INTRODUCTION

In today’s world, technology plays an integral role in the daily life of people of all ages. It affects where we live, how we work, how we interact with each other, and what we aspire to accomplish. “Rocket science” has become verbal shorthand for complexity. Saying that something is “not rocket science” suggests that it is simple and easily grasped. The expression, in turn, says something about the way we think of rockets: fantastically complex, unimaginably powerful, the highest of high technology.

Newton’s third law states that “To every action force, there is an equal and opposite reaction force.” A rocket exploits Newton’s third law in the same way that a deflating balloon does. A force pushes a steady stream of gas out behind the rocket, and a force of equal magnitude pushes the rocket itself in the opposite direction, ie; forward. The balloon is “fueled” with air that is blown into it, held momentarily by clamping the neck shut, and then released when the neck is opened. The rocket is fueled with combustible chemicals, that when burned inside the rocket, yield a cloud of hot gas. Every gas (be it the exhaust gas in a rocket or air in a balloon) expands to fill its container. Hotter gasses expand more rapidly than colder ones, as their molecules move faster. The burning of a rocket’s propellant steadily adds more and more hot gas to the confined space inside the rocket, raising the pressure that the gas exerts. The pressure forces a steady stream of gas out through the open vent (or vents) at the rear of the rocket: the exhaust plume, whose acceleration in one direction causes the rocket to accelerate in the opposite direction.

The force produced by a rocket is called “thrust,” and is usually measured in pounds or kilograms. The most critical measures of a rocket’s performance are tied directly to the amount of thrust it produces. The “specific impulse” of a rocket is the amount of thrust produced by 1 pound of propellant in 1 second—a measure of the fuel’s potency and the engine’s efficiency. The “thrust-to-weight ratio” is exactly what its name suggests: a comparison between the thrust that a rocket produces and its weight. The higher the thrust-to-weight ratio, the greater the rocket’s ability to carry a payload and the propellant required to make the rocket function. Payload capacity, range, and altitude measurements of a rocket are directly linked to the thrust it produces.

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HISTORY OF ROCKETS

The evolution of the rocket has made it an indispensable tool in the exploration of space. For centuries, rockets have provided ceremonial and warfare uses starting with the ancient Chinese, the first to create rockets. The rocket apparently made its debut on the pages of history as a fire arrow used by the Chin Tartars in 1232 AD for fighting off a Mongol assault on Kai-feng-fu.

One of the first devices to successfully employ the principles essential to rocket flight was a wooden bird. The writings of Aulus Gellius, a Roman, tell a story of a Greek named Archytas who lived in the city of Tarentum, now a part of southern Italy. Somewhere around the year 400 B.C., Archytas mystified and amused the citizens of Tarentum by flying a pigeon made of wood. Escaping steam propelled the bird suspended on wires. The pigeon used the action-reaction principle, which was not stated as a scientific law until the 17th century.

About three hundred years after the pigeon, another Greek, Hero of Alexandria, invented a similar rocket-like device called an aeolipile. It too used steam as a propulsive gas. Hero mounted a sphere on top of a water kettle. A fire below the kettle turned the water into steam, and the gas traveled through pipes to the sphere. Two L-shaped tubes on opposite sides of the sphere allowed the gas to escape, and in doing so gave a thrust to the sphere that caused it to rotate.

Just when the first true rockets appeared is unclear. Stories of early rocket like devices appear sporadically through the historical records of various cultures. Perhaps the first true rockets were accidents. In the first century A.D., the Chinese reportedly had a simple form of gunpowder made from saltpeter, sulfur, and charcoal dust. To create explosions during religous festivals, they filled bamboo tubes with a mixture and tossed them into fires. Perhaps some of those tubes failed to explode and instead skittered out of the fires, propelled by the gases and sparks produced by the burning gunpowder.

The lineage to the immensely larger rockets now used as space launch vehicles is unmistakable. But for centuries rockets were in the main rather small, and their use was confined principally to weaponry, the projection of lifelines in sea rescue, signaling, and fireworks displays. Not until the 20th century did a clear understanding of the principles of rockets emerge, and only then did the technology of large rockets begin to evolve. Thus, as far as spaceflight and space science are concerned, the story of rockets up to the beginning of the 20th century was largely prologue.

Legendary characters used the power of mythology to fly through the heavens. About 100 BC a Greek inventor known as Hero of Alexandria came up with a new invention that depended more on the mechanical interaction of heat and water. He invented a rocket-like device called an Aeolipile. It used steam for propulsion. Hero mounted a sphere on top of a water kettle. A fire below the kettle turned the water into steam, and the gas traveled through the pipes to the sphere. Two L-shaped tubes on opposite sides of the sphere allowed the gas to escape, and in doing so gave a thrust to the sphere that caused it to rotate. They sounded more like fireworks than rockets but the Chinese used rockets in battle. In 1232 AD the Chinese used rockets against the Mongols

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who were besieging the city of Kai-fung-fu. An arrow with a tube of gunpowder produced an arrow of flying fire.

In 1696, Robert Anderson, an Englishman, published a two-part treatise on how to make rocket molds, prepare the propellants, and perform the calculations. uring the early introduction of rockets to Europe, they were used only as weapons. Enemy troops in India repulsed the British with rockets. Later in Britain, Sir William Congreve developed a rocket that could fire to about 9,000 feet. The British fired Congreve rockets against the United States in the War of 1812. The English confrontation with Indian rockets came in 1780 at the Battle of Guntur. The closely massed, normally unflinching British troops broke and ran when the Indian Army laid down a rocket barrage in their midst. William Congreve's incendiary rocket used black powder, an iron case, and a 16-foot guide stick.

Early in the 20th century, an American, Robert H. Goddard (1882-1945), conducted practical experiments in rocketry. He had become interested in a way of achieving higher altitudes than were possible for lighter-than-air balloons. He published a pamphlet in 1919 entitled A Method of Reaching Extreme Altitudes. It was a mathematical analysis of what is today called the meteorological sounding rocket.

The V-2 rocket (in Germany called the A-4) was small by comparison to today's rockets. It achieved its great thrust by burning a mixture of liquid oxygen and alcohol at a rate of about one ton every seven seconds. Once launched, the V-2 was a formidable weapon that could devastate whole city blocks. With the fall of Germany, many unused V-2 rockets and components were captured by the Allies in October 4, 1957, the world was stunned by the news of an Earth-orbiting artificial satellite launched by the Soviet Union. Called Sputnik I, the satellite was the first successful entry in a race for space between the two superpower nations. Less than a month later, the Soviets followed with the launch of a satellite carrying a dog named Laika on board. Laika survived in space for seven days before being put to sleep before the oxygen supply ran out. A few months after the first Sputnik, the United States followed the Soviet Union with a satellite of its own. Explorer I was launched by the U.S. Army on January 31, 1958.

Soon, many people and machines were being launched into space. Astronauts orbited Earth and landed on the Moon. Robot spacecraft traveled to the planets. Space was suddenly opened up to exploration and commercial exploitation. Satellites enabled scientists to investigate our world, forecast the weather, and to communicate instantaneously around the globe. As the demand for more and larger payloads increased, a wide array of powerful and versatile rockets had to be built.

Since the earliest days of discovery and experimentation, rockets have evolved from simple gunpowder devices into giant vehicles capable of traveling into outer space. Rockets have opened the universe to direct exploration by humankind.

The world of rocketry and space exploration has deep roots in the past. Today the dream of human advancement into the heavens has turned to reality.

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ROCKET TECHNOLOGY

The principle of the rocket is that the fuel contained within the body of the rocket goes through a chemical reaction as it comes out of the end of the rocket.  This reaction then causes thrust and propels the rocket forward.  This is an example of one of Sir Isaac Newton's fundamental laws.  “For every action, there is an equal and opposite reaction”. Propellants are combined in a combustion chamber where they chemically react to form hot gases which are then accelerated and ejected at high velocity through a nozzle, thereby imparting momentum to the engine. The thrust force of a rocket motor is the reaction experienced by the motor structure due to ejection of the high velocity matter.

This is a representation of Newton's law.

A rocket is a machine that develops thrust by the rapid expulsion of matter. 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 payloads 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. 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. At present, rockets are the only means capable of achieving the altitude and velocity necessary to put a payload into an orbit.

The rockets are classified based on their applications, number of stages, size and range, and the propellants used. Basically rockets are represented based on their propellants used. Most rockets today operate with either solid or liquid propellants.The fuel is the chemical the rocket burns but, for the burning to take place, an oxidizer (oxygen) must be present. Jet engines draw oxygen into their engines from the surrounding air. Rockets carry oxygen with them into space, where there is no air.

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. Liquid propellants, which are often gases that have been chilled until they turn into liquids, are kept in separate containers, one for the fuel and the other for the oxidizer. Just before firing, the fuel and oxidizer are mixed together in the engine. A solid-propellant rocket has the simplest form of engine. It has a nozzle, a case,

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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.

This is a diagram of how a solid fuel rocket engine looks before and after ignition.The solid fuel is in dark green, and then in orange as it is ignited to propel the rocket.

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, sending mass out the nozzle at a higher rate and speed. This results in greater thrust. Some propellant cores are star shaped to increase the burning surface even more.

To ignite 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 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. Other igniters are more advanced than the hot wire device. Some are encased in a chemical that ignites first, which then ignites the propellants. Still other igniters, especially those for large rockets, are rocket engines themselves. The small engine inside the hollow core blasts a stream of flames and hot gas down from the top of the core and ignites the entire surface area of the propellants in a fraction of a second.

The other main kind of rocket engine is one that uses liquid propellants, which may be either pumped or fed into the engine by pressure. 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

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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 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. 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 thechamber operates under high pressures, the propellants need to be forced inside.

Modern liquid rockets use powerful, lightweight turbine pumps to take care of this job. With any rocket, and especially with liquid propellant rockets, weight is an important factor. In general, the heavier the rocket, the more the thrust needed to get it off the ground. Because of the pumps and fuel lines, liquid engines are much heavier than solid engines. One especially good method of reducing the weight of liquid engines is to make the exit cone ofthe nozzle out of very lightweight metals. However, the extremely hot, fast-moving gases that pass through the cone would quickly melt thin metal. Therefore, a cooling system is needed. A highly effective though complex cooling system that is used with some liquid engines takes advantage of the low temperature of liquid hydrogen. Hydrogen becomes a liquid when it is chilled to -253oC. Before injecting the hydrogen into the combustion chamber, it is first circulated through small tubes that lace the walls of the exit cone. In a cutaway view, the exit cone wall looks like the edge of corrugated cardboard. The hydrogen in the tubes absorbs the excess heat entering the cone walls

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and prevents it from melting the walls away. It also makes the hydrogen more energetic because of the heat it picks up. We call this kind of cooling system, regenerative cooling.

STAGING OF ROCKETS

There are a few factors that decide the performance of the rocket. Weight of the rocket is one among them. More the rocket weight, higher the thrust required. Once the fuel and oxidizers are consumed, the empty tanks are a burden for the rockets. It will be better if it can be discarded from the rockets. To achieve this, the concept of multi-staging was introduced.

The main reasons for staging are;

1. To improve the performance by eliminating dead weight during powered flight.

2. To maintain acceleration within reasonable limits by reducing thrust in mid-flight.

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The figure above illustrates how the staging is helpful to attain higher altitude.In multistage rockets, the first stage is at the bottom and is usually the largest, the second stage and subsequent upper stages are above it, usually decreasing in size. In parallel staging schemes solid or liquid rocket boosters are used to assist with lift-off. These are sometimes referred to as 'stage 0'. In the typical case, the first stage and booster engines fire to propel the entire rocket upwards. When the boosters run out of fuel, they are detached from the rest of the rocket (usually with some kind of small explosive charge) and fall away. The first stage then burns to completion and falls off. This leaves a smaller rocket, with the second stage on the bottom, which then fires. Known in rocketry circles as staging, this process is repeated until the final stage's motor burns to completion. In some cases with serial staging, the upper stage ignites before the separation- the inter-stage ring is designed with this in mind, and the thrust is used to help positively separate the two vehicles.

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Figure illustrates a 2-stage and 3-stage rockets.Once the fuel is exhausted, the space and structure which contained it and the motors themselves are useless and only add weight to the vehicle which slows down its future acceleration. By dropping the stages which are no longer useful, the rocket lightens itself. The thrust of future stages is able to provide more acceleration than if the earlier stage were still attached, or a single, large rocket would be capable of. When a stage drops off, the rest of the rocket is still traveling near the speed that the whole assembly reached at burn-out time. This means that it needs less total fuel to reach a given velocity and/or altitude.

A further advantage is that each stage can use a different type of rocket motor each tuned for its particular operating conditions. Thus the lower stage motors are designed for use at atmospheric pressure, while the upper stages can use motors suited to near vacuum conditions. Lower stages tend to require more structure than upper as they need to bear their own weight plus that of the

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stages above them, optimizing the structure of each stage decreases the weight of the total vehicle and provides further advantage.

ROCKET COMPONENTS AND NOZZLES

A typical rocket engine consists of the nozzle, the combustion chamber, and the injector. The combustion chamber is where the burning of propellants takes place at high pressure. The chamber must be strong enough to contain the high pressure generated by, and the high temperature resulting from, the combustion process. Because of the high temperature and heat transfer, the chamber and nozzle are usually cooled. The chamber must also be of sufficient length to ensure complete combustion before the gases enter the nozzle.

The performance of rocket engines is highly dependent on the expansion nozzle. The function of the nozzle is to convert the chemical-thermal energy generated in the combustion chamber into kinetic energy. The nozzle converts the slow moving, high pressure, high temperature gas in the combustion chamber into high velocity gas of lower pressure and temperature. Since thrust is the product of mass and velocity, a very high gas velocity is desirable. Nozzles consist of a convergent and divergent section. The minimum flow area between the convergent and divergent section is called the nozzle throat. The flow area at the end of the divergent section is called the nozzle exit area. The nozzle is usually made long enough (or the exit area is great enough) such that the pressure in the combustion chamber is reduced at the nozzle exit to the pressure existing outside the nozzle.

There are three major types of nozzle used to date for the rocket propulsion. They are conical nozzles, annular or plug nozzles and bell typed nozzles. Each one have their own significance in the rocket propulsion according to their design and operation.

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The conical nozzle was used often in early rocket applications because of its simplicity and ease of construction. The cone gets its name from the fact that the walls diverge at a constant angle. A small angle produces greater thrust, because it maximizes the axial component of exit velocity and produces a high specific impulse (a measure of rocket efficiency). The penalty, however, is a longer and heavier nozzle that is more complex to build. At the other extreme, size and weight are minimized by a large nozzle wall angle. Unfortunately, large angles reduce performance at low altitude because the high ambient pressure causes overexpansion and flow separation.

The annular nozzle, also sometimes known as the plug or "altitude-compensating" nozzle, is the least employed of those discussed due to its greater complexity. The term "annular" refers to the fact that combustion occurs along a ring, or annulus, around the base of the nozzle. "Plug" refers to the center body that blocks the flow from what would be the center portion of a traditional nozzle. "Altitude-compensating" is sometimes used to describe these nozzles since that is their primary advantage, a quality that will be further explored later.

Bell typed nozzles are the most commonly used nozzle currently for most of the rocket applications. They are also called ‘De Laval nozzle’ and CD nozzle. They have significant advantages over the other type of nozzles, in terms of performance and size of the nozzle. It was first developed by a Swedish inventor Gustaf de Laval in 1888 for use on a steam turbine and the principle was first used in a rocket engine by Robert Goddard, an American physicist and rocket pioneer in 1926.

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Figure shows the variations in Pressure, Temperature and velocity of the flow across a De Laval nozzle

The operation of a de Laval nozzle relies on the flow properties of gas flowing at subsonic and supersonic speeds. The speed of a subsonic flow of gas will increase as the area reduces, because the mass flow rate is constant. The gas flow through the nozzle is isentropic and at subsonic flow the gas is compressible. At the throat, where the cross sectional area is a minimum, the gas velocity will reach Mach number equal to 1. The flow will be chocked. As the nozzle cross sectional area increases the gas begins to expand and the gas flow increases to supersonic mach number. The nozzle will chock at the throat only if the pressure and mass flow through the nozzle is sufficient to reach sonic speeds, otherwise supersonic flow will not be reached at the diverging section of the nozzle.

When the pressure at the exit of the nozzle is equal to the ambient pressure (ie: Pe=Pa), the thrust is maximum and the nozzle is said to be ideally expanded. When Pe is greater than Pa, the nozzle is under-extended and when Pe is less than Pa, the nozzle is said to be over-expanded.

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Nozzle expansion

Over expansion: Pexit less than Patmosphere. This case often happens for a rocket at the time of lift-off. Because most launch pads are near sea level, the atmospheric pressure is at a maximum. This atmospheric pressure can cause shock waves to form just inside the nozzle. These shock waves represent areas where kinetic energy turns back into enthalpy (heat and pressure). In other words, they reduce kinetic energy of the flow, lowering the exhaust velocity and thus decreasing the overall thrust.

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Under expansion: Pexit greater than Patmosphere. In this case, the flow is not expanded as much as they could have within the nozzle and thus there is a loss in the sense that all the enthalpy is not converted into velocity. This is the normal case for a rocket operating in a vacuum, because P e is always higher than Pa (Pa is 0 in vacuum). Unfortunately, an infinitely long nozzle is needed to expand the flow to zero pressure, so in practice there will be some loss in efficiency.

The total expansion in the nozzle always depends on its design. And this will depend on the factor Area ratio Ae/Ath where Ae is the nozzle exit area and Ath is the nozzle throat area.

THRUST OF THE ROCKET

The "strength" of a rocket engine is called its thrust. Thrust is generated by the propulsion system of the rocket through the application of Newton's third law of motion. Hot exhaust gases expand in the diverging section of the nozzle. The nozzle is usually made long enough (or the exit area great enough) such that the pressure in the combustion chamber is reduced at the nozzle exit to the pressure existing outside the nozzle. It is under this condition that thrust is maximum and the nozzle is said to be adapted, also called ideal or correct expansion. The magnitude of the thrust can be determined by the general thrust equation.

F = m × Ve + (Pe - Pa) × Ae

where F = Thrust m = Propellant mass flow rate Ve = Velocity of exhaust gases Pe = Pressure at nozzle exit Pa = Ambient pressure Ae = Area of nozzle exit

The magnitude of the thrust depends on the mass flow rate of the working fluid through the engine and the exit velocity and pressure of the working fluid. The efficiency of the propulsion system is characterized by the specific impulse; the ratio of the amount of thrust produced to the weight flow of the propellants.

ANALYSIS OF DE LAVAL NOZZLE PERFORMANCE

ASSUMPTIONS:-

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The analysis of gas flow through de Laval nozzles involves a number of concepts and assumptions:

1. For simplicity, the gas is assumed to be an ideal gas.

2. The gas flow is isentropic (i.e., at constant entropy). As a result the flow is reversible (frictionless and no dissipative losses), and adiabatic (i.e., there is no heat gained or lost).

3. The gas flow is constant (i.e., steady) during the period of the propellant burn.

4. The gas flow is along a straight line from gas inlet to exhaust gas exit (i.e., along the nozzle's axis of symmetry).

5. The gas flow behaviour is compressible since the flow is at very high velocities.

METHODOLOGY:-

Let us consider a rocket system with a convergent divergent nozzle which is designed to operate at an exit Mach number of 2.5. The Combustion chamber temperature (T0) is 3000 K, combustion chamber pressure (P0) is 855 KPa and the ambient pressure (Pa) is 50 KPa. The nozzle is designed with an exit area of 0.5 m2.

CALCULATION:-

Case 1:-

Assuming ideal expansion at the exit (no shock waves or expansion waves). This is a real design case which should be achieved.

For an exit Mach number of 2.5,

The temperature ratio, T0/T = 2.25

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Therefore, the exit temperature, Te = 1333.33 K

The Area ratio (Ae/Ath) for the nozzle is 2.6367

Thus, as per the design, the throat area, Ath = 0.19 m2

The propellant mass flow rate through the system, m = PeRTe

∗M∗√γRTe∗Ae

ie; m = 119.55 Kg/s

The velocity of the gas, Ve = M∗√γRTe = 1829.84 m/s

Finally, we calculate the thrust,

F = m * Ve + (Pe – Pa) * Ae

Since the ambient pressure and the exit pressure is equal (Pe = Pa), the thrust due to pressure force will be zero. So, the total thrust will be equal to the momentum thrust.

ie; F = 119.55 * 1829.84 = 218.76 KN

Case 2:-

Assuming the presence of a normal shock wave in the diverging portion of the nozzle where

As/Ath = 1.3

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As/Ath = A1/A1* = 1.3

From the isentropic flow tables, we can find out that M1 = 1.66

P02/P01 = A1*/A2

* = 0.872

Ie; P02 = 0.872 * 855= 745.56 KPa

Ae/A2* = Ae/Ath * Ath/A1

* * A1*/A2

*

= 2.64 * 1 * 0.872 = 2.30

For Ae/A2*=2.30, Exit mach number, Me = 0.262

Te/T0 = 0.986

Which implies, Te = 0.986 * 3000 = 2959.5 K

Also,

Pe/P02 = 0.9535

Which implies, Pe = 0.9535 * 745.56 = 710.89 KPa

From these values, we can find out the velocity of the flow.

Velocity, Ve = Me∗√(γRTe)

= 0.262 * √(1.4∗287∗2959.5)

= 285.70 m/s

Now, we have obtained all the values required to find out the mass flow rate.

m = PeRTe

∗M∗√γRTe∗Ae

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= 119.546 Kg/s ://The mass flow will remain constant.

Since we have the mass flow rate, we can now find out the thrust obtained.

Thrust, F = mVe + (Pe + Pa) * Ae

= 119.546 * 285.70 + (710.89 – 50) * 0.5

= 34.485 KN

This shows that the maximum thrust is obtained during an ideal expansion without any shock waves. The

presence of a shock wave inside the nozzle affects the nozzle performance and the thrust gets

considerably lower. In this case, the thrust reduced from 218.76 KN to 34.48 KN.

The percentage loss in thrust can be calculated by,

% loss = [(Fideal – Fshock)/Fideal ] * 100= [(218.76 - 34.48)/218.76] * 100

= 84.2 %

Practically, in a rocket nozzle with the given design, the presence of a shock becomes the prime reason

for the thrust to reduce by 84.2 % as compared to the ideal expansion case without a normal shock wave.

From this calculation, we can understand the power of a normal shock wave and its overall effect in the

performance. There are cases where a normal shock wave is advantageous, but in this example, it proves

that a normal shock wave inside the divergent section of a nozzle makes the flow subsonic and it affects

the thrust.

TRENDING DEVELOPMENTS IN ROCKET TECHNOLOGY

The year 2013 marked an incredible one for spaceflight, with space agencies around the world making giant leaps in their own exploration of the solar system, while NASA welcomed the addition of a new commercial cargo ship to its list of supplies for the International Space Station.

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Also this year, Virgin Galactic and other private spaceflight companies made strides in their work to make space tourist flights a reality, while one Canadian astronaut became a social media mega-star by showing what life is truly like in space. Scientists are making progress on an advanced space propulsion system aimed at a variety of uses, including reboosting space stations, cleaning up space junk and powering superfast journeys that could reach Mars in less than two months.

Led by former NASA astronaut Franklin Chang-Díaz, Ad Astra Rocket Co. is developing the versatile, high-tech engine, which is known as the Variable Specific Impulse Magnetoplasma Rocket, or VASIMR for short. Engine work has been underway for more than 25 years, and is based on NASA and U.S. Department of Energy research and development in plasma physics and space propulsion technology. Commercializing the VASIMR electric propulsion engine is the flagship project of Ad Astra, which has been in business for nine years and has invested $30 million to date to mature the concept.

VASIMR heats plasma — an electrically charged gas — to extreme temperatures using radio waves. Strong magnetic fields then funnel this plasma out the back of the engine, creating thrust. The most advanced VASIMR engine is Ad Astra's 200-kilowatt VX-200.

The Falcon Heavy is a new rocket being developed by SpaceX – Space Exploration Technologies Corporation – one of two private companies that NASA has contracted to transport cargo to the International Space Station.

Designed to lift satellites or spacecraft into orbit weighing more than 53 tons, or 117,000 pounds, it has over twice the capacity of the Space Shuttle and Delta IV Heavy launcher. At full power, its thrust is equivalent to fifteen 747's. This makes it the most powerful rocket since the Saturn V which took astronauts to the Moon.

Expansion deflection nozzle

The expansion-deflection nozzle is an advanced rocket nozzle which achieves altitude compensation through interaction of the exhaust gas with the atmosphere, much like the plug and aerospike nozzles. It appears much like a standard bell nozzle, but at the throat is a 'centrebody' or 'pintle' which deflects the flow towards the walls. The exhaust gas flows past this in a more outward direction than in standard bell nozzles while expanding before being turned towards the exit. This allows for shorter nozzles than the standard design whilst maintaining nozzle expansion ratios. Because of the atmospheric boundary, the atmospheric pressure affects the exit area ratio so that atmospheric compensation can be obtained up to the geometric maximum allowed by the specific nozzle.

The nozzle operates in two distinct modes: open and closed. In closed wake mode, the exhaust gas fills the entire nozzle exit area. The ambient pressure at which the wake changes from open to closed modes is called the design pressure. If the ambient pressure reduces any further, additional expansion will occur outside the nozzle much like a standard bell nozzle and no altitude compensation effect will be gained. In open wake mode, the exit area is dependent on the ambient pressure and the exhaust gas exits the nozzle as an annulus as it does not fill the entire

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nozzle. Because the ambient pressure controls the exit area, the area ratio should be perfectly compensating to the altitude up to the design pressure.

Like the aerospike and plug nozzles, if modular combustion chambers were used in place of a single combustion chamber, then thrust vectoring would be achievable by throttling the flow to various chambers.

The Orion Crew Exploration Vehicle was originally part of NASA's Constellation Program which was cancelled in 2010. However, the design was carried forward as the Orion Multi-Purpose Crew Vehicle (Orion MPCV), as part of NASA's new plans for manned exploration to the Moon, Mars and asteroids. The first test flight is in 2014. For this particular mission, the capsule is unmanned. Nevertheless, it reaches a higher altitude than any spacecraft intended for human use since 1973. Orion makes two highly elliptical orbits of the Earth, before re-entering the atmosphere and splashing down in the Pacific Ocean. This test supports the development of the Space Launch System – a new dedicated rocket, which itself will be tested in 2017. The first manned flight of Orion will occur in the 2020s, depending on Nasa's future funding.

Even now, Rockets remain a popular military weapon. The use of large battlefield rockets of the V-2 type has given way to guided missiles. However rockets are often used by helicopters and light aircraft for ground attack, being more powerful than machine guns, but without the recoil of a heavy cannon and by the early 1960s air-to-air missiles became favored. Shoulder-launched rocket weapons are widespread in the anti-tank role due to their simplicity, low cost, light weight, accuracy and high level of damage. Current artillery systems such as the MLRS or BM-30 Smerch launch multiple rockets to saturate battlefield targets with munitions.

Commercially, rocketry is the enabler of all space technologies particularly satellites, many of which impact people's everyday lives in almost countless ways. Scientifically, rocketry has opened a window on the universe, allowing the launch of space probes to explore the solar system and space-based telescopes to obtain a clearer view of the rest of the universe. However, it is probably manned spaceflight that has predominantly caught the imagination of the public. Vehicles such as the Space Shuttle for scientific research, the Soyuz increasingly for orbital tourism and SpaceShipOne for suborbital tourism may show a trend towards greater commercialisation of manned rocketry.

CONCLUSION

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Thrust is what pushes the rocket forward. So, maximum thrust means maximum efficiency. From the study we conducted, we understood that the ideal rocket engine without any shocks in its nozzle produced a thrust of 218.76 KN. But the same nozzle, with a normal shock in the diverging section of its nozzle produced only 34.49 KN. The presence of a normal shock created a loss of 84.2 % in its overall thrust. This shows the strength of a normal shock when a supersonic flow is incident on it. The normal shock slashed down the Mach number of the flow from 2.3 to 0.262. This reduced the resultant thrust.

From the analysis we conducted, we can conclude that the presence of a normal shockwave affects the resultant thrust of the rocket engine. This is one of the design conditions when constructing a rocket engine. The future of rocket engines aims at maximum thrust and minimum weight. And finally, the efficiency is calculated based on the velocity of the flow coming out of the nozzle.

BIBLOGRAPHY

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1. Humble, R. J., Gary, H. N., and Larson, W. J. 1995. Space Propulsion Analysis and Design.

2. Gregory Vogt, Carla B. Rosenberg, Deborah A. Shearer, published by NASA. Rockets: an educator's guide with activities in science, mathematics, and technology.

3. A.Bowdoin Van Riper., Greenwood press 2004. Rockets & Missiles: The life story of a technology.

4. Multistage rockets, Valkyrie report No: 5105. Vashon Industries Inc.

5. www.braeunig.us/space/

6. www.aerospaceweb.org/design

7. en.wikipedia.org/wiki/De_Laval_nozzle

8. en.wikipedia.org/wiki/Multistage_rocket

9. en.wikipedia.org/wiki/Rockets

10. www.geaviation.com

11. www.inventors.about.com

12. http://history.msfc.nasa.gov.html

13. www.howstuffworks.com/rocket.htm/

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