"It is the worst disaster in the history of the American space program." Forty years ago on January 28, 1986, the space shuttle Challenger exploded 73 seconds after liftoff from Cape Canaveral, killing all seven crew members, including school teacher Christa McAuliffe from New Hampshire, who had won a national competition to become the first teacher in space. Peter Jennings anchored ABC's World News Tonight from Washington, with John Quiñones leading off the broadcast's coverage. | ABC World New