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[WIP][1.8.1, 1.9.1, 1.10.1, 1.11.0–2, 1.12.2–4] Principia—version Ἱπποκράτης, released 2022-11-23—n-Body and Extended Body Gravitation


eggrobin
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How might one go about making Principia configs for a planet pack(KSRSS)? Just looking for someone to point me in the right direction, won't ask for any help if the configuration isn't stable. 

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23 hours ago, DA299 said:

How might one go about making Principia configs for a planet pack(KSRSS)? Just looking for someone to point me in the right direction, won't ask for any help if the configuration isn't stable. 

The configuration files which are used to describe a solar system are documented here.

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4 hours ago, pleroy said:

The configuration files which are used to describe a solar system are documented here.

Thanks, the gravity model should be pretty easy to change, however the initial state is something which would take quite some time. I just wanted to ask, did you make the initial state manually, or is there some kind of calculator that you used (For the 6 values.)?

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5 minutes ago, DA299 said:

Thanks, the gravity model should be pretty easy to change, however the initial state is something which would take quite some time. I just wanted to ask, did you make the initial state manually, or is there some kind of calculator that you used (For the 6 values.)?

For the real solar system, it's quite easy, we used the JPL Horizon System which gives us real-life numbers.  For a fictitious system, however, things might get more challenging.

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On 8/6/2022 at 10:57 AM, DA299 said:

Thanks, the gravity model should be pretty easy to change, however the initial state is something which would take quite some time.

Sort of along these same lines, does anyone know if Principia ships with a non-spherical gravity model for the various stock KSP bodies? 

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7 hours ago, Arrowstar said:

Sort of along these same lines, does anyone know if Principia ships with a non-spherical gravity model for the various stock KSP bodies? 

Nope, but you should be able to use RSS values and play with those in stock. People have done it before, it just takes some config changing.

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10 hours ago, DA299 said:

Nope, but you should be able to use RSS values and play with those in stock. People have done it before, it just takes some config changing.

Great, no worries.  The next version of KSPTOT is going ship with a spherical harmonics gravity model system and I just wanted to make sure I had grabbed all the coefficients for any stock celestial bodies, if they existed.  Since they don't, that makes my life easy.  Thanks!

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On 7/29/2022 at 7:36 AM, Krazy1 said:

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.

AFAIK it's a core/stock KSP behavior, nothing to do with principia code.

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On 8/12/2022 at 9:03 AM, ZAJC3W said:

AFAIK it's a core/stock KSP behavior, nothing to do with principia code.

Granted but couldn't it be eliminated with Click Through Blocker support? It would be nice to add that anyway to prevent click-through to other mod panels. 

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Hello, I use the pricipia mod on Ksp rss ro and I noticed that if I was in the most perfect possible low polar circular orbit around the Earth the geocentric speed of my ship always slows down when it passes above poles and reaccelerates when it passes over the equator. Is this normal? A ship in a perfectly circular orbit would be supposed to always stay at the same geocentric speed, wouldn't it?

Thank you !

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1 hour ago, yomahabaca said:

Is this normal? A ship in a perfectly circular orbit would be supposed to always stay at the same geocentric speed, wouldn't it?

Believe it or not, the Earth is not a perfect sphere.  It is flattened at the poles (oblate) and it has mountains and oceans that make its gravity field inhomogeneous.  Principia simulates this, so for instance geostationary orbits are only stable in some places (over India and Mexico), elsewhere they need stationkeeping.

The effect you are seeing is mostly due to oblateness.

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So the equatorial bulge in addition to being able to cause nodal precession it can also slightly accelerate and decelerate a satellite in orbit. I didn't know that, thanks ! Incredible, the detail and the realism of this mod !

Are you sure there are stable geostationary orbit positions? I believed that no position in geostationary orbit was truly stable and required all stationkeeping due to the influence of the Moon.

Edited by yomahabaca
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  • 2 weeks later...

For the new moon (lunation number 280), the new release (Ἵππαρχος) is out.

  • A bug in RCS thrust estimation with some parts was fixed by @Flibble.
  • The UI of the flight plan tolerance selector has been improved, matching the changes to the prediction tolerance selector in Hilbert.
  • The axes used by Principia have been made consistent: MechJeb and Principia should now report a similar longitude of the ascending node for an active vessel in a sufficiently Keplerian orbit, instead of differing by 90°. Thanks to @rnlahaye for spotting a bug in that change shortly before the release.

 See the change log for more details.

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  • 2 weeks later...

Hi @eggrobin I did a Jool 5 with Principia. Thanks for a great mod. 

I found a problem with burn time calculation with engines that are in "flame-out!" status. The burn time calculation in the Flight Plan window uses "active engines" despite being flamed-out. The navball timer (correctly IMO) ignores flamed-out engines.

I made an SSTO with FL-C1000 tanks which have solid fuel thrusters.  Solid fuel engines cannot be deactivated. I expect any depleted SRBs in space would do this. Jet engines could be disabled but it's a potential pitfall too (I haven't tested a jet engine). 

Picture below shows Flight Plan duration uses both the LV-Ns and FL-C1000s (about 5 minutes) and navball uses only LV-N (almost 10 minutes).

1jYGpvk.jpg

9/4 Update:

I was able to hack my save file to rearm the solid fuel engines in the staging, so it did not include these in the time calculation in the flight plan. 

4E7Yedz.png

 

Edited by Krazy1
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For anyone who didn't see, I've done a bunch of work speeding up reading and writing ConfigNode for KSPCommunityFixes, which significantly speeds up Principia saves and loads. If you haven't updated yet (or don't have KSPCF installed) I suggest you give it a try. :)

 

 

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Currently I am having troubles with my space station, because the parts are moving away from each other over time - usually after some wobbling occurred, it gets worse. This also has the negative effect, that Kerbals have trouble climbing on ladders of capsules.

Uninstalling Principia and loading the game has the effect, that the parts show up in their initial positions before the diverging happened.

Do I understand it correct, that Principia takes over the physics of part-movement? If so, is it possible to switch off that functionality and just keep the N-body-orbital movement active?

I would appreciate ideas on how to prevent this diverging from becoming worse (reducing the station size is not a viable solution for me).

This picture below shows my problem. Initially, the parts (stock + USI-mods) were all aligned to each other, but over time they diverged more and more.

5t6lAbc.jpg

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  • 2 weeks later...
On 9/14/2022 at 6:39 PM, mhoram said:

Do I understand it correct, that Principia takes over the physics of part-movement? If so, is it possible to switch off that functionality and just keep the N-body-orbital movement active?

Technically, Principia doesn't quite control the movement of parts.  It does control the movements of parts-that-are-in-contact-with-each-other (we call these things "pile-up") and let KSP do the part placement within the pile-ups.  There is no way to separate this from N-body physics because precisely N-body physics is the integration of the motion of pile-ups.

On 9/14/2022 at 6:39 PM, mhoram said:

This picture below shows my problem. Initially, the parts (stock + USI-mods) were all aligned to each other, but over time they diverged more and more.

At least, that's a nice picture :confused:.  But obviously, it's not supposed to happen.

Ideally, if you could reproduce the problem with the stock game and give us a save, that would be great.  If not, I would suggest looking at the mods that you use and see if any one of them believes that it can change the location of parts; mods that do this are typically incompatible with Principia (see the FAQs for details).  You can try removing the mods one-by-one to determine which one interacts with Principia.

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On 9/25/2022 at 3:44 PM, pleroy said:

There is no way to separate this from N-body physics because precisely N-body physics is the integration of the motion of pile-ups.

I would have guessed, that physics of part movement would be a system that is completely distinct from the system that moves vessels in orbit. Thank you for this clarification.

On 9/25/2022 at 3:44 PM, pleroy said:

But obviously, it's not supposed to happen.

Ideally, if you could reproduce the problem with the stock game and give us a save, that would be great. If not, I would suggest looking at the mods that you use and see if any one of them believes that it can change the location of parts

Thank you for confirming that this is a bug.  I am quite certain, that Principia is the only Mod, that changes physics in my installation, but one can never know for certain. I can try to replicate this issue in Stock+Principia and will get back to you.

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These are probably silly noob questions, but I promise I searched for the answers.

Are there Lagrange points in the Kerbin-Mun system? Everything I could find talked about RSS, but nothing about Kerbin-Mun points. I don't even know if the mass ratio is sufficient between them. Okay, I found that there at least USED to be Kerbin-Mun Lagrange points, so I'll assume they're still around.

What reference frame do I use and what direction do I fire my thrusters when I get to them to achieve orbit. I brute forced it a couple times in RSS, but I wanna understand in a more principled way. Obviously there isn't an L4-inertial reference frame I can select, so I thought I should use Kerbin-inertial so I could point along the direction of the Mun's orbit, but after an hour of tweaking knobs, I haven't even seen evidence that the L4 exists.

Is there a tutorial somewhere that I missed in my searching?

Okay, I think I get it now. So the process for the L4/L5 points is to start in Kerbin-inertial and get your apoapsis to about where you think the Lagrange point is. Then, still in Kerbin-inertial, make a maneuver node to circularize your orbit. If your guess was good, you should have something that looks like an erratic circle. Switching to the Mun-Kerbin-Orbit reveals a kidney bean shape.

If your guess wasn't good, keep moving both maneuvers around in time until you succeed.

This works, but is it the Right way?

EDIT: Okay, I think I'm finally internalizing this. So what's cool about L4/L5 isn't that you're orbiting the Lagrange point, it's that orbiting the Lagrange point can make patched conics be an Actually Pretty Good Approximation. No station keeping, no worrying about Jupiter, just vibes. Is that about right?

 

Edited by Waifu Art Thou Romeo
Found some of my own answer
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6 hours ago, kerbalboi said:

im looking into using this in ksp, what things should i know?

Things are not too different, your standard transfer maneuvers will still work, give or take some n-body funkiness.

Get used to the Principia UI and how trajectories look in different frames. It will make things so much easier.

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