The scientific and literary developments that occurred in the two hundred years following the publication of Newton's Principles laid the groundwork for the first generation of modern space scientists. Myth and fantasy gradually gave way to science fiction, which led in turn to serious engineering analysis of the problems of space flight and extraterrestrial habitation. The emergence of a space profession was heralded in the 1920's and -30's by the formation of "rocket societies" in Europe and America:
Many of their members were more interested in space exploration than in rocketry itself, and focused much of their attention on the requirements of extraterrestrial travel. The general public regarded such pursuits with considerable skepticism: the study of interplanetary travel was so ridiculed that in 1934 the American Interplanetary Society changed its name to the American Rocket Society, and the British society considered a similar move . As late as the 1950's, a major rocket company threatened to withdraw corporate sponsorship from the American society "if the Society didn't stop all this 'foolishness' about spaceflight" . As a result, despite the growing membership and scientific professionalism of these societies, space station design was a private pursuit - a hobby - carried on by individual members without corporate or governmental support.
Preliminary calculations left no doubt that travel to the Moon and planets would be impossible until an orbiting space station was established. As late as 1957 (only four years before John F. Kennedy's "man on the Moon" speech), Oberth wrote : "A liquid-propelled rocket intended to fly direct from the Earth to the Moon would have to be so large and heavy that no sensible engineer would consider designing and building one." Ley wrote : "Unless an entirely new principle is unpredictably discovered within the next few years this type of spaceship will have to wait until the space station is completed and fully operable."
Thus, the space station was initially conceived as a construction site and fuel depot for interplanetary space ships; or as an observatory for studying the heavens and the Earth; or as a military outpost for waging war or enforcing peace. Weightlessness was generally seen as a curiosity to be exploited within isolated laboratories, and a nuisance or health hazard elsewhere. Access to weightlessness was not the main objective of the space station, and it was taken for granted that artificial gravity would be provided. According to Ley :
The wheel shape of the station and its rotation for the purpose of creating pseudo gravity for convenience in the daily routine is something definite ... The main purpose of pseudo gravity would be to make things stay put, so that, say, a plate of food placed on a table would stay there and cigarette smoke would rise to the ceiling and the air-conditioning outlet, instead of forming a dense near-spherical cloud around the smoker's head.
Space station concepts from the period 1878-1957 are dominated by artificial gravity. They display a theoretically correct application of Newtonian physics but a lack of appreciation for the technical difficulties of construction. The assumption was that large space stations would be assembled almost completely in orbit, with little or no prefabrication on the ground. Consequently, the designs are often rather monolithic - like ships or submarines - and lack the kind of modularity that could be accommodated by an assembly of individually-launched prefabricated sections.
"July 8, 1878, Sunday, Ryazan. This was when I started to draw astronomical designs. K. Tsiolkovsky." Konstantin Eduardovich Tsiolkovsky (Константин Эдуардович Циолковский) was the first to devote a thorough scientific study to the problems of space flight, a study he pursued for more than fifty years . He wrote his first monograph on the subject, entitled Free Space (Свободное Пространство), in 1883. For the next twenty years he worked to develop his earlier musings into precise theories for space exploration via rocket propulsion with liquid fuels, and in 1903 he published The Exploration of Space by Means of Jet Devices (Исследование Мировых Пространств Реактивными Приборами) in the journal Scientific Review (Научное Обозрение).
In 1896 Tsiolkovsky began writing several chapters of what would become his science fantasy Beyond the Planet Earth (Вне Земли). The work was completed in 1916, but did not see publication until 1920. Beyond the Planet Earth was a vehicle for popularizing his ideas on rocketry and space travel. As a work of literature, it reads like a story problem in Newtonian physics. (He went so far as to name his characters after famous scientists: Laplace, Newton, Helmholtz, Franklin, Galileo, Ivanov.) Forty-five years before anyone had actually flown in space, Tsiolkovsky was able to anticipate many of the problems associated with living and working in a weightless environment, including the loss of muscle tone and the need for foot and waist restraints at workstations. More to our purposes, he described how artificial gravity could be produced by rotating the space ship, and he anticipated the significance of the radius of rotation and the movement of people relative to the rotating environment :
Most of the men had felt nothing at all, particularly when the radius of rotation was large. But in the case of a man's moving rapidly and independently, the artificial gravity created by centrifugal force produced a very interesting effect, which we may have occasion to describe later.
Unfortunately, he does not find the occasion in this book to elaborate on the interesting effects of artificial gravity.
Tsiolkovsky describes a cylindrical space ship: 100 meters long, 4 meters in diameter, rotating end-over-end about its "central transverse diameter", with an endpoint velocity between 1 and 10 meters per second, producing an angular velocity between (approximately) 0.2 and 2.0 rotations per minute, and a gravity level between 0.002 and 0.2 g. These numbers were chosen to illustrate a concept, and should not be taken too seriously. Nevertheless, they show that Tsiolkovsky understood the problems associated with high angular velocities, and the practicality of artificial gravity levels of less than one full g.
Logsdon and Butler provide an illustration of a more elaborate Tsiolkovsky space station concept , which they date from 1903.
Hermann Ganswindt, a contemporary of Tsiolkovsky, independently developed circa 1890 a concept for a space ship that incorporated reaction propulsion and artificial gravity. His mathematical skills were not as well developed as Tsiolkovsky's, and this limited his ability to either apply or contribute useful theories.
The crew compartment of Ganswindt's ship was to be a horizontal cylinder suspended by shock-absorbing springs below the engine assembly. An exhaust well was to be cut cross-wise through the center of this cylinder to allow the passage of spent steel shells from the explosion chamber above. (Ganswindt did not believe that mere gaseous exhaust could produce sufficient reaction thrust.) Ganswindt understood that the crew would experience weightlessness when the engine was shut off, and proposed to provide artificial gravity by rotating the vehicle around the exhaust well, so that the ends of the crew cylinder would become floors. Apparently, this scheme was never worked out in detail [17, 18].
Hermann Oberth has been referred to as the "father of space travel". Working independently of both Tsiolkovsky and Goddard, Oberth also developed theories for liquid fueled rockets, and went on to develop detailed space station design concepts based on mission objectives. His first book, The Rocket into Interplanetary Space (Die Rakete zu den Planetenräumen), was published in 1923 and "became the sole cornerstone of all later space travel ideas" . In 1929 he expanded this work into The Road to Space Travel (Wege zur Raumschiffahrt). In 1957 he published Man into Space (Menschen im Weltraum), which updated his earlier work and drew upon the work of other space travel theorists as well.
Oberth described four types of space stations: the springboard station or space port; the fixed-orbit station; the strategic (military) station; and the experimental station far out in space. These stations differ primarily in the equipment and orbital characteristics (altitude, inclination, period) necessary to accomplish their assigned missions; the habitation requirements are essentially the same for each.
The springboard station was to be assembled in orbit, in several steps: The first two supply ships were to be connected together by 8000 meters of tapered tether and set into rotation, with a peripheral velocity of 200 meters per second, producing approximately 0.5 rotations per minute and a gravity level of approximately 1 g. These were to become the living quarters. Elevators would climb back and forth along the tether between the living quarters and a central spherical work area. Connected to this would be an air lock and an assortment of trusses, storage containers, and space telescopes. The whole assembly was to be surrounded by a spherical net of cables bearing "watchdog bombs".
Oberth believed that 8000 meters was the optimum diameter for producing Earth-force gravity: he believed that smaller diameters would require unacceptably high angular velocities, while larger diameters would suffer unacceptably large tidal accelerations. He did not discuss the possible advantages of lower gravity levels .
Hermann Noordung (the pen name of a Captain Potocnic of the Austrian Imperial Army) published The Problem of Exploring Space (Das Problem der Befahrung des Weltraums) in 1928. This book described Noordung's concept for a space station: a "living wheel" ("Wohnrad") rotating around a hub, connecting to a power plant, an observatory, and an air lock. The wheel was to be 30 meters in diameter, rotating nearly 8 times per minute, to produce 1 g of gravity at the rim. Movement between the rotating wheel and the non-rotating hub was to be via radial elevators and spiral stairs. (The stairs were to be straight in "plan" but spiral in "elevation".) The wheel was to be surrounded by a toroidal paraboloid mirror to concentrate sunlight on the rim [21, 22].
Noordung acknowledged that a gravity differential would exist between the head and the feet of a person standing within the rotating wheel, and stated that moving around within it would require some sort of compensation.
Ley faults Noordung for designing the wheel to support full Earth gravity rather than some lesser amount : "Noordung drew all his units massive enough for exhibit on the ground; they would even have survived being tossed around on an angry ocean without much damage."
As early as 1930, Noordung also published two proposals for large space settlements: the "wheel station" and the "roller station". The wheel station would consist of a pair of counter-rotating disks connected by a truss structure. Each disk would be 6 to 8 kilometers in diameter and 100 meters thick, rotating once every 110 to 127 seconds, yielding 1 g of gravity at the rim. The disks would be divided into as many as fifty concentric levels, with the higher levels (closer to the center) experiencing less gravity than the lower ones. The fronts of the disks would be composed of a translucent material to admit diffuse solar radiation, while the backs would be shielded by a reflecting material to reduce the radiant heat loss. As the station orbited, it would keep its translucent side pointed toward the sun. Because the disks would rotate in opposite directions, their precessional movements would cancel; the precessional torque would be sustained by the connecting truss structure. The station would orbit the sun at twice the Earth's orbital distance, once every three years (approximately). This orbit was chosen so that the wheel station would assume the same temperature as the Earth: The ratio of radiating surface to cross section is only one fourth as great for the flat wheel as for the spherical Earth (assuming that the back of the wheel is shielded by a reflecting material). Consequently, the wheel should assume the same temperature as the Earth when it is exposed to one fourth the intensity of solar radiation - at twice the Earth's orbital distance.
The roller station would derive its energy not from the sun but from its own nuclear reactor. Therefore, it would not need to maintain any particular orbit or orientation, and the scheme of pairing counter-rotating sections would be unnecessary. Oberth interprets Noordung's roller station as a cylinder, eight kilometers in diameter and "ten, one-hundred, or one-thousand kilometers long", with rotational parameters similar to those for the wheel station .
J. D. Bernal published a utopian essay in 1929 entitled The World, the Flesh, and the Devil . The title refers to the three aspects of human existence in which Bernal predicted revolutionary changes: physical, biological, and psychological. As a scientist himself, Bernal was well aware of the rapid progression of all branches of science and technology. He saw in this the capacity - the necessity - for the unlimited spread of humanity throughout the universe. He imagined that large segments of the population would leave the confines of Earth to live in self-sufficient space colonies.
Bernal envisioned a spherical shell ten miles in diameter, constructed from asteroidal material and other space debris. He described this "epidermis" in almost biological terms: a tough, translucent skin; a network of vessels carrying a chlorophyll-like fluid; stores of water, oxygen, and hydrocarbons. The total shell thickness might be more than a quarter of a mile. The interior would be designed to support a "three-dimensional, gravitationless way of living". Bernal acknowledged that the human body did not evolve to thrive in such an environment, but imagined that its current limitations would become irrelevant. Gradually, during a "larval, unspecialized existence" lasting sixty to one hundred twenty years, inadequate body parts would be replaced, and new sensory and motor mechanisms would be grafted on. Finally, a person "would emerge as a completely effective, mentally-directed mechanism, and set about the tasks appropriate to his new capacities."
Bernal's radical concept of adapting the human body to the environment is counter to most space habitation proposals, which prefer to do things the other way around. Nevertheless, his vision of large, permanent space colonies has been inspirational for later twentieth-century visionaries. An alternative to the "Stanford Torus" colony, first proposed in 1975, has been dubbed the "Bernal sphere".
Wernher von Braun was the chief designer of the German A-4 rocket, better known as the V-2 (for Vergeltungswaffe, the name it was given by Hitler). At the end of World War II von Braun was brought to the United States to help establish the American missile program, and its offspring, the space program. Circa 1950 he began to devote serious study to the requirements of a manned Mars expedition, which he published as The Mars Project (Das Marsprojekt) in 1952. He concluded that one of the prerequisites was a space station.
An early design sketch of von Braun's station from 1951 shows a rotating twenty-sided polygonal "torus" connected by two spokes to a barrel-shaped hub. The polygonal concept was presumably inspired by a quest for modularity and ease of construction: each of the twenty sections would be formed from simple straight cylinders. A large paraboloid mirror mounted on the hub was to concentrate solar energy on a boiler for generating power. Because this mirror would need to be kept aligned with the sun, it did not rotate with the rest of the station.
Later that year, von Braun participated in a symposium on space travel hosted by Collier's magazine, which published a series of articles in its March 22, 1952 edition, under the collective title "Man Will Conquer Space Soon". Von Braun wrote an article entitled "Crossing the Last Frontier" that described his concept for the construction and support of the space station, to occur "within the next ten or fifteen years" . Ley contributed a small supporting article entitled "A Station in Space" . Chesley Bonestell and Fred Freeman provided detailed renderings of von Braun's concept.
Collier's introductory editorial, "What Are We Waiting For?" is rife with the cold war rhetoric of the 50's. Von Braun himself, in his opening sentence, described the station as "a man-made satellite that could be either the greatest force for peace ever devised, or one of the most terrible weapons of war - depending on who makes and controls it." It seems that scientific investigation or commercial exploitation of the micro-gravity environment were not top priorities in developing the station concept. It was to be a military vessel, akin to a modern submarine. The character of the cutaway view rendered by Freeman reinforces the submarine analogy.
Von Braun envisioned a torus approximately 30 feet wide and 250 feet in diameter, containing three decks. The polygonal form of his earlier concept was replaced by a round form: the twenty rigid cylinders were replaced by as many sections of flexible nylon-and-plastic fabric. The sections were to be carried aloft in a collapsed state, assembled, and inflated in orbit. The internal pressure would provide the necessary structural rigidity as well as a breathable atmosphere for the crew. To reduce the mass of both the structure and the atmosphere itself, the pressure would be only half of normal sea-level pressure, and nitrogen would be replaced by helium. The gravity level and rate of rotation were left open to discussion: von Braun allowed that "for a number of reasons, it may be advantageous not to produce one full g." The optimum level was thought to be one third of normal Earth gravity, which would require slightly less than 3 rotations per minute. The torus would be kept in balance by redistributing utility water between trim tanks located under the floor in each section. Black heat-absorbing panels mounted on the outside of the torus behind white reflective "venetian blind" shutters would help to control the interior temperature. Two spokes would connect the torus to a spherical hub, and a non-rotating docking turret would project from the hub along the axis. The hub-mounted paraboloid mirror of the earlier concept was replaced by a toroidal paraboloid mirror trough mounted on one side of the torus. This mirror was to concentrate solar energy on a boiler pipe, vaporizing mercury to drive a turbo-generator.
The station would orbit the Earth once every two hours at an altitude of 1,075 miles. The orbit would be nearly polar, inclined ninety degrees to the ecliptic. The rotation of the torus would be coplanar with its orbit, and oriented such that the paraboloid mirror always faced the sun. Thus, over the course of a year, the station's orbital plane would need to precess through 360 degrees; the article does not discuss this.
The painting by Freeman, narrated by Ley, shows many details that may or may not be due to von Braun. The cutaway view shows the joints between the twenty torus modules. The modules themselves - divided into three decks, crisscrossed by plumbing, and filled with equipment - appear neither flexible nor collapsible; it seems that much of the internal construction was to take place in orbit, after the module "skins" were connected and inflated. Freight elevators and ladders in the two cylindrical spokes provide access between the torus and the hub. Spiral stairs in other parts of the torus provide access between its three decks. The outer metal cladding of the meteor shield gives the station a heavy, armored, monolithic appearance, though it was estimated to be only half a millimeter thick [28, 29].