What are the main parts of a model rocket?

INTROGUCTION

About Rockets

A rocket essentially is a container propelled in one direction by exhaust going in the opposite direction. Rockets help spacecraft get into space, stay in space, and maneuver in space. The launch and flight of a rocket are governed by Newton's Laws of Motion.

What are the main parts of a model rocket?

Nose cone — The nose cone is the leading, tapered or pointed section of the rocket. It helps reduce aerodynamic drag.

Body tube — The body tube is the central structure of the rocket. It holds the engine, propellant tanks, and payload.

Engine — The engine burns the propellant and converts it to exhaust to provide the force (thrust) to accelerate the rocket.

Fins — The fins help to guide the rocket and provide a stabilizing force.

Payload — The payload is the cargo to be delivered by the rocket (such as Hubble Telescope or International Space Station components). In some cases (like for satellites), it is the system being put directly into space.

Parachute — The parachute is released when the spacecraft returns to Earth. The parachute creates drag and slows the descent so that, upon landing, the rocket is not damaged. The model rocket in this activity does not have a parachute because it will not fly high enough to require one. Model rockets that fly over 100 feet high need parachutes.

I. Answer the following questions:

1. What is a rocket?

2. What are the main purposes of rockets?

3. What is the main purpose of the nose cone?

4. What is the parachute for?

II. Ask questions to your groupmate about the main parts of the rocket and give answers trying not to look into the text.

III. Make grammar analyses of the sentence:

A rocket essentially is a container propelled in one direction by exhaust going in the opposite direction.

IV. Find the examples of Present Indefinite Passive tense in the text. When do we use the tense?

UNIT 1

How do rockets engines work?

There are two main types of rocket engines: liquid-propellant engines and solid-propellant engines.

Propellant for liquid rockets is stored in large tanks. The propellant components of the fuel (for example, hydrogen) and the oxidizer (for example oxygen) are stored in separate tanks. The propellant is pumped into a combustion chamber, where it is mixed and ignited. The propellant burns, creating gases under high temperatures and pressures. The expanding gases escape through the nozzle at the lower end of the rocket. The nozzle has a narrow throat through which the exhaust is squeezed. The throat limits the amount of gas that can escape, causing the gas to accelerate as it leaves the engine (up to speeds of 5000 to 10,000 miles per hour). As the exhaust is forced out of the nozzle, it propels the rocket in the opposite direction.

In the case of a solid-propellant rocket engine the propellant is a dry mixture of fuel and oxidizer. It is stored in an insulated case. Under normal conditions the propellant does not burn. Upon launch, however, the propellant is ignited and combustion begins. Like the liquid-propellant engines, combustion of the propellant creates hot, expanding gas that escapes through a nozzle at high pressure, generating thrust.

What kind of fuel do rocket engines use?

Most rockets use liquid or solid chemical propellants. A propellant includes fuel — the part that burns — and an oxidizer (like oxygen) that enables combustion. Jets use jet fuel and burn it using oxygen. In space, there is no oxygen, so rockets have to carry their own.

The space shuttle uses liquid hydrogen as its fuel. It also carries liquid oxygen. These are combined in the space shuttle engines to produce water and heat.

The heat produced by the combustion of hydrogen and oxygen heats up the water (H2O) and creates an immense volume of steam. The steam is released as exhaust and propels the rocket in the opposite direction.

Solid rocket propellants are a dry mixture of fuel (often hydrogen and carbon) and the oxidizing component (oxygen). Only the exposed surfaces of the dry propellant burns, so scientists work to find ways to have as much surface area exposed as possible so that the propellant burns quickly and produces the most exhaust (thrust).

The combustion of liquid-propellant engines can be controlled more easily than solid propellant, so that a lot or a little thrust can be created, depending on whether you are trying to get the rocket off the launch pad and need lots of thrust, or trying to make a small alteration to the rocket's direction and need only a little thrust. Once a solid rocket propellant is ignited, it burns all at once, making it challenging to limit the amount of combustion. However, lighter engines can be made if solid rocket propellant is used; liquid is heavier and requires more massive rockets and engines. Solid rocket propellant is also easier to store. Liquid propellants such as liquid hydrogen and oxygen require complex cooling and storage systems. Solid rocket propellants are common for military uses such as missiles — and are the most common propellants for model rockets. Liquid-propellant systems are more commonly used by the space industry for human and non-human research and exploration.

Vocabulary

liquid-propellant engine - жидкостный реактивный двигатель

solid-propellant engine - твердотопливный реактивный двигатель

propellant - топливо для реактивных двигателей

tank - топливный бак

fuel - топливо, горючее

hydrogen - водород

oxidizer - окислитель

oxygen - кислород

pump - насос, подавать под давлением

combustion chamber - камера сгорания

ignite - воспламенять; зажигаться

nozzle - жиклёры, сопло

throat - горловина

propel – приводить в движение

launch - запуск

combustion - горение

thrust - тяга

jet - реактивная струя

steam - пар

immense - огромный

volume - объем

exhaust - выхлоп; выпуск, выброс

store - хранить, запасать

I. Answer the following questions:

1. What are the main parts of rocket engines?

2. What is the main principle of liquid-propellant engines operation?

3. What is the main principle of solid -propellant engines operation?

4. What does space shuttle use as its fuel?

5. What are the advantages and disadvantages of using solid propellants and liquid propellants?

II. Give definitions to the following words. Use different vocabularies and mark the difference in definitions.

Propellant, combustion, engine, fuel, tank, nozzle, launch.

III. Make grammar analyses of the sentence:

The combustion of liquid-propellant engines can be controlled more easily than solid propellant, so that a lot or a little thrust can be created, depending on whether you are trying to get the rocket off the launch pad and need lots of thrust, or trying to make a small alteration to the rocket's direction and need only a little thrust.

IV.Find the examples of Present Indefinite Passive tense in the text. When do we use the tense?

V. Render the text using following word-combinations:

Main types; large tanks; propellant; liquid propellant engines; solid propellant engines; space shuttle uses; combustion of hydrogen and oxygen; dry mixture of fuel; oxidizer.

VI. Project. Discuss the problems of using solid propellants and liquid propellants.

UNIT 2

Newton's Laws of Motion

In 1687 Isaac Newton developed his Laws of Motion. These laws govern the movement of all objects, including rockets. Understanding the Laws of Motion permits NASA scientists and engineers to accurately guide spacecraft across our solar system.

Newton's First Law:

An object at rest will stay at rest. An object in motion will stay in motion in a straight line at the same speed as long as no force is applied (more accurately, no unbalanced force).

Newton's Second Law:

An object's acceleration is proportional to the force applied to it. The force to accelerate an object is proportional to the object's mass. In equation form, if we call the force "F," the object's mass "m," and the acceleration "a," then Newton's Second Law is F = m × a, the most famous form of this fundamental principle of physics. Rocket thrust is a type of force.

Newton's Third Law:

For every action there is an equal and opposite reaction.

Vocabulary

Laws of Motion - законы движения

movement - движение

speed - скорость

force - сила

acceleration - ускорение

equation - равенство; уравнивание

equal - равный

launch pad - стартовая платформа

exceed - превышать

payload – полезная нагрузка

generate – вырабвтывать

vent – выпускать

airborne - находиться в воздухе

drag - торможение

roughness - погрешность; приближённость

ascend – набирать высоту

I. Answer the following questions:

1. What is Newton’s first law?

2. What is Newton’s second law?

3. What is Newton’s third law?

4. What helps to reduce drag?

5. What can cause a satellite to be placed in the wrong orbit?

UNIT 3

Types of Rocket Engines

Rocket engines have advanced dramatically since the 1960's, when they were used to take people to the moon. Liquid and solid fuel engines are used currently in the U.S. space program. The future holds newer technologies, including experimentation with nuclear and other engine types. These advanced engines will burn cleaner and use fuel more efficiently, but still provide the power needed to go into space.

Solid Fuel Rocket Engine

This is the main engine used during launch. This type of engine can only be ignited once, but has tremendous thrust power and great reliability. This engine is also made up of fewer movable parts. The fuel in the engine is mixed with an oxidizer and becomes a solid. This solid is "cemented," or coats, the inside of the rocket casing. When ignited, the fuel burns all at once inside the rocket, creating an explosion of gases out of the bottom of the rocket. This explosion is focused through the nozzle at the bottom of the rocket.

Nuclear Rocket Engines

A nuclear rocket engine passes liquid hydrogen through the reactor's center, creating a propellant gas that is expelled through the nozzle below for thrust. The hydrogen in its liquid state can be stored in a single tank. This engine is currently being researched for use in the future.

Vocabulary

advanced - перспективный

tremendous - огромный

reliability - надежность

coat - изоляционный слой

casing - обшивка

explosion - взрыв

versatile - многосторонний

precisely - точно

liquid monopropellant - жидкое однокомпонентное ракетное топливо

hydrogen peroxide - перекись водорода

decompose - разлагать на составные части

mesh – ячейка

nuclear rocket engine - ядерный ракетный двигатель

I. Answer the following questions:

1. What new engine types are used?

2. How does Solid Fuel Rocket Engine work?

3. How does Liquid Bipropellant Rocket Engine work?

4. Describe the way Liquid Monopropellant Rocket Engine work.

5. What is the most effective type of engine to your mind?

UNIT 4

Rocket Propellant

Rocket propellant is a material used by a rocket as, or to produce in a chemical reaction, the reaction mass (propulsive mass) that is ejected, typically with very high speed, from a rocket engine to produce thrust, and thus provide spacecraft propulsion. In chemical rocket propellants undergo exothermic chemical reactions to produce hot gas. There may be a single propellant, or multiple propellants; in the latter case one can distinguish fuel and oxidizer. The gases produced expand and push on a nozzle, which accelerates them until they rush out of the back of the rocket at extremely high speed. For smaller attitude control thrusters, a compressed gas escapes the spacecraft through a propelling nozzle.

In ion propulsion, the propellant is made of electrically charged atoms (ions), which are electromagnetically pushed out of the back of the spacecraft. Magnetically accelerated ion drives are not usually considered to be rockets however, but a similar class of thrusters use electrical heating and magnetic nozzles.

A potential other method is that the propellant is not burned but just heated, as in the proposed nuclear thermal rocket concept. In the proposed pulse propulsion, a heavy, metallic base acquires the force from an explosion behind it, for example from an atomic bomb, and a transfers it to a dampening system that reduces the shock to the payload. Rockets create thrust by expelling mass backwards in a high speed jet (see Newton's Third Law). Chemical rockets, the subject of this article, create thrust by reacting propellants within a combustion chamber into a very hot gas at high pressure, which is then expanded and accelerated by passage through a nozzle at the rear of the rocket. The amount of the resulting forward force, known as thrust, that is produced is the mass flow rate of the propellants multiplied by their exhaust velocity (relative to the rocket), as specified by Newton's third law of motion. Thrust is therefore the equal and opposite reaction that moves the rocket, and not by interaction of the exhaust stream with air around the rocket. Equivalently, one can think of a rocket being accelerated upwards by the pressure of the combusting gases against the combustion chamber and nozzle. This operational principle stands in contrast to the commonly-held assumption that a rocket "pushes" against the air behind or below it. Rockets in fact perform better in outer space (where there is nothing behind or beneath them to push against), because there is a reduction in air pressure on the outside of the engine, and because it is possible to fit a longer nozzle without suffering from flow separation, in addition to the lack of air drag.

The maximum velocity that a rocket can attain in the absence of any external forces is primarily a function of its mass ratio and its exhaust velocity. The mass ratio is just a way to express what proportion of the rocket is propellant (fuel/oxidizer combination) prior to engine ignition. Typically, a single-stage rocket might have a mass fraction of 90% propellant, 10% structure, and hence a mass ratio of 10:1. The impulse delivered by the motor to the rocket vehicle per weight of fuel consumed is often reported as the rocket propellant's specific impulse. A propellant with a higher specific impulse is said to be more efficient because more thrust is produced while consuming a given amount of propellant.

Lower stages will usually use high-density (low volume) propellants because of their lighter tankage to propellant weight ratios and because higher performance propellants require higher expansion ratios for maximum performance than can be attained in atmosphere. Thus, the Apollo-Saturn V first stage used kerosene-liquid oxygen rather than the liquid hydrogen-liquid oxygen used on its upper stages Similarly, the Space Shuttle uses high-thrust, high-density solid rocket boosters for its lift-off with the liquid hydrogen-liquid oxygen Space Shuttle Main Engines used partly for lift-off but primarily for orbital insertion.

Vocabulary

propulsion - реактивное движение

single propellant - однофазное ракетное топливо

multiple propellant - многофазное ракетное топливо

distinguish - различать

control thruster - рулевой двигатель

propelling nozzle - реактивное сопло

acquire - приобретать

assumption - приём радиосигналов

attain - достигать

single-stage rocket - одноступенчатая ракета

specific impulse - удельная тяга

lift-off - отрыв от земли, взлетать; взлёт

insertion - выведение на орбиту

high-density - повышенной плотности

I. Answer the following questions:

1. What happens in chemical rockets with propellants?

2. How does rockets produce thrust?

3. Where do rockets better perform?

4. Why did the Apollo-Saturn V first stage use kerosene-liquid oxygen?

5. What mass ratio a single-stage rocket might have?

UNIT 5

Solid propellants

The earliest rockets were created hundreds of years ago by the Chinese, and were used primarily for fireworks displays and as weapons. They were fueled with black powder, a type of gunpowder consisting of a mixture of charcoal, sulfur and potassium nitrate (saltpeter). Rocket propellant technology did not advance until the end of the 19th century, by which time smokeless powder had been developed, originally for use in firearms and artillery pieces. Smokeless powders and related compounds have seen use as double-base propellants.

Solid propellants (and almost all rocket propellants) consist of an oxidizer and a fuel. In the case of gunpowder, the fuel is charcoal, the oxidizer is potassium nitrate, and sulfur serves as a catalyst. (Note: sulfur is not a true catalyst in gunpowder as it is consumed to a great extent into a variety of reaction products such as K2S. The sulfur acts mainly as a sensitizer lowering threshold of ignition.) During the 1950s and 60s researchers in the United States developed what is now the standard high-energy solid rocket fuel. The mixture is primarily ammonium perchlorate powder (an oxidizer), combined with fine aluminium powder (a fuel), held together in a base of PBAN or HTPB (rubber-like fuels). The mixture is formed as a liquid, and then cast into the correct shape and cured into a rubbery solid. Solid fueled rockets are much easier to store and handle than liquid fueled rockets, which makes them ideal for military applications. In the 1970s and 1980s the U.S. switched entirely to solid-fuelled ICBMs: the LGM-30 Minuteman and LG-118A Peacekeeper (MX). In the 1980s and 1990s, the USSR/Russia also deployed solid-fuelled ICBMs (RT-23, RT-2PM, and RT-2UTTH), but retains two liquid-fuelled ICBMs (R-36 and UR-100N). All solid-fuelled ICBMs on both sides have three initial solid stages and a precision maneuverable liquid-fuelled used to fine tune the trajectory of the reentry vehicle.

Their simplicity also makes solid rockets a good choice whenever large amounts of thrust are needed and cost is an issue. The Space Shuttle and many other orbital launch vehicles use solid fuelled rockets in their first stages (solid rocket boosters) for this reason.

However, solid rockets have a number of disadvantages relative to liquid fuel rockets. Solid rockets have a lower specific impulse than liquid fueled rockets. It is also difficult to build a large mass ratio solid rocket because almost the entire rocket is the combustion chamber, and must be built to withstand the high combustion pressures. If a solid rocket is used to go all the way to orbit, the payload fraction is very small. (For example, the Orbital Sciences Pegasus rocket is an air-launched three-stage solid rocket orbital booster. Launch mass is 23,130 kg, low earth orbit payload is 443 kg, for a payload fraction of 1.9%. Compare to a Delta IV Medium, 249,500 kg, payload 8600 kg, payload fraction 3.4% without air-launch assistance.)

A drawback to solid rockets is that they cannot be throttled in real time, although a predesigned thrust schedule can be built into the grain during manufacture.

Solid rockets can often be shut down before they run out of fuel. Essentially, the rocket is vented or an extinguishant injected so as to terminate the combustion process. In some cases termination destroys the rocket, and then this is typically only done by a Range Safety Officer if the rocket goes awry. The third stages of the Minuteman and MX rockets have precision shutdown ports which, when opened, reduce the chamber pressure so abruptly that the interior flame is blown out. This allows a more precise trajectory which improves targeting accuracy.

Finally, casting very large single-grain rocket motors has proved to be a very tricky business. Defects in the grain can cause explosions during the burn, and these explosions can increase the burning propellant surface enough to cause a runaway pressure increase, until the case fails.

Vocabulary

weapon – оружие

powder - порох

gunpowder – черный порох

charcoal - древесный уголь

sulfur – сера

potassium nitrate (saltpeter) - нитрат калия

firearm - огнестрельное оружие

double-base propellants - двухосновное ракетное топливо, ракетный порох на нитроцеллюлозной и нитроглицериновой основе

threshold - пороговый сигнал

ammonium perchlorate - перхлорат аммония

PBAN (Polybutadiene Acrylonitrile) - горючее РДТТ (ракетный двигатель твёрдого топлива); полибутадионовый акрилонитрил

HTPB (hydroxyl-terminated polybutadiene) - полибутадиен с концевыми гидроксильными группами

ICBM (Inter-Continental Ballistic Missile) - МБР; межконтинентальная баллистическая ракета

LGM (land-based guided missile) - управляемая ракета наземного базирования

deploy - раскрывать, применять

precision - точность

tune – регулировка

withstand - выдержать (что-л.); противостоять; сопротивляться

drawback - недостаток

throttle - тормозить

grain - элемент заряда

extinguishant - огнегасящий состав

abruptly - внезапно; резко

I. Answer the following questions:

1. Who invented the first rockets?

2. What fuel did the first rockets use?

3. When was the standard high-energy solid rocket fuel developed?

4. What does the standard high-energy solid rocket fuel include?

5. What are solid rockets disadvantages?

UNIT 6

Liquid propellants

Liquid fueled rockets have better specific impulse than solid rockets and are capable of being throttled, shut down, and restarted. Only the combustion chamber of a liquid fueled rocket needs to withstand combustion pressures and temperatures. On vehicles employing turbopumps, the fuel tanks carry very much less pressure and thus can be built far more lightly, permitting a larger mass ratio. For these reasons, most orbital launch vehicles and all first- and second-generation ICBMs use liquid fuels for most of their velocity gain.

The primary performance advantage of liquid propellants is the oxidizer. Several practical liquid oxidizers (liquid oxygen, nitrogen tetroxide, and hydrogen peroxide) are available which have much better specific impulse than ammonium perchlorate when paired with comparable fuels.

Most liquid propellants are also cheaper than solid propellants. For orbital launchers, the cost savings do not, and historically have not mattered; the cost of fuel is a very small portion of the overall cost of the rocket, even in the case of solid fuel.

The main difficulties with liquid propellants are also with the oxidizers. These are generally at least moderately difficult to store and handle due to their high reactivity with common materials, may have extreme toxicity (nitric acids), moderately cryogenic (liquid oxygen), or both (liquid fluorine, FLOX- a fluorine/LOX mix). Several exotic oxidizers have been proposed: liquid ozone (O3), ClF3, and ClF5, all of which are unstable, energetic, and toxic.

Liquid fuelled rockets also require potentially troublesome valves and seals and thermally stressed combustion chambers, which increase the cost of the rocket. Many employ specially designed turbopumps which raise the cost enormously due to difficult fluid flow patterns that exist within the casings.

Though all the early rocket theorists proposed liquid hydrogen and liquid oxygen as propellants, the first liquid-fuelled rocket, launched by Robert Goddard on March 16, 1926, used gasoline and liquid oxygen. Liquid hydrogen was first used by the engines designed by Pratt and Whitney for the Lockheed CL-400 Suntan reconnaissance aircraft in the mid-1950s. In the mid-1960s, the Centaur and Saturn upper stages were both using liquid hydrogen and liquid oxygen.

The highest specific impulse chemistry ever test-fired in a rocket engine was lithium and fluorine, with hydrogen added to improve the exhaust thermodynamics. The combination delivered 542 seconds (5.32 kN·s/kg, 5320 m/s) specific impulse in a vacuum. The impracticality of this chemistry highlights why exotic propellants are not actually used: to make all three components liquids, the hydrogen must be kept below -252 °C (just 21 K) and the lithium must be kept above 180 °C (453 K). Lithium and fluorine are both extremely corrosive, lithium ignites on contact with air, fluorine ignites on contact with most fuels, and hydrogen, while not hypergolic, is an explosive hazard. Fluorine and the hydrogen fluoride (HF) in the exhaust are very toxic, which damages the environment, makes work around the launch pad difficult, and makes getting a launch license that much more difficult. The rocket exhaust is also ionized, which would interfere with radio communication with the rocket.

The common liquid propellant combinations in use today:

- LOX (liquid oxygen) and kerosene (RP-1). Used for the lower stages of most Russian and Chinese boosters, the first stages of the Saturn V and Atlas V, and all stages of the developmental Falcon 1 and Falcon 9. Very similar to Robert Goddard's first rocket. This combination is widely regarded as the most practical for civilian orbital launchers.

- LOX and liquid hydrogen, used in the Space Shuttle, the Centaur upper stage, the newer Delta IV rocket, the H-IIA rocket, and most stages of the European Ariane rockets.

- Nitrogen tetroxide (N2O4) and hydrazine (N2H4), MMH, or UDMH. Used in military, orbital and deep space rockets, because both liquids are storable for long periods at reasonable temperatures and pressures. This combination is hypergolic, making for attractively simple ignition sequences. The major inconvenience is that these propellants are highly toxic, hence they require careful handling. Hydrazine also decomposes energetically to nitrogen, hydrogen, and ammonia, making it a fairly good monopropellant.

Vocabulary

nitrogen tetroxide - четырёхокись азота

ammonium perchlorate - перхлорат аммония

nitric acid - азотная кислота

moderately - умеренно, средне, в меру

fluorine - фтор

troublesome valve - клапан, который может легко выйти из строя

turbopump - турбонасосный агрегат

reconnaissance aircraft - разведывательный летательный аппарат

lithium - литий

hazard - источник опасности

booster - стартовый ускоритель

hydrazine - гидразин, диамид

monopropellant - однокомпонентное топливо

I. Answer the following questions:

1. What are the advantages of liquid fueled rockets?

2. Name some liquid oxidizers.

3. The solid propellants are cheaper than liquid ones, aren’t they?

4. What are the main difficulties with oxidizers?

5. Why is not used the combination of lithium and fluorine with hydrogen added?

UNIT 7

Hybrid propellants

A hybrid rocket usually has a solid fuel and a liquid or gas oxidizer. The fluid oxidizer can make it possible to throttle and restart the motor just like a liquid fuelled rocket. Hybrid rockets are also cleaner than solid rockets because practical high-performance solid-phase oxidizers all contain chlorine, versus the more benign liquid oxygen or nitrous oxide used in hybrids. Because just one propellant is a fluid, hybrids are simpler than liquid rockets.

Hybrid motors suffer two major drawbacks. The first, shared with solid rocket motors, is that the casing around the fuel grain must be built to withstand full combustion pressure and often extreme temperatures as well. However, modern composite structures handle this problem well, and when used with nitrous oxide or hydrogen peroxide relatively small percentage of fuel is needed anyway, so the combustion chamber is not especially large.

The primary remaining difficulty with hybrids is with mixing the propellants during the combustion process. In solid propellants, the oxidizer and fuel are mixed in a factory in carefully controlled conditions. Liquid propellants are generally mixed by the injector at the top of the combustion chamber, which directs many small swift-moving streams of fuel and oxidizer into one another. Liquid fuelled rocket injector design has been studied at great length and still resists reliable performance prediction. In a hybrid motor, the mixing happens at the melting or evaporating surface of the fuel. The mixing is not a well-controlled process and generally quite a lot of propellant is left unburned Fact|date=July 2007, which limits the efficiency and thus the exhaust velocity of the motor. Additionally, as the burn continues, the hole down the center of the grain (the 'port') widens and the mixture ratio tends to become more oxidizer rich.

There has been much less development of hybrid motors than solid and liquid motors. For military use, ease of handling and maintenance has driven the use of solid rockets. For orbital work, liquid fuels are more efficient than hybrids and most development has concentrated there. There has recently been an increase in hybrid motor development for nonmilitary suborbital work:

- The Reaction Research Society (RRS), although known primarily for their work with liquid rocket propulsion, has a long history of research and development with hybrid rocket propulsion.

- Several universities have recently experimented with hybrid rockets. Brigham Young University, the University of Utah and Utah State University launched a student-designed rocket called Unity IV in 1995 which burned the solid fuel hydroxy-terminated polybutadiene (HTPB) with an oxidizer of gaseous oxygen, and in 2003 launched a larger version which burned HTPB with nitrous oxide.

- Portland State University also launched several hybrid rockets in the early 2000's.

- The Rochester Institute of Technology is currently creating a HTPB hybrid rocket to launch small payloads into space and to several near Earth objects. Its first launch is scheduled for Summer 2007.

- Scaled Composites SpaceShipOne, the first private manned spacecraft, is powered by a hybrid rocket burning HTPB with nitrous oxide. The hybrid rocket engine was manufactured by SpaceDev. SpaceDev partially based its motors on experimental data collected from the testing of AMROC's (American Rocket Company) motors at NASA's Stennis Space Center's E1 test stand. Motors ranging from as small as 1000 lbf (4.4 kN) to as large as 250,000 lbf (1.1 MN) thrust were successfully tested. SpaceDev purchased AMROCs assets after the company was shut down for lack of funding.

Vocabulary

chlorine - хлор

benign - неопасный, облегченный, легкий

nitrous oxide - оксид одновалентного азота

swift-moving - быстро движущийся

melt - плавить

evaporate - испарять

widen - расширять

hydroxy-terminated polybutadiene - полибутадиен c гидроксильными концевыми группами

purchase - покупать

asset - ценный вклад

I. Answer the following questions:

1. What is a characteristic of a hybrid rocket?

2. What are the drawbacks of hybrid motors?

3. Now they pay much more attention to the development of hybrid motors if to compare with solid and liquid motors, don’t they?

4. What countries continue to develop these motors?

UNIT 8

Mixture ratio

The theoretical exhaust velocity of a given propellant chemistry is a function of the energy released per unit of propellant mass (specific energy). Unburned fuel or oxidizer drags down the specific energy. Surprisingly, most rockets run fuel-rich.

The usual explanation for fuel-rich mixtures is that fuel-rich mixtures have lower molecular weight exhaust, which by reducing M supposedly increases the ratio frac{sqrt{T_c{M}which is approximately equal to the theoretical exhaust velocity. This explanation, though found in some textbooks, is wrong. Fuel-rich mixtures actually have lower theoretical exhaust velocities, because sqrt{T_c} decreases as fast or faster than M.

The nozzle of the rocket converts the thermal energy of the propellants into directed kinetic energy. This conversion happens in a short time, on the order of one millisecond. During the conversion, energy must transfer very quickly from the rotational and vibrational states of the exhaust molecules into translation. Molecules with fewer atoms (like CO and H2) store less energy in vibration and rotation than molecules with more atoms (like CO2 andH2O). These smaller molecules transfer more of their rotational and vibrational energy to translation energy than larger molecules, and the resulting improvement in nozzle efficiency is large enough that real rocket engines improve their actual exhaust velocity by running rich mixtures with somewhat lower theoretical exhaust velocities.

The effect of exhaust molecular weight on nozzle efficiency is most important for nozzles operating near sea level. High expansion rockets operating in a vacuum see a much smaller effect, and so are run less rich. The Saturn-II stage (a LOX/LH2 rocket) varied its mixture ratio during flight to optimize performance.

LOX/hydrocarbon rockets are run only somewhat rich (O/F mass ratio of 3 rather than stoichiometric of 3.4 to 4), because the energy release per unit mass drops off quickly as the mixture ratio deviates from stoichiometric. LOX/LH2 rockets are run very rich (O/F mass ratio of 4 rather than stoichiometric 8) because hydrogen is so light that the energy release per unit mass of propellant drops very slowly with extra hydrogen. In fact, LOX/LH2 rockets are generally limited in how rich they run by the performance penalty of the mass of the extra hydrogen tankage, rather than the mass of the hydrogen itself.

Another reason for running rich is that off-stoichiometric mixtures burn cooler than stoichiometric mixtures, which makes engine cooling easier. And as most engines are made of metal or carbon, hot oxidizer-rich exhaust is extremely corrosive, where fuel-rich exhaust is less so. American engines have all been fuel-rich. Some Soviet engines have been oxidizer-rich.

Additionally, there is a difference between mixture ratios for optimum "I"sp and optimum thrust. During launch, shortly after takeoff, high thrust is at a premium. This can be achieved at some temporary reduction of "I"sp by increasing the oxidiser ratioinitially, and then transitioning to more fuel-rich mixtures. Since engine size is typically scaled for takeoff thrust this permits reduction of the weight of rocket engine, pipes and pump sand the extra propellant use can be more than compensated by increases of acceleration towards the end of the burn by having a reduced dry mass.

Vocabulary

exhaust velocity - скорость истечения

conversion - преобразование

rotational - вращающийся

vibrational - вибрационный, колебательный

improve - улучшать

drops off - постепенно уменьшаться

tankage - система топливных баков

stoichiometric - стехиометрический

permit - позволять, разрешать, обеспечивать

reduction - снижение; понижение; уменьшение; сокращение

I. Answer the following questions:

1. What is an explanation for fuel-rich mixtures?

2. What happens with thermal energy of the propellant?

3. What happens with molecules with different quantity of atoms?

4. What are the reasons for running rich?

INTROGUCTION

About Rockets

A rocket essentially is a container propelled in one direction by exhaust going in the opposite direction. Rockets help spacecraft get into space, stay in space, and maneuver in space. The launch and flight of a rocket are governed by Newton's Laws of Motion.

What are the main parts of a model rocket?

Nose cone — The nose cone is the leading, tapered or pointed section of the rocket. It helps reduce aerodynamic drag.

Body tube — The body tube is the central structure of the rocket. It holds the engine, propellant tanks, and payload.

Engine — The engine burns the propellant and converts it to exhaust to provide the force (thrust) to accelerate the rocket.

Fins — The fins help to guide the rocket and provide a stabilizing force.

Payload — The payload is the cargo to be delivered by the rocket (such as Hubble Telescope or International Space Station components). In some cases (like for satellites), it is the system being put directly into space.

Parachute — The parachute is released when the spacecraft returns to Earth. The parachute creates drag and slows the descent so that, upon landing, the rocket is not damaged. The model rocket in this activity does not have a parachute because it will not fly high enough to require one. Model rockets that fly over 100 feet high need parachutes.

I. Answer the following questions:

1. What is a rocket?

2. What are the main purposes of rockets?

3. What is the main purpose of the nose cone?

4. What is the parachute for?