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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 [email protected]