Under the NextSTEP program led by Aerojet Rocketdyne in collaboration with NASA Glenn Research Center the University of Michigan, and the Jet Propulsion Laboratory, the XR-100 100 kW Electric Propulsion system is being developed to Technology Readiness Level (TRL) 5. As part of this program, the X3, a Nested Hall Thruster (NHT) designed to operate at powers up to 200kW, is being further developed through parallel modeling and experimental efforts with the ultimate goal of supporting a 100kW-100hr system test in the final year of the NextSTEP program. Recent developments for the X3 subsystem are presented including a summary of testing and modeling results and design updates in anticipation of a risk reduction test scheduled for the summer of 2018

Gallimore, Alec D.

Gilland, James

Goebel, Dan M.

Hall, Scott J.

Hofer, Richard R.

Jorns, Benjamin A.

Mikellides, Ioannis

Peterson, Peter Y.

NASA Technical Reports Server

University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Update on the Nested Hall Thruster Subsystem 
for the NextSTEP XR-100 Program
Benjamin A. Jorns and Alec D. Gallimore
University of Michigan
Scott J. Hall and Peter Y. Peterson
Vantage Partners, NASA Glenn Research Center
James E. Gilland
Ohio Aerospace Institute, NASA Glenn Research Center, 
Dan M. Goebel , Richard R. Hofer, Ioannis Mikellides
Jet Propulsion Laboratory, California Institute of Technology
https://ntrs.nasa.gov/search.jsp?R=20180007749 2019-08-30T04:54:15+00:00Z
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
There is a need for next-generation electric 
propulsion systems capable of processing this power
Cargo and crewed 
missions to Mars 
and moonsHighest power EP  thruster 
flying (4.5-5 kW)
Available solar power in space is increasing rapidly
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Will we have electric propulsion systems that can 
utilize this power?
Cargo and crewed 
missions to Mars 
and moonsHighest power EP  thruster 
flying (4.5-5 kW)
Available solar power in space is increasing rapidly
Metric XR-100 Goal
Req. TRL 5 demonstration 
power
100 kW
TRL 5 steady state 
operation time
100 h
Objective Specific Impulse ~2,000 to ~5,000 s
Thrust per thruster > 5 N
Operational lifetime 
capability
> 10,000 h
System efficiency >60%
Power per thruster 100 kW
System kg/kW < 5 kg/kW
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Three contracts selected for NextSTEP program
VASIMR
ELF
XR-100
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
The XR-100 system
X3 Nested Hall 
thruster (UM)300 A LaB6cathode (JPL)
XFC
(AR)
100 kW PPU
(AR)
Propulsion element
Power/flow element
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
The XR-100 system
X3 Nested Hall 
thruster (UM)300 A LaB6cathode (JPL)
XFC
(AR)
100 kW PPU
(AR)
Propulsion element
Power/flow element
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
X3:  Propulsion element for the XR-100 system
• Why this technology?
• Merits and history of the X3
• Year 1 and 2 activities
• Remaining risk reduction 
activities
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Motivation for nested Hall thrusters (NHT)
Scale a single channel
• High level of maturity
• Decades of heritage
Hall effect thrusters 
(4.5-12.5 kW) 
Array of smaller thrusters
3 nested channels 
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
200 kW system example of nesting
150	cm	
diameter
80	cm	
diameter
Nested Hall thrusters (X3) offer mass savings, improved throttling, and redundancy*
1.85	kg/kW at	300	V2.425	kg/kW	at	300	V
*S. Hall, B. Jorns, A. Gallimore, and R. Hofer. AIAA-2017-4729
Motivation for nested Hall thrusters (NHT)
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
X3 thruster
X3 design specifications
Power 2-200 kW
Efficiency > 60%
Thrust 0.2 N– 10 N
Specific impulse 1550 – 3500 s on xenon
Diameter 80 cm
Mass 250 kg
Cooling Passive
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Development history of X3
1999-2011 NASA program to 
investigate 50 kW-class, high-
efficiency Hall thrusters
2009-2013 X2, 10 kW, two 
channel nested Hall thruster 
built and tested at UM
2009-2012 X3 designed and built 
by AFRL, AFOSR, JPL, NASA 
Glenn, and UM
2013 X3 fired for first time at 
30-kW at UM
2013-2015 X3 tested below 30 
kW at UM. Efficiencies and 
performance below predictions
2016 NextSTEP program awarded 
to Aerojet Rocketdyne
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Challenges for X3 at beginning of XR-100 program
Metric XR-100 Goal
Req. TRL 5 demonstration 
power
100 kW
TRL 5 steady state 
operation time
100 h
Objective Specific Impulse ~2,000 to ~5,000 s
Thrust per thruster > 5 N
Operational lifetime 
capability
> 10,000 h
System efficiency >60%
Power per thruster 100 kW
System kg/kW < 5 kg/kW
• System had not been demonstrated at 100 kW
• Open questions about extensibility to key 
program objectives
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
X3:  Propulsion element for the XR-100 system
• Why this technology?
• Merits and history of the X3
• Year 1 and 2 activities
• Remaining risk reduction 
activities
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Parallel research paths for Years 1 and 2 activities on X3
Year 3: 100 h 
test at 100 kW
Demonstrate 
extensibility
beyond Year 3
Testing
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Modeling efforts on X3 to date:  thermal
Sample result*
*S. Reilly and R. Hofer.  ICES-2017-345
Sample thermal couple 
placement on X3
1 2 3 4
11
12
13
14
15
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Modeling efforts on X3 to date:  thermal
Sample result*
Status
• Thermal model developed and 
validated against limited data set
• Existing thermal data sets from 
low-power testing (2016) had not 
reached thermal equilibrium for 
model calibration
• Follow on testing scheduled for 
Summer 2018 to provide 
additional calibration data 
*S. Reilly and R. Hofer.  ICES-2017-345
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Modeling efforts on X3 to date:  magnetic field
Coil 
current 
setting 1
Coil 
current 
setting 2
Coil 
current 
setting 1+2
Coil current 
setting 
(corrected)
S. Cusson, S. Hall, R. Hofer, B. 
Jorns, and A. Gallimore, IEPC-
2017-507
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Modeling efforts on X3 to date:  magnetic field
Coil 
current 
setting 1
Coil 
current 
setting 2
Coil 
current 
setting 1+2
Coil current 
setting 
(corrected)
Status
• Improved and validated magnetic field model generated
• Coil current settings identified for optimized magnetic field configurations
• Configurations demonstrated in 2017 risk reduction test
S. Cusson, S. Hall, R. Hofer, B. 
Jorns, and A. Gallimore, IEPC-
2017-507
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Modeling efforts on X3 to date:  plasma
Goals
• Generated experimentally-
validated plasma-based model of 
NHT operation
• Use validated model to assess life 
and explore design iterations for 
demonstrating NextSTEP lifetime 
objectives (10,000 h life)
Notional geometry and meshing in model
I. Mikellides and A. Lopez-Ortega, IEPC-2017-220
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Modeling efforts on X3 to date:  plasma
Plasma density
I. Mikellides and A. Lopez-Ortega, IEPC-2017-220
300 V and 100 kW simulation results
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Modeling efforts on X3 to date:  plasma
Plasma density Electron temperature
300 V and 100 kW simulation results
I. Mikellides and A. Lopez-Ortega, IEPC-2017-220
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Modeling efforts on X3 to date:  plasma
I. Mikellides and A. Lopez-Ortega, IEPC-2017-220
300 V and 100 kW simulation results
Plasma density Electron temperature
Status
• Model validated against one experimental operating condition (400 V and 49.6 kW)
• 5% within measured specific impulse
• 10% measured efficiency
• On-going efforts to validate against other measured operating conditions
• Key missing element is internal plasma measurements (beyond scope of Year 3)
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Modeling summary
• Thermal model built and validated against 
existing data sets.  Full calibration pending 
thermal equilibrium measurements in 2018.
• Plasma model built and validated against one 
operating conditions.  Efforts proceeding to 
validate against other conditions.
• Magnetic field model built and applied 
to optimize thruster performance
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Work path for Years 1 and 2 activities on X3
Year 3: 100 h 
test at 100 kW
Extensibility 
beyond Year 3
Testing
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
X3 250 A LaB6 hollow cathode testing
Overview
• Three generations of 250-A class 
LaB6 cathode tested during 
NextSTEP program.  All three have 
sufficient life and performance for 
100 h test
• Design iterations in Years 1 and 2 
performed to demonstrate 
extensibility to 10,000 hour lifetime 
objective of NextSTEP program. 
• Characterization testing performed to 
prove out these features
D. Goebel, G. Becatti, S. Reilly, K. Tilley, and S. Hall, IEPC-2017-303
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
X3 250 A LaB6 hollow cathode testing
Overview
• Three generations of 250-A class 
LaB6 cathode tested during 
NextSTEP program.  All three have 
sufficient life and performance for 
100 h test
• Design iterations in Years 1 and 2 
performed to demonstrate 
extensibility to 10,000 hour lifetime 
objective of NextSTEP program. 
• Characterization testing performed to 
prove out these features
Orifice plate temperature
Ion energy
D. Goebel, G. Becatti, S. Reilly, K. Tilley, and S. Hall, IEPC-2017-303
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
X3 250 A LaB6 hollow cathode testing
Overview
• Three generations of 250-A class 
LaB6 cathode tested during 
NextSTEP program.  All three have 
sufficient life and performance for 
100 h test
• Design iterations in Years 1 and 2 
performed to demonstrate 
extensibility to 10,000 hour lifetime 
objective of NextSTEP program. 
• Characterization testing performed to 
prove out these features
Orifice plate temperature
Ion energy
Status:  3rd generation cathode in use on X3.
Cathode life now projected to be > 10,000 hours
D. Goebel, G. Becatti, S. Reilly, K. Tilley, and S. Hall, IEPC-2017-303
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
X3 risk reduction test at NASA GRC
97	kW	at	550	V
S. Hall, B. Jorns, A. Gallimore, H. Kamhawi, T. Haag, J. 
Mackey, J. Gilland, P. Peterson, and M. Baird. IEPC-2017-228
Goals
• Demonstrate thruster for first time at 
NextSTEP power levels (100 kW)
• Evaluate performance metrics against 
NextSTEP goals
• Identify any follow on actions for 
thruster or facility in preparation for 
100 h, 100 kW demonstration test.
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
97	kW	at	550	V
Inner (I) Middle (M) Outer (O)
I+O
Thrust throttled through 47 conditions
I+M M+O I+M+O
S. Hall, B. Jorns, A. Gallimore, H. Kamhawi, T. Haag, J. 
Mackey, J. Gilland, P. Peterson, and M. Baird. IEPC-2017-228
X3 risk reduction test at NASA GRC
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
97	kW	at	550	V
S. Hall, B. Jorns, A. Gallimore, H. Kamhawi, T. Haag, J. 
Mackey, J. Gilland, P. Peterson, and M. Baird. IEPC-2017-228
Goals
• Demonstrate thruster for first time at 
NextSTEP power levels (100 kW)
• Evaluate performance metrics against 
NextSTEP goals
• Identify any follow on actions for 
thruster or facility in preparation for 
100 h, 100 kW demonstration test.
X3 risk reduction test at NASA GRC
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
97	kW	at	550	V
Results from 2018 test at 
NASA GRC*
X3 risk reduction test at NASA GRC
S. Hall, B. Jorns, A. Gallimore, H. Kamhawi, T. Haag, J. 
Mackey, J. Gilland, P. Peterson, and M. Baird. IEPC-2017-228
Thrust
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
97	kW	at	550	V
5.4 N at 400 V, 
98 kW
Results from 2018 test at 
NASA GRC*
X3 risk reduction test at NASA GRC
S. Hall, B. Jorns, A. Gallimore, H. Kamhawi, T. Haag, J. 
Mackey, J. Gilland, P. Peterson, and M. Baird. IEPC-2017-228
Thrust
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
97	kW	at	550	V
Results from 2018 test at 
NASA GRC*
X3 risk reduction test at NASA GRC
S. Hall, B. Jorns, A. Gallimore, H. Kamhawi, T. Haag, J. 
Mackey, J. Gilland, P. Peterson, and M. Baird. IEPC-2017-228
Specific impulse
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Metric XR-100 Goal
Requirement TRL 5 
demonstration 
power
100 kW
TRL 5 steady state 
operation time
100 h
Objective Specific Impulse ~2,000 to ~5,000 s
Thrust per thruster > 5 N
Operational lifetime 
capability
> 10,000 h
System efficiency >60%
Power per thruster 100 kW
System kg/kW < 5 kg/kW
Demonstrated thrust at 100 kW: 5.4 ± 0.1 N
Demonstrated specific impulse at 100 kW: 2600 s
Demonstrated efficiency at 100 kW:  67%  
X3 risk reduction test at NASA GRC
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
10-kW systems level test
Overview
• Demonstrate X3 system commanded 
and controlled by Aerojet DSU and 
XFC
• Only inner channel operated at 10 
kW
S. Shark et al. , “Test Resuls from a 10 kW Demonstration of the XR-100 Hall Propulsion System,” 
in 65th Joint Army Navy NASA Air Force Propulsion Meeting, Long Beach, CA , 2018
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
10-kW systems level test
Status
• Test conducted at University of 
Michigan in January 2018
• Paper on it in this session (AIAA-
2018-4419)
• New understanding of load 
impedance and transients informing 
Year 3 developments
S. Shark et al. , “Test Results from a 10 kW Demonstration of the XR-100 Hall Propulsion 
System,” in 65th Joint Army Navy NASA Air Force Propulsion Meeting, Long Beach, CA , 2018
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Testing summary
• Third-generation LaB6 hollow cathode design 
tested and lifetime projected to be > 10,000 h
• Systems level test demonstrated XR-100 
capability at reduced power (10-kW)
• Risk reduction test on X3 performed at 
NASA GRC and demonstrated thruster 
performance at 100 kW
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Work path for Years 1 and 2 activities on X3
Year 3: 100 h 
test at 100 kW
Extensibility 
beyond Year 3
Testing
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Design modifications
• Demonstrate a discharge chamber ring 
modification at temperature
• Demonstrate ring modification works at high 
voltage (> 700 V)
• Generate additional thermal steady-state data 
for model validation
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
X3:  Propulsion element for the XR-100 system
• Why this technology?
• Merits and history of the X3
• Year 1 and 2 activities
• Remaining risk reduction 
activities
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Final risk reduction test
X3 with new ring design installed in upgraded LVTF at UM (June 2018)
Thruster has passed reference firing conditions. Currently 
performing high-voltage tests.
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Summary
• XR-100 one of three selected technologies for NextSTEP program.   Goal is to 
advance system to TRL 5 in three years.
• X3 is a Nested Hall Thruster (NHT) propulsion element for the XR-100
• Efforts on X3 subsystem in Years 1 and 2 have focused on 
– Modeling development
– Risk reduction testing
– Low power systems level demonstrations
• Thruster has demonstrated performance levels meeting NextSTEP requirements 
(thrust, efficiency, specific impulse)
• Small design modifications identified during 2017 RRT and have been 
implemented.   Modifications undergoing final risk reduction test at UM now
• Thruster subsystem is on track for demonstration in late 2018 100 h, 100 kW test.
University of Michigan – Plasmadynamics and Electric Propulsion Laboratory
Acknowledgements
PEPL Lab Group 2018


Update on the Nested Hall Thruster Subsystem for the NextSTEP XR-100 Program

Update on the Nested Hall Thruster Subsystem for the NextSTEP XR-100 Program

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