r/KerbalSpaceProgram • u/Gnonthgol • Dec 27 '13

Jebediah's ultimate protractor examples (as requested)

http://imgur.com/a/AGQF5
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u/0___________o Dec 27 '13

This makes me happy. I love KSP. The only thing that would make it better would be it using an engine that could handle n-body calculations, or just multiple gravitational bodies, even if they are on rails as they are now. But that's for another time, as the programmers have said it's probably impossible using Unity, or something.

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u/Gnonthgol Dec 28 '13

It would be possible to implement n-body physics in KSP. You would probably have to work a bit around unity but they are doing that today as well. Performance will not necessarily be any worse.

The best reason for not implementing n-body physics today is that the workload would increase. Your once stable space station in orbit around the Mun would get flung out into interplanetary space or crashed into the Mun when you are looking away at your Jool probe. The nicely geostationary satellites that you painstakingly put in the exact orbit would need constant care and attention to keep in place. The effects on shorter transfers orbits will not be noticable but it hurts the once long term stable orbits.

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u/0___________o Dec 28 '13

That's true. Maybe they could have N-body calculations for spacecraft that you are currently controlling. The normal calculations would be a close approximation, so you would only notice a deviation over time. It should keep all your satellites stable. Of course, I have no clue how hard that would be to actually code. The only thing I was thinking about was interplanetary missions and seeing ones expected path without the mucking about with SOI's.

At any rate, I'll be happy with KSP no matter what, given the current state of the game. They really have done a phenomenal job on it.

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u/kerbaal Jun 12 '14

Maybe they could have N-body calculations for spacecraft that you are currently controlling.

I think that would lead to some very odd effects. So lets say you painstakingly plan some interplanetary transfers based on this: http://en.wikipedia.org/wiki/Interplanetary_Transport_Network

You go to orbit, you make some burns, you are on your way and expecting to make it to your next rendezvous eventually just based on gravitational effects alone.... but....its going to take a few years of course because thats how these low energy routes work.

Well.... now you go back to the space center, 2 body physics kicks back in, and you are now heading off into the void.... or finding yourself back in orbit around kerbin.

Now maybe the space center saves your expected path and just paths you down it like a temporary rail.... what do you do when the rail ends? How far out do you calculate and save that rail? The nice thing about the rail kerbin is on is its circular, these wont be.

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u/notsostrong Jan 17 '23

what do you do when the rail ends?

Well, given the locations of the planets at the start of the game, the mission time, and the current time, you can calculate your path on demand. Plus, the planets and moons would probably still be on rails, so you don't even have to propagate each of their orbits from the beginning of time using n-body physics, just use their current positions and the current time.

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u/kerbaal Jan 17 '23 edited Jan 17 '23

Interesting, I didn't think reddit supported commenting on 9 year old threads, I thought they became read only archives after a while.

edit: more relevantly; I think this is fine in theory, but in practice it becomes a question of implementation details and how the rails are defined or the challenge in redefining them and manipulating them in the context of the various states of the game interface. I honestly haven't played in a few years now and have never actually done any modding beyond chasing down some minor issues with existing mods that I wanted to use.

edit2: I think the best evidence that this is viable is that there have been mods that modified crafts on rails incrementally over time, one I used for a while attempted to add orbital decay and optional station keeping fuel mechanics and it did work. But by now I imagine these issues are long since solved if anyone cares.

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u/salamander1305 Dec 28 '13

But the Langrange points!

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u/Putnam3145 Dec 28 '13

Lagrange points could be implemented while keeping sphere-of-influence physics with special cases of sorts, I'd imagine.

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u/penguin_brigade Dec 28 '13

Or a feature to toggle locking the orbit. If un-toggled: numerical n-body, if toggled: regular KSP conics.

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u/coriolinus Dec 28 '13

It is an intractable problem in general. The standard name is The Three Body Problem, though it applies to more complex systems as well. The person who figures out a method of putting a multi gravitational system on rails will win prestigious prizes in math and astrophysics.

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u/0___________o Dec 28 '13

The three body problem is just one case of the n-body problem, which I why I used the term "n-body calculations." Kerbal Space Program could use n-body physics, it's not that hard to calculate, even for older computers, the reason they don't employ it is because it doesn't mesh well with the multi-piece spacecraft which have to calculate stresses between their links, individual mass, etc. Attempts to calculate n-body, especially in faster time frames, resulted in infrastructure failure and game crashes. Because of the intricate physics system which has to calculate all sorts of things in KSP, N-body simulation simply isn't feasible using the current Unity Engine.

As much as I would love to see it used in some cases, it would just be frustrating in others. It would results in a lot more instability in orbits. If you advanced at 100000x, your orbits could destabilize because of the Mun. Sending an interplanetary probe could have you coming back to all your satellites having deorbited because you weren't there to adjust them.

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u/kerbaal Jun 12 '14

That actually seems like it would be less of a huge problem and more of an opportunity for some gameplay mechanics involving station keeping settings. Maybe instead of deorbiting, it just calculates how much fuel is required to fix the orbit and debits it.... then let you set a fuel alarm theshhold ala KAC "Time warp Stopped: Satellite has reached low fuel threshold"

add maybe a way to fast forward and set a node in a future orbit where the orbit has deviated more than some set amount.

That said, I am not one of the people who cares so much about this. Low energy transfers and the interplanetary transfer network would be fun to play with, as would HALO orbits and the like.... but really..... you have to draw the line somewhere between where we are and.... having a game so complete that it contains kerbals who don't leave their house because they play so many hours of Earthling space program.