SPACE CENTER, Houston (AP) One week after the space shuttle Columbia broke apart as it streaked over Texas just minutes from home, NASA still has more questions than answers. Searchers have recovered remains of all seven astronauts and more than 12,000 shards of metal, wires and debris that rained down across two states. But the findings so far have yielded few clues. The most significant discovery has been a 2-foot section of shuttle wing, including the carbon-covered leading edge designed to protect Columbia