Nicholas A. Schifer and Maxwell H. Briggs

Glenn Research Center, Cleveland, Ohio

Environmental Loss Characterization of 

an Advanced Stirling Convertor (ASC-E2) 

Insulation Package Using a Mock Heater Head

NASA/TM—2012-217291

January 2012

AIAA–2011–5577
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Nicholas A. Schifer and Maxwell H. Briggs

Glenn Research Center, Cleveland, Ohio

Environmental Loss Characterization of 

an Advanced Stirling Convertor (ASC-E2) 

Insulation Package Using a Mock Heater Head

NASA/TM—2012-217291

January 2012

AIAA–2011–5577

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

9th International Energy Conversion Engineering Conference (IECEC)

sponsored by the American Institute of Aeronautics and Astronautics

San Diego, California, July 31–August 3, 2011
Acknowledgments

This work is funded through the National Aeronautics and Space Administration (NASA) Science Mission Directorate and the 

Radioisotope Power Systems Program Office. The authors wish to acknowledge the key GRC technical team supporting ASC 

Stirling Net Heat Determination. Team leadership and direction was given by Scott Wilson and Jeff Schreiber. Analytical modeling 

efforts were performed by Dave Gubics and Terry Reid. Lab mechanical support was provided Wayne Gerber.

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paper, intended to solicit comments and 

ideas from a technical peer group.

This report contains preliminary findings, 

subject to revision as analysis proceeds.
NASA/TM—2012-217291 1

Environmental Loss Characterization of an Advanced Stirling 

Convertor (ASC-E2) Insulation Package Using a Mock Heater Head

Nicholas A. Schifer and Maxwell H. Briggs

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Abstract

The U.S. Department of Energy (DOE) and Lockheed Martin Space Systems Company (LMSSC) 

have been developing the Advanced Stirling Radioisotope Generator (ASRG) for use as a power system 

for space science missions. This generator would use two high-efficiency Advanced Stirling Convertors 

(ASCs), developed by Sunpower, Inc., and NASA Glenn Research Center (GRC). The ASCs convert 

thermal energy from a radioisotope heat source into electricity. As part of ground testing of these ASCs, 

different operating conditions are used to simulate expected mission conditions. These conditions require 

achieving a particular operating frequency, hot end and cold end temperatures, and specified electrical 

power output for a given net heat input. While electrical power output can be precisely quantified, thermal 

power input to the Stirling cycle cannot be directly measured. Traditionally, the environmental losses 

have been characterized based on testing a non-operating convertor. However, the thermal profile of a 

non-operating convertor does not adequately characterize the thermal profile of an operating convertor 

and, therefore, does not accurately predict net heat input. In an effort to improve net heat input 

predictions, numerous tasks have been performed which provided a more accurate value for net heat input 

into the ASCs, including testing validation hardware, known as the Mock Heater Head, to provide a direct 

comparison to numerical and empirical models used to predict convertor net heat input. The Mock Heater 

Head was primarily constructed of existing test hardware which had the same relative thermal paths as a 

convertor. The dominant conduction path is a removable rod that interfaces the interior dome of the Mock 

Heater Head. Two different diameter rods were used to vary the thermal load on the heater. While the rod 

and heater head cylinder wall provided conductive paths from the hot end to the cold end, the resulting 

thermal profile did not accurately simulate that of an operating convertor. The Mock Heater Head also 

served as the pathfinder for a higher fidelity version of validation test hardware, known as the Thermal 

Standard. This paper describes how the Mock Heater Head was tested and utilized to validate a process 

for the Thermal Standard through test configuration, instrumentation, calculations performed, test

methods, and data reduction.

Nomenclature

A cross-sectional area

ASC(-E2) Advanced Stirling Convertor (second-generation engineering unit)

ASRG Advanced Stirling Radioisotope Generator

CSAF Cold Side Adapter Flange

DOE Department of Energy

GRC NASA Glenn Research Center

HT high-temperature

IR infrared

K thermal conductivity

LM Lockheed Martin

Q̇ heat flow

Q̇

conducting rod heat flow through the conducting rod
NASA/TM—2012-217291 2

Q̇

env loss heat lost to the environment

Q̇

heater head heat flow through the heater head

Q̇

heater power electrical power provided to the heater

Q̇

HH insulation heat flow through the insulation plug in the heater head

∆T change in temperature

TC thermocouple

∆X change in location

1.0 Introduction

Accurately quantifying Stirling convertor efficiency and performance is important for designing the 

Advanced Stirling Radioisotope Generator (ASRG) and for mission planning. While electrical power 

output can be precisely quantified, thermal power input to the Stirling cycle cannot be directly measured.

The past technique to estimate thermal power input to the convertor relies on accurately determining the 

environmental losses through the surrounding insulation of an operating convertor and subtracting these 

losses from the gross heat input (or electrical input) into the heat source. Traditionally, the environmental 

losses have been calculated and characterized based on testing a non-operating convertor. Using that 

characterization, the net heat input to the convertor has been calculated by subtracting the empirically 

modeled environmental losses from the measured heat source power. This method has previously worked 

well for convertors with lower operating temperatures and heaters that did not require some portion of the 

heater cartridge to be exposed to air. This technique did not characterize the system at the full heat flux 

and heat source temperature of an operating convertor and was suspected to contribute inaccuracies in 

performance and efficiency predictions. In an attempt to validate results from empirical models, a twofold 

path was taken to develop hardware capable of accurately imitating the thermal character of an operating 

and non-operating Advanced Stirling Convertors (ASC) without gas dynamics. The first path was to 

modify existing hardware, which enabled a quick turnaround and initiation of testing at the cost of an 

inaccurate representation of the thermal profile of an ASC. This path became known as the Mock Heater 

Head and is the focus of this paper. The second path was to develop higher fidelity hardware which could 

accurately simulate the thermal profile of an operating ASC. Convertor aspects, such as heat transfer area, 

lengths, diameters, material conductivity, and heat transfer paths were optimized to give the most accurate 

thermal profile possible. The second path became known as the Thermal Standard.

The Mock Heater Head was developed as a test unit to help better understand the environmental 

losses through the insulation package used while operating ASC in air. A key component to the design of 

the Mock Heater Head is a removable rod that mates to the interior dome of the heat head. Its purpose is 

to provide a conductive path representative of the heat input into the Stirling cycle. Two different 

conducting rods made of GRCop-84 and nickel were used to vary the thermal load and subsequently 

increase the thermal load on the heater. The Mock Heater Head test was utilized to investigate GRCop-84, 

which is a ternary Cu-Cr-Nb alloy developed at NASA GRC for high heat flux, high temperature 

applications, as a potential material for the conducting rod in the Thermal Standard. The copper material, 

GRCop-84, was selected as a candidate because of its high thermal conductivity (80 percent of pure 

copper) and ability to maintain yield strength greater than 100 MPa at temperatures up to 900 °C (Ref. 1).

Also, nickel plating was applied to the GRCop-84 rod and tested as protection against oxidation at 

elevated temperatures.

While the physics presented in this paper hold true for the Mock Heater Head, a one-to-one 

comparison of the Mock Heater Head test results to the ASC-E2 convertor test results should not be made 

because the differences in head geometry and conductivity. Rather, performing various tests with the 

Mock Heater Head 1) gave insight into materials and coating selection for the conducting rod, 2) 

identified important design considerations for mounting, assembly, and accurate heat flow paths, and 3) 

verified test methods and data analysis techniques. This paper outlines the Mock Heater Head test 
NASA/TM—2012-217291 3

configuration, instrumentation, calculations performed, testing, and results, while presenting its 

usefulness as a pathfinder for the Thermal Standard.

2.0 Test Configuration

The test station for the Mock Heater Head is shown in Figure 1 along with a completed section view 

of the assembly. Note that the section view does not show the copper cooling coils that reject heat from 

the conducting rod or the Viton tubing that connects the cooling loops for the cold side adapter flange 

(CSAF) and conducting rod to the circulators, nor does it show the Kaowool blanket insulation that fills 

the voids inside the insulation housing and insulates the exposed portions of the conducting rod. The 

components inside of the insulation housing shown in Figure 1 relied on a preload rather than fasteners to 

affix the heater head to the CSAF and the heat source to the heater head. The CSAF was fastened to the 

bulk head and carried the mechanical load transferred through the other components. The thin wall of the 

Mock Heater Head was mated to a locating spotface on the CSAF and fixed through compression.

Depending on the test, either an insulating thermal barrier made of ceramic paper or an alumina disk 

(further explanation will be given later) was placed between the heat source and heat collector plate. The 

heat source was concentrically located on top of the heater head with a button on the heater head that fits 

into the heat source. A preload stud was fit into the heat source and connected to a spring loaded plate 

attached to the top plate of the insulation housing. The insulation housing was held in tension from the 

preload and maintained static equilibrium of the system. The interior void of the heater head was filled 

with Kaowool blanket insulation as shown in Figure 1 except for a volume in the center for the 

conducting rod. The nickel rod mated to the interior dome of the heater head with a very thin piece of 

ceramic paper (0.178 mm thick) sandwiched in between and held in place with a preload. After operation 

with the nickel rod, oxidation on the interior dome of the head served as a diffusion barrier for the 

GRCop-84 rod and therefore, ceramic paper was not used. When a conducting rod was not used, its void 

was filled with Kaowool insulation.

Figure 1.—Completed Mock Heater Head assembly ready for operation (left) and mechanical hardware 

section view (right).
NASA/TM—2012-217291 4

The Mock Heater Head was adapted from a test heater head previously designed and fabricated to be 

used in testing a heat flux sensor. The original heater head was constructed from a solid piece of nickel 

201 and matched a production heater head only in its heat collector interface plate and thermal mass. Its 

design intent was to flow a similar amount of energy to an operating convertor through the head to a 

rejection loop, but not to match exact geometry. Modifications for the Mock Heater Head did not match 

production geometry nor did it match thermal mass. The design intent was to conduct 110 W through the 

wall of the head and an additional 90 W through a nickel conducting rod that interfaced the heater head 

dome. The resulting 200 W would be representative of the energy rejected at the cold end of the 

convertor. A second rod made of GRCop-84 was designed to conduct 230 W with the intent that the 

incremental increases in thermal loading of the two rods would serve to quantify changes in the 

environmental losses.

3.0 Instrumentation

The Mock Heater Head, conducting rods, surrounding insulation, and insulation housing were 

instrumented with numerous thermocouples. Figure 2 shows a map of the thermocouples (TCs) in their 

approximate locations on a cross-sectional view of the hardware. Not including the TCs on the conducting

rods, there were a total of thirty-three TCs used: sixteen 0.032–in. Type-N TC probes, three 0.020–in.

Type-N TC probes, and fourteen Type-K surface mount TCs. Also, a Fluke i45 Infrared (IR) camera was 

used to measure temperatures on the exposed high-temperature (HT) firerod leads.

The Mock Heater Head was instrumented with seven thermocouples, as shown in Figure 3. There 

were four located 90° apart radially at a location 8.00 mm from the heat collector face. An additional

three TCs were added in line along the axial length of the smaller diameter portion of the heater head. The 

locations of these TCs were measured from the cold side of the heater head and their measurements were 

10.7, 36.6, and 67.7 mm.

The nickel 201 conducting rod was instrumented with four 0.032–in. Type-N thermocouples. The 

TCs were mounted to the surface of the rod using Inconel band straps that were spotwelded to the nickel 

rod. The TCs were mounted in-line along the length of the rod, and their locations measured from the

smaller diameter end interfacing the hot-end of the heater head were 26.4, 50.0, 76.2, and 101.6 mm.

These TCs were necessary for the calculation of the heat rejected through the conducting rod and the 

estimated environmental losses, which will be described in detail later.

Figure 2.—Thermocouple locations for the Mock Heater Head test setup.
NASA/TM—2012-217291 5

Figure 3.—Thermocouple instrumentation on the Mock Heater Head (left) and cross-sectional view 

with dimensions (right).

Figure 4.—Thermocouple instrumentation 

on the GRCop-84 conducting rod.

The nickel-plated GRCop-84 conducting rod was instrumented with five 0.020–in. Type-N 

thermocouples. The TCs were mounted to the surface of the rod using 0.010–in. steel band straps that 

were spotwelded to the nickel plating. Initially, there was an attempt to use Inconel straps, but even at 

high levels of current, the spotwelder did not work. The TCs were mounted in-line along the length of the 

rod, and their locations measured from the smaller diameter end interfacing the hot-end of the heater head 

were 6.3, 12.5, 25.3, 63.1, and 101.3 mm, as seen in Figure 4. These TCs were also used to calculate the 

heat rejected through the conducting rod for the estimation of the environmental losses.

4.0 Testing

A series of tests were performed using the Mock Heater Head to accurately represent standard testing 

performed at GRC using an ASC-E2 convertor. An ASC-E2 convertor typically undergoes an insulation 

thermal loss characterization, during which the convertor does not operate, and then operates through a 

series of test points representative of anticipated mission conditions. In practice, two variations of 

insulation thermal loss characterization have been performed. One in which ceramic paper disks were 

placed between the heat source and the heater head to act as a thermal barrier. The intent of using the 

thermal barrier was to increase the temperature difference between to the heater head and the heat source 

to be more representative of temperatures observed during convertor operation. The second variation 

involves an alumina disk placed between the heat source and the heater head, which prevents the heat 

source from diffusion bonding to the heater head. Both of these insulation thermal loss characterization 

tests were performed using the Mock Heater Head, where the non-operating convertor was represented by 

not installing a conducting rod. An operating convertor was represented by testing with each of the two 
NASA/TM—2012-217291 6

conducting rods. The two rods had different thermal conductivities and were therefore representative of 

varying the piston amplitude in a Stirling convertor. For each of the four test cases described above, a test 

matrix consisting of four points was performed and is summarized in Table I. Additionally, tests were 

also performed to investigate the potential for ambient conditions (forced convection) and orientation to 

affect environmental losses, and are discussed in greater detail in the results section. In total five tests 

were performed, as summarized in Table II under the Results section. All tests were conducted by 

controlling the heat source temperature. The heat source temperature is normally the controlled parameter 

in a thermal loss test using a thermal barrier on an actual convertor, and since the thermal barrier test was 

the first performed, this approach was adopted for the remainder of Mock Heater Head testing. Therefore, 

for an equivalent heat source temperature, the hot-end temperature decreased for all simulated operating 

points. As a result of our experience with the Mock Heater Head, it was determined that it would be better 

to control hot-end temperature in Thermal Standard testing (because the control parameter in convertor 

testing is the hot end) to more easily show that the environmental loss increases as the heat source and/or 

hot end temperatures increase. For each steady-state test point, a 5-min average of heater power, current 

and voltage, and all temperature data were collected. In addition, an infrared photograph of the exposed 

HT firerod leads was taken.

TABLE I.—TEST MATRIX

Point Heat source 

temperature 

(°C)

CSAF 

temperature 

(°C)

1 960 52

2 860 52

3 750 52

4 600 52

5.0 Calculations

All calculations served the end goal of determining the environmental losses for various test conditions.

A comparison of the environmental losses gave insight into the sensitivity of environmental losses to 

changes in the thermal gradient as a result of increased thermal loading. The key calculations were heater 

head conduction, rod conduction, and conduction through the insulation inside the heater head. The 

summation of these calculations gives the cold-end losses and when subtracted from the heater power 

gives the environmental losses as shown in Eq. (1).

Q̇

env loss = Q̇heater power − �Q̇heater head + Q̇conducting rod + Q̇HH insulation� (1)

The heater power was directly measured using a Yokogawa WT230 powermeter. Conduction through the 

heater head, conducting rod, and heater head insulation was calculated using Fourier’s law in Eq. (2).

Q̇ = KA ∆T

∆X (2)

The thermal conductivities used in the calculations were manufacturer values chosen from a temperaturedependent function based on the average temperature. The temperature-dependent thermal conductivities 

are shown in Figure 7 to Figure 9 in the Appendix. The cross-sectional areas used in the calculations were 

143.9 mm2 for the heater head, 938.1 mm2 for the Kaowool insulation, 248.4 mm2 for the nickel rod, and 

214.2 mm2 for the GRCop-84 rod. The temperatures used in the heater head calculation were taken from 

the 1st and 3rd TCs on the smaller diameter portion of the heater head, and the length between them was 

53.3 mm. The temperatures used in the Kaowool calculation were an average of the four hot-end TCs on 

the heater head and an average of the two CSAF TCs. The length between them was 80.0 mm. The 

temperatures used in the nickel rod calculation were taken from the first and third TCs in reference from 
NASA/TM—2012-217291 7

the hot-end of the rod, and the length between them was 49.8 mm. Lastly, the temperatures used in the 

GRCop-84 rod calculation were taken from the 1st and 5th TCs in reference from the hot-end of the rod,

and the length between them was 95.0 mm.

6.0 Results

Table II summarizes all tests in the sequence performed and includes key measured and calculated 

data for point 1 from Table I. Also, Figure 5 graphically shows a comparison of environmental losses to 

heat source temperature for all tests performed.

TABLE II.—SUMMARY OF TEST PERFORMED ON THE MOCK HEATER HEAD

Test Interface between

heat source

and hot end

Conducting

rod

Additional

variable

Heat source 

temperature

(°C)

Hot-end 

Temperature

(°C)

Cold end 

loss

(W)

Environmental

loss 

(W)

1 Thermal Barrier None 959 892 96 149

2 Alumina disk Nickel

Rod 960 915 167 148

3 Alumina disk Nickel

Rod

Forced

Convection 959 915 166 164

4 Alumina disk none 958 922 98 146

5 Alumina disk GRCop-84

Rod 956 861 314 125

It was expected that the environmental losses would show a substantial increase in Test 2 and Test 5 

where a conducting rod was installed when compared to the Test 1 and Test 4 where a rod was not 

installed. Rather, the trends showed that the environmental losses decreased when a greater thermal load 

was applied to the heat source via the conducting rods. In comparing Test 4 to Test 5 in Figure 5, the 

environmental losses decrease by 21 W as a result of installing the GRCop-84 rod. This phenomenon is 

most likely the result of the 61 °C drop in hot-end temperature. One might also expect a similar, yet 

smaller, decrease in hot-end temperature when the nickel rod was installed, but the hot-end temperature 

only dropped 7 °C in this case, making the change in environmental losses nearly indistinguishable from 

the other test points without a rod installed. This phenomenon is believed to be the result of the 

differences in heat transfer paths on the Mock Heater Head compared to an actual convertor. In the Mock 

Heater Head the conducting rod directly interfaced to the dome of the heater head, which acted as a direct 

heat sink to the heat source and varied the thermal gradients in a manner that was not desirable for 

comparison to convertor data. These results drove an effort for accurate heat flow paths in the Thermal 

Standard.

Test 3, which is represented by a single, worst case point in Figure 5, was performed to further 

investigate the affect of ambient conditions on environmental losses. This test involved using a

Multicomp (Model: MC1123HST) fan placed at four distances from the HT Firerod leads to induce 

varying intensities of forced convection. A thermal anemometer was used to estimate the air velocity at 

the lead wires for each case, and an observed average value was recorded. Table III summarizes distance,

air velocity, and gross heat input measurements during Test 5, and Figure 6 shows the observed 

relationship to air velocity. The thermal anemometer measurements are representative of velocities 

experienced at a location approximately 25 mm from the heater lead wires and in the path between the fan 

and wires. At ambient conditions, which are represented as an infinite distance in Table III, the 

approximate measured air velocity was 0.1 m/s and the gross heat input was 321.5 W. This point served 

as a baseline for comparison to the other points, with “Additional Heat Input,” shown in Figure 6, being 

defined as the difference in gross heat input between any point and the baseline. As the fan was

positioned closer to the exposed heater cartridges and lead wires, the heater worked harder to maintain 

temperature as a result of the increased convection. At some location between fan positions of 203 mm 

(3.5 m/s) and 559 mm (1.0 m/s), additional air flow appeared to have limited effect on the gross heat 

input. For this reason, the trend shown in Figure 6 is truncated. The phenomenon of increased flow 
NASA/TM—2012-217291 8

approaching a limit in convective effects was expected, but not further investigated for the determination 

of that transition point. The results and trends of this test should be used as reference for gaining a better 

understanding of the heat source losses under different environmental conditions.

Other air velocity measurements were also made near the test article. A measurement taken directly 

below the air conditioning vent, which is at a distance of approximately 1.5 m from the test article and 

does not blow directly toward the test article, had an output velocity of 1.5 m/s. Other measurements 

taken in the general vicinity of the test article without operation of the fan never exceeded 0.2 m/s. For 

this particular test, it is unlikely that forced convection changes affected the gross heat input by more than 

±1.1 W.

Figure 5.—Summary of environmental losses versus heat source 

temperature for tests performed.

TABLE III.—AIR VELOCITY MEASUREMENTS FROM

THE FORCED CONVECTION INVESTIGATION

Distance

(mm)

Air velocity

(m/s)

Gross heat input

(W)

∞ 0.1 321.5

1,626 0.4 322.6

965 0.9 327.5

559 1.0 330.1

203 3.5 339.3

Figure 6.—Additional heat input as a function of air velocity.

65

85

105

125

145

165

580 680 780 880 980

Environmental Losses, W

Heat Source Temperature, °C

Mock Heater Head Test Results 

Test 1: Thermal Barrier, No Rod

Test 2: Alumina Disk, Nickel Rod

Test 3: Forced Convection

Test 4: Alumina Disk, No Rod

Test 5: Alumina Disk, Cu Rod

y = 8.1653x2 + 0.4217x – 0.0842

R2 = 0.9994

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

0 0.2 0.4 0.6 0.8 1 1.2

Additional Heat Input. W

Approximate Air Velocity, m/s
NASA/TM—2012-217291 9

7.0 Conclusions

The need to flow heat through the validation hardware much like an operating ASC was determined to 

be a requirement for this validation effort because the Mock Heater Head did not result in a thermal 

profile adequate for use in validating empirical and numerical models. That being said, the Mock Heater 

Head test served as a pathfinder for selection of the following items for the Thermal Standard test:

verifying materials used for the conducting Rod, identifying design features for the heat collector and 

CSAF, identifying instrumentation locations for calculating heat conducted to the cold end, designing the 

heat rejection system mounting method for ease of disassembly and shipment, and identifying preferred 

test methods used for characterization such as how to control the heat input. The GRCop-84 material was 

identified as having superior strength at expected test temperatures, and nickel plating was found to be 

suitable for protecting the copper rod from oxidation during the test. Additionally, diffusion bonding 

between the rod and heater head was prevented by installing a thin layer of Cotronics ceramic paper 

between the heater block and head. Lastly, the Mock Heater Head test verified the methodology and use 

of an IR camera to measure temperatures on the exposed surfaces of the heat source, namely the HT 

firerod leads for input into a thermal model.

In addition to this paper, three other papers have been written to explain the work performed in the 

effort to accurately determine the environmental losses through the surrounding insulation of an operating 

convertor and quantify Stirling convertor performance and efficiency. This paper has described the first 

step in a process that has directly played a role in the successful testing of the Thermal Standard 

validation hardware, described in the paper titled, “Evaluation of Advanced Stirling Convertor Net Heat 

Input Correlation Methods using a Thermal Standard,” (Ref. 2) as well as the successful validation of the 

computation model described in the paper titled, “A Computational Methodology for Simulating Thermal 

Loss Testing of the Advanced Stirling Convertor” (Ref. 3). A final paper titled, “Overview of Heat 

Addition and Efficiency Predictions for an Advanced Stirling Convertor,” (Ref. 4) provides an overview 

of the entire effort.

NASA/TM—2012-217291 11

Appendix

Figure 7 to Figure 9 show the thermal conductivities of nickel 201, Kaowool, and GRCop-84, 

respectively.

Figure 7.—Manufacturer’s thermal conductivity of nickel 201 (Ref. 5).

Figure 8.—Manufacturer’s thermal conductivity of Kaowool (Ref. 6).

Figure 9.—Thermal conductivity of GRCop-84 (Ref. 7).
NASA/TM—2012-217291 12

References

1. Ellis, David L., “GRCop-84: A High-Temperature Copper Alloy for High-Heat-Flux Applications”, 

NASA/TM—2005-213566, 2005.

2. Briggs, M.H., “Evaluation of Advanced Stirling Convertor Net Heat Input Correlation Methods using 

a Thermal Standard,” Proceedings of the Ninth International Energy Conversion Engineering 

Conference (IECEC 2011) American Institute for Aeronautics and Astronautics, 2011.

3. Reid, T.V., “A Computational Methodology for Simulating Thermal Loss Testing of the Advanced 

Stirling Convertor,” Proceedings of the Ninth International Energy Conversion Engineering 

Conference (IECEC 2011) American Institute for Aeronautics and Astronautics, 2011.

4. Wilson, S.D., “Overview of Heat Addition and Efficiency Predictions for an Advanced Stirling 

Convertor,” Proceedings of the Ninth International Energy Conversion Engineering Conference 

(IECEC 2011) American Institute for Aeronautics and Astronautics, 2011.

5. “Nickel 200 & 201,” Specialty Metals [online technical bulletin], URL: 

http://www.specialmetals.com/documents/Nickel%20200%20&%20201.pdf [cited 14 July 2011].

6. “Thermal Ceramics – Blanket Products,” Thermal Ceramics [online technical bulletin], URL: 

http://www.barteltinsulation.com/pdfs/CERAMICBLANKET.pdf [cited 14 July 2011].

7. Thermophysical Properties Research Laboratory Inc. Report #4629 November 2010. 

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1. REPORT DATE (DD-MM-YYYY)

01-01-2012 

2. REPORT TYPE

Technical Memorandum 

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Environmental Loss Characterization of an Advanced Stirling Convertor (ASC-E2) Insulation 

Package Using a Mock Heater Head 

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Schifer, Nicholas, A.; Briggs, Maxwell, H. 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

WBS 138494.05.02.04.03 

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-17827 

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-2012-217291 

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited 

Subject Category: 20 

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

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

13. SUPPLEMENTARY NOTES

14. ABSTRACT

The U.S. Department of Energy (DOE) and Lockheed Martin Space Systems Company (LMSSC) have been developing the Advanced 

Stirling Radioisotope Generator (ASRG) for use as a power system for space science missions. This generator would use two highefficiency Advanced Stirling Convertors (ASCs), developed by Sunpower Inc. and NASA Glenn Research Center (GRC). As part of ground 

testing of these ASCs, different operating conditions are used to simulate expected mission conditions. These conditions require achieving a 

specified electrical power output for a given net heat input. While electrical power output can be precisely quantified, thermal power input 

to the Stirling cycle cannot be directly measured. In an effort to improve net heat input predictions, the Mock Heater Head was developed 

with the same relative thermal paths as a convertor using a conducting rod to represent the Stirling cycle and tested to provide a direct 

comparison to numerical and empirical models used to predict convertor net heat input. The Mock Heater Head also served as the pathfinder 

for a higher fidelity version of validation test hardware, known as the Thermal Standard. This paper describes how the Mock Heater Head 

was tested and utilized to validate a process for the Thermal Standard.

15. SUBJECT TERMS

Stirling; Net heat input; Insulation loss; Environmental loss; Thermal loss 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

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20 

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

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b. ABSTRACT

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443-757-5802 

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