Invert the rotation of a moving object

I need to rotate an object instantly by 180 degrees at the press of a button. The object is moving, I can rotate it on its Z axis using the joypad. Then, if I press a key I need my object to immediately invert its direction (ie: if it's moving left, it flips and starts moving right).

I tried using Quaternion.Inverse, but it's not working :/

Can you explain to me why not and point me to the right way to do it? (Sorry I'm kinda a newbie with Quaternions)

 var craftSpeed:Vector3 = Vector3 (20,0,0);
 var eulerAngleVelocity:Vector3=Vector3 (0,0,200);
 var controlAxis:String ="HorizontalP1";
 
 function Start () {
     rigidbody.velocity =  craftSpeed;
 }
 
 function FixedUpdate () {
     // this aligns the velocity with the right vector, it makes the plane move towards its nose
     rigidbody.velocity = Vector3.zero;
     rigidbody.velocity = transform.right * craftSpeed.magnitude;
 
     //this one just rotates my plane on input
     var deltaRotation : Quaternion = Quaternion.Euler(eulerAngleVelocity * Time.deltaTime* Input.GetAxis(controlAxis));
     rigidbody.MoveRotation(rigidbody.rotation * deltaRotation);
 
     //and this one SHOULD make the plane invert direction on input
     if (Input.GetKeyDown ("q"))
     {
         rigidbody.MoveRotation(Quaternion.Inverse(rigidbody.rotation));
     }
 }