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Space Propulsion and Power Systems Flashcards

1
Q

List the three classifications of thrust generating systems

A

Thermodynamic
Electrostatic
Electromagnetic

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2
Q

List the four applications of rocket missions

A

Defence and Research Applications
Space Launches
Time-critical maneuvers such as transfers, ΔV<1000m/s
mass-limited missions, ΔV>2000m/s, Low Thrust

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3
Q

List the four types of conventional thermochemical rocket systems

A

Liquid Rocket - Fuel + Oxidizer
Soild Rocket - Solid Propellant and Charges
Hybrid Rocket - Liquid Oxidizer and Solid Fuel
Gaseous Rocket - Gaseous Propellant

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4
Q

What is the optimal nozzle expansion ratio?

A

When Pe=Pa, ε = Ae/At
If Pe<Pa, flow is over expanded
If Pe>Pa, flow is under-expanded

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5
Q

Describe the advantages and disadvantages of a liquid rocket engine

A

Adv: High performance, variable thrust, can be stopped and restarted
Dis: Complex, less reliable, fuel is cyrogenically stored and hypogolic, and low in density even when stored under pressure

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6
Q

List the four basic components of a SRM

A

Motor Case/Combustion Chamber
Nozzle
Solid Propellant Grain
Igniter

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7
Q

Describe the advantages and disadvantages of a solid rocket propellant?

A

Adv: High Propellant Density, Long lasting chemical stability, proven in service, cheaper, simplier and more reliable
Dis: Lower Isp, difficult to vary thrust on demand, smokey exhaust, performance affected by ambient temperature

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8
Q

Describe how a ram-jet rocket operates

A

Ram-jet rockets are hybrid motors using SRM and airbreathing methods for combustion. Fuel is solid propellant, oxidizer is coming from air. Requires a booster to reach pressure in combustion chamber

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9
Q

List the five assumptions for an ideal nozzle

A

Gas flowing through nozzle is ideal
Flow is frictionless and no heat or mass is exchanged/lost
No combustion of gases during nozzle flow
Flow is quasi-stationary and quasi-1D
Cross section transitions in nozzle are smooth

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10
Q

How do Pressure, Temperature and Velocity vary through a CD nozzle?

A

Pressure and Temperature start high, with temperature always being greater. Velocity starts low.
Towards throat, v increases exponentially, T and P decrease exponentially. Plots become vertical in throat, then decay exponentially in diverging section

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11
Q

List losses in the propulsive characteristics of a real nozzle as described in the Landsbaum equation

A

K-in-d-BL-ic-t
Kinematics
Immersed Nozzle
Divergence
Boundary Layer frictional and heat losses
Inefficient Combustion
Two-Phase Flow

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12
Q

Describe the relationships of pressure and volume in polytropic processes

A

pV(n) = constant
For isobaric processes, n=0, meaning p=constant
For isothermal processes, n=1, meaning pV=constant
For Isochoric processes, n=inf, meaning V=constant
For isentropic processes, n=k (=gamma for air)

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13
Q

Describe the operation of a liquid monopropellant

A

Chemical substance in liquid form capable of being decomposed into hot gases when in contact with catalyst
low power but simple and reliable
Used in satellite thrusters and APU’s gas generators
Common example is passing Anhydrous hyrdrazine over iridium

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14
Q

Describe how liquid bipropellants are stored under normal conditions and in space

A

Normal conditions:
Liquid under normal conditions and pressures, stored in tanks and reserviors on board rocket. Liquids are often hypogolic

Space Storable conditions
Liquified gases are stored cyogenically. They have very high performance and used in demanding civil applications

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15
Q

Describe what is meant by ‘green’ liquid bipropellants

A

Minimal environmental impact from reduced production of greenhouse gases, ozone depleting chemicals and acid rain
Low or non-toxicity, which improves safety and reduces costs
An example is hydrogen peroxide + ethanol, which produces mainly CO2 and water

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16
Q

Describe what gelatinous liquid propellants are

A

Continuous solid skeleton enclosing a continuous liquid phase.
Gelling improves safety, handling and storage properties. Combine the advantages of solid and liquid propellants. Common examples include silicon dioxide or cellulose

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17
Q

Describe how hybrid rocket motors operate

A

An liquid oxidizer is connected to the main solid fuel tank with a valve. The oxidizer is injected into the tank and ignited. Varying injection rates enables thrust control. More complex than SRM but more manoeuvrable

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18
Q

How are different propulsion method’s performances measured?

A

Using:
Characteristic velocity, c * = (Pc * At)/mdot
Specific impulse, Isp = c * x Cf
Thrust, T = Isp x mdot = c * x CF x Sb x r x rho

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19
Q

List the key properties of solid rocket propellants (3,3,4)

A

Characterstic velocity, c*
Specific impulse Isp
Burning rate r

Density
Mechanical properties
Storage properties

Combustion signiture
Vulnerability and safety in handling
Environmental Impact
Life Cycle costs

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20
Q

List the three main types of solid rocket propellants and their basic composition

A

Homogeneous (Double Base):
Molecule that contains oxidiser and fuel, such as nitroglyerine

Heterogeneous (Composite):
A crystralline oxidiser in a hydrocarbon based polymetric fuel/binder

Composite double base:
Double base composition with added oxider and metallic fuel

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21
Q

Describe and compare two methods used for creating double base propellants

A

Extruded - NC/NG mixtures extruded horizontally through die then inserted into motor. Higher c* and burn rate, grains have smaller web thickness
Cast - NG-based casting liquid added to an NC-based casting powder, set at elevated temp inside motor for a few days. Better mechanical properties, single grain can be made with boost and sustain sectors

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22
Q

Describe and compare the two types of composite rocket propellant

A

Plastic:
Mixture of Ammonium perchlorate, aluminium and preformed thermoplastics. Tends to slump

Rubbery:
AP and Al in cross-linked elastomeric binder/fuel, formed by reacting liquid prepolymer with a curing agent. Usually cast for large motors but can be extruded for small.

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23
Q

Describe additives in double based propellants

A

Stabilisers: Increase propellant storage life by delaying autocatalytic decomposition of NC and NG

Burning rate catalyst: Increase propellant burn rate and plateauing buring

Non-energetic plasticisers: improve mechanical properties of grain at low temperatures

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24
Q

Describe an additive in rubbery composite propellants

A

Antioxidants - Extend grain life by suppressing reaction between oxygen and carbon double bonds. Degrades mechanical properties

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25
Describe the advantages and disadvantages of double base (homogenous) propellants
Adv: Minimum smoke combustion Super-rate and plateau burning Dis: Relatively weak mechanical properites low energies
26
Describe the advantages and disadvantages of rubbery composite (hetreogeneous) propellants
Adv Good mechanical properties at low temperatures High energy High densities low temperature coefficients Wide range of burning rates Dis: Smoky combustion signature
27
List the 5 zones of burning homogeneous propellant
Virgin Material Foam Zone Fizz Zone Dark zone Flame Zone
28
What is erosive burning and why is it detrimental?
Erosive burning is when high-speed combustion gases increase the burning rate of the popellant. It is caused by grain geometry and high initial operation conditions. It is detrimental as it increases initial thrust and affects stability. Can also damage exposed motor case
29
Describe the thrust profiles for various military and space rockets
Military rocket motors prefer nearly constant thrust as this minimises the thickness of chamber Space rockets have regressive thrust to avoid over-accleration for fragile payloads Air-to-air rockets have large initial thrust followed by continued decreased thrust Missile Launchers have huge acceleration to burn out before missle clears launch tube
30
List common propellant geometries and their burn characteristics
Front cigarette burning: No oriffices, long low thrust burn Central Oriffice: Progressive short burn Central Oriffice + Slot: Regressive short burn Star: Progressive with neutral region, long
31
Describe the upper and lower extremes of recombination reactions for actual expansion
In nozzle, recombinations are too slow due to low temperature from expansion slowing down reaction rates, This makes flow 'chemically frozen' and reduces performance In the case recombination reactioons do occur along flow, it is called equilibrium expansion. Increased performance Actual performance falls between these two
32
What is stoichiometric combustion and why is do engines not use stoichiometric ratios?
proportions of fuel and oxidizer are those for which, if the reaction were complete, no excess of either would be left Ensures maximum heat release per unit mass, however this can clash with limits of materials melting temperature Jet engines and gas generators in rocket turbopump operate far from stoichiometric ratio Rocket engines use reactant proportions close to stoichiometric to achieve maximum high specific impulse
33
Name and Describe the two basic combinations of SRM case and propellant grain
Case Bonded Charge - Propellant grain molded directly in motor case. Thermally insults SRM case during burning Cartridge Loaded Propellant - Propellant grain molded separately to motor case. Case requires internal thermal insultation
34
List flight conditions considered when deciding SRM case strength
Must be able to withstand: Internal combustion pressure Lateral inflight g forces Longitudinal g forces during launch Typical safety factor of 1.2 for UTS Design pressure: Pd = (1.1 Pc +10 ) bar
35
List and Describe options for material selection of SRM case
Ratio of max stress to density used as merit Steel - high performance, low cost, heavy Aluminium or Titanium alloys - Lighter than steel, high performance, lower thermal resistance and higher costs Composites - light, good thermal resistance and low conductance, higher cost
36
What is "Inhibition" in the context of SRM rockets
Inhibition prevents the exposed propellant grain surface from burning. This is done by stopped the propellant from separating under load, and by having similar thermal expansion between propellant and inhibitor
37
List and Describe various methods for cooling nozzles
Radiation cooling: nozzle is made of lightweight, heat-resistant material. Nozzle walls reach thermal equilibrium. Heat Sink: Heavy, uncooled nozzle with large thermal capacity used as heat sink. Only works for short burn times Ablative Cooling: nozzle is lined with fiber reinforced organic material which undergoes progressive endothermic decomposition Insulation: Low thermal conductivity coatings such as graphite or ceramics used as insulation Film cooling: A regenerative method using a cool burning propellant at nozzle end to form boundary larger within nozzle
38
Why are bell shaped nozzles only used for space applications?
On a graph displaying ratio of L/Dt on y axis and Ae/At on x axis, the ideal bell shape gives best performance and lowest losses but also has highest L/Dt ratio
39
List igniter design requirements
Produce a high flame temperature (>3000K) Have a high burn rate Be chemically stable Have a high bulk density Have minimum ignition delay Produce minimum igniter debris Be insensitive to EM radiation
40
List the SRM and LRM igniter types
SRM: Confined, unconfined, Ballistic LRM: Hypergolic
41
Describe the use of confined igniters
Use total containment of ignition material. A Powder Can is used, which is a metal case with a weakened section that bursts towards the end of the ignitier brun time
42
Describe the use of unconfined igniters
Use the chamber and nozzle for confinement during ignition. Low weight and little debris, Fragile and produces high shocks. Types include jelly roll, pyrocore explosive train and film igniter
43
Describe the use of ballistic igniters
Consist of partially confined chamber from which reaction products are vented into motor. Either basket or rocket type
44
Describe the use of hypergolic injection
Sponaneous ignition between fuel and oxidiser in a LRM as sson as they come into contact
45
Describe how a nuclear thermal propulsion rocket produces thrust, and describe the 3 types
Nuclear reactor heats working fluid, usually hydrogen, which is ejected to create thrust low thrust-to-weight ratio, LH low molar weight, cannot be used as first stages Solid core has Isp limited by reactor melting temps Liquid core isnt limited, therefore higher Isp, but has radioactive exhaust Gas core offer even higher Isp values, can be open or closed system
46
Describe how a nuclear pulse propulson rocket produces thrust
Small (10-100T of TNT) nuclear explosions behind a protective plate accelerate the rocket from outside Can achieve Isp of 2000-3000. High thrust so rocket mass not limited
47
Describe how a nuclear radioisotope propulson rocket produces thrust
Decay of radioactive isotopes provide heat to working fluid, which is then ejected to create thrust Low thrust, significantly less power produced than nuclear reactor engine.
48
Describe how a nuclear electric propulson rocket produces thrust
A nuclear reactor is used to supply electricity to an electrical propulsion system Nuclear reactor provides large power, so higher thrust available
49
What are the advantages and disadvantages of nuclear rocket engines
Adv: high Isp, small profile, less fuel volume, more reliable Dis: Radioactive fuel, launch failure with onboard nuclear material could be disaster, hazardous for crews
50
What are the requirements of a rocket to achieve orbit?
High thrust High efficiency Low precision
51
What are the requirements of a propulsion system used for orbital adjustment?
High Precision Efficiency not an issue
52
What are the requirements for disposal?
High Efficiency High Dormant reliability low precision
53
What are the advantages and disadvantages of electrical compared to chemical propulsion?
Adv Less propellant mass used as higher exhaust velocity Higher efficiency Able to provide low thrust for extended periods of time Dis Limited momentum change means less thrust
54
What are the three major categories of electrical propulsion?
Electrostatic Electromagnetic Electrothermal
55
List types of electrostatic propulsion
Gridded Ion Hall effect - types 1, 2 and 3 Microwave Ion Plasma seperator Ion Radioisotopic Ion Ion bombardment Colloid Ion Contact Ion
56
List types of electromagnetic propulsion
MagnetoPlasmoDynamic Variable specific impulse plasma Pulsed plasma/Pulsed Inductive Helicon plasma
57
List types of electrothermal propulsion methods
Resistojet Arcjet Microwave Electrothermal Pulsed Electrothermal Electrothermal Hydrazine
58
List common uses for electrical propulsion
Used in low thrust manoeuvres and high velocity increments such as: North-South station keeping Orbit raising Orbit transfers Attitude control in LEO
59
Describe the general principle behind electrothermal propulsion
Electrical power from another source (usually solar) is used to heat a fluid or gas, which is then vented out of an exhaust nozzle. Low thrust but more efficient than chemical
60
Describe the operation of a resistojet thruster
Passing electricity through a resistor powered by an external power source, the propellant is heated by the thermal energy, converting it to kinetic. Propellant is then expelled through high expansion ratio nozzle. Propellants include hydrogen, helium, water, etc
61
Describe the operation of an arcjet thruster
Central cathode surronding ring shaped anode, high voltage electric field generated between them. Propellant is pumped in, passes through arc and is electrically heated. Hot gas then expands in nozzle
62
Why do GEO satellites require North-South keeping control?
Geostationary orbits compensate for effect of solar/lunar gravitational peturbations, approx 0.85deg/year. This requires delta V of 49m/s/year correction
63
Describe the operation of a microwave thruster
By heating a propellant gas by means of a free-floating microwave generated plasma within a resonant cavity. Gas is then expelled out of nozzle
64
What is 'frozen flow loss'?
frozen flow losses are an inefficiency percentage of input energy added to propellant gas that does not appear in the form of exit KE. losses include dissociation of propellant molecules, ionization processes and excitation.
65
What is the general principle of electromagnetic propulsion?
accelerating an object by the use of a flowing electrical current and magnetic field
66
What is the Lorentz force?
Combination of electric and magnetic forces on a point charge due to EM fields A force created when current flows through a conductor in a magnetic field, pushes the conductor in a direction perpendicular to both current and MF
67
Describe the operation of a Magnetoplasmadynamic (MPD) Thruster
Operates by passing an arc between anode and cathode through propellant gas, ionizing the propellant into plasma and accelerating it using the Lorentz force, which is generated from the current and magnetic field.
68
What are the disadvantages of a Magnetoplasmadynamic thruster and how can they be resolved?
Dis: Consumes alot of power high efficiency only reach over high power cathode prone to erosion Solution: Some problems solved with Li-Lorentz force acclerator
69
Describe the operation of a Variable Specific Impulse Magnetoplasma rocket (VASIMR)
Gaseous propellent is injected into a quartz tube, where it is ionized by radio waves. Magentic coils confine and heat the plasma to millions of degrees, then expands out of magentic nozzle
70
Describe the operation of a pulsed plasma thruster
Electricity passes through fuel, causing ablation and sublimation. Heat generated by this turns gas into plasma. Plasma is propelled between anode and cathode, allowing current flow through plasma, generating Lorentz force
71
Describe the operation of a pulsed inductive thruster
Capacitors release pulse of electric current, generating a radial magnetic field, acclerating the propellant using these electric and magnetic fields. . No eletrodes required
72
What do each finger represent in Fleming's left hand rule?
Thumb (pointing up) is motion/force Index is field direction Middle is current direction
73
Assuming constant thrust, what is the relation between specific impulse and propellant flow rate
The higher the specific impulse, the lower the propellant flow rate, or in other words, less propellant needed for a given delta V
74
What is the general principle of electrostatic propulsion?
Uses high-voltage electrodes to accelerate ions with electrostatic forces.
75
What is Coulomb's law
the magnitude of the electrostatic force of interaction between two point charges is directly proportional to the scalar multiplication of the magnitude of the charges and inversley proportional to the distance between them
76
What is ionization?
The process of electrically charging an atom or molecule by adding or removing electrons
77
What is a plasma?
an ionized gas consisting of positive ions and free electrons. Overall charge is roughly zero
78
Describe the operation of a Gridded Ion Thruster
Propellant atoms are injected into discharge chamber, where they are ionized into a plasma by electron bambardment. Positively charged ions move towards extraction grids by diffusion, and accelerated by potential difference between first and second grid. The greater this difference, the greater the acceleration. Electrons are redirected into discharge chamber by magents
79
Describe the operation of Type 1 Hall Effect Thrusters (Stationary Plasma Thruster)
Electrons generated by hollow cathode. Anode channel is charged to high potential by power supply. Electron trapped by MF. Propellant is injected into thruster channel and ionized into plasma by trapped electrons. This plasma is accelerated by the electric field out of the thruster
80
Describe the operation of Type 2 Hall effect thrusters (TAL - Thruster with Anode Layer)
Electrons generated by hollow cathode. Anode channel is charged to high potential by power supply. Electron trapped by MF. Propellant ionized into plasma downstream of thruster exit. Plasma then accelerated by electric field out of thruster
81
Describe the operation of Type 3 Hall Effect Thrusters (Cylindrical Hall Thrusters)
Ion thrust is generated by the axial component of the Lorentz force, proportional to the radial magnetic field and the azimuthal electron current
82
What is a solar sail and how does it operate?
A form of propulsion that uses radiation pressure to push large, ulta-thin mirrors to high speeds. Photons carry momentum due to their energy, which is transferred to mirror when they bounce off reflective material momentum = E/c where E is flux density
83
What are the material requirements for a solar sail?
Lightweight Highly reflective High temperature resistance
84
List and describe the three types of Solar Sails
Square Sail - Large square area, supported by booms Heliogyro - Uses long arms that all spin around payload for stability Spinning Disc Sail - sail controlled by moving the centre of mass relative to centre of light pressure
85
List satellite primary power sources
SNEFS Solar Concentrator (Rankine-Brayton Cycles) Nuclear Thermoelectric Electrodynamic Tether Fuel cell using acid electrolyte Solar Photovoltaic
86
Describe how a fuel cell operates as a primary power source for a satellite
An anode and cathode provided with hydrogen and oxygen respectively placed in electrolyte. Hydrogen gas at the anode loses an electron, travels to the cathode through the external circuit
87
Describe how a solar concentrator operates as a primary power source
Solar radiation is focused by a parabolic concentrator onto a receiver, which boils a fluid or gas. If fluid, steam then drives a steam turbine (Rankine Cycle). If Gas, heated gas drives a turbine (Brayton Cycle). More efficient than solar cell
88
What is a PMAD system and what types are there?
Power Management and distribution system. Buses can be either: Regulated (constant) voltage regulated Unregulated (varying) voltage within range around average Semiregulated, voltage regulated during excess power times Hybrid where addition solar array is linked to battery charge regulator
89
Describe how an electrodynamic tether operates
Induces a current in a wire as the satellite is moving through the MF of the planet is orbits.
90
Describe how a solar array operates to as a primary power source
Using the photovoltaic effect. Photon energy is converted directly into electrical energy. If an incoming photon's energy is greater than the band gap, the photons are absorbed by a semiconductor. This absorbed energy causes a semiconductor electron to jump from the valence band to the conduction band, and creating an electron-hole pair. In-built electric field at the p-n junction separates these pairs, allowing electrons to flow and provide electrical current when connected to external circuit
91
What is the definition of Calender and Cycle life of a battery?
Calender life - The time a battery or part of its capacity beomes usless, regardless of whether if it has been operated Cycle Life - Number of charge-discharge cycles a battery can perform before parts of its energy content fall. Depends on its depth of discharge
92
Describe the operation of a regenerative fuel cell
Can perform the function of a fuel cell in either direction, either producing electricity from hydrogen and oxygen, or producing hydrogen and oxygen from the electrolysis of water
93
Describe the operation of a flywheel as an energy storage device
Provides and extracted electricity to accelerate and decelerate a flyhweel with a motor-generator, maintaining the energy in the system as rotational energy.
94
List and describe the four main tasks of a propulsion system, and what propellants are commonly used for each task
Apogee Injection - bipropellent - Engine activated at the apogee to move satellite into required circular orbit Orbit Control - monopropellant - North-South and East-West keeping, injection into graveyard orbit Attitude control - mono/bipropellant - Orientation control of satellite Path Correction - Electric propulsion - Precise course correction during years long flight, large delta V
95
What is the defintion of specific impulse?
The amount of thrust produced per unit of propellant flow rate. Units in s. A high Isp indicates an efficient use of propellant. It is used to compare the efficiency of different engines and propellants

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