Lagrange Points in KSP

[Tanner Rawlings]

first off incase you dont know what a Lagrange point is heres the wiki:http://en.wikipedia.org/wiki/Lagrangian_point

Got it? Good!

I was wondering if it was possible in the games physics to set up a satellite in one of the lagrange points

feel free to discus this in the doobly doo

[Klingon Admiral]

No.

10chars

[NecroBones]

Currently no, because the game isn't simulating multi-body physics. Your ship is only being gravitationally pulled by one planet/moon at a time (and then switched to "on rails" simple kepler orbits when you switch control away from that ship). In reality, the gravitation of multiple bodies is what creates the Lagrange effect.

[MalfunctionM1Ke]

n-body-physics would kill the fun in the game. You couldnt even timewarp without having your ship leaving its Orbit and Floating all over the place

[Tanner Rawlings]

NecroBones- Currently no, because the game isn't simulating multi-body physics. Your ship is only being gravitationally pulled by one planet/moon at a time (and then switched to "on rails" simple kepler orbits when you switch control away from that ship). In reality, the gravitation of multiple bodies is what creates the Lagrange effect.

thanks for explaining

[Guest]

n-body-physics would kill the fun in the game. You couldnt even timewarp without having your ship leaving its Orbit and Floating all over the place

No, it won't. But I can see why Squad doesn't want n-body. Because most people can't understand it, and how much of an improvement it would really be. And probably because it requires quite a bit of physics and mathematics knowledge to implement.

Fortunately, Squad only makes the core game. There's a mod in development out there called Principia, which is implementing proper, manageable and playable n-body physics.

[Red Iron Crown]

L4 and L5 can be approximated in KSP by being in the same orbit as the orbiting body, just 60 degrees ahead of or behind it. Same with L3, just 180 degrees away. Nothing to be done for L1 and L2, though.

Not true Lagrange points, but they do keep a constant geometry similar to them.

[Doozler]

And probably because it requires quite a bit of physics and mathematics knowledge to implement.

To elaborate, n-body physics does not have a "simple solution" i.e. a formula, which means that you essentially have to "simulate" the motion time step by time step. This would be very computer intensive (and I think make time warp of orbits subject to the same kind of wobbles as physics time warp on launch).

Without n-body, one you know what the orbit parameters are, you know where the craft/ body will be for all times in the future with a simple formula.

In practice, n-body physics wouldn't have too much of an effect apart from a few special cases - like the lagrange points.

[Ravenchant]

Because most people can't understand it, and how much of an improvement it would really be.

So we gain Lagrange points and lose the annoying SOI transitions, but setting up any kind of long-term stable orbit around Duna or Jool would be next to impossible. It would be nice to have more realism, but it isn't a perfect solution.

[RuBisCO]

It could be possible to simulate L points though while maintaining CPU un-intensive 1-body physic. All that is needed is to have L points become invisible bodies with their own SOI. Of course L1 and L2 would not be spheres but more like Disks Of Influence, so they would need to implement non-uniform gravity or more complex code for non-spherical areas of influence. At present though you can sort of simulate L4 and L5 orbits, just put a ship in a matching orbit with your body that shifted.

[psyper]

I think this has been talked about to death and each time it resurfaces we get in to an argument and the thread gets locked so I just want to put my 2 pence in before it does!!

What if someone could create a mod for some of the L points - the stable ones (can't remember what they are) they will basically be moons, they will be on rails and orbit in their correct position between planets or in the same line as them, they will have no collision mesh or texture but will have a SOI and a gravity well which will keep any ship in orbit around it.

.... actually I'm thinking now - what about a mod which puts some trojan object in - tiny moons that float in the L points but basically produce the L point gravity - the moons cause the gravity well not the other way around - to a craft there will be practically no difference?

[Monger]

Hmm... I don't get the n-body physics argument. KSP works with patched conics, i.e. at a Lagrange point you should continuously oscillate between leaving one influence sphere and entering the other.

Edit: at least L1 and L2 should oscillate like that. L3 is kind of guaranteed, if the second physical body isn't calculated. About L4 and L5 I'm unsure.

Edited March 27, 2014 by Monger

[Ravenchant]

the moons cause the gravity well not the other way around - to a craft there will be practically no difference?

The whole point of Lagrange points is that there's no local gravity well there- once you move away from them, you fall into one. Okay, part of the point. But still

[Kasuha]

In my humble opinion, true N-body physics would be annoyance, not an improvement in KSP. Stable and deterministic orbits are comfortable, easy to understand, easy to handle. So many players can't even work with anything but an equatorial orbit, these would definitely not appreciate existence of lagrangian points because they would have no idea how to even find them, not mentioning how to place something into them.

So yes, a few advanced players would probably know how to handle them. For the rest, the learning curve for KSP would just become a bit steeper. More would not make it.

[NecroBones]

It could be possible to simulate L points though while maintaining CPU un-intensive 1-body physic. All that is needed is to have L points become invisible bodies with their own SOI. Of course L1 and L2 would not be spheres but more like Disks Of Influence, so they would need to implement non-uniform gravity or more complex code for non-spherical areas of influence. At present though you can sort of simulate L4 and L5 orbits, just put a ship in a matching orbit with your body that shifted.

I like this idea. I do hope they'll simulate them at some point, even if it's just L4 and L5, since they're the relatively stable ones.

[DMagic]

If you want to know more about all the in-depth, make-your-head-spin details about n-body physics in KSP just check the thread in the add-on development forum. If you want to know why Squad will never actually include something like this, just scroll down to the bottom of the first post and see if you can make sense if the orbital paths shown there.

[JtPB]

I think that only L3, L4, L5 can be pseudo-simulated. You can put your ship in any point at the orbit of the desired planet, out of its SOI, and that is the langragian area of the orbit.

[Guest]

Squad probably won't implement this because they're game devs not mathematicians. The guy making Principia is a mathematician, and maintaining an N-body system would pretty much require them to have one full-time physics/maths expert, with experience in numerical integration. That said, with NASA cooperation and all that, it should not be impossible to find one if they wanted. Oh, and if you actually knew a thing or two about orbital physics, you'd see that the orbits Principia gives are fine. Better than "high-school model" orbits currently in KSP, in fact.

So we gain Lagrange points and lose the annoying SOI transitions, but setting up any kind of long-term stable orbit around Duna or Jool would be next to impossible. It would be nice to have more realism, but it isn't a perfect solution.

Wrong. It's perfectly possible to set up a stable orbit around Jupiter, so around Duna or Jool it'll be possible, too. It won't be a perfect Keplerian orbit, and will probably precess, but you shouldn't get ejected or launched into a planet if you do it right. As for the gains? Immense. Sun-synchronous orbits, Lagrange points Interplanetary Transfer Network (look it up) and much more.

To elaborate, n-body physics does not have a "simple solution" i.e. a formula, which means that you essentially have to "simulate" the motion time step by time step. This would be very computer intensive (and I think make time warp of orbits subject to the same kind of wobbles as physics time warp on launch).

In practice, n-body physics wouldn't have too much of an effect apart from a few special cases - like the lagrange points.

Wrong on both counts. Yes, the n-body simulation does not have a formula, the solutions are chaotic. But calculating them can be done in an efficient, CPU-light way. All thanks to something called symplectic integration. Check out Principia thread on a detailed (and math-heavy) explanation.

As for the second, see above. It's a common misconception, and it's utterly and completely wrong. N-body would change the game unimaginably. We'd need better tools for trajectory plotting and some sort of automated stationkeeping, but the main uses of it would be maintaining otherwise unstable orbits, which can be of great use. And even without auto stationkeeping, it'd still make for a much better experience.

Edited March 27, 2014 by Guest

[PhaserArray]

Well, somebody already made some kind of a basic NBody plugin.

[Kasuha]

I agree with most of what you wrote, with exception of a few words.

you'd see that the orbits Principia gives are fine. Better than "high-school model" orbits currently in KSP, in fact.

More realistic and more complex does not automatically mean better. They are pretty but I don't think they are better or even fine for purposes of KSP as a game.

It's perfectly possible to set up a stable orbit around Jupiter, so around Duna or Jool it'll be possible, too. It won't be a perfect Keplerian orbit, and will probably precess, but you shouldn't get ejected or launched into a planet if you do it right.

There's no Ike around Mars, there's no Tylo around Jupiter. Both are navigation hazard even in current game, avoiding them in N-body physics would be a nightmare. The 'if you do it right' is gross understatement of what you'd have to be able to do.

As for the gains? Immense. Sun-synchronous orbits, Lagrange points Interplanetary Transfer Network (look it up) and much more.

Neither are something to strive for, IMO. A point in space where you can sit but there's nothing there. Pretty trajectory lines telling you that your ship will fall or fly away if you don't pay attention to it. Interplanetary transfer network is possible (at somewhat lower technical difficulty) with current system.

But calculating them can be done in an efficient, CPU-light way.

I don't think the performance figures in the Principia thread suggest it is exactly "CPU-light". But I can agree that it would be usable. The only problem is that current implementation has technically unlimited upper limit of time warp. Numerical integration has always certain level over which it cannot go.

We'd need better tools for trajectory plotting and some sort of automated stationkeeping, but the main uses of it would be maintaining otherwise unstable orbits, which can be of great use.

I don't think it would be more fun for everyone.

And even without auto stationkeeping, it'd still make for a much better experience.

I consider that 'better' word very subjective.

[roblamb98]

In my humble opinion, true N-body physics would be annoyance, not an improvement in KSP. Stable and deterministic orbits are comfortable, easy to understand, easy to handle. So many players can't even work with anything but an equatorial orbit, these would definitely not appreciate existence of lagrangian points because they would have no idea how to even find them, not mentioning how to place something into them.

So yes, a few advanced players would probably know how to handle them. For the rest, the learning curve for KSP would just become a bit steeper. More would not make it.

good job wording that.

[Joe32320]

In my humble opinion, true N-body physics would be annoyance, not an improvement in KSP. Stable and deterministic orbits are comfortable, easy to understand, easy to handle. So many players can't even work with anything but an equatorial orbit, these would definitely not appreciate existence of lagrangian points because they would have no idea how to even find them, not mentioning how to place something into them.

So yes, a few advanced players would probably know how to handle them. For the rest, the learning curve for KSP would just become a bit steeper. More would not make it.

This basically, aside from implementing it in the game that surely must increase computer load a bit, given that you could no longer have however many craft on rails when unfocused. I think 2 body physics is a good level of detail to have in the game.

Some of the maths is taught to most people by the time they leave school, and the variables such as orbital period are usually given in fairly easy to use formulas, so if people want to find out the information they discover in the game, it's easy to do so.

Adding that extra layer just means all the 2 body maths becomes an approximation, and that just obscures the players ability to understand what is going on, which is not a good thing.

Edited March 27, 2014 by Joe32320

[Vanamonde]

Some subjects have been discussed, suggested, and argued about until the sheer bulk of repetitive posting began to clog up the forum without ever resolving anything, and so those subjects were placed on the list of subjects not to suggest. Lagrange points and N-body gravity is, unfortunately, one of those subjects, so we'll be closing this thread now. Someone is working on a mod, however, which might be of interest.