Erratics movements from my rigidbody : why does it behave like that?

Hello. I'm making a basic MoonLander in 2D space. For that I control a spaceship by applying force or torque to its rigidbody. For some reason, when my object is spinning and moving, after a while it become crazy, and near teleport in random position. Here's a video to show you what it looks like :

http://www.youtube.com/watch?v=E-f7RfywI-k&feature=youtu.be

and my code : i din't include CollisionSettings because it's only used for collisions but the rest is as it is

 class ThrustSettings{
  var positiveThrust : int = 300;//define, in percentage, the power of the thrust over the gravity : acceleration = thrust/gravity
  var negativeThrust : int = 100;
  var sideThrust : int = 100;
  
  function ComputeThrust(input : float) : float{
  if(input>0.01) return positiveThrust;
  else return negativeThrust;
  }
 }
 
 class RotationalSettings{
  var angularAcceleration : float = 10;//the angular acceleration, in degree/sec^2
  var normalDrag : float = 0.0;
  var stabilizerStandardDrag : float = 1.0;
  var stabilizerStopDrag : float = 10.0;
  var maxStabilizerSpeed : float = 5.0;
  var stoppingSpeedStabilizer : float = 0.3;
  var stabilizerOn : boolean = true;
  
  //return the correct rotationnal drag
  function ComputeDrag (velocity : Vector3, input : float) : float{
  //check that the stabilizer is on, and that there is no input, and that the rotation speed isn't too high
  if(stabilizerOn && Mathf.Abs(input)<0.01 && Mathf.Abs(velocity.z*360/6.28)<maxStabilizerSpeed){
  if(Mathf.Abs(velocity.z*360/6.28)<stoppingSpeedStabilizer) return stabilizerStopDrag;
  return stabilizerStandardDrag;
  }
  else return normalDrag;
  }
 }
 
 /*End of classes definitions
 ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 */
 
 
 var positionalMovement : ThrustSettings;
 var rotationalMovement : RotationalSettings;
 var collisionSettings : CollisionSettings;
 var canControl : boolean =true;
 var tankSize : int = 30;//each unit here represent one second of full main thrust
 @HideInInspector
 var fuelLeft : float;
 var hullPoints : int = 100;
 var spawnPoint : GameObject;
 
 function Start(){
  collisionSettings.Setup(this.gameObject);
  fuelLeft=tankSize;
 }
 
 function FixedUpdate () {
  //retrieve input (range -1..1) and scale them to match gravity or degree instead of radian
  verticalThrust = Input.GetAxis("Vertical")*Physics.gravity.magnitude;
  lateralThrust = Input.GetAxis("Horizontal")*Physics.gravity.magnitude;
  turn = Input.GetAxis("Rotational")*2*3.14/360;
 
  if(fuelLeft<=0 && canControl) canControl = false;
  if(!canControl){verticalThrust=0.0; lateralThrust=0.0; turn = 0.0;}
  fuelLeft=Mathf.Max(0, fuelLeft-(verticalThrust+lateralThrust+turn)*Time.deltaTime);
  
  // compute the correct thrust force, depending on it's direction (up or down), then add correct relative vertical force to the rigidBody
  //also add lateral thrust if any
  rigidbody.AddRelativeForce(lateralThrust * positionalMovement.sideThrust/100,
  verticalThrust * positionalMovement.ComputeThrust(verticalThrust)/100,
  0, ForceMode.Acceleration);
  //add torque
  rigidbody.AddRelativeTorque(0, 0, turn * rotationalMovement.angularAcceleration, ForceMode.Acceleration);
  //Compute the correct drag for rotation
  rigidbody.angularDrag=rotationalMovement.ComputeDrag(rigidbody.angularVelocity, turn);
 }
 
 function SetSpawnPoint(spawn : GameObject){
  this.spawnPoint = spawn;
 }
 
 function ReceiveDamage(value : int){
  hullPoints=Mathf.Max(hullPoints-value, 0);
  if(hullPoints==0){
  Crash();
  }
 }
 
 function Crash(){
  if(spawnPoint){
  Destroy(this.gameObject);
  spawnPoint.SendMessage("Respawn", spawnPoint);
  }
  else Debug.LogError("no spawn point given to respawn", this.gameObject);
 }
 
 function OnCollisionEnter(collision : Collision) {
  for(contact in collision.contacts){
  collisionSettings.ApplyDamage(collision.relativeVelocity, contact.thisCollider);
  collisionSettings.UpdateTempColliders(contact);
  }
  collisionSettings.Switch();//this switch tempColliders with usedColliders and reset tempColliders
  //print("Collision enter --> " + collisionSettings.GetUsedColliders().ToString());
 }
 
 function OnCollisionStay(collision : Collision) {
  for(contact in collision.contacts){
  Debug.DrawRay(contact.point, collision.relativeVelocity);
  collisionSettings.UpdateTempColliders(contact);
  collisionSettings.Compare(contact, collision.relativeVelocity);
  }
  collisionSettings.Switch();
 }
 
 function OnCollisionExit(collision : Collision){
  collisionSettings.ClearColliders();
 }
 
 
 @script RequireComponent (Rigidbody)