Electric PropulsionElectric Propulsion

Limitations of Chemical RocketsLimitations of Chemical Rockets

• Chemical rocket: exhaust ejection velocity Chemical rocket: exhaust ejection velocity intrinsically limitedintrinsically limited by the propellant-oxidizer reactionby the propellant-oxidizer reaction

• Larger velocity increment of the spacecraft could be obtained Larger velocity increment of the spacecraft could be obtained only with a only with a larger ejected masslarger ejected mass flow. flow.

• Mission Mission practical limitationpractical limitation: exceedingly large amount of : exceedingly large amount of propellant that needs to be stored aboardpropellant that needs to be stored aboard

The Rocket EquationThe Rocket Equation

Understanding the motion of a spacecraftUnderstanding the motion of a spacecraft

The Rocket Equation (II)The Rocket Equation (II)

• The rocket equation links the mass of The rocket equation links the mass of exhaustedexhausted propellantpropellant MM, the relative exhaust velocity , the relative exhaust velocity uuexex and the and the velocity velocity

incrementincrement of the spacecraft of the spacecraft v:v:

0 1 expex

vm M

u

• For a given v, the larger uex , the smaller M, and viceversa

• A large M requires the storage of a large amount of propellant on board, reducing the useful payload

Advanced (Electric) PropulsionAdvanced (Electric) Propulsion

The Concept:The Concept:

• Definition - Definition - Electric propulsionElectric propulsion: A way to accelerate a : A way to accelerate a propellant through electro(magnetic) fieldspropellant through electro(magnetic) fields

• There is There is no intrinsic limitationno intrinsic limitation (other than the relativistic one) (other than the relativistic one) to the speed to which the propellant can be acceleratedto the speed to which the propellant can be accelerated

• Energy available on board is the only Energy available on board is the only practical limitationpractical limitation

Advanced (Electric) Propulsion Advanced (Electric) Propulsion (II)(II)

Understanding what’s behind it:Understanding what’s behind it:

• Tradeoff 1Tradeoff 1: more energy available, less propellant, less mass : more energy available, less propellant, less mass requiredrequired

• Tradeoff 2Tradeoff 2: more time allowed for a maneuver, less power : more time allowed for a maneuver, less power neededneeded

Advanced (Electric) Propulsion Advanced (Electric) Propulsion (III)(III)

Features:Features:

• High exhaust speed (High exhaust speed (i.e.i.e. high specific impulsehigh specific impulse), much greater ), much greater than in conventional (chemical) rocketsthan in conventional (chemical) rockets

• Much Much less propellant consumptionless propellant consumption (much higher efficiency in (much higher efficiency in the fuel utilization)the fuel utilization)

• Continuous propulsionContinuous propulsion: apply a smaller thrust for a longer : apply a smaller thrust for a longer timetime

• Mission Mission flexibilityflexibility (Interplanetary travel, defense) (Interplanetary travel, defense)

• Endurance (Endurance (commercial satellitescommercial satellites))

Electric Propulsion ConceptsElectric Propulsion Concepts

• Variety of designs to accelerate Variety of designs to accelerate ions or plasmasions or plasmas

• Most concepts utilize grids or electrodes: Most concepts utilize grids or electrodes: power and power and endurance limitationsendurance limitations

• Ion EngineIon Engine

• Hall ThrusterHall Thruster

• RF Plasma Thrusters (ECR, VASIMR, Helicon Double Layer)RF Plasma Thrusters (ECR, VASIMR, Helicon Double Layer)

• Magnetoplasma Dynamic (MPD) ThrustersMagnetoplasma Dynamic (MPD) Thrusters

• Plasmoid Accelerated ThrustersPlasmoid Accelerated Thrusters

Ion EngineIon Engine

• Scheme of a gridded ion engine with neutralizationScheme of a gridded ion engine with neutralization

Ion EngineIon Engine

NASA’s Deep Space One Ion EngineNASA’s Deep Space One Ion Engine

Ion EngineIon Engine

NASA’s Evolutionary Xenon Thruster (NEXT) at NASA’s JPLNASA’s Evolutionary Xenon Thruster (NEXT) at NASA’s JPL

Hall ThrusterHall Thruster

The Hall effect

Hall Thruster (II)Hall Thruster (II)

The Hall thruster scheme

Hall Thruster (III)Hall Thruster (III)

The Hall thruster: the Hall effect confines electrons

Hall Thruster (III)Hall Thruster (III)

High Voltage Hall Accelerator (HiVHAC) Thruster - Hall Thruster (NASA Glenn R.C.)

MagnetoPlasma Dynamic ThrusterMagnetoPlasma Dynamic Thruster

The MPD thruster

MagnetoPlasma AccelerationMagnetoPlasma Acceleration

The VASIMR ® concept (Ad Astra Rocket Co.)

Helicon Double Layer Thruster ExperimentHelicon Double Layer Thruster Experiment

Artists rendering of a Helicon Double Layer Thruster concept(Australian National University)

Helicon Double Layer Thruster ExperimentHelicon Double Layer Thruster Experiment

2003 Helicon Double Layer Thruster Experiment (Australian National University)

2005 Helicon Double Layer Thruster Experiment (European Space Agency, EPFL, Switzerland)

Plasmoid Thruster Experiment (PTX)Plasmoid Thruster Experiment (PTX)

PTX Schematic (NASA MSFC/U. Alabama)

Electric Propulsion ApplicationsElectric Propulsion Applications

1.1. ISSISS

2.2. Interplanetary MissionsInterplanetary Missions

3.3. Commercial/DefenseCommercial/Defense

• ISS meeds drag compensationISS meeds drag compensation

• Currently ISS is “Currently ISS is “reboostedreboosted” periodically” periodically

• PresentlyPresently Shuttle Shuttle (or Soyuz) perform this operation (or Soyuz) perform this operation

• Very high cost: 9000 lbs/yr propellant at $5,000/lbs = Very high cost: 9000 lbs/yr propellant at $5,000/lbs = 45M$/yr45M$/yr!!

Example: ISS Electric Propulsion BoostingExample: ISS Electric Propulsion Boosting