Rocket Principles

A consquence of Newton's laws of motion is that for any object, or collection of objects, forces which only involve those objects and nothing else ("internal forces") cannot shift the center of gravity. For example, an astronaut floating in a space suit cannot shift his position without involving something else, e. g. pushing against his spacecraft. The center of gravity--or "center of mass"--is a fixed point, which cannot be moved without outside help (turning around it, however, is possible).

By throwing a heavy tool in one direction, the astronaut could get moving in the opposite direction, though the common center of gravity of the two would always stay the same. Given a bottle of compressed oxygen, the same result follows from squirting out a blast of gas (a scene that appeared in an early science fiction film). A rocket does much the same, except that the cold gas is replaced by the much faster jet of glowing gas produced by the burning of suitable fuel. At present, rockets are the only means capable of achieving the altitude and velocity necessary to put a payload into orbit.

A rocket engine is a machine that develops thrust by the rapid expulsion of matter. Most rockets today operate with either solid or liquid propellants. The word propellant does not mean simply fuel, as you might think; it means both fuel and oxidizer. The fuel is the chemical rockets burn but, for burning to take place, an oxidizer (oxygen) must be present. Jet engines draw oxygen into their engines from the surrounding air. Rockets do not have the luxury that jet planes have; they must carry oxygen with them into space, where there is no air.

There are a number of terms used to describe the power generated by a rocket.

• Thrust is the force generated, measured in pounds or kilograms. Thrust generated by the first stage must be greater than the weight of the complete launch vehicle while standing on the launch pad in order to get it moving. Once moving upward, thrust must continue to be generated to accelerate the launch vehicle against the force of the Earth's gravity. To place a satellite into orbit around the Earth, thrust must continue until the minimum altitude and orbital velocity have been attained or the launch vehicle will fall back to the Earth. Minimum altitude is rarely desirable, therefore thrust must continue to be generated to gain additional orbital altitude.

• The impulse, sometimes called total impulse, is the product of thrust and the effective firing duration. A shoulder fired rocket has an average thrust of 600 lbs and a firing duration of 0.2 seconds for an impulse of 120 lb-sec. The Saturn V rocket, used during the Apollo program, not only generated much more thrust but also for a much longer time. It had an impulse of 1.15 billion lb-sec.

• The efficiency of a rocket engine is measured by its specific impulse (Isp). Specific impulse is defined as the thrust divided by the mass of propellant consumed per second. The result is expressed in seconds. The specific impulse can be thought of as the number of seconds that one pound of propellant will produce one pound of thrust. If thrust is expressed in pounds, a specific impulse of 300 seconds is considered good. Higher values are better. A rocket's mass ratio is defined as the total mass at lift-off divided by the mass remaining after all the propellant has been consumed. A high mass ratio means that more propellant is pushing less launch vehicle and payload mass, resulting in higher velocity. A high mass ratio is necessary to achieve the high velocities needed to put a payload into orbit.

There are three categories of chemical propellants for rocket engines: liquid propellant, solid propellant, and hybrid propellant. The propellant for a chemical rocket engine usually consists of a fuel and an oxidizer. Sometimes a catalyst is added to enhance the chemical reaction between the fuel and the oxidizer. Each category has advantages and disadvantages that make them best for certain applications and unsuitable for others.

Solid Propellant Rockets:

A solid-propellant rocket has the simplest form of engine. Solid propellant rockets are basically combustion chamber tubes packed with a propellant that contains both fuel and oxidizer blended together uniformly. It has a nozzle, a case, insulation, propellant, and an igniter. The case of the engine is usually a relatively thin metal that is lined with insulation to keep the propellant from burning through. The propellant itself is packed inside the insulation layer.

Solid rocket propellants, which are dry to the touch, contain both the fuel and oxidizer combined together in the chemical itself. Usually the fuel is a mixture of hydrogen compounds and carbon and the oxidizer is made up of oxygen compounds. The principal advantage is that a solid propellant is relatively stable therefore it can be manufactured and stored for future use. Solid propellants have a high density and can burn very fast. They are relatively insensitive to shock, vibration and acceleration. No propellant pumps are required thus the rocket engines are less complicated.

Disadvantages are that, once ignited, solid propellants cannot be throttled, turned off and then restarted because they burn until all the propellant is used. The surface area of the burning propellant is critical in determining the amount of thrust being generated. Cracks in the solid propellant increase the exposed surface area, thus the propellant burns faster than planned. If too many cracks develop, pressure inside the engine rises significantly and the rocket engine may explode. Manufacture of a solid propellant is an expensive, precision operation. Solid propellant rockets range in size from the Light Antitank Weapon to the 100 foot long Solid Rocket Boosters (SRBs) used on the side of the main fuel tank of the Space Shuttle.

Many solid-propellant rocket engines feature a hollow core that runs through the propellant. Rockets that do not have the hollow core must be ignited at the lower end of the propellants and burning proceeds gradually from one end of the rocket to the other. In all cases, only the surface of the propellant burns. However, to get higher thrust, the hollow core is used. This increases the surface of the propellants available for burning. The propellants burn from the inside out at a much higher rate, and the gases produced escape the engine at much higher speeds. This gives a greater thrust. Some propellant cores are star shaped to increase the burning surface even more.

To fire solid propellants, many kinds of igniters can be used. Fire-arrows were ignited by fuses, but sometimes these ignited too quickly and burned the rocketeer. A far safer and more reliable form of ignition used today is one that employs electricity. An example of an electrically fired rocket is the space shuttle's SRM. An electric current, coming through wires from some distance away, heats up a special wire inside the rocket. The wire raises the temperature of the propellant it is in contact with to the combustion point.

The nozzle in a solid-propellant engine is an opening at the back of the rocket that permits the hot expanding gases to escape. The narrow part of the nozzle is the throat. Just beyond the throat is the exit cone. The purpose of the nozzle is to increase the acceleration of the gases as they leave the rocket and thereby maximize the thrust. It does this by cutting down the opening through which the gases can escape.

To see how this works, you can experiment with a garden hose that has a spray nozzle attachment. This kind of nozzle does not have an exit cone, but that does not matter in the experiment. The important point about the nozzle is that the size of the opening can be varied. Start with the opening at its widest point. Watch how far the water squirts and feel the thrust produced by the departing water. Now reduce the diameter of the opening, and again note the distance the water squirts and feel the thrust. Rocket nozzles work the same way.

As with the inside of the rocket case, insulation is needed to protect the nozzle from the hot gases. The usual insulation is one that gradually erodes as the gas passes through. Small pieces of the insulation get very hot and break away from the nozzle. As they are blown away, heat is carried away with them.

Liquid Propellant Rockets:

The other main kind of rocket engine is one that uses liquid propellants. This is a much more complicated engine, as is evidenced by the fact that solid rocket engines were used for at least seven hundred years before the first successful liquid engine was tested. Liquid propellants have separate storage tanks - one for the fuel and one for the oxidizer. They also have pumps, a combustion chamber, and a nozzle. The fuel of a liquid-propellant rocket is usually kerosene or liquid hydrogen; the oxidizer is usually liquid oxygen. They are combined inside a cavity called the combustion chamber. High pressure turbopumps provide an example of the rocket engine. Here the propellants burn and build up high temperatures and pressures, and the expanding gas escapes through the nozzle at the lower end. To get the most power from the propellants, they must be mixed as completely as possible. Small injectors (nozzles) on the roof of the chamber spray and mix the propellants at the same time. Because the chamber operates under high pressures, the propellants need to be forced inside. Powerful, lightweight turbine pumps between the propellant tanks and combustion chambers take care of this job.

The major components of a chemical rocket assembly are a rocket motor or engine, propellant consisting of fuel and an oxidizer, a frame to hold the components, control systems and a cargo such as a satellite. A rocket differs from other engines in that it carries its fuel and oxidizer internally, therefore it will burn in the vacuum of space as well as within the Earth's atmosphere. The cargo is commonly referred to as the payload. A rocket is called a launch vehicle when it is used to launch a satellite or other payload into space. A rocket becomes a missile when the payload is a warhead and it is used as a weapon.

Many different types of rocket engines have been designed or proposed. Currently, the most powerful are the chemical propellant rocket engines. Other types being designed or that are proposed are ion rockets, photon rockets, magnetohydrodynamic drives and nuclear fission rockets; however, they are generally more suitable for providing long term thrust in space rather than launching a rocket and its payload from the Earth's surface into space.

A cryogenic propellant is one that uses very cold, liquefied gases as the fuel and the oxidizer. Liquid oxygen boils at -297 F and liquid hydrogen boils at -423 F. Cryogenic propellants require special insulated containers and vents to allow gas from the evaporating liquids to escape. The liquid fuel and oxidizer are pumped from the storage tanks to an expansion chamber and injected into the combustion chamber where they are mixed and ignited by a flame or spark. The fuel expands as it burns and the hot exhaust gases are directed out of the nozzle to provide thrust.

Advantages of liquid propellant rockets include the highest energy per unit of fuel mass, variable thrust, and a restart capability. Raw materials, such as oxygen and hydrogen are in abundant supply and a relatively easy to manufacture. Disadvantages of liquid propellant rockets include requirements for complex storage containers, complex plumbing, precise fuel and oxidizer injection metering, high speed/high capacity pumps, and difficulty in storing fueled rockets.

Hypergolic Propellant Rockets:

A hypergolic propellant is composed of a fuel and oxidizer that ignite when they come into contact with each other. There is no need of an ignition mechanism in order to bring about combustion. In hypergolic propellants, the fuel part normally includes hydrazine and the oxidizer is generally nitrogen tetroxide or nitric acid.

The easy start and restart capability of hypergolic propellants make them ideal for spacecraft maneuvering systems. They are also used for orbital insertion as their combustion can be easily controlled and thus allows the precise adjustments required for insertion into orbit. Hypergolic propellants are also employed for altitude control.

Hypergolic propellants remain in liquid state at normal temperatures. They do not need the temperature-controlled storage as in case of cryogenic propellants. But, as compared to cryogenic propellants, hypergolic propellants are less energetic. That is they produce less energy per unit mass. For example: in a moon bound shuttle, 75% of the onboard mass would be fuel, in case of cryogenic propellants. But in case of hypergolic propellants, the number raises to 90%. In comparison to cryogenic propellants, hypergolic propellants are very poisonous. They react with living tissues as well cause injuries. So it is mandatory for technicians to wear full-body Self-Contained Atmospheric Protection Ensemble (SCAPE) suits. They are corrosive therefore storage requires special containers and safety facilities. It is necessary that they be stored safely, with no possible contacts between the fuel parts.

The Rocket Pioneers :

Authors Jules Verne and H. G. Wells wrote about the use of rockets and space travel and serious scientists soon turned their attention to rocket theory.

It was, of course, the 20th century that witnessed an explosion in the field of rocketry. By the end of the 19th century, the three men considered to be the primary pioneers of modern rocketry had been born and begun their studies, Konstantin Tsiolkovsky (Russian), Hermann Oberth (German) and Robert Goddard (American).

In 1898, a Russian schoolteacher, Konstantin Tsiolkovsky (1857-1935), proposed the idea of space exploration by rocket. In a report he published in 1903, Tsiolkovsky suggested the use of liquid propellants for rockets in order to achieve greater range. Tsiolkovsky stated that the speed and range of a rocket were limited only by the exhaust velocity of escaping gases. For his ideas, careful research, and great vision, Tsiolkovsky has been called the father of modern astronautics.

Hermann Oberth, a German scientist, also contributed to the theory and design of rockets. In 1923 he published a work in which he proved flight beyond the atmosphere is possible. In a 1929 book called "The Road to Space Travel" Oberth proposed liquid-propelled rockets, multistage rockets, space navigation, and guided and re-entry systems. He also advanced the idea of a transatlantic postal rocket for quick mail delivery. It was taken seriously at the time but never attempted.

From 1939 to 1945 he worked on German war rocket programs with such notables as Wernher von Braun. After the war he came to the United States where he again worked with von Braun. During the war one of the weapons the scientists were designing was reminiscent of Oberth's postal rocket. The German's wanted to build a rocket which would carry a bomb from Europe to strike New York City.

Most historians call Oberth and Tsiolkovsky the fathers of modern rocket theory. If that is so, an American, Dr. Robert H. Goddard, can be called the father of the practical rocket. His designs and working models eventually led to the German big rockets such as the V-2 used against the Allies in World War II. All three men are enshrined in the International Space Hall of Fame in Alamogordo, N.M.

Although rockets were used during World War I, they were of limited value. As was the case during the U.S. Civil War, rockets were simply not as effective as artillery weapons of the day. Rockets sometimes were employed both on land and at sea to lay smoke screens. Allied forces also used rockets as a method of illuminating battlefields. Rockets were exploded in a brilliant flash that could illuminate a battlefield for several seconds. Some rockets carried a parachute with a flare attached. As the parachute and flare dropped toward the ground, a battlefield could be illuminated for about 30 seconds.

Robert Goddard:

Robert Hutchings Goddard was born on October 5, 1882 in Worcester, Massachusetts. Early in his life, Goddard was inspired by works of science fiction, primarily "War Of The Worlds" by H.G. Wells and "From The Earth To The Moon" by Jules Verne. Completely independent of Tsiolkovsky, Goddard realized that the reaction principle would provide a foundation for space travel. But rather than focus entirely on theory, Goddard set out at an early age to become equipped to build and test the hardware he believed was necessary to best demonstrate the reaction principle. Again independent of Tsiolkovsky, he too theorized that a combination of liquid hydrogen and liquid oxygen would make an ideal propellant.

Considered a staunch patriot until his death, Goddard went to work for the Army in 1917 with the goal of designing rockets that would aid in the war effort. The work was conducted in California, and yielded the development of a small, hand-held rocket launcher similar to what was later called the bazooka. In 1919, Goddard published a work entitled "A Method Of Reaching Extreme Altitudes", which contained a detailed compilation of much of the research he had completed to date. It also included speculation on the possibilities of spaceflight. Goddard concluded that a combination of liquid oxygen and gasoline were the only practical fuels that could be used in his continuing research in the development of liquid-fueled rocket motors.

By 1924, Goddard had developed and tested a liquid oxygen pump and engine that functioned. The unit, however, was too small to actually be employed on a working rocket. But, with a working design, he began to plan more elaborate research. Goddard successfully test fired a pressure-fed liquid oxygen engine inside the Clark University physics laboratory on December 6, 1925. The engine was attached to a small test rocket housed inside a fixed stand. The engine was fired for about 24 seconds and lifted the rocket for about 12 seconds within its stand. On March 16, 1926 Goddard launched a 10-foot long rocket from a 7-foot long frame. The rocket reached a maximum altitude of 41 feet at an average velocity of 60 m.p.h. The rocket remained in the air for 2.5 seconds and flew a distance of 184 feet. While this flight did not even come close to matching the performance of gunpowder propelled rockets of years past, it remains one of the most significant events in the history of rocketry. Powered by a combination of liquid oxygen and gasoline, the rocket launched by Goddard on March 16, 1926 was the first to ever be launched using liquid fuel.

Following this flight, Goddard realized that his rocket was too small to be refined. He decided to develop larger rockets for further tests. Work was also begun on the development of a more elaborate launch tower. The new rockets incorporated innovative technology like flow regulators, multiple liquid injection, measurement of pressure and lifting force and an electrically fired igniter to replace a gunpowder fired igniter used previously. A turntable was also designed to produce spin stabilization.

The fourth launch of a liquid-fueled rocket occurred on July 17, 1929. Considered much more elaborate than the first three, Goddard equipped the rocket with a barometer, thermometer and a camera to record their readings during flight. The rocket achieved a maximum altitude of 90 feet in an 18.5-second flight covering a distance of 171 feet. The scientific payload was recovered safely via parachute. However, the launch was so noisy and bright that it captured much public attention. Many eyewitnesses believed an aircraft had crashed in the area. Local fire officials quickly forced Goddard to discontinue his launch operations at the Auburn site.

Goddard then made a large move after deciding to embark on his first full-time effort at constructing and testing rockets. He set up shop at the Mescalero Ranch near Roswell, New Mexico in July, 1930. The relocation was initially financed through the Guggenheim grant. The first Roswell launch occurred on December 30, 1930 using a rocket 11 feet long by 12 inches wide and weighing 33.5 pounds empty. The test was impressive as the rocket reached a maximum altitude of 2,000 feet and maximum speed of 500 m.p.h. The rocket employed a new gas pressure tank to force the liquid oxygen and gasoline into the combustion chamber.

In the years approaching World War II, Goddard had agreed to allow military officials to review his research. On May 28, 1940 Goddard and Harry F. Guggenheim had met with a joint committee of Army and Navy officials in Washington, D.C. A complete report was given to these officials by Goddard which outlined his advances in both solid-fueled and liquid-fueled rockets. The Army rejected the prospect of long-range rockets altogether. The Navy expressed a minor interest in liquid-fueled rockets. Goddard later characterized these responses as negative. Neither branch of service was interested in an innovative rocket aircraft that had been patented by Goddard on June 9, 1931. The lack of military interest in rocketry had confounded Goddard for years, since he understood that only the government had adequate resources to fund proper research.

• First American to explore mathematically the practicality of using rocket propulsion to reach high altitudes and to traject to the moon (1912)
• First to receive a U.S. patent on the idea of a multistage rocket (1914)
• First to prove, by actual static test, that rocket propulsion operates in a vacuum, that it needs no air to push against (1915-1916)
• First to develop suitable lightweight pumps for liquid-fuel rockets (1923)
• First to develop and successfully fly a liquid-fuel rocket (March 16, 1926)
• First to launch a scientific payload (a barometer, a thermometer, and a camera) in a rocket flight (1929)
• First to use vanes in the rocket engine exhaust for guidance (1932)
• First to develop gyroscopic control apparatus for guiding rocket flight (1932)
• First to fire a liquid-fuel rocket faster than the speed of sound (1935)
• First to launch and successfully guide a rocket with an engine pivoted by moving the tail section (as if on gimbals) controlled by a gyro mechanism (1937)

Wernher von Braun:

In 1927, an eager 17-year-old scientist named Wernher von Braun joined the VfR, or Verein fur Raumschiffahrt (Society for Space Travel), which had been formed in June, 1927. This group of mainly young scientists immediately began designing and building a variety of rockets. Membership in the VfR quickly soared to about 500, a sufficient member base to allow the publication of a periodic journal, "Die Rakete" (The Rocket). A number of VfR members, including Walter Hohmann, Willy Ley and Max Valier, had written, and continued to write, popular works on the field of rocketry.

Hohmann's book "Die Erreichbarkeit der Himmelskorper" (The Attainability of Celestial Bodies) published in 1925 was so technically advanced that it was consulted years later by NASA. Valier would later seek to popularize rocketry by helping to organize tests of German rocket cars, gliders, train cars and snow sleds. Other VfR members, including Hermann Oberth and von Braun, participated in the Ufa Film Company project in the late 1920's through 1930, which also sought to popularize the field of rocketry.

Germans also developed the first rocket-powered aircraft, the Ente (Duck), a sailplane powered by two Sander rockets. An Ente flew a distance of three-quarters of a mile in just under one minute during a test flight on June 11, 1928. The test was conducted by the German glider group Rhon-Rossitten Gesellschaft. Not to be out-done, the publicity-seeking Fritz von Opel piloted a glider powered by 16 Sander rockets on September 30, 1928. The glider reached a maximum speed of 95 m.p.h.

Russian Rocketry Research Continues:

In 1930, Russian government rocket design teams led by Fridrikh Arturovitch Tsander and Valentin Petrovitch Glushko began testing a number of liquid-fueled rocket engines. Tsander published "Problems of Flight by Means of Reactive Devices" in 1932 while Glushko published "Rockets, Their Construction and Utilization" in 1935. These Russian rocket tests continued through 1937, and tested liquid-fueled rocket engine concepts burning such combinations as gasoline/gaseous air, toluene/nitrogen tetroxide, gasoline/liquid oxygen, kerosene/nitric acid and kerosene/tetranitromethane.

One of the Russian rocket designs emerging from these tests was called GIRD-X, which weighed 65 pounds, was 8.5 feet long and 6 inches wide. A GIRD-X rocket reached a maximum altitude of three miles during a test on November 25, 1933. Another of the Russian rockets, called Aviavnito, weighed 213 pounds, was 10 feet long and 1 foot wide. An Aviavnito rocket reached an altitude of 3.5 miles in 1936.

VfR Rocket Tests:

Also in 1930, the VfR set up permanent offices in Berlin and began testing rockets which would ultimately change the nature of warfare and propel the world into the space age. These at first humble tests began at an abandoned German ammunition dump at Reinickendorf nicknamed Raketenflugplatz (Rocket Airfield).

By August, 1930 tests began on the first of the VfR rockets, called Mirak-1 (Minimum Rocket-1). Powered by a combination of liquid oxygen and gasoline, Mirak-1 employed a 12-inch long liquid oxygen tank that shrouded a combustion chamber, thus cooling it. Gasoline was carried in a three-foot long tail stick. Mirak-1 was successfully static test fired in August, 1930 at Bernstadt, Saxony. During a second static test firing in September, 1930 Mirak-1 exploded when its liquid oxygen tank burst.

The VfR was forced to disband in the winter of 1933/1934 because the organization could not meet its financial obligations. Rocketry experiments ceased at the Raketenflugplatz facility in January, 1934 and the area resumed operation as an ammunition dump. Upon the disbanding of VfR, all private rocket testing in Germany ceased. Wernher von Braun, however, went to work officially for the German Army at Kummersdorf. There, the Heereswaffenamt-Prufwesen (Army Ordnance Research and Development Department) established the Versuchsstelle Kummersdorf-West as a static testing site for ballistic missile weapons.

Kummersdorf also became a site for the development and testing of a number of prototype jet-assisted take-off (JATO) units for aircraft. These tests were conducted by Wernher von Braun in association with Major von Richthofen and Ernst Heinkel. Under the direction of Captain Walter Dornberger, the Kummersdorf team was quickly able to design and build the A-1 (Aggregate-1) rocket. The A-1 was powered by a combination of liquid oxygen and alcohol, and could develop a thrust of about 660 pounds.

A 70-pound flywheel gyroscope was carried in the nose of the rocket to provide stability during flight. The A-1 was ultimately unsuccessful because its small fiberglass liquid oxygen tank housed inside its alcohol tank was fire prone. In addition, the gyroscope was located too far from the center of the rocket to be effective. The A-1 was soon followed by the A-2, which employed separate alcohol and liquid oxygen tanks. The A-2 gyroscope was located near the center of the rocket between the two fuel tanks. In December, 1934 two A-2 rockets, nicknamed Max and Moritz, were launched from the North Sea island of Borkum. Each reached an altitude of about 6,500 feet. But the feasibility of effective military rockets remained speculative at best, exemplified by the fact that in 1935, Adolph Hitler rejected a proposal from Artillery General Karl Becker for a long-range bombardment rocket.

German Rocket Tests Commence At Peenemunde

In April, 1937 all of the German rocket testing was relocated to a top-secret base at Peenemunde on the Baltic Coast. The first task of engineers at what was established as the Heeresversuchsstelle Peenemunde (Army Experimental Station Peenemunde) was to develop and test a new rocket called the A-3. By the end of 1937, the Peenemunde team had developed and tested the 1,650-pound, 21-foot long A-3 rocket, which burned a combination of liquid oxygen and alcohol. Although the propulsion system of the A-3 functioned well, its experimental inertial guidance system did not. The guidance problems were solved, and larger rockets were planned.

By 1938, Germany had begun invading huge portions of Eastern Europe, and Adolph Hitler began recognizing the need for an effective ballistic missile weapon. The German Ordnance Department requested that the Peenemunde team develop a ballistic weapon that had a range of 150 to 200 miles and could carry a one-ton explosive warhead. An interim test vehicle to bridge the gap between the A-3 and the A-4 was named the A-5. The A-5 was similar in design to the A-3, but employed a simpler, more reliable guidance system and stronger structure. The A-5 was fashioned with the exterior appearance of the proposed A-4 weapon. A-5 tests were conducted from the fall of 1938 through 1939. The rockets were launched both horizontally and vertically, and were often recovered by parachute and launched again. The first A-5 launched vertically reached an altitude of 7.5 miles.

Civilian and military efforts in the field of rocketry in all other nations combined paled in comparison with the strides made in Germany, where the first A-4 was tested with complete success on October 3, 1942. The very first A-4 rocket reached an altitude of 50 miles and flew a distance of 120 miles. The A-4, later renamed V-2, would go on to lay the cornerstone of modern rocketry.

V-1 Buzz Bomb

Although Germany produced and deployed a number of rocket and missile weapons during World War II, the potency of their weapons was based on the so-called "V" weapons. The "V" was short for "Vergeltungswaffen", roughly translated "weapons of retaliation", "weapons of reprisal" or "weapons of vengeance". The V-1 was the first of the numbered V-weapons. The V-1 was a pilotless bomber that employed a gasoline-powered pulse-jet engine that could produce a thrust of about 1,100 pounds. The entire V-1 weighed about 4,900 pounds. V-1 test flights began in 1941 over the Peenemunde range. The V-1 was originally called the Fieseler Fi-103. The V-1 bore no resemblance to the V-2, which was under development at Peenemunde at the same time.

British intelligence received information that secret weapons were under development at Peenemunde, so hundreds of Allied heavy bombers attacked Peenemunde on August 17, 1943. About 800 people were killed, including Dr. Walter Thiel, who at the time was in charge of V-2 engine development. Allied forces did not know the extent of weapons development at Peenemunde, nor that their bombing raids did not significantly hinder development of the weapons themselves. Indeed, the V-weapons were soon to be used in combat. V-1 attacks aimed at targets in England began in June, 1944. Each V-1 was launched from a ramp, and was unguided. After it was launched, the V-1 flew a preset course until a switch cut off its engine, causing the V-1 to simply fall on whatever was under it.

The distinctive sound of the V-1 engine resulted in the vehicle being nicknamed the "buzz bomb" by Allied forces. People on the ground knew they were relatively safe if the buzzing sound came and then faded as the weapon passed out of range. However, if the buzzing sound stopped abruptly, it was quickly understood that a powerful explosion could occur nearby. Each V-1 carried about 2,000 pounds of explosives, and was capable of causing great damage. But, since the V-1 was unguided, the weapon rarely hit a specific target. The V-1 had a top speed of about 390 m.p.h. so could be intercepted by fighter aircraft or destroyed by anti-aircraft artillery.

The V-1 airframe was also prone to failure due to engine vibration. It is believed that about 25 percent of all V-1 missiles launched were destroyed by airframe failure before reaching their targets. Although specific numbers vary from source to source, a British report released after the war indicated that 7,547 V-1 missiles were launched at England. Of these, the report indicated that 1,847 were destroyed by fighter aircraft, 1,866 were destroyed by anti-aircraft artillery, 232 were destroyed by flying into barrage balloon cables and 12 were destroyed by Royal Navy ship artillery. That left about half of all V-1 missiles launched at England unaccounted for, and a large number were able to cause extensive property damage. The British reported that 6,139 people were killed as a direct result of V-1 attacks, about three times the number that were killed by the V-2.

A Pilot For The German V-1 Buzz Bomb

It is lesser known that the Germans designed a manned version of the V-1 called the V-1e. The V-1e was not intended to be recovered. It would have been launched, then guided to its target by a pilot on a suicide mission. Similar to the Japanese kamikaze concept, the V-1e group was code-named Project Reichenberg. The V-1e was about 27 feet long and employed a cockpit and pilot instrumentation. The V-1e was test flown several times by German test pilot Hanna Reitsch.

Reitsch confirmed that the basic V-1 airframe was prone to severe vibration resulting from engine noise. She believed the deployment of the V-1e as introduced would result in significant pilot losses, even if the pilot had agreed to perform a suicide mission. The Germans could not sustain design changes late in the war, so the V-1e was never deployed in combat.

German V-2 Is Designed And Tested

The German V-2 rocket, developed under the designation A-4, is believed to be one of the most significant scientific advances of World War II, second only to the development of the atomic bomb. Aerodynamic data was generated for the basic V-2 design during wind tunnel tests conducted in 1936 and 1937. Certain V-2 components were in production as early as the spring of 1939, when launches of a test version of the rocket called the A-5 were being conducted. Through 1942, development of the V-2 was conducted 24 hours per day under the supervision of Wernher von Braun. The first models of the V-2 were ready for firing by the spring of 1942.

The first test launch of a V-2 occurred on June 13, 1942. The rocket pitched out of control and crashed as a result of a propellant feed system failure. The second V-2 test launch was conducted on August 16, 1942. This V-2 flight was also considered a failure, but the vehicle became the first guided missile to exceed the speed of sound. On just its third test launch on October 3, 1942 the V-2 scored a complete success. The rocket achieved a maximum altitude of 50 miles and maximum range of 120 miles, meeting the initial performance criteria for the weapon.

Following this achievement, Adolph Hitler, just a few years earlier unreceptive to the potential of guided ballistic missiles, established a military production committee within the Ministry of Armaments and War Production to manage further development of the V-2. While this did inject needed resources for the V-2 program, Wernher von Braun later stated that the military organization placed in charge of V-2 development by Hitler lacked scientific judgment, and ultimately hindered the capabilities of the weapon significantly. Indeed, von Braun was not to participate in the V-2 development program without great personal risk.

German V-2 Enters Production

Wartime production of the V-2 began at a virgin facility at the Peenemunde Experimental Center. Following the Allied bombing of Peenemunde on August 17, 1943 V-2 production was relocated to an underground facility at Mittelwerk, near Nordhausen in the Harz Mountains. The site was converted from an oil depot. The Mittelwerk site consolidated all of the production efforts previously carried out at Peenemunde, and eventually became the sole location for V-2 production. V-2 production plants were originally under construction at sites near Vienna, Berlin and Friedrichshafen, but construction of these sites was abandoned because of a persistent threat of Allied attacks.

Certain individual V-2 components were manufactured at sites throughout Germany, and troop training was also conducted at other sites. But V-2 production was based at the plant at Mittelwerk. A remarkable 900 V-2 missiles per month were being produced at the Mittelwerk plant by the close of the war.

Each V-2 was 46 feet long, had a diameter of 5 feet, 6 inches and finspan of 12 feet. The entire rocket weighed about 27,000 pounds at launch. The top six feet of the V-2 was a warhead containing up to 2,000 pounds of conventional explosives. Below the warhead was a 5-foot section containing instrumentation, a 20-foot section containing the fuel tanks and a 15-foot section containing the engine. The instrumentation section contained an automatic pilot, accelerometer and radio equipment. The automatic pilot was made up of two electric gyroscopes that stabilized the rocket's pitch, roll and yaw motions. As the rocket moved about the axes of the gyroscopes, the movement was measured by electronic potentiometers. This caused electric command signals to be sent to a series of steering vanes at the base of the rocket.

The V-2 employed two sets of steering vanes. An external set of four steering vanes was made up of one steering vane at the base of each of the four V-2 fins. An internal set of four steering vanes was located at the base of the engine. Both sets of steering vanes were designed to work together to deflect the engine exhaust and steer the rocket. Movement of the steering vanes was intended to cause the potentiometers in the instrumentation section to read zero voltage, thus keeping the rocket on a predetermined path. Whenever the potentiometers read any voltage, an electric command would be sent to corresponding steering vanes to correct the motion of the rocket until the voltage again read zero. The steering vanes were controlled by electrohydraulic mechanisms. The accelerometer was used to measure the velocity of the rocket, while the radio equipment was used for a variety of purposes. In some instances, the radio equipment was used merely to receive commands from the ground to shut off fuel flow to the engine.

The V-2 contained two fuel tanks. One contained liquid oxygen, while the second contained a combination of 75% alcohol and 25% water. These were the fuels that powered the V-2 engine. The engine itself was composed of a combustion chamber, venturi, fuel pipes, a liquid oxygen fuel pump, an alcohol fuel pump, a steam-driven turbine that drove the two fuel pumps and hydrogen peroxide auxiliary fuel that operated the steam turbine. Through a natural chemical breakdown, the hydrogen peroxide decomposed into oxygen and water. The breakdown occurred at a high enough temperature to instantly turn the water into steam, which in turn drove the turbine. The turbine then pumped fuel into the engine.

German V-2 Deployment And Launch

Completed V-2 rockets were transported by rail car from the factory to storage areas, where they were moved to special trailers by portable cranes. Storage time was kept to a few days, since testing determined that excessive storage time resulted in more V-2 failures. After being stored, the V-2 rockets were moved by truck and trailer to their launch sites. Although deploying the V-2 at fixed launch sites would simplify launch processing, it was felt that fixed launch sites would be too prone to attack. Therefore, the V-2 was deployed as a mobile missile.

Prior to launch, each V-2 missile was transferred to a vehicle called a "meillerwagen". Here, the rocket was clamped to a cradle in a horizontal position. The cradle on the "meillerwagen" was then raised by hydraulic pistons until the rocket reached a vertical position. A launching platform was then raised up until it assumed the full weight of the rocket. The cradle clamps were then released, and the "meillerwagen" was withdrawn several feet. The launching platform was a 10-foot rotatable ring housed in a square, angle-iron framework supported at its corners by jacks. The launching platform was very simple in design, and could be readily moved from launch site to launch site.

Each launch site was supported by about 30 vehicles, including transport trucks and trailers, the "meillerwagen", propellant storage trucks, command and control trucks, personnel carriers and military support vehicles. The operation was very efficient, and a V-2 could typically be launched from four to six hours after a suitable launch site was selected. Electrical power for the V-2 was provided by ground sources when it rested on the launching platform and by batteries while in flight. Ground power was necessary for launch preparations, including the firing system.

The actual launch was controlled from a remote location some 200 to 300 yards away from the rocket. An armored vehicle of some type was typically used as a "firing room". When the rocket was ready for launch, the control officer would fire the igniters by electric command. The flow of fuel would then be activated by solenoid valves. The liquid oxygen and alcohol then flowed by gravity to the exhaust nozzle, where they were lit by the igniters, which resembled a 4th of July pinwheel. This burning in itself was not sufficient to launch the rocket, but it did give the control officer a visual indication that the rocket was functioning properly. Once the control officer believed the rocket was ready for launch, an electric command was sent to start the fuel pumps. After about three seconds, the fuel pump steam turbine reached full speed, the fuel flow reached its full value of 275 pounds-per-second and the engine thrust reached about 69,000 pounds.

The V-2 was then launched, and began to rise slowly. It continued in a vertical rise for about four seconds, then was pitched to its programmed launch angle by the gyroscopic guidance system. The maximum pitch angle was typically about 45 degrees, which produced the greatest range. After about 70 seconds, the V-2 fuel flow was stopped, and the engine shut down. By this time, the rocket had achieved a speed of 5,000 to 6,000 feet-per-second. The rocket would then complete an unpowered ballistic trajectory, reaching its target just five minutes after being launched. Achieving a maximum altitude of 50 to 55 miles, the V-2 could impact a target within an operational design range of 180 to 190 miles, although some are believed to have flown as many as 220 miles. Because the V-2 flew so high and so fast, there was no defense against it. The missiles could not be detected until they exploded on the ground.

German V-2 Becomes A Weapon Of War

The first hostile V-2 missiles were launched on September 6, 1944. On that day, two V-2 missiles were launched toward Paris but failed to inflict any damage. V-2 attacks on England began on September 8, 1944. V-2 missiles were typically launched toward London and Antwerp, Belgium. Allied forces also reported that eleven V-2 rockets impacted near Remagen, Germany on March 9 and 10, 1945 as the Germans made an unsuccessful attempt to prevent engineers from completing a pontoon bridge across the Rhine River and hinder an Allied advance there.

Specific numbers vary from source to source, but it is generally believed that about 1,100 V-2 missiles reached England until V-2 attacks ceased on March 27, 1945. About 2,800 people are believed to have been killed and another 6,500 injured as a direct result of V-2 attacks. It is generally believed that about 5,000 V-2 missiles were manufactured by the Germans prior to the close of World War II. About 600 were used for test launches and troop training, with the remainder launched toward targets. Given these numbers, the V-2 failure rate was quite large. The V-2 failure rate was due to a number of factors. In many instances, the missiles failed to be successfully launched. In other instances, the guidance system failed, causing the missile to miss its target. The missile often exploded or broke up due to the stress of supersonic flight, and in many cases the V-2 explosive warhead failed to detonate after impacting a target.

Both the V-1 and V-2 proved themselves to be potent weapons, but they suffered from basic weaknesses that did not allow the weapons to turn the tide for Germany at the close of World War II. The weapons were rushed into deployment before they could be completely tested and refined. As a result, they lacked accuracy and the ability to carry explosive payloads large enough to compensate for this lack of accuracy. While barrages of huge numbers of V-1 and V-2 missiles might have compensated for the basic weaknesses of the weapons, the Germans were unable to introduce sufficient numbers to overwhelm Allied advances.

It should be noted that a number of follow-up versions of the V-2 were envisioned by German engineers, and historians will continue to wonder how World War II would have played out if Germany had the time to develop these concepts, along with perhaps an atomic or biological weapons payload. The German concept weapons carried the "A" designation, like the A-4 which eventually became known as the V-2. The A-5 actually preceded the A-4, and was used as an interim test prototype of the A-4. German concept vehicles considered to follow the V-2 began with the A-6.

Although design of the A-6 was completed, the vehicle was never built. The A-6 would have been identical to the V-2 with the exception of fuel. The A-6 would have used nitric-sulfuric acid as oxidizer and vinyl isobutyl ether mixed with aniline as fuel. These fuels were storable, and were intended to quicken the speed and ease with which the weapons could be handled and launched. The same operational improvement was incorporated when the U.S. Air Force liquid-oxygen burning Titan I was replaced by the Titan II, which employed storable propellants.

The A-7 was a winged missile based upon the design of the A-5. Dummy versions of the A-7 were dropped from aircraft for the purpose of gathering ballistic flight data. Test versions of the A-7 were launched using a 3,500-pound thrust engine adapted from the A-5. The A-7 was found to have a 30-mile glide path when launched from an aircraft flying at an altitude of five miles, or a 15-mile range when launched from the ground. The vehicle was intended for testing only, and was never deployed as a weapon. The A-8, which was never built, would have been a winged version of the A-6.

The A-9, similar in concept to the short-lived A-4b, was proposed to increase the range of the V-2 to 400 miles through the incorporation of wings. The wings would allow the A-9 to glide toward its target, rather than drop to the ground, at the end of its ballistic flight. However, since the A-9 would have a greater range than the V-2, it would be required to glide toward its target at relatively low speeds. Like the V-1, the A-9 would have been relatively easy to intercept in flight. As a result, the A-9 was neither built nor tested. An interesting application of the A-9 concept was a manned version of the A-9 employing a triangular landing gear. Had it been built, the manned A-9 could potentially have carried a pilot a distance of 400 miles in just 17 minutes.

The designation A-10 was given to what would have been the first stage of a missile employing the A-9 as a second stage. The A-10 stage would have been 65 feet long and had a diameter of 13 feet, 8 inches. It was designed to produce a 400,000-pound thrust by burning nitric acid and diesel oil. Calculations indicated that the A-10 first stage coupled with an A-9 second stage could carry a 2,000-pound payload a distance of 2,500 miles. If built, this would have been the world's first intermediate-range ballistic missile.

But, the von Braun design team did not stop there, and indeed had plans on the drawing board that could have resulted in the first space launch vehicles. The designation A-11 was given to the first stage of a vehicle that would have employed an A-10 as second stage and an A-9 as third stage. The specific intention of von Braun was to carry a manned A-9 third stage into space.

The A-12 designation was given to a powerful first stage concept capable of producing a liftoff thrust of 2.5 million pounds. The A-12 would have been mated to an A-11 second stage and an A-10 third stage. Calculations indicated that the total vehicle could have carried a 60,000-pound payload into space.

Topical Questions:

• What is the meaning of thrust, total impulse and specific impulse?