OTD…May 11 and STS-125

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

#OTD in 2000…Atlantis launched on a mission to make the International Space Station a home in orbit

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.