Astronaut's Wife Found Valentine's Day Card After He Died in Space Shuttle Challenger Explosion

This story from the PEOPLE archives has been updated to mark the 34th anniversary of the Challenger Space Shuttle tragedy. 
The images are indelible: On the clear, cold morning of Jan. 28, 1986, the space shuttle Challenger embarked on its 10th milestone mission. But disaster struck 73 seconds later when the shuttle exploded, killing the seven astronauts on board.
The shuttle commander was Dick Scobee. He was joined by six other astronauts: Michael J. Smith, Ronald McNair, Ellison Onizuka,