CAPE CANAVERAL, Fla. - Twenty years ago, space shuttle Challenger blew apart into jets of fire and plumes of smoke, a terrifying sight witnessed by the families of the seven astronauts and by those who came to watch the historic launch of the first teacher in space. The disaster shattered NASA's spit-shined image and the belief that spaceflight could become as routine as airplane travel. The investigation into the accident's cause revealed a space agency more concerned with schedules and public relations than safety and sound decision-making.