Electric Propulsion Systems Flashcards
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Orbit Achievement requirements
High Thrust, High efficiency, Low precision
Orbit adjustment requirements
High precision, efficiency not an issue
Disposal requirements
High Dormant reliability, High efficiency, low precision
Advantages of Electrical over Chemical propulsion?
Less propellant used
Higher efficiency
able to provide low thrust for a long period of ime
Three major categories of electric propulsion
Electrostatic
Electromagnetic
Electrothermal
Types of electrostatic propulsion
Ion bombardment Colloid Ion Contact Ion Field Emission Microwave (radiofrequency) ion Plasma seperator Ion Radioisotopic Ion Hall effect
Types of Electromagnetic propulsion
MagnetoPlasmoDynamic
-Steady state vs Quasi-steady state
-Self-field vs applied field
Pulsed plasma
Helicon plasma
Inductive pulsed plasma
Electron-cyclotron resonance
Variable specific impulse plasmaTypes of electrothermal
Resistojet Arcjet (Dc vs Ac vs Pulsed) Electrothermal Hydrazine Microwave Electrothermal Pulsed Electrothermal
Characteristics of an Electric propulsion system
Typically uses much less propellant than chemical rockets due to a higher exhaust velocity
Due to limited momentum change the thrust is much weaker than chemical rockets (unsuitable for launch from earths surface)
Electric propulsion can provide a small thrust for a long period of time (ideal for deep space)
Why choose Electric propulsion?
Used in low-thrust manoeuvres
Attractive mass savings
Applications requiring high velocity increments
for N-S station keeping (50 m/s per year)
for orbit raising (1 to 5 km/s)
for orbit transfer from LEO to GEO (6km/s)
Attitude control in LEO
what is an ion
A charged atom or molecule
What is Ionisation
The process of electrically charging an atom or molecule by adding or removing electrons
What is Plasma?
An electrically neutral medium of unbound positive and negative particles
What is the net charge on a plasma?
roughly zero
Main principles of a Resistojet
Propellant is heated
Usually using an incandescent filament
Thermal Energy converted into Kinetic energy in nozzle with a high expansion ratio
Common propellants for a resistojet
Hydrogen, Helium, Water, Ammonia and Hydrazine
Principles of an Arcjet
Centrally located cathode surrounded by an anode, High voltage electric field is generated between them.
Propellant is injected between the two electrodes, passing through an arc and being electrically heated.
Hot gas is then accelerated through a nozzle thermodynamically
Arcjet Propellants
Hydrogen
Ammonia
Hydrazine
Hydrogen Considerations
Advantages
High specific heat and thermal conductivity
Disadvantages
Difficulty in storage
Suffers from Frozen Flow losses in Nozzle Expansion
Ammonia Considerations
Advantage
Liquid does not require refrigeration
Disadvantage
Heavy molecule which dissociates into low-molecular-mass constituents which introduces frozen flow losses
Hydrazine Considerations
Advantages:
Can be dual used for a combination propulsion system on satellites. Can be easily stored
Disadvantages
Chemical erosion problems are intensified at higher specific impulses. Heat transfer problems at the nozzle and chamber.
What is FAC?
Flow Accelerated Corrosion
What is MET?
Microwave Electrothermal
Principles of MET
Heat a propellant gas using a microwave-generated plasma
CD gas-dynamic nozzle expansion
How many electrodes does a MET use to generate plasma?
none; plasma generated without electrodes
What is Flemings left hand rule used for?
Electric motors
What is Flemings right hand rule used for?
Electric Generators
What does MPD stand for?
MagnetoPlasmoDynamic
Advantages of MPD?
Isp in the range of 1500-8000s
Efficiencies of 30-40%+
Exhaust Velocity beyond 110,000 m/s
MPD Issues?
Consumes a lot of power
High efficiencies (30+%) are only reached above 100kW
Cathode erosion
When operated below 200kW, the self induced magnetic field becomes insufficient; external field required
what does VSIMR stand for?
Variable Specific Impulse Magnetoplasma Rocket
How does VSIMR Work?
Helicon Antenna ionises gas to form plasma
Magnetic coils create a field to confine plasma
ICRH antenna heats plasma to millions of degrees
Magnetic Nozzle directs plasma flow, accelerates gas; converting Et to Ek.
what does PPT stand for?
Pulsed Plasma Thruster
How does PPT work?
Arc passes through fuel, causing ablation and sublimation.
Heat generated by arc converts gas from sublimation to plasma.
Plasma is propelled between cathode/anode
Lorentz force is exerted on the plasma, causing thrust
What does PIT stand for?
Pulsed Inductive Thruster
How does PIT work?
Uses a perpendicular Electric and Magnetic field to accelerated a propellant (Usually Ammonia or Argon)
PIT requires no electrodes
What are the considerations in the Left hand rule and how are they oriented?
Thrust - thumb
Field - forefinger
Current - Second finger
What are the considerations in the Right hand rule and how are they oriented?
Thrust - thumb
Field - forefinger
Current - Second finger
What are the Left- and Right-hand rules applications of?
Lorentz force
What is Electron Bombardment?
A process where neutral atoms are converted to positive ions by bombarding them with electrons.
Electrons are dislodged from the atoms by the fast moving injected electrons, forming ions.
Types of solar sail
Square
Heligyro
Spinning disk sails
Solar Concentrator operation principles
Parabolic Concentrator focuses the sun’s heat on to a receiver to heat a fluid/gas
Steam produced in a receiver drives a steam turbine (Rankine Cycle)
Heated gas drives a turbine (Brayton Cycle)
What does DIPS stand for?
Dynamic Isotope Power Systems
What does ORC stand for?
Organic Rankine Cycle
Orbital considerations when using solar to power satellites?
Altitude, eccentricity, inclination, local time, durations of sunlit and eclipse phases
What is PMAD?
Power Management and Distribution
What are the 6 types of PMAD systems?
Regulated bus (BR) with DET Unregulated Bus (BU) with DET Semi-regulated bus (BS) with DET Regulated bus (BR) with MPPT Unregulated bus (BU) with MPPT Hybrid bus (BH) with DET
What is DET?
Direct Energy Transfer
What is SR? What does it do?
Shunt Regulation, Bleeds of excess power
What is MPPT? What does it do?
Maximum Power Point Tracking. Extracts the appropriate SA power to maximum
What is SA?
Solar Array
Which processes are responsible for the generation of power in a solar array?
Absorption of solar radiation, generating electron-hole pairs
The separation of the electrons and holes across a semiconductor junction, thus generating an EMF.
Short circuit current parameters
V=0, R=0;
Open circuit voltage parameters, Voc
I=0, R=inf
Maximum power point current parameter, Imp
Current at maximum solar cell output
Maximum Power point voltage
Vmp
Fill Factor
(IscVoc)/(ImpVmp)
Silicon Solar cells
convert the visible solar spectrum into electrical power
Which bands are TJ-GAS sensitive to?
Infrared and UV
Power storage types
Battery
flywheels
regenerative fuel cells
Main tasks for satellite propulsion systems, plus thrust levels and propulsion method
Apogee injection - Bipropellant, 400-600N
Orbit control - mono/bi propellant, 10-22N
Attitude control, Mono/bi prop, 1-22N
Additional tasks; Electric, millinewtons-1N
What is Isp?
Propellant efficiency or thrust/mass rate
What is electromagnetic propulsion?
The principle of accelerating an object by the utilisation of a flowing electrical current and magnetic field
Briefly describe Lorentz force in terms of the combination of
electric force and magnetic force
A Lorentz force pushes the
conductor in a direction perpendicular to the conductor and
the magnetic field
(It is the combination of electric and magnetic force on a point
charge due to electromagnetic fields)
How can you reduce the cathode erosion problem in an MPD thruster?
Use multichannel hollow cathode and lithium propellant
How does electromagnetic propulsion (EMP) differ from
electrothermal propulsion system?
EMP uses magnetic and electric fields to accelerate an object, ETP uses purely thermodynamic effects.
How do you calculate the Electrostatic force?
abs(F)=Ke*(Q1Q2)/r^2
where Ek is coulombs constant, Q1 and Q2 are the charges and r is the distance between them
What is a solar sail?
A form of space propulsion which uses radiation pressure on large, ultra-thin mirrors to accelerate to high velocities.
Working principle of a solar sail?
Solar radiation exerts a pressure on the sail due to reflection
What 6 components make up the EPS block diagram?
Primary power source, Power conditioning, Energy storage Charge/discharge control Power distribution Power consumer
3 types of Hall thruster
Stationary Plasma Thruster (SPT)
Thruster with Anode layer (TAL)
Cylindrical Hall thruster (CHT)
Advantages/Disadvantages of using a Nuclear Thermoelectric device?
Advantage:
No power storage required as constant power generation
Disadvantage: requires lots of shielding, dangerous.
Other requirements for EPS design
Achieve low cost recurring cost for flight components
Utilisation of flight-proven components
Redundancy concepts
Functional and human-safety related requirements
Facilitation of an architecture with growth potential
Design which can be tested under flight-representative conditions
increased hardness against space radiation
Advantages and Disadvantages of BCR and BDR
Advantages:
Simplified thermal design
Good electromagnetic compatibility
Disadvantages:
Increased weight from BCR and BCD
More SA power required due to losses in BCR and BCD
Higher control loop effort for bus voltage regulation
