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…
<queqiao->
⟨test_account9540⟩ Target frame is very good, right now you should traven to a node, burn to decrease relative inclination to zero, then arrange the closest approach near the target, warp until that closest approach and cancel relative velocity using MJ... and that's it, you will be very close to the target.
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⟨test_account9540⟩ * travel
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⟨test_account9540⟩ * to be near the target (as close as possible),
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⟨Joshua Wood⟩ I have no idea what is happening to my actual orbit when doing ANY of this though, the target frame is only good because there is no other place that gives the information it does
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it is simply worse than the way the stock patched conics does it
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⟨Joshua Wood⟩ Having closest approach and relative inclination show in MCI would give me ALL the information you just mentioned, allow the exact same manoeuvres and show the actual relevent information i need
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⟨Joshua Wood⟩ i'm not warping several days to the closest approach when i have a few hours of life support, that is shitty advice
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i need to alter my orbit in a way that causes me to intercept in VERY specific ways which doesn't involve the target frame AT ALL
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the only time i even opened target frame AT ALL was to check my closest approach time and distance? which could easily be put in every other frame of reference
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⟨nazfib⟩ From here, what I can read in this plot:
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- You are significantly out-of-plane relative to the target; fix that first.
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- In around 3 orbits, you'll pass directly overhead of the target (extrapolating a little bit; the prediction doesn't quite go far enough).
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- You are in a higher orbit than the target at all points along your orbit.
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⟨test_account9540⟩ It's best to use MJ smartass RV- mode to cancel relative velocity rather than hope it will be retrograde or something
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⟨nazfib⟩ If you hit the target exactly at the apex, it will be (you're basically preforming a hohmann transfer to the target). But indeed, as you get close you can use the relative velocity marker instead.
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⟨test_account9540⟩ yes the marker works too (even better because it's precise, I use it for docking)
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⟨Joshua Wood⟩ 1. Not true i was less than 1 degree out
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2. Deliberately so
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I know HOW to rendez-vous, the UI is just terrible for it, putting closest approach point in other reference frames would have saved me 25mins out of 30 flicking back and forth trying to figure out wtf is going on
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3.3 orbits untill i change my orbit i got there in 2 using <150m/s total
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⟨nazfib⟩ How would you see the closest approach many orbits in advance, with stock patched conics? And how would you see how much your relative distance changes per orbit?
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⟨test_account9540⟩ Less than 1 degree out is a lot 🤣
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⟨Joshua Wood⟩ blocking test account, last time i have a conversation with them
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⟨Joshua Wood⟩ +50m/s is not a lot
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⟨test_account9540⟩ The problem with blocking is that empty messages appear and the rest of the conversation makes no sense(
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⟨test_account9540⟩ because of that i don't block anymore, even those who just spam threads
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⟨nazfib⟩ Yes, 50 m/s is a lot; especially in a lunar orbit, where the orbital velocity is quite small. You can see that in the target-relative frame because the trajectory varies north/south a lot.
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⟨test_account9540⟩ * channels
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⟨Joshua Wood⟩ it simply is not a lot, out of 4km/s of dv 50m/s is basically nothing, a 2second difference in breaking burn is more than 50m/s of dv
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⟨nazfib⟩ That means that your engine is enormously overpowered for such a burn. When you're in-plane with the target, the rendez-vous should take less than 10 m/s of Δv, total.
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⟨Joshua Wood⟩ it's less dv than a dog leg would take to get to the same orbit, an inclination change is by far the cheapest way to achieve a co-planar orbit here
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⟨nazfib⟩ * this
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⟨nazfib⟩ Sure, this would be the best way to get co-planar. But compared to all the other burns that this rendez-vous will take, 50 m/s is by far the largest of them all.
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⟨Joshua Wood⟩ No it isn't. It's simply how suicide burns work. 2s puts me 500m further up than otherwise, in which time i gain 50m/s more vertical velocity
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if you burn too early you would need to pitch up
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⟨Joshua Wood⟩ it wasn't even the largest nevermind by far
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⟨Joshua Wood⟩ you just are making assumptions and stating them as fact?
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⟨Joshua Wood⟩ No it isn't. It's simply how suicide burns work. 2s puts me 500m further up than otherwise, in which time i gain 50m/s more vertical velocity
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if you burn too late* you would need to pitch up
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⟨Joshua Wood⟩ No it isn't. It's simply how suicide burns work. 2s puts me 500m further up than otherwise, in which time i gain 50m/s more vertical velocity
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if you burn too late* you would need to pitch up wasting dv
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⟨nazfib⟩ You're in a 120 km roughly circular orbit; I assume the target is in a 100 km roughly circular orbit. A hohmann transfer between those takes 8.8 m/s around the Moon.
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⟨drveyl⟩ I have very very few blocks, and that happens.
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I find that if the conversation will make no sense for that reason, I also don't need to participate in it.
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⟨nazfib⟩ +The target-relative frame gives you the information to perform that transfer, 2.5 to 3 orbits from now.
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⟨Joshua Wood⟩ I didn't do a homan transfer
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the target relative frame only gives you that information because it isn't anywhere else for some reason
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you could put closest approach in every reference frame (like stock does) and now the target relative frame gives 0 new information and i would literally never open it?
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⟨nazfib⟩ Do the stock patched conics give you relative distance, approach direction and speed many orbits in advance?
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⟨Joshua Wood⟩ yes?
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⟨Joshua Wood⟩ wdym? 🤣
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⟨nazfib⟩ How would you know, with patched conics, that you need to start your Hohmann transfer 2.5 orbits from now?
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⟨Joshua Wood⟩ it gives you a time? there is literally a time on it? compare that to orbital period and viola 2.5orbits from now?
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(personally i would just use mechjeb which also gives you that)
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⟨nazfib⟩ IIRC, it only gives you the closest approach on the next orbit; not any further orbits after that.
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⟨Joshua Wood⟩ well you don't remember correctly ¯\_(ツ)_/¯
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⟨Joshua Wood⟩ there is some settings you need to enable which aren't enabled by default, but a setting is still "stock"
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⟨nazfib⟩ 🤷 Maybe you can do it with stock patched conics. I find the relative motion plot a lot more intuitive; the only thing missing IMO is to be able to create manoeuvres in the target-relative frame.
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⟨Joshua Wood⟩ also, none of this matters because if you had the closest approach available in other reference frames you could have several or many manies with principia, nothing is stopping you
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it would give you ALL the information of the target reference frame but i don't need to go back and forth constantly
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not to mention "predicted apo + peri" aren't named differently between the target craft and current craft, you just have to guess or work out which is which
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and they move around constantly on the moon so it's an absolute pain to figure out which is which
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⟨nazfib⟩ No, it gives you a lot _less_ information; but you may be able to perform a rendez-vous with only the information the closest approach markers give you, anyway.
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⟨nazfib⟩ * you.
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⟨Joshua Wood⟩ target relative reference frame gives you closest approach and angle, that is it
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the shape of the orbit is just pretty it doesn't actually tell you anything
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⟨nazfib⟩ It does if you know what you're looking at.
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⟨Joshua Wood⟩ only if you can't figure that out from the other reference frame, which anyone with 1/2 a brain can
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⟨nazfib⟩ Why should you need to carefully figure out some information about the relative trajectory, when Principia can give you the whole trajectory and you can see everything about it at a glance?
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⟨nazfib⟩ I _really_ think that the difference is just that you're not used to seeing such a relative trajectory plot. There's a reason that IRL rendez-vous profiles are _always_ shown in this way.
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⟨Joshua Wood⟩ when i say "figure out" i mean "look at it and understand"
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⟨Joshua Wood⟩ i have literally not once ever seen rendez-vous profiles shown this way
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⟨Joshua Wood⟩ and if you google it, none of them are there either
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Here's a PDF with lots of these plots. There are also a few inertial plots, but most of them show the relative trajectory; because that is _much more useful_.
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⟨Joshua Wood⟩ +(1 out of 30)
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⟨Joshua Wood⟩ None of those plots are what is shown with the principia window
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⟨nazfib⟩ Yes, they are: all of the relative trajectory plots are exactly what Principia shows you.
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⟨Joshua Wood⟩ literally not once in the first 20 are the same
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they are all from ground up, front/back etc.
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⟨nazfib⟩ They are usually a side-view (not a top-down view as you had in your screenshot) because the rendez-vous is performed in-plane. Principia shows you the 3D version that those 2D plots are a projection of.
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⟨Joshua Wood⟩ except not one of my orbits from any view ever have a point
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⟨Joshua Wood⟩ and every single one of these do
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⟨nazfib⟩ Yep, you're in a different trajectory than those plots. Doesn't make it a different plot, though.
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⟨GoForPDI (less drag=more faster)⟩ you are also almost certainly not doing what real spacecraft are doing during rendezvous, which is _not_ a Hohmann transfer
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⟨GoForPDI (less drag=more faster)⟩ the transfer angle is closer to 130 degrees than 180
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⟨GoForPDI (less drag=more faster)⟩ this means you approach from the underside and have a decent amount of relative velocity, but can also tune that relative velocity easily and naturally brake a bit due to orbital mechanics
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⟨GoForPDI (less drag=more faster)⟩ Gemini and Apollo spacecraft, at least, also started from a slightly non-circular orbit (constant altitude difference from the target). Shuttle did something very different and more complicated
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⟨nazfib⟩ Yep. It also means that you don't have to burn your engines directly at the target.
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⟨Joshua Wood⟩ it's a lunar surface reference frame
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⟨GoForPDI (less drag=more faster)⟩ it's a target LVLH frame
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⟨nazfib⟩ No, the lunar surface is just shown for reference (since the target is in a circular orbit, the lunar surface is at constant distance below it)
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⟨GoForPDI (less drag=more faster)⟩ the target is always in the upper left corner
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⟨Joshua Wood⟩ i don't think you understand the irony so i'm screenshotting it
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⟨nazfib⟩ The lunar surface moves at roughly 1600 m/s rightwards in that plot; this is not shown, because it is irrelevant; the trajectory is plotted relative to the target, not to the fixed lunar surface.
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⟨nazfib⟩ * Anything on the
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⟨nazfib⟩ +The surface is just shown to give a sense of scale to the plot.
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⟨Joshua Wood⟩ the part you hightlight is curved in game, its only not curved because they've made it relative to the surface
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which isn't done in game
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⟨Joshua Wood⟩ it's not the same kind of plot
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⟨GoForPDI (less drag=more faster)⟩ no, it's curved in game because you don't have a constant delta height
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⟨nazfib⟩ All right, Principia curves the plot around the body. I don't believe that qualifies as a significant enough difference to call it completely different.
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⟨nazfib⟩ * "completely different".
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⟨GoForPDI (less drag=more faster)⟩ the chaser is always a certain distance below the target's orbit
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⟨nazfib⟩ +It's like plotting on a cylinder instead of a flat piece of paper.
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⟨Joshua Wood⟩ it doesn't give the same information in the same way and doesn't use the same reference points/axis
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these are representations of data, not a visual plot of what an object sees
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i don't know which other point principia choses to reference the axis to for target reference frame, if it's your own craft that is absolutely nuts but it certainly isn't the surface either
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⟨Joshua Wood⟩ * frame (i assume "the universe" / distant stars),
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⟨nazfib⟩ It _does_ use the same reference point and axes; except that with Principia those axes are curved, where for the IRL plots those axes are straightened out.
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⟨Joshua Wood⟩ my target reference frame orbit goes THROUGH the surface at points
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it cannot use the same reference point and axes as these because that's impossible, you would hit the surface (which i did not)
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⟨nazfib⟩ The reference axes (in Principia, and IRL) are the local vertical of the target, and the projection of the velocity vector onto the local horizon.
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⟨nazfib⟩ * its
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⟨nazfib⟩ Maybe this is because the target is not exactly in a circular orbit, so the position of the Lunar surface changes over time.
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⟨nazfib⟩ +That even more clearly indicates that it is not a surface-relative frame.
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⟨Joshua Wood⟩ in the plots you mention if the line was to go through the surface the object would be impacting the surface, it isn't so in game
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the distances are altitudes vs the surface, which they aren't in game
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part of their reference is in reference to the surface
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⟨nazfib⟩ That is only because, in _that special case_, the target is (assumed to be) in a circular orbit (and therefore, the surface is at a fixed distance). The distances are measured from the target.
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⟨nazfib⟩ * distance, and it is shown to give a sense of scale to the plot).
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⟨nazfib⟩ +No measurement in those plots is relative to the surface.
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⟨Joshua Wood⟩ the axis are locked to horizonal or perpandicular to the surface, they don't make sense if you don't do that
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which is why the in-game ones don't make sense
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⟨GoForPDI (less drag=more faster)⟩ The target in these Apollo plots is in a 60 nautical mile circular orbit
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⟨Joshua Wood⟩ in ALL the cases i can see that is the case
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⟨nazfib⟩ The in-game ones are _also_ fixed perpendicular to the surface; except in the IRL ones, the plot is flattened out, while Principia shows you the full 3D view.
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⟨Joshua Wood⟩ then they are bugged because mine are not
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⟨Joshua Wood⟩ like i said, it shows me traveling through the surface which should not be possible
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⟨nazfib⟩ No, it does not show you travelling through the surface. The surface is not at a fixed place in your case; it is only fixed in surface-relative plotting frames.
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⟨Joshua Wood⟩ I was literally below the surface on the map mode at one point
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⟨Joshua Wood⟩ i don't know what definition of "show you travelling through the surface" you have but being literally below the surface and traveling and i can see it is mine
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⟨egg⟩ What on Earth is going on in here.
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⟨egg⟩ Joshua Wood, screenshotting the conversation and posting it into the conversation does not, to quote the wording used by the rules, « contribute to something meaningful », and clutters the backlog. Don’t do that again.
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⟨egg⟩ Also, Nazfib et al. actually understand what they are on about, and you don’t. Try to listen to them, and to ask questions when you don’t understand, instead of insisting that they are wrong, because, well, you are, and this is getting noisy.
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⟨sichelgaita⟩ Also, test_account was giving relevant advice and they suddenly got blocked. What is this, Twitter?
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⟨nazfib⟩ Anyway, in conclusion:
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- The target-relative frame is very useful for rendez-vous, because it shows you your trajectory relative to the target.
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- IRL they use very similar plots, except that they use a 2D projection into the orbital plane of the target, and they straighten out the V-bar axis.
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- While stock patched conics' distance markers can show you some of the information the target-relative trajectory gives you, if you know how to read the plot you can glance a lot more from it than just the closest approach information.
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That ends my involvement in this discussion.
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⟨Joshua Wood⟩ By no one’s definition is “less than one degree” a lot
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He is constantly joining conversations with snarky ill thought out comments and I’m sick of it
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⟨nazfib⟩ +Have a nice day.
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⟨Joshua Wood⟩ It shows distance to the target with angle relative to some unknown quantity
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They do not use even close to the same plots irl mostly because they are missing an entire dimension and their angles are sensibly routed to a known body
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The stock patches conics system gives more information “at a glance” and requires less menus to get such information
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This could be implemented visually into principia very easily and provide the best of both
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No idea if the code works out that way but it would surprise me if it was as computationally taxing as the current target relative frame
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⟨Joshua Wood⟩ In conclusion
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It shows distance to the target with angle relative to some unknown quantity providing no actual useful information that isn’t instantly gleamed from normal reference frame
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They do not use even close to the same plots irl mostly because they are missing an entire dimension and their angles are sensibly routed to a known body
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The stock patches conics system gives more information “at a glance” and requires less menus to get such information
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⟨egg⟩ You, again, have not the faintest idea what you are on about. This conversation can serve no further purpose and shall be dropped.
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⟨Joshua Wood⟩ * frame. “It’s not on any priority list” would be a fine response
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⟨Joshua Wood⟩ That Is just exceptionally rude and I can only assume you haven’t read what I have said
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⟨Joshua Wood⟩ My ship was occluded by the surface of the planet, it can’t possibly show accurate information if it is showing me below the surface travelling at 1.6km/s
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⟨Joshua Wood⟩ In conclusion
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It shows distance to the target with angle relative to some unknown quantity providing no actual useful information that isn’t instantly gleamed from normal reference frame
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They do not use even close to the same plots irl mostly because they are missing 2 entire dimensions and their angles are sensibly routed to a known body
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The stock patches conics system gives more information “at a glance” and requires less menus to get such information
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> The stock patches conics system gives more information “at a glance” and requires less menus to get such informationis kinda fair, a lot of the info in principia is within menus instead of just being readily available, which is kinda annoying as you need to have the massive principia window open
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⟨clayel⟩ * available on the screen,
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⟨clayel⟩ related to having the massive principia window open, it would be nice if maneuvers could be planned without having that thing open, as closing it also closes the maneuver window
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⟨clayel⟩ +principia
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⟨egg⟩ The information relevant to rendez-vous is on the map view markers in various reference frames as in stock, not in the analyser or other menus.
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⟨clayel⟩ o i shouldve specified stuff like the an/dn info, i havent actually used the rendezvous frame myself
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⟨egg⟩ (And the rendez-vous has consistently been the thing that Principia users find easier to do with Principia than in stock, so it seems to be working fine.)
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⟨egg⟩ -the
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⟨egg⟩ That is an interesting point; there are times when one could do with just the child windows for a while (plotting frame selector, a flight plan, maybe the analyser).
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⟨egg⟩ There is a strong hierarchy between those windows though, so this might be a bit tricky.
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⟨butcher6994⟩ Rendezvous is much easier in Principia than patched conics if you read the trajectory correctly
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⟨butcher6994⟩ I say this as someone who built a moon base in polar orbit.
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⟨clayel⟩ maybe a "minimize" button would be helpful? could be applied to all of the windows as well