http://www.newsweek.com/how-nasa-has-made-space-travel-safer-since-challenger-1674242

In the 36 years since the space shuttle Challenger exploded over the Florida skies, the National Aeronautics and Space Administration (NASA) has made a number of advancements in ensuring that space travel is as safe as possible.

Seventy-three seconds into its January 28, 1986, flight out of Cape Canaveral, the Challenger violently broke apart, resulting in the deaths of all seven astronauts aboard. It was the first fatal accident involving an in-flight American spacecraft.