[WIP][1.8.1, 1.9.1, 1.10.1, 1.11.0–2, 1.12.2–5] Principia—releases every new moon—n-Body and Extended Body Gravitation

[MAFman]

I'm still very confused about the different frames of reference. In which frame of reference would a Sun-Kerbin L2 halo orbit look like an ellipse around the Lagrange point that moves with Kerbin?

  On 7/23/2022 at 9:21 PM, MAFman said:

I'm still very confused about the different frames of reference. In which frame of reference would a Sun-Kerbin L2 halo orbit look like an ellipse around the Lagrange point that moves with Kerbin?

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Like this picture:

Edited July 23, 2022 by MAFman

[Delay]

  On 7/23/2022 at 9:21 PM, MAFman said:

I'm still very confused about the different frames of reference. In which frame of reference would a Sun-Kerbin L2 halo orbit look like an ellipse around the Lagrange point that moves with Kerbin?

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I haven't played KSP in a bit, and maybe some things have changed in the Principia UI that I don't know of yet.

But there are two reference frames that draw your orbit in relation to a line connecting the selected celestial and its parent. Whichever options remain after discarding the rotating and the inertial frames.

These are the frames of reference used in images like this. This reference frame is also really handy for planning things like trans-lunar injections because you know exactly where you will be relative to the Moon.

[MAFman]

Oh also, why do the celestials also have to be simulated to interact, instead of being on-rails?

[pleroy]

  On 7/23/2022 at 4:25 PM, MAFman said:

I'm really confused about the interface. I'm just trying to get something into the Kerbin-Sun L2 Lagrange point, and I have no clue what I'm doing.

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Have you read the concepts page and taken a look at @rsparkyc's tutorial?  I'd suggest doing so before randomly clicking buttons.

[justaRegular911]

Hello, is the latest version( "Hesse") not compatible with KSP 1.12.0? I tried to run it, and it gives error in KSP/glog. If so, what is the last version compatible wit 1.12.0

[pleroy]

  On 7/24/2022 at 8:29 PM, justaRegular911 said:

Hello, is the latest version( "Hesse") not compatible with KSP 1.12.0? I tried to run it, and it gives error in KSP/glog. If so, what is the last version compatible wit 1.12.0

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There was never a version that supported 1.12.0.  Any reason why you couldn't upgrade to 1.12.3?

[Krazy1]

I installed a planet pack that repatched the Jool system, then I removed that planet mod. Then I launched a ship and almost to orbit I switched to the map view and it gave me the "an apocalypse occurred" error due to Laythe trajectory not converging.  I can see all the Jool moons are going the same direction like stock. I'll reinstall Principia but is that savefile doomed now? I'm still on day 1.

 

[mateusviccari]

  On 7/25/2022 at 1:44 AM, Krazy1 said:

I installed a planet pack that repatched the Jool system, then I removed that planet mod. Then I launched a ship and almost to orbit I switched to the map view and it gave me the "an apocalypse occurred" error due to Laythe trajectory not converging.  I can see all the Jool moons are going the same direction like stock. I'll reinstall Principia but is that savefile doomed now? I'm still on day 1.

 

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Afaik changing the system midgame is asking for problems to happen, regardless of Principia being installed. If you're on day 1 why do you care anyway? Just start a new save. 

[Krazy1]

  On 7/25/2022 at 2:18 AM, mateusviccari said:

If you're on day 1 why do you care anyway? Just start a new save. 

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Well, I deleted and re-copied the Principia (Hesse) folder and started a new save and it did not fix the issue... Jool system looks like stock in the tracking station with patched conics on. I'm sure Bop was retrograde before. Apparently something changed outside of the Gamedata/Principia folder and the original savefile.  

UPDATE: I found this in a Google log "glog" warning file: 

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W0724 19:15:48.382647  1216 plugin.cpp:231] This is an unknown system, we don't know anything about its stability:

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But it's stock... it should recognize it and change Bop's orbit. 

INFO log

WARNING log

ERROR log

UPDATE2: I found this in the first glog files before installing the planet pack: 

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W0704 20:59:19.560848  9836 plugin.cpp:209] This appears to be the dreaded KSP stock system!

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Edited July 25, 2022 by Krazy1
update2

[justaRegular911]

  On 7/24/2022 at 10:42 PM, pleroy said:

There was never a version that supported 1.12.0.  Any reason why you couldn't upgrade to 1.12.3?

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Thanks, I somehow forgot my steam password. Any way to override the version checker in Principia.

[eggrobin]

  On 7/25/2022 at 1:44 AM, Krazy1 said:

I installed a planet pack that repatched the Jool system, then I removed that planet mod.

 

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  On 7/25/2022 at 2:36 AM, Krazy1 said:

Well, I deleted and re-copied the Principia (Hesse) folder and started a new save and it did not fix the issue... Jool system looks like stock in the tracking station with patched conics on. […]

But it's stock... it should recognize it and change Bop's orbit. […]

UPDATE2: I found this in the first glog files before installing the planet pack: [This appears to be the dreaded KSP stock system!]

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It looks like you did not correctly remove the planet pack.

[ZAJC3W]

  On 7/23/2022 at 8:50 PM, Kaduloso_007 said:

Hi!

 I'm really enjoying using this mod and it's one of my favorites, but I learned that another mod called Orbital Decay conflicts with this one. I would like to know if it is possible (in one of the future updates) for Principia to put the same idea of having an orbital decay in relation to atmospheric drag, radiation pressure and among other factors? I was missing having this in the Principia mod and I was in this doubt.

 Thanks in advance!

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Orbital decay was discussed/proposed before. Around 2016/2017 if my memory serves...

TBH I as much as I enjoyed it(orbital decay mod) in non principia games I don't miss it one bit with Principia.

Give it a go, when your comms network won't last a month due to orbit perturbation, only thing you'll miss will be your sanity
First post mentions orbital decay as a thing "relatively easy" to add once the mod is playable ;), but at this stage I don't thing there is anything easy about this(amazing) mod.
And there are always other things do improve, add or bugs to smash, so iguess it slipped to the bottom of the to-do list.

[eggrobin]

  On 7/25/2022 at 10:22 PM, ZAJC3W said:

First post mentions orbital decay as a thing "relatively easy" to add once the mod is playable

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I should rewrite the first post someday; that section aged poorly :-)

While atmospheric drag would likely take quite a bit of work in and of itself, the real difficulty would be that, as you point out, it would make things unplayable without stationkeeping to match. Stationkeeping is not happening in the foreseeable future; it would involve thrusting in timewarp (its own rabbit hole of messy interactions with KSP), optimization to figure out when to thrust (which is hard, though at least interesting), and figuring out how the player should specify what properties of the orbit are being kept (so something like the orbit analyser, but with input instead of being an already overwhelming read-only report).

Solar radiation pressure is similar.

[Krazy1]

  On 7/25/2022 at 9:28 AM, eggrobin said:

It looks like you did not correctly remove the planet pack.

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It's Corelian. I used KCAN to install/ remove. I just checked/ uncheck the box. 

I reinstalled Corelian and all the saves I played when it was removed now CTDT a few seconds after trying to load them at the main menu. I didn't lose anything significant. Starting a new save works fine again. 

It's great that it plots the actual path and dV during a burn. A 7 minute burn leaving LKO to Minmus actually takes ~1km/s, not 920 m/s for an impulse. And the xCxF mode shows what ground you'll pass over in multiple orbits. I used Trajectories for that before. 

[ZAJC3W]

  On 7/25/2022 at 11:12 PM, eggrobin said:

I should rewrite the first post someday; that section aged poorly :-)

While atmospheric drag would likely take quite a bit of work in and of itself, the real difficulty would be that, as you point out, it would make things unplayable without stationkeeping to match. Stationkeeping is not happening in the foreseeable future; it would involve thrusting in timewarp (its own rabbit hole of messy interactions with KSP), optimization to figure out when to thrust (which is hard, though at least interesting), and figuring out how the player should specify what properties of the orbit are being kept (so something like the orbit analyser, but with input instead of being an already overwhelming read-only report).

Solar radiation pressure is similar.

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I'm thinkig as i type so bear with me.

Or, you could simplify it all.

Calculate station keeping cost in dV/day.

Put vessel on rails and deduct propellant based on time spent on rails, that's roughly how station keeping in OrbitalDecay mod worked.

Sounds simple but putting vessel "on rails" would probably mean rewriting half of the integrator.(I know nothing about it)

On the other hand thrusting in timewap would potentialy work better with limited ignitions engines like in realism overhaul, that's assuming ignition counter would be affected.

I wish I had the skill to help more than just throw ideas around.

edit

Big prolem with atmospheric drag and solar pressure is that their influence strongly depends on vessel orientation, unless vessel is a sphere.
I think every principia player would appreciate station keeping that  "just" deals with orbital perturbations.

Maybe starting point would be adding flight  planner option to calculate burn to return to current orbit in user selectable number of days?

 

Edited July 26, 2022 by ZAJC3W

[eggrobin]

  On 7/26/2022 at 7:35 PM, ZAJC3W said:

Put vessel on rails and deduct propellant based on time spent on rails, that's roughly how station keeping in OrbitalDecay mod worked.

Sounds simple but putting vessel "on rails" would probably mean rewriting half of the integrator.(I know nothing about it)

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That would eliminate the optimization problem. The other difficulties would remain, and overall things would get much worse. First, « rails » means an analytic solution, so it would mean bypassing the integrator, which programmatically would be a mess. But let’s set aside software engineering concerns for a second, what those rails do is an even bigger nightmare; keeping the Keplerian orbit unchanging is neither what you do nor what you want.

For a perturbed Keplerian orbit around an extended body, you have various precessions; stationkeeping doesn’t cancel all of those, that would be completely impractical, ridiculously costly, and counterproductive for sun-synchronous orbits. Instead it preserves some properties of the orbit as it precesses (such as the alignment with respect to the ground, or sun-synchronicity, etc.).

And then you have orbits that don’t even look like Keplerian orbits, such as things hovering about Lagrange points etc.

And of course there are those software engineering concerns; mixing various types of propagation (analytic, likely with many kinds of analytic models, and numerical) would be a mess that we are not willing to contemplate.

 

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Maybe starting point would be adding flight  planner option to calculate burn to return to current orbit in user selectable number of days?

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That eliminates the interaction with KSP, which admittedly is the boring and tedious part in addition to being difficult. But that leaves you with:

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optimization to figure out when to thrust (which is hard, though at least interesting), and figuring out how the player should specify what properties of the orbit are being kept (so something like the orbit analyser, but with input instead of being an already overwhelming read-only report).

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which is probably the harder part (though the more interesting one).

 

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Big prolem with atmospheric drag and solar pressure is that their influence strongly depends on vessel orientation, unless vessel is a sphere.

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That aspect is actually not that bad, since we control orientation, including in timewarp.

Right now we assume that vessels tumble inertly in timewarp, but obviously attitude-keeping is a thing. Attitude-keeping is a much more bounded problem than stationkeeping; it requires defining a handful of attitude control laws, but it does not involve optimization, and there are only so many attitude control laws that are interesting (point at the sun, put the hinge of the antenna in the plane containing the Earth, like Молния; point at the Earth, put the hinge of the solar panel in the plane containing the Sun,  like satellites with hinged solar panels, etc.).

I could imagine adding attitude keeping (though in order for that to be really useful, other mods, such as RealAntennas, should take the attitude into account); there is an open issue (#2556) about that.

 

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I wish I had the skill to help more than just throw ideas around.

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As usual, there is an appropriate xkcd; telling the trivial from the intractable takes deep familiarity with the problem.

If you want to gain some familiarity with the subject, I strongly recommend this book if you want to learn more about orbits, how they are perturbed, how you either take advantage of that or avoid it, and more generally why you pick an orbit for a given mission (an English translation exists, titled Handbook of Satellite Orbits: From Kepler to GPS). The orbit analyser in Principia is inspired by that book; so is the career mode mod I’ve started working on, Σκοπός.

[ksmDD]

你好，麻烦上传到ckan上

 

[justaRegular911]

  On 7/25/2022 at 6:33 AM, justaRegular911 said:

Thanks, I somehow forgot my steam password. Any way to override the version checker in Principia.

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Anyone?

[pleroy]

  On 7/27/2022 at 4:18 AM, ksmDD said:

你好，麻烦上传到ckan上

 

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Please read this post and the posts it references.  TL;DR: it's not possible, it won't happen.

[eggrobin]

For the new moon (lunation number 279), the new release (Hilbert) is out.

• Improvements have been made to the flight planning tool:
  • It now supports multiple flight plans;
  • Buttons have been added to move an orbital manœuvre to the preceding or next revolution;
  • The digits may be individually adjusted by scrolling over them or using the arrow keys.
• A button has been added to declutter map view when it is overwhelmed by noodles or by apsis and node markers.
• A bug has been fixed whereby the camera spinning wildly when hovering over the UI of some mods.
• The issue of map view markers jumping around as the trajectory changes has been improved somewhat.

 See the change log for more details.

[scimas]

  On 7/28/2022 at 10:46 AM, justaRegular911 said:

Anyone?

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https://github.com/mockingbirdnest/Principia/wiki/Principia-configuration-files#the-principia_override_version_check-configuration

But pay attention where it says you will not get any support. And since KPS 1.12.3 is the final bug fixed version anyway, I would suggest recovering your steam password instead. I'm sure there are alternative ways of obtaining the game anyway, after all it seems you have bought it.

[Krazy1]

On Hesse, I found double-clicking in the Map view resets the target selection. This usually happens when quickly clicking the flight plan controls. Double-clicking the background outside the mod windows always resets the target. Double-click within mod windows sometimes resets it but it's not consistent. It would be nice to fix this so only the Clear button resets the target.

[MAFman]

Is Principia compatible with the kOS mod?

[scimas]

  On 8/1/2022 at 9:18 PM, MAFman said:

Is Principia compatible with the kOS mod?

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Search for kOS in this topic and you will find plenty of discussion about how to work with the two mods. Like this for example,

 

[Krazy1]

Note to Principia newbies... If you are used to using the navball maneuver countdown make sure you set the +/-% to 0 not 50%.

Principia already calculates the burn time an accounts for this: the maneuver marker is at the beginning of the burn not the middle. 

Otherwise you'll do a 30 minute burn and wonder why it's way off like I just did