In laymans terms: The external foam from the external tank is as hard as ice, from the very cold liquid oxygen and liquid hydrogen inside the tank. The shuttle tiles are hard but BRITTLE. When hard, strikes hard and brittle, hard and brittle loses. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>
It's a matter of mass and velocity.<br /><br />Imagine your buddy throws a half dollar coin at you - annoying. Now imagine you're shot with a .40 cal 180 grain bullet - you're dead.<br /><br />Same mass, different velocity.