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Space shuttle astronauts training on the KC-135 zero-g aircraft

Space shuttle “Teacher in Space” astronaut Christa McAuliffe (at top), her backup crew member, Barbara Morgan (bottom), and Payload Specialist Greg Jarvis (top right) training on the KC-135 zero-g aircraft. STS-51-L was the 25th mission of the NASA Space Shuttle program and the final flight of Space Shuttle Challenger. Planned as the first "Teacher in Space" Project, in addition to observing Halley's Comet for 6 days, the mission never achieved orbit; a structural failure during ascent 73 seconds after launch from Kennedy Space Center on January 28, 1986, killed all seven crew members and destroyed the orbiter. Morgan was not onboard the ill-fated STS-51-L mission of the Space Shuttle Challenger; she later trained as a Mission Specialist and flew on the STS-118 mission of Space Shuttle Endeavor in August 2007, more than 20 years after the Challenger disaster. (Source: NASA [S85-44833]. Public domain.)