Lee Mason

Glenn Research Center, Cleveland, Ohio

Recent Advances in Power Conversion

and Heat Rejection Technology for

Fission Surface Power

NASA/TM—2010-216761

July 2010

NETS–2009–204298
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Lee Mason

Glenn Research Center, Cleveland, Ohio

Recent Advances in Power Conversion

and Heat Rejection Technology for

Fission Surface Power

NASA/TM—2010-216761

July 2010

NETS–2009–204298

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

Nuclear and Emerging Technologies for Space (NETS–2009)

cosponsored by ANS and AIAA 

Atlanta, Georgia, June 14–18, 2009
Acknowledgments

This work was performed for the NASA Exploration Technology Development Program and the Fission Surface Power (FSP) 

project. The author wishes to acknowledge the contributions of Don Palac, Steve Geng, Cheryl Bowman, Art Birchenough, 

Dave Hervol, and Don Jaworske in writing this FSP overview paper.

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://gltrs.grc.nasa.gov

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—2010-216761 1 

Recent Advances in Power Conversion and 

Heat Rejection Technology for 

Fission Surface Power 

Lee Mason 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

Under the Exploration Technology Development Program, 

the National Aeronautics and Space Administration (NASA) 

and the Department of Energy (DOE) are jointly developing 

Fission Surface Power (FSP) technology for possible use in 

human missions to the Moon and Mars. A preliminary 

reference concept was generated to guide FSP technology 

development. The concept consists of a liquid-metal-cooled 

reactor, Stirling power conversion, and water heat rejection, 

with Brayton power conversion as a backup option. The FSP 

project has begun risk reduction activities on some key 

components with the eventual goal of conducting an end-toend, non-nuclear, integrated system test. Several power 

conversion and heat rejection hardware prototypes have been 

built and tested. These include multi-kilowatt Stirling and 

Brayton power conversion units, titanium-water heat pipes, 

and composite radiator panels.

Introduction 

Nuclear Fission Surface Power (FSP) is a candidate power 

technology for human exploration missions to the Moon and 

Mars. FSP offers the potential to provide abundant power 

during the day and night with long service life. With the 

proper design approach, FSP can also be made to be 

affordable (Ref. 1). 

Fission Surface Power Concept 

The National Aeronautics and Space Administration 

(NASA) and the Department of Energy (DOE) have 

developed a preliminary reference FSP system concept that 

includes a liquid-metal-cooled, fast-neutron reactor with 

Stirling power conversion and water-based heat rejection 

(Ref. 1). The reactor uses UO2 fuel pins in a cylindrical core 

with external drum reflectors. Heat is transferred to the 

Stirling power convertors by a pumped sodium-potassium 

(NaK) coolant loop. The core structure and coolant piping is 

constructed of stainless steel to reduce cost and development 

risk. The Stirling convertors generate single-phase alternating 

current (ac) output that is converted to direct current (dc) for 

user loads. Stirling waste heat is removed by a pumped water 

coolant loop that is coupled to a series of two-sided, vertical 

radiator panels. The radiator panels are composed of titaniumwater heat pipes in a composite facesheet sandwich. The FSP 

concept is designed to produce a net power of 40 kWe with a 

full-power service life of 8 years. This same design could be 

used for missions at essentially any location (equator to poles) 

on the lunar or Mars surface. 

The reactor core is located at the bottom of a 2 m deep 

excavation with an upper plug shield to protect the equipment 

above from direct radiation. The NaK pumps, Stirling 

convertors, and water pumps are mounted on a 5-m-tall truss 

structure that attaches to the top face of the shield. Two 

symmetric radiator wings are deployed via a scissor 

mechanism from the truss. Each radiator wing is 

approximately 4 m tall by 16 m long and is suspended 1 m 

above the lunar surface. In its stowed configuration, the FSP 

system is approximately 3 by 3 by 7 m tall. 

The preliminary reference system schematic is shown in 

Figure 1. The use of redundant components and parallel fluid 

loops allows the system to produce partial power in the event 

of unexpected failures. The schematic shows the system 

energy balance and the anticipated temperatures, pressures, 

and flow rates at some of the key interfaces. 

The reactor produces approximately 186 kWt with a peak 

fuel pin clad temperature of 860 K. It delivers heated NaK at 

850 K to a pair of intermediate heat exchangers (IHX) using 

two fully-redundant electromagnetic primary pumps. The IHX 

is a NaK-to-NaK heat exchanger that provides a buffer 

between the primary NaK and the Stirling convertors, and a 

means to adjust the NaK flow rate and resulting temperature 

drop across the Stirling convertors separately from the reactor 

flow and temperature drop. Each intermediate NaK loop 

services two Stirling convertors at a supply temperature of 

824 K. The effective Stirling hot-end temperature is 778 K. 

The secondary NaK loops include an intermediate pump of 

similar design to the primary NaK pump. 
NASA/TM—2010-216761 2 

Figure 1.—FSP preliminary reference concept schematic. Reactor is Rx, intermediate heat exchanger is IHX, primary 

pump is PP, intermediate pump is IP, Stirling convertor is Stir, radiator is Rad, parasitic load radiator is PLR. 

Each Stirling convertor is composed of two axially opposed 

Stirling heat engines and two linear alternators. Power 

conversion efficiency is estimated at 26 percent. The 

alternators deliver 6 kWe each at 400 Vac and 75 Hz to a 

Power Management and Distribution (PMAD) subsystem. A 

Local Power Controller (LPC), located approximately 100 m 

from the reactor, converts the 400 Vac to 120 Vdc for 

distribution to the Electrical Load Interface (ELI). The 

48 kWe gross Stirling output power provides sufficient 

capacity to account for electrical losses (~3 kWe) and system 

parasitic loads (~5 kWe) and still deliver 40 kWe net for user 

loads. A Parasitic Load Radiator (PLR) dissipates electric 

power that is not required by the user loads, and allows the 

system to be operated at constant power thus eliminating the 

complexity of thermal system load following. The ELI serves 

as the primary power bus and system interface for commands 

and telemetry. A 5 kWe photovoltaic (PV) array and a 

10 kW-hr battery are included with the FSP PMAD for startup 

and backup power. 

The heat rejection subsystem is composed of four water 

heat transport loops and two radiator wings (two loops per 

wing). The radiator wing receives heated water at 420 K from 

the Stirling convertors and returns the water at 390 K using a 

mechanical radiator pump (RP), while rejecting approximately 

35 kWt per loop. The resulting Stirling cold-end temperature 

is 425 K. The total heat load is approximately 140 kWt and 

the total two-sided FSP system radiator area is 184 m2

assuming a 250 K effective sink temperature and 10 percent 

area margin. Each radiator wing includes 10 subpanels, each 

measuring approximately 2.7 m wide by 1.7 m tall. 

The FSP preliminary reference concept provides a guide for 

technology development. The unit power levels, temperatures, 

pressures, flow rates, and efficiencies become notional 

requirements for early hardware prototypes. Some of the key 

component technologies to be developed under FSP include 

NaK pumps, heat exchangers, multi-kilowatt power 

conversion units, and water radiator panels (Ref. 2). One of 

the major goals of the FSP technology development project is 

to show that the components can be assembled and operated 

as an integrated system. To support this goal, an end-to-end 

integrated Technology Demonstration Unit (TDU) using fullscale components and a non-nuclear reactor simulator is 

planned. 

The ensuing sections describe some of the current efforts in 

power conversion and heat rejection technology development 

related to FSP. Reactor-related technology development for 

FSP is the responsibility of DOE. NASA and DOE share 

responsibility for system-level technology development and 

demonstration (Ref. 2). 
NASA/TM—2010-216761 3 

Power Conversion Technology 

NASA has initiated development of several power 

conversion technologies to support FSP. A key objective is to 

develop a high-power and high-efficiency power conversion 

unit that is compatible with the 900 K NaK reactor heat 

source. NASA Glenn Research Center (GRC) is evaluating 

both free-piston Stirling and closed Brayton cycle options. 

Both technologies provide a feasible path to meet the power, 

efficiency, and lifetime goals for FSP (Ref. 3). Stirling 

appears to offer the highest efficiency and lowest system 

radiator area. The main challenges include convertor scaling 

and system integration. Brayton may provide lower 

development risk given the large industrial base for terrestrial 

microturbines, making it an attractive backup option. 

However, Brayton would still require development to address 

FSP system integration issues. 

Free-Piston Stirling 

There are three separate but coordinated free-piston Stirling 

efforts under FSP: 1) NaK Stirling demonstration test, 2) 

Stirling PMAD development, and 3) Stirling radiation testing. 

Here, the underlying goal is to improve the understanding of 

the various Stirling interfaces and learn how they may 

influence the design of a Stirling-based FSP system. 

The NaK Stirling test will attempt to demonstrate Stirling 

convertor electrical power generation using a pumped liquidmetal heat source under thermal conditions that represent the 

FSP reactor. In 2007, GRC procured a pair of commercial 

1-kWe Stirling convertors from Sunpower Incorporated. The 

convertors were tested at GRC in a dual-opposed 

configuration with electrical resistance heating to generate a 

performance map under varied hot-end temperature, cold-end 

temperature, and piston amplitude. The pair produced over 

2 kWe at the design operating temperatures of 823 K hot-end 

and 323 K cold-end with thermal-to-electric efficiency of 

nearly 30 percent. In parallel, GRC developed a NaK shell 

heat exchanger design that could be readily integrated with the 

existing Stirling heater head (Ref. 4). 

The resulting NaK Stirling test assembly is shown in 

Figure 2. The heat exchanger allows NaK to enter axially, 

flow over the Stirling heat acceptor, and discharge radially 

from a toroidal manifold. This assembly has been delivered to 

Marshall Space Flight Center (MSFC) and has been integrated 

with their NaK Primary Test Circuit. Both steady-state and 

transient testing will be performed at MSFC in 2009 with the 

goal of replicating the GRC performance map and 

demonstrating efficient heat transfer from the liquid metal to 

the Stirling heater head. 

The second FSP Stirling activity is meant to address the 

PMAD electrical interface using a High Power Linear 

Alternator Test Rig (HPLATR). The HPLATR includes two 

opposed 5-kWe linear alternators driven by two pressure wave 

generators that simulate the Stirling heat engine interface. 

Figure 2.—NaK Stirling test assembly. 

Figure 3.—High power linear alternator test rig. 

The test rig, shown in Figure 3, was procured by GRC from 

the Clever Fellows Innovative Consortium. It provides an 

accurate representation of the Stirling alternator dynamics to 

allow focused PMAD technology development (Ref. 4). 

Initial testing was performed in 2008 using a GRCdeveloped 600-W Field Effect Transistor (FET)-based 

module. The module processed the single-phase 300-Vac 

alternator output and delivered regulated 120 Vdc power. The 

testing successfully demonstrated ac-to-dc rectification, power 

factor correction, parasitic load control, and voltage regulation 

with overall efficiency greater than 90 percent. In 2009, a 

second module was developed and operated in parallel with 

the first at power levels up to 1500 W demonstrating 

channelized power sharing that could improve PMAD 

reliability. Future versions are planned that will use InsulatedGate Bipolar Transistor (IGBT)-based electronics to perform 

the same functions and accommodate even higher power 

levels. 

The third FSP Stirling effort is focused on the radiation 

tolerance of Stirling convertor materials and subcomponents. 

Two separate test articles have been developed by GRC. The 

first is an array of material coupons that will be gamma 

irradiated at Oak Ridge National Laboratory in the High Flux 

Isotope Reactor (HFIR) spent fuel pool. The materials to be 

tested include polymer adhesives, elastomers, tribological 

coatings, and wiring insulation. The coupons will be irradiated 
NASA/TM—2010-216761 4 

Figure 4.—Stirling alternator radiation test article. 

under prototypic conditions in an inert gas environment with 

heaters for temperature control. Post-irradiation 

characterization of the polymer chemistry and mechanical 

properties will be performed to evaluate radiation-induced 

degradation. 

A second test article, the Stirling Alternator Radiation Test 

Article (SARTA), will be tested at the Sandia National 

Laboratories Gamma Irradiation Facility (GIF). Shown in 

Figure 4, the SARTA is an 80-W linear alternator fabricated 

by Sunpower Incorporated. It will be electrically motored 

while being exposed to gamma irradiation from a cobalt-60 

source. The alternator will be operated at representative 

pressure and temperature and monitored for performance 

changes. Testing will be conducted at gamma dose levels that 

are relevant to both FSP and Radioisotope Power System 

(RPS) mission applications. The Oak Ridge and Sandia 

irradiation tests are expected to begin in 2009. 

Closed Brayton Cycle 

There are two main Brayton-related efforts under the FSP 

project: 1) dual Brayton test loop and 2) direct drive gas 

Brayton test. These efforts are intended to demonstrate 

Brayton performance under various FSP-derived operating 

scenarios. 

The dual Brayton test loop is shown in Figure 5. It includes 

two turbine generators that utilize a common nitrogen working 

fluid inventory and a shared electrical-resistance heat source. 

The test system was designed and built by Barber Nichols 

Incorporated in 2007. The turbine generators are commercial 

open-cycle units with annular recuperators that were modified 

for closed-cycle operation. Waste heat rejection is provided by 

two separate pumped-water cooling loops. The main test 

objective was to investigate interactions that may occur 

between redundant Brayton units in a common gas loop. A 

secondary objective was to validate analytical models. 

The system was installed at GRC and testing was 

completed in 2008 (Ref. 5). The system produced up to 

22 kWe at a turbine inlet of 950 K, compressor inlet of 300 K, 

and shaft speed of 90 000 rpm. Performance mapping was 

completed for a range of turbine inlet temperatures and shaft 

Figure 5.—Dual Brayton test loop. 

Figure 6.—Direct drive gas Brayton test system. 

speeds. In addition, testing was conducted to evaluate the 

performance impacts of operating at unequal shaft speeds and 

the operational differences for staggered and simultaneous 

turbine startup. Results showed that imbalanced shaft speed 

operation led to undesirable working gas redistribution from 

the higher-speed unit to the lower-speed unit and system 

performance penalties. For the same heater input power, 

staggered turbine startup required less total motoring energy 

than the simultaneous startup, but took longer to reach system 

break-even power. 

The second Brayton effort is a joint activity with MSFC to 

test a space-configured 2-kWe Brayton unit with a direct drive 

gas (DDG) reactor simulator. Figure 6 shows the test system 

installed at GRC’s Vacuum Facility #6. The GRC Brayton 

unit was assembled in the 1990s for the Solar Dynamic Flight 

Demonstrator Project. The MSFC reactor simulator includes 

an array of pin-type electrical-resistance heating elements 

arranged in a bundle similar to a reactor core. The gas inlet 

and outlet ducts are coupled to the Brayton unit as they would 

be in a direct gas-cooled reactor system. The working fluid is 

a mixture of helium and xenon. 

Testing was completed in 2009 (Ref. 6). The main 

objective was to demonstrate stable and controllable operation 

of the integrated system. Test variables included heater power 

and shaft speed. Nominal operating conditions were 850 K 

turbine inlet, 285 K compressor inlet, and 46 000 rpm shaft 

speed. A portion of the testing was dedicated to reactivity 
NASA/TM—2010-216761 5 

control simulation. Two types of test series were performed. In 

the first series, the reactivity feedback controller simulated the 

response to a step change in Brayton shaft speed. Testing 

showed that shaft speed perturbations resulted in stable and 

predictable heater response. In the second series, a control 

drum maneuver was replicated by commanding the reactivity 

controller to simulate insertion of positive or negative 

reactivity. A simulated negative reactivity insertion produced a 

stable but lower heater exit temperature and a corresponding 

reduction in Brayton output power as expected. 

Full-Scale Power Conversion Unit 

These individual Stirling and Brayton hardware activities 

are “pathfinders” toward the development of a full-scale 

12-kWe Power Conversion Unit (PCU) for the FSP 

Technology Demonstration Unit (TDU). In 2008, GRC 

initiated a procurement and awarded parallel contracts to 

Sunpower and Barber Nichols. Sunpower is developing a freepiston Stirling design employing two opposed 6-kWe engines. 

Barber Nichols is developing a single 12-kWe recuperated 

Brayton unit. Both designs include the requisite heat 

exchangers to operate with an 850 K NaK heat source and a 

375 K water cooling supply, representative of the anticipated 

FSP reactor and radiator interfaces. Both designs also include 

the appropriate PMAD to convert the ac output power and 

deliver 120 Vdc to a bus. A single contract down-select for 

fabrication and test is expected in 2010. Once exercised, that 

contract would deliver a 12-kWe unit for the TDU test in the 

2012 timeframe. 

Heat Rejection Technology 

FSP heat rejection technology development is focused on 

titanium-water heat pipes and composite radiators. The 

objective is to develop efficient and reliable heat rejection 

systems that are compatible with the power conversion coldend temperature (approximately 400 K) and heat load (up to 

140 kWt). The current FSP heat rejection concept utilizes a 

pumped water cooling loop coupled to radiator panels with 

embedded heat pipes. 

Heat Pipes 

Heat pipes provide an efficient method for spreading heat 

and also reducing the potential for single-point failure by 

segmenting the radiator surface. GRC began titanium-water 

(Ti-H2O) heat pipe development during the Jupiter Icy Moons 

Orbiter (JIMO) Program to address the need for 500 K 

radiators. Ti-H2O heat pipes are well suited for operating 

temperatures between 350 and 500 K. This temperature range 

has very limited heat pipe fluid choices. 

Figure 7.—Titanium-water heat pipe life test. 

An initial step in developing high-temperature water heat 

pipes was the evaluation of performance, life, and 

manufacturing capability (Ref. 7). To that end, GRC 

established a heat pipe lab and populated it with nine Ti-H2O 

heat pipes as shown in Figure 7. The heat pipes were provided 

by three different vendors—Advanced Cooling Technologies 

(ACT), Swales, and Thermacore—each utilizing a different 

wick structure. All nine heat pipes share common design 

features of 500 K operating temperature, 25-cm evaporator, 

90-cm condenser, 1.27-cm outside diameter, and CP–2 

titanium envelope. After initial testing verified performance 

expectations, the heat pipes were placed on life-test in 

December 2006 and have accumulated over 2 years of 

operation at 500 K with minimal performance change 

observed. 

Another key issue for implementing heat pipe radiators 

with the FSP system is the efficient transfer of waste heat 

from the pumped water loop to the heat pipe evaporators. The 

temperature drop from the pumped water loop to the radiator 

has a significant impact on the radiator area and mass. GRC 

built a test rig to evaluate various heat exchanger options. In 

2008, testing was completed on a myriad of heat exchanger 

geometries based on an immersed evaporator configuration 

(convectively coupled). Testing showed that heat pipes with 

abraded evaporator surface outperformed those that were plain 

or enhanced with fins. In 2009, the test rig will be modified 

for testing conductively coupled heat pipe evaporators. The 

conductive interface places the evaporator on the outside of 

the coolant channel. This approach results in a larger 

temperature drop, but much less cooling loop pressure drop 

resulting in lower pumping power. 

Radiator Panels 

With respect to radiator panels, GRC has two ongoing 

technology development activities: 1) subscale Radiator 

Demonstration Units (RDU), and 2) full-scale Second 

Generation RDU.
NASA/TM—2010-216761 6 

These main activities are complemented by a number of Small 

Business Innovative Research (SBIR) efforts addressing FSP 

radiator concepts. Composite panels are favored in the FSP 

application due to their low mass and high heat transfer 

effectiveness. The underlying objectives for panel 

development are to verify fabrication methods and 

demonstrate performance under realistic conditions. 

The subscale RDU activity started with a GRC contract to 

ACT for the design and fabrication of three different 0.5-mwide by 1-m-tall radiator assemblies. Each assembly contains 

three 1.9-cm-diameter Ti-H2O heat pipes sandwiched between 

two Polymer Matrix Composite (PMC) facesheets. The heat 

pipe condensers are encased in individual graphite thermal 

saddles to allow effective bonding to the facesheets, and 

aluminum-honeycomb is added as a filler material between 

heat pipes. The facesheets use K13D2U graphite fibers and 

three different resin binders, the main discriminator among the 

panels. 

Initial thermal-vacuum testing of the RDUs completed at 

GRC in 2007 showed the panels to exhibit similar 

performance and reject about 1 kWt each (Ref. 8). In 2008, 

the vacuum facility was outfitted with quartz lamps to 

simulate lunar insolation. The RDU panels were subjected to a 

cold-soak startup with frozen heat pipes similar to what would 

be expected after delivery and setup of the FSP system at the 

Moon. Test results revealed that the heat pipes could be 

reliably started with a combination of simulated sunlight and 

evaporator heat input as envisioned for the FSP application 

(Ref. 9). In 2009, two of the RDU panels will be coated with a 

high-emissivity, low-absorptivity thermal coating and some of 

the performance tests will be repeated. A photo of an RDU 

panel coated with white emissive paint is shown in Figure 8. 

The Second Generation RDU, shown in Figure 9, is a 

full-scale radiator assembly measuring 2.7-m-wide by 1.7-mtall. It is similar in size to one of 10 subpanels that would be 

needed in a FSP radiator wing. The test hardware was 

designed and fabricated by Material Innovations Incorporated. 

The panel assembly builds on lessons learned from the initial 

RDUs, including construction materials and manufacturing 

techniques. A major addition is a titanium manifold that 

transfers heat from a pumped water loop to the heat pipes 

using individual immersion heat exchangers connected in 

series. The heat exchangers are configured for annular water 

flow over the heat pipe evaporators with consideration given 

to minimizing the water pressure drop. 

The Second Generation RDU has 16 Ti-H2O heat pipes. 

There are two independent water flow channels each 

contacting eight heat pipes in an alternating arrangement. The 

heat pipes have a 25-cm-long evaporator and a 170-cm-long 

condenser. Like the previous RDUs, the heat pipe condensers 

are encased in graphite saddles that are bonded to PMC 

facesheets. A composite c-channel edge surrounds the panel 

for stiffness in lieu of the honeycomb filler. The panel is 

designed to reject 6 kWt with a water supply temperature of 

400 K and total flow rate of 0.5 kg/s. Thermal-vacuum 

Figure 8.—Radiator demonstration unit. 

Figure 9.—Second generation RDU. 

testing of the Second Generation RDU will begin at GRC’s 

Vacuum Facility #6 in 2009. The Second Generation RDU is 

a prototype of a future Heat Rejection System (HRS) radiator 

panel that would be used in the system-level TDU test. 

Technology Demonstration Unit 

The basic TDU test plan is to subject the system to realistic 

operating conditions and gather data to better understand 

performance sensitivity, control stability, and response 

characteristics. The TDU reactor simulator is planned to 

include a core simulator with electrical pin-heaters and a NaK 

heat transport system, representative of the FSP concept. The 

reactor simulator would be coupled to the 12 kWe Power 

Conversion Unit (PCU) discussed earlier. The TDU HRS 

would reject the PCU waste heat using a pumped-water 

cooling loop and multiple 2.7-m-wide by 1.7-m-tall radiator 

panels connected in a series. The Stirling-based PCU is 

estimated to require six panels while the Brayton-based PCU 

would require approximately eight panels. Under the current 

plan, the TDU HRS would be implemented after an initial test 

phase that includes a DOE/MSFC-developed reactor simulator 

with the full-scale PCU and an external Facility Cooling 

System (FCS). The HRS procurement is expected to begin in 

2010 or 2011. A notional test layout for the TDU with the sixpanel HRS is shown in Figure 10. 
NASA/TM—2010-216761 7 

Conclusions 

Fission Surface Power (FSP) systems are currently being 

studied by NASA as an option for future human exploration 

missions to the Moon and Mars. NASA and the Department of 

Energy have partnered to help mature FSP technology so that 

it may be considered for future flight development. The FSP 

team has generated a preliminary FSP reference concept to 

help guide technology development. A portion of the FSP 

project is focused on designing, building, and testing some of 

the key FSP components in order to demonstrate technology 

readiness. This paper discusses some of the progress being 

made in power conversion and heat rejection technology. 

Under power conversion technology, multi-kilowatt Stirling 

and Brayton “pathfinder” tests are underway to improve our 

understanding of system integration issues. In heat rejection 

technology, the focus has been on titanium-water heat pipes 

and composite radiators with the goal of developing sound 

fabrication methods and demonstrating performance under 

realistic operating conditions. Ultimately, the FSP project 

plans to assemble and test an end-to-end system-level 

Technology Demonstration Unit (TDU) using full-scale 

components and a non-nuclear reactor simulator. 

References 

1. L. MASON, D. Poston, and L. Qualls, “System Concepts 

for Affordable Fission Surface Power,” NASA/TM—

2008-215166, January 2008. 

2. D. PALAC, L. Mason, and S. Harlow, “Fission Surface 

Power Technology Development Status,” NASA/TM—

2009-215602, March 2009. 

3. L.S. MASON and J.G. Schreiber, “A Historical Review 

of Brayton and Stirling Power Conversion Technologies 

for Space Applications,” NASA/TM—2007-214976, 

November 2007. 

4. S.M. GENG, L.S. Mason, R.W. Dyson, and L.B. 

Penswick, “Overview of Multi-Kilowatt Free-Piston 

Stirling Power Conversion Research at Glenn Research 

Center,” NASA/TM—2008-215061, March 2008. 

5. D.S. HERVOL, M. Briggs, A.K. Owen, and T.A. Lavelle, 

“Experimental and Analytical Performance of a Dual 

Brayton Power Conversion System,” NASA/TM—2009-

215511, February 2009. 

6. D.S. HERVOL, M. Briggs, K. Owen, S.M. Bragg-Sitton 

and T.J. Godfroy, “Test Results from a Direct Drive Gas 

Reactor Simulator Coupled to a Brayton Power 

Conversion Unit,” Proc. of Nuclear and Emerging 

Technologies for Space (NETS–2009), paper 204416 

(2009). 

7. J.L. SANZI, “Thermal Performance of High Temperature 

Titanium-Water Heat Pipes by Multiple Heat Pipe 

Manufacturers,” NASA/CR—2007-214820, July 2007. 

8. D.A. JAWORSKE, D.E. Beach, and J.L. Sanzi, “Heat 

Rejection Systems Utilizing Composites and Heat Pipes: 

Design and Performance Testing,” Proc. of the 5th

International Energy Conversion Engineering Conference 

(IECEC), AIAA–2007–4822 (2007). 

9. D.A. JAWORSKE, J.L. Sanzi, and J. Siamidis, “Cold 

Start of a Radiator Equipped with Titanium-Water Heat 

Pipes,” Proc. of the 6th International Energy Conversion 

Engineering Conference (IECEC), AIAA–2008–5749 

(2008). 
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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY)

01-07-2010 

2. REPORT TYPE

Technical Memorandum 

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Recent Advances in Power Conversion and Heat Rejection Technology for Fission Surface 

Power 

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Mason, Lee 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

WBS 463169.01.03.01.01 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

Cleveland, Ohio 44135-3191 

8. PERFORMING ORGANIZATION

 REPORT NUMBER

E-17029 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

10. SPONSORING/MONITOR'S

 ACRONYM(S)

NASA 

11. SPONSORING/MONITORING

 REPORT NUMBER

NASA/TM-2010-216761 

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited 

Subject Category: 20 

Available electronically at http://gltrs.grc.nasa.gov 

This publication is available from the NASA Center for AeroSpace Information, 443-757-5802

13. SUPPLEMENTARY NOTES

14. ABSTRACT

Under the Exploration Technology Development Program, the National Aeronautics and Space Administration (NASA) and the Department 

of Energy (DOE) are jointly developing Fission Surface Power (FSP) technology for possible use in human missions to the Moon and Mars. 

A preliminary reference concept was generated to guide FSP technology development. The concept consists of a liquid-metal-cooled 

reactor, Stirling power conversion, and water heat rejection, with Brayton power conversion as a backup option. The FSP project has begun 

risk reduction activities on some key components with the eventual goal of conducting an end-to-end, non-nuclear, integrated system test. 

Several power conversion and heat rejection hardware prototypes have been built and tested. These include multi-kilowatt Stirling and 

Brayton power conversion units, titanium-water heat pipes, and composite radiator panels.

15. SUBJECT TERMS

Fission surface power; Liquid-metal cooled reactor; Power conversion technology 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

 ABSTRACT

UU 

18. NUMBER

 OF 

 PAGES

13 

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email:help@sti.nasa.gov) 

a. REPORT

U 

b. ABSTRACT

U 

c. THIS 

PAGE

U 

19b. TELEPHONE NUMBER (include area code)

443-757-5802 

Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. Z39-18