Lee Mason

Glenn Research Center, Cleveland, Ohio

David Poston

Los Alamos National Laboratory, Los Alamos, New Mexico

Louis Qualls

Oak Ridge National Laboratory, Oak Ridge, Tennessee

System Concepts for Affordable Fission 

Surface Power

NASA/TM—2008-215166

January 2008
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Lee Mason

Glenn Research Center, Cleveland, Ohio

David Poston

Los Alamos National Laboratory, Los Alamos, New Mexico

Louis Qualls

Oak Ridge National Laboratory, Oak Ridge, Tennessee

System Concepts for Affordable Fission 

Surface Power

NASA/TM—2008-215166

January 2008

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

Space Technology and Applications International Forum (STAIF–2008)

sponsored by the Institute for Space and Nuclear Power Studies at the University of New Mexico

Albuquerque, New Mexico, February 10–14, 2008
Acknowledgments

This concept defi nition resulted from a 12 month joint NASA/DOE study. In addition to the authors, the main study team 

consisted of Joe Nainiger, Dick Shaltens, and Bob Sefcik from GRC, Mike Houts from MSFC, Shawn Quinn from KSC, 

Paul Van Damme from JPL, Ray Holdaway, Dwight Clayton, and Becky Moses from ORNL, Jim Werner from INL, and 

Steve Wright from SNL. Abe Weitzberg, Sterling Bailey, and Sam Bhattacharyya served as consultants. John Warren 

was the NASA Headquarters sponsor, and Scott Harlow was the DOE Headquarters representative. This work was 

performed for the NASA Exploration Systems Mission Directorate, Advanced Capabilities Division.

Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

5285 Port Royal Road

Springfi eld, VA 22161

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.

This report is a preprint of a paper intended for presentation at a conference. 

Because changes may be made before formal publication, this preprint is made available 

with the understanding that it will not be cited or reproduced without 

the permission of the author.
NASA/TM—2008-215166 1 

System Concepts for Affordable Fission Surface Power 

Lee Mason 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

David Poston 

Los Alamos National Laboratory 

Los Alamos, New Mexico 87545 

Louis Qualls 

Oak Ridge National Laboratory 

Oak Ridge, Tennessee 37831 

Abstract 

This paper presents an overview of an affordable Fission Surface Power (FSP) system that could be 

used for NASA applications on the Moon and Mars. The proposed FSP system uses a low temperature, 

uranium dioxide-fueled, liquid metal-cooled fission reactor coupled to free-piston Stirling converters. The 

concept was determined by a 12 month NASA/DOE study that examined design options and development 

strategies based on affordability and risk. The system is considered a low development risk based on the 

use of terrestrial-derived reactor technology, high efficiency power conversion, and conventional 

materials. The low-risk approach was selected over other options that could offer higher performance 

and/or lower mass. 

Introduction 

Under the Vision for Exploration, NASA is evaluating options for human missions to the Moon and 

Mars. New and more capable power systems will be required to supply energy for sustained surface 

outposts. Lunar missions are expected to begin in the early 2020s. Mars missions may occur later, 

possibly in the 2030s. Some potential surface power electrical loads include landers, habitats, in-situ 

resource utilization plants, mobility and construction equipment, and science experiments. Total power 

requirements could range from 10 kWe to more than 100 kWe. The unique environments of the Moon and 

Mars pose many challenges for power systems. The 29.5-day lunar rotational period requires that 

extended surface missions include the capability for at least 354 hr of nighttime energy storage. Other 

lunar mission challenges include tenacious dust adhesion and extreme surface temperatures ranging from 

375 K at lunar noon to 100 K during lunar night. The typical Mars equatorial day is 24.6 hr long with 

about 12 hr of night, so energy storage requirements are significantly less than the Moon. However, 

because of the greater distance from the Sun and the attenuation through the atmosphere, insolation at the 

Martian surface is reduced to about 20 percent of that on the Moon, and that value decreases significantly 

with dust storms. The potentially corrosive, carbon-dioxide atmosphere at Mars may also present 

problems for the power system. For either the Moon or Mars, power systems must be highly reliable to 

assure steady and continuous power for crew safety. The combination of high power, difficult 

environmental conditions, and assured reliability make fission-based power systems an advantageous 

option among the various power system choices. 

One of the major challenges to the implementation of space fission power systems is development 

cost. In April 2006, NASA and DOE initiated the Affordable Fission Surface Power System Study 

(AFSPSS) to determine the design features and expected costs of a representative Fission Surface Power 

(FSP) system. A government study team with members from several NASA field centers and Department 
NASA/TM—2008-215166 2 

Figure 1.—Simplified FSP system block diagram.

of Energy (DOE) laboratories evaluated technology options and design variables and selected a reference 

concept based on affordability and risk. A low-risk approach was selected over other options that could 

offer higher performance and/or lower mass. The reference concept does not reflect a decision or downselection for system development, but merely a strawman for the purposes of estimating system cost. The 

reference concept is considered representative of a number of potential affordable designs. This paper 

describes the reference concept and reviews the top-level screening studies conducted by the government 

team as a basis for the selection. 

The FSP system block diagram, shown in figure 1, is defined by four major subsystems: (1) Reactor, 

(2) Power Conversion, (3) Heat Rejection, and (4) Power Conditioning and Distribution (PCAD). Heat is 

transferred from the Reactor to the Power Conversion and from the Power Conversion to the Heat 

Rejection. Electrical power generated by the Power Conversion is processed through the PCAD to the 

User Loads. The PCAD provides power for Power Conversion startup and for auxiliary loads associated 

with the Reactor and Heat Rejection. The PCAD also provides the primary communications link for 

command, telemetry, and health monitoring of the FSP system. 

Screening Studies 

The sections below describe some of the key trades performed by the government team in arriving at 

the reference concept selection. The primary design variables considered in arriving at the reference 

concept were: (1) Power Level and Life, (2) Reactor-Converter Combination, and (3) System 

Configuration. Power level and design life have a major influence on cost. Higher power increases design 

complexity. Longer life expands test qualification requirements. The decision on reactor and power 

conversion type affects system performance and complexity. The use of mature technology minimizes 

development risk and cost. System configuration relates to the packaging options and installation 

requirements of the system. Two options were considered. The “emplaced” option uses regolith shielding 

to reduce mass and permit near outpost siting. The “landed” option reduces the reliance on crew and 

equipment for installation. 

Power Level and Life 

A notional lunar outpost power profile was assumed at 30 kWe for the first 5 years and 80 kWe for 

15 years thereafter, as shown in figure 2, with power levels specified at the user load interface. Five FSP 

architectures were considered by the government team: 
NASA/TM—2008-215166 3 

Figure 2.—Assumed mission power profile. 

(1) 80 kWe/20-yr design operated at a de-rated power level of 30 kWe for the first 5 years, 

(2) 80 kWe/15-yr design with the first system de-rated to 30 kWe/5-yr and the second system 

delivered in year five, 

(3) 80 kWe/8-yr design with the first system de-rated to 30 kWe/5-yr and subsequent systems 

delivered in year five and year twelve, 

(4) 40 kWe/8-yr design with the first system de-rated to 30 kWe/5-yr and subsequent systems 

delivered in pairs in year five and year twelve, and 

(5) 40 kWe/5-yr design with the first system de-rated to 30 kWe and subsequent systems delivered in 

pairs in year five, year ten, and year fifteen. 

In all cases, the design rating forms the basis for the system design and development effort. In cases 

where the initial system is de-rated, the qualification effort could be reduced in scope commensurate with 

the de-rating. 

Based on a qualitative assessment of the options, the government team selected the 40 kWe/8-yr 

design option for the AFSPSS costing exercise. This results in a requirement for five systems and three 

launches to meet the 20 yr mission profile. The lower power and shorter life were considered major 

benefits in achieving an affordable system. The use of two independent systems to meet the out-year 

power requirements was considered advantageous. 

Reactor-Converter Combination 

A matrix of system concepts, as shown in table I, was generated by selecting reactor fuel, primary 

coolant, power conversion type, and radiator coolant. These combinations were considered as practical 

options for this study given the assumed power requirements and affordability goal. The affordability goal 

led to a decision by the government team to limit reactor fuel-clad temperature to 900 K to minimize fuel 

and material development costs and maximize the use of existing technology. Fuel options were UO2, 

UN, U10Zr (all fast-spectrum), and UZrH (moderated). The coolant options included pumped liquid 

metal (either sodium-potassium (NaK) or sodium (Na)), potassium heat pipes, and inert gas (HeXe). The 

power conversion options included Free-Piston Stirling (FPS), Closed Brayton Cycle (CBC), PbTe/TAGS 

Thermoelectrics (TE), and Organic Rankine Cycle (ORC). All of the options, with the exception of the 

TE concept, use a water-based radiator cooling system. The higher rejection temperature for TE required 

the use of NaK as the radiator coolant. 
NASA/TM—2008-215166 4 

TABLE I.—REACTOR-CONVERTER COMBINATIONS AND TRADE SPACE 

Concept A B C D E F G H I J 

Reactor Fuel UO2 UO2 UO2 UN U10Zr UZrH 

(Mod.) 

UO2 UO2 UO2 UO2 

Primary Coolant NaK Na K HP NaK NaK NaK HeXe NaK NaK NaK 

Power Conversion FPS FPS FPS FPS FPS FPS CBC CBC TE ORC 

Radiator Coolant H2O H2O H2O H2O H2O H2O H2O H2O NaK H2O 

149%

460%

93%

214%

261%

284%

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Free-Piston

Stirling

Closed Brayton

Cycle

PbTe

Thermoelectric

Organic Rankine

Cycle

Q/Qref

A/Aref

Figure 3.—Screening study sample results.

An initial screening of these concepts by the government team resulted in estimates for reactor 

thermal power, radiator area, and system mass. A sample of the screening study results is provided in 

figure 3 showing a comparison of reactor thermal power and radiator area for the various power 

conversion options assuming a 900 K pumped-NaK reactor heat source. Based on these and other 

screening study results and a qualitative assessment of technology readiness, the government team 

selected Concept A (UO2, NaK, FPS) as the reference for the AFSPSS costing exercise. This concept 

uses relatively low-risk reactor technology combined with a power conversion approach that provides 

high conversion efficiency and low radiator area. 

System Configuration 

There were two system configurations studied by the government team: landed and emplaced. The 

landed configuration, shown in figure 4, assumes the FSP system remains on a dedicated lander with 

integral, Earth-delivered shielding. The primary advantage of this configuration is ease of deployment 

because no regolith moving equipment is needed for the installation and it is possible that it could be 

deployed without crew assistance. The system is located approximately 1 km from the outpost in order to 

reduce shield mass. The integral, shaped 4-pi shield reduces radiation levels to less than 5 rem/yr at 1 km 

in the direction of the outpost and less than 50 rem/yr elsewhere. The PCAD subsystem converts the 

400 V power conversion output to 2000 V for transmission and 120 Vdc for distribution to the loads. The 

installation of the power transmission cable would require crew assistance or a tele-operated rover. An 

autonomously deployed, vertical radiator is extended from the lander via a truss structure. 
NASA/TM—2008-215166 5 

Figure 4.—Landed configuration. Figure 5.—Emplaced configuration. 

Figure 6.—Shield geometry assumptions. 

The emplaced configuration, shown in figure 5, assumes the FSP system is off-loaded from a cargo 

lander and installed with the assistance of crew and construction equipment. The line-of-sight reactor 

shielding to the habitat is provided by regolith, either by burying the reactor or moving regolith to form a 

berm. Additional Earth-delivered shielding would be provided to protect power conversion and heat 

rejection equipment mounted above the reactor. The FSP system is located approximately 100 m from the 

outpost. The combination of regolith and integral shielding reduces radiation levels to less than 5 rem/yr 

at 100 m in all directions (360°). The improved shielding allows the potential for simple, short-term 

maintenance tasks such as electrical part replacements or radiator surface cleaning during temporary zeropower shutdowns. The PCAD subsystem directly transmits the 400 V power conversion output to the load 

distribution node where it is converted to 120 Vdc. An autonomously deployed, vertical radiator is 

extended above the reactor and power conversion equipment. The availability of crew to oversee the 

deployment could potential simplify design and qualification requirements. The shielding geometry 

assumptions for the two configurations are shown in figure 6. 
NASA/TM—2008-215166 6 

The landed configuration is considered an excellent choice if the first system must be delivered before 

suitable construction infrastructure is available for the emplaced configuration. However, the FSP system 

mass for the landed configuration was estimated to be approximately twice that of the emplaced 

configuration. The landed configuration would also impose some potential constraints on crew operations 

and outpost expansion. Based on the lower mass and reduced operational constraints, the government 

study team selected the emplaced configuration as the reference approach for the costing exercise. 

However, the self-shielded, landed configuration with high voltage transmission was retained as a 

potential design option. 

Preliminary Reference Concept 

The reference FSP system for the AFSPSS costing effort is a stainless-steel, UO2 fueled, pumpedNaK cooled reactor with Stirling power conversion and pumped-water heat rejection. Figure 7 presents a 

notional layout for the concept. The deployed span is approximately 34 m tip-to-tip and 5 m above grade. 

The bottom edge of the radiators is approximately 1 m above the surface to minimize the potential for 

dust on the radiator surfaces. The reactor is located at the bottom of a 2 m excavation with an upper plug 

shield protecting the equipment above from direct radiation. Figure 8 shows the concept in a stowed 

configuration for delivery to the lunar site. The stowed envelope is approximately 3 by 3 by 7 m tall. The 

NaK pumps, Stirling power converters, and radiator pumps are mounted on a 5 m tall truss structure that 

attaches to the top face of the plug shield. The two symmetric radiator wings are deployed via a scissor 

mechanism from the truss, similar in concept to the International Space Station (ISS) radiators. The 

vertical orientation permits two-sided radiation, providing a much smaller footprint than one-sided 

horizontal radiators that view only deep space. A pair of cavity radiators remove waste heat from 

components within the excavated hole, with deployment linkages that are connected to the main radiator’s 

mechanism. 

Figure 7.—Reference concept layout. 
NASA/TM—2008-215166 7 

Figure 8.—Reference concept in stowed configuration. 

Figure 9.—Reference concept system schematic. 

System Schematic 

The preliminary system schematic for the emplaced FSP configuration is shown in figure 9. The 

schematic indicates the reference fluid selections, operating temperatures, component redundancy levels, 

and overall PCAD architecture. The reactor (Rx) produces approximately 175 kWt with a peak clad 

temperature of 900 K and delivers heated NaK at 890 K to a pair of intermediate heat exchangers (IHX) 

via two, redundant primary pumps. The IHX is a NaK-to-NaK heat exchanger that isolates the primary 

NaK from the Stirling converters and permits the NaK interface temperatures to be optimized for the 
NASA/TM—2008-215166 8 

Stirling, while the primary NaK conditions can be tailored for the reactor. Each intermediate NaK loop 

includes redundant pumps and services two Stirling converters at a supply temperature of 880 K. The 

average Stirling hot-end temperature is 830 K. Each Stirling converter has a dedicated cooling loop with a 

400 K water exit temperature. The effective radiator temperature is 380 K. The use of redundant 

components and parallel fluid loops permit the system to produce partial power in the event of failures. 

Each Stirling converter is comprised of two, axially opposed Stirling heat engines and two linear 

alternators. The alternators deliver 6 kWe each at 400 Vac and 100 hz to a Local Power Controller, 

located 100 m from the reactor. The power controller converts the 400 Vac to 120 Vdc for distribution to 

the Electrical Load Interface. The 48 kWe gross output power provides sufficient margin for electrical 

losses (~3 kWe) and system parasitic loads (~5 kWe) in meeting the 40 kWe of user loads. A full power 

Parasitic Load Radiator (PLR) dissipates power that is not required by the user loads, and allows the 

system to be operated in a near-steady thermal mode by isolating it from electrical load fluctuations. The 

Load Interface serves as the primary power bus and system interface for commands and telemetry. A 

5 kWe solar array and 10 kWh battery are included for startup and backup power. 

Reactor and Shield 

The reactor and shield concepts developed for this cost study are described in detail in a companion 

paper by Poston, et al. (2008). The reactor core is shown in figure 10 and the overall reactor assembly is 

depicted in figure 11. The core consists of 85 UO2 fuel pins (93 percent enrichment) in stainless steel 

cladding, and is approximately 20 cm in diameter. The peak fuel burn-up is estimated at 1.3 at.% for the 

8 yr design life. Reactivity control is provided by six radial beryllium (Be) reflector drums. The outer 

stainless steel vessel is dodecagon-shaped for tight packaging with the radial reflectors. The reactor 

coolant is a 78 percent Na, 22 percent K mixture that can more easily be maintained as a liquid prior to 

startup because of its relatively low 262 K freezing temperature. Both the primary and intermediate loops 

use electromagnetic pumps with an assumed pumping efficiency of 10 percent. A water heat pipe cooling 

shroud surrounds the buried portion of reactor module and removes about 5 kWt of fission power that is 

deposited in the reflectors and shield. The heat pipes transfer the heat to the cavity cooling radiator panels 

located above the surface. The shield consists of boron-carbide (B4C) in a stainless steel container 

providing both neutron and gamma attenuation. The axial plug shield is approximately 1.2 m thick and 

has an elliptical top face of 1.2 by 1.5 m to accommodate the Stirling assembly footprint. A thinner radial 

shield, as shown in figure 11, may also be needed to reduce neutron leakage through the regolith. In the 

buried/emplaced configuration, the need for shielding is largely driven by the dose limits of the power 

conversion components. The baseline shield is designed to limit dose to 2 Mrad and 1×1014 n/cm2

 fast 

fluence to the Stirling alternator region, and the human dose limit of 5 rem/yr at the outpost location. A 

key safety feature of the FSP system is that the reactor remains subcritical during all planned and credible 

unplanned mission events prior to startup. 

Figure 10.—Core cross-section. Figure 11.—Reactor and shield layout. 
NASA/TM—2008-215166 9 

Figure 12.—12 kWe dual-opposed stirling convertor concept. 

Power Conversion and PCAD 

The FSP system uses four Stirling converters that produce approximately 12 kWe each. A notional 

Stirling converter is shown in figure 12. The converter is comprised of two, axially opposed free-piston 

engines coupled to linear alternators and is approximately 1.2 m in length. The engines are connected via 

a common expansion space similar to the Space Power Demonstration Engine (SPDE) from the early 

1980s. The Stirling engine is heated by pumped, single-phase NaK from the intermediate heat 

exchangers. A common liquid metal (LM) heat exchanger (HX) assembly transfers heat from the NaK 

into the Stirling heater heads. The HX assembly includes a single centered inlet manifold, flow annulus, 

and two exit manifolds that form a jacket over the monolithic heater heads. The HX provides uniform 

heating with reasonable fluid velocity and negligible pressure drop. The Stirling converter uses an IN718 

heater head and operates at 830 K hot-end and 415 K cold-end, which is well within the experience base 

for free-piston Stirling technology. Under these conditions, the Stirling converter is approximately 

28 percent efficient. The linear alternators deliver 6 kWe each at 400 Vac, 100 hz single-phase directly to 

the Local Power Controller, where the power is converted to 120 Vdc for the loads. A PLR provides a full 

power electrical shunt to compensate for user load variations, and allows the Stirling converters to operate 

in a constant power mode. 

Heat Rejection 

The heat rejection subsystem includes pumped water heat transport and two-sided composite radiator 

panels with titanium-water heat pipes. The heat rejection subsystem is comprised of four water heat 

transport loops and two radiator wings (two loops per wing). Figure 13 shows a fluid schematic for one 

wing, which services two Stirling converters. Each heat rejection loop has a dedicated pump and volume 

accumulator. The radiator assembly receives heated water at 400 K from the Stirling converters and 

returns the water at 370 K, while rejecting approximately 30 kWt per loop. The radiator wings include 

individual radiator panels with flexible interconnects that can be stowed in an “accordion” arrangement 

prior to deployment. The radiator panels use a sandwich construction with aluminum honeycomb filler 

and regularly spaced titanium-water heat pipes between two polymer-matrix composite facesheets. The 

circular heat pipes are supported in graphite saddles that provide the thermal interface to the facesheets. 

Heat is transferred from the pumped water heat transport loops to the water heat pipes via a manifold with 

bumper shielding for protection from micrometeoroids. The heat pipes include a bent evaporator section 

to maximize heat transfer area and provide efficient packaging with the two coolant channels. The total 

heat rejected is approximately 120 kWt and the total two-sided FSP system radiator area is 175 m2

, 

including a 10 percent area margin. Radiator sizing is based on worst-case, equatorial sun angles and the 
NASA/TM—2008-215166 10 

Figure 13.—Heat rejection and radiator panel concepts.

TABLE II.—REFERENCE CONCEPT MASS SUMMARY 

 Mass, 

kg 

Comment 

Reactor 913 93 percent enriched UO2, NaK coolant, SS–316 cladding/structure, Be drum 

reflectors, 1 primary and 2 intermediate loops, 6 EM pumps, 175 kWt, 900K peak 

clad temp, cavity radiators 

Shield 1676 B4C and SS–316, 1.2-m-thick axial plug, 1.2 by 1.5 m elliptical face, <2 Mrad and 

1×1014 n/cm2 at Stirling converters, lunar regolith augmentation, <5 rem/yr at 100 m 

radial distance 

Power conversion 344 Free-piston Stirling, 4 dual-opposed converters, 8 linear alternators × 6 kWe, 100 Hz, 

TH = 830 K, TC = 415 K 

Heat rejection 615 Pumped H2O coolant, 4 independent loops, 400 K inlet temp, composite radiator 

panels with Ti/H2O heat pipes, scissor deployment, mylar surface apron, 175 m2

 total 

area 

Power conditioning 

 and distribution 

559 400 Vac distribution, 100 m cabling, 120 Vdc user bus, parasitic load control, 

comm/telemetry link, 5 kWe solar array, 10 kWh battery 

Subtotal 4107 

Margin 821 20 percent 

Total 4928 

use of a low-absorptivity, low-emissivity mylar surface apron to reduce the thermal contribution from the 

surface, resulting in an effective radiator sink temperature of about 250 K. A radiator wing includes 10 

sub-panels, each measuring approximately 2.5 m wide by 1.75 m tall. 

System Mass 

The FSP system mass summary is presented in table II. The total system mass is approximately 

4100 kg, and less than 5000 kg with 20 percent mass margin. The reactor, including the fuel pins, vessel, 

control drums, heat transport, and cavity cooling, is 913 kg, or 22 percent of the total mass. The shield is 

the heaviest subsystem comprising over 41 percent of the total mass. The shield also has the greatest 

potential for mass reduction, should the radiation limits at the Stirling converters be relaxed or alternative 

shield materials such as water or lithium-hydride be considered. The power conversion mass is the 

smallest at 344 kg, or 8 percent of the total mass. The Stirling converters account for the majority of 

the power conversion subtotal having a specific mass of approximately 6 kg/kWe. The heat rejection 

subsystem is about 15 percent of the total mass at 615 kg. The radiator panels are about 4.3 kg/m2

 (based 
NASA/TM—2008-215166 11 

Figure 14.—System mass scaling for emplaced and landed configurations.

on 1-sided area), while the overall heat rejection subsystem is about 7 kg/m2

. The PCAD mass is 

estimated at 559 kg or 14 percent of the total mass. This mass includes the 5 kWe solar array (based on 

100 W/kg array technology) and the 10 kWh battery (based on 100 Whr/kg battery technology). 

Figure 14 shows the estimated system mass scaling over the power range from 10 to 50 kWe, 

including the 20 percent margin. Both the emplaced (reference) and landed configurations masses are 

shown, with the landed configuration based on the assumptions stated previously (full earth-delivered 

on-board shielding, 1 km separation, and 2000 V power transmission). At 40 kWe, the landed system is 

estimated to be 8800 kg, an 80 percent increase over the emplaced configuration. The two curves exhibit 

a relatively shallow slope which is typical of space reactors. While there is modest mass savings by 

reducing power level, there is also modest mass increase for higher power systems. 

Conclusion 

NASA and DOE conducted a 12 month study to estimate the cost of a FSP system for lunar and 

Mars missions. Screening studies were performed to evaluate technology options and design variables 

before selecting a preliminary reference concept for costing. The screening studies led to a UO2-fueled, 

NaK-cooled reactor with Stirling power conversion and water-based heat rejection capable of providing 

40 kWe with an 8 yr design life. The reference system is emplaced in a pre-excavated hole to allow nearoutpost siting and reduce radiation levels to less than 5 rem/yr at 100 m separation distance. The reactor 

uses stainless steel construction, limiting nominal coolant temperatures to less than 900 K, in order to 

minimize development cost and leverage terrestrial technology. Stirling power conversion is well suited 

to the operating temperature, providing high efficiency at relatively high heat rejection temperature. The 

use of water heat transport and water heat pipe radiator panels provides efficient waste heat removal, 

using a deployment approach that is derived from the ISS radiators. The FSP system concept is extensible 

to Mars, with materials and design strategies that are fully compatible with the Martian environment. The 

total system mass with 20 percent margin is less than 5000 kg. 

Reference 

Poston, D.I., Kapernick, R.J., Dixon, D.D., Amiri, B.W., and Marcille, T.F., “Reference Reactor Module 

for the Affordable Fission Surface Power System,” in the Proceedings of the Space Technology and 

Applications International Forum (STAIF–2008), edited by M.S. El-Genk, AIP Conference 

Proceedings, Melville, New York, 2008. 
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E-16409 

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

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

10. SPONSORING/MONITORS 

 ACRONYM(S)

NASA 

11. SPONSORING/MONITORING 

 REPORT NUMBER

NASA/TM-2008-215166 

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, 301-621-0390

13. SUPPLEMENTARY NOTES

14. ABSTRACT

This paper presents an overview of an affordable Fission Surface Power (FSP) system that could be used for NASA applications on the 

Moon and Mars. The proposed FSP system uses a low temperature, uranium dioxide-fueled, liquid metal-cooled fission reactor coupled to 

free-piston Stirling converters. The concept was determined by a 12 month NASA/DOE study that examined design options and 

development strategies based on affordability and risk. The system is considered a low development risk based on the use of terrestrialderived reactor technology, high efficiency power conversion, and conventional materials. The low-risk approach was selected over other 

options that could offer higher performance and/or lower mass. 

15. SUBJECT TERMS

Nuclear electric power generation 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 

 ABSTRACT

UU 

18. NUMBER 

 OF 

 PAGES

17 

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)

301-621-0390 

Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. Z39-18