import bpy
from math import sqrt
from mathutils import Vector
from random import random

class ModalTimerOperator(bpy.types.Operator):
    """Operator which runs its self from a timer"""
    bl_idname = "wm.orbitsim"
    bl_label = "Orbit visualiser"

    _obj = None
    _dt = None
    _p = None
    _v = None
    _mu = None
    def modal(self, context, event):
        if event.type in {'RIGHTMOUSE', 'ESC'}:
            print("Stopping script")
            return {'CANCELLED'}

        if event.type == 'TIMER':
            a = -self._mu/self._p.magnitude**3*self._p
            self._p = self._p + self._v*self._dt + 0.5*a*self._dt**2
            self._v = self._v + a*self._dt
            self._obj.location = self._p
        return {'PASS_THROUGH'}

    def execute(self, context):
        print("NEW RUN")
        self._dt = 0.04
        self._mu = 5
        wm = context.window_manager
        self._timer = wm.event_timer_add(self._dt, window=context.window)
        wm.modal_handler_add(self)

        self._p = Vector((10,0,0))
#Circular orbit:
        #self._v = sqrt(self._mu/self._p.magnitude)*Vector((random(),random(),random())).cross(self._p).normalized()
#Elliptic orbit:
        semi_major = (random()+0.6)*self._p.magnitude
        self._v = sqrt(self._mu*(2/self._p.magnitude-1/semi_major))*Vector((random(),random(),random())).cross(self._p).normalized()

        self._obj = bpy.data.objects['Cube']
        self._obj.location = self._p

        return {'RUNNING_MODAL'}


    def cancel(self, context):
        wm = context.window_manager
        wm.event_timer_remove(self._timer)

def register():
    bpy.utils.register_class(ModalTimerOperator)


def unregister():
    bpy.utils.unregister_class(ModalTimerOperator)

if __name__ == "__main__":
    register()
    bpy.ops.wm.orbitsim()