Book excerpt: Proceedings of the XXth International Astronautical Congress compiles selected papers presented at the 20th International Astronautical Congress held in Mar del Plata, Argentina in 1969. This book is divided into five main topics—spacecraft engineering, astrodynamics, astrionics, bioastronautics, and problems of education. In these topics, this compilation specifically discusses the equatorial vibrations of a long flexible boom on a spin-stabilized satellite of non-zero radius; heat transfer to linear bodies in two-dimensional hypersonic low density; and limits of accuracy of general perturbations for satellites moving under constant forces. The rapid optimization of multiple-burn rocket flights; data transmission for planetary studies; and comparison of theoretical and experimental attitude data for the DODGE spacecraft are also elaborated. This text also covers the Apollo life-support and protective systems; bioastronautical aspects of Apollo biomedical operations; and development and applications of hot water rockets. This publication is recommended for astrophysicists and scientists of other disciplines related to astronomy.