Page 1 of 2 12 LastLast
Results 1 to 10 of 17

Thread: Lagrange points?

  1. #1

    Lagrange points?

    Anyone know if the L points exist in KSP and if so what the location/math for them is based on scale and gravity? Oh, and especially how you'd calculate them based on the impact of Minimums (which, pardon the pun, I assume would be minimal impact due to its much greater orbital diameter and smaller size/gravity compared to the Mun).

    Just thinking about in the future trying to setup a station and/or relay satellites in a few of the L points

    Thanks!

  2. #2
    L points are not simulated in KSP, since the way gravity is simulated uses only 2 bodies: the spacecraft and the planet/moon/star. Maybe a special way to implement them exists, but it is not planned as of now (nor is switching to n-body, AFAIK).
    You can still find their theoretical position using the formula of gravity: F = G m/r² where m is the mass of the body you are orbiting, and r is the distance to the center of gravity (altitude + radius).
    Kerbal Research & Random Stupidity (KSP videos) || Join #kspfrench to talk with French-speaking KSP players!

  3. #3
    Lagrangian points aren't existing in KSP, because of patched conics system specification (and for making Lagrangian points simulation possible we need major changes in game, not friendly for game performance anyway),
    Also Lagrangian points aren't too useful for KSP, because orbits around Lagrangian points are generally unstable (they only places when gravity forces of two bodies are equal, so they counteracting each other) ,Even small Deviation from L points center made orbit unstable, so you need surgical precision ,even for putting small satellites .
    It's not easy being green... Polska sekcja

  4. #4
    Lagrange points aren't places where the gravity forces between the two bodies are equal hey're places in which the gravity of both the larger and the smaller object provive gravitation in the proper direction to make at least limited stable orbits possible in 1:1 resonance.

    L1 (a point between the two objects), L2 (a point farther out from the central body than the satellite), and L3 (a point on the opposite side of the sattelite's orbit of the central body, a little farther out than the satellite) are only stable in limited directions, so objects tend not to stay there.

    L4 (60 degrees ahead of the satellite) and L5 (60 degrees behind) provide stability in all directions, so those can wind up occupied naturally. There are over five thousand known asteroids occupying the L4 and L5 points of Jupiter's orbit, and two of Saturn's moons have smaller moons occupying the L4 and L5 points in their orbits (Tethys has Telesto and Calypso, Dione has Helene and Polydeuces).
    Last edited by maltesh; 29th August 2012 at 09:29.
    Orbital parameters in the persistence.sfs file (Work in progress)
    KSP Celestial Body Details in v0.18.2.
    Timing Hohmann Transfers for interplanetary travel (WIP)
    YouTube Channel with KSP videos. Tetrahedral Satellite Challenge

  5. #5
    AKA Scott Manley
    Join Date
    Jul 2011
    Location
    Oakland, California
    Posts
    377
    Blog Entries
    1
    Quote Originally Posted by karolus10 View Post
    Lagrangian points aren't existing in KSP, because of patched conics system specification (and for making Lagrangian points simulation possible we need major changes in game, not friendly for game performance anyway),
    Also Lagrangian points aren't too useful for KSP, because orbits around Lagrangian points are generally unstable (they only places when gravity forces of two bodies are equal, so they counteracting each other) ,Even small Deviation from L points center made orbit unstable, so you need surgical precision ,even for putting small satellites .
    Please stop spreading the myth that proper orbital mechanics are somehow hard to simulate because of performance issues! The extra number crunching required is relatively trivial compared to things like the graphics and simulation or inter-part interactions of a rocket.

    It is simply that it would take developer time and there are many more things that developers could be doing that would affect a lot more people. The number of players who legitimately have interesting things to do with lagrange points is tiny, from a simple cost-benefit analysis devs are better to look elsewhere.

    Anyway, to clarify the nature of Lagrange points - they are places where the restricted 2 body system produces exact solutions to the equations of motion which can be solved analytically, these are places where the gravitation forces exactly balance the rotational psuedo forces and allow massless particles to follow orbital solutions that are exact.

    The main uses that we find in reality aren't that interesting. The comsat people would probably love to put a satellite in a halo orbit around the point on the far side of the mun, but that's not stable. L4/L5 are stable, but not that interesting from a utility purpose. And while you can use them for low energy transfer orbits, such orbits take a really long time and very few people will have the patience and skill to exploit weak stability boundaries (AKA the interplanetary super highway).
    Fly Safe

  6. #6
    Well, outside of the boundries of the game, the advantages of using the L points would be to place a satellite at L3 and at L4 or L5 and with 2 satellites you could have LOS communications to all points of the Moon, I mean the Mun, with the exceptions of deep craters in a few spots and a few spots on the poles that might render the satellite below the local horizon also due to terrain features. For the unstable L points, yes they are unstable, but it also doesn't require a significant amount of station keeping. A low powered ion engine would work great for long term positioning on one of those L points.

    You'd basically either have LOS directly from the main body to the satellite or you'd have the L4/5 to L3 relay to the far side of the satellite.

    Anyway, thanks for answering my question on whether they existed in the game or not.

  7. #7
    Using L4 and L5 as relays for munar communications would double the light-lag time. You're better off having three sats in the Munar orbit high enough above the surface that each one has LOS to the other two.
    Orbital parameters in the persistence.sfs file (Work in progress)
    KSP Celestial Body Details in v0.18.2.
    Timing Hohmann Transfers for interplanetary travel (WIP)
    YouTube Channel with KSP videos. Tetrahedral Satellite Challenge

  8. #8
    Depends. You would have larger lag, but you'd also have greater cost involved in placing those satellites. In the context of the game (with no current implemented cost/resource structure), at least additional time required to place them in combination with addional objects for the game to have to track and for the Remotetech mod, additional required antennas on the satellites. Current lag, with Remotetech mod at least, is low enough that a doubling of the lag is still on the order of being insignificant.

  9. #9
    There's no real extra time or cost involved.. You propose two satellites at the distance of the Mun (L4, and L5), and a third satellite farther out than the Mun (which would be L2, not L3), that the game can't currently model.

    Easier and quicker to just put three satellites in a circular orbit just inside the Munar SOI, separated by 120 degrees in their orbits, and ignore the lagrange points entirely.
    Orbital parameters in the persistence.sfs file (Work in progress)
    KSP Celestial Body Details in v0.18.2.
    Timing Hohmann Transfers for interplanetary travel (WIP)
    YouTube Channel with KSP videos. Tetrahedral Satellite Challenge

  10. #10
    Spherical Scientist NovaSilisko's Avatar
    Join Date
    Jul 2011
    Location
    Central Michigan
    Posts
    4,438
    Blog Entries
    2
    The single most important reason is this: An n-body system makes it impossible to easily predict what's going to happen ahead of time. With the two-body system in place now, you can set yourself on an interplanetary trajectory, then observe the SoI shifts hundreds of days in advance. With an n-body system, however, you would have to simulate the entire path ahead of time, instead of simply doing a bit of math to predict where you'll be. Also, it renders timewarp basically impossible but that's another story.


    As such, it's not going to happen, ever. The advantages of the patched conics system are far too great.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •