The 1986 Challenger explosion shocked the world. We had become so complacent with the idea of space travel that seeing the shuttle blow up on live TV was something we couldn't even comprehend. The tragedy was bad enough. What's worse was NASA knew it was going to happen.

Rockets are big tubes of explosive fuel. They are under tremendous stress during launch, so engineers have to make them perfect. No component can be subpar, even down to the screws and seals. An important part of the shuttle's rocket boosters was their O-ring seals, which kept key joints in the rockets together. O-rings are made out of rubber, which, though strong, is susceptible to temperature changes.

Before the 1986 launch, the contractors who designed Challenger's O-rings realized that a recent cold spell had ruined them. Engineer Roger Boisjoly knew the rings wouldn't hold. He called up NASA to tell them that the space shuttle would blow up and they had to delay the launch. NASA refused. Poor Boisjoly went home knowing that the astronauts were going to die. The next day, they did.

For years afterward, Boisjoly blamed himself for the explosion, running over the events and punishing himself. But everybody else knew the truth. Boisjoly wasn't to blame. NASA killed their own astronauts.