The concept of aeroassisting for orbital transfer has been recognized as one of the critical technologies for pioneering the space frontier. In space transportation systems, aeroassisting (or aerobraking), defined as the deceleration resulting from the effects of atmospheric drag upon a vehicle during orbital operations, opens new mission opportunities, especially with regard to the establishment of the permanent Space Station Freedom and space explorations to other planets such as Mars. The main areas of research reported in this monograph are atmospheric entry problem by the method of matched asymptotic expansions, coplanar and non-coplanar orbital transfers with aeroassist technology, orbital plan change with aerocruise, and neighbouring optimal guidance. A special feature is the bibliography which will provide the reader with a literature status for further research.