Closer to the present, especially since the beginning of the 17th Century, many stories (more or less mythical) and proposals have appeared, some of which prefigured the real “flying machines” that came later. Often the question was not just voyages in the air, but up into space, as, for example, in the novel by the Englishman, Godwin, The Man in the Moon, which appears to have inspired Savinien de Cyrano, known as Bergerac (1619-1655), in his stories “Voyage to the Moon” and “The Comic History of the States and Empires of the Sun.” Remarkably, Cyrano speaks explicitly of the propulsion of one of these machines by rockets.

A century later, at Marseilles in 1806, the artisan Claude Ruggieri accomplished the practical application of this means of propulsion, on a scale far surpassing that of the fireworks known since the time of ancient China. By means of a necklace of rockets, Ruggieri succeeded in lifting a live sheep more than 600 feet into the air, bringing it to a soft landing with a parachute.

However, as such accomplishments did no more than utilize Archimedes’ buoyancy principle for the medium of air (in the case of the baloonists), or the principle of action and reaction (in the case of rockets), the fight against weight had only succeeded in counterbalancing the effects, without modifying them a bit. The principle of the airplane—a craft “heavier than air”—so widely in use today, was not an exception to the general rule. Thus, even today, we do not know how to fight against weight, except by opposing to it forces of another nature, the which cannot be done without posing some delicate problems of a dimensional type, as we will see below.

What differentiates the mode of propulsion of a rocket from all the others (both the lighter- and heavier-than-air vehicles) is that it works in a vacuum—even better than in the air. So, almost 50 years ago, the birth and development of astronautics took place, which, even at the end of the first 40 years of this century, seemed more like science fiction than reality.

As experience teaches, the dreams of pioneers are often realized much more rapidly than their contemporaries could have imagined. Our present time abounds in facts of this kind. This was the case for radar, antibiotics, nuclear power plants, the transistor, television, intercontinental missiles, the high-speed train (TGV), organ transplants, computers, the genome, and so on.

On cursory examination, there seems no limit to the speed of the technological revolution, which tends to take on an exponential character.

Yet, there remains an area, in addition to that of controlled nuclear fusion, in which man’s ingenuity seems to have been dancing around for the last 30 years: the realm of interplanetary space travel—which, at the beginning, had taken off with fireworks (both figuratively and literally). In the 1960s, we moved quickly from the rudimentary Sputnik to a trip to the Moon, and even, by use of robotics, to the confines of the solar system. But, today, we still use the same techniques, which are so costly that it is not even financially possible to repeat the accomplishments of the past, and, for example, to colonize the Moon.

In this domain, an apparently invincible enemy blocks progress: weight—the tangible manifestation of a phenomenon studied since antiquity and defined and codified under a general form, three centuries ago, by Newton as “gravitation.” . . .