See what I mean? They'll commemorate anything, anytime. Not that the MERCURY SEVEN (71A: & 1D: first American astronauts) don't deserve fêting, they do, it's just that, well, what about Earth Day!?
All that aside, however, this was a decent puzzle. Working in all seven names, as well as the MERCURY, SEVEN, ROCKET (9D: NASA vehicle), and SPACERACE (12D: Old U.S./Soviet rivalry), and even what I'm calling bonus theme commentary, ATROPHIED (21D: Weakened due to inactivity) (like America's manned space program) - that's a lot of fill!
You end up with a little bit of KAON (38D: Unstable subatomic particle) (unstable fill?), OTOE, and Crossword's favorite family, ALOU (35D: Baseball family name), but there's plenty of good non-theme stuff, too. VAMOOSE (17A: Blow the joint), TORRID (31A: Not just hot), GNASH (8D: Grind), and my favorite clue today 13D: It's a crock (OLLA). Hah!
I liked it.