The Russian scientist Konstantin Eduardovich Tsiolkovsky (1857-1935) formulated the mathematical fundamentals of modern astronautics. He showed that space travel was possible only by means of rocket propulsion.

Konstantin Tsiolkovsky was born on Sept. 17, 1857, in the village of Izhevskoye, Ryazan Province. His father was successively a forester, teacher, and minor government official. When he was ten Konstantin contracted scarlet fever, which left him with permanently impaired hearing. He became passionately interested in science and mathematics. At the age of 16 he went to Moscow. He made an ear trumpet himself and attended lectures and studied in libraries. Regular attendance at the university was out of the question because of the costs involved and his deafness.

## Hardships in Moscow

Tsiolkovsky seriously began considering the problems of space exploration. While still not completely schooled in physics, he developed a machine that he thought might someday reach outer space by means of centrifugal force. It was a box in which there were two steel rods with balls on their ends. When the rods were set in motion, their vibrations (in Tsiolkovsky's theory) would produce an upward movement because of centrifugal force, but they did not.

In 1876 Tsiolkovsky went home, which was now in Viatka in the Urals. There he became a private tutor in physics and mathematics. He converted a room into a workshop in which he built machines. In 1878, the family returned to Ryazan, and Tsiolkovsky received a certificate as a "people's school teacher, " the lowest classification in the educational system of the day. He took a job as a teacher of arithmetic, geometry, and physics at the district school in Borovsk near Moscow.

In 1880 Tsiolkovsky wrote his first serious scientific paper, "The Graphical Depiction of Sensations." It was an attempt to reduce to mathematical models the experience of human senses. The following year he submitted the paper "The Theory of Gas" to the Physical and Chemical Society in St. Petersburg. Later he submitted another paper, "The Theoretical Mechanics of a Living Organism, " for which he was elected to the society. In 1883 he published a purely qualitative study entitled "Free Space, " in which he examined the motion of a body not under the influence of a gravitational field or some medium that offered resistance to its movement; the paper contained a drawing of a rocket-powered space ship.

After 1884 three areas of science occupied Tsiolkovsky. He began to concentrate on aeronautics: a streamlined airplane, an aerostation, an all-metal dirigible, and space travel. In 1886 he published an essay on the theory of the dirigible and was invited to Moscow to lecture on his ideas. His concept of the dirigible was highly imaginative and theoretically feasible, but it posed serious problems for the engineering of the day. He proposed all-metal airships with a variable volume to preserve constant buoyancy at different temperatures and altitudes. A corrugated metal envelope with an internal system of pulleys was to vary the volume as the temperature or altitude changed. The lifting gas (hydrogen) was to be heated by passing the exhaust gases from the engines through the envelope before they were discharged to the atmosphere. His plans submitted to the Russian Technical Society's Aeronautical Department in 1891 brought a reply that "inasmuch as the project cannot have any considerable practical importance, the society did not find it possible to comply with your request for a grant to construct a model." The tone of this letter was to become familiar to him over the remainder of his life. The only funds he ever received from any outside source came from the Academy of Sciences and amounted to only 470 rubles ($235).

In 1892 Tsiolkovsky became a high school teacher in Kaluga. In 1894 he published the article "The Airplane or Bird-like Flying Machine."

## First Wind Tunnel

In 1897 Tsiolkovsky built the first wind tunnel in Russia. In it, he tested a number of different airfoils to determine their lift coefficients. The results of these pioneering experiments in aeronautical engineering were published the following year, and the Academy of Sciences in St. Petersburg granted him 470 rubles to expand and exploit his research in this field. He built a bigger machine, but even as he was wrapped up with his wind tunnel, he found time to think about rockets and space travel.

In 1897 Tsiolkovsky derived the relationship of the exhaust velocity of a rocket and its mass ratio to its instantaneous velocity. Known today as the basic rocket equation, it is expressed as *V* = *c* In (*W* i /*W*f ), in which *V* is the final velocity, *c* is the exhaust velocity of propellant particles expelled through the nozzle, *W*i is the initial weight of the rocket, and *W* f is the final, or burnt-out, weight of the rocket. Of course, it does not consider the retarding forces of
gravity and drag, which Tsiolkovsky knew affected the rocket and later took into account in refining his equation. What his equation proved was that the velocity of a rocket in space depends on the velocity of its exhaust and the ratio of the weight of the rocket at lift-off and at burn-out. This realization permitted him to conceive of many ways of increasing the exhaust velocity and of decreasing the mass fraction.

Even more important from the astronautical viewpoint, Tsiolkovsky demonstrated that the answer to space travel lay in building what he called "step, or train, " rockets. Today this concept is known as "staging." He saw, from his mathematical investigations, that a rocket could attain greater velocities if it could grow continuously lighter. Thus, he suggested that rockets could be clustered in the tandem, or parallel, configuration. As stages burned out, they dropped away, and upper stages gained in velocity as a result—as his rocket equation proved.

## Contributions to Astronautics

In 1903 Tsiolkovsky finished a paper that was to become his famous article "Investigation of Outer Space by Reaction Devices." It did not appear in print until 1911 and 1912, when it was published serially in the *Aeronautical Courier* (*Vestnik Vozdukhoplavaniva*). This work represents his major contribution to astronautical engineering. He reiterated his rocket equation and modified it to include the forces of gravity and drag. He examined the energies involved in a vertical and horizontal launching, and he considered the best overall shape for a rocket. Also, he demonstrated that solid propellants lacked the energy needed for interplanetary travel. In considering various liquid propellants, he arrived at liquid hydrogen and liquid oxygen as the most practical. He also mentioned the theoretical advantage of ozone instead of diatomic oxygen. The concept of the regeneratively cooled engine is also found in this work.

During the late 1920s and the early 1930s, Tsiolkovsky's interests shifted to the airplane, especially the rocket-propelled model. Of the articles appearing in this period, typical are "The New Airplane" (1929), "The Reaction Airplane" (1930), and "Rocketplane" (1930). After Tsiolkovsky retired from teaching, he continued to write on space and aeronautics.

In 1934, as he knew he was dying of cancer, Tsiolkovsky became worried about the future welfare of his family. On Sept. 13, 1935, he wrote a letter to the Central Committee of the Communist Party bequeathing all of his writings "to the Bolshevik Party and the Soviet Government." In so doing, he hoped he might obtain a pension for his family. He died on September 19.

For several years Tsiolkovsky's books and manuscripts were stored in the central offices of Aeroflot and then given to various museums. His home in Kaluga was made into a museum, and some of the material was returned to it. During World War II the museum suffered depredation by the invading Germans, but the staff managed to save much of the material. Following the orbiting of *Sputnik 1,* the world's first satellite, the Tsiolkovsky Museum became a very popular attraction in the Soviet Union.

## Further Reading on Konstantin Eduardovich Tsiolkovsky

There is no readily accessible biography of Tsiolkovsky in English. A. Kosmodemyansky, *Konstantin Tsiolkovsky: His Life and Work* (Moscow, 1956), is not well known in the United States and suffers from a heavy burden of political propaganda. Much more objective is V. N. Sokolsky, *K. E. Tsiolkovsky: Selected Works* (Moscow, 1968); it is a compendium of Tsiolkovsky's works with a short biography appended, but it is also not widely available in the United States. Perhaps the best sources in English, which draw heavily on the above-cited references, are Willy Ley, *Rockets, Missiles, and Men in Space* (1952; rev. ed. 1968); Beryl Williams and Samuel Epstein, *The Rocket Pioneers on the Road to Space* (1958); and Albert Parry, *Russia's Rockets and Missiles* (1960).