Space Propulsion and Power Systems Flashcards
List the three classifications of thrust generating systems
Thermodynamic
Electrostatic
Electromagnetic
List the four applications of rocket missions
Defence and Research Applications
Space Launches
Time-critical maneuvers such as transfers, ΔV<1000m/s
mass-limited missions, ΔV>2000m/s, Low Thrust
List the four types of conventional thermochemical rocket systems
Liquid Rocket - Fuel + Oxidizer
Soild Rocket - Solid Propellant and Charges
Hybrid Rocket - Liquid Oxidizer and Solid Fuel
Gaseous Rocket - Gaseous Propellant
What is the optimal nozzle expansion ratio?
When Pe=Pa, ε = Ae/At
If Pe<Pa, flow is over expanded
If Pe>Pa, flow is under-expanded
Describe the advantages and disadvantages of a liquid rocket engine
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
List the four basic components of a SRM
Motor Case/Combustion Chamber
Nozzle
Solid Propellant Grain
Igniter
Describe the advantages and disadvantages of a solid rocket propellant?
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
Describe how a ram-jet rocket operates
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
List the five assumptions for an ideal nozzle
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
How do Pressure, Temperature and Velocity vary through a CD nozzle?
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
List losses in the propulsive characteristics of a real nozzle as described in the Landsbaum equation
K-in-d-BL-ic-t
Kinematics
Immersed Nozzle
Divergence
Boundary Layer frictional and heat losses
Inefficient Combustion
Two-Phase Flow
Describe the relationships of pressure and volume in polytropic processes
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)
Describe the operation of a liquid monopropellant
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
Describe how liquid bipropellants are stored under normal conditions and in space
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
Describe what is meant by ‘green’ liquid bipropellants
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
Describe what gelatinous liquid propellants are
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
Describe how hybrid rocket motors operate
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
How are different propulsion method’s performances measured?
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
List the key properties of solid rocket propellants (3,3,4)
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
List the three main types of solid rocket propellants and their basic composition
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
Describe and compare two methods used for creating double base propellants
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
Describe and compare the two types of composite rocket propellant
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.
Describe additives in double based propellants
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
Describe an additive in rubbery composite propellants
Antioxidants - Extend grain life by suppressing reaction between oxygen and carbon double bonds. Degrades mechanical properties
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
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
List the 5 zones of burning homogeneous propellant
Virgin Material
Foam Zone
Fizz Zone
Dark zone
Flame Zone
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
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
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
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
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
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
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
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
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
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
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
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
List the SRM and LRM igniter types
SRM: Confined, unconfined, Ballistic
LRM: Hypergolic
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
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
Describe the use of ballistic igniters
Consist of partially confined chamber from which reaction products are vented into motor. Either basket or rocket type
Describe the use of hypergolic injection
Sponaneous ignition between fuel and oxidiser in a LRM as sson as they come into contact
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
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
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.
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
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
What are the requirements of a rocket to achieve orbit?
High thrust
High efficiency
Low precision
What are the requirements of a propulsion system used for orbital adjustment?
High Precision
Efficiency not an issue
What are the requirements for disposal?
High Efficiency
High Dormant reliability
low precision
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
What are the three major categories of electrical propulsion?
Electrostatic
Electromagnetic
Electrothermal
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
List types of electromagnetic propulsion
MagnetoPlasmoDynamic
Variable specific impulse plasma
Pulsed plasma/Pulsed Inductive
Helicon plasma
List types of electrothermal propulsion methods
Resistojet
Arcjet
Microwave Electrothermal
Pulsed Electrothermal
Electrothermal Hydrazine
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
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
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
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
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
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
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.
What is the general principle of electromagnetic propulsion?
accelerating an object by the use of a flowing electrical current and magnetic field
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
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.
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
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
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
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
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
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
What is the general principle of electrostatic propulsion?
Uses high-voltage electrodes to accelerate ions with electrostatic forces.
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
What is ionization?
The process of electrically charging an atom or molecule by adding or removing electrons
What is a plasma?
an ionized gas consisting of positive ions and free electrons. Overall charge is roughly zero
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
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
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
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
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
What are the material requirements for a solar sail?
Lightweight
Highly reflective
High temperature resistance
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
List satellite primary power sources
SNEFS
Solar Concentrator (Rankine-Brayton Cycles)
Nuclear Thermoelectric
Electrodynamic Tether
Fuel cell using acid electrolyte
Solar Photovoltaic
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
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
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
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.
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
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
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
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.
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
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
