MetroWest Daily News FRAMINGHAM, Mass. – Thirty-five years ago, the space shuttle Challenger exploded just over a minute after liftoff, killing all seven crewmembers, including New Hampshire schoolteacher Christa McAuliffe. NASA leaders, retired launch directors, families of fallen astronauts and space fans marked the 35th anniversary on Thursday, vowing never to forget the seven who died during liftoff. The Challenger explosion on Jan. 28, 1986, happening just 73 seconds after liftoff due to an O-ring seal failure, was the first fatal accident for NASA since 1967. The millions who watched the liftoff were inspired by McAuliffe, 37, who was the first American civilian to board a space shuttle. She was chosen from a pool of 11,000 teachers to board the Challenger mission as part of a NASA program called the "Teacher in Space Project."