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 The Past and Future of Rocket Engine Propulsion
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Part I: Chemical Propulsion and the Dawn of Rocket Science

Ready Reference
Heron of Alexandria

motion

Newton, Sir Isaac

rocket

space exploration

The Columbia Electronic Encyclopedia

The fall of 2002 marks humankind's 45th year as a space-faring society. Our world changed irreversibly on October 4, 1957, when the Soviet Union successfully launched Sputnik I, the world's first artificial satellite. Sputnik I was about the size of a basketball, weighed only 183 pounds and took about 98 minutes to orbit the Earth. That launch ushered in new political, military, technological, business and scientific developments. While the Sputnik I launch was a single event, it marked the start of the Space Age and the US-USSR space race that ultimately led to the piloted Moon landings between 1969 and 1972. Some 30 years after humans last walked on the Moon, access to space has become almost routine. On any given day, hundreds of spacecraft orbit our planet, relaying television images, tracking weather patterns, and enabling us to pay for our gasoline at the pump. We now have a space station the size of an airliner constantly inhabited with a three-person crew and have sent space probes to every planet in our solar system except Pluto. We see wondrous images of distant planets, quasars and galaxies from our orbiting space telescopes. The Mars Odyssey spacecraft recently detected hydrogen throughout the surface of Mars--but particularly at the poles--which is most likely indicative of an enormous amount of water ice near the surface.

[sputnik]
NASA
audio Listen to telemetry, information signaled remotely to ground observers, from Sputnik I as it passed overhead in 1957. (10 sec)
Concept for rocket motor operation.
Regents of the University of Michigan
enlarge Concept for rocket motor operation.

While the list of wondrous stories associated with space travel is almost endless, it is hard to imagine that a little over 100 years ago, no human had flown even one foot off the ground in a powered vehicle. In fact, scientists of the day debated whether space travel would even be possible since, as some argued, "there was no air for the rocket motor propellant to push against to impart thrust." We now realize--as Sir Isaac Newton did centuries earlier--how specious this argument was. However, it is important to realize how rapidly the field of rocket propulsion developed from a largely ineffective weapon to what it is today. With this in mind, Part 1 is devoted to providing a brief review of how rocketry came into being and to tracking the field's progress through the mid-twentieth century.

As alluded to above, the concept of expelling objects in one direction to propel an object in the opposite direction, though fully explained by Newton's laws of motion, was not fully embraced by the scientific community until the beginning of the last century. Hero of Alexandria demonstrated the concept of "reactive thrust" approximately 2,000 years ago by heating a free-spinning chamber that contained water. As the water turned to steam, it emerged from the chamber through a series of nozzles aligned tangentially along the perimeter of the chamber, thus causing the chamber to spin at great speed. It was not until the seventeenth century, when Newton formulated his laws of dynamics, that a rigorous explanation for Hero of Alexandria's demonstration could be offered.

Ready Reference
Goddard, Robert Hutchings

Tsiolkovsky, Konstantin Eduardovitch

The Columbia Electronic Encyclopedia

Modern rockets such as the space shuttle solid rocket booster can trace their roots to China. Chinese alchemists first developed gunpowder around 850 BCE (apparently by accident) and by 1040 had printed its formula for widespread use. The Chinese developed the first rockets in the mid-twelfth century for fireworks displays. These rockets, dubbed "running rats," consisted of bamboo tubes filled with gunpowder. The gunpowder was ignited on one end, and the resulting high-pressure gas escaped the tube through a small hole, causing the tube to shoot across the floor. Soon afterward, a stick was fastened to the end of the tube for stability, and flying versions of the running rats were created.

Over the ensuing centuries, the Chinese, Mongols, Indians and Arabs experimented with solid propellant rockets for military use. During the War of 1812, Sir William Congreve of England developed a solid-propellant rocket with a range of 3,000 yards. By the late 1800s, rockets had found use in a number of nonmilitary applications, including signaling, whaling and transferring lifelines between ships. However, the notion of using rocket propulsion for space travel did not emerge until the early twentieth century. The three individuals most often regarded as the early pioneers of modern rocketry are Konstantin Ziolkovsky (1857-1935), Robert Goddard (1882-1945) and Hermann Oberth (1894-1989).

[Ziolkovsky]
NASA
Konstantin Eduardovitch Ziolkovsky.

Konstantin Eduardovitch Ziolkovsky (Tsiolkovsky) was born in Ijevsk, Russia. He became a quiet schoolteacher in Kaluga, Russia (1892-1920), where he studied the problem of sending vehicles into space. He built Russia's first wind tunnel in 1891 and in 1903 published his first scientific paper on space flight, "Exploration of Space with Reactive Devices." In this seminal paper, Ziolkovsky showed how a rocket ship could be used to send people beyond Earth orbit and performed calculations that led him to the idea of using multiply-staged rockets to increase payload mass. (The Chinese had apparently experimented with multiply-staged rockets centuries earlier.) In 1924 he presented conceptual studies for piloted orbital spacecraft capable of re-entering the Earth's atmosphere from space. His outstanding work on the fundamental physics and engineering of space vehicles has long since been recognized by Soviet, later Russian, and American authorities (NASA translated all of his publications into English in 1965). Perhaps his most lasting development, however, is the so-called Rocket Equation (called the Ziolkovsky equation in Russia), which shows the relationship between payload mass fraction (i.e., final to initial mass of a vehicle), the speed the payload must reach (ΔV), and the speed at which rocket propellant gas leaves the rocket motor (Ue). This equation will be considered later when we discuss electric propulsion.

Dr. Robert Hutchings Goddard was born in Worcester, Massachusetts, in 1882. As a 16-year-old, he read H. G. Wells's science fiction classic War of the Worlds and dreamed of space flight. Goddard later became a professor of physics at Clark University in the town where he was born. In 1914 he was granted a US patent for the design of a rocket combustion chamber/nozzle and propellant feed system. He also received a patent for the multistage rocket. While Goddard started his rocketry career with solid propellants, he soon recognized the enormous potential of liquid-propellant motors and identified liquid oxygen and liquid hydrogen--the propellants used in the Apollo Saturn V launch vehicle and the space shuttle--as an ideal combination. In 1919 Goddard published A Method of Reaching Extreme Altitudes through the Smithsonian Institution in Washington, DC. In it, he showed mathematically how a rocket could be developed to send payloads to the Moon. He spent most of the next 20 years experimenting with gasoline/liquid-oxygen propelled rockets and devoted much of this time to developing rocket thrust chambers and turbopumps to transfer propellant from the tanks to the rocket chamber.

[Liquid Fuel Rocket]
NASA
Liquid Fuel Rocket, March 16, 1926.
[Goddard]
NASA
enlarge In this image slideshow, learn more about Robert H. Goddard, the "father of rocketry."
Ready Reference
Propellant

Rocket propulsion

Chemical fuel

The McGraw-Hill Concise Encyclopedia of Science and Technology

By 1926 Goddard had designed, built and launched the world's first liquid-propellant rocket. While recognized by some for his genius, Goddard was ridiculed by the press for suggesting that rockets could be flown to the Moon. His experiments in rocketry were supported largely by the Smithsonian Institution and championed by Charles Lindbergh, the first person to fly across the Atlantic Ocean in an airplane. All modern liquid-propellant rockets can trace their lineage (and design) to those Goddard developed through the 1940s. Ironically, the US military stopped funding his research at the onset of World War II because a clear military application for liquid-propellant rockets to the war effort was not apparent. He died in 1945 holding over 200 patents in rocket technology. In memory of this brilliant engineer, NASA dedicated the Goddard Space Flight Center in Greenbelt, Maryland, NASA's lead center in space science, on May 1, 1959. To this day, Robert Goddard is the figure most often referred to as the "father of rocketry."

[Oberth]
NASA
Professor Hermann Julius Oberth (center).

Hermann Julius Oberth was born on June 25, 1894, in Hermannstadt, Austria-Hungary (now Sibiu, Romania), and spent his childhood in the German-speaking part of Transylvania in the Austro-Hungarian Empire. His lifelong interest in space travel was awakened at the early age of 11 by two Jules Verne books: From the Earth to the Moon and Journey Around the Moon. In 1913 Oberth went to Munich, Germany, to study medicine. However, his studies were interrupted by World War I, in which Oberth served in the Austro-Hungarian army medical corps. After the war, Oberth studied physics and concluded his studies in Munich, G�ttingen and finally Heidelberg, with a 1922 Ph.D. dissertation about rocket-propelled space travel entitled Rockets into Interplanetary Space. His dissertation was rejected by the professional community at the time as being too utopian. Nevertheless, in 1923, Oberth published his work as a small booklet, Die Rakete zu den Planetenr�umen (The Rocket into Interplanetary Space), at his own expense. The ideas Oberth presented in this booklet caused great controversy in the world press. Oberth discussed the concept of using hydrogen and alcohol propellants for interplanetary space vehicle propulsion.

Oberth worked as a teacher of mathematics and physics at a school in Mediasch, Transylvania, from 1924 to 1938. He published The Road to Space in 1929 as a follow-on to his 1923 booklet. Influenced by Oberth's writings, the German Society for Space Travel was established in the late 1920s. This society demonstrated the use of rocket propulsion to propel cars, sleds and airplanes and, through 1934, experimented with liquid rocket propellants such as gasoline and liquid oxygen. This work helped propel Germany's efforts to build a large ballistic missile, the V-2, during World War II.

Discussion
Both Goddard and Oberth were influenced early in their lives by science fiction. Discuss the role of science fiction in aiding advancements in science.

The V-2 was an alcohol/liquid-oxygen propellant missile that was built at the Peenem�nde rocket plant under the direction of Walter Dornberger and Wernher von Braun. The V-2 was by far the most advanced rocket of the time. While Oberth spent most of World War II at the Technical Colleges of Vienna and later Dresden, late in the war he became a consultant for Peenem�nde, where his pupil von Braun developed the world's first mass-produced large rocket.

After the war, Oberth joined von Braun, who had established an American institute for space exploration in Huntsville, Alabama. Like Goddard and Ziolkovsky, Oberth had written about the virtues of using electric power for space vehicle propulsion. Von Braun was so enamored with Oberth's revolutionary thinking, he assigned a young engineer named Ernst Stuhlinger--who went on to direct electric propulsion research at NASA's George C. Marshall Space Flight Center--the task of "giving the subject of an electric spaceship propulsion further thought."
Ready Reference
guided missile

The Columbia Electronic Encyclopedia
"Professor Oberth has been right with so many of his proposals; I wouldn't be a bit surprised if one day we flew to Mars electrically!" von Braun said in assigning the study task to a reluctant Stuhlinger. In 1960 Oberth was hired by Convair as a technical consultant on the Atlas rocket, the vehicle used to send the first American in orbit. Oberth retired in 1962 and devoted the latter years of his life to studying alternative energy sources such as wind-power stations. He died in Feucht, near Nuremberg, Germany, in 1989.



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