OTD…Oct. 20 and STS-73

#OTD in 2001…Discovery launched on an International Space Station crew exchange mission

#OTD in 1983…Challenger launched with America’s first woman astronaut. Watch the launch:

Today marks the 40th anniversary — July 20, 1976 — of the first U.S. robotic landing on another planet by the Viking 1 spacecraft on Mars.