Deep Space Propulsion Systems

Dr. Joshua L. RoveyAssistant Professor of Aerospace EngineeringMissouri University of Science & Technology

Presented to:Missouri S&T Physics Colloquium

January 28th, 2010

Outline

I. Rocket Propulsion Basics1) Propulsion, an energy conversion process2) Mustang vs. Prius, Chemical vs. Electric3) Deep-space, the Need for Speed

II. State-of-the-Art Deep Space Propulsion1) SoA Ion Thrusters2) Ion Thruster Physics3) Effects of Long-lifetime Operation

III. The FUTURE!1) Available Power in Space2) Why Plasmoid Propulsion?3) Current efforts in Plasmoid Propulsion

PART I:Rocket Propulsion Basics

Propulsion Basics

Stored Chemical/Electric Energy

An Energy Conversion Process

Propellant Stream Kinetic Energy

Vehicle Kinetic Energy

Propulsion Categories

• Chemical Propulsion– Energy liberation limited by

chemical reaction– Limited to ~ 4000 m/sec

exhaust velocity (10,000 mph)– High-thrust, due to high mass

flow rate (1 mustang per sec)– Best for escaping near-Earth

gravity• Electric Propulsion

– Energy limited by power supply

– Higher-exhaust velocity (50,000 to 200,000 mph)

– Low-thrust, due to low mass flow rate (1 paper clip every min)

– Space propulsion

Mustang vs. PriusChemical Propulsion Electric Propulsion

Electric Propulsion Categories

Electric Propulsion

Electrothermal Electromagnetic Electrostatic

MPDsArcjet PPT Hall Thrusters Ion Thrusters

Type

Thrust Range (mN)

Specific Impulse

(sec)

Thruster Efficiency

(%) Thrust

Duration Typical Propellant

Kinetic Power per Unit Thrust

(W/mN) Resistojet (thermal) 200-300 200-350 65-90 Months NH3, N2H4, H2 0.5-6 Arcjet (thermal) 200-1000 400-1000 30-50 Months H2, N2, N2H4, NH3 2-3 Ion thruster 0.01-200 1500-5000 60-80 Months Xe, Kr, Ar 10-70 PPT 0.05-10 600-2000 10 Years Teflon 10-50 MPD 0.001-2000 2000-5000 30-50 Weeks Ar, Xe, H2, Li 100 Hall thruster 0.01-2000 1500-2000 30-50 Months Xe, Ar 100

Monopropellant rocket 30-100,000 200-250 87-97 Hours or Minutes N2H4

Electric Propulsion in Orbit

Deep Space Missions: the Need for Speed

1.0

0.8

0.6

0.4

0.2

0.0

mf /

mi

101 102 103 104 105 106 107

Specific Impulse, Isp (s)

AdvancedChemical

AdvancedNEP System

System

Earth to LEO (7.6 km/s)LEO to Earth Escape (3.2 km/s)LEO to Mars, 40 days (85 km/s)LEO to Mars, 0.7 yr (5.7 km/s)Jupiter Icy Moons Orbiter (50 km/s)LEO to Alpha Centauri (30,000 km/s)g

cgm

TIsp =≡&

cU

o

f eMM Δ−

=

fpo MMM +=

∫=t

TdtI0

PART II:State-of-the-Art Ion Thruster

What is Plasma? What is it good for?

• Ionized Gas• Gas of free charged

particles; electrons and ions

• High temperatures remove electrons from atoms

• Plasma can exert forces (E&M, pressure, etc.)

• Plasma can be manipulated using electric and magnetic fields

Ion Thruster Physics

• How an Ion Thruster Works1) Hollow cathode

creates/emits electrons

2) Electrons collide with xenon atoms to create plasma

3) Plasma ions expelled at high velocity

NASA Ion Thrusters

• NSTAR – 30 cm diameter– NASA design– Manufactured by Boeing

(now L3-communications)– 2 kW, Xenon propellant, 100

mN, 3500 sec– Deep-space One (1998 -2001,

comet Borelly)– DAWN (2007 – 2015, Vesta,

Ceres 2011 – 2012)• NEXT – 40 cm diameter

– NASA design– Manufactured by Aerojet– 8 kW, Xenon propellant, 350

mN, 4500 sec– Completed almost 2 yrs of life

testing

Why does the cathode erode?

Cathode after approximately 3.5 years of operation inside an ion thruster

NSTAR Ion Thruster

Experiment

Results

TH8

TH15

Trajectory & Erosion Simulation

DCA Keeper

Impacting Ion Trajectories

near-DCA Electric Field Structure

40 60 80 1000

0.5

1

1.5

Radial Location (% Keeper Radius)Er

osio

n (N

o. o

f Spu

ttere

d A

tom

s) Cold Ion ProfileWarm Ion Profile

• Near-Cathode potential structure focuses ions into Cathode• Ions have enough energy to cause sputtering erosion• Over time, this leads to destruction of the cathode • And eventually termination of engine operation

PART III:The FUTURE!

How much POWER!?

212

P mv= &

12 spP TI g=

• Fixed Power• Specific impulse

decreases with increasing thrust!

0.001

0.01

0.1

1

10

100

1000

Thru

st (N

)

1032 3 4 5 6 7

1042 3 4 5 6 7

105

Specific Impulse (sec)

1 kW

1 MW

HET Ion10 kW

100 kW

0.1 kW

Plasmoid Thruster

10 MW

Scale-up Ion Thrusters?

• Increased Power requires Increased Size

• Size correlates with Weight

• Need:– Increased Power

Density– Increased Thrust

Density– Increased Plasma

Density

0

10

20

30

40

50

0 20 40 60 80Thruster Diameter (cm)

Pow

er L

evel

(kW

)

Max Possible Poweri

NSTARXIPS

SERTII

NEXT

NEXIS

Missouri Plasmoid Experiment (MPX)

• Aid the development of future Plasmoid Propulsion devices

• Study – Formation processes– Energy conversion– Loss mechanisms– Instabilities

• How?– MPX, a cylindrical pulsed

inductive plasmoid test article– High-speed probes and

spectroscopy– Advanced MHD and

collisional-radiative modeling

Summary

I. Rocket Propulsion Basics– Chemical vs. Electric = Mustang vs. Prius– Electric Propulsion is FLYING NOW!

II. State-of-the-Art Deep Space Propulsion– Ion Thrusters are the State-of-the-Art for Deep

Space propulsion– NASA DAWN mission thrusters are on NOW!

III. The FUTURE!– Higher Power, Higher Thrust, Higher Exhaust

Velocity– Pulsed Inductive Thrusters?

QUESTIONS?

Aerospace Plasma Laboratoryhttp://campus.mst.edu/aplabProf. Joshua Rovey112 Toomey Hallroveyj@mst.edu