The books by Ley and von Braun provide ample evidence that many supposedly "modern" ideas of space habitation have their roots in antiquity. Much of the historical ground that they cover is beyond the scope of this chapter, but it is worth noting a few key developments in the "pre-history" of artificial gravity.
Philosophical debate concerning the "plurality of worlds" and the habitability of the Moon and planets occurred in ancient Greece more than twenty-five centuries ago. The first tale of extraterrestrial travel, Lucian's True History (Vera Historia), was written in A.D. 160. Nevertheless, widespread interest in the physical universe beyond the confines of Earth did not emerge until the Renaissance and scientific revolution of the sixteenth and seventeenth centuries. Since approximately 1500, there has been a steady stream of scientific, philosophical, and fictional literature regarding the nature of the cosmos, the habitability of celestial objects, their inhabitants, and interplanetary travel; Ley and von Braun summarize more than forty books and articles published between 1500 and 1900.
The astronomical revolution led by Nicholas Copernicus, Johannes Kepler, and Galileo Galilei culminated in 1687, when Isaac Newton published his Mathematical Principles of Natural Philosophy (Philosophiae naturalis principia mathematica). Newton's Principles contain everything that is needed to explain acceleration, orbit, free-fall, weightlessness, and artificial gravity. Although many people knew of the existence of the Principles, far fewer actually understood them; it would be nearly 200 years before they were properly applied to the problem of space travel. Before Newton, space flight was conceived as aerial flight, gravity as a sort of magnetism, and the Earth as an enormous lodestone. After Newton, as devices for space travel, birds' wings were gradually replaced by strange electrical devices, catapults, powder rockets, giant guns, and anti-gravity materials. Yet the problems associated with weightlessness were generally ignored. There was a persistent misconception that weightlessness would occur only at the "balance point" between neighboring gravitational fields.
At least six stories of space travel were published in 1865, the most influential of these being Jules Verne's From the Earth to the Moon (De la Terre à la Lune). The sequel, Around the Moon (Autour de la Lune), was published in 1867. Verne was known and respected by working scientists for basing his adventures as much as possible on established science; Tsiolkovsky, Ganswindt, Goddard, and Oberth were among his readers [5, 6]. For this reason, his stories bear closer examination:
Verne's astronauts notice debris floating outside their vessel, apparently weightless, accompanying them on a common trajectory toward the Moon. But inexplicably, the astronauts themselves fail to float within the vessel. Instead, their apparent weight gradually decreases until they approach the "neutral point" between the Earth and Moon, where they experience "scarcely an hour" of weightlessness before Lunar gravity takes over. While Verne correctly applied Newtonian physics to describe the relative weightlessness of objects floating outside, he somehow failed to realize that the same effects would occur inside as well . Still, it is a testimony to Verne's influence that scientists have felt compelled to study his work in order to identify such errors .
Achille Eyraud's Voyage to Venus (Voyage à Vénus), also published in 1865, was the first to describe a space ship operating on the reaction principle (Newton's third law of motion), which is the basis of modern rocket theory.
Edward Everett Hales's "The Brick Moon", published in the Atlantic Monthly in 1869, was the first to describe a permanent, manned, artificial satellite - a space station.