void OnTriggerEnter(Collider other)
 {
     if (other.tag == "Boundary")
     {
         return;
     }
     Instantiate(explosion, transform.position, transform.rotation);
     game_ctrl.Gameover();
     Destroy(other.gameObject);
     Destroy(gameObject);
 }
 void OnTriggerEnter(Collider other)
 {
     if (other.tag == "Boundary" || other.tag == "asteroids")
     {
         return;
     }
     Instantiate(explosion, transform.position, transform.rotation);
     if (other.tag == "Player")
     {
         Instantiate(playerexplosion, other.transform.position, other.transform.rotation);
         game_ctrl.Gameover();
     }
     game_ctrl.addscore(score);
     Destroy(other.gameObject);
     Destroy(gameObject);
 }