Kerbal - Mun Lagrange 1?

[Wijbrandus]

Has anyone determined the Lagrange 1 point between Kerbal and the Mun? Does it even exist with Minmus involved?

If it does exist, I would be very interested in finding out the details. I am finding the calculations (considering Minmus) to be a little beyond my ability at the moment.

Thanks!

[Nibb31]

There are no Lagrange points in KSP.

[Wijbrandus]

Well, that is disappointing, but thank you for the quick answer.

[hydropos]

Follow-up question: are there any regions/trajectories that would result in a craft switching back and forth between kerbin and the Mun to act like a Lagrange point?

[Streetwind]

KSP doesn't have Lagrange points because it uses the patched conics model for simulating gravity interactions. Only one celestial body can affect your ship with gravity at any one time. That means you're trying to balance on an infinitessimally narrow knife's edge - no matter what you do, you will fall down one side. At best, you could get a trajectory where you drop out of the Mun's SoI and then get recaptured shortly after, but this definitely won't be stable for any length of time.

What you could do is try to assume an orbit perfectly identical to that of the Mun, and position yourself a few hundred meters ahead or behind the edge of the Mun's SoI. This would be functionally identical to a Lagrange point in the sense that the craft will maintain a fixed distance to both the Mun and to Kerbin forever, but it wouldn't be in between the Mun and Kerbin.

[Wijbrandus]

What you could do is try to assume an orbit perfectly identical to that of the Mun, and position yourself a few hundred meters ahead or behind the edge of the Mun's SoI. This would be functionally identical to a Lagrange point in the sense that the craft will maintain a fixed distance to both the Mun and to Kerbin forever, but it wouldn't be in between the Mun and Kerbin.

Thank you for the explanation Streetwind.

In regards to your idea, I think that is absolutely brilliant, and that may be an excellent solution for my problem. Thanks!

[Wijbrandus]

As an afterthought, if we can only be affected by one gravity well, it is theoretically possible to establish a geosynchronous orbit around Kerbal that is in line with the Mun. While this would not be a true Lagrange point, it might meet my intention of a halfway station.

Any suggestions on how I might actually establish that? Most days I'm pretty lucky just getting into orbit with fuel left, but sometimes I can follow a flight plan pretty well.

[SuperFastJellyfish]

As an afterthought, if we can only be affected by one gravity well, it is theoretically possible to establish a geosynchronous orbit around Kerbal that is in line with the Mun. While this would not be a true Lagrange point, it might meet my intention of a halfway station.

Any suggestions on how I might actually establish that? Most days I'm pretty lucky just getting into orbit with fuel left, but sometimes I can follow a flight plan pretty well.

AFAIK, you would have to be under constant thrust to hold position in line with Mun and Kerbin. As soon as you use the warp function, you would quickly outpace Mun as lower orbits travel faster horizontally.

[Drunkrobot]

Here's a questions: Given the masses and positions of Kerbin and the Mun, exactly where in the Kerbin/Mun system would the Lagrange Points be, assuming that gravity fields in KSP worked in the same way it does in real life? Maybe at some point in the future, the devs could implement some very small spheres of influence positioned where the L.P.s would be, and a craft that entered those SOIs could get captured, and "orbit" the point?

[Nibb31]

As an afterthought, if we can only be affected by one gravity well, it is theoretically possible to establish a geosynchronous orbit around Kerbal that is in line with the Mun. While this would not be a true Lagrange point, it might meet my intention of a halfway station.

Any suggestions on how I might actually establish that? Most days I'm pretty lucky just getting into orbit with fuel left, but sometimes I can follow a flight plan pretty well.

You can't have two orbits in phase at different altitudes. Orbital speed is a function of orbital altitude.

[Nibb31]

Here's a questions: Given the masses and positions of Kerbin and the Mun, exactly where in the Kerbin/Mun system would the Lagrange Points be, assuming that gravity fields in KSP worked in the same way it does in real life? Maybe at some point in the future, the devs could implement some very small spheres of influence positioned where the L.P.s would be, and a craft that entered those SOIs could get captured, and "orbit" the point?

This has been suggested and rejected like hundreds of times since KSP exists. That's not how Lagrange points work, so it would be pointless.

[Streetwind]

Maybe at some point in the future, the devs could implement some very small spheres of influence positioned where the L.P.s would be, and a craft that entered those SOIs could get captured, and "orbit" the point?

That's not a bad idea in theory, since it's actually possible IRL to "orbit" Lagrange points because the interaction from both gravity wells with its own movement can temporarily lock a spacecraft into repeating movement patterns near the point, which is far more stable than trying to sit still in the nullzone itself. This is called a halo orbit. Technically they exist only in the mathematical three-body problem and the real world needs to make do with the far less stable Lissajous orbit that won't hold for long around L1, L2 and L3 without stationkeeping, but L4 and L5 are much more stable.

As a simplification, KSP could use tiny SoI's about a kilometer across or so where the player can put a ship into a tiny, near-stationary orbit around a center of very weak gravity but no actual celestial body there.

This issue is that five Lagrange points exist for any three-body problem (i.e. any two celestials orbiting a common barycenter plus your spaceship), and as such, KSP would need a very, very large number of such points. And then there's higher n-body systems - for starters, Kerbin itself is one, with its two moons. Maybe the Lagrange points for the Kerbin-Mun system and the Kerbin-Minmus system respectively end up positioned such that Minmus could move its SoI over Kerbin-Mun L2, or the Mun could move its SoI over Kerbin-Minmus L1 or L3? In such a system, these points would be practically nonexistant because the close periodic passing of a gravity well would completely obliterate it. That's where having small static SoI's breaks down in a hurry.

Edited February 12, 2014 by Streetwind

[FanaticalFighter]

There's a mod being developed by Eggrobin called Principia that puts N-Body physics into KSP. With N-Body Physics, all masses effect all others (well, actually, I'm not too sure if Principia does this, as most of the time the effect by masses really far away is ignored, and of course other crafts are ignored as well) and therefore we'll have our Lagrange points.