Advances in Space Science and Technology, Volume 3 presents the development in space science and space technology. This book considers the engineering problems applicable to the attainment of astronautical objectives and examines a critical aspect of manned space flight. Organized into eight chapters, this volume begins with an overview of the role of geology in lunar exploration programs. This text then discusses the preliminary considerations of Venus as an astronautical objective. Other chapters consider a schematic representation of the positions of the Sun, Earth, Mars, and Venus at the approximate times of closest approach of the latter two planets to Earth. This book demonstrates as well that a fuller understanding of each individual body will contribute much to an over-all understanding of the nature and history of the Solar System itself. The final chapter deals with the phenomenon of weightlessness associated with orbital flight. This book is a valuable resource for astronomers, scientists, and engineers.