The year 1968 is memorable for any number of reasons, science writer Zimmerman reminds us, not the least of which was the historic flight of Apollo 8, the first manned space flight to slip out of Earth's gravitational tethers. Apollo 8, with Frank Borman, James Lovell, and William Anders aboard, blasted off in late December of 1968, its intention to journey beyond Earth's orbit, slip into a lunar orbit, then escape again, and return. Its success was a momentous occasion--the frontiers of space had been effectively pushed out, way out--although it was overshadowed six months later by the actual lunar landing. Zimmerman, a science and technology writer who has contributed to American Heritage, the Sciences, and other publications, has chosen two aspects of the Apollo 8 mission to emphasize. First, he depicts a space program then still the venue of the hero/ace pilot who, sacrificing family priorities and personal safety, was the Cold Warrior nonpareil. In relating this, Zimmerman situates the flight within the context of that electrifying and appalling year--the Tet Offensive, the Soviet invasion of Czechoslovakia, student uprisings, the Chicago Democratic convention, the assassinations of Martin Luther King and Robert Kennedy--when more than a spacecraft appeared to be spinning out of orbit. Zimmerman keeps in check this potentially hyperbolic drama, giving it a nice steady rhythm, but he loses that touch when he goes after his second theme, attempting to infuse the event with righteousness. It showed the world, Zimmerman claims, an ""American vision of moral individuality, religious tolerance and mutual respect,"" though it's difficult to see the space race as an expression of such respect or to decipher the meaning of ""moral individuality"" in this context. Zimmerman does realize that perhaps the most lasting achievement of Apollo 8 is a photograph of Earthrise over the Moon. Never before had our planet seemed so small, so lonely, so vulnerable--or so priceless.