<p>SAN JOSE, Calif.(AP) - As the space shuttle program took shape in the late 1960s, engineers had to find technology that could withstand the heat of re-entry without being too heavy, unreliable or costly.</p>
<p>They settled on the small silica tiles that brought shuttles home safely more than 100 times, but have fallen under suspicion in Saturday's loss of Columbia as it descended over Texas.</p>