From Project Mercury to Gemini to Apollo, our country soared with the heroes of the cosmos and glorified in our achievements. Then, on one historic day, we achieved a crowning moment in the epoch of mankind: We set foot on the moon and walked the surface of a lunar landscape, stark and forbidding. We had journeyed to a heavenly body, separate and mysterious from our Earth, but the question remained: What next? We answered with more moonwalks and exploration. The Saturn rocket gave way to the Space Shuttle and 135 flights of fantastic engineering called Columbia, Challenger, Discovery, Atlantis, and Endeavor, plus the launching of dozens of unmanned vehicles.