On 28 January 1986, people watched in horror as Challenger, one of America's four space shuttles, erupted into a ball of flames just over a minute after lift off, killing everyone on board. Sue MacGregor looks back on one of Nasa's darkest tragedies with Scobee Rodgers, the widow of Challenger space shuttle commander Richard "Dick" Scobee; Steve Nesbitt, Nasa chief commentator; astronaut Norman Thagard; and Allan McDonald, former Morton Thiokol director of the Space Shuttle Rocket Booster Project.