object placement on sphere, rotation deform

So i have a Tower Defense game that im making, and im attaching my towers to a sphere wich is the game level. But the tower is deformed when an enemy comes in range and it rotates towards it.

 void Update ()
     {
 
         if (target) {
             aim_pan.LookAt (target);
             aim_pan.eulerAngles = new Vector3 (0, aim_pan.localEulerAngles.y, 0);
             aim_tilt.LookAt (target);
 
             pivot_pan.rotation = Quaternion.Lerp (pivot_pan.rotation, aim_pan.rotation, Time.deltaTime * turnSpeed);
             pivot_tilt.rotation = Quaternion.Lerp (pivot_tilt.rotation, aim_tilt.rotation, Time.deltaTime * turnSpeed);
 
             if (Time.time >= nextFireTime) {
                 FireProjectile ();
             }
         }
     
     }

this is what rotates the tower, when i first place it its rotation is correct. aim_pan and aim_tilt are child objects. The base that rotates arount the y and the top that tilts up and down

     GameObject newStructure = Instantiate (allStructures [structureIndex], 
 lastHitObject.transform.position, lastHitObject.transform.parent.rotation) as GameObject;

this is the instantiation of the tower, lastHitObject is a child plane to the sphere world. its rotated correctly aswell.