OTD…June 25 and STS-50

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.

#OTD in 1992…Discovery launched with the first International Microgravity Laboratory.

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