OTD…July 23 and STS-93

#OTD…The first launch of Challenger in 1983 and Columbia’s shortened Spacelab mission in 1997

The first crew to inhabit Skylab — Conrad, Weitz and Kerwin — launched today in 1973 for a 28-day mission that successfully made critical repairs, brought the station into operation and conducted solar astronomy, Earth resources and medical experiments.

#OTD in 1985…Discovery launched on the first classified space shuttle mission for the Department of Defense. Watch the liftoff: