OTD…May 4 and STS-30

#OTD in 1995…Endeavour launched to deploy and retrieve solar satellite and Wake Shield Facility

#OTD in 2000…Discovery launched on the 100th space shuttle mission

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.