Teleport active vessel to another vessel

[whoshotdk]

This is my first foray into plugin development and I know there are many plugins that do teleport stuff already, but this is a learning experience for me.

Even after checking code from other plugins, I’m having issues getting this to work…

I’ve built two ‘Jump Gates’ - Jump Gate LKO (in 100km orbit) & Jump Gate HKO (in 1000km orbit). Each of these has a Jump Gate Device part attached.

I have player Ship in Kerbin orbit close to Jump Gate LKO.

Jump Gate Device on Jump Gate LKO has been assigned Jump Gate HKO as a destination via right-click menu.

With Player Ship active, I right click the Jump Gate Device attached to Jump Gate LKO and click ‘Jump’.

What is supposed to happen:

Player ship instantly teleports to Jump Gate HKO, matching its orbit. The player ship should teleport, the Jump Gates should not.

What actually happens:

Player ship does teleport to HKO, but the orbit is not set correctly - Player ship is now on escape trajectory. Furthermore - and this is the *really* strange bit - the Jump Gate HKO has also had its orbit changed; it’s also now on an escape trajectory too. Jump Gate LKO is fine though.

Heres the relevant part of the code (part of ‘JumpDevice : PartModule’ class:

    [KSPField(isPersistant = true, guiActive = true, guiName = "Target")]
    public string targetJumpGateName = "Not set";

    [KSPEvent(guiActiveUnfocused = true, externalToEVAOnly = false, unfocusedRange = 50f, guiName = "Jump")]
    public void JumpEvent() {

        // At this point, targetJumpGateName has been set to a destination; i.e ‘Jump Gate HKO’.
        Vessel targetJumpGate = findVesselByName(targetJumpGateName);

        // Check the Jump Gate target vessel exists
        if(targetJumpGate) {

            // Check the Jump Gate target has a Jump Gate Device - i.e is it actually a Jump Gate
            if(hasJumpGateDevice(targetJumpGate)) {

                Vessel activeVessel = FlightGlobals.ActiveVessel;

                activeVessel.GoOnRails();

                // I probably need to add some distance between ship and jump gate so as not to collide, but for now they’re not
                activeVessel.SetWorldVelocity(targetJumpGate.orbit.GetVel());
                activeVessel.SetPosition(targetJumpGate.GetWorldPos3D());

                activeVessel.GoOffRails();

            } else {

                // Target vessel does not have a Jump Gate Device part
            }
        } else {

            // Target not found (might’ve been deleted)
        }
    }

    public Vessel findVesselByName(string _name) {

        List<Vessel> allVessels = FlightGlobals.Vessels;

        foreach(var vessel in allVessels) {

            if(vessel.GetName() == _name) {

                return vessel;
            }
        }

        return null;
    }

The positioning code is based on plugin source I found here: http://forum.kerbalspaceprogram.com/threads/16684-Hyperjump-System-Work-in-Progress-Models-wanted-Demo-Attached?highlight=teleport+orbit

I’ve also tried creating a new orbit (see below) but I get the same problem (though this time its a sub-orbit straight into Kerbin, and the destination Jump Gate HKO still gets moved too, which it shouldn’t):

    Orbit newOrbit = new Orbit(

        targetJumpGate.orbit.inclination,
        targetJumpGate.orbit.eccentricity,
        targetJumpGate.orbit.semiMajorAxis,
        targetJumpGate.orbit.LAN,
        targetJumpGate.orbit.argumentOfPeriapsis,
        targetJumpGate.orbit.meanAnomalyAtEpoch,
        targetJumpGate.orbit.epoch - 1, // In theory this’ll give us some distance so the ship doesn’t collide with the destination Jump Gate
        targetJumpGate.orbit.referenceBody
    );

    activeVessel.orbitDriver.orbit = newOrbit;
    activeVessel.orbitDriver.orbit.Init();
    activeVessel.orbitDriver.orbit.UpdateFromUT(Planetarium.GetUniversalTime());

That orbit code is based on what I could find & understand of the HyperEdit source (https://github.com/Ezriilc/HyperEdit/blob/master/Model/OrbitEditor.cs).

So I need help with two problems really:

1. Getting the ship into a correct orbit nearby the destination Jump Gate

2. Getting the destination Jump Gate to keep its damn orbit

Any help would be much appreciated!

Thanks

Dave

[sashan]

Check HyperEdit, it does that successfully. As far as I understand it simply edits orbit to match another body, with small difference in epoch.

[whoshotdk]

Thanks for the reply Sashan,

I am already looking at the HyperEdit code; specifically here:

https://github.com/Ezriilc/HyperEdit/blob/master/Model/OrbitEditor.cs

In particular the 'HardsetOrbit' method. However, I must be missing something as when I use very similar code to what I find in HyperEdit, I still have the problem I mentioned above.

I'll try looking over HyperEdit code again and see if I can disseminate the procedure it uses to get a stable orbit.

[whoshotdk]

I fixed it; I found that the problem was two-fold;

First up, I needed to set the orbit of the vessel like I did in the second section of code I posted above. However, the line:

    activeVessel.orbitDriver.orbit = newOrbit;

was doing too much; I only needed to copy certain properties of the orbit, not all of them. So that line is replaced with:

    activeVessel.orbitDriver.orbit.inclination = newOrbit.inclination;
    activeVessel.orbitDriver.orbit.eccentricity = newOrbit.eccentricity;
    activeVessel.orbitDriver.orbit.semiMajorAxis = newOrbit.semiMajorAxis;
    activeVessel.orbitDriver.orbit.LAN = newOrbit.LAN;
    activeVessel.orbitDriver.orbit.argumentOfPeriapsis = newOrbit.argumentOfPeriapsis;
    activeVessel.orbitDriver.orbit.meanAnomalyAtEpoch = newOrbit.meanAnomalyAtEpoch;
    activeVessel.orbitDriver.orbit.epoch = newOrbit.epoch;
    activeVessel.orbitDriver.orbit.referenceBody = newOrbit.referenceBody;

In addition to copying the orbit, I also needed to set the vessel position and velocity; like so:

    // Add distance between player vessel and target jump gate (this is temporary, needs something more intelligent really)
    Vector3d offset = new Vector3d(10, 0, 0);

    // Set position and velocity of player
    activeVessel.SetWorldVelocity(targetJumpGate.orbit.GetVel());
    activeVessel.SetPosition(targetJumpGate.GetWorldPos3D() - offset);

Since getting this to work I’ve majorly refactored my code so the above is not quite what I’m using right now. However I thought it’d be helpful to have this here nonetheless.

If/when I upload my Jump Gate plugin I’ll add a link to the full source here.

Dave

[lo-fi]

I'm really interested to see your source, as I think it'll solve a few problems for a project of mine. Looking forward to the link

Thanks for posting what you have already!

[whoshotdk]

Hey

I'm looking forward to getting this mod working properly!

I've spent the past few days learning blender and have made a stock-ish looking Jump Device; this way you can build your own Jump Gate / Beacon out of your own parts rather than being stuck with just one model. You can also place multiple devices on one vessel so that it becomes a sort of intergalactic train station

Still got one final problem to fix: the jump beacon you start from is still getting its orbit changed when the teleport completes. I've still no idea why this is happening but I'm working on it.

If I do get this thing working properly I'll post all the code with comments someplace and link it here!