I'm a big fan of history and space and I'm not sure if I'd ever even seen these cards before.
I'm sure Series 1 was similar, but the cards range from the early days of NASA and Space Exploration right up to the present day, which was 1991 when this set came out. Very cool. Plus the back of the cards have a ton of great information. This set would have been great had it included some autographs of these American Heroes.