Is there a way to program orbit of a ship to L2?

astroclu · 08 Sep 2020 10:54

Hi,
I'm working on a mod of JWST. I already got the 3D model but I'm wondering how to put orbit parameter so that it stays close to L2 lagrangian point,
Orbital parameters are generally defined with one gravitational reference and works fine in most cases but L2 is just one of these point where the gravity of 2 objects are to be taken into account, in this case the Sun and the Earth.
Is there a way to establish the orbit of my model to the Sun-Earth L2 point?

09 Sep 2020 12:40

You can use this little script.

Barycenter    "L2-Sol-Earth"
{
    ParentBody     "Sol"
    
    Orbit
    {
        Epoch          2451545
        RefPlane      "Ecliptic"
        Period         1.0
        SemiMajorAxis  1.0100045459234 // Behind Earth
        Eccentricity   0.0167086342
        Inclination    0.0
        AscendingNode  348.739
        LongOfPericen  102.93734808
        MeanLongitude  100.46645683
    }
}

I put a 'Barycenter' there, but you can also put an object there.
But it is not very accurate because it is a Kepler orbit, and the earth and moon (and the other planets in the solar system) use a special ephemeris file that is more accurate than Kepler's orbits.

For example, you could use something like this script for the telescope.

Object  "James Webb Space Telescope"
{
    Type           "Spacecraft"
    Model          "spacecraft/[path to the .sss file]/JWST.sss"
    ParentBody     "Sol"
    
    //MassKg          ???
    //Radius          ???
    //RotationPeriod  ???
    //RotationOffset  ???
    //Obliquity       ???
    //TidalLocked     false
    
    Orbit
    {
        Epoch          2451545
        RefPlane      "Ecliptic"
        Period         1.0
        SemiMajorAxis  1.0100045459234 // Behind Earth
        Eccentricity   0.0167086342
        Inclination    0.0
        AscendingNode  348.739
        LongOfPericen  102.93734808
        MeanLongitude  100.46645683
    }
}

astroclu · 10 Sep 2020 08:03

Thank you for that. I had tried that putting the object directly in that orbit but somehow Space Engine recalculated the orbit and since period is 1 year it was calculating semimajor axis to be 1 UA and was putting the JWST inside Earth, as you mentionned in a Keplerian way.
But you gave me a great idea with the barycenter. In fact that's even more realistic since JWST will be in a halo orbit around L2, so I'll use the barycenter, and then put the JWST in orbit around that barycenter.
I'm gonna try that and I hope soon I can publish the whole thing in the steam workshop or I'll get back to you.