Book excerpt: Winner of the Summerfield Book Award! This best-selling, comprehensive text documents the fundamental theoretical developments in astrodynamics and space navigation that led to man's ventures into space. It includes the essential elements of celestial mechanics, spacecraft trajectories, and space navigation, as well as the history of the underlying mathematical developments. The material presented in the text represents a 25-year evolution in course material developed by Dr. Battin. Former students who benefitted from this material include three of the astronauts who walked on the moon. The text format offers flexibility for the user. Chapters are largely independent of each other and may be read or taught in any order, offering the opportunity to organize an undergraduate or graduate course that meets the needs of students having various levels of background and preparation. Further, the book covers more subject matter than is covered in a single course of instruction, thereby motivating students to stray from the beaten path of the classroom.