All eyes were watching the Challenger lift off, carrying aboard the first ordinary U.S. civilian. Christa McAuliffe, a high school teacher from New Hamshire, won a competition making her one of seven crew members to travel into space. The space shuttle took off with millions watching, including McAuliffe's students and family. Seventy-three seconds after take-off it exploded, killing all seven crew members on board. Accident investigators determined that the cause of the explosion was a faulty "O-ring" seal in one of the solid-fuel rockets. NASA grounded astronauts for more than two years while the shuttle was redesigned.