Draw an orbital trajectory of a ship

Hi guys i'm working on a game in which it will be possible to take a spaceship to go between differents planets. I already have a Sun with some planets turning around with a simple script :

 #pragma strict
 
     var rotation : Quaternion;
     var radius = Vector3(5,0,0);
     var degrees:float = 10;
     var moonCurrentRotation = 0.0;
     var planete : GameObject;
      
     
     function Update(){
     
     moonCurrentRotation += degrees*Time.deltaTime;
     rotation.eulerAngles = Vector3(0, moonCurrentRotation, 0);
     
     transform.rotation.eulerAngles = Vector3(0, moonCurrentRotation*30, 0);
     transform.position = rotation * radius + planete.transform.position;
     
     
     }

I have an other script which implement circular gravity so i can walk on the planet, take of, make an orbit and go to the moon (on foot ^^). So my problem is to draw the trajectory line of my ship where we can find the apoapsis and periapsis. In fact i would like to make something similar as you can see in Kerbal Space Program. I'm a beginner and i don't know what to do at first. I know a little bit mechanics but i don't know how i can use it for tracing a trajectory.

Thanks in advance for answers and excuse me for my english i'm french ^^.