Nearly three years after the government began $100 million worth of tests on lasers that could thwart missiles aimed at planes, the Homeland Security Department says the systems are too fragile and expensive to put on commercial jets. And despite concerns that a terrorist armed with a shoulder-fired missile could fire on a jet carrying Americans, Homeland Security spokesman Christopher Kelly says it will be 18 more months before analysts determine whether the defense systems can be made to last and installed without a hefty price tag. Full Story