OTD…June 21 and STS-57

#OTD in 2007…NASA’s Dawn probe launched to explore the uncharted worlds of Vesta and Ceres in the heart of the asteroid belt.

#OTD in 2002…Atlantis launched the outward expansion of the space station’s truss backbone

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.