AE1351-NOL

8/6/2019 AE1351-NOL

http://slidepdf.com/reader/full/ae1351-nol 1/50

AE-1351

PROPULSION-II

8/6/2019 AE1351-NOL


UNIT-1

AIRCRAFT GAS TURBINES

8/6/2019 AE1351-NOL


Gas Turbine

In an aircraft gas turbine the output of theturbine is used to turn the compressor

(which may also have an associated fan or propeller). The hot air flow leaving theturbine is than accelerated into theatmosphere through an exhaust nozzle(Fig. la) to provide thrust or propulsion

power:

8/6/2019 AE1351-NOL


FUNCTION OF TURBINE A portion of the kinetic energy of the

expanding gases is extracted by the

turbine section, and this energy istransformed into shaft horsepower whichis used to drive the compressor andaccessories.

8/6/2019 AE1351-NOL


TYPES OF TURBINES

AXIAL FLOW TURBINERADIAL FLOW TURBINE

8/6/2019 AE1351-NOL


AXIAL FLOW TURBINE

It consists of two main elements

A set of stationary vanes followed by a turbine rotor.

Axial-flow turbines may be of the single-rotor or multiple-rotor type.

A stage consists of two main components: a turbine nozzle and a turbine rotor or wheel.

8/6/2019 AE1351-NOL


RADIAL FLOW TURBINE

The radial flow turbine is similar in design and construction to thecentrifugal-flow compressor .

Advantages

-ruggedness and simplicity

-relatively inexpensive and easy to manufacture when compared to

the axial-flow turbine.

8/6/2019 AE1351-NOL


BLADE TYPES

IMPULSE TYPEREACTION TYPE

8/6/2019 AE1351-NOL


Single-rotor, Single-stage Turbine Multiple-rotor, Multiple-stage Turbine

Multirotor - Multistage Turbine.

8/6/2019 AE1351-NOL


TURBINE BLADE COOLINGCurrent turbine inlet temperatures in gas turbine engines are beyond the melting point of the turbine blade material.To prevent the blades from melting, turbine blade cooling methods areapplied to the first turbine stages. Sinceconvectively cooled flow fields and temperature fields are coupled and interact strongly, it is necessary to understand the flow physics in order to accurately predict how cooling will behave. In case of the rotating turbine blades, the effectsof rotation also influence the flow. Centrifugal forces as well as theCoriolis force have to be included in the analysis.The present research project is an experimental and computational investigation of the flow through internal turbine

blade cooling passages. In the first phase, the flow in a straight,stationary cooling channel is observed. Pressuremeasurements as well as hot-wire and PIV measurements are used todetermine efficacy of different turbulator geometries. In the phase 2, the flow in a rotating cooling channel withan 180° bend will be investigated using PIV.

8/6/2019 AE1351-NOL


Advantages of the gas turbineIt is capable of producing large amounts of useful power for arelatively small size and weightSince motion of all its major components involve pure rotation (i.e.no reciprocating motion as in a piston engine), its mechanical life islong and the corresponding maintenance cost is relatively low.

Although the gas turbine must be started by some external means (asmall external motor or other source, such as another gas turbine), itcan be brought up to full-load (peak output) conditions in minutes ascontrasted to a steam turbine plant whose start up time is measuredin hours.

A wide variety of fuels can be utilized. Natural gas is commonly usedin land-based gas turbines while light distillate (kerosene-like) oilspower aircraft gas turbines. Diesel oil or specially treated residualoils can also be used, as well as combustible gases derived fromblast furnaces, refineries and the gasification of solid fuels such ascoal, wood chips and bagasse.

8/6/2019 AE1351-NOL


Difference between impulse and

reaction turbine

8/6/2019 AE1351-NOL


UNIT-II

RAMJET PROPULSION

8/6/2019 AE1351-NOL


A ramjet , sometimes referred to as a stovepipe jet , or an athodyd ,is a form of jet engine that contains no major moving parts. Unlikemost other airbreathing jet engines, ramjets have no rotarycompressor at the inlet, instead, the forward motion of the engineitself 'rams' the air through the engine. Ramjets therefore requireforward motion through the air to produce thrust.Ramjets require considerable forward speed to operate well, and asa class work most efficiently at speeds around Mach 3, and this typeof jet can operate up to speeds of at least Mach 5.Ramjets can be particularly useful in applications requiring a smalland simple engine for high speed use; such as missiles. They havealso been used successfully, though not efficiently, as tip jets onhelicopter rotors.Ramjets are frequently confused with pulsejets, which use anintermittent combustion, but ramjets employ a continuouscombustion process, and are a quite distinct type of jet engine

8/6/2019 AE1351-NOL


RAMJET ENGINE PARTS

8/6/2019 AE1351-NOL


RAMJET ENGINE THRUST

8/6/2019 AE1351-NOL


Axial turbine blade vortex balding

A turbine blade for a turbine engine having one or more cavities in atrailing edge of the turbine blade for forming one or more vortices ininner aspects of the trailing edge.In at least one embodiment, the turbine blade may include one or more elongated cavities in the trailing edge of the blade formed by

one or more ribs placed in a cooling chamber of the turbine blade.The elongated cavity in the trailing edge may have one or moreorifices in the rib on the upstream side of the cavity. The orifice maybe positioned relative to a vortex forming surface so that as a gas ispassed through one or more orifices into the elongated cavity, oneor more vortices are formed in the cavity. The gas may be expelledfrom the cavity and the blade through one or more orifices in aninner wall forming the pressure side of the turbine blade

8/6/2019 AE1351-NOL


8/6/2019 AE1351-NOL


INLETSSUBSONIC INLETSFor aircraft that cannot go faster than the speed of sound, like large airliners, a simple, straight, short inlet worksquite well. On a typical subsonic inlet, the surface of the inlet from outside to inside is a continuous smooth curvewith some thickness from inside to outside. The most upstream portion of the inlet is called the highlight, or theinlet lip. A subsonic aircraft has an inlet with a relatively thick lip.SUPERSONIC INLETS

An inlet for a supersonic aircraft, on the other hand, has a relatively sharp lip. The inlet lip is sharpened tominimize the performance losses from shock waves that occur during supersonic flight. For a supersonic aircraft,the inlet must slow the flow down to subsonic speeds before the air reaches the compressor. Some supersonicinlets, like the one at the upper right, use a central cone to shock the flow down to subsonic speeds. Other inlets,like the one shown at the lower left, use flat hinged plates to generate the compression shocks, with the resultinginlet geometry having a rectangular cross section. This variable geometry inlet is used on the F-14 and F-15fighter aircraft. More exotic inlet shapes are used on some aircraft for a variety of reasons. The inlets of the Mach3+ SR-71 aircraft are specially designed to allow cruising flight at high speed. The inlets of the SR-71 actuallyproduce thrust during flight.HYPERSONIC INLETSInlets for hypersonic aircraft present the ultimate design challenge. For ramjet-powered aircraft, the inlet mustbring the high speed external flow down to subsonic conditions in the burner. High stagnation temperatures arepresent in this speed regime and variable geometry may not be an option for the inlet designer because of possible flow leaks through the hinges. For scramjet-powered aircraft, the heat environment is even worsebecause the flight Mach number is higher than that for a ramjet-powered aircraft. Scramjet inlets are highlyintegrated with the fuselage of the aircraft. On the X-43A, the inlet includes the entire lower surface of the aircraftforward of the cowl lip. Thick, hot boundary layers are usually present on the compression surfaces of hypersonicinlets. The flow exiting a scramjet inlet must remain supersonic.

8/6/2019 AE1351-NOL


INLE T EFFICIENCY

An inlet must operate efficiently over the entire flight envelope of the aircraft. At verylow aircraft speeds, or when just sitting on the runway, free stream air is pulled intothe engine by the compressor. In England, inlets are called intakes, which is a moreaccurate description of their function at low aircraft speeds. At high speeds, a goodinlet will allow the aircraft to maneuver to high angles of attack and sideslip withoutdisrupting flow to the compressor. Because the inlet is so important to overall aircraftoperation, it is usually designed and tested by the airframe company, not the enginemanufacturer. But because inlet operation is so important to engine performance, allengine manufacturers also employ inlet aerodynamicists. The amount of disruption of the flow is characterized by a numerical inlet distortion index . Different airframesuse different indices, but all of the indices are based on ratios of the local variation of pressure to the average pressure at the compressor face.The ratio of the average total pressure at the compressor face to the free stream totalpressure is called the total pressure recovery . Pressure recovery is another inlet

performance index; the higher the value, the better the inlet. For hypersonic inlets thevalue of pressure recovery is very low and nearly constant because of shock losses,so hypersonic inlets are normally characterized by their kinetic energy efficiency. If the airflow demanded by the engine is much less than the airflow that can becaptured by the inlet, then the difference in airflow is spilled around the inlet. Theairflow mis-match can produce spillage drag on the aircraft.

8/6/2019 AE1351-NOL


SCRAMJET A scramjet (s upersonic c ombustion ramjet ) is a variation of a ramjet with the distinction being that some or all of the combustion process takes place supersonically. At higher speeds, it is necessary to combust supersonically tomaximize the efficiency of the combustion process. Projections for the top speed of a scramjet engine (withoutadditional oxidiser input) vary between Mach 12 and Mach 24 (orbital velocity). The X-30 research gave Mach 17due to combustion rate issues. By way of contrast, the fastest conventional air-breathing, manned vehicles, suchas the U.S. Air Force SR-71, achieve approximately Mach 3.4 and rockets from the Apollo Program achievedMach 30+.Like a ramjet, a scramjet essentially consists of a constricted tube through which inlet air is compressed by thehigh speed of the vehicle, a combustion chamber where fuel is combusted, and a nozzle through which the

exhaust jet leaves at higher speed than the inlet air. Also like a ramjet, there are few or no moving parts. Inparticular, there is no high-speed turbine, as in a turbofan or turbojet engine, that is expensive to produce and canbe a major point of failure.

A scramjet requires supersonic airflow through the engine, thus, similar to a ramjet, scramjets have a minimumfunctional speed. This speed is uncertain due to the low number of working scramjets, relative youth of the field,and the largely classified nature of research using complete scramjet engines. However, it is likely to be at leastMach 5 for a pure scramjet, with higher Mach numbers (between 7 and 9) more likely. Thus scramjets requireacceleration to hypersonic speed via other means. A hybrid ramjet/scramjet would have a lower minimumfunctional Mach number, and some sources indicate the NASA X-43A research vehicle is a hybrid design. Recenttests of prototypes have used a booster rocket to obtain the necessary velocity. Air breathing engines should havesignificantly better specific impulse while within the atmosphere than rocket engines.

However, scramjets have weight and complexity issues that must be considered. While very short suborbitalscramjet test flights have been successfully performed, perhaps significantly no flown scramjet has ever beensuccessfully designed to survive a flight test. The viability of scramjet vehicles is hotly contested in aerospace andspace vehicle circles, in part because many of the parameters which would eventually define the efficiency of sucha vehicle remain uncertain. This has led to grandiose claims from both sides, which have been intensified by thelarge amount of funding involved in any hypersonic testing. Some notable aerospace gurus such as HenrySpencer and Jim Oberg have gone so far as calling orbital scramjets 'the hardest way to reach orbit', or even'scamjets' due to the extreme technical challenges involved. Major, well funded projects, like the X-30 werecancelled before producing any working hardware

8/6/2019 AE1351-NOL


Axial turbine blade cooling

8/6/2019 AE1351-NOL


UNIT-III

FUNDAMENTALS OF ROCKETPROPULSION

8/6/2019 AE1351-NOL


INTERNAL BALLISTICSInternal ballistics is what happens inside a weapon when it is fired. Thefiring pin makes a distinct mark on the cartridge. Then explosive pressurecauses the bullet to expand slightly to fill the spiral 'rifling' grooves cut in thebore. This makes the bullet spin as it passes down the barrel, but it leavestell-tale marks on the bullet that are unique to that particular firearm. Thepresence of rust or spider silk indicates the gun has not been fired recently.

At close range, particles from a wound may lodge inside the barrel.External ballistics is what happens to the bullet and residues outside thegun, including the direction and velocity of the shot, as well as any deviationin the trajectory.Terminal ballistics looks at the changes in trajectory and speed caused byricochet and penetration of objects, as well as the layered deposits on partsof the bullet accumulated as it contacts these objects. Terminal ballistics

includes examination of the shape of wounds and the extent of tissuedamage. If a bullet cannot be removed for examination, its calibre can bemeasured by CT scanning.

8/6/2019 AE1351-NOL


NOZZLES

8/6/2019 AE1351-NOL


ROCKET NOZZLECLASSIFICATION

FIXED NOZZLEMOVABLE NOZZLE

SUBMERGED NOZZLE

8/6/2019 AE1351-NOL


UNIT-IV

CHEMICAL ROCKETS

8/6/2019 AE1351-NOL


ADVANTAGES OF SOLIDROCKET MOTOR

A dvantages/DisadvantagesSolid fueled rockets are relatively simple rockets. This istheir chief advantage, but it also has its drawbacks.Once a solid rocket is ignited it will consume the entiretyof its fuel, without any option for shutoff or thrustadjustment. The Saturn V moon rocket used nearly 8million pounds of thrust that would not have beenfeasible with the use of solid propellant, requiring a highspecific impulse liquid propellant.The danger involved in the premixed fuels of monopropellant rockets i.e. sometimes nitroglycerin is aningredient.

8/6/2019 AE1351-NOL


SOLID ROCKET MOTOR

8/6/2019 AE1351-NOL


A simple solid rocket motor consists of a casing, nozzle, grain(propellant charge), and igniter.The grain behaves like a solid mass, burning in a predictablefashion and producing exhaust gases. The nozzle dimensions arecalculated to maintain a design chamber pressure, while producing

thrust from the exhaust gases.Once ignited, a simple solid rocket motor cannot be shut off,because it contains all the ingredients necessary for combustionwithin the chamber that they are burned in. More advanced solidrocket motors can not only be throttled but can be extinguished andthen re-ignited by controlling the nozzle geometry or through the useof vent ports. Also, pulsed rocket motors which burn in segmentsand which can be ignited upon command are available.Modern designs may also include a steerable nozzle for guidance,avionics, recovery hardware (parachutes), self-destructmechanisms, APUs, controllable tactical motors, controllable divertand attitude control motors and thermal management materials

8/6/2019 AE1351-NOL


8/6/2019 AE1351-NOL


Thrust is the force which moves a rocket through the air. Thrust is generated by the rocket engine through the reaction of accelerating a mass of gas. The gas isaccelerated to the the rear and the rocket is accelerated in the opposite direction. To accelerate the gas, we need some kind of propulsion sys tem. We will discuss thedetails of various propulsion systems on some other pages. For right now, let us just think of the propulsion system as some machine which accelerates a gas.From Newton's second law of motion, we can define a force to be the change in momentum of an object with a change in time. M omentum is the object's mass times thevelocity. When dealing with a gas, the basic thrust equation is given as:F = mdot e * Ve - mdot 0 * V0 + (pe - p0) * AeThrust F is equal to the exit mass flow rate mdot e times the exit velocity Ve minus the free stream mass flow rate mdot 0 times the free stream velocity V0 plus thepressure difference across the engine pe - p0 times the engine area A e .For liquid or solid rocket engines, the propellants, fuel and oxidizer, are carried on board. There is no free stream air brought into the propulsion system, so the thrustequation simplifies to:F = mdot * Ve + (pe - p0) * Aewhere we have dropped the exit designation on the mass flow rate.Using algebra, let us divide by mdot:

F / modt = Ve + (pe - p0) * Ae / mdotWe define a new velocity called the equivalent velocity Veq to be the velocity on the right hand side of the above equation:Veq = Ve + (pe - p0) * Ae / mdotThen the rocket thrust equation becomes:F = mdot * VeqThe total impulse ( I) of a rocket is defined as the average thrust times the total time of firing. On the slide we show the total time as "delta t". (delta is the Greek symbolthat looks like a triangle):I = F * delta tSince the thrust may change with time, we can also define an integral equation for the total impulse. Using the symbol (Sdt) for the integral, we have:I = S F dtSubstituting the equation for thrust given above:I = S (mdot * Veq) dtRemember that mdot is the mass flow rate; it is the amount of exhaust mass per time that comes out of the rocket. Assuming the equivalent velocity remains constantwith time, we can integrate the equation to get:

I = m * Veqwhere m is the total mass of the propellant. We can divide this equation by the weight of the propellants to define the specific impulse . The word "specific" just means"divided by weight". The specific impulse Isp is given by:Isp = Veq / g0where g0 is the gravitational acceleration constant (32.2 ft /sec^2 in English units, 9.8 m/sec^2 in metric units). Now, if we substitute for the equivalent velocity in terms of the thrust:Isp = F / (mdot * g0)Mathematically, the Isp is a ratio of the thrust produced to the weight flow of the propellants. A quick check of the units for Isp shows that:Isp = m/sec / m/sec^2 = sec

8/6/2019 AE1351-NOL


8/6/2019 AE1351-NOL


A bipropellant rocket engine is a rocket engine thatuses two propellants (very often liquid propellants) whichare kept separately prior to reacting to form a hot gas tobe used for propulsion.

In contrast, most solid rockets have single solidpropellant, and hybrid rockets use a solid propellantlining the combustion chamber that reacts with aninjected fluid. Because liquid bipropellant systems permitprecise mixture control, they are often more efficient thansolid or hybrid rockets, but are normally more complexand expensive, particularly when turbopumps are usedto pump the propellants into the chamber to save weight

8/6/2019 AE1351-NOL


Liquid propellantThousands of combinations of fuels and oxidizers have been tried over the years. Some of the more common and practical ones are:liquid oxygen (LOX, O2) and liquid hydrogen (LH2, H2) - Space Shuttle main engines, Ariane 5 main stage and the Ariane 5 ECA secondstage, the first stage of the Delta IV, the upper stages of the Saturn V, Saturn IB, and Saturn I as well as Centaur rocket stageliquid oxygen (LOX) and kerosene or RP-1 - Saturn V, Zenit rocket, R-7 Semyorka family of Soviet boosters which includes Soyuz, Delta,Saturn I, and Saturn IB first stages, Titan I and Atlas rocketsliquid oxygen (LOX) and alcohol (ethanol, C2H5OH) - early liquid fueled rockets, like German (World War II) A-4, aka V-2, and Redstoneliquid oxygen (LOX) and gasoline - Robert Goddard's first liquid-fuel rocketT-Stoff (80% hydrogen peroxide, H2O2 as the oxidizer) and C-Stoff (methanol, CH3OH, and hydrazine hydrate, N2H4 n (H2O as the fuel)- Walter Werke HWK 109-509 engine used on Messerschmitt Me 163B Komet a rocket fighterplane of (World War II)nitric acid (HNO3) and kerosene - Soviet Scud-A, aka SS-1

inhibited red fuming nitric acid (IRFNA, HNO3 + N2O4) and unsymmetric dimethyl hydrazine (UDMH, (CH3)2N2H2) Soviet Scud-B,-C,-D,aka SS-1-c,-d,-enitric acid 73% with dinitrogen tetroxide 27% (=AK27) and kerosene/gasoline mixture - various Russian (USSR) cold-war ballisticmissiles, Iran: Shahab-5, North Korea: Taepodong-2hydrogen peroxide and kerosene - UK (1970s) Black Arrow, USA Development (or study):hydrazine (N2H4) and red fuming nitric acid - Nike Ajax Antiaircraft Rocket

Aerozine 50 and dinitrogen tetroxide - Titans 2±4, Apollo lunar module, Apollo service module, interplanatary probes (Such as Voyager 1and Voyager 2)Unsymmetric dimethylhydrazine (UDMH) and dinitrogen tetroxide - Proton rocket and various Soviet rocketsmonomethylhydrazine (MMH, (CH3)HN2H2) and dinitrogen tetroxide - Space Shuttle Orbital maneuvering system (OMS) engines

Robert Goddard and his rocketOne of the most efficient mixtures, oxygen and hydrogen, suffers from the extremely low temperatures required for storing hydrogen andoxygen as liquids (around 20 K or í253 °C)) and low fuel density (70 kg/m³), necessitating large and heavy tanks. The use of lightweightfoam to insulate the cryogenic tanks caused problems for the Space Shuttle Columbia's STS-107 mission, as a piece broke loose,damaged its wing and caused it to break up and be destroyed on reentry.For storable ICBMs and interplanetary spacecraft, storing cryogenic propellants over extended periods is awkward and expensive.Because of this, mixtures of hydrazine and its derivatives in combination with nitrogen oxides are generally used for such rockets.Hydrazine has its own disadvantages, being a very caustic and volatile chemical as well as being toxic. Consequently, hybrid rocketshave recently been the vehicle of choice for low-budget private and academic developments in aerospace technology

8/6/2019 AE1351-NOL


UNIT-V

ADVANTAGES OF PROPULSIONTECHNIQUES

8/6/2019 AE1351-NOL


Chemical rocket engines, like those on the space shuttle, work byburning two gases to create heat, which causes the gases to expandand exit the engine through a nozzle. In so doing they create thethrust that lifts the shuttle into orbit. Smaller chemical engines areused to change orbits or to keep satellites in a particular orbit.For getting to very distant parts of the solar system chemicalengines have the drawback in that it takes an enormous amount of fuel to deliver the payload. Consider the Saturn V rocket that putmen on the moon: 5,000,000 pounds of it's total take off weight of 6,000,000 pounds was fuel.Electric rocket engines use less fuel than chemical engines andtherefore hold the potential for accomplishing missions that are

impossible for chemical systems. To understand how, we have tounderstand a number called specific impulse.

8/6/2019 AE1351-NOL


A resistojet simply uses electricity passing through aresistive conductor, something like the wires in your toaster, to heat a gas as it passes over the conductor. Asthe conductor heats up the gas is heated, expands, exitsthrough a nozzle and creates thrust.

In real resistojets the conductor is a coiled tube throughwhich the propellant flows. This is done to get maximumheat transfer from the conductor to the propellant.

diagram of a resistojet

8/6/2019 AE1351-NOL


An arcjet is simply a resistojet where instead of passing the gas through aheating coil it's passed through an electric arc.

diagram of an arcjetBecause arcs can achieve temperatures of 15,00 degrees C. this means thepropellant gets heated to much higher temperatures (typically 3,000degrees C.) than in resistojets and in so doing achieve higher specificimpulses, anywhere from 800 sec for ammonia to 2,000 seconds for hydrogen. Arcjets tend to be higher power devices, typically 1 to 2 kilowatts,and used for higher thrust applications, like station keeping of largesatellites. Several are currently in orbit.

8/6/2019 AE1351-NOL


8/6/2019 AE1351-NOL


Ion engines:Rub a balloon against your hair or shirt and then hold it near your arm, the hairs on your arm willfeel tingly and be attracted to the balloon. Bring the balloon near the carpet and bits of lint will bepulled to it. What's happening is that electrons have been deposited onto or removed from theballoon depending on what it was rubbed against, giving it an electrostatic charge, which createsan electrostatic field. A similar field can be used to produce thrust in a rocket engine called an ionthruster.

ion engine diagram As propellant enters the ionization chamber (the small n s on the left), electrons (small -s in themiddle) emitted from the central hot cathode and attracted to the outer anode collide with themknocking an electron off and causing the atoms of the propellant to become ionized ( +s on theright). This means that they have an electric field around them like the balloon. As these ions driftbetween two screens at the right hand side of the ionization chamber, the strong electric field of the "+" side repels them and the "-" side attracts them, accelerating them to very high velocities.The ions leave the engine and since the engine pushes on them to accelerate them, they in turnpush back against the engine creating thrust. Ion thrusters typically use Xenon (A very heavy,

inert gas) for propellant, have specific impulses in the 3,000 to 6,000 range and efficiencies up to60 percent. An average thruster is one to two feet in diameter, produces thrust on the order of small fractions of a pound and weighs some tens of pounds.

8/6/2019 AE1351-NOL


8/6/2019 AE1351-NOL


Nuclear rocket motor

8/6/2019 AE1351-NOL


In a nuclear thermal rocket a working fluid, usuallyhydrogen, is heated to a high temperature in a nuclear reactor, and then expands through a rocket nozzle tocreate thrust.

The nuclear reactor's energy replaces the chemicalenergy of the reactive chemicals in a traditional rocketengine.Due to the higher energy density of the nuclear fuelcompared to chemical ones, about 107 times, theresulting efficiency of the engine is at least twice as goodas chemical engines even considering the weight of thereactor, and even higher for advanced designs.

8/6/2019 AE1351-NOL


Risk in nuclear rocket motor There is an inherent possibility of atmospheric or orbital rocket failure whichcould result in a dispersal of radioactive material, and resulting fallout .Catastrophic failure, meaning the release of radioactive material into theenvironment, would be the result of a containment breach. A containmentbreach could be the result of an impact with orbital debris, material failuredue to uncontrolled fission, material imperfections or fatigue and humandesign flaws. A release of radioactive material while in flight could disperseradioactive debris over the Earth in a wide and unpredictable area. Thezone of contamination and its concentration would be dependent onprevailing weather conditions and orbital parameters at the time of re-entry.However given that oxide reactor elements are designed to withstand hightemperatures (up to 3500 K) and high pressures (up to 200 atm normaloperating pressures) it's highly unlikely a reactor's fuel elements would bereduced to powder and spread over a wide-area. More likely highly

radioactive fuel elements would be dispersed intact over a much smaller area, and although individually quite lethal up-close, the overall hazard fromthe elements would be confined to near the launch site and would be muchlower than the many open-air nuclear weapons tests of the 1950s.

8/6/2019 AE1351-NOL


Solar sail

8/6/2019 AE1351-NOL


8/6/2019 AE1351-NOL


The spacecraft arranges a large membrane mirror whichreflects light from the Sun or some other source.The radiation pressure on the mirror provides a smallamount of thrust by reflecting photons.Tilting the reflective sail at an angle from the Sunproduces thrust at an angle normal to the sail.In most designs, steering would be done with auxiliaryvanes, acting as small solar sails to change the attitudeof the large solar sail.The vanes would be adjusted by electric motors.

8/6/2019 AE1351-NOL


Limitation of solar sail

Solar sails don't work well, if at all, in low Earth orbit below about800 km altitude due to erosion or air drag. Above that altitude theygive very small accelerations that take months to build up to usefulspeeds. Solar sails have to be physically large, and payload size isoften small. Deploying solar sails is also highly challenging to date.Solar sails must face the sun to decelerate. Therefore, on trips awayfrom the sun, they must arrange to loop behind the outer planet, anddecelerate into the sunlight.There is a common misunderstanding that solar sails cannot gotowards their light source. This is false. In particular, sails can gotoward the sun by thrusting against their orbital motion. This reducesthe energy of their orbit, spiraling the sail toward the sun

AE1351-NOL

Documents

Transcript of AE1351-NOL