two vehicles sitting next to each other, by looking at the target frame of the other
<discord->
egg. — @Damien basically my idea is to first change the meaning of the basic SAS "hold attitude" to mean "hold attitude in the current reference frame" (right now it is "hold attitude inertially if the altitude is high enough, otherwise hold attitude in the reference frame that ortates with the planet" which is really dumb)
<discord->
egg. — then to somehow measure how well attitude is being held in that reference frame, and if it is held well enough to hold it through timewarp
<discord->
egg. — but if you want to use that to keep the attitude of a classic satellite which always points the same end towards the Earth, you need a reference frame that rotates like the orbit
<discord->
egg. — the "point prograde" command could be used for something roughly equivalent, but that is notably different for eccentric orbit
<discord->
egg. — the "point prograde" command could be used for something roughly equivalent, but that is notably different for eccentric orbits (edited)
<discord->
Butcher. — > Is this a feature request for a "rebase flight plan" button? I think we could have that now
<discord->
Butcher. — @egg more or less. I set up a mcc to fix my Periselene, I align my craft and the predicted Periselene moves, then I burn and I miss the planned manoeuvre.
<discord->
Butcher. — I suppose I could plan, align, replan.
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<discord->
egg. — you would need to adjust your plan in any case
<discord->
egg. — but the fact that you need to delete and recreate your plan from scratch is quite the annoyance
<discord->
Butcher. — Yes, that's the annoyance.
<discord->
egg. — @Butcher any thoughts on attitude keeping, a hypothetical self LVLH frame, and whether one does rendez-vous on hyperbolic trajectories?
<discord->
egg. — and why the sea is boiling hot, and whether pings have wings
<discord->
Butcher. — Lvlh?
<discord->
egg. — local vertical local horizontal
<discord->
egg. — like target LVLH, but centred on yourself rather than the target
<discord->
Butcher. — Also, why would one do rendezvous on hyperbolic trajectories?
<discord->
egg. — I don't know
<discord->
egg. — does one ever do that?
<discord->
egg. — if one does not, then maybe I can autodetect the parent body for the target LVLH frame
<discord->
Butcher. — Hmm, lvlh with no target is useful for what?
<discord->
egg. — looking at map view from the perspective of the orbiting satellite, and attitude keeping in that frame
<discord->
lpg. — would capturing straight into deimos "orbit" qualify as rendez-vous on hyperbolic trajectory?
<discord->
egg. — (most satellites are attitude-kept in that frame: one end points down, one end points forward)
<discord->
egg. — @lpg I mean rendez-vous with another vessel
<discord->
egg. — where the target is on a hyperbolic arc
<discord->
lpg. — the _target_? oof. aldrin cycler?
<discord->
egg. — yeah that sort of thing I guess
<discord->
egg. — although there it is basically a solar orbit rendez-vous
<discord->
egg. — since the cycler should not be meaningfully perturbed by the Earth, lest it cease being a cycler
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<discord->
egg. — OK so I guess this yields the following possibility for a reorganization of the plotting frame selector:
<discord->
egg. — - you select the fixed body from a tree similar to the current one, + self & target if any;
<discord->
egg. — - for each choice of fixed body, you have three options:
<discord->
egg. — - body-centred nonrotating,
<discord->
egg. — - body-centred body-fixed (except for vessels, I don't think we want to look at the spinning reference frame wherein your spinning Салют 7 is fixed),
<discord->
egg. — - body-centred orbit (except for the Sun; called LVLH if the body is a vessel; currently called _C_A but that is a terrible name).
<discord->
egg. —
<discord->
egg. — The barycentric rotating frame gets ditched.
<discord->
egg. — To deal with issues with circumbinary we may eventually want to look at making body-centred orbit point at the barycentre of the inner system rather than a single primary body.
<discord->
egg. — OK so obviously sometimes you want to keep pointing at the sun from Earth orbit
<discord->
egg. — doing that in the "fixed attitude in the frame" model would mean using the orbital frame wrt the sun, while you are in earth orbit
<discord->
egg. — oh, the Geocentric Ecliptic frame suffices
<discord->
egg. — @Butcher @Damien @lpg, thoughts on the proposal marked by an egg above?
<discord->
Butcher. — That sounds like a reasonable set of frames.
<discord->
Damien. — @egg looks reasonable to me. Regarding hyperbolic rendezvous, intercepting asteroids (potatoroids) on earth flybys perhaps
<discord->
lpg. — As far as the frame selector goes, sounds fine to me. I haven't followed closely the 'fixed attitude' topic; I'm unclear on how (if at all) any of this would interact with SmartASS's own "advanced" reference frames
<discord->
lpg. — (in particular, something commonly used for the "point at the sun" scenario)
<discord->
egg. — I think SmartASS could replicate some of the functionality except I am not going to interface with it so it will not work through timewarp
<discord->
egg. — Hmm.
<discord->
egg. — > This results in the requirement to keep (with
<discord->
egg. — > a given accuracy) XOZ plane where the antenna
<discord->
egg. — > is placed in the Q plane of the centers of the Sun,
<discord->
egg. — > the Earth and the satellite
<discord->
egg. — that constraint doesn't map to a very nice reference frame...
<discord->
egg. — turns out while it is easier to express than stationkeeping, the set point of attitude keeping is quite tricky already
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<discord->
egg. — hm. the alternative would be to somehow make it possible to decouple the attitude-keeping frame from the plotting frame, but that sounds complex
<discord->
egg. — This is the attitude that Молния 1 keeps
<discord->
egg. — pointed directly at the Sun, and then spun so that the antenna is in the Sun-Earth-Satellite plane (it then hinges in that plane to point at the planet)
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<_whitenotifier-d13c>
[Principia] eggrobin labeled pull request #2605: Next release is Gallai - https://git.io/JfbCP
<discord->
egg. — OK self-centred plotting frames are pretty dumb (no self trajectory, and largely useless celestial body trajectories), so perhaps the answer is that we should have a way to decouple the attitude-keeping frame from the plotting frame
<discord->
egg. — and then the attitude-keeping frame can have all sorts of exotic options like Sun direction, Sun-Earth plane, or Earth direction, orbit plane, etc.
<discord->
egg. — but then what should be used to signal that the attitude frame is different? We could change the navball, but then the navball would no longer serve as a visual indication of what the plotting frame is
<discord->
egg. — on the other hand the navball is only ever a partial indication of the plotting frame, since it does not change colour depending on the reference body; so maybe that would be fine?