Aerospace Power Know the basic facts and general operating principle of rocket engines. 1. Outline the history of rocket engines. 2. Describe how rocket.

Aerospace Power Know the basic facts and general operating principle of rocket engines. 1. Outline the history of rocket engines. 2. Describe how rocket engines operate. 3. List the types of rocket engines. 4. Describe advanced propulsion systems. Lesson Objective: Know the basic facts and general operating principle of rocket engines. Samples of Behavior/Main Points 1. Outline the history of rocket engines. 2. Describe how rocket engines operate. 3. List the types of rocket engines. 4. Describe advanced propulsion systems.

Overview 1. History of Rocket Engines 2. How Rocket Engines Operate
3. Types of Rocket Engines 4. Advanced Propulsion Systems In this lesson we will discuss: 1. History of rocket engines 2. How rocket engines operate 3. Types of rocket engines 4. Advanced propulsion systems

Warm Up Questions CPS Questions (1-2)

History of Rocket Engines
The Chinese used rockets as early as A.D In A.D they used “fire arrows” in a battle known as Kai-Feng-Fu. History of Rocket Engines The Chinese used rockets as early as A.D In A.D they used “fire arrows” in a battle known as Kai-Feng-Fu and thus became the first civilization to us rockets as weapons of war.

In 1405, Von Eichsteadt, a German engineer, devised a rocket that was propelled by gunpowder, and in 1429 the French used rockets to defend Orleans against the British. In 1405, Von Eichsteadt, a German engineer, devised a rocket that was propelled by gunpowder, and in 1429 the French used rockets to defend Orleans against the British.

By 1630 rockets that exploded and sent small pieces of metal in all directions were developed for military use. Rockets were used in 1807 at the battle of Copenhagen, and in 1812, the British formed a rocket brigade. By 1630 rockets that exploded and sent small pieces of metal in all directions were developed for military use. During the Thirty Years’ War ( ), rockets weighing as much as 100 pounds were fired. In the battle of Panipat in India, as many as 1,000 rockets were fired at one time. Rockets were used in 1807 at the battle of Copenhagen, and in 1812, the British formed a rocket brigade. This brigade saw action in the Napoleonic Wars at Leipzig in 1813 and at Waterloo in 1815.

During the end of the 18th century and early into the 19th century, rockets experienced a brief revival as a weapon of war. Col. William Congreve, a British artillery expert, developed a rocket with fins for more controlled flight through better stabilization. Congreve’s rockets were successful in the bombing of Fort McHenry in the War of They inspired Francis Scott Key to write “the rockets’ red glare,” in his poem that later became The Star Spangled Banner. During the end of the 18th century and early into the 19th century, rockets experienced a brief revival as a weapon of war. Col. William Congreve, a British artillery expert, developed a rocket with fins for more controlled flight through better stabilization. Congreve’s rockets were successful in the bombing of Fort McHenry in the War of They inspired Francis Scott Key to write “the rockets’ red glare,” in his poem that later became The Star Spangled Banner.

In the mid 1900’s, William Hale, a British subject, used spin stabilization for his rockets. Rockets were used to carry lifelines to ships wrecked along coastlines, and in World War I, troops used rockets to carry signal flares to light up the battlefield at night and to carry messages during battle. In the mid 1900’s, William Hale, a British subject, used spin stabilization for his rockets. In this method, the escaping exhaust gases struck small vanes at the bottom of the rocket, causing it to spin much as a bullet does in flight. Variations of these principles are still used today. Rockets were used to carry lifelines to ships wrecked along coastlines, and in World War I, troops used rockets to carry signal flares to light up the battlefield at night and to carry messages during battle. Also, troops used rockets in at least one World War I airplane. These rockets, placed in holding tubes, were attached to the biplane’s wing struts.

Dr. Robert H. Goddard in the United States and Dr. Hermann Oberth in Germany brought increasing interest in rocketry. Dr. Goddard, known as the “Father of Modern Rocketry,” was the first scientist to use liquid fuels (liquid oxygen and gasoline) in rockets. Dr. Oberth’s work with liquid oxygen and alcohol fuels closely followed that of Dr. Goddard. These “firsts” in the use of liquid fuels occurred in the late 1920’s. The work of Dr. Robert H. Goddard in the United States and Dr. Hermann Oberth in Germany brought about increasing interest in rocketry. Dr. Goddard, known as the “Father of Modern Rocketry,” was the first scientist to use liquid fuels (liquid oxygen and gasoline) in rockets. Dr. Oberth’s work with liquid oxygen and alcohol fuels closely followed that of Dr. Goddard. These “first” in the use of liquid fuels occurred in the late 1920’s. Dr. Goddard’s work in liquid fuels rocketry was strictly a private venture. Rocketry in Germany, however, had the attention and support of their government. As war drew near for the United States, Dr. Goddard's work was directed toward developing quick-takeoff propulsion units for U.S. Navy aircraft. In Germany rocketry went forward with the development of powerful engines for rockets. These rockets were ultimately known as V-2s, and more than a thousand fell on England as high-explosive bombs.

After World War II, both the United States and the Soviet Union acquired German personnel with rocketry expertise. The United States began a program with high-altitude atmospheric sounding rockets, one of Goddard’s early ideas. These became the starting point of the U.S. space program. After World War II, both the United States and the Soviet Union acquired German personnel with rocketry expertise. Both the United States and the Soviet Union realized the potential of rocketry as a military weapon and began a variety of experimental programs. The United States began a program with high-altitude atmospheric sounding rockets, one of Goddard’s early ideas. Later, a variety of medium and long-range intercontinental ballistic missiles were developed. These became the starting point of the U.S. space program. Missiles such as the Redstone, Atlas, and Titan would eventually launch astronauts into space.

Learning Check #1 CPS Questions (3-4)

How Rocket Engines Operate
Rocket propulsion, flight, and control are achieved applying certain laws of science that Galileo Galilei and Sir Isaac Newton discovered. How Rocket Engines Operate Rocket propulsion, flight, and control are achieved applying certain laws of science that Galileo Galilei and Sir Isaac Newton discovered.

Physical laws are based on gravitation, the force of attraction that exists between all matter within the universe. A body of small mass attracts a body of large mass just as the large mass attracts the small mass. Mutual gravitation exists between all bodies regardless of size. Physical laws are based on gravitation, the force of attraction that exists between all matter within the universe. A body of small mass attracts a body of large mass just as the large mass attracts the small mass. Mutual gravitation exists between all bodies regardless of size. Theoretically when a pencil falls to the floor, the Earth attracts the pencil as the pencil attracts the Earth. But because the Earth is so much more mass than the pencil, we actually see the pencil falling toward the Earth while the Earth remains constant.

Galileo experimented with gravitation by dropping a solid iron ball from the Leaning Tower of Pisa. Galileo experimented with gravitation by dropping a solid iron ball from the Leaning Tower of Pisa. His experiment showed that objects of varying weight would strike the ground at the same time if they were released simultaneously and from the same height above the surface. This holds true even if one of the objects is thrown horizontally.

Sir Isaac Newton concluded that bodies in space, such as planets and their moons, are attracted toward each other in a special way. Sir Isaac Newton concluded that bodies in space, such as planets and their moons, are attracted toward each other in a special way. The amount of mass involved determines how much gravitational attraction is possible; and the distance between the two bodies determines the effects of the gravitation — the greater the distance the less effect.

Rocket propulsion is based on Sir Isaac Newton’s three laws of motion. The third law is the heart of rocketry because the action of the rocket engine produces the forward motion of the rocket. Rocket propulsion is based on Sir Isaac Newton’s three laws of motion. The third law is the heart of rocketry because the action of the rocket engine produces the forward motion of the rocket.

The relationship of force, weight, and mass is defined by Newton’s law of universal gravitation. It states that,“Every object in the Universe attracts every other object with a force directly along the line of centers for the two objects that is proportional to the product of their mass and inversely proportional to the square of the separation between the two objects.” Expressed by the equation F = M1M2/r2. The relationship of force, weight, and mass is defined by Newton's law of universal gravitation. It states that, "Every object in the Universe attracts every other object with a force directly along the line of centers for the two objects that is proportional to the product of their mass and inversely proportional to the square of the separation between the two objects." Expressed by the equation F = M1M2/r2. F represents the force in pounds. M1 and M2 are masses of the two objects. r is the separation between the two. The measured gravitational acceleration at the Earth's surface is found to be about 32.2 feet per second/per second. The gravitational force of a symmetrical sphere acts as if its entire mass was focused at its center. Since Earth approximates such a sphere, the distance between the Earth and a body upon or near its surface is equal approximately to the Earth's radius. The mass of the Earth, M1, remains constant. From these values the force of the Earth's gravity, which corresponds to the weight of body M2, is found to be 32.2 pounds-force for each unit of mass. This ratio is called the gravitational conversion constant.

The weight of a body, the Earth’s gravitational attraction to it, may be measured by using a spring scale. The obvious weight of a body depends upon the force exerted upon it by another larger body in close proximity. The degree of force exerted depends upon the masses of both bodies. However, the mass of a body, the quantity of matter it contains, never changes. It is the property of matter that enables a body to occupy space. The weight of a body, the Earth's gravitational attraction to it, may be measured by using a spring scale. The obvious weight of a body depends upon the force exerted upon it by another larger body in close proximity. The degree of force exerted depends upon the masses of both bodies. However, the mass of a body, the quantity of matter it contains, never changes. It is the property of matter that enables a body to occupy space.

Momentum is the product of mass and velocity. Newton found that the action of force on a body changes the body’s momentum at a rate proportional to the force and the direction of force. If the mass of a body remains constant, any change in momentum is reflected in a change in velocity. Momentum is the product of mass and velocity. Newton found that the action of force on a body changes the body's momentum at a rate proportional to the force and the direction of force. If the mass of a body remains constant, any change in momentum is reflected in a change in velocity. If a brick is dropped from the roof of a building, the brick will be accelerated by the force of gravity at the rate of 32.2 feet per second per second. The mass of the brick does not change; its velocity and momentum change at a rate proportional to the force of Earth's gravity.

Newton’s three laws of motion as they apply to rocketry. The first law states that when launching a rocket vertically, the propulsion system must produce enough thrust to overcome the inertia of the launch vehicle. The thrust, in pounds, must be greater than the weight of the rocket. Newton’s second law states that the amount of force required to accelerate a body depends on the mass of the body. Newton's three laws of motion as they apply to rocketry. The first law states that when launching a rocket vertically, the propulsion system must produce enough thrust to overcome the inertia of the launch vehicle. The thrust, in pounds, must be greater than the weight of the rocket. Newton's second law states that the amount of force required to accelerate a body depends on the mass of the body. At the moment of lift-off, the total mass of the rocket is slightly less than the force being produced by the engines. Every second the rocket's mass is being deceased by burning and expelling the rocket's fuel as thrust. At the same time, the amount of force being produced remains constant. Thus, the force becomes increasingly greater than the dwindling mass and this results in a rapid second-by-second acceleration until the fuel is used up.

Newton’s third law of motion relates to what occurs in a rocket engine prior to launch. Newton's third law of motion relates to what occurs in a rocket engine prior to launch. All chemical rockets develop thrust by burning fuel and expelling mass from their exhaust nozzles at a high velocity. The thrust produced is a reactive force acting in a direction opposite to the direction of the exhaust. When the fuel burns in the combustion chamber, the gases produced are very hot and create a lot of pressure inside the chamber. This pressure forces the gases through the exhaust nozzle to the lower pressure outside the rocket. As the gases move out of the combustion chamber they pass through the throat of the nozzle, which constricts the exhaust and thereby increases velocity. The bell shaped nozzle allows the escaping exhaust to expand, which lowers its pressure. The expansion of the escaping exhaust accomplishes two important things. Keeps pressure in the nozzle lower than inside the combustion chamber. Permits only rearward motion of the exhaust gas, which develops forward thrust.

Airframe The airframe and propulsion system of a rocket engine exists to deliver whatever cargo the rocket is carrying. Provides the rocket with the streamlined shape. It must be as lightweight as possible. The Atlas rocket was a prime example of how engineers designed airframes that were both strong and lightweight. Airframe The airframe and propulsion system of a rocket engine exists to deliver whatever cargo the rocket is carrying. Provides the rocket with the streamlined shape. It must be structurally sound and capable of withstanding heat, stress, and vibration. It must be as lightweight as possible because every pound of weight saved in the airframe allows an additional pound of weight that can be added to the payload. The Atlas rocket was a prime example of how engineers designed airframes that were both strong and lightweight. The skin or surface of the rocket also served as the wall of the propellant tanks, eliminating the need for separate internal tanks and providing savings in weight. The surface of the Atlas was thinner than a dime, and when no fuel was aboard, it had to be pressurized to keep it from collapsing.

The most spectacular airframe ever constructed for a rocket was the Saturn V launch vehicle. The most spectacular airframe ever constructed for a United States rocket was the Saturn V launch vehicle. In its Apollo lunar flight configuration, the Saturn V stood 363 feet tall. The first stage, as an example of its airframe, had a diameter of 33 feet and a length of 138 feet. At the bottom was the thrust structure that contained the vehicle's five engines. It was a complex group of beams and bracing made mainly of aluminum alloy plus steel. Surrounding the thrust structure was a skin assembly that provided additional strength and better aerodynamics. The skin assembly lessened the effect of drag caused by the rocket pushing its way through the air.

Other aerodynamic features attached to the thrust structure included fairing and fins. The fairings were drag reducers and the fins helped stabilize the rocket's flight through the atmosphere. Fuel and oxidizer tanks made up a great portion of the Saturn's first-stage airframe, which is true of all liquid-propellant rockets. The walls of these tanks formed a large part of the rocket's exterior surface or skin. Within each of the tanks were slosh baffles that added strength to the airframe and stabilized the propellant's motion as the rocket vibrated and tilted in flight. The oxidizer and kerosene could, without slosh baffles, set up sloshing and swirling motions that could have made the rocket uncontrollable. The interstage structure included the skin portion used to join the three rocket stages. Where the propellant tank walls exposed to the airstream were smooth, the metal skirts forming the intertank and interstage structure were corrugated. This was necessary to give greater strength to a relatively thin part of the structure. Although the airframes of all liquid propellant rockets posses certain aspects of the Saturn V's structural characteristics, there are differences. These difference depend on the size and purpose of the rocket. The primary objective is to build a structure that will withstand the stresses while using the least possible weight.

Propulsion System The rocket’s propulsion system includes the propellant used, the containers for the propellant, all the plumbing that may be required to get the propellant from the containers to the engine and the rocket engine itself. The rocket's propulsion system includes the propellant used, the containers for the propellant, all the plumbing that may be required to get the propellant from the containers to the engine and the rocket engine itself.

Propulsion System Chemical systems usually involve the mixing and burning of a chemical fuel and a chemical oxidizer. The gas-heating system design would use an “external” heat source to heat the propellant and build the pressure. Electric systems use magnetic fields and currents to propel matter in small amounts. Propulsion systems used in rocketry generally are classified as chemical, gas-heating and electric systems. Chemical systems usually involve the mixing and burning of a chemical fuel and a chemical oxidizer to produce the hot, expanding gases needed to provide thrust. The gas-heating system design would use an "external" heat source to heat the propellant and build the pressure necessary to exit the exhaust nozzle at high velocity to provide thrust. Electric systems use magnetic fields and currents to propel matter in small amounts.

Types of Rocket Engines
Liquid Propellant Liquid-propellant rockets can operate on most of the combustion fuels plus an oxidizer. In some cases, liquid propellants permit intermittent operations. Combustion can be stopped and started by controlling propellant flow. Liquid Propellant Liquid-propellant rockets can operate on most of the combustion fuels plus an oxidizer. The selection of propellants for a particular mission requires a complete analysis of available fuels to ensure mission success. In some cases, liquid propellants permit intermittent operations. Combustion can be stopped and started by controlling propellant flow.

Liquid Propellant Classifications Monopropellants Contains its oxidizer and fuel in one solution. May be a single chemical compound. The compounds are stable at ordinary temperatures and pressures, but break down when heated and pressurized, or when the breaking down process is started by a catalyst. Monopropellant rockets are simple since they need only one propellant tank and associated equipment. Liquid propellant classifications Monopropellants Contains its oxidizer and fuel in one solution. May be a single chemical compound, such as nitromethane, or a mixture of several chemicals compounds, such as hydrogen peroxide and alcohol. The compounds are stable at ordinary temperatures and pressures, but break down when heated and pressurized, or when the breaking down process is started by a catalyst. The most common monopropellant system uses hydrazine, a colorless fuming corrosive, and a catalyst. Generally, monopropellants also require more heat for ignition and react more slowly than bipropellants. These characteristics mean that monopropellants require larger combustion chambers. Monopropellant rockets are simple since they need only one propellant tank and associated equipment. The design of a liquid-monopropellant system is much simpler than that of a bipropellant system because a monopropellant systems requires only half the storage, pumping, and controlling equipment. The draw back is its sensitivity to temperatures and shock. This sensitivity results in instability and restricts its handling.

Liquid Propellant Classification Bipropellant A combination of fuel and oxidizer, which is not mixed until after they have been injected into the combustion chamber. More stable and capable of better performance than monopropellants. In addition to a fuel and oxidizer, a liquid bipropellant may include a catalyst to increase the speed of the reaction, or other additives to improve the physical, handling, or storage properties. Bipropellant A combination of fuel and oxidizer, which is not mixed until after they have been injected into the combustion chamber. More stable and capable of better performance than monopropellants. In addition to a fuel and oxidizer, a liquid bipropellant may include a catalyst to increase the speed of the reaction, or other additives to improve the physical, handling, or storage properties.

Bipropellant Bipropellant A combination of fuel and oxidizer, which is not mixed until after they have been injected into the combustion chamber. More stable and capable of better performance than monopropellants. In addition to a fuel and oxidizer, a liquid bipropellant may include a catalyst to increase the speed of the reaction, or other additives to improve the physical, handling, or storage properties.

Liquid Propellant Classification Tripropellant A combination of three compounds. The third compound is added to improve the basic bipropellant’s ability to increase the vehicle’s velocity. All liquid-propellant systems have propellant tanks; a propellant feed system, a thrust chamber, and controls such as regulators, valves, and sequencing and sensing equipment. Tripropellant A combination of three compounds. The third compound is added to improve the basic bipropellant's ability to increase the vehicle's velocity. All liquid-propellant systems have propellant tanks; a propellant feed system, a thrust chamber, and controls such as regulators, valves, and sequencing and sensing equipment.

Solid Propellant In a solid propellant rocket system the fuel and oxidizer are mixed together from the start. The rocket case is the combustion chamber and holds the propellants. There are no valves, pumps, or sensors. Additives, if needed to increase temperature or to control burning, are simply mixed with propellant grains. Solid Propellant The chemical system of a rocket may have a solid rather than a liquid propellant. In a solid propellant rocket system the fuel and oxidizer are mixed together from the start. The rocket case is the combustion chamber and holds the propellants. There are no valves, pumps, or sensors. Additives, if needed to increase temperature or to control burning, are simply mixed with propellant grains. The grains are made by passing a mixture of solid chemical fuel and oxidizers through a die. This produces a specially shape grain. Once the grain is ignited, it is capable of sustained burning. Fuels used in solid propellants include asphalts, waxes, oils, plastics, metal, rubbers, and resins. Ignited by a composition that both heats the grain to ignition temperature and increases the pressure in the combustion chamber until propellant reaction is assured. Older propellant mixtures could be ignited by the heat of a short-resistance electrical wire. This type of ignition device is found in model rocket-launching devices. Today’s rockets use devices like the squib. The squib consists of an enclosure filled with a combustible powder, which is ignited electrically. The flame of the burning squib ignites the grain.

Hybrid Propellant Hybrid propellants use a combination of both liquid and solid propellants within the same engine. When solid fuel is used, it is packed into the rocket engine as an inactive material, without its oxidizer. The gases, approaching each other from opposite directions, unite and burn just above the face of the fuel grain. Hybrid Propellant Hybrid propellants use a combination of both liquid and solid propellants within the same engine. Usually, solid material is used as the fuel, and a liquid is used as the oxidizer. However, there are engine systems that use liquid fuels and solid oxidizers. When solid fuel is used, it is packed into the rocket engine as an inactive material, without its oxidizer. The liquid oxidizer is stored in a separate tank. To create combustion and to generate thrust, the oxidizer is fed into the solid-fuel combustion chamber. In this system, the solid fuel and the oxidizer do not come into actual contact. Instead, the heat of ignition vaporizes the oxidizer and the fuel. The gases, approaching each other from opposite directions, unite and burn just above the face of the fuel grain. The thrust produced by a hybrid rocket can be increased or decreased simply by increasing or decreasing the flow of oxidizer over the fuel charge. Thrust is stopped when the flow of oxidizer is closed off. .

Hybrid Propellant Hybrid propellants combine in a single rocket engine many of the advantages of both liquid and solid propellant rockets. Flexibility gives the hybrid rocket its biggest operational advantage. It can be throttled from zero to full thrust and can be stopped and started in flight. Hybrid propellants combine in a single rocket engine many of the advantages of both liquid and solid propellant rockets. Hybrid propellant systems have the flexibility, controllability, and high performance of liquid-propellant rockets, plus the simplicity, reliability, and relative economy of solid-propellant rockets. Flexibility gives the hybrid rocket its biggest operational advantage. It can be throttled from zero to full thrust and can be stopped and started in flight. .

Advanced Propulsion Systems
Electric Propulsion Electric propulsion systems use power generated by an on-board source to apply electric currents to matter that exits the engine at high velocity. The primary drawback to electric propulsion is that comparatively little thrust is produced. Depending on the space vehicle, batteries may be the backup or intermediate source of power. Electric Propulsion Electric propulsion systems use power generated by an on-board source to apply electric currents to matter that exits the engine at high velocity. The primary drawback to electric propulsion is that comparatively little thrust is produced. However, the velocity of the propellant is very high; and over a long period of application, a vehicle being propelled by an electric system would achieve very high velocity. Depending on the space vehicle, batteries may be the backup or intermediate source of power. Silver-zinc batteries were used during the Apollo flights for short-duration power needs. Nickel-cadmium and silver-zinc batteries have powered many satellites over the years.

Electric Propulsion Batteries for spacecraft operations are recharged by an arrangement of solar cells called an array or a paddle. The Sun radiates the equivalent of 130 watts of electrical energy per square foot on any surface that is perpendicular to the Sun’s rays. Batteries for spacecraft operations are recharged by an arrangement of solar cells called an array or a paddle. The Sun radiates the equivalent of 130 watts of electrical energy per square foot on any surface that is perpendicular to the Sun’s rays. Solar cells must be perpendicular to the Sun to reach their highest efficiency. Even a slight slanting angle can result in a great deal of power loss. Body-mounted solar panels on a spacecraft are less efficient than an array, which can be directed toward the Sun. Sun-oriented arrays also have disadvantages. They add to the mechanical complexity and power requirements of the vehicle. Another problem is that portions of the vehicle and its solar array may throw shadows on other portions, including the sensors and antennas. For these reasons, the less efficient but more reliable body-mounted solar panels are often used.

Electric Propulsion Another device that provides electricity from a chemical reaction is the fuel cell. Fuel cells, unlike batteries, use chemical fuels and oxidizers that are stored outside the cell. Two porous nickel electrodes are submerged in a solution of sodium or potassium hydroxide. Pressurized hydrogen and oxygen are fed to these electrodes and spread throughout them. Another device that provides electricity from a chemical reaction is the fuel cell. Fuel cells, unlike batteries, use chemical fuels and oxidizers that are stored outside the cell. Two porous nickel electrodes are submerged in a solution of sodium or potassium hydroxide. Pressurized hydrogen and oxygen are fed to these electrodes and spread throughout them. Chemical reactions between the hydrogen and the solution and the oxygen and the solution take place on the electrodes. Positive ions move through the solution, and negative electrons flow through the external circuit to provide power. From a weight standpoint, fuel cells are best suited for uses requiring up to 10 kilowatts of power for operating a few days or several months. Another advantage of the hydrogen-oxygen fuel cells is that the chemical reaction produces water. The Apollo space program used the fuel cell as a primary source of in-space electrical power and drinking water.

Electric Propulsion Nuclear energy is a fourth means of generating electricity. Basically there are two ways of using nuclear energy to generate electricity: the radioisotope method and the nuclear fission method. Nuclear fission is the splitting of atoms as in the process that takes place in an atomic bomb. Nuclear energy is a fourth means of generating electricity. Basically there are two ways of using nuclear energy to generate electricity: the radioisotope method and the nuclear fission method. Radioisotope thermoelectric (relationship between heat and electricity) generator depends on the decay of certain radioactive metals. As these metals decay, turn into new isotopes, energy is given off as heat. The resulting heat is changed to usable power by thermoelectric means. Creating usable heat is slow and creates less heat than do other applications of nuclear power. This means that the radioisotope method generates relatively small amounts of electricity and must be used where low power is all that is needed. Although this method generates smaller amounts of electricity it can last for years. This makes it applicable as a power source of probes going to the outer planets. Nuclear fission is the splitting of atoms as in the process that takes place in an atomic bomb. Nuclear fission can be slowed to the point where the fission process is extended over a long period of time and the tremendous heat resulting from the process can be used to produce large amounts of electricity. The nuclear fission method powers ships and electric generating plants. The drawback of this process is the heavy shielding required to protect against harmful radiation. The weight of the shielding poses a problem for fission reactors on space vehicles launched for Earth; the thrust required to counteract the extra weight is very costly. Whatever the drawbacks in the use of nuclear power sources, they still are the greatest hope for space power and propulsion in the future.

Unit of Electric Propulsion Electric propulsion techniques produce very little total thrust, but the amount of thrust is extended over a very long time. No propulsion system, electric or otherwise, can work without a propellant mass. In space, sustaining thrust is more desirable than the intensity of thrust. Electric engines are expected to yield specific impulses of 2,000 to 30,000 seconds or more. Chemical propulsion units produce large amounts of thrust over short periods of time. Electric propulsion techniques produces very little total thrust but the amount of thrust is extended over a very long time. This works well for long voyages in space because constant thrust means constant acceleration. No propulsion system, electric or otherwise, can work without a propellant mass. The concept of a working fluid, a substance that is heated or otherwise energized and propelled at high velocity through an exhaust nozzle, is basic to all kinds of electric propulsion. Therefore, the specific impulse is applicable. Just as with chemical propellants, the specific impulse of a working fluid is proportional to the ratio of combustion temperature (TC) to the average molecular weight of the combustion products (m). The ratio is stated as TC/m. Based on these criteria, a pound of working fluid will yield so many pounds of force in one second. In space, sustaining thrust is more desirable than the intensity of thrust. There is more interest in specific impulse as an indication of how far a spacecraft can be propelled than in specific impulse as an indication of how much thrust can be produced. Specific impulses of chemical propellants may never exceed 600 seconds, theoretical limit; electric engines are expected to yield specific impulses of 2,000 to 30,00 seconds or more.

Types of Electric Engines Resistojet Engines Resitojet is the name given to miniature thrusters designed to deliver precisely controlled thrust for spacecraft attitude control and station keeping (keeping satellite in required position). Heat is generated by passing an electric current through a special wire or tube. A stream of hydrogen or ammonia is passed over the heating element and energized to high velocity as it travels out an exhaust nozzle similar to that of a conventional chemical rocket. Types of Electric Engines Resistojet Engines Resitojet is the name given miniature thrusters designed to deliver precisely controlled thrust for spacecraft attitude control and station keeping (keeping satellite in required position). Heat is generated by passing an electric current through a special wire or tube, which presents high resistance to the passage of current. This resistance develops heat. A stream of hydrogen or ammonia is passed over the heating element and energized to high velocity as it travels out an exhaust nozzle similar to that of a conventional chemical rocket. Resistojets may be about 6 inches long and 2 inches in diameter and weigh about ½ a pound. A unit this size provides about 10 millipounds of thrust at specific impulses of seconds, depending on the type of propellant. Resistance heating is the principle on which electrical heating appliances like toasters and irons operate. The practical resistojets currently in use or under development use low-level power sources.

Types of Electric Engines Arc Jet Engines Electricity jumping this gap or “arcing” creates very high temperatures. As with the resistojet, the operating time is limited more by the fuel supply than by the duration of the power source. Teamed with a nuclear reactor, the arc jet might some day compete with more direct means of nuclear propulsions. Arc Jet Engines The arc jet differs form the resistojet; instead of a resisting wire or tube, there is simply a gap between electrodes. Electricity jumping this gap or "arcing" creates very high temperatures. Electricity jumping this gap or "arcing" creates very high temperatures. Hydrogen passing through this arc is heated to thousands of degrees and expanded through a nozzle. Theoretically, extremely high exhaust velocities, high thrust, as well as long endurance; (specific impulses up to 2,000 seconds) are possible. As with the resistojet, the operating time is limited more by the fuel supply than by the duration of the power source. Nevertheless, these devices get the most mileage out of a supply of liquid hydrogen. Present power sources are not sufficient to realize the arc jet's possibilities to any practical degree. Teamed with a nuclear reactor, the arc jet might some day compete with more direct means of nuclear propulsions.

Types of Electric Engines Ion Engines Ion or electrostatic engines are in use as supplementary propulsion sources for north-south satellite station keeping and attitude control. Rate of fuel consumption is low and they can sustain thrust over long periods. The ion rocket is the first example of propulsion by some means other than gaseous heating. Ion Engines Ion or electrostatic engines are in use as supplementary propulsion sources for north-south satellite station keeping and attitude control. The practical models, however, are of very low thrust and are limited to the slow, prolonged acceleration in deep space that may be desired in some instances. Rate of fuel consumption is low and they can sustain thrust over long periods. Other desirable features of ion "rockets" are their lightness of weight and the ease with which they can be stopped and restarted. The ion rocket is the first example of propulsion by some means other than gaseous heating. Ion rockets produce thrust by electrostatic acceleration of charged atomic and subatomic particles. When subject to heat, the fuel for an ion engine is vaporized and ionized; the heat causes the atomized fuel's atoms to give up an electron. The atoms are then positively charged ions. These ions pass through an electric grid, which accelerates their movement toward the exit nozzle to tremendous speeds. The stripped-off electrons follow another path and are fed back into the exhaust stream to produce an electrically neutral exhaust. Otherwise, the engine and the whole vehicle with it would build up a dangerous electrical charge.

Types of Electric Engines Plasma Engines A plasma is made up of ions, free electrons, neutrons, and other subatomic particles; they are not made up of molecules. Plasma engines first employ electric power to heat a gas and break it down into plasma. Specific impulse is directly proportional to exhaust velocity. Pulsed plasma thrusters have a number of advantages in missions requiring precise maneuvers. Plasma Engines A final type of electric engine is the plasma or electromagnetic engine. A plasma is made up of ions, free electrons, neutrons, and other subatomic particles; they are not made up of molecules. Plasma engines first employ electric power to heat a gas and break it down into plasma. Then, it subjects the plasma to electromagnetic fields of force, which accelerate the plasma to super velocities. Specific impulse is directly proportional to exhaust velocity. It is the extremely high exhaust velocity of electric engines of the ion and plasma types that give them such high specific impulses. Pulsed plasma thrusters have a number of advantages in missions requiring precise maneuvers. This is particularly true where a large number of accurately controlled thrust pulses are needed such as on a spin-stabilized spacecraft. The plasma thruster has no valves, requires little power, and needs no warm-up time to function. The initial application of the plasma thruster was on a NASA synchronous meteorological satellite (SMS) for station keeping and for proper aiming of antennas. A larger application of the plasma jet was launched in The pulsed plasma thrusters on the satellite NOVA-1 were used to control the satellite against drag and solar pressure. Another function of the two thrusters is to trim (adjust) the satellite's time of one complete orbit.

Nuclear Propulsion Nuclear Energy for Rocket Application Nuclear Energy for Rocket Vehicle Application (NERVA) is a project started in 1961 to develop a nuclear propulsion unit. The NERVA could develop 75,000 pounds of thrust with a specific impulse of 825 seconds. The NERVA engine’s capability for easy stopping, restarting, and thrust regulation plus high specific impulse give it the means of using a propellant supply with efficiency. Nuclear Propulsion Nuclear Energy for Rocket Application Nuclear Energy for Rocket Vehicle Application (NERVA) is a project started in 1961 to develop a nuclear propulsion unit. In the NERVA rocket, the reactor applied direct heating to hydrogen for rocket propulsion. Sometimes called a gaseous heating or nuclear thermal system. The NERVA could develop 75,000 pounds of thrust with a specific impulse of 825 seconds, double that achieved so far with chemical propulsion, but not as high as that of electric propulsion. An objective of the NERVA is to combine both high thrust and high specific impulse to achieve a super rocket. The NERVA rocket would be capable of carrying heavy payloads deep into space, achieving high velocity rapidly, and possibly relaunching from another planet. The NERVA engine's capability for easy stopping, restarting, and thrust regulation plus high specific impulse give it the means of using a propellant supply with efficiency. Weight is a problem with all nuclear rocket propulsion systems. Another drawback to the NERVA concept is radioactivity. The hydrogen working fluid, as it passes through or around the reactor and is heated, is also irradiated, loaded with particles coming from the reactor's fissioning atoms.

Nuclear Propulsion Gas Core Nuclear Engines Gas core nuclear rockets, include the coaxial flow reactor and the light bulb reactor, have a specific impulse as high as 5,000 seconds compared to around a 1,000 seconds with the NERVA rocket. The nuclear light bulb (NLB) reactor system would consist of several cylindrical cavities. Thermal radiation would pass through the transparent wall to heat the hydrogen to desired temperatures. Gas Core Nuclear Engines Gas core nuclear rockets, include the coaxial flow reactor and the light bulb reactor have a specific impulse as high as 5,000 seconds compared to around a 1,000 seconds with the NERVA rocket. The coaxial flow reactor would consist of a large, nearly spherical cavity surrounded by a system that controls and confines the radiation and the high temperatures at work. A gaseous uranium substance would be centered in the cavity, held there by the action of the hydrogen propellant flowing through the porous walls of the cavity. Heat generated in the fissioning uranium plasma would be transferred to the hydrogen by thermal radiation. Some of the uranium would escape with the hydrogen. The nuclear light bulb (NLB) reactor system would consist of several cylindrical cavities, each containing a transparent wall of fused silica (glassy mineral) used to separate the gaseous uranium from the hydrogen propellant. Thermal radiation would pass through the transparent wall to heat the hydrogen to desired temperatures. This construction, the transparent wall surrounding the hot reactor core, is similar to a light bulb's construction and gives the engine its name. An NLB powered vehicle is seen as a totally recoverable winged combination airplane and space ship, with a single-stage power plant to carry it through all phases of aerodynamic flight and spaceflight. It would have the thrust, duration, and ease of stopping and restarting needed for launch, prolonged or deep space flight, and aerodynamic reentry and landing.

Nuclear Propulsion Fusion and Photo Engines A fusion engine is a concept that goes far back beyond NERVA and NLB in that it proposes use of a reactor for controlled thermonuclear energy. A photon system is a futuristic concept that would convert matter into radiation or light energy. Another system is a passive one, which involves photons. Fusion and Photo Engines A fusion engine is a concept that goes far back beyond NERVA and NLB in that is proposes use of a reactor for controlled thermonuclear energy. This is the energy of the so-called hydrogen bomb, many times as powerful as the fission reaction employed in present-day nuclear reactors of the NERVA concept. Based on the fusing of nuclei of the hydrogen-isotopic atoms called deuterium and tritium. Perhaps the immense heat needed to begin such a reaction could somehow be generated, and the reaction then contained and controlled by means of an electromagnetic field. Through adding or cutting off a coolant and working fluid in the exhaust flow, specific impulse could be controlled for either extremely high thrust levels or for extremely high specific impulses, up to a million seconds or more. A photon system is a futuristic concept that would convert matter into radiation or light energy. Photons are the elements of light, and their velocity is that of the speed of light. If a means is found to effectively change matter into radiant energy, then the photon system will be developed. Although the thrust value would be low, the speed of the spacecraft propelled in this manner would eventually be quite fast. Another system is a passive one, which involves photons. This idea is called solar sail and would rely on the pressure of the radiant energy coming from the Sun for propulsion. It involves a massive reflective area, which would look something like the sail of a boat. Photons and other forms of radiant energy coming from the sun would strike the sail with enough force to push the spacecraft outward away from the Sun. It does have drawbacks as the force of the Sun's radiation diminishes the further away from the Sun a satellite gets. The spacecraft would also have to have another type of propulsion system if it were traveling toward the Sun.

Review Questions CPS Questions (9-10)

Summary 1. History of Rocket Engines 2. How Rocket Engines Operate
3. Types of Rocket Engines 4. Advanced Propulsion Systems In this lesson we discussed: 1. History of Rocket Engines 2. How Rocket Engine Operate 3. Types of Rocket Engines 4. Advanced Propulsion Systems

Aerospace Power Know the basic facts and general operating principle of rocket engines. 1. Outline the history of rocket engines. 2. Describe how rocket.

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Aerospace Power Know the basic facts and general operating principle of rocket engines. 1. Outline the history of rocket engines. 2. Describe how rocket.

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Presentation on theme: "Aerospace Power Know the basic facts and general operating principle of rocket engines. 1. Outline the history of rocket engines. 2. Describe how rocket."— Presentation transcript:

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