Published in 1960 by Flammarion as Book VIII of Astronomie Populaire Camille Flammarion, this 64-page monograph presents the scientific foundations of astronautics at the dawn of the space age: orbital mechanics, reaction propulsion, artificial satellites, and the first interplanetary probes. Written by André Danjon, director of the Paris Observatory and member of the Institut de France, with the collaboration of Paul Muller, it covers achievements from the Sputnik era through Pioneer V (March 1960) and TIROS I (April 1960), including the discovery of the Van Allen radiation belts and the circumlunar Lunik missions.