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…
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<queqiao->
<Kerbinator(no guarantee suggest)> pEdro: not really
<queqiao->
<Kerbinator(no guarantee suggest)> the worst stuff is short, hyperaccurate manoeurves
<queqiao->
<Kerbinator(no guarantee suggest)> For long manoeurves engine spool-up time is averaged out, however in shorter ones it goes problematic
<queqiao->
<egg> Yes, that is what pEdro is saying.
<queqiao->
<egg> What pEdro says is that the accuracy of the computation done by Principia with respect to what it models is not a problem.
<queqiao->
<egg> The problem is deviations from that model, such as spool-up, or reaction time.
<queqiao->
<Kerbinator(no guarantee suggest)> And accuracy depends on what you are doing, for example, trying to do a L2 keeping burn which can last 3 orbits, you need 1E-8 precision
<queqiao->
<Kerbinator(no guarantee suggest)> on my test save (don't have RO, recently I just switched back to stock RSS), by limiting RCS to 0.5% and use heavy craft(4xS3-14400), I get a maximum precision about 1E-5 m/s.
<queqiao->
<Kerbinator(no guarantee suggest)> However 1E-6 is easily achieveable with MJ for stock nodes, though.
<queqiao->
<Kerbinator(no guarantee suggest)> And accuracy requirement depends on what you are doing, for example, trying to do a L2 keeping burn which can last 3 orbits without further correction, you need 1E-8 precision
<queqiao->
<egg> Kerbinator(no guarantee suggest): If you need to be accurate in the tens of nanometres per second to do Lagrange point stationkeeping, you are doing something very very wrong. Real life engines are nowhere near that accurate, and stationkeeping burns are few and far between (see for instance https://discord.com/channels/319857228905447436/480397772248580098/901098937132404766 re. DSCOVR stationkeeping).
<queqiao->
<Kerbinator(no guarantee suggest)> That's only because I wanted to see the shape of completely inertial orbit in several laps
<queqiao->
<egg> Nevertheless, you shouldn’t need that precision unless your orbit is very poor to start with.
<queqiao->
<Kerbinator(no guarantee suggest)> In practice, correcting every 1 lap won't require that much accuracy at all (for Sun-Earth L2 as example, accuracy requirement increase about 100 times per lap
<queqiao->
log 100 ≈ 4.6, 4.6 * 23 days = 105.8 days, so it sounds like you are in an orbit on an orbit slightly tighter than SOHO’s (178 days, see https://www.esa.int/esapub/bulletin/bullet88/vande88.htm; that’s 𝐿₁, but they behave similarly as far as timescales are concerned).
<queqiao->
An even tighter orbit would have a shorter period, so it would have gone through more revolutions in those few months (with about the same drift); if you want to see lots of revolutions before things completely break down, you can probably try moving closer to the Lagrange point.
<queqiao->
<egg> (note, importantly, that the drift is time-dependent, but should be mostly unrelated to the specific orbit chosen; thus how much things drift per revolution will depend on that orbit.)
<queqiao->
<Kerbinator(no guarantee suggest)> ?
<queqiao->
<Kerbinator(no guarantee suggest)> isn't orbit around L1/L2 have a period of 1/2 year
<queqiao->
<Kerbinator(no guarantee suggest)> test has been made for large-size and small-size lyapunov orbit. Seems to have similar precision requirement in station keeping manoeurves measured in laps (100 times per lap)
<queqiao->
<Kerbinator(no guarantee suggest)> I didn't noticed problem of period actually, may go into it later this day
<queqiao->
<Kerbinator(no guarantee suggest)> right, it was this
<queqiao->
<egg> I really wouldn’t expect the that kind of drift to scale with the duration of those revolutions about the point; everything I saw quoted the Ляпунов time (aka e-folding time) of the Lagrange point (or the corresponding doubling time) as the relevant timescale—and that time is obviously not associated with a specific orbit.
<queqiao->
<egg> Al2Me6 by the way, sichelgaita looked at your save, it appears to be compressed with gipfeli as expected, and evidently it loads fine otherwise you would have complained, so the weird patterns must be gipfeli getting a bit confused somehow and not doing a great job; we’re probably going to merrily ignore this, the study of compression algorithms isn’t really our thing.
<queqiao->
<egg> Al2Me6 any news re. save growth etc. in your save?
<queqiao->
<Al2Me6> Sorry, haven't played any more. Will report back in ~a few days.
<queqiao->
<Stocky> Does anyone use the station keeping mod with principia?
<queqiao->
<Al2Me6> No, because they're incompatible.
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<egg|laptop|egg>
but on this side the bridge is sad
<raptop>
rename the bot TacomaNarrows?
<raptop>
(FIU-Sweetwater UniversityCity Pedestrian Bridge would be a bit too long)
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<queqiao->
⟨egg⟩ test
<queqiao->
⟨Stocky⟩ Does launching to the LAN of the moon work with principia? Im finding it difficult to get an encounter without being on a wacky angle
<queqiao->
⟨egg⟩ so, to clarify, by _launching to the LAN of the moon_, you mean launching into the orbital plane of the Moon?
<queqiao->
⟨egg⟩ if that is the case, you can only do that from Cape Canaveral for a short while every eighteen years or so.
<queqiao->
⟨Stocky⟩ well normally all i would do before using principia is target the moon and launch to LAN of the moon then my inclination around earth would match the inclination of the moon aroun earth so it was just the matter of using a prograde manuever to get there
<queqiao->
⟨egg⟩ right, launching into the orbital plane of the moon.
<queqiao->
⟨Stocky⟩ How do you change launch site in RP?
<queqiao->
⟨egg⟩ You cannot do that from the Cape, it is too far North.
<queqiao->
⟨egg⟩ Unsure about the RP-1 aspects, perhaps someone in #rp1-general may have an answer
<queqiao->
⟨Al2Me6⟩ You'll want KSCSwitcher
<queqiao->
⟨egg⟩ yeah that applies more generally to RSS launch site switching, but then my understanding is that RP-1 has progress tied to launch sites, which you’d want to migrate
<queqiao->
⟨DRVeyl⟩ Presumably you can cheat yourself funds and buy the pad and facility upgrades. Unlikely you are too far if you're only starting to throw things at the moon, so mostly just VAB points
<queqiao->
⟨Stocky⟩ Okay so in RP1 basically the closest ill get is just launching into LAN?
<queqiao->
⟨Al2Me6⟩ No, not _in RP1_, but _at Cape Canaveral, with Principia_ (because that's how it is IRL)
<queqiao->
⟨Al2Me6⟩ If your launch site is above the inclination of the target, then you can't launch into the target's plane
<queqiao->
⟨Al2Me6⟩ Stock RSS artificially pins the Moon to its highest inclination to make things less complicated
<queqiao->
⟨Stocky⟩ So with mechjeb you have launch into orbital plane and then you have launch into target LAN
<queqiao->
The orbital plane one doesnt usually work so i use LAN
<queqiao->
What is the difference?
<queqiao->
⟨egg⟩ the question we are answering here isn’t which buttons to press in MechJeb, but what is physically possible. You are going to have to speak in terms of what you want from your orbit in relation to that of the Moon if that conversation is to make sense.
<queqiao->
⟨egg⟩ You (most of the time) cannot, when launching from Cape Canaveral, launch into an orbit coplanar with that of the Moon.
<queqiao->
⟨Stocky⟩ Basically i just want to impact the moon from earth
<queqiao->
I dont really have any specifics other than that
<queqiao->
So besides building launchpads at other sites what options do i have to get to the moon?
<raptop>
off-plane intercepts
<queqiao->
⟨egg⟩ launch at the right time of the month, and do an off-plane intercept. There is a pinned message with a fancy drawing by Al2Me6 illustrating that.
<queqiao->
⟨Al2Me6⟩ (Note that 'the right time' is best determined via a kOS script...)
<queqiao->
⟨egg⟩ but for a Principia beginner, I would highly recommend relocating to Kourou, to not stack the difficulty.
<queqiao->
⟨egg⟩ (indeed when starting with Principia, I would recommend sandbox first to get used to everything being different…)
<queqiao->
⟨Stocky⟩ i somehow bluffed my way to the moon on my previous launch but yeh i cant pull it off this time obviously being a different time of the year etc
<queqiao->
⟨Stocky⟩ RP1 doesnt show what Kourous is
<queqiao->
⟨egg⟩ it’s really about the time of the month, not the time of the year; but yes, you can’t be lucky every time
<queqiao->
⟨egg⟩ Stocky: as Al₂Me₆ said, you need KSCSwitcher; that will cover the tracking station map with icons showing available launch sites.
<queqiao->
⟨Stocky⟩ Cool and that will negate anything else RP1 is trying to do with the launchpad progression etc
<queqiao->
⟨egg⟩ Stocky: What do you mean? it is part of the RSS/RO mod suite; RP-1 understands KSCSwitcher. As DrVeyl said, if you want to replicate your Floridian progression in French Guyana, you will have to cheat it there somehow.
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<queqiao->
⟨egg⟩ What do you mean? it is part of the […] ⮪ (reply testing intensifies)
<queqiao->
⟨egg|matrix|egg⟩ ⟪egg⟫ (reply testing intensifies) ⮪ the testing will continue until interoperability improves
<egg|laptop|egg>
raptop: OK hopefully this should make replies understandable
<raptop>
yay
<queqiao->
⟨egg⟩ (for those on platforms that support replies, those on IRC now see
<queqiao->
> ⟨ReplySender⟩ ⟪OriginalSender⟫ Original message snippet […] ⮪ Text of the replyfor replies, which should help alleviate the confusion that arose from replies to old messages showing up as plain messages in another discussion.
<queqiao->
⟨egg⟩ * discussion.)
<queqiao->
⟨egg⟩ * (For
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<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ Hmm I though of a thing
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ * thought
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ for Moon launch at almost any time in Principia, seems that WenChang is a good choice
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ it's close to the minimum inclination of the Moon relative to equator
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ Kourou launch into plane of Moon, because of very low latitude, may require tilting the launch itself (toggling your HDG off 90°)
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ * latitude much lower than 18.6°,
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ for Moon max inclination or 2body case, Xichang is a good choice (it has higher altitude which increase efficiency a bit)
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ * bit, and usage of semi-vacuum engines for stage 1)
<queqiao->
⟨egg⟩ ⟪Kerbinator(no guarantee suggest)⟫ for Moon launch at almost any time in […] ⮪ Yeah; that won’t quite work all the time, but it’s close. Satish Dhawan also works (and that one works all the time).
<queqiao->
⟨egg⟩ ⟪Kerbinator(no guarantee suggest)⟫ Kourou launch into plane of Moon, […] ⮪ This is irrelevant unless you are piloting by hand and are not very good at it.
<queqiao->
⟨egg⟩ Yeah, good point; that won’t quite work all the time, but it’s close. Satish Dhawan also works (and that one works all the time).
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ and the orbit is split into two ellipses because of the eccentricity of Venus orbit (0.00676)
<queqiao->
This can also be explained by 2 revolution per Venus year
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ If you are saying « Venus year is shorter than Earth year » then it sounds reliable
<queqiao->
I'm talking about stability issues relative to number of revolutions in xyO(/xCyA) frame
<queqiao->
⟨Butcher⟩ ⟪egg⟫ it’s really about the time of the […] ⮪ I would say time of day, you get two easterly launched off plane intercepts per day.
<queqiao->
⟨Quadrupole⟩ But at the wrong time of the month, easterly launches can give you bad transfer time (1 days or 6 days) and thus greater Δv requirements.
<queqiao->
⟨egg⟩ On the other hand I probably got it backward: the period gets shorter as 𝑟ₚ decreases, but 𝑟ₚ is the perilune radius, so a smaller 𝑟ₚ means a more out-of-plane orbit, rather than one that is tighter around the Lagrange point.
<queqiao->
⟨egg⟩ (found that paper via this stackexchange reply by the first author, which summarizes the relevant behaviour well: https://space.stackexchange.com/a/24026)
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<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ * maybe, for my way to enter lyapunov it seems to be half period
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ idk whether it's related to methods and orbit splitting, but just for a single-circle (circular) or double-circle (like the Venusian one)
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ maybe, for my way to enter lyapunov it seems to be half period
<queqiao->
In this GMT+8 morning I'm saying only about my orbits' stationkeeping manoeurves, not anything else in the class of orbits)
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ maybe, for my way to enter lyapunov it seems to be half period of 2nd object in CRTBP)
<queqiao->
In this GMT+8 morning I'm saying only about my orbits' stationkeeping manoeurves, not anything else in the class of orbits)
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ Example of small-size Halo orbit of S-V L2, whose period is 108 days (still only a bit less than half a Venusian year)
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ Another thing is that I never get really injected into a orbit perpendicular to S-V orbital plane, it just tilts (patched conics display only serves as reference of orbit plane, here)
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ * into a orbit exactly
<queqiao->
⟨Butcher⟩ ⟪Quadrupole⟫ But at the wrong time of the month, […] ⮪ You get two 4 day transfers per day with easterly launches. Relative inc doesn't make much difference to dv requirements ime.
<_whitenotifier>
[Principia] eggrobin edited pull request #3266: Fix some linguistic issues in the Russian translation - https://git.io/JyD2G
<queqiao->
⟨egg⟩ oh, the bridge forwards those notices, that might get a bit obnoxious
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ ⟪egg⟫ I am going to guess that *you* are the […] ⮪ by the way, what is the in-page linked paper's reference frame
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ not quite looks like in the commomly used (by me) xyO frame for plotting
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ (looks like MCI?)
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ not quite looks like in the commomly used (by me) xyO frame for plotting (looks like MCI?)
<queqiao->
⟨egg⟩ I think they work in the rotating frame of the CR3BP throughout, so it would correspond to XYO (otherwise it makes no sense to show Lagrange points or to show both bodies, those things are immobile only in the rotating frame).
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ however for xyO frame, the halo should be _outside_ instead of _around_ the moon
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ And they determine the orbit by periLune, not closest distance to L2 point (the orbit is also not bean or ellipse-shaped)
<queqiao->
⟨Quadrupole⟩ ⟪Butcher⟫ You get two 4 day transfers per day […] ⮪ Okay, I see there are two windows each day for all transfer times for easterly launches, though they often coalesce.
<queqiao->
As for relative inclination, I found that to be more of an issue for high latitude sites. For cape, it is ~25 m/s max, but for Plesetsk, it is ~50 m/s max. I would agree it is relatively small though. Not small if you are though.
<queqiao->
⟨Quadrupole⟩ * At a lunar inclination of 23 degree, it is ~25 m/s max for cape, but it is ~50 m/s max for Plesetsk.
<queqiao->
⟨egg⟩ ⟪Kerbinator(no guarantee suggest)⟫ however for xyO frame, the halo should […] ⮪ See figure 1; they are dealing with a family of orbits which starts from what you expect (red: small beans around the Lagrange point) but goes all the way to things that look very different and swing far off-plane with a very low perilune (purple). The figure is admittedly a bit hard to read: the ecliptic is horizontal throughout figure 1, and both the...
<queqiao->
... Earth and the Moon are shown, as well as L₁ and L₂; each colour is a single orbit in the family.
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ Yes; but I'm not talking about extreme conditions; as the orbit you said having small period have very bad stability index
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ +Stabler orbits have higher periLune (50000km PeriLune meaning it is close to a dot arount L2)
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ * L2), thus smaller circle in xyO frame
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ * in MEO
<queqiao->
⟨egg⟩ I think you are reading the stability index backward:
<queqiao->
> t; the higher the value of ν, the faster a perturbed halo orbit will tend to depart its nominal pathso lower stability index means more stable: those super-low perilune/highly off-plane orbits are the most stable (which is what the first author says in https://space.stackexchange.com/a/24026):
<queqiao->
> The orbits actually get more stable as the families grow out of plane. The flatter halos are unstable.
<queqiao->
⟨egg⟩ I think you are reading the stability index backward:
<queqiao->
> A stability index greater than one corresponds to an unstable halo orbit; the higher the value
<queqiao->
> of ν, the faster a perturbed halo orbit will tend to depart its nominal path.so lower stability index means more stable: those super-low perilune/highly off-plane orbits are the most stable (which is what the first author says in https://space.stackexchange.com/a/24026):
<queqiao->
> The orbits actually get more stable as the families grow out of plane. The flatter halos are unstable.
<queqiao->
⟨egg⟩ I think you are reading the stability index backward:
<queqiao->
> A stability index greater than one corresponds to an unstable halo orbit; the higher the value of ν, the faster a perturbed halo orbit will tend to depart its nominal path.so lower stability index means more stable: those super-low perilune/highly off-plane orbits are the most stable (which is what the first author says in https://space.stackexchange.com/a/24026):
<queqiao->
> The orbits actually get more stable as the families grow out of plane. The flatter halos are unstable.
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ Halos flatten to inclination=0 means Lyapunov?
<queqiao->
⟨egg⟩ I think this is what they say on page 2, yes.
<queqiao->
⟨egg⟩ > The halo orbits are well-known families near the collinear libration points L₁, L₂, and L₃. In the Earth-Moon system, the L₁ and L₂ families bifurcate from planar Lyapunov orbits around the libration points and evolve out of plane until they approach the Moon.
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ Well, usually 0 insertion results in a 1/3 sized L orbit (bean-shaped)
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ for me sizing index is (orbit diameter)/(2*distance of L2 and secondary object)
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<queqiao->
⟨lancis man⟩ how do I use the manevuer system in principia? I am trying to go to the moon
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ ⟪lancis man⟫ how do I use the manevuer system in […] ⮪ switch to ECI, flight plan, create, add manoeurve, type in 3000m/s at prograde
<queqiao->
switch to MEO(formerly MCEA), tune your time of manoeurve (from 1min later to 1h40min later) until you have a Moon impact
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ Then, to execute, firstly use "show on navball" and use stock SAS to point to there
<queqiao->
(MJ is useless and will wobbling when pointing Principia's fake stock nodes)
<queqiao->
please wait until ignition T-0.0s and start your burn
<queqiao->
(only for stock; in RO the engine spool-up time doesn't count so you need to start *before* 0.0s depending on your engine)
<queqiao->
⟨Kerbinator(no guarantee suggest)⟩ switch to ECI, flight plan, create, add manoeurve, type in 3100m/s at prograde, then raise it a bit so that your orbit get to same height as moon
<queqiao->
switch to MEO(formerly MCEA), tune your dv and time of manoeurve (from 1min later to 1h40min later) until you have a Moon impact
<queqiao->
Then fine-tune your manoeurve dv so it get to a close Moon periapsis
<_whitenotifier>
[Principia] eggrobin commented on issue #3235: The camera rotates in the plotting frame when KSP uses a rotating reference frame - https://git.io/Jyde4
<_whitenotifier>
[Principia] eggrobin reopened issue #3235: The camera rotates in the plotting frame when KSP uses a rotating reference frame - https://git.io/JDS3H
<_whitenotifier>
[Principia] eggrobin commented on issue #3235: The camera rotates in the plotting frame when KSP uses a rotating reference frame - https://git.io/Jydfs
<_whitenotifier>
[Principia] eggrobin commented on issue #3235: The camera rotates in the plotting frame when KSP uses a rotating reference frame - https://git.io/JydZw
<queqiao->
⟨egg⟩ Moon-Earth-Orbit.
<queqiao->
⟨Tak⟩ ok, so then I basically just use the "plan length" to get the ends of my maneuver and the moon's orbit line to meet?
<queqiao->
⟨egg⟩ ⟪Tak⟫ ok, so then I basically just use the […] ⮪ No.
<queqiao->
1. There is no moon’s orbit line in MEO.
<queqiao->
2. _plan length_ just says how much you want us to draw, it doesn’t change what the planned trajectory is ; to tune where you are going, you need to change the parameters of the actual manœuvre.
<queqiao->
⟨egg⟩ Don’t use patched conics !
<queqiao->
⟨egg⟩ what part of « do not use for flight planning » is unclear
<queqiao->
⟨egg⟩ this is going to completely mislead you. The moon does not move in MEO.
<queqiao->
⟨Tak⟩ That’s not pat he’s conics…
<queqiao->
⟨Tak⟩ Not patched conics*
<queqiao->
⟨Tak⟩ That’s the end of the moons trajectory
<queqiao->
⟨egg⟩ ⟪Tak⟫ That’s not pat he’s conics… ⮪ The Display patched conics check box is ticked.
<queqiao->
⟨Tak⟩ In the first one yeah, I was using it to get close to the right plane
<queqiao->
⟨egg⟩ And here, you are not in MEO, you are in ECI.
<queqiao->
⟨egg⟩ you are completely misusing the tools put at your disposal by Principia
<queqiao->
⟨egg⟩ the _Display patched conics_ option exists mostly as a way to make fun of stock by comparing your actual trajectory with the unperturbed one. You should never use it in practice.
<queqiao->
⟨egg⟩ if you want to approach the moon, you must use a reference frame where the moon doesn’t move.
<queqiao->
⟨Tak⟩ oh, both the plotting and maneuver need to be in MEO. I had plotting in ECI and maneuver in MEO
<queqiao->
⟨egg⟩ those reference frames are MCI, MCMF, and MEO. Hovertexts on the buttons explain to you which one to use for what part of the mission.
<queqiao->
⟨egg⟩ ⟪Tak⟫ oh, both the plotting and maneuver need […] ⮪ To be honest, the manœuvre could reasonably be in ECI just as well. But understanding the various plotting frames, and constantly switching between them depending on what you care about, is a critical skill when using Principia.
<queqiao->
⟨egg⟩ If you want to look at your overall transfer to the Moon, MEO is appropriate, because the Moon is fixed (so you are not trying to hit a moving target), and the direction of the Earth is fixed (indeed the Earth is almost fixed), so that you know where you are coming from. This is the reference frame where a free return looks like a figure eight.
<queqiao->
⟨egg⟩ If you want to look at your orbit about the Moon, you want MCI. If you want to hit or land on the Moon in a specific spot, you want MCMF, so that the surface doesn’t move (again, don’t try to hit moving targets).
<queqiao->
⟨Tak⟩ so what's the proper way to get close to the moons plane? I was looking at patched conics to try and figure out what time of day I needed to launch. Also is there a tool to help you figure out when in the moons orbit you should launch?
<queqiao->
⟨egg⟩ Where are you launching from?
<queqiao->
⟨egg⟩ Since you are new to this, I highly recommend launching from Kourou, not from the Cape.
<queqiao->
⟨Tak⟩ yeah im at cape haha
<raptop>
KSC has extremely limited windows where the Moon is at high enough inclination to launch into its plane