Vostok and Columbia
 

Old article from 2011 here about the two highly significant spaceflights that took place exactly twenty years apart, April 12th 1961 and April 12th 1981:

https://www.nasaspaceflight.com/2011...years-shuttle/

A heck of a lot happened in those twenty years..in the forty years since....????

I'm slightly too young to remember Vostok 1 but I do recall Columbia. All hunky dory or so it seemed at the time but Rowland White's book Into the Black tells the story of concerns about missing thermal tiles and how NASA were able to examine damage to the Orbiter via a rather clandestine method!! Must reread, and also John Young's book...