Twenty-Five Years of Progress Toward Space Flight

In the first phase, corresponding roughly to the first quarter of.theiwentiafch ceiituryr.±ha theoretical basis of rocket flight was worked out. The task was accomplished by three men working independently in three different countries. The three had much in common—they were teachers, one at a small university, the other two in secondary schools. Each one pondered the problem for many years before committing his findings to publication. But what is most important, all three were 'motivated -by the desire to -explore TuteTpiaTietaTy space and presented their findings with conviction, even though they were regarded by most of their contemporaries as prophetic dreamers. The men and their works are now well known. They are: Ziolkovsky ("The Exploration of Cosmic Space by Reaction Machines"), 1903 Goddard ("A Method of Reaching Extreme Altitudes"), 1919 Oberth ("The Rocket Into Interplanetary Space"), 1923. Any one of these three publications, had it been widely read and accepted, would have sufficed to lay the groundwork for space travel, because each man clearly understood and asserted the following fundamental concepts: 1. That escape from the earth is possible by the application of a moderate acceleration over a substantial period of time—at least several minutes. 2. That such acceleration can be produced in a vacuum by a rocket. 3. That the rocket must (a) have high thermal efficiency (i.e., high velocity of the ejected matter), and (b) consist mainly of propellant material (i.e., have a high ratio of fuel weight to total weight). 4. That high thermal efficiency would be obtained most readily from the chemical combustion of liquid fuels. Ziolkovsky (l) started by examining Jules Verne's cannon and also the balloon as a means of reaching very high altitudes. Both approaches died quickly under mathematical analysis. He proceeded next to the rocket and developed the fundamental equation of rocket action in free space. Realizing that energetic fuels were required, he determined from thermochemical calculations the heat release of various liquid combinations. When he computed the velocity that could be attained, in theory at least, he realized it was sufficient for escape from the earth. Goddard (2), alone of the three, proceeded from experiment to theory. Using smokeless powder in a heavy-walled steel combustion chamber, he produced a jet velocity of almost 8000 ft per sec, a sevenfold improvement over ordinary rockets and the highest velocity of matter attained up to that time outside of electrical discharge tubes. Also, he 1 Technical Director of Project Vanguard. Mem. ARS Board of Directors. 2 One, Herman Oberth, became a teacher after his fundamental work had been completed. 3 Numbers in parentheses indicate References at end of paper. 4 Jules Verne, in his novel "From the Earth to the Moon," projected his space ship to escape velocity, from a long cannon sunk in the ground. proved by tests in a vacuum that a rocket does not produce its force by pushing on the air behind it, a fact he knew from basic physics but that he felt had to be demonstrated. He observed correctly that the jet velocity was greater in a vacuum, but he attributed it erroneously to more efficient ignition. Although Goddard did not turn to liquid fuels until after his basic paper was published, he achieved the first flight of a liquid rocket, an event that took place on March 16, 1926. Goddard (3) continued his experiments for more than two decades during which time he developed, in rudimentary form, almost every component of modern rocketry. Not one of his components would be considered reliable by presentday standards; realizing the prodigious task he had set out to accomplish, he would repeatedly add a new component before perfecting the previous one. In retrospect^ it appears that Goddard was attempting, single-handed, to encompass the entire field of liquid-rocket development, a task that would eventually tax the abilities of thousands of engineers and scientists. Oberth (4), in his treatise, gave the most complete theoretical analysis and carried it farther -into the realm of •spacetravel than either of the others. He stated at the outset the four propositions he would attempt to prove: 1. Considering the present state of science and technology, it is possible to build machines that could rise beyond the atmosphere. 2. After further development these machines will be able to attain such velocities that, left undisturbed in the depths of outer space, they will not fall back to the earth and will even be able to leave the zone of terrestrial attraction. 3. These machines could be constructed so as to transport human beings, probably without damage to their health. 4. Under certain economic conditions, the construction of such machines might be profitable. Oberth began by developing the theory of the liquid rocket and describing its construction. He proceeded to discuss applications of the rocket, first as a high-altitude sounding vehicle, then as an earth satellite, and finally as a space ship for interplanetary travel. He developed the concept of synergic (minimum energy) ascent trajectories. Without doubt, almost every later book on space flight owes much to Oberth's encompassing study.