Fixed force in direction of touch.

Hello, I'm making a 2D game based in space. Right now I use AddForce to push my rigidbody in the direction of where I touch. My problem is that the force is greater the further I touch from my rigidbody. I've tried using normalise but I still have the same problem. I want to be able to have my rigidbody move at a fixed value force in the direction of where I touch so how far I touch has no effect.

Here's my code: C#

     public float Speed = 10;
 
     private Vector3 force;
     private Vector3 direction;
     private Vector3 touchPosition;
     private Vector3 touchPosAtScreen;
 
     // Update is called once per frame
     void Update () 
     {
         foreach (Touch touch in Input.touches)
         {
             if (touch.tapCount < 2 && touch.phase == TouchPhase.Ended)
             {
                 touchPosition = touch.position;
                 touchPosAtScreen = Camera.main.ScreenToWorldPoint(touchPosition);
 
                 direction = (touchPosAtScreen - rigidbody.transform.position);
 
                 force = (direction.normalized * Speed);
 
                 rigidbody.AddForce(force);
 
                 Debug.Log("Force = " + force);
             }
         }

Thanks,

Giles.