public override void Update()
        {
            // don't do anything if the alien is dead
            if (!AlienAlive)
            {
                return;
            }

            // Update the position of the sprite
            base.Update();

            if (spriteValue.IntersectsWith(rocketValue.spriteValue))
            {
                AlienAlive = false;
                rocketValue.TakeDamage();
                spriteValue.Hide();
                return;
            }
        }