Lee Mason, Donald Palac, and Marc Gibson

Glenn Research Center, Cleveland, Ohio

Michael Houts

Marshall Space Flight Center, Huntsville, Alabama

John Warren

Headquarters, Washington, DC

Jim Werner

Idaho National Laboratory, Idaho Falls, Idaho

David Poston

Los Alamos National Laboratory, Los Alamos, New Mexico

Arthur Lou Qualls

Oak Ridge National Laboratory, Oak Ridge, Tennessee

Ross Radel

Sandia National Laboratories, Albuquerque, New Mexico

Scott Harlow

Department of Energy, Germantown, Maryland

Design and Test Plans for a Non-Nuclear Fission 

Power System Technology Demonstration Unit

NASA/TM—2011-217100

December 2011

NETS–2011–3327
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 NASA Center for AeroSpace Information (CASI)

 7115 Standard Drive

 Hanover, MD 21076–1320
Lee Mason, Donald Palac, and Marc Gibson

Glenn Research Center, Cleveland, Ohio

Michael Houts

Marshall Space Flight Center, Huntsville, Alabama

John Warren

Headquarters, Washington, DC

Jim Werner

Idaho National Laboratory, Idaho Falls, Idaho

David Poston

Los Alamos National Laboratory, Los Alamos, New Mexico

Arthur Lou Qualls

Oak Ridge National Laboratory, Oak Ridge, Tennessee

Ross Radel

Sandia National Laboratories, Albuquerque, New Mexico

Scott Harlow

Department of Energy, Germantown, Maryland

Design and Test Plans for a Non-Nuclear Fission 

Power System Technology Demonstration Unit

NASA/TM—2011-217100

December 2011

NETS–2011–3327

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

Nuclear and Emerging Technologies for Space (NETS-2011)

cosponsored by the ANS Aerospace Nuclear Science and Technology Division, the ANS Trinity Section,

and the AIAA

Albuquerque, New Mexico, February 7–10, 2011
Acknowledgments

This work was performed by the fi ssion power system team for the Exploration Technology Development Program, which is 

now transitioning to the Enabling Technology Development and Demonstration Program. It should be noted that the author list 

includes the main point-of-contact from each of the partner organizations, but that many more individuals at those organizations 

contribute toward making the project successful.

Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

5301 Shawnee Road

Alexandria, VA 22312

Available electronically at http://www.sti.nasa.gov

Trade names and trademarks are used in this report for identifi cation 

only. Their usage does not constitute an offi cial endorsement, 

either expressed or implied, by the National Aeronautics and 

Space Administration.

Level of Review: This material has been technically reviewed by technical management. 

This report contains preliminary fi ndings, 

subject to revision as analysis proceeds.
NASA/TM—2011-217100 1 

Design and Test Plans for a Non-Nuclear Fission Power System 

Technology Demonstration Unit 

Lee Mason, Donald Palac, and Marc Gibson 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Michael Houts 

National Aeronautics and Space Administration 

Marshall Space Flight Center 

Huntsville, Alabama 35812 

John Warren 

National Aeronautics and Space Administration 

Headquarters 

Washington, DC 20546 

Jim Werner

Idaho National Laboratory 

Idaho Falls, Idaho 83415 

David Poston 

Los Alamos National Laboratory 

Los Alamos, New Mexico 87545 

Arthur Lou Qualls 

Oak Ridge National Laboratory 

Oak Ridge, Tennessee 37831 

Ross Radel 

Sandia National Laboratories 

Albuquerque, New Mexico 87185 

Scott Harlow 

Department of Energy 

Germantown, Maryland 20874

Abstract 

A joint National Aeronautics and Space Administration (NASA) and Department of Energy (DOE) 

team is developing concepts and technologies for affordable nuclear Fission Power Systems (FPSs) to 

support future exploration missions. A key deliverable is the Technology Demonstration Unit (TDU). 

The TDU will assemble the major elements of a notional FPS with a non-nuclear reactor simulator 

(Rx Sim) and demonstrate system-level performance in thermal vacuum. The Rx Sim includes an 

electrical resistance heat source and a liquid metal heat transport loop that simulates the reactor thermal 

interface and expected dynamic response. A power conversion unit (PCU) generates electric power 

utilizing the liquid metal heat source and rejects waste heat to a heat rejection system (HRS). The HRS 

includes a pumped water heat removal loop coupled to radiator panels suspended in the thermal-vacuum 

facility. The basic test plan is to subject the system to realistic operating conditions and gather data to 

evaluate performance sensitivity, control stability, and response characteristics. Upon completion of the 

 
NASA/TM—2011-217100 2 

testing, the technology is expected to satisfy the requirements for Technology Readiness Level 6 

(System Demonstration in an Operational and Relevant Environment) based on the use of high-fidelity 

hardware and prototypic software tested under realistic conditions and correlated with analytical 

predictions. 

Nomenclature 

ALIP annular linear induction pump 

DAS data acquisition system 

DOE Department of Energy 

ELS electric load simulator 

FCS facility cooling system 

FPS Fission Power System 

FSP Fission Surface Power 

HRS heat rejection system 

INL Idaho National Laboratory 

JIMO Jupiter Icy Moons Orbiter 

LANL Los Alamos National Laboratory 

MSFC Marshall Space Flight Center 

NASA National Aeronautics and Space Administration 

PMAD power management and distribution 

ORNL Oak Ridge National Laboratory 

PCU power conversion unit 

PID proportional-integral derivative 

Rx Sim reactor simulator 

SNL Sandia National Laboratories 

TDU Technology Demonstration Unit 

VF6 vacuum facility 6 

Fission Power Project 

The Fission Power System (FPS) technology project is a joint collaboration of the National 

Aeronautics and Space Administration (NASA) and Department of Energy (DOE) aimed at establishing 

the technology readiness of space reactor power systems for future exploration missions (Refs. 1 and 2). 

The FPS project resides under the Enabling Technology Development and Demonstration Program, one 

of five initial demonstration projects selected for near-term development. Up until recently, the project 

was focused on lunar and Mars surface power applications. The current effort has been expanded to 

address other fission power applications that may be derived from NASA’s new broader, more flexible 

mission path. The primary project goals, as defined during the surface mission focus, remain essentially 

unchanged: 1) develop concepts that meet the expected power requirements at reasonable cost with added 

benefits over other options, 2) establish a hardware-based technical foundation for design concepts and 

reduce overall development risk, 3) reduce the cost uncertainties and establish greater credibility for flight 

system cost estimates, and 4) generate the key products to allow NASA decision makers to consider 

fission systems as a preferred option for flight development. 

The former Fission Surface Power (FSP) project was initiated in 2006 as the NASA Prometheus 

Program and the Jupiter Icy Moons Orbiter (JIMO) mission were phased out. As a first step, NASA 

Headquarters commissioned the Affordable Fission Surface Power System Study to evaluate the potential 

for an affordable FSP development approach (Ref. 3). With a cost-effective FSP strategy identified, the 
NASA/TM—2011-217100 3 

FSP team evaluated design options and selected a Preliminary Reference Concept to guide technology 

development (Refs. 4 to 6). Since then, the FSP preliminary reference concept has served as a point-ofdeparture for several NASA mission architecture studies examining the use of nuclear power (Ref. 7) and 

has provided the foundation for a series of “pathfinder” hardware tests (Refs. 8 to 12). The project goal is 

a Technology Demonstration Unit (TDU) integrated system test using full-scale components and a nonnuclear reactor simulator. 

The fission power team consists of Glenn Research Center (GRC), Marshall Space Flight Center 

(MSFC), and the DOE National Laboratories at Los Alamos (LANL), Idaho (INL), Oak Ridge (ORNL), 

and Sandia (SNL). The project is organized into two main elements: concept definition and risk reduction. 

Under concept definition, the team performs trade studies, develops analytical tools, and formulates 

system concepts. Under risk reduction the team develops hardware prototypes and conducts laboratorybased testing. 

Technology Demonstration Unit Overview 

The TDU is an end-to-end system test of a reactor simulator (Rx Sim), power conversion unit (PCU), 

and heat rejection system (HRS) in thermal vacuum. The TDU is intended to demonstrate the major 

elements of a notional fission power system using a non-nuclear heat source. The Rx Sim includes an 

electrical resistance heat source and a liquid metal (sodium potassium or NaK) heat transport loop that 

simulate the reactor thermal interface and expected dynamic response. The PCU generates electric power 

utilizing the heated liquid metal and rejects waste heat to the HRS. The HRS includes a pumped water 

heat removal loop coupled to radiator panels suspended in the thermal-vacuum facility. An intermediate 

test configuration, prior to the installation of the HRS, includes a facility cooling system (FCS) to reject 

PCU waste heat utilizing an external air-cooled heat exchanger. The data acquisition and control, and 

power management and distribution (PMAD) equipment would be external to the vacuum facility and 

provide prototypic functionality using commercially available, rack-mounted components. 

The TDU was devised to demonstrate the technology for a 40-kWe FPS and includes one of four fullscale power conversion strings, permitting the test system to produce 10 kWe under nominal conditions. 

The technology is broadly applicable to fission power systems with pumped liquid-metal-cooled reactors 

and dynamic power conversion for power levels up to at least 100 kWe. The test configuration is based on 

the surface power application with a below-grade reactor core beneath a vertical truss structure that 

supports the NaK heat transport components, PCU, and HRS water pump as shown in Figure 1. The twosided vertical radiator panels are mounted adjacent to the truss and supported by a central monorail from 

the ceiling of the vacuum chamber. The entire Rx Sim, PCU, and HRS assembly is contained in a 21-mlong horizontal vacuum chamber at NASA GRC, known as vacuum facility 6 (VF6). Separate external 

computer controllers are anticipated for the Rx Sim, PCU, and HRS to accommodate checkout testing at 

supplier facilities prior to integration at GRC. The separate controllers would be integrated at GRC to 

permit data exchange to a central data acquisition system via an Ethernet communications network. 

Figure 1.—TDU test layout with the Core 

Simulator, NaK heat transport components, 

and Stirling PCU in the vertical truss and 

the Six HRS radiators supported by the 

central monorail. 
NASA/TM—2011-217100 4 

Test Objectives 

The primary objective of the TDU is to demonstrate the technology readiness of an integrated FPS 

using a non-nuclear heat source. Upon completion of the testing, the technology is expected to satisfy the 

requirements for Technology Readiness Level 6 (System Demonstration in an Operational and Relevant 

Environment). This is based on the use of high-fidelity hardware and prototypic software tested under 

realistic conditions and correlated with analytical predictions. Many past space reactor projects have 

produced impressive reports and insightful analyses, but few have assembled prototype components into a 

system and demonstrated operational performance. 

The nuclear reactor core will be simulated in the TDU to avoid the complexity of a nuclear heated 

test. The FSP design uses relatively mature reactor technology based on terrestrial heritage permitting the 

reactor development to be deferred to a follow-on flight program, if NASA chooses to pursue the option 

further. Some nuclear-related technology development will be conducted in parallel with the TDU 

including reflector control drive testing, shield development, and material and component irradiation 

testing. Some of the major challenges that the TDU testing will address are the liquid metal heat transport, 

electric power generation, and waste heat removal. The basic test plan is to subject the system to realistic 

operating conditions and gather data to evaluate performance sensitivity, control stability, and response 

characteristics. The TDU will not demonstrate system lifetime or launch and landing survivability, since 

both of those items are better addressed in a flight program when the requirements are better defined and 

the design is more mature. 

Block Diagram 

The TDU block diagram is shown in Figure 2. The Rx Sim includes a core simulator and a primary 

NaK heat transport loop. The core simulator includes a series of pin-type electrical resistance heating 

elements arranged to represent the reactor fuel pin bundle. The NaK loop includes an electromagnetic 

pump and volume accumulator. A NaK fill and drain system provides the capability for charging and 

discharging the NaK loop. An Rx Sim controller collects data, relays command signals, and supplies 

electric power for the Rx Sim components. The Rx Sim controller provides the means to control core 

simulator NaK outlet temperature and NaK flow rate. It also includes the software to simulate the 

expected temperature-reactivity feedback dynamics of a fission reactor. 

Figure 2.—TDU block diagram with the fluid, electrical, and data interfaces shown for the major TDU components. 
NASA/TM—2011-217100 5 

The PCU consists of the power converter, PCU controller, and gas fill and drain system. The power 

converter includes a NaK-to-gas heat exchanger for heat input and a gas-to-water heat exchanger for 

waste heat removal. Two power conversion technologies were considered during early design studies: 

closed Brayton and free-piston Stirling. The Brayton option, developed by Barber Nichols, included a 

single heat engine with a rotating turbine-alternator-compressor and gas-to-gas recuperator (Ref. 13). The 

Stirling option by Sunpower utilized two free-piston heat engines with integral regenerators and linear 

alternators in an opposed configuration to balance vibration (Ref. 14). Following the design studies, the 

Stirling option was selected for fabrication and test. The gas fill and drain system provides the capability 

for charging and discharging the Stirling converter’s helium working fluid. The PCU controller collects 

data, relays command signals, and supplies startup electric power for the converter. It also processes the 

electric output of the converter providing alternating current (ac)–direct current (dc) conversion, parasitic 

load control, and voltage regulation. 

The HRS consists of the radiator, pumped water heat transport loop, and HRS controller. The 

radiators are two-sided vertical panels with embedded titanium-water heat pipes. The radiator panels 

include a manifold with heat exchangers to transfer heat from the pumped water loop to the heat pipe 

evaporators. The heat pipes transfer the heat to the condenser section and then to the panel surface where 

it is radiated to the walls of the thermal-vacuum chamber. The water heat transport loop provides direct 

cooling of the power converter and includes a pump and volume accumulator. The HRS controller 

collects data, relays command signals, controls the pump flow rate, and supplies pump power. Prior to the 

HRS installation, the FCS will provide waste heat removal for the power converter. The FCS will also 

utilize water coolant and will include all of the equipment to circulate the water and remove the waste 

heat using a commercial air-cooled heat exchanger located outside the vacuum chamber. The water fill 

and drain provides the capability for charging and discharging the water loop with either the HRS or FCSbased test configuration. 

The balance of the test system is associated with the facility. The facility includes the vacuum 

chamber (VF6), liquid nitrogen (LN2) cold wall, LN2 fill and drain system, facility controller, facility 

power, electric load simulator (ELS), and data acquisition system (DAS). The vacuum chamber is a 21-mlong by 7.6-m-diameter horizontal cylindrical tank with cryogenic pumps. The LN2 cold wall extends 

along the center 16.2 m of the chamber length and covers all but the bottom 60° of the circumference. The 

LN2 sections would operate at LN2 temperature (77 K) while the bottom and end-cap sections would be at 

ambient temperature (300 K). The LN2 fill and drain provides the capability for charging and discharging 

the cold wall. The facility controller provides the operations interface for the vacuum chamber and LN2

cold wall. The facility power supplies electric power for the TDU components with availability of 110, 

220, 440, and 208 V service. The ELS receives the regulated electric power from the PCU controller and 

provides a user interface for switching typical loads. The ELS also provides the power bus for starting the 

power converter. The DAS provides a central data collection node for the Rx Sim, PCU, and HRS 

controllers as well as facility instrumentation. A communication network is envisioned that will permit 

the transfer of data between the various controllers and the DAS. 

Design Requirements 

A detailed TDU Design Specification containing system, subsystem, and component design 

requirements was generated to guide hardware development. The specified values are based on the 

expected operating conditions of the reference FSP system concept defined in Reference 5. In some cases 

the values are modified based on the single-string test configuration and/or the inability to represent the 

flight system with less than fully prototypic test articles. The requirements are based on the Stirling PCU 

selection and are based on nominal operating conditions with margin, if appropriate. The TDU test plan 

will include test points to evaluate off-nominal conditions. In some cases where those conditions could be 

predicted, a range of values is specified. 

 
NASA/TM—2011-217100 6 

Figure 3.—Key performance requirements for the major TDU components. 

A summary of the key TDU performance requirements is shown in Figure 3. The core simulator 

nominal input power is 48 kWe producing a primary NaK outlet temperature of 850 K. The Stirling PCU 

generates 12 kWe and transfers 36 kWt to the water heat removal loop with an inlet temperature of 

approximately 375 K. A 55-m2

 radiator with an outlet temperature of 375 K rejects the 36 kWt to the 

thermal-vacuum chamber cold sink of 200 K. The 400 Vac Stirling alternator output power is processed 

through an electrical controller that delivers 10 kWe to the ELS at 120 Vdc. The TDU system is intended 

to function over a wide range of operating points and transient conditions, representative of what could 

occur in a flight mission. The primary test variables are core simulator power, primary NaK flow rate, 

Stirling piston amplitude, water flow rate, sink temperature, and user load demand. 

Development Status 

The TDU System Requirements Review was held in December 2008 at which time a draft TDU 

System Specification was generated to guide the design process. In February 2009, the TDU Preliminary 

Design Review formally kicked off the development of the TDU. An independent review panel evaluated 

the readiness of the TDU system and component designs to proceed to final design. In May 2009, a 

second independent panel reviewed the final designs and fabrication readiness of the main TDU 

components: core simulator, NaK pump, NaK accumulator, intermediate heat exchanger, and PCU. An 

additional product of the May review was a final management-approved TDU System Specification. The 

design formulation process culminated with the TDU System Final Design Review in October 2009 

where a third independent panel evaluated the system design readiness and recommended that the project 

proceed. All major components of the TDU are now in development, and test facility preparations are in 

process. In October 2010, project budget reductions forced the deletion of the intermediate NaK loop, 

which was originally included in the TDU to reflect the expected surface power configuration. Work is 

proceeding on a single NaK loop Rx Sim that still meets the technical objectives. The paragraphs below 

provide a brief status on the Rx Sim and PCU. 

The core simulator, shown in Figure 4, includes 36 individual pin-type electrical-resistance heating 

elements arranged in a bundle that represents the reactor core plus one center pin allocated for 

instrumentation wires. The custom heater elements, developed by MSFC, are made of graphite with a 

stainless steel sleeve and a helium cover gas. The heater geometry and thermal performance is intended to 

approximate a reactor fuel pin. Testing at MSFC has demonstrated long-term heater operation at power 

levels in excess of 2.5 kWe. Electric power is provided to the core simulator through 12 separate power 

supplies with three heater elements in series per circuit. The 37 pins are contained in a stainless steel 
NASA/TM—2011-217100 7 

Figure 4.—The core simulator internal assembly showing the 36 pin-type heating elements. 

Figure 5.—The dual opposed Stirling PCU with central NaK heat exchanger manifold and water coolant lines. 

vessel with NaK flow geometry and thermal capacitance that is based on the notional reactor core. The 

NaK is circulated through the core and delivered to the PCU by an annular linear induction pump (ALIP) 

developed by INL. The ALIP has no moving parts; it uses a series of magnetic coils to propel the 

electrically conductive fluid through a flow annulus. The ALIP power supply provides the means to vary 

flow rate by adjusting input frequency and voltage.

The 12-kWe PCU, shown in Figure 5, is a free-piston Stirling converter under development by 

Sunpower Incorporated with dual opposed engines that are thermodynamically coupled via a common 

helium expansion space (Ref. 15). The PCU uses gas bearings and planar springs to maintain noncontacting operation of the displacer and power piston within the cylinder housing. The converter is 

designed to operate at a temperature ratio of 2.2, frequency of 60 Hz, and a mean pressure of 6.2 MPa. At 

the hot end, the PCU has a stainless steel NaK heat exchanger that directs the flow axially through a radial 

gap across the heater head to heat the internal copper acceptor. The NaK heat exchanger uses a unique 

design approach where the primary helium pressure containment is outside of the NaK flow annulus. A 

small 1-mm stainless steel wall provides the fluid boundary between the NaK and the internal acceptor, 

thus minimizing the temperature drop. On the cold end, pumped water is routed through circumferential 

flow passages in the copper rejector to remove waste heat. A small fraction of the water flow is supplied 

to a cooling jacket that surrounds the alternator vessel for thermal management. The moving magnet 

linear alternator uses samarium-cobalt magnets in a titanium structure. 

Checkout testing is expected to begin in 2011 with the Rx Sim primary loop verification test, 

including the core simulator, primary pump, and primary volume accumulator, with a gaseous nitrogen 

heat exchanger for heat removal. The two 6-kWe Stirling engines will be built and tested separately using 

electrically heated test heads, and then tested as a thermodynamically coupled pair before installing the 
NASA/TM—2011-217100 8 

NaK heater head. Delivery of the completed Rx Sim and PCU is expected at GRC in mid-2012. The 

ensuing TDU test program will occur in two phases. During the first phase, the Rx Sim and PCU will be 

assembled in VF6 and the system will be tested under thermal-vacuum conditions with the external FCS 

providing PCU heat rejection. Phase 1 hardware checkout testing is scheduled to begin in late-2012. Also 

during the first phase, the HRS design and fabrication will be completed. After the phase 1 testing, the 

HRS will be integrated into the TDU test assembly. Phase 2 testing of the fully integrated system is 

scheduled for completion in late-2014, establishing system-level technology readiness of fission power 

for NASA exploration applications. 

Preliminary Test Program 

The TDU test program will be defined in detail at the Test Readiness Review prior to starting the 

initial test phase. The test program will consist of a number of test sequences, with each sequence having 

a specific test objective. A test sequence would produce a series of data points that address the test 

objective. The test system will be fully instrumented with temperature sensors (thermocouples and 

resistive temperature devices), pressure transducers, fluid flow meters, and electrical sensors (voltage, 

current, and frequency). Of particular interest is the ability to accurately determine the system energy 

balance based on heat delivered by the NaK loop, power generated by the Stirling converter, and heat 

removed by the water loop. A major goal for the testing is to demonstrate the functionality of the system 

over a wide range of operating conditions. 

Testing would be conducted by varying available test parameters and collecting transient and steadystate data. There are a limited number of test parameters that can be varied as listed in Table 1. A pretest 

analytical simulation would be generated to guide the test sequence and assure that the system is operated 

within prescribed limits. Test sequences would be conducted on a 24 hr per day operation schedule and 

could last from several days to over a week in duration. At the conclusion of a test sequence, the system 

would be shut down and the test team would thoroughly review the data. The test data would be used to 

update the analytical model and provide improved accuracy for the next test sequence. 

TABLE 1.—POTENTIAL TDU TEST VARIABLES 

1. Core simulator power a) Constant power mode―adjust the heater power 

supplies to achieve a set power output. 

b) NaK exit temperature control mode―adjust the 

heater power supplies to achieve a set NaK exit 

temperature. 

c) Reactivity feedback control mode―adjust the 

heater power supplies to respond to temperature 

changes based on reactivity feedback algorithms. 

2. NaK flow rate Adjust NaK pump power supply voltage and/or 

frequency. 

3. Stirling piston amplitude Adjust the alternator voltage through control of the 

terminal voltage and bidirectional energy (current) flow 

between the PCU controller and alternator. 

4. Facility cooling system supply 

temperature 

Adjust the amount of heat removed or added to the FCS 

water loop. (Note: this is not possible with the HRS.) 

5. Water flow rate Adjust water pump power supply voltage and/or current. 

6. Radiator area Use insulation to mask portions of the radiator surface 

prior to establishing vacuum. 

7. Test environment a) Vacuum―operate the facility at vacuum. 

b) Thermal-vacuum―operate the facility at vacuum 

and fill the cold walls with LN2. 

 
NASA/TM—2011-217100 9 

A preliminary test plan has been developed to guide the design process and identify operational 

expectations for the test hardware. The overall test philosophy is to start simple and introduce greater 

complexity as operations experience is gained. The preliminary test plan is summarized in Table 2. It 

starts with hardware installation and checkout to verify overall functionality and control. Initial hot testing 

would provide the proportional-integral-derivative (PID) coefficients to permit core simulator temperature 

control. Variable cold- and hot-end testing would be performed to evaluate performance sensitivity before 

proceeding into a full system map that would optimize system performance over a matrix of hot- and 

cold-end operating temperatures. With the performance mapped, the test system would be subjected to 

various heat-up profiles to optimize the startup sequence and various environmental transients to verify 

stable operation. The transient performance data will provide confidence to begin reactor feedback 

simulations that exercise the system over a range of operational perturbations while evaluating different 

feedback coefficients and component reactivity effects. With the system fully characterized and the 

control stability adequately evaluated, the test system would be subjected to a number of adverse 

transients that might be encountered during an actual mission including overheating, overcooling, loss of 

NaK flow, loss of water flow, PCU shutdown/restart, and extended cold soak. Before conducting these 

tests, the conditions will be carefully evaluated to assure that the system does not exceed its design limits 

and that no intentional damage occurs to the test hardware. 

TABLE 2.—PRELIMINARY TEST PLAN

A1. Rx-PCU Install and 

Checkout 

All electrical connections, software, and instrument functionality will be 

verified. All fluid systems will be leak-checked and filled. All pumps and valves 

will be operated. The Core Sim will be heated to low temperature. The PCU will 

be cold motored. 

A2. Initial Hot Test The system will be started at low power and gradually ramped to full 

temperature and power to gather general performance characteristics. 

A3. Core Sim Temp 

Control 

The Core Sim will be operated in Temperature Control Mode and exercised over 

a range of conditions to verify stable operation. 

A4. Variable Cold End The FCS and water loop will be exercised over a range of conditions with a 

fixed hot end to evaluate system performance sensitivity. 

A5. Variable Hot End The Core Sim and NaK loop will be exercised over a range of conditions with a 

fixed cold end to evaluate system performance sensitivity. 

A6. System Performance 

Map 

The system will be exercised over a matrix of hot- and cold-end temperatures. 

The PCU will be tuned by varying piston amplitude to optimize performance at 

each setting to create a system performance map. 

A7. Lunar Environments The system will be subjected to various startup scenarios to determine minimum 

start time and minimum start energy. The system will be subjected to a 

simulated lunar/night cycle to verify stable operation. 

A8. Reactor Feedback 

Simulation 

The Core Sim will be operated in Reactor Feedback Mode and exercised over a 

range of conditions to verify stable operation. The reactivity feedback 

coefficients will be varied to evaluate system response characteristics. 

A9. Transients and 

Faults 

The system will be subjected to a series of adverse transients (e.g., reactor overtemp, loss of NaK flow, radiator over-temp, loss of water flow, PCU shutdown, 

hot restart, and electrical load faults) in a controlled manner to evaluate system 

response characteristics. 

A10. Cold Soak Start The system will be subjected to an extended thermal cold soak and started to 

evaluate system response characteristics. 

B1. HRS Install and 

Checkout 

All electrical connections, software, and instrument functionality will be 

verified. All fluid systems will be leak checked and filled. All pumps and valves 

will be operated. The HRS will be partially heated. 

BX. Repeat Rx-PCU 

Tests With HRS 

B2. Initial Hot Test 

B3. Core Sim Temperature Control 

B4. Variable Cold End 

B5. Variable Hot End 

B6. System Performance Map 

B7. Lunar Environments 

B8. Reactor Feedback Simulation 

B9. Transients and Faults 

B10. Cold Soak Start 
NASA/TM—2011-217100 10 

This same basic test plan will be repeated following HRS installation and checkout. The majority of 

this test phase will be conducted with the LN2 coldwalls filled to provide the thermal environment for the 

HRS radiators. The system performance and dynamic behavior will be considerably different with the 

HRS due to the fixed heat rejection capacity of the radiators as compared to the FCS. The integrated 

system testing with the HRS will provide a more realistic indication of operating performance, similar to 

what would be expected during actual space operations. 

Conclusions 

The Fission Power System project has adapted to program and agency-level changes and is on track 

to demonstrate the technology readiness of fission power systems for space applications. The NASA and 

DOE team have completed concept development studies and “pathfinder” component tests that have 

positioned the project to conduct a full-scale, non-nuclear integrated system test. The team will assemble 

an electrically heated reactor core simulator, NaK heat transport loop, Stirling power conversion unit, and 

radiator heat rejection system into a FPS Technology Demonstration Unit that will be operated in a 

thermal-vacuum environment to demonstrate system-level performance. The basic test plan will subject 

the system to realistic operating conditions and gather data to evaluate system performance sensitivity, 

control stability, and response characteristics. The testing is scheduled to begin in late-2012 and continue 

through 2014, at which time the requirements for Technology Readiness Level 6 should be achieved 

allowing FPS to transition into flight development if needed to support future NASA missions. 

References 

1. Palac, D.T., Mason, L.S., Houts, M.G., and Harlow, S., “Fission Surface Power Technology 

Development Status,” NASA/TM—2010-216249, April 2010. 

2. Palac, D.T., Mason, L.S., Houts, M.G., and Harlow, S., “Fission Surface Power Technology 

Development Update,” AIAA–2010–8711, AIAA SPACE 2010 Conference and Exposition, 

Anaheim, California, 30 Aug.–2 Sept. 2010. 

3. Affordable Fission Surface Power System Study Final Report, Exploration Systems Mission 

Directorate Memorandum for the Record, 5 October 2007. 

4. Executive Summary of Reference Fission Surface Power System Concept Selection, Exploration 

Systems Mission Directorate Memorandum for the Record, 23 July 2008. 

5. Mason, L., Poston, D., and Qualls, L., “System Concepts for Affordable Fission Surface Power,” 

NASA/TM—2008-215166, January 2008. 

6. Fission Surface Power Team, “Fission Surface Power System Initial Concept Definition,” 

NASA/TM—2010-216772, August 2010. 

7. Mason, L.S., and Poston, D.I., “A Summary of NASA Architecture Studies Utilizing Fission Surface 

Power Technology,” Proceedings of the 8th International Energy Conversion Engineering 

Conference, AIAA–2010–6599, Nashville, Tennessee, 25-28 July 2010. 

8. Mason, L., “Recent Advances in Power Conversion and Heat Rejection Technology for Fission 

Surface Power,” NASA/TM—2010-216761, July 2010. 

9. Ellis, D., and Mason, L.S., “Performance Testing Of A Full-Scale Radiator for Fission Surface Power 

Applications,” Proceedings of the 8th International Energy Conversion Engineering Conference, 

AIAA–2010–6760, Nashville, Tennessee, 25-28 July 2010. 

10. Polzin, K.A., Pearson, J.B., Schoenfeld, M.P., Webster, K., Houts, M.G., Godfroy, T.J., and Bossard, 

J.A., “Performance Testing of a Prototypic Annular Linear Induction Pump for Fission Surface 

Power,” NASA/TP—2010-216430, May 2010. 

11. Birchenough, A.G., Hervol, D.S., and Gardner, B.G., “Test Results From a High Power Linear 

Alternator Test Rig,” NASA/TM—2010-216910, November 2010. 
NASA/TM—2011-217100 11 

12. Briggs, M.H., Geng, S.M., Pearson, J.B., and Godfroy, T.J., “Summary of Test Results From a 

1 kWe-Class Free-Piston Stirling Power Convertor Integrated With a Pumped NaK Loop,” 

NASA/TM—2010-216934, December 2010. 

13. Fuller, R.L., “Closed Brayton Cycle Power Conversion Unit for Fission Surface Power, Phase I Final 

Report,” NASA/CR—2010-215673, June 2010. 

14. Wood, G.J., Buffalino, A., Holliday, E., Penswick, B., and Gedeon, D., “Free-Piston Stirling Power 

Conversion Unit for Fission Surface Power, Phase I Final Report,” NASA/CR—2010-216750, 

July 2010. 

15. Wood, G.J., Holliday, E., Cale, T., and Stanley, J., “The Design and Development of a 12 kWe 

Stirling Power Conversion Unit for Fission Power Technology Demonstration,” Proceedings of 

Nuclear and Emerging Technologies for Space, NETS–2011, Paper 3488, Albuquerque, New Mexico, 

7-10 February 2011. 
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4. TITLE AND SUBTITLE

Design and Test Plans for a Non-Nuclear Fission Power System Technology Demonstration 

Unit 

5a. CONTRACT NUMBER

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6. AUTHOR(S)

Mason, Lee; Palac, Donald ; Gibson, Marc; Houts, Michael; Warren, John; Werner, Jim; 

Poston, David; Qualls, Arthur, Lou; Radel, Ross; Harlow, Scott 

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WBS 429698.01.03 

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14. ABSTRACT

A joint National Aeronautics and Space Administration (NASA) and Department of Energy (DOE) team is developing concepts and 

technologies for affordable nuclear Fission Power Systems (FPSs) to support future exploration missions. A key deliverable is the 

Technology Demonstration Unit (TDU). The TDU will assemble the major elements of a notional FPS with a non-nuclear reactor simulator 

(Rx Sim) and demonstrate system-level performance in thermal vacuum. The Rx Sim includes an electrical resistance heat source and a 

liquid metal heat transport loop that simulates the reactor thermal interface and expected dynamic response. A power conversion unit (PCU) 

generates electric power utilizing the liquid metal heat source and rejects waste heat to a heat rejection system (HRS). The HRS includes a 

pumped water heat removal loop coupled to radiator panels suspended in the thermal-vacuum facility. The basic test plan is to subject the 

system to realistic operating conditions and gather data to evaluate performance sensitivity, control stability, and response characteristics. 

Upon completion of the testing, the technology is expected to satisfy the requirements for Technology Readiness Level 6 (System

Demonstration in an Operational and Relevant Environment) based on the use of high-fidelity hardware and prototypic software tested 

under realistic conditions and correlated with analytical predictions.

15. SUBJECT TERMS

Space power; Fission power systems; Space reactor; Free-piston Stirling 

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