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Dr. Omicron

Does Principia work with mechjeb

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Posted (edited)

Does Principia mod mechanics work with the mechjeb transfer planner - autopilot?

 

 

And can I get tylo on a crash course?

Edited by MarkvirsII

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Posted (edited)

The Principia thread would be the best place to ask your question, but in this case, I can answer it:  no.  The MechJeb transfer planner relies on instantaneous velocity changes in the same way that the stock manoeuvre node system does.  The difference is that MechJeb is a lot better at choosing precise solutions quickly--though it certainly has its limits in that area, as well.  There's a reason that Principia comes with its own flight planner; if you use MechJeb, then you probably won't get the encounter.  I'm not saying that it's impossible, but the entire design of MechJeb is established with the stock game in mind (with a few notable exceptions--but Principia is not one of them).

For your second question, I don't know what you mean:  if you are asking whether you can crash into Tylo, then yes, you can crash into it just the same as in the stock game.  If you're asking whether you can crash Tylo into something else, then no.  Principia has an orbit configuration file designed to prevent  that kind of thing, and my understanding is that planetary collisions resulting from unstable or otherwise badly-designed orbits cause unacceptable bugs anyway.

Edited by Zhetaan

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It depends on where you’re using it. Somewhere like eve, where the planet is dramatically more massive than its moon, will probably not be too different in principia; while somewhere like the jool system with its mess of moons will diverge more significantly. 

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Moving to Add-on Discussions.

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On 6/4/2019 at 5:53 AM, Zhetaan said:

The Principia thread would be the best place to ask your question, but in this case, I can answer it:  no.  The MechJeb transfer planner relies on instantaneous velocity changes in the same way that the stock manoeuvre node system does.  The difference is that MechJeb is a lot better at choosing precise solutions quickly--though it certainly has its limits in that area, as well.  There's a reason that Principia comes with its own flight planner; if you use MechJeb, then you probably won't get the encounter.  I'm not saying that it's impossible, but the entire design of MechJeb is established with the stock game in mind (with a few notable exceptions--but Principia is not one of them).

For your second question, I don't know what you mean:  if you are asking whether you can crash into Tylo, then yes, you can crash into it just the same as in the stock game.  If you're asking whether you can crash Tylo into something else, then no.  Principia has an orbit configuration file designed to prevent  that kind of thing, and my understanding is that planetary collisions resulting from unstable or otherwise badly-designed orbits cause unacceptable bugs anyway.

wait Principia has its own planner?

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4 hours ago, MarkvirsII said:

wait Principia has its own planner?

Yes, because flying a course in full N-body gravitation by hand can easily become complicated enough to require a few degrees in mathematics.  Since Principia already solves those equations, why not use the same solver for flight planning?  It isn't an autopilot, but it will help you plan your trip.

To quote from the Principia Wiki:

Quote

Flight planning

In stock KSP, flight planning is done using manœuvre nodes. Manœuvre nodes are only a rough approximation of the real behaviour of your rocket because they assume that any change of velocity is instantaneous. You may notice this when trying to effect a burn planned using a manœuvre node: you never quite get things right because the actual burn doesn't cause an instantaneous change of velocity.

This is good enough for fly-by-the-seat-of-your-pants, cowboy-style piloting, but it's entirely inappropriate for more complex missions where it's important to make the best use of your engines. Thus, Principia includes an elaborate flight planning system which let you plan burns in a much more realistic manner.

While Principia makes it possible to plan complex trajectories, it's important to understand that there are two things that it doesn't do because, well, they are part of the fun of using realistic N-body physics:

  • Principia doesn't help you optimise the flight plan, e.g. by minimising the Δv. You've got to look for good flight plans yourself, using intuition and trial and errors. You'll get better over time. And yes, it's hard, that's why they hire PhDs to do this.

  • Principia doesn't help you execute the flight plan. Once you are done with the planning, you need to execute the manœuvres by hand by starting and cutting off the engines just at the right time. You will not get this completely right, and in some cases a delay of a fraction of a second may cause significant changes to the trajectory down the road. That's ok, don't try to overdo it, you can always schedule a minor correction to compensate for any inaccuracies. In real life rocket scientists do just that as they learn more about the gravitational fields around unexplored celestials or because of intrinsic inaccuracies in the intensity of the burns.

The controls that let you plan your flight won't allow you to tune your Δv or your burn times extremely precisely (typically no finer than 1 mm/s). That's intentional: even if you were able to construct a flight plan that way, you wouldn't be able to execute it. If a small change of your Δv has a large effect on your future trajectory, you probably want to make smaller burns at different points along your mission.

 

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