On January 28, 1986, the space shuttle Challenger exploded. All seven astronauts were killed. Eyewitness Frank Mottek described the scene: Just then we both stood up and looked up at the shuttle making its way farther and farther into the sky. Suddenly, I was struck by a pattern I had never seen before. From our vantage point, it appeared that an extra flame was trailing from the shuttle. Then, in that split second, a silent fireball appeared in the sky. Then there was silence, the silence of alarm. . . Investigations later revealed that two rubber O-rings, which were designed...