eggrobin

[WIP][1.5.1, 1.6.1, 1.7.x] Principia—version פרנקל, released 2019-11-26—n-Body and Extended Body Gravitation, axial tilt

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Just a note : 

I've downloaded the latest Cristoffel on a stock system and I am having the same result.  Was this ever resolved?  

Currently, at about 80-100 days, Vall is ejected from the system.  At a year and a half, I had lost Laythe as well.    I discovered this rather by accident, as my ship arrived in the Joolian system and readied for transfer to Laythe...but, that's odd, she doesn't appear on the scopes, like she isn't even there.   Let's check out that small moon over there....if that's even what it is....

On 4/26/2014 at 10:37 AM, chaoko99 said:

can planets affect each other?

because if so, vall will be ejected from orbit in a few days-one week (what is vall's orbital period?)

- - - Updated - - -

can planets affect each other?

because if so, vall will be ejected from orbit in a few days-one week (what is vall's orbital period?)

 

 

 

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hi guys! hope everyone is enjoying these last days of 2017!

I just wanted to offer a humble suggestion for the mod, if I may. 

I think it would be useful to have the ability to provide inputs to the Flight Plan (delta-v to be burnt & time of the manoeuvre) by typing them with the keyboard rather than only having the log sliders. I mean, the sliders work just great, but if you experience performance drops & heavy stuttering, they can prove tricky to set right easily.

This is of course a kind suggestion, as the solution to my issue simply lies in getting a better PC (though currently using an i7 4770k, 32gb RAM & GTX 780ti - it's incredible how my heavily modded install is killing my CPU;.;). I am working with long duration flights, and struggling with performance when increasing the length of the prediction of my trajectory - stuttering makes it annoying to get the sliders to the values I want.

Thank you for this wonderful mod!!!

Edited by hypervelocity

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On 12/28/2017 at 4:47 AM, Bosun said:

I've downloaded the latest Cristoffel on a stock system and I am having the same result.  Was this ever resolved?  

Currently, at about 80-100 days, Vall is ejected from the system.  At a year and a half, I had lost Laythe as well.    I discovered this rather by accident, as my ship arrived in the Joolian system and readied for transfer to Laythe...but, that's odd, she doesn't appear on the scopes, like she isn't even there.   Let's check out that small moon over there....if that's even what it is....

 

@Bosun: The stabilization of the Jool system was introduced in Brouwer around February 2016.  We have a regression test to make sure that it is not lost when KSP or Principia evolves, so I'd be surprised if it had vanished in Christoffel.  Two observations, though:

  • The stabilization only works for the stock solar system.  If you have any mod that does any modification to the stock system, Principia won't try to stabilize Jool.  In the case of a mod that just adds more celestials, the FAQ has some information about how to stabilize Jool.  For more general changes to the system, you're on your own.
  • If you are using a very old save, the Jool stabilization may not be present in the save.  You'll need to start anew.

 

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On 12/29/2017 at 7:34 PM, hypervelocity said:

I think it would be useful to have the ability to provide inputs to the Flight Plan (delta-v to be burnt & time of the manoeuvre) by typing them with the keyboard rather than only having the log sliders. I mean, the sliders work just great, but if you experience performance drops & heavy stuttering, they can prove tricky to set right easily.

Yeah, this has been suggested before, see issue #947.  The reality is that:

  • We are not UI people so we are not very motivated to invest lots of times in the UI when we could be playing with numerics or astronomy.
  • As is customary with UI, things get sticky when you look at the details, and everybody has their own opinion as to how it should work.
  • Unity is somewhat limited in the kind of UI devices that it lets you build.

So don't hold your breath.  On the other hand, we would welcome contributions in this area: it's fairly isolated from the rest of Principia and could be developed/improved independently :wink:.

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On 1/4/2018 at 12:39 PM, pleroy said:

@Bosun: The stabilization of the Jool system was introduced in Brouwer around February 2016.  We have a regression test to make sure that it is not lost when KSP or Principia evolves, so I'd be surprised if it had vanished in Christoffel.  Two observations, though:

  • The stabilization only works for the stock solar system.  If you have any mod that does any modification to the stock system, Principia won't try to stabilize Jool.  In the case of a mod that just adds more celestials, the FAQ has some information about how to stabilize Jool.  For more general changes to the system, you're on your own.
  • If you are using a very old save, the Jool stabilization may not be present in the save.  You'll need to start anew.

 

Pleroy - Thanks, I actually had to download the fix separately that stabilized Jool.   Currently I still lost Vall - but I retained laythe, so, that's tolerable.   

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I was re reading Clarke's Imperial Earth last night1 and a wild thought struck me: Principia models the orbits & rotation of celestial bodies, right? Would I be able to stop a moon's rotation by firing a booster latched to the ground at the equator? or maybe de-orbit it using the infinite propellant cheat & lots of timewarping?
___________________________________________________________________________

1: Project Argus required Mnemosyne's spin to be stopped for the omni antenna to work.

 

 

Edited by hypervelocity

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@hypervelocity: This is a question that gets asked all the time.  The answer is that you cannot do that, Principia doesn't let vessels exercise a force on celestials.  That would be very expensive to compute and pointless as demonstrated by Scott Manley here.

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1 hour ago, pleroy said:

@hypervelocity: This is a question that gets asked all the time.  The answer is that you cannot do that, Principia doesn't let vessels exercise a force on celestials.  That would be very expensive to compute and pointless as demonstrated by Scott Manley here.

Damn. I can't steal Gilly.

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I've been meaning to reply to this for a long time, but never got around to it; apologies for the delay.

On 02/11/2017 at 12:55 AM, Nittany Tiger said:

I want to burn to inject into an Earth-Venus-Mars trajectory. 

During the burn, the two silver external tanks get depleted, so I jettison them mid-burn.

The flight plan does not currently support staging events, so the results of the plan will be somewhat inaccurate.

Quote

When I set up the burn, I use either the Earth-Centered Inertial frame, Venus-Centered Inertial Frame, or Mars-Centered Inertial frame.  When doing the burn, I use the Earth-Centered Inertial frame.  I'm not sure if you have to stick to one reference frame when doing the planning and burning.  Would make it hard for me to do this flyby since I need to switch reference frames to see where I need to tweak my flight plan to fly by Venus and intercept Mars.

I'm also not certain if you have to set both the flight prediction frame of reference and flight planning frame of reference to the same frame when manipulating a maneuver node or doing a burn.  I always see a warning message when those two frames don't match, but when I have the frames match, I sometimes get nonsensical trajectories like burns that never exit Earth's SOI.

There is no prediction frame. There is a plotting frame, which is the reference frame in which you are drawing the trajectories, and a manoeuvre frame for each manoeuvre, which is the reference frame used to define what "tangent" means when you burn tangent.

They need not be the same; indeed, when planning an escape burn from Earth, the manoeuvre should be tangent in ECI (i.e. along the path of your orbit around the Earth), but you probably want to look at the trajectory in a frame where your target is fixed (probably Venus-centred, Sun-aligned).

The warning should be seen more as a reminder that when burning "forward" isn't going to burn forward along the trajectory that is drawn, but along the trajectory in another reference frame.

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I've always wanted to ask this, and finally got to taking screenshots today. What do the various markers (pro/retro grade, radial in/out) mean in LVLH navball and where does the ship point when I use the SAS pro/retro grade, radial in/out modes?

Spoiler

AlP3Uf3.png

qdJy4gM.png

As you can see, I've target prograde, and in no frame of reference that I can think of should the ship be pointing radially outward from Kerbin and the navball showing radial in. The orbit is fairly circular and the second screenshot shows that even in LVLH frame, my velocity prograde should be about parallel to Kerbin's surface.

The SAS pointing to pro/retro grade in target frame is always off by a big amount when the distance is large, even when you do come close (within 200m) there's usually a slight difference in prograde marker direction and where the SAS points.

Edited by scimas

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@eggrobin I think I meant plotting and maneuver frames when I said prediction and planning frames respectively. 

Anyway, thanks for the response.  I'll probably try not staging those tanks until after the burn and also performing the burn in the ECI frame.  Hopefully the latter that fixes the problem of the wildly-moving maneuver node marker on the navball.

Also, started using NASA's GMAT to plan trajectories with my RSS + Principia save.  Real physics model calls for the real tools.

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Can anybody say 1-2 sentences about what extended-body gravitation means for principia? Are the bodies modeled as oblated spheroids, or is the simulation even more precise with measured gravitation maps, taking continents etc into account?

Edited by Mike`

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3 minutes ago, Mike` said:

Can anybody say 1-2 sentences about what extended-body gravitation means for principia? Are the bodies modeled as oblated spheroids, or is the simulation even more precise with measured gravitation maps, taking continents etc into account?

The bodies are modeled as oblate spheroids.  We only go to the J2 term, and this introduces some inaccuracies for celestials where S22 or C22 are large (Mars is one example, and the orbits of Phobos and Deimos are significantly off).

No higher spherical harmonics or gravitation maps as the force computations are in the critical loop and have a very tight CPU budget.

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Does Principia support RSS Constellations and/or other exasolar planet packs?

Or, perhaps I should ask if it should? KSP crashes on load when I try to load both at the same time.

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For the new moon (lunation number 223), the new release (Clifford) is out.

A bug in the implementation of DoublePrecision that caused a test to fail on Macintosh, as reported by @awang and @Jim DiGriz, was fixed.

Solar system designers can now pick an integrator more suited to their solar system, as requested by @GregoxMun whose surprisingly stable Alternis Kerbol Rekerjiggered does not fare well with Principia's default integration parameters, which were chosen (in Cartan) to work for stock KSP and the real solar system.

See the change log for more details.

Again, we support two versions of KSP: downloads are available for 1.3.1 and for 1.2.2. Make sure you download the right one (if you don't, the game will crash on load).

Thanks to @awang for contributions (clang warning cleanups) during this lunation.

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11 hours ago, Omnipius said:

Does Principia support RSS Constellations and/or other exasolar planet packs?

Or, perhaps I should ask if it should? KSP crashes on load when I try to load both at the same time.

I think this is documented in the FAQs: if you have more planets than the basic RSS, the game will crash.  You could confirm this by looking at the log files.  Even if it didn't crash, it's unclear if RSS Constellations would work well with Principia as the floating-point granularity would become problematic when you move very far away from the main solar system.

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3 hours ago, Kobymaru said:

Hey there, I was wondering: is there any particular reason why Principia is not on CKAN?

The reasons are a bit lost in the mists of time.  I vaguely remember that when we started Principia 4 years ago, CKAN had limitations that were problematic for us.  Also, we were only targeting Windows at the time and CKAN didn't support mods that wouldn't work on all platforms.

It's possible that all the problems have been solved since then, and it's just a matter of writing a configuration.  There may be minefields, though: for instance I see that they recommend to use ASCII digits and letters in the version names, but we take great pride in using all the possible writing systems in our version names.

Edited by pleroy

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On 18.1.2018 at 10:31 PM, pleroy said:

The reasons are a bit lost in the mists of time.  I vaguely remember that when we started Principia 4 years ago, CKAN had limitations that were problematic for us.  Also, we were only targeting Windows at the time and CKAN didn't support mods that wouldn't work on all platforms.

Well considering that my installation procedure consisted of literally downloading and unpacking it, it seems that those limitations might be a thing of the past :wink: 

 

On 18.1.2018 at 10:31 PM, pleroy said:

It's possible that all the problems have been solved since then, and it's just a matter of writing a configuration. 

It is really not that hard, and I could assist you with doing that. What's required is a simple .spec file, and a pull request for it to the NetKAN repository.

What would make things easier is an AVC version file, and for the zip file downloads to be hosted on GitHub (a while back they allowed to add binaries to a Release).

 

On 18.1.2018 at 10:31 PM, pleroy said:

There may be minefields, though: for instance I see that they recommend to use ASCII digits and letters in the version names, but we take great pride in using all the possible writing systems in our version names.

To quote the CKAN spec specification:

Quote

While the CKAN will accept any string as a mod_version, mod authors are encouraged to restrict version names to ASCII-letters, ASCII-digits, and the characters . + - _ (full stop, plus, dash, underscore) and should start with a digit.

Looking on GitHub, I saw that you number your release by release date, so that's already a clear lexicographical ordering and should do the trick. Whether or not the CKAN  client and many bots will eat your non-ASCII characters is another question. It's probably simpler and safer to omit them in the version specification files (you can keep them everywhere else obviously), but depending on how deep your pride runs one could take it up with the CKAN maintainers or simply try it out.

Another thing that might need attention is conflicts, but they could be seen as an advantage rather than a burden: CKAN allows you to specify exactly which versions of KSP a release was built for, and gives you the opportunity to mark certain Mods as incompatible. I bet a mod that alters KSP fundamentally would have many of those. Additionally, you could suggest or recommend mods that go especially well with Principia.

Especially as a player, I must say that I find CKAN to be an immense help. Installing one single mod manually is not a big deal - but when you start installing a lot of them, then the going to the forum threads, looking for download links, downloading and unpacking gets really old really quick. That's why I always appreciate it when put their mods into the CKAN registry.

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19 hours ago, Kobymaru said:

Especially as a player, I must say that I find CKAN to be an immense help. Installing one single mod manually is not a big deal - but when you start installing a lot of them, then the going to the forum threads, looking for download links, downloading and unpacking gets really old really quick. That's why I always appreciate it when put their mods into the CKAN registry.

CKAN is crowd-sourced, you can just submit a PR to add Principia metadata to it.

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8 minutes ago, Jim DiGriz said:

CKAN is crowd-sourced, you can just submit a PR to add Principia metadata to it.

Yes, but submitting it without the approval of Mod authors is frowned upon. Which is what I am requesting here.

Additionally, configs and hassle could be even less with a few changes (mentioned above) inside the mods repository.

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So I have been trying to use the flight planner of Principia, and I have to say... it's a bit of a mess. It's especially hard to get it to work with RemoteTech, which is kind of a "must" for a realist experience with Realism Overhaul.

The reason why Maneuver Nodes exist in KSP in the first place is not only for flight planning, but also as an Aid for Maneuver execution.

Now Principia cripples this aid, and seemingly for no reason:

  • Maneuver nodes disappear after the burn time is supposedly over. That wouldn't be too bad, except RemoteTech and Principia don't seem to agree on the passage of time (Did you happen to implement relativity? :wink:) and over the course of a few days, the RemoteTech clock is a few minutes behind, starts the burn too late and then tries to chase a maneuver node that doesn't exist anymore. Why does this have to be deleted? Wouldn't it be better to just leave the maneuver node there?
  • It seems that when checking "Show on Navball", Principia is constantly trying to overwrite the Maneuver Node. This seems like an OK idea until you actually try to do a Burn with it: first, you have no idea how much error you made and where to point the ship to correct it. Second, the timer and the Delta-V countdown is constantly stuck at the initial position. So how am I supposed to know when the burn is over? Do I have to use a stop watch?
  • After a maneuver has been executed, the flight plan is null and void, because the real trajectory and the flight plan will never match up. That means, you have to
    • Delete all maneuvers except the first, one by one by one
    • Delete the flight plan
    • Create the flight plan
    • Recreate all maneuvers,  one by one by one

As you can see, this is is not particularly user-friendly. Couldn't there be a button with "refresh flight plan" or something like it?
And maybe a readout that the flight plan is "stale"? Because it happened 3 times to me already that I executed a maneuver that was based on a stale flight plan accidentally, and ended up in a pretty useless Orbit.

  • In the middle of the burn, about when my eccentricity went above zero, the maneuver node jumped to a different location, wrecking my burn. I checked both the Maneuver frame and the Plotting Frame, and both were on "non-rotating fixing center of the earth", with the Navball displaying ECI

 

I'm kind of curious how people actually execute maneuvers, and whether I am the only one with RemoteTech.

I understand that many things with Principia change and therefor not all concepts of the Stock game apply. But it just seems that Principia makes it unnecessarily difficult. For example, I absolutely don't understand the fight with maneuver nodes. Here, the Stock game has simple, intuitive concepts that could be wonderfully put to use in Principia. Why doesn't it? Instead of "Show on Navball", why can't there be a button that simply places a maneuver node exactly at the right time with the right burn vector?

Then users could very easily execute the burn either manually (stock-style) or by slaving known tools such as the RemoteTech flight compuer or MechJeb to the maneuver node.

Edited by Kobymaru

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5 hours ago, Kobymaru said:

It seems that when checking "Show on Navball", Principia is constantly trying to overwrite the Maneuver Node. This seems like an OK idea until you actually try to do a Burn with it: first, you have no idea how much error you made and where to point the ship to correct it. Second, the timer and the Delta-V countdown is constantly stuck at the initial position. So how am I supposed to know when the burn is over? Do I have to use a stop watch?

Principia doesn't completely overwrite the manoeuvre node, it just keeps resetting the delta V value and updates the direction of the burn. That's how you get more efficient burns (stock burns are directed at a constant direction. Which is why your orbit gets bigger and bigger when doing inclination change, you aren't burning normal to your trajectory at all times, you are burning along normal to the trajectory at the start of the burn). There is a Time to engine cutoff readout in the flight planner, no need of a stop watch. And if you prefer the stock like burns, there's the option to have inertially fixed burns. Which I think should give you a stock ticking down node.

5 hours ago, Kobymaru said:
  • After a maneuver has been executed, the flight plan is null and void, because the real trajectory and the flight plan will never match up. That means, you have to
    • Delete all maneuvers except the first, one by one by one
    • Delete the flight plan
    • Create the flight plan
    • Recreate all maneuvers,  one by one by one

As you can see, this is is not particularly user-friendly. Couldn't there be a button with "refresh flight plan" or something like it?

Completely agree. You can never perform a perfect burn and due to the nonlinear chaotic nature of N-body gravitation the error between planned and actual post burn trajectory just keeps on increasing the further you move from the burn. So I tend to create long flight plans only for initial visualization. After I'm satisfied with that, I just delete the plan and create single manoeuvres plans as I go. This has been brought up before too though; I guess the devs will improve it when they get time.

6 hours ago, Kobymaru said:

I'm kind of curious how people actually execute maneuvers, and whether I am the only one with RemoteTech.

I am using RemoteTech in one my saves right now, but I don't use its flight computer. Unless I want extremely precise manoeuvres that would require manually changing thrust limits, I use a kOS script to execute my burns.

6 hours ago, Kobymaru said:

except RemoteTech and Principia don't seem to agree on the passage of time

Don't know about RT, but I have noticed kOS getting out of sync with the game clock for as much as 5 - 10 seconds when time warping. But it corrects the error almost immediately.

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The Principia flight plan window shows the time to node near the top left. Once the node has been reached it counts down to burn completion, so no stopwatch needed.

I use RemoteTech's flight computer to conduct burns. I usually put the required delta-V in the Burn duration field, set the throttle to 100%, use the Node button to set the attitude and smack the Burn button when the node countdown hits zero. If you use Kerbal Engineer Redux and have the time to node showing you can close the Principia windows and initiate the burn using that. This also restores the stock deltaV countdown.  

One thing to watch out for is if there is multiple manoeuvres on the flight plan - to prevent the ship from immediately altering its attitude to the next node's position I switch from Node to Kill mode just before the burn completes. That way I still have the ability to nudge with RCS if the plot has drifted too far. Even so, sometimes the calculated burn ends up under or overshooting the plotted path by a considerable distance (RT vs P time?). If so I F9 and do the burn again by eyeball. Possibly some of the time calculation issues are down to my game requiring a whopping 36Gb of memory and I only have 16Gb RAM installed.

I'm still messing around in the vicinity of Gael in GPP, so not much issue with lightspeed time delay.  

I treat the multiple node flight plan as a "can it be done?" calculator. Once I have completed the first burn I immediately delete the plan and rebuild. I am so accustomed to this that I even delete the plan on those oh-so-rare perfect burns.  

 

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