After rounding the moon, viewing a solar eclipse and traveling farther than any human had before, the four astronauts of Artemis 2—the first manned lunar mission in more than five decades—will re-enter Earth’s atmosphere tomorrow. Beyond those milestones, the mission represents a step toward establishing a long-term human presence in space and sets up the moon as a lens for considering the future of exploration. “The moon is definitely where it’s at,” says Robert Braun, an aerospace engineer...