Steven M. Geng

Glenn Research Center, Cleveland, Ohio

Maxwell H. Briggs

Analex Corporation, Brook Park, Ohio

L. Barry Penswick

SEST Inc., Middleburg Heights, Ohio

J. Boise Pearson

Marshall Space Flight Center, Huntsville, Alabama

Thomas J. Godfroy

Maximum Technology Corporation, Huntsville, Alabama

Test Results From a Pair of 1-kWe Dual-Opposed 

Free-Piston Stirling Power Convertors Integrated 

With a Pumped NaK Loop

NASA/TM—2011-216266

March 2011
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 NASA Center for AeroSpace Information (CASI)

 7115 Standard Drive

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Steven M. Geng

Glenn Research Center, Cleveland, Ohio

Maxwell H. Briggs

Analex Corporation, Brook Park, Ohio

L. Barry Penswick

SEST Inc., Middleburg Heights, Ohio

J. Boise Pearson

Marshall Space Flight Center, Huntsville, Alabama

Thomas J. Godfroy

Maximum Technology Corporation, Huntsville, Alabama

Test Results From a Pair of 1-kWe Dual-Opposed 

Free-Piston Stirling Power Convertors Integrated 

With a Pumped NaK Loop

NASA/TM—2011-216266

March 2011

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
Available from

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7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

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

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

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

either expressed or implied, by the National Aeronautics and 

Space Administration.

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2011-216266 iii 

Contents 

Abstract ......................................................................................................................................................... 1

Background ................................................................................................................................................... 1

Summary ....................................................................................................................................................... 2

1.0 Introduction .......................................................................................................................................... 2

2.0 Purpose of Test ..................................................................................................................................... 3

3.0 Test Facility .......................................................................................................................................... 4

4.0 Test Article ........................................................................................................................................... 4

5.0 Test Procedure ...................................................................................................................................... 5

6.0 Results and Discussion ......................................................................................................................... 5

6.1 Steady-State Testing ................................................................................................................... 5

6.2 Transient Testing ........................................................................................................................ 6

7.0 Summary of Results ............................................................................................................................. 8

8.0 Conclusions .......................................................................................................................................... 9

Appendix A.—Test Plan ............................................................................................................................. 33

Appendix B.—Performance Map Data ....................................................................................................... 41

Appendix C.—NaK Heat Exchanger Drawings.......................................................................................... 59

References ................................................................................................................................................... 60

NASA/TM—2011-216266 1 

Test Results From a Pair of 1-kWe Dual-Opposed Free-Piston 

Stirling Power Convertors Integrated With a Pumped NaK Loop 

Steven M. Geng 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Maxwell H. Briggs 

Analex Corporation 

Brook Park, Ohio 44142 

L. Barry Penswick 

SEST Inc. 

Middleburg Heights, Ohio 44130 

J. Boise Pearson 

Marshall Space Flight Center 

Huntsville, Alabama 35812 

Thomas J. Godfroy 

Maximum Technology Corporation 

Huntsville, Alabama 35814 

Abstract 

As a step towards development of Stirling power conversion for potential use in Fission Surface 

Power (FSP) systems, a pair of commercially available 1-kW-class free-piston Stirling convertors were 

modified to operate with a NaK (sodium (Na) and potassium (K)) liquid metal pumped loop for thermal 

energy input. This was the first-ever attempt at powering a free-piston Stirling engine with a pumped 

liquid metal heat source and is a major FSP project milestone towards demonstrating technical feasibility. 

The convertors were successfully tested at the Marshall Space Flight Center (MSFC) from June 6 through 

July 14, 2009. The convertors were operated for a total test time of 66 hr and 16 min. The tests included 

(a) performance mapping the convertors over various hot- and cold-end temperatures, piston amplitudes, 

and NaK flow rates and (b) transient test conditions to simulate various startup (i.e., low-, medium-, and 

high-temperature startups) and fault scenarios (i.e., loss of heat source, loss of NaK pump, convertor stall, 

etc.). This report documents the results of this testing. 

Background 

In 2007, two P2A (formerly known as EG–1000) 1-kW free-piston Stirling power convertors were 

procured from Sunpower Inc., of Athens, OH. The P2As are designed to produce 1.1 kWe at their design 

operating conditions of 550 C hot-end temperature, a 50 C cold-end temperature, a mean working space 

pressure of 3.0 MPa, and a piston amplitude of 10 mm. The P2As are typically configured with gas 

burners for thermal energy input; however, the P2As delivered to the Glenn Research Center were 

configured with electrically heated heads to simplify testing. In early 2008, the P2As were tested at Glenn 

to establish the baseline convertor performance. 
NASA/TM—2011-216266 2 

Figure 1 shows the convertor power performance map generated during baseline testing for the 

convertors configured with electrically heated heads. As expected, the total power output increases with 

both increasing temperature ratio and increasing piston amplitude. At the design operating conditions, the 

convertors produced 2030 W of electric power at a gross thermal efficiency of 28.1 percent. The maximum 

total power output of 2240 We was measured at a 550 °C hot-end and a 40 °C cold-end temperature with a 

piston amplitude of 10.5 mm. This power level was achieved at a gross thermal efficiency of 28.6 percent. 

The maximum efficiency achieved by these convertors was 30 percent, which occurred at a hot-end 

temperature of 550 °C, a cold-end temperature of 30 °C, and a piston amplitude of 9 mm. 

After baseline testing was completed, the convertors were retrofitted with new heater heads featuring 

NaK (sodium (Na) and potassium (K)) heat exchangers designed by Glenn to allow the convertors to be 

interfaced with a pumped NaK loop. 

In October of 2008, the convertors were delivered to Marshall Space Flight Center (MSFC) for 

integration and testing in the Fission Surface Power (FSP) Primary Test Circuit (PTC). A safety review 

meeting (February 2009) and a test readiness review (April 2009) were held at MSFC in preparation for 

this test. Permission to proceed with testing was granted by the test readiness review board in May 2009. 

Summary 

A comparison of the performance map recorded for the convertors configured with the NaK heater 

heads with the baseline data (for electric heater heads) indicated that the NaK Stirling convertors 

performed similar to the baseline configuration in terms of both power and efficiency. In addition, the 

convertor performance was relatively insensitive to NaK mass flow over the range tested. A total of 43 

steady-state, 9 transient, and 8 reactivity feedback data points were acquired during this test. During these 

tests, the convertors were operated at hot-end temperatures ranging from 400 to 550 °C, cold-end 

temperatures from 30 to 70 °C, and piston amplitudes ranging from 6 to 11 mm. The total NaK mass flow 

to both convertors ranged from 500 to 900 g/s. This test met all objectives and the test unit operated as 

expected. 

1.0 Introduction 

Free-piston Stirling power conversion has been identified as a viable option for potential FSP systems 

on the Moon and Mars (Refs. 4 and 5). Recent studies have examined the use of Stirling convertors 

coupled to a low-temperature (<900 K), uranium-dioxide fueled, and liquid-metal-cooled reactor for 

potential lunar application in the year 2020. The concept resulted from a 12-month NASA and 

Department of Energy (DOE) study that examined design options and development strategies based on 

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

terrestrial-derived reactor technology and conventional materials. The low development risk approach 

was selected over other options that could offer higher performance and/or lower mass. 

To further reduce development risk and address design questions related to the free-piston Stirling 

FSP system, NASA has begun long lead technology development on multikilowatt Stirling power 

conversion under the Fission Surface Power Technology Project. A key step in the development of 

Stirling technology relative to FSP systems is to demonstrate that a Stirling convertor can be successfully 

integrated with a pumped liquid metal loop. 

Liquid metal loop integration involved two separate subtasks. First, a pair of 1-kW commercial freepiston Stirling convertors were procured and assembled into a test rig. In parallel, a liquid metal heat 

exchanger was designed and fabricated for use on the 1-kW convertors to permit integrated testing with 

an existing pumped NaK heat loop (Ref. 3) at MSFC. This activity was aimed at providing data to support 

the design of a full-scale FSP power conversion unit (PCU) prototype for use in an end-to-end system 

Technology Demonstration Unit (TDU) test. The TDU test would be conducted with a pair of 6-kW 

opposed piston heat engines coupled to a liquid metal reactor simulator and a full-scale radiator in 

thermal vacuum. 
NASA/TM—2011-216266 3 

NASA Glenn of Cleveland, OH; SEST Inc., Middleburg Heights, OH; and Sunpower Inc., Athens, OH, 

teamed to develop a NaK heat exchanger and heater head design for the P2A convertors. While earlier 

NASA Glenn efforts (Ref. 2) have clearly demonstrated the application of liquid metals as the heat transport 

medium for a Stirling cycle convertor, it is important to note that these heat exchangers utilized heat pipes in 

the energy transfer process. The resulting condensing liquid metal vapor heat transfer characteristics are 

totally different from the conditions expected in the hot-end heat exchanger in the current pumped liquid 

metal loop heat transport system. During the design phase of the heat exchanger, careful consideration was 

given to the unique manufacturing and assembly constraints imposed by the P2A hardware. For example, 

the NaK heat exchanger was to be fabricated by welding a jacket to the outside of a P2A heater head. The 

P2A heater head consists of a stainless steel dome with a finned copper heat exchanger brazed to the inside 

surface. It was extremely important that the melt temperature of the braze material was not exceeded during 

the weld operation. The relative performance and hardware integration risk of each potential approach was 

evaluated. Throughout the design process, an effort was made, whenever possible, to employ currently 

understood liquid metal system “best practices” so as to ensure that the resulting heat exchanger is as 

representative as possible to those needed in future FSP systems. Particular emphasis was placed on the use 

of materials with proven track records (316 stainless steel), proven joining techniques (emphasis on 

welding), and maintaining low liquid metal flow velocities. 

Computation Fluid Dynamic (CFD) analyses techniques were used to guide the design of the NaK 

heat exchanger design using FLUENTTM (ANSYS, Inc.). Several numerical approaches that directly 

solved the Navier-Stokes equations with a specified temperature or heat flux profile along the heater head 

were employed. The effects of gravity, inlet flow distortion, and exiting pressure drop were included in 

this analysis. A sampling of the results of the CFD analysis for the selected NaK heat exchanger design is 

shown in Figure 2. 

The resulting integrated liquid metal heat exchanger, P2A heater head, and convertor configuration 

for a single convertor is shown in Figure 3. Detailed drawings of the P2A heater head design are shown in 

Appendix C. The dual-opposed convertor configuration employed two independent heat engines and heat 

exchanger assemblies mounted “head to head” so as to minimize vibration-induced loads on the test 

setup. A mechanical support structure connected the alternator pressure vessel portions of the two 

convertors and acted as the mounting structure for the entire assembly within the vacuum chamber 

portion of the FSP–PTC. A common supply line from the test facility provided the liquid metal to each 

convertor. The convertors mounted in the MSFC test facility are shown in Figure 4. 

2.0 Purpose of Test 

There were four major goals planned for this test: (1) To gain the experience of integrating a Stirling 

power convertor with a pumped NaK loop. Lessons learned in this process will be useful in making 

design decisions for future systems including the TDU and future flight or flight-like systems. (2) To 

evaluate the performance of the custom-made NaK heater head. The most significant difference between 

baseline testing (electrically heated) and NaK testing is the method of thermal input, so differences in 

performance from the baseline data could be used to evaluate the design of the heater head and heat 

exchangers. (3) To better understand the effects of a pumped fluid heat source on Stirling operation. 

During baseline testing, hot-end temperature was affected by a single parameter, the input electrical 

power from the heater. During testing at MSFC, the P2A hot-end temperature is affected both by NaK 

temperature and NaK flow rate. Running at the same hot-end temperature, using different values of flow 

rate and NaK inlet temperature, could be used to improve Stirling cycle analysis and system optimization. 

(4) To evaluate the system response transient scenarios such as loss of heater power, stall and restart, and 

loss of NaK flow. 
NASA/TM—2011-216266 4 

3.0 Test Facility 

The FSP–PTC mounted in a 9-ft-diameter vacuum chamber is shown in Figures 4 and 5. The usable 

internal length is 18 ft and a rail structure and support table provides a surface for mounting of hardware 

systems. The chamber can reach an ultimate vacuum level in the low 10–7 torr range or better and can be 

pumped by a combination of four diffusion pumps (32 000 l/s each) backed by three roughing pumps 

(34 000 l/min each). However, only the roughing pumps were used for the FSP–PTC for the Stirling 

convertor testing. Primary test article power is provided by a 1.5-MW switchboard unit (480 VAC 3–P 

(three-phase)) and is distributed to four racks of alternating current (ac) to direct current (dc) power 

supplies. Each of these racks is equipped with four 15-kW (150-VDC) supplies for a total of 32 supplies 

capable of delivering up to 480 kW of power. Four power supplies were used to power the FSP–PTC core 

simulator (heat source). A master power system program (LabVIEW based) controls the power supplies, 

regulating the power per supply and providing any special ramping or profiling that is required. This system 

has been used very successfully to provide high-speed power supply response. Data is captured and 

recorded on a Citadel database system using a number of LabVIEW-based virtual instrument programs. A 

local instrumentation network has been established to route the flow of information in the test facility. 

Control and feedback signals (valves, pressure transducers, etc.) are processed with National Instruments 

Field Point modules while thermocouple data is processed using an IO-Tech DAQ Scan system currently 

configured for 168 channels (capacity up to 896 channels). Four cameras are mounted inside the vacuum 

chamber for increased view coverage of the experiment and chamber prior to entry by personnel. 

A Chromalox water circulating temperature controller (model CMX–250–9) was used to provide 

cooling water to the Stirling power convertor. The Chromalox controller was used to control both the 

cooling water temperature and flow rate to the Stirling convertor. 

Figure 6 shows a rendering of the FSP–PTC major component configuration. The system was 

designed to be gravity drained, consistent with previous circuit designs. Due to the size of the Stirling 

engines and other components, care was given to placement of all the components. Taking advantage of 

the rebuild, many design upgrades and improvements were incorporated. The layout shown was selected 

to provide the greatest access to the system components by technicians and engineers as well as provide 

complete test functionality. All connection and disconnection points were relocated to the front of the 

chamber to facilitate safe and rapid disconnection of experiment in the event of a NaK spill. Cameras and 

LED (light-emitting diode) lights were added to the chamber to provide better illumination and more 

comprehensive visual inspection of system after test. 

The core, heat exchanger, ALIP (Annular Linear Induction Pump), valve, flow meter, and remoteoperated valve were reused from previous NaK testing. To accommodate the increase in NaK volume, 

new lower and upper reservoirs were constructed. The tubing wall thickness was reduced from 0.095 to 

0.065 in. Pressure and delta pressure devices were used as in systems prior. Overflow tanks were 

upgraded with overflow indicators and drain valves. Figure 7 shows the FSP–PTC completed and 

installed into the vacuum chamber prior to insulation weeks before testing. 

4.0 Test Article 

As previously mentioned, a pair of commercially available 1-kWe P2A free-piston Stirling power 

convertors were purchased from Sunpower in 2007. The P2As are designed to produce 1.1 kWe of output 

power at their design operating conditions of 550 C hot-end temperature, 50 C cold-end temperature, a 

mean working space pressure of 3.0 MPa, and a piston amplitude of 10 mm. The working space fluid is 

helium. The P2A is a beta-type Stirling convertor consisting of two moving parts: a displacer piston and a 

power piston. A linear alternator connected to the power piston converts mechanical energy into 

electricity. The P2A was originally designed to operate in a cogeneration system (Ref. 1). Cogeneration is 

the use of a heat engine to simultaneously generate both electricity and useful heat. A side-by-side 

comparison of the commercially available P2A and the P2A as modified for the NaK test is shown in 

Figure 8. 
NASA/TM—2011-216266 5 

Each NaK heater head was insulated using multilayer insulation (MLI). The MLI consisted of four 

layers of stainless steel foil (annealed temper type 304, 0.002-in.thick, and maximum temperature of 

870 °C), separated by three layers of 0.125-in.-thick fiberglass insulation paper (temperature range of 

−220 to 650 °C; heat flow rate of 1.68 W by cm/m2

 at 24 °C). The P2A configured with the NaK heater 

head with the MLI installed is shown in Figure 9. 

5.0 Test Procedure 

At the beginning of each test day, the Stirling convertor data acquisition system time clock was 

synchronized with the FSP–PTC facility computer system. The Stirling convertor cooling water pump 

was turned on to provide a water flow of ten lpm to each convertor at a temperature of 25 °C. The 

convertors were then pressurized with helium to the manufacturer’s recommended charge pressure of 

363 psia with the convertor at 25 °C. The helium working fluid had to be topped off daily to compensate 

for a helium leak (~1 psi per hour) believed to be located in the piston/displacer position transducers. 

After pressurization, the cooling water temperature set point was changed to the desired cold-end 

temperature for the data points to be acquired. The convertors were then briefly motored to verify the 

piston motions were centered properly and that their mean position did not drift. The NaK pump was then 

powered up at a low/moderate flow setting while the NaK temperatures and flow rates were monitored to 

ensure normal operation of the NaK system. Next, the NaK pump was adjusted to provide the maximum 

flow rate and the NaK heaters were switched on. The Stirling convertor pistons were locked in place 

using the convertor control system until the convertor hot-end temperatures reached 250 °C. At this point, 

the convertors were motored briefly (a few seconds) at a piston amplitude of ~3 mm, then motored at a 

piston amplitude of 6 mm (this is the piston amplitude that engages the gas bearings). The convertors 

were started this way to avoid piston/displacer contact. As the hot-end temperature increased, the piston 

amplitude was increased until both the hot-end temperature and piston amplitude reached their desired set 

points for the data point to be acquired. 

Descriptions of transient test procedures differed depending on the nature of the test (high flow 

startup, low flow startup, convertor stall, etc.). These procedures are detailed in the Test Plan located in 

Appendix A, as well as in Section 6.0. 

6.0 Results and Discussion 

6.1 Steady-State Testing 

Steady-state testing was conducted in two phases. During the first phase, the performance of the 

convertors was measured at most of the same operating conditions (temperatures and piston amplitudes) 

for which data was acquired during baseline testing using electric heater heads, as described in the 

Background section. During these tests, the convertors were operated at hot-end temperatures ranging 

from 400 to 550 °C, cold-end temperatures from 30 to 70 °C, and piston amplitudes ranging from 6 to 

11 mm, as described in the test plan found in Appendix A. The performance map testing was conducted 

with the NaK pump operating at full power. The total mass flow to both convertors at full pump power 

ranged from 700 to 900 g/s. The NaK flow tended to decrease as the test proceeded and the pump 

temperature increased. The steady-state test data can be found in Appendix B. It should be noted that the 

data contained in the tables of Appendix B were obtained by averaging the measurements over a 5-min 

time period. The first column in each table is labeled “Test Pt.” The test point numbers shown in this 

column correspond to the operating conditions given in the Performance Map table (Table I) of the test 

plan of Appendix A. For the test points denoted with the letter “B,” these points were not originally 

planned, but were added by the test director to compensate for planned test points that could not be 

achieved. Some of the planned test points could not be achieved mostly due to instability in the 

electronics used to control the engines at the operating conditions of those planned test points. 
NASA/TM—2011-216266 6 

Figure 10 shows the combined power output of both convertors plotted as a function of piston 

amplitude that was acquired during the first phase of steady-state testing. The power output of the 

convertors using NaK for thermal input is very similar to the baseline data acquired for the convertors 

equipped with the electric heater heads. Power output increases with both temperature ratio and piston 

amplitude. The power output at the design condition was 2026 W for the convertor pair. The maximum 

power output was 2375 W at a hot-end temperature of 550 °C, cold-end temperature of 50 °C, and piston 

amplitude of 11 mm. A tabular collection of all performance map data can be found in Appendix B. It 

should be noted that Appendix B includes an estimate of convertor efficiency; however, due to large 

uncertainties in both NaK mass flow as well as temperature difference across the NaK head, the heat 

input to the convertors and therefore the convertor efficiency measurement have large associated errors. 

Consequently, efficiency data is considered unreliable and is not reported in this section. 

Figures 11 and 12 compare the power output of the dual P2As configured with the NaK heater heads 

with that of the P2As configured with the electric heater heads (baseline data). The convertors configured 

with the NaK heater heads either equaled or outperformed the convertors configured with electric heater 

heads. The comparisons shown in Figures 11 and 12 are representative of comparisons made at other 

temperature ratios as well. These comparisons verify that Stirling convertors can be interfaced with a 

pumped NaK loop successfully, without any sacrifice to engine performance. 

During the second phase of steady-state testing, the sensitivity of the Stirling convertor electrical 

output power to changes in NaK mass flow was measured. Figure 13 shows the total power output at 

design hot-end (550 °C) and cold-end (50 °C) temperatures at piston amplitudes of 8, 9, and 10 mm. Over 

the range of flow rates tested, convertor electrical output was insensitive to reductions in NaK mass flow. 

The maximum NaK mass flow in each case was limited by the NaK pump output capacity and the lower 

limit was conservatively chosen to constrain the temperature difference across the heater head and 

thereby limit thermal stresses. In addition, the power requirement of the NaK pump decreased from 

roughly 4 kW to roughly 2 kW for a reduction in mass flow from 900 to 600 g/s, suggesting that 

reductions in mass flow during startup could result in substantial energy savings. This statement must be 

qualified, however, because the pump used in this test is operating far from its design point, and is 

therefore very inefficient, so the benefit of reducing mass flow using a more prototypic NaK pump would 

be less significant. 

6.2 Transient Testing 

Transient testing was conducted to study fault tolerance scenarios, possible startup scenarios, and 

reactivity feedback response of the reactor simulator. 

Three fault tolerance scenarios were examined: (1) NaK pump loss, (2) heat source loss (i.e., loss of 

reator), and (3) shutdown/restart of Stirling convertors. These scenarios were examined to determine the 

effects on the system and to determine possible methods of recovery. 

Figure 14 shows the system response to the loss of the NaK pump with the convertors still running. 

Within 30 s the average hot-end temperature had dropped more than 50 °C, which greatly exceeded the 

predetermined limit of 10 °C per min and the temperature gradients across the heater heads had exceeded 

their upper limit of 40 °C so the test was stopped by stalling the convertors. At the conclusion of this test 

there was a slug of relatively cold NaK (490 °C) in the region of the heater heads. The remainder of the 

loop, with the exception of the NaK heater remained at 550 °C. During this time, the NaK heater 

remained on causing the stationary NaK within the heater to reach 620 °C. To avoid thermally shocking 

the convertor heater heads, the pump was not restarted and the entire system was allowed to cool to 

ambient temperature. This scenario is regarded as a dangerous one since it causes NaK temperatures to 

change quickly and creates hot and cold slugs of fluid throughout the system, which prevents restart. This 

study suggests that both the NaK heater and the convertors should be shut down immediately in the event 

of NaK pump loss. Since immediate stall of the convertors results in an immediate stoppage of heat 

transfer to the cold end, considerations will also have to be made to prevent freezing of the water loop. 
NASA/TM—2011-216266 7 

Figure 15 shows the response of the system to a loss of heater power. In this scenario, the hot-end 

temperature gradually decreases, reducing the heat input to the convertors, resulting in decreased electric 

power output. As the heat input to the convertors approaches the heat input to the NaK due to the 

inefficiency of the NaK pump, an equilibrium temperature is reached. As stated previously, the pump 

used in this test operates inefficiently, which causes this equilibrium temperature to be somewhat higher 

than it would be in a more prototypic system. This failure mode is thought to be more benign because 

changes in heat input to the convertors occurs slowly, resulting in slow temperature changes on both the 

hot end and cold end. However, it should also be noted that the cooling rate of the NaK seen during this 

test is specific to this system. If other systems were to cool the NaK at a faster rate, it could violate a 

system constraint on transient heating and cooling time. If this were the case, some type of piston 

amplitude modification would be required to reduce the amount of heat removed from the NaK by the 

convertors. 

There is currently no established startup scenario for the proposed FSP system or the TDU, so it is 

important to note that these scenarios may not be representative of actual startup scenarios. The startup 

scenario tests are simply an examination of the trade between optimizing conditions within the reactor 

and minimizing the required startup energy. It is important to note that the relative importance of each of 

these is not currently well defined. Nevertheless, several startup scenarios were run, each following a 

similar form: (1) the NaK pump was initiated to deliver flow at the desired mass flow rate, (2) the heater 

was then used to elevate the NaK temperature to an initial set point, (3) the convertors were started and 

operated at an initial piston amplitude of 6 mm, (4) the system was then allowed to reach steady state, and 

(5) the NaK temperature was then ramped up to the Stirling convertor design hot-end temperature of 

550 °C while the piston amplitude was ramped to 10 mm (design amplitude). The parameters varied 

during startup testing were the NaK mass flow and the initial temperature set point. A full test plan and 

procedural description can be found in appendix A. The initial Stirling hot-end temperature set point 

ranged from 200 to 500 °C and the NaK mass flow ranged from 600 to 900 g/s (for both convertors). The 

results of the startup (transient) testing are shown in Figures 16 through 21. The data shows that the 

Stirling convertors are quite robust in their ability to handle these starting conditions. 

Figure 22 shows the transient data taken when the convertor pistons were stalled. The hot-end 

temperature was maintained at a constant value by the heater controller so the heater power was reduced 

accordingly. In this test the convertors were then restarted at a piston amplitude of 6 mm, then brought to 

full amplitude of 10 mm. The convertors recovered to full power almost immediately. 

Data acquired during the reactivity portion of the testing are shown in Figures 23 through 30. 

Figure 23 shows the system response to a convertor stall with the heater in reactivity feedback control, 

which simulates the response of a fission reactor. At first glance, this fault scenario appears somewhat 

benign because it is feasible to recover to full power if the convertors can be restarted and if the 

temperature fluctuations of the reactor are not large enough to cause serious problems on the hot end. 

However, in this test, the cold-end temperature was being controlled using a proportional-integralderivative (PID) controller on the water loop, so cold-end temperature remained constant despite a 

dramatic reduction of the heat input to the water loop. In a flight system, this decrease in heat input could 

cause a decrease in the cold-side temperature that might potentially freeze the water coolant. 

The other class of transient tests that were run examined the system response to various perturbations 

when the NaK heater controller is simulating the response of a nuclear reactor using a point kinetics 

algorithm. These tests were performed to aid modeling efforts and estimate time constants for system 

response, when the NaK heater behavior is more characteristic of a reactor. Figures 24 through 27 show 

the system response to a 1 mm increase, 1 mm decrease, 2 mm increase, and 2 mm decrease in piston 

amplitude, respectively. 

Figures 28 and 29 show the system response to step changes in NaK mass flow. 

Figure 30 shows the system response to an insertion of reactivity. 
NASA/TM—2011-216266 8 

7.0 Summary of Results 

The 1-kW Stirling convertors were shown to produce the same power at nominal operating conditions 

whether heated by electrical resistance heaters or a pumped NaK loop. Full-power operation at nominal 

operating conditions was further demonstrated over a range of NaK mass flows (530 to 850 g/s total for 

convertor pair). Over the range of mass flows tested, convertor performance was insensitive to NaK mass 

flow at both nominal and off-nominal piston amplitude. Performance maps generated using the pumped 

NaK loop for thermal input consistently show the convertors performing as well or better than they had 

during operation with electric heater heads. A potential explanation for the slightly better performance is 

that the convertor-body radiation losses were reduced due to operation in vacuum. Uncertainty in the 

measurement of thermal input to the Stirling convertors made it difficult to obtain reliable efficiency data; 

however, consistent improvements in power output when operating in the pumped NaK configuration at 

similar operating conditions suggest improvements in the efficiency over those measured during electrical 

baseline testing. 

Several possible startup tests were conducted to generate data relevant to future TDU and FSP system 

startups. The Stirling convertors were started at several different hot-end temperatures ranging from 200 

to 500 °C. This data shows that the Stirling convertors are sufficiently robust to handle a wide range of 

startup scenarios. This flexibility will be useful to future system designers who will likely find restrictions 

on reactor startup and required pump power to be more constraining. In addition, startup scenarios were 

run at different NaK mass flow rates. This data shows that a reduction of mass flow from 850 to 600 g/s 

(total for convertor pair) resulted in a reduction in required pump power from ~4000 to ~2000 W. 

Furthermore, reductions in mass flow were shown to have little effect on total time to reach nominal 

operation. This data suggests that startup scenarios should occur at low mass flows to minimize the total 

energy required for pumping. However, we must again qualify this statement by noting that the NaK 

pump used in this test is operating far from its nominal operating condition and therefore exaggerates the 

benefits of reducing NaK flow rate and that the choice of startup scenario will have to take into account 

reactor requirements in addition to pump power restrictions. Further analysis of a more representative 

system would be necessary to draw more specific conclusions. 

Fault recovery tests were also conducted to assess the effect of component failures and to identify 

possible recovery procedures. The loss of the heat source was shown to be a somewhat benign failure for 

this system resulting in slow reductions in hot-end temperature and power output. The convertor stall test 

revealed that the system could return quickly to full power operation if control of the convertors is 

regained. However, precautions must be taken to ensure that a sudden reduction in heat flow to the 

Stirling convertor cold end is handled appropriately. Finally, simulation of a NaK pump failure while 

maintaining convertor operation revealed that the NaK contained in the Stirling convertor heater heads 

and heater head metal temperatures will drop rapidly. During this time transient, temperature ramp-rate 

restrictions are likely to be violated as well as maximum temperature gradient restrictions within the hot 

end. In addition, if the convertors are permitted to run without NaK flow, the NaK contained in the heater 

head volume could overcool and cause a thermal shock in the convertor heater head once NaK pump 

operation is restored. The only method of recovery is to wait for the system to reach thermal equilibrium, 

which could take many hours. Therefore, the convertors should be stopped immediately in the event of a 

NaK pump failure. Precautions must then be taken to accommodate the loss of heat input to the coolant. 

The NaK heater controller was used to simulate reactivity feedback of a fission reactor. The transient 

response of the system to changes in mass flow, piston amplitude, and reactivity insertion were evaluated. 

These were considered follow-on tests done to assist the efforts of future controller designers and system 

modelers. The data taken during these tests are presented for completeness, but the usefulness of the 

results and the conclusions drawn are outside the scope of the paper. 
NASA/TM—2011-216266 9 

8.0 Conclusions 

The operation of a pair of kilowatt-class Stirling power convertors using a pumped NaK loop for 

thermal input was demonstrated. The convertors generated full power at nominal operating conditions and 

performed as well or better than they did when heated electrically. 

Startup scenarios showed that Stirling convertors may be initiated through a wide range of hot-end 

temperatures and NaK flow rates suggesting that limitations on startup will likely come from either 

reactor or pump power requirements. 

Fault tolerance tests were run to recognize the risks associated with several fault scenarios, which 

may be encountered in future system-level testing. 

Figure 1.—Baseline performance map with P2A convertors configured with electrically heated heads. 

Power shown in plot is the total power for two convertors. 
NASA/TM—2011-216266 10 

Figure 2.—NaK flow particle trace and heater head temperature profile assuming a NaK mass flow rate of 

0.36 kg/s and 4000 W of thermal energy transfer into the Stirling convertor. 

Figure 3.—Single P2A free-piston Stirling power convertor with NaK heat exchanger prior to 

installation of multilayer insulation (MLI). 
NASA/TM—2011-216266 11 

Figure 4.—Dual P2A Stirling power convertors mounted in the MSFC test facility. 

Figure 5.—Dual P2A Stirling power convertors installed in FSP–PTC test facility. 
NASA/TM—2011-216266 12 

Figure 6.—Rendering of dual P2A Stirling power convertors installed in FSP–PTC test facility. 

Figure 7.—FSP–PTC completed and installed into the vacuum chamber prior to insulation. 
NASA/TM—2011-216266 13 

Figure 8.—Comparison of commercially available P2A configuration with modified configuration. 

Figure 9.—MLI installed on NaK heater head of P2A Stirling power convertor. 
NASA/TM—2011-216266 14 

Figure 10.—Combined power output of dual P2A Stirling power convertors configured with NaK 

heater heads vs. piston amplitude. 

Figure 11.—Combined power output of dual P2A Stirling power convertors configured with NaK 

heater heads vs. piston amplitude compared with baseline data. 
NASA/TM—2011-216266 15 

Figure 12.—Combined power output of dual P2A Stirling power convertors configured with NaK 

heater heads vs. piston amplitude compared with baseline data. 

Figure 13.—Sensitivity of P2A Stirling power output for various NaK mass flow rates. 
NASA/TM—2011-216266 16 

Figure 14.—Transient operating conditions―simulate loss of the ALIP pump and intermediate 

NaK loop at full NaK flow―transient condition 1. 
NASA/TM—2011-216266 17 

Figure 15.—Transient operating conditions―simulate loss of reactor power and primary NaK loop at 

full NaK flow―transient condition 2. 
NASA/TM—2011-216266 18 

Figure 16.—Transient operating conditions―minimum temperature startup at full NaK flow―transient 

condition 3. 
NASA/TM—2011-216266 19 

Figure 17.—Transient operating conditions―medium temperature startup at full NaK flow―transient 

condition 4. 
NASA/TM—2011-216266 20 

Figure 18.—Transient operating conditions―full (high) temperature startup at full NaK flow―transient 

condition 5. 
NASA/TM—2011-216266 21 

Figure 19.—Transient operating conditions―minimum temperature startup at 75 percent NaK flow―

transient condition 6. 
NASA/TM—2011-216266 22

Figure 20.—Transient operating conditions―medium temperature startup at 75 percent NaK flow―

transient condition 7.
NASA/TM—2011-216266 23 

Figure 21.—Transient operating conditions―full (high) temperature startup at 75 percent NaK flow―

transient condition 8. 
NASA/TM—2011-216266 24 

Figure 22.—Transient operating conditions―simulate shutdown/restart of Stirling convertors―transient 

condition 9. 
Figure 23.—System response to Stirling convertor stall with reactivity feedback control. 

NASA/TM—2011-216266 25
NASA/TM—2011-216266 26 

Figure 24.—System response to 1-mm Stirling convertor piston amplitude increase with reactivity 

feedback control. 
NASA/TM—2011-216266 27 

Figure 25.—System response to 1-mm Stirling convertor piston amplitude decrease with reactivity 

feedback control. 
NASA/TM—2011-216266 28 

Figure 26.—System response to 2-mm Stirling convertor piston amplitude increase with reactivity 

feedback control. 
NASA/TM—2011-216266 29 

 

Figure 27.—System response to 2-mm Stirling convertor piston amplitude decrease with reactivity 

feedback control. 
NASA/TM—2011-216266 30 

Figure 28.—System response to increase in NaK mass flow with reactivity feedback control. 
NASA/TM—2011-216266 31 

Figure 29.—System response to decrease in NaK mass flow with reactivity feedback control. 
NASA/TM—2011-216266 32 

Figure 30.—System response to positive reactivity insertion. 
NASA/TM—2011-216266 33 

Appendix A.—Test Plan 
NASA/TM—2011-216266 34 

Revision History 

Revision Description Date 

0 Original issue April 2009 

Configuration Management 

The latest version of this document is maintained on the RPT eRoom as a controlled document. Prior 

to printing, it is the user’s responsibility to verify this document is the current revision. Printed copies of 

this document will be considered uncontrolled. The test plans are located at 

https://collaboration.grc.nasa.gov/eRoom/NASAm1f1/RPTThermalEnergyConversionBranch/0_92eb0 

Background 

In 2007, two P2A (formerly known as EG–1000) 1-kW free-piston Stirling power convertors were 

procured from Sunpower Inc., of Athens, OH. The P2As are designed to produce 1.1 kWe at their design 

operating conditions of 550 C hot-end temperature, 50 C cold-end temperature, and a mean working 

space pressure of 3.0 MPa. The P2As are typically configured with a gas burner for thermal energy input; 

however, the P2As delivered to Glenn for performance map testing replaced the gas burners with electric 

cartridge heaters to simplify testing. Testing performed at Glenn with electric heating established baseline 

convertor performance. After baseline testing was completed, the convertors were retrofitted with new 

heater heads to allow the P2A convertors to interface with a pumped NaK loop at MSFC. This test will 

demonstrate Stirling convertor electrical power generation using a pumped liquid metal heat source. 

Purpose of the Test 

There are four major goals of testing at MSFC: (1) To gain the experience of integrating a Stirling 

power convertor with a pumped NaK loop. Lessons learned in this process will be useful in making 

design decisions for future systems including the Technology Demonstration Unit (TDU) and future 

flight or flight-like systems. (2) To evaluate the performance of the custom-made NaK heater head. The 

most significant difference between baseline testing and NaK testing is the method of thermal input, so 

differences in performance from the baseline could be used to evaluate the design of the heater head and 

heat exchangers. (3) During baseline testing, hot-end temperature was affected by a single parameter, the 

input electrical power from the heater. During testing at MSFC, the P2A hot-end temperature is affected 

both by NaK temperature and NaK flow rate. Running at the same hot-end temperature, using different 

values of flow rate and NaK inlet temperature could be used to improve Stirling cycle analysis and 

system optimization. (4) To evaluate the system response transient scenarios such as loss of heater power, 

stall and restart, and loss of NaK flow. 

Safety Precautions and Notes 

 If any step does not proceed as planned, bring the system to a safe state, cease action, and notify 

cognizant engineer. 

 For the first few days of testing, a minimum of two people shall participate in operating the P2A 

Stirling convertors for executing this test plan. 

 The Stirling convertor cooling water must be flowing at ten lpm per convertor prior to flowing 

hot NaK. 

 The temperature drop (NaK inlet–NaK outlet temperature) across the Stirling NaK heat 

exchanger (heater head) must be kept below 40 °C. The circumferential temperature gradient for 

each Stirling heater head (as measured by thermocouples TCExHOT5 through TCExHOT8) must 

be kept below 30 °C. 
NASA/TM—2011-216266 35 

 The ac bus current must be maintained between 2 and 7 Arms. 

 The alternator power factors must be monitored to ensure that when the voltage leads the current, 

the power factor remains above 0.94, and when the voltage lags the current, the power factor 

remains above 0.83. 

 The Stirling convertor heater heads should not be allowed to exceed 570 °C at any time. 

 Transient effects should be limited by taking small incremental steps in piston amplitude 

(0.5 mm). 

 Limit Stirling convertor output to 2.8 kWe (total for both convertors). 

Applicable Documents 

P2A–001A Instrumentation Rack Checkout Procedure for the P2A 

P2A–002A Data System Shutdown Check-Out Procedure 

P2A–003A Evacuation, Backfill, & Top-Off Procedure for the P2A Convertor 

P2A–004A Centering Procedure for the P2A Convertor 

P2A–005A Startup Procedure for Operating P2A Stirling Convertor with Pumped NaK Loop 

P2A–007A Manual Shutdown Procedure for the P2A with Pumped NaK Loop 

Fission Surface Power Primary Test Circuit (FSP–PTC) 

MSFC facility operators are responsible for operating the FSP–PTC facility during this test. Glenn 

personnel are responsible for operating the Stirling engines. Glenn test operators will notify the MSFC 

facilities operators when adjustments to the NaK parameters are needed. The parameters to be controlled 

are NaK inlet (to the Stirling convertors) temperature and NaK flow rate. 

Test Plan 

1. Verify that P2A–001A (Instrumentation Rack Checkout Procedure for the P2A), P2A–002A (Data 

System Shutdown Check-Out Procedure), and P2A–003A (Evacuation, Backfill, & Top-Off 

Procedure for the P2A Convertor), have been performed and that the piston limits have been set for 

the Failsafe Protection Circuit.

2. Verify that the LabVIEW system is properly configured for the test. See Table III for the settings.

3. Synchronize TIME between Glenn data acquisition system computer and the MSFC facility data 

acquisition system computer. 

4. Turn on the cooling fans for the engine loads and the data system rack.

5. Charge the P2As with helium to the design charge pressure of 363 psig at 25 C according to 

procedure P2A–003A. 

6. Bring the P2As to the startup operating point according to procedure P2A–005A. The initial hot-end 

temperature set point should be 400 C while the cold-end temperature and NaK flow rate should be 

the nominal value selected for the current test. Hot-end temperature is based on the average of the 

eight thermocouples placed on the heater head on either side of the acceptor. The cold-end 

temperature is defined as the average of the coolant inlet and coolant outlet temperatures. 

7. Once the startup set point has been reached, notify the MSFC facility operator to gradually increase 

NaK temperature to achieve the desired Stirling convertor hot-end temperature. Do not let any 

individual heater head temperature reading exceed 570 C. To minimize the NaK temperature 

difference across the heater head, it is desirable to run at minimum piston amplitude. The minimum 

safe P2A piston amplitude is 6 mm. Also, the minimum ac bus power output is 2A. Both of these 

constraints must be monitored during heatup. 

8. Once the desired steady-state temperature has been reached, gradually increase the piston amplitude 

to the desired value. Increases in piston amplitude will result in larger temperature gradients across 
NASA/TM—2011-216266 36 

the NaK head. The largest allowable gradient (NaK inlet–NaK outlet temperature) is 40 C. If this 

limit is exceeded, the piston amplitude must be reduced. If the piston amplitude is reduced to 6 mm 

and the temperature gradient is still above 40 C, the following steps must be performed: 

a. Shut down engines by setting the ac bus output voltages to 0. 

b. Notify MSFC NaK facility operator to turn off NaK heater and turn on NaK cooler while 

maintaining NaK flow. 

9. Obtain steady-state operation at the chosen set point (see Phase I—Steady-State Operating Conditions 

and Phase II—Transient Operating Conditions sections below) with the heater head average 

temperatures and average coolant temperatures within ±3 C of the set point and changing at a rate of 

less than 2 C per 10 min, and the alternator gas temperatures changing at a rate of less than 1 °C per 

10 min. 

10. Return to the reference set point of 400 C hot end at the end of each test day (set points within 

±3 C, and heater head average temperatures, average coolant temperatures, and alternator gas 

temperatures changing at a rate of less than 2 C over a 10 min period) and record the data so that it 

can be compared with the initial data point recorded at the beginning of the test day. Any 

discrepancies in convertor performance should be evaluated prior to the continuation of this test. 

11. Shut down convertors per the P2A–007A procedure. 

Phase I—Steady-State Operating Conditions 

Table I lists the convertor operating conditions (i.e., test points) that were either achieved or 

attempted at Glenn. Not all of these operating conditions could be reached due to either voltage 

limitations of the electric heater head (will not be an issue for the test at MSFC), or the ac bus power 

factor limitations. In Table I, an asterisk (*) denotes the subset of test points proposed as the minimum set 

for this test. Additional test points may be obtained if time permits. 

Table II lists the operating conditions used to examine the sensitivity of the Stirling engines to 

changes in NaK mass flow. The off-nominal mass flow rates appearing in Table II may result in an 

unacceptable circumferential temperature gradient (TCExHOT5 through TCExHOT8 must be kept below 

30 °C) across each NaK head. As a result, these values are subject to change or removal from the test 

matrix entirely. In Table II, an asterisk (*) denotes the subset of test points proposed as the minimum set 

for this test. Additional test points may be obtained if time permits. 

TABLE I.—PERFORMANCE MAP 

Test Pt. Thot (°C) Tcold 

(°C) 

Tratio Pist Ampl. 

(mm) 

NaK Mass 

Flow 

(kg/s-conv) 

400 50 2.55 10 .55 

1* 550 50 2.55 10 .55 

2* 550 50 2.55 11 .55 

3* 550 50 2.55 9 .55 

4* 550 50 2.55 8 .55 

5* 550 50 2.55 7 .55 

6* 550 50 2.55 6 .55 

400 50 2.55 10 .55 

 400 30 2.72 10 .55 

7 550 30 2.72 10 .55 

8* 550 30 2.72 9 .55 

9 550 30 2.72 11 .55 

 400 30 2.72 10 .55 

 400 70 2.40 10 .55 
NASA/TM—2011-216266 37 

TABLE I.—Concluded. 

Test Pt. Thot (°C) Tcold 

(°C) 

Tratio Pist Ampl. 

(mm) 

NaK Mass 

Flow 

(kg/s-conv) 

10* 550 70 2.40 10 .55 

11 550 70 2.40 9 .55 

12 550 70 2.40 11 .55 

400 70 2.40 10 .55 

 400 50 2.39 10 .55 

13 500 50 2.39 10 .55 

14 500 50 2.39 9 .55 

15 500 50 2.39 11 .55 

 400 50 2.39 10 .55 

400 30 2.55 10 .55 

16 500 30 2.55 10 .55 

17 500 30 2.55 9 .55 

18 500 30 2.55 11 .55 

400 30 2.55 10 .55 

 400 70 2.25 10 .55 

19 500 70 2.25 10 .55 

20 500 70 2.25 9 .55 

21 500 70 2.25 11 .55 

 400 70 2.25 10 .55 

400 50 2.24 10 .55 

22 450 50 2.24 10 .55 

23 450 50 2.24 9 .55 

24 450 50 2.24 11 .55 

400 50 2.24 10 .55 

 400 30 2.39 10 .55 

25 450 30 2.39 10 .55 

26 450 30 2.39 9 .55 

27 450 30 2.39 11 .55 

 400 30 2.39 10 .55 

400 70 2.11 10 .55 

28 450 70 2.11 10 .55 

29 450 70 2.11 9 .55 

30 450 70 2.11 11 .55 

400 70 2.11 10 .55 

31 400 50 2.08 10 .55 

32 400 50 2.08 9 .55 

33 400 50 2.08 11 .55 

 400 50 2.08 10 .55 

34 400 30 2.22 10 .55 

35* 400 30 2.22 9 .55 

36 400 30 2.22 11 .55 

400 30 2.22 10 .55 

37* 400 70 1.96 10 .55 

38 400 70 1.96 9 .55 

39 400 70 1.96 11 .55 

 400 70 1.96 10 .55 
NASA/TM—2011-216266 38 

TABLE II.—MASS FLOW SENSITIVITY 

Test Pt. Thot 

(°C) 

Tcold 

(°C) 

Pist Ampl. 

(mm) 

NaK Mass 

Flow 

(kg/s-conv) 

40* 550 50 10 .41 

41 550 50 9 .41 

42 550 50 8 .41 

43* 550 50 10 .27 

44 550 50 9 .27 

45 550 50 8 .27 

 400 50 MIN .55 

Phase II—Transient Operating Conditions 

1. Simulate loss of the ALIP pump/intermediate NaK loop at full NaK flow: 

1.1. Bring convertors to steady state at nominal operating condition (Thot = 550 °C, Tcold = 50 °C, 

and Piston Amplitude = 10 mm) with NaK flow rate of 0.55 kg/s. 

1.2. Notify the MSFC facility operator to turn off the NaK pump. 

1.3. Allow the system to run down with thermal energy stored in NaK and heater head structure 

until the power output of the Stirling convertors reaches 0 W. 

1.4. Set the voltage on the ac bus to 0 V, then press “enter” on both power supplies 

SIMULTANEOUSLY to stop convertors. 

1.5. Monitor minimum temperature limits on NaK loop to avoid freeze. NaK-78 freezes at about 

−11 °C. DO NOT RESTART THE NaK PUMPS UNTIL THE NaK TEMPERATURES 

THROUGHOUT THE LOOP HAVE STABILIZED. 

2. Simulate loss of reactor power/primary NaK loop at full NaK flow: 

2.1. Bring convertors to steady state at nominal operating conditions (Thot = 550 °C, Tcold = 50 

°C, and Piston Amplitude = 10 mm) with NaK flow rate of 0.55 kg/s. 

2.2. Notify the MSFC facility operator to turn off the NaK heater, but continue NaK flow. 

2.3. Allow the convertors to run down until their output power either stabilizes or reaches 0 W. 

2.4. Set the voltage on the ac bus to 0 V, then press “enter” on both power supplies 

SIMULTANEOUSLY to stop convertors. 

3. Minimum temperature system startup at full NaK flow: 

3.1. Motor convertors (Thot = 250 °C, Tcold = 50 °C, Piston Amplitude = 6 mm) with a NaK flow 

rate of 0.55 kg/s (per convertor) for 30 min. 

3.2. Notify the MSFC facility operator to ramp up the NaK temperature (at a rate not to exceed 

10 °C per min) to 550 °C. 

3.3. As the Stirling convertor hot-end temperatures rise, increase the piston amplitude (at a rate not 

to exceed 1 mm per 10 min) to 10 mm. 

4. Medium temperature system startup at full NaK flow: 

4.1. Motor convertors (Thot = 375 °C, Tcold = 50 °C, and Piston Amplitude = 6 mm) with a NaK 

flow rate of 0.55 kg/s (per convertor) for 30 min. 

4.2. Notify the MSFC facility operator to ramp up the NaK temperature (at a rate not to exceed 

10 °C per min) to 550 °C. 

4.3. As the Stirling convertor hot-end temperatures rise, increase the piston amplitude (at a rate not 

to exceed 1 mm per 5 min) to 10 mm. 
NASA/TM—2011-216266 39 

5. Full temperature system startup at full NaK flow: 

5.1. Motor convertors (Thot = 500 °C, Tcold = 50 °C, and Piston Amplitude = 6 mm) with a NaK 

flow rate of 0.55 kg/s (per convertor) for 30 min. 

5.2. Notify the MSFC facility operator to ramp up the NaK temperature (at a rate not to exceed 

10 °C per min) to 550 °C. 

5.3. Increase the piston amplitude (at a rate not to exceed 1 mm per min) to 10 mm. 

6. Minimum temperature system startup at 75 percent NaK flow: 

6.1. Motor convertors (Thot = 250 °C, Tcold = 50 °C, and Piston Amplitude = 6 mm) with a NaK 

flow rate of 0.41 kg/s (per convertor) for 30 min. 

6.2. Notify the MSFC facility operator to ramp up the NaK temperature (at a rate not to exceed 

10 °C per min) to 550 °C. 

6.3. As the Stirling convertor hot-end temperatures rise, increase the piston amplitude (at a rate not 

to exceed 1 mm per 5 min) to 10 mm. 

7. Medium temperature system startup at 75 percent NaK flow: 

7.1. Motor convertors (Thot = 375 °C, Tcold = 50 °C, and Piston Amplitude = 6 mm) with a NaK 

flow rate of 0.41 kg/s (per convertor) for 30 min. 

7.2. Notify the MSFC facility operator to ramp up the NaK temperature (at a rate not to exceed 

10 °C per min) to 550 °C. 

7.3. As the Stirling convertor hot-end temperatures rise, increase the piston amplitude (at a rate not 

to exceed 1 mm per 5 min) to 10 mm. 

8. Full temperature system startup at 75 percent NaK flow: 

8.1. Motor convertors (Thot = 500 °C, Tcold = 50 °C, and Piston Amplitude = 6 mm) with a NaK 

flow rate of 0.41 kg/s (per convertor) for 30 min. 

8.2. Notify the MSFC facility operator to ramp up the NaK temperature (at a rate not to exceed 

10 °C per min) to 550 °C. 

8.3. Increase the piston amplitude (at a rate not to exceed 1 mm per min) to 10 mm. 

9. Simulates shutdown/restart of Stirling convertors: 

9.1. Bring convertors to steady-state operation at moderate power level (Thot = 550 °C, Tcold = 

50 °C, and Piston Amplitude = 8 mm). 

9.2. Stall the convertors while NaK flow continues. 

9.3. Restart convertors as follows: 

9.3.1. Set the voltage on the ac bus to 50 V, then press enter on both power supplies 

SIMULTANEOUSLY. 

9.3.2. Set the voltage on the ac bus to 150 V, then press enter on both power supplies 

SIMULTANEOUSLY. Verify ~6 mm of piston amplitude. 

9.3.3. Gradually increase the ac bus voltage until the piston amplitude is 8 mm. 
NASA/TM—2011-216266 40 

TABLE III.—LABVIEW WARNING AND SHUTDOWN SETTINGS 

Parameter High alarm High 

warning 

Low 

warning 

Low 

alarm 

Action 

TCE1HOT1-8 570 °C 560 °C 10 °C 0 °C Alarm and Auto 

Shutdown 

TCE2HOT1-8 570 °C 560 °C 10 °C 0 °C Alarm and Auto 

Shutdown 

TCE1H2OIN 75 °C 73 °C 22 °C 20 °C Alarm and Auto 

Shutdown 

TCE2H2OIN 75 °C 73 °C 22 °C 20 °C Alarm and Auto 

Shutdown 

TCE1LAGAS 100 95 ------- ------- Alarm and Auto 

Shutdown 

TCE2LAGAS 100 95 ------- ------- Alarm and Auto 

Shutdown 

XPE1POS 12 mm 11.5 mm ------- ------- Alarm and Auto 

Shutdown 

XPE2POS 12 mm 11.5 mm ------- ------- Alarm and Auto 

Shutdown 

XDE1POS 12 mm 11.5 mm ------- ------- Alarm and Auto 

Shutdown 

XDE2POS 12 mm 11.5 mm ------- ------- Alarm and Auto 

Shutdown 

PRE1CHRG 486 psig 478 psig 348 psig 333 psig Alarm and Auto 

Shutdown 

PRE2CHRG 486 psig 478 psig 348 psig 333 psig Alarm and Auto 

Shutdown 

FME1COOL 16 lpm 15 lpm 8 lpm 7 lpm Alarm and Auto 

Shutdown 

FME2COOL 16 lpm 15 lpm 8 lpm 7 lpm Alarm and Auto 

Shutdown 
Appendix B.—Performance Map Data 

STEADY STATE (PHASE I—STIRLING CONVERTOR DATA) 

Test Pt. TCE1 

HOT1 

(°C) 

TCE1 

HOT2 

(°C) 

TCE1 

HOT3 

(°C) 

TCE1

HOT4 

(°C) 

TCE1

HOT5 

(°C) 

TCE1

HOT6 

(°C) 

TCE1

HOT7 

(°C) 

TCE1

HOT8 

(°C) 

TCE1 

PRVSL1 

(°C) 

TCE1

PRVSL2

(°C) 

TCE1

PRVSL3

(°C) 

TCE1

H2OIN 

(°C) 

TCE1

H2OUT

(°C) 

TCE1

LAGAS

(°C) 

TCE1 

PVH2OUT

(°C) 

1* 555.2 553.7 557.0 557.2 543.2 546.4 544.4 544.2 68.2 68.7 67.0 50.7 53.4 71.5 50.8 2* 555.6 554.5 557.7 557.7 541.6 545.6 543.4 543.0 71.1 72.2 69.9 50.6 54.0 75.1 50.8 3* 554.7 553.0 556.1 556.3 543.9 546.7 545.0 544.8 65.4 66.2 64.4 50.5 52.7 68.7 50.6 4* 554.0 552.0 555.6 555.4 544.9 547.5 545.9 545.9 62.4 63.1 62.0 50.6 52.7 65.5 50.6 5* 553.8 551.8 555.4 555.2 546.2 548.3 546.9 546.8 60.0 60.7 59.6 50.6 52.4 62.7 50.8 7* 556.0 554.8 557.9 558.1 543.6 547.2 545.4 545.1 48.5 49.4 47.5 30.5 32.8 51.9 30.9 8* 555.3 553.6 557.0 556.9 544.1 547.2 545.7 545.6 45.4 46.5 44.8 30.3 32.3 48.4 30.6 

10* 555.2 553.9 556.8 557.1 543.1 546.4 544.6 544.4 86.7 87.4 86.2 70.0 72.9 90.2 70.2 11* 554.8 553.4 556.4 556.6 544.4 547.2 545.5 545.3 83.3 84.3 82.7 69.5 71.9 86.4 69.7 12* 556.3 554.7 558.0 557.8 542.3 546.1 543.9 543.6 89.6 90.4 88.6 70.3 73.6 93.6 70.4 

13 504.6 503.4 506.1 506.2 493.1 496.0 494.5 494.2 66.8 67.2 65.7 50.6 53.3 70.1 50.8 14 504.7 503.0 505.9 506.2 494.8 497.3 495.7 495.6 63.6 64.2 63.1 50.4 52.7 66.8 50.5 15 504.5 503.4 506.3 506.0 491.4 494.8 493.1 492.7 69.5 70.3 68.4 50.7 53.7 73.3 51.0 17 504.9 503.2 506.2 506.5 495.0 497.4 496.0 495.8 44.8 45.2 43.8 30.3 32.5 47.9 30.2 

17B 504.7 502.8 505.8 506.1 496.1 498.3 496.9 496.7 42.5 43.1 42.0 30.2 32.0 45.5 30.2 

19* 504.6 503.3 506.3 506.5 493.3 496.6 494.6 494.5 85.6 86.4 85.0 70.5 73.5 88.8 71.2 20* 504.4 503.2 506.1 506.1 494.8 497.2 495.5 495.6 84.6 85.5 84.2 70.7 73.3 87.7 71.3 21* 504.5 503.4 506.4 506.4 491.7 495.0 493.3 493.0 89.2 89.7 87.9 70.9 74.3 92.5 71.8 

22 453.6 452.4 455.2 454.9 442.8 445.7 444.2 443.9 66.0 66.4 64.7 50.8 53.6 69.2 51.1 23 453.8 452.3 455.1 454.8 444.6 446.8 445.3 445.1 63.6 63.9 62.9 50.7 52.9 66.6 51.0 24 454.5 453.5 456.2 456.1 442.5 445.6 444.2 443.7 68.5 68.9 67.0 50.8 54.1 72.0 51.3 26 454.0 452.4 455.2 455.0 444.4 446.7 445.4 445.4 43.6 44.1 43.0 30.2 32.4 46.7 30.2 

26B 453.8 452.2 454.9 454.9 445.5 447.6 446.3 446.5 41.6 42.2 40.8 30.3 32.1 44.2 30.3 

28 454.8 453.6 455.9 455.8 444.1 446.7 445.4 444.9 84.9 85.1 83.9 70.6 73.4 88.3 71.0 29 454.7 453.4 455.8 455.7 445.4 447.9 446.5 446.4 81.9 82.3 81.5 70.3 72.7 85.0 70.8 30 454.7 453.8 456.0 455.8 442.4 445.5 444.0 443.5 87.3 87.6 86.2 70.4 73.9 90.9 71.0 31 405.0 404.0 406.0 405.9 394.4 397.2 395.8 395.5 67.4 68.3 66.1 50.4 52.9 70.6 50.9 32 405.0 404.0 406.0 405.7 395.7 398.0 396.9 396.8 65.0 65.5 64.0 50.4 52.2 67.9 50.7 

32B 404.8 403.6 405.6 405.7 397.0 398.8 397.6 397.7 62.4 63.2 61.6 50.3 52.0 64.9 50.8 

NASA/TM—2011-216266 41
STEADY STATE (PHASE I—STIRLING CONVERTOR DATA).—Concluded. 

Test Pt. TCE1 

HOT1 

(°C) 

TCE1 

HOT2 

(°C) 

TCE1 

HOT3 

(°C) 

TCE1

HOT4 

(°C) 

TCE1

HOT5 

(°C) 

TCE1

HOT6 

(°C) 

TCE1

HOT7 

(°C) 

TCE1

HOT8 

(°C) 

TCE1 

PRVSL1 

(°C) 

TCE1

PRVSL2

(°C) 

TCE1

PRVSL3

(°C) 

TCE1

H2OIN 

(°C) 

TCE1 

H2OUT 

(°C) 

TCE1

LAGAS

(°C) 

TCE1 

PVH2OUT

(°C) 

35 404.5 403.5 405.5 405.3 395.2 397.5 396.3 396.3 45.8 46.7 44.7 29.8 31.3 48.8 30.0 

35B 404.4 402.9 405.1 405.0 396.3 398.2 396.9 397.1 43.5 44.6 42.9 29.9 31.2 46.3 30.0 

37 404.6 403.8 405.9 405.8 394.5 397.0 395.5 395.2 85.2 85.7 84.0 70.6 73.4 88.4 71.3 38 404.6 403.6 405.6 405.8 395.9 398.0 396.7 396.6 83.3 84.1 82.8 70.7 73.3 86.4 71.2 39 404.7 404.1 406.2 406.1 392.9 396.0 394.4 394.0 87.9 88.4 86.5 70.5 74.1 91.2 71.4 

NASA/TM—2011-216266 42
STEADY STATE (PHASE I—STIRLING CONVERTOR DATA) 

Test 

Pt. 

TCE2

HOT1 

(°C) 

TCE2

HOT2 

(°C) 

TCE2

HOT3 

(°C) 

TCE2

HOT4 

(°C) 

TCE2

HOT5 

(°C) 

TCE2

HOT6 

(°C) 

TCE2

HOT7 

(°C) 

TCE2

HOT8 

(°C) 

TCE2 

PRVSL1 

(°C) 

TCE2 

PRVSL2 

(°C) 

TCE2 

PRVSL3 

(°C) 

TCE2

H2OIN 

(°C) 

TCE2 

H2OUT 

(°C) 

TCE2 

LAGAS 

(°C) 

TCE2 

PVH2OUT 

(°C) 

1* 556.9 556.2 556.8 556.3 543.4 540.9 547.1 542.5 66.6 67.3 66.7 50.8 53.2 69.9 51.4 2* 557.4 556.6 557.1 556.7 541.4 539.6 546.1 541.4 69.3 70.4 69.6 50.7 53.8 72.9 51.5 3* 556.1 555.2 555.8 555.5 544.0 541.1 547.3 543.0 64.3 65.1 64.3 50.7 52.9 67.3 51.3 4* 555.3 554.6 555.6 555.0 545.3 542.1 547.9 543.6 61.8 62.2 61.7 50.7 52.2 64.2 51.2 5* 555.0 554.3 555.5 554.8 546.8 543.1 548.7 544.5 59.5 59.9 59.5 50.6 51.8 61.6 51.1 7* 557.9 557.1 557.7 557.1 544.2 542.1 548.1 543.4 46.3 47.3 46.5 30.3 32.9 49.5 30.9 8* 556.6 555.8 556.7 556.2 545.2 542.6 548.5 543.9 43.6 44.6 43.9 30.1 32.3 46.6 30.6 

10* 556.8 556.0 556.6 556.1 543.8 541.2 547.0 543.1 85.3 86.1 85.5 69.9 72.7 88.4 70.8 11* 556.4 555.7 556.2 555.7 545.0 542.0 547.8 543.9 82.5 82.8 82.5 69.2 71.4 84.9 69.9 12* 557.4 556.9 557.4 557.2 542.6 540.4 546.5 542.4 88.0 89.0 88.2 69.8 73.2 91.3 70.9 

13 506.4 505.5 506.1 505.6 493.1 490.8 496.6 492.7 65.3 66.1 65.7 50.6 53.0 68.6 51.2 14 506.3 505.3 506.2 505.7 494.9 492.1 497.8 494.0 62.6 63.3 62.9 50.7 52.7 65.6 51.2 15 506.3 505.4 506.0 505.7 491.3 489.2 495.2 491.3 67.5 68.6 67.8 50.5 53.8 71.2 51.1 17 506.6 505.5 506.5 505.9 494.7 492.0 497.9 493.8 43.4 44.5 43.8 30.6 32.6 46.6 30.5 

17B 506.2 505.0 506.3 505.8 496.5 493.2 498.8 495.0 41.6 42.1 41.6 30.6 32.0 44.1 30.5 

19* 506.3 505.4 505.9 505.6 494.1 492.2 497.2 493.6 83.9 85.0 84.2 70.4 73.1 87.1 71.4 20* 506.0 505.2 505.9 505.4 495.7 493.3 498.0 494.6 83.2 84.0 83.3 70.6 72.8 86.1 71.6 21* 505.9 505.3 505.9 505.6 492.1 490.4 495.6 491.9 87.1 88.1 87.5 70.7 74.0 90.7 72.0 

22 455.3 454.3 454.8 454.5 442.8 440.6 445.4 442.5 64.6 65.5 64.9 50.9 53.4 67.8 51.5 23 455.2 454.2 454.8 454.5 444.3 442.1 446.7 443.7 62.4 63.2 62.7 50.8 52.9 65.3 51.3 24 456.3 455.3 456.0 455.5 442.4 440.4 445.4 442.4 66.2 67.2 66.7 51.0 53.8 70.1 51.6 26 455.2 454.2 455.1 454.9 444.7 442.1 447.3 443.7 42.2 43.1 42.5 30.5 32.4 45.2 30.5 

26B 455.0 453.9 455.0 454.7 445.9 443.1 448.1 444.6 40.5 41.2 40.8 30.3 31.8 43.0 30.6 

28 456.0 455.0 455.9 455.8 444.3 441.9 446.9 443.6 83.5 84.0 83.8 70.3 72.9 86.6 71.0 29 456.0 454.9 455.9 455.7 445.8 443.6 448.1 445.2 80.8 81.5 81.0 70.2 72.3 83.6 70.8 30 456.1 455.1 455.9 455.8 442.7 440.7 445.8 442.6 85.3 86.3 85.7 70.2 73.5 89.0 71.0 31 406.0 405.0 405.7 405.6 394.5 392.6 396.9 394.2 65.7 66.3 65.8 50.0 52.7 69.0 51.1 32 406.0 405.0 405.6 405.4 395.8 393.7 397.9 395.1 63.7 64.5 63.9 50.0 52.4 66.6 50.8 

32B 405.9 404.8 405.6 405.3 397.1 394.8 398.7 396.1 61.6 62.3 61.7 50.1 51.9 64.0 50.8 

NASA/TM—2011-216266 43
STEADY STATE (PHASE I—STIRLING CONVERTOR DATA).—Concluded. 

Test Pt. TCE2

HOT1 

(°C) 

TCE2

HOT2 

(°C) 

TCE2

HOT3 

(°C) 

TCE2H

OT4 

(°C) 

TCE2

HOT5 

(°C) 

TCE2

HOT6 

(°C) 

TCE2

HOT7 

(°C) 

TCE2

HOT8 

(°C) 

TCE2 

PRVSL1 

(°C) 

TCE2 

PRVSL2 

(°C) 

TCE2 

PRVSL3 

(°C) 

TCE2

H2OIN 

(°C) 

TCE2 

H2OUT 

(°C) 

TCE2 

LAGAS 

(°C) 

TCE2 

PVH2OUT 

(°C) 

35 405.6 404.5 405.1 404.9 395.3 393.0 397.4 394.5 44.5 45.3 44.6 29.8 31.8 47.4 30.3 

35B 405.4 404.2 404.9 404.6 396.4 393.9 397.9 395.2 43.0 43.1 42.6 30.0 31.7 45.1 30.5 

37 405.9 404.9 405.6 405.3 394.7 392.7 396.8 394.2 83.8 84.7 84.0 70.2 72.7 87.1 71.3 38 405.9 404.9 405.7 405.4 396.2 394.3 397.9 395.5 82.5 83.0 82.5 70.3 72.7 85.3 71.3 39 406.1 405.2 405.9 405.6 393.0 391.4 395.4 392.9 86.3 87.1 86.6 70.4 73.6 89.8 71.4 

NASA/TM—2011-216266 44
STEADY STATE (PHASE I—STIRLING CONVERTOR DATA) 

Test 

Pt. 

TCPV

H2OIN 

(°C) 

TC 

CABLE

TRAY 

(°C) 

XPE1

POS 

(mm) 

XDE1

POS 

(mm) 

LAE1 

VOLT 

(V) 

LAE1

CUR 

(A) 

LAE1

POW 

(W) 

XPE2

POS 

(mm) 

XDE2

POS 

(mm) 

LAE2 

VOLT 

(V) 

LAE2

CUR 

(A) 

LAE2

POW 

(W) 

TCPV

H2OIN 

(°C) 

OVR

STRK 

(V) 

FME1

COOL 

(l/min) 

FME2

COOL 

(l/min) 

1* 50.9 68.1 10.1 10.0 240.7 4.5 1026.8 9.9 9.7 241.2 4.3 991.2 50.9 0.0 10.7 10.8 2* 50.9 74.2 11.2 10.8 263.9 4.8 1193.2 10.9 10.6 264.4 4.6 1172.6 50.9 0.0 10.7 10.8 3* 50.8 61.4 9.1 9.2 217.7 4.1 859.9 8.9 9.0 218.1 4.1 843.4 50.8 0.0 10.7 10.8 4* 50.8 51.8 8.1 8.3 194.5 3.7 694.1 7.9 8.2 195.0 3.7 680.5 50.8 0.0 10.7 10.8 5* 50.7 42.1 7.1 7.4 171.3 3.4 551.4 6.9 7.4 171.7 3.4 535.0 50.7 0.0 10.7 10.8 7* 30.4 50.5 10.2 9.9 246.9 4.8 1066.8 9.8 9.5 247.3 4.5 1020.7 30.4 0.0 10.4 10.4 8* 30.5 43.2 9.1 9.1 223.7 4.4 907.7 8.9 8.7 224.2 4.1 848.5 30.5 0.0 10.4 10.4 

10* 70.2 84.8 10.1 10.1 236.2 4.2 966.7 9.9 9.6 236.7 3.9 910.8 70.2 0.0 10.6 10.8 11* 69.7 81.5 9.1 9.2 213.6 3.9 814.7 8.9 9.0 214.1 3.8 780.7 69.7 0.0 10.6 10.8 12* 70.4 87.6 11.1 10.8 258.3 4.4 1106.1 10.9 10.4 258.8 4.2 1063.3 70.4 0.0 10.7 10.8 

13 50.8 57.7 10.1 9.9 243.7 4.1 905.8 9.9 9.7 244.2 3.9 904.4 50.8 0.0 10.7 10.8 14 50.7 54.2 9.1 9.1 221.6 3.7 774.2 8.9 9.0 222.1 3.7 769.7 50.7 0.0 10.7 10.8 15 51.1 60.6 11.2 10.6 265.8 4.5 1025.1 10.8 10.4 266.3 4.1 1036.8 51.1 0.0 10.7 10.8 17 30.7 46.1 9.1 8.9 225.6 3.9 804.4 8.9 8.9 226.1 3.9 822.5 30.7 0.0 10.7 10.8 

17B 30.7 41.1 8.1 8.2 200.6 3.6 673.4 7.9 8.0 201.0 3.6 656.7 30.7 0.0 10.7 10.8 

19* 70.6 68.4 10.1 9.9 239.7 3.7 840.0 9.9 9.5 240.2 3.5 801.2 70.6 0.0 10.4 10.4 20* 70.8 71.4 9.1 9.2 216.1 3.4 715.5 8.9 8.7 216.6 3.2 674.2 70.8 0.0 10.4 10.4 21* 71.0 74.9 11.1 10.7 262.3 3.8 948.9 10.9 10.3 262.9 3.7 927.3 71.0 0.0 10.4 10.4 

22 50.9 53.7 10.1 9.8 247.7 3.5 780.3 9.9 9.7 248.1 3.5 800.2 50.9 0.0 10.7 10.8 23 50.8 51.7 9.1 9.0 223.6 3.2 674.2 8.9 9.0 224.1 3.3 687.0 50.8 0.0 10.7 10.8 24 51.0 55.6 11.1 10.4 266.9 4.0 856.0 10.7 10.3 267.3 3.6 882.8 51.0 0.0 10.7 10.8 26 30.5 36.8 9.1 8.9 228.5 3.5 724.1 8.9 8.7 229.0 3.5 725.5 30.5 0.0 10.7 10.8 

26B 30.3 33.1 8.1 8.2 204.0 3.2 611.1 8.0 8.0 204.4 3.3 603.7 30.3 0.0 10.7 10.8 

28 70.6 60.9 10.1 9.8 243.8 3.1 713.6 9.9 9.6 244.1 3.1 716.3 70.6 0.0 10.7 10.8 29 70.3 59.5 9.1 9.0 219.6 2.9 614.4 8.9 8.7 220.0 2.8 594.8 70.3 0.0 10.7 10.8 30 70.4 62.1 11.1 10.5 267.9 3.2 802.1 10.9 10.2 268.3 3.1 800.8 70.4 0.0 10.7 10.8 31 50.5 73.3 10.1 9.7 247.6 3.3 640.4 9.8 9.6 248.0 3.0 684.2 50.5 0.0 10.6 10.7 32 50.3 74.6 9.1 9.0 225.6 2.9 573.9 8.9 9.0 226.0 2.9 602.1 50.3 0.0 10.6 10.7 

32B 50.2 75.8 8.1 8.2 201.0 2.6 486.2 8.0 8.2 201.4 2.7 502.7 50.2 0.0 10.6 10.7 

NASA/TM—2011-216266 45
STEADY STATE (PHASE I—STIRLING CONVERTOR DATA).—Concluded. 

Test 

Pt. 

TCPV

H2OIN 

(°C) 

TC 

CABLE

TRAY 

(°C) 

XPE1

POS 

(mm) 

XDE1

POS 

(mm) 

LAE1

VOLT 

(V) 

LAE1

CUR 

(A) 

LAE1

POW 

(W) 

XPE2

POS 

(mm) 

XDE2

POS 

(mm) 

LAE2 

VOLT 

(V) 

LAE2

CUR 

(A) 

LAE2

POW 

(W) 

TCPV

H2OIN 

(°C) 

OVR

STRK 

(V) 

FME1

COOL 

(l/min) 

FME2

COOL 

(l/min) 

35 30.3 77.6 9.0 8.8 228.1 3.2 604.2 8.9 8.8 228.5 3.1 648.9 30.3 0.0 10.6 10.6 

35B 30.4 78.0 8.1 8.0 204.6 2.8 518.7 7.9 8.1 205.0 3.0 545.9 30.4 0.0 10.6 10.7 

37 70.4 58.0 10.1 9.8 246.5 2.6 587.3 9.9 9.6 246.9 2.5 586.6 70.4 0.0 10.6 10.6 38 70.5 62.6 9.1 9.0 221.5 2.4 514.0 8.9 8.8 221.9 2.4 507.2 70.5 0.0 10.6 10.6 39 70.5 67.8 11.1 10.5 270.7 2.6 642.3 10.9 10.4 271.1 2.6 664.7 70.5 0.0 10.6 10.7 

NASA/TM—2011-216266 46
STEADY STATE (PHASE I—STIRLING CONVERTOR DATA) 

Test Pt. ACCELX 

(V) 

ACCELY 

(V) 

ACCELZ 

(V) 

FME1PV

COOL 

(L/min) 

FME2PV

COOL 

(L/min)

PRE1

CHRG 

(psig) 

PRE2

CHRG 

(psig) 

FreqE1

(Hz) 

FreqE2

(Hz) 

Phase 

XpXdE1 

(deg) 

Phase 

XpXdE2

(deg) 

QWE1

OUT 

(W) 

QWE2

OUT 

(W) 

PlossE1I

2R 

(W) 

PlossE2I

2R 

(W) 

VdropE1

IR 

(V) 

VdropE2

IR 

(V) 

1* 0.02 0.01 0.04 3.9 3.8 440.3 440.3 50.0 50.0 51.6 47.9 1975.4 1824.1 4.2 3.9 0.9 0.9 2* 0.02 0.01 0.05 3.9 3.8 443.2 443.2 50.0 50.0 53.0 49.9 2513.1 2238.7 4.8 4.5 1.0 1.0 3* 0.01 0.01 0.02 3.9 3.8 437.7 437.7 50.0 50.0 50.1 46.8 1615.5 1619.8 3.5 3.5 0.9 0.9 4* 0.01 0.01 0.02 3.9 3.8 434.3 434.3 50.0 50.0 48.5 44.8 1485.3 1095.4 2.9 3.0 0.8 0.8 5* 0.01 0.01 0.02 3.9 3.8 431.1 431.1 50.0 50.0 47.4 43.5 1343.3 960.1 2.4 2.5 0.7 0.7 7* 0.0 0.0 0.0 2.1 2.1 416.8 416.8 50.0 50.0 52.9 49.0 1684.5 1847.5 4.7 4.3 1.0 1.0 8* 0.0 0.0 0.0 2.1 2.1 414.0 414.0 50.0 50.0 52.0 47.3 1420.6 1626.3 4.0 3.6 0.9 0.9 

10* 0.02 0.01 0.03 3.8 3.7 460.0 460.0 50.0 50.0 50.0 46.1 2109.5 2068.8 3.6 3.3 0.9 0.8 11* 0.01 0.01 0.02 3.8 3.7 456.7 456.7 50.0 50.0 48.4 44.7 1716.8 1661.4 3.1 3.0 0.8 0.8 12* 0.02 0.01 0.03 3.8 3.7 462.7 462.7 50.0 50.0 51.2 47.7 2455.8 2514.4 3.9 3.7 0.9 0.9 

13 0.01 0.01 0.04 3.9 3.8 433.3 433.3 50.0 50.0 52.4 49.8 2054.8 1818.8 3.5 3.2 0.8 0.8 14 0.01 0.01 0.03 3.9 3.8 430.7 430.7 50.0 50.0 51.3 48.4 1692.3 1486.6 2.9 2.9 0.8 0.8 15 0.02 0.01 0.05 3.9 3.8 435.7 435.7 50.0 50.0 53.7 51.7 2165.3 2472.3 4.1 3.6 0.9 0.9 17 0.01 0.01 0.03 3.9 3.8 411.7 411.7 50.0 50.0 52.9 49.7 1625.2 1481.0 3.1 3.3 0.8 0.8 

17B 0.01 0.01 0.02 3.9 3.8 410.1 410.1 50.0 50.0 52.0 47.7 1341.7 1091.8 2.7 2.8 0.7 0.8 

19* 0.0 0.0 0.0 1.9 2.0 452.8 452.8 50.0 50.0 51.1 47.6 2073.7 1928.2 2.8 2.5 0.8 0.7 20* 0.0 0.0 0.0 1.9 2.0 452.7 452.7 50.0 50.0 49.3 45.9 1768.0 1616.9 2.4 2.2 0.7 0.7 21* 0.0 0.0 0.0 1.9 2.0 456.2 456.2 50.0 50.0 52.4 49.4 2449.5 2370.4 2.9 2.8 0.8 0.8 

22 0.01 0.01 0.03 3.9 3.8 430.0 430.0 50.0 50.0 53.8 50.7 2108.8 1840.8 2.5 2.5 0.7 0.7 23 0.01 0.01 0.03 3.8 3.8 428.1 428.1 50.0 50.0 52.9 49.2 1626.9 1626.6 2.1 2.3 0.7 0.7 24 0.02 0.01 0.05 3.9 3.8 432.1 432.1 50.0 50.0 54.7 51.8 2396.7 2115.8 3.3 2.7 0.8 0.8 26 0.01 0.01 0.03 3.9 3.8 409.0 409.0 50.0 50.0 54.5 50.8 1660.8 1430.1 2.5 2.6 0.7 0.7 

26B 0.01 0.01 0.03 3.9 3.8 407.3 407.3 50.0 50.0 53.6 49.4 1373.6 1157.0 2.2 2.3 0.7 0.7 

28 0.01 0.02 0.03 3.8 3.7 448.6 448.6 50.0 50.0 52.3 49.2 2055.2 1949.3 1.9 2.0 0.6 0.6 29 0.01 0.02 0.03 3.8 3.7 446.1 446.1 50.0 50.0 51.0 47.0 1783.2 1618.6 1.7 1.7 0.6 0.6 30 0.02 0.02 0.03 3.8 3.7 450.5 450.5 50.0 50.0 53.5 50.4 2595.8 2438.6 2.1 2.1 0.7 0.7 31 0.01 0.01 0.03 1.9 2.0 432.1 432.1 50.0 50.0 54.8 52.1 1836.4 2003.0 2.2 1.9 0.7 0.6 32 0.01 0.01 0.02 1.9 2.1 429.8 429.8 50.0 50.0 53.8 50.7 1335.1 1737.8 1.7 1.7 0.6 0.6 

32B 0.01 0.01 0.02 1.9 2.0 427.4 427.4 50.0 50.0 52.6 49.1 1192.5 1256.1 1.4 1.5 0.5 0.6 

NASA/TM—2011-216266 47
STEADY STATE (PHASE I—STIRLING CONVERTOR DATA).—Concluded. 

Test Pt. ACCELX 

(V) 

ACCELY 

(V) 

ACCELZ 

(V) 

FME1PV

COOL 

(L/min) 

FME2PV

COOL 

(L/min)

PRE1

CHRG 

(psig) 

PRE2

CHRG 

(psig) 

FreqE1 

(Hz) 

FreqE2

(Hz) 

Phase 

XpXdE1 

(deg) 

Phase 

XpXdE2

(deg) 

QWE1

OUT 

(W) 

QWE2

OUT 

(W) 

PlossE1I

2R 

(W) 

PlossE2I

2R 

(W) 

VdropE1

IR 

(V) 

VdropE2

IR 

(V) 

35 0.01 0.01 0.03 2.0 2.1 409.4 409.4 50.0 50.0 55.0 51.9 1063.5 1472.8 2.2 2.1 0.7 0.7 

35B 0.01 0.01 0.02 2.0 2.1 407.2 407.2 50.0 50.0 54.2 50.6 914.2 1193.8 1.7 1.9 0.6 0.6 

37 0.01 0.01 0.03 1.8 2.0 449.2 449.2 50.0 50.0 53.6 49.7 2066.5 1869.0 1.3 1.3 0.5 0.5 38 0.01 0.01 0.03 1.8 2.0 448.4 448.4 50.0 50.0 52.2 48.0 1896.7 1728.5 1.2 1.2 0.5 0.5 39 0.01 0.01 0.03 1.8 2.0 451.7 451.7 50.0 50.0 54.6 51.7 2621.4 2320.2 1.4 1.4 0.5 0.6 

NASA/TM—2011-216266 48
STEADY STATE (PHASE I—FACILITY AND STIRLING CONVERTOR DATA) 

Test 

Pt. 

E1 

NaK Inlet 

Temp 

(°C) 

E1 

NaK 

Outlet 

Temp 

(°C) 

E2 

NaK 

Inlet 

Temp 

(°C) 

E2 

NaK 

Outlet 

Temp 

(°C) 

E1 & 

E2 

NaK 

Flow 

(kg/s) 

E1 

Q in 

(W) 

E2 

Q in 

(W) 

E1 

Eff 

(%) 

E2 

Eff 

(%) 

E1 

Piston 

Amp 

(mm) 

E2 

Piston 

Amp 

(mm) 

AVG E1

NaK 

Head T 

(°C) 

AVG E2 

NaK 

Head T 

(°C) 

AVG E1

PV T 

(°C) 

AVG E2

PV T 

(°C) 

Avg E1

Cool 

H2O T 

(°C) 

Avg E2

Cool 

H2O T

(°C) 

E1 

Qout 

(W) 

E2 

Qout 

(W) 

Total 

Elec 

Power 

(We) 

Combined 

Efficiency 

(%) 

1* 555.0 545.9 554.6 545.8 0.7877 3188.0 3,078.9 32.3 32.3 10.1 9.9 549.2 550.0 68.0 66.9 52.0 52.0 1975.4 1824.1 2026.1 32.3 2* 555.9 545.0 555.4 544.8 0.7690 3710.7 3,637.1 32.3 32.4 11.2 10.9 548.8 549.5 71.1 69.8 52.3 52.2 2513.1 2238.7 2375.2 32.3 3* 553.8 546.2 553.4 545.9 0.8048 2705.5 2,678.6 31.9 31.6 9.1 8.9 549.2 549.8 65.4 64.5 51.6 51.8 1615.5 1619.8 1710.3 31.8 4* 552.7 546.6 552.4 546.4 0.8419 2271.0 2,262.3 30.7 30.2 8.1 7.9 549.4 549.9 62.5 61.9 51.7 51.5 1485.3 1095.4 1380.4 30.5 5* 552.1 547.4 552.0 547.2 0.8704 1816.2 1,843.0 30.5 29.2 7.1 6.9 549.9 550.4 60.1 59.6 51.5 51.2 1343.3 960.1 1091.2 29.8 7* 555.3 546.0 555.6 546.6 0.8284 3395.3 3,294.9 31.6 31.1 10.2 9.8 550.0 551.0 48.5 46.7 31.6 31.6 1684.5 1847.5 2096.5 31.3 8* 553.4 546.3 554.4 547.2 0.8518 2692.4 2,735.8 33.9 31.1 9.1 8.9 549.8 550.7 45.6 44.1 31.3 31.2 1420.6 1626.3 1763.9 32.5 

10* 555.2 545.9 554.6 546.1 0.7172 2952.0 2,697.4 32.9 33.9 10.1 9.9 549.2 550.1 86.8 85.6 71.4 71.3 2109.5 2068.8 1884.4 33.4 11* 554.4 546.7 553.9 546.6 0.7312 2494.4 2,339.9 32.8 33.5 9.1 8.9 549.6 550.3 83.5 82.6 70.7 70.3 1716.8 1661.4 1601.6 33.1 12* 556.4 545.6 555.8 545.6 0.7009 3351.8 3,176.5 33.1 33.6 11.1 10.9 549.3 550.1 89.6 88.4 71.9 71.5 2455.8 2514.4 2177.1 33.3 

13 504.1 495.8 504.0 495.4 0.7839 2822.6 2,953.7 32.2 30.7 10.1 9.9 498.8 499.6 66.6 65.7 52.0 51.8 2054.8 1818.8 1816.9 31.5 14 503.8 496.9 503.7 496.5 0.7992 2377.6 2,514.0 32.7 30.7 9.1 8.9 499.6 500.3 63.6 62.9 51.6 51.7 1692.3 1486.6 1549.6 31.7 15 504.4 494.6 504.4 494.1 0.7737 3315.8 3,440.1 31.0 30.2 11.2 10.8 498.0 498.8 69.4 68.0 52.2 52.2 2165.3 2472.3 2069.7 30.6 17 503.9 497.1 503.8 496.5 0.8319 2458.3 2,651.1 32.8 31.2 9.1 8.9 499.8 500.4 44.6 43.9 31.4 31.6 1625.2 1481.0 1633.3 32.0 

17B 503.2 497.6 503.3 497.6 0.8556 2081.6 2,143.6 32.5 30.8 8.1 7.9 500.2 500.8 42.5 41.8 31.1 31.3 1341.7 1091.8 1335.5 31.6 

19* 503.9 495.9 504.2 495.8 0.7813 2725.4 2,831.8 30.9 28.4 10.1 9.9 499.0 500.0 85.7 84.4 72.0 71.7 2073.7 1928.2 1646.5 29.6 20* 503.5 497.1 503.7 496.9 0.7709 2157.6 2,286.3 33.3 29.6 9.1 8.9 499.6 500.5 84.8 83.5 72.0 71.7 1768.0 1616.9 1394.3 31.4 21* 504.1 494.8 504.3 494.5 0.7574 3079.3 3,224.7 30.9 28.8 11.1 10.9 498.2 499.1 88.9 87.6 72.6 72.3 2449.5 2370.4 1881.9 29.9 

22 453.1 445.7 452.6 445.0 0.8041 2532.5 2,626.5 30.9 30.6 10.1 9.9 448.3 448.8 65.7 65.0 52.2 52.1 2108.8 1840.8 1585.5 30.7 23 452.8 446.8 452.2 446.0 0.8167 2104.8 2,190.6 32.1 31.5 9.1 8.9 449.0 449.4 63.5 62.8 51.8 51.8 1626.9 1626.6 1365.7 31.8 24 454.3 445.8 453.9 445.1 0.7978 2907.5 3,015.1 29.6 29.4 11.1 10.7 448.6 449.2 68.1 66.7 52.5 52.4 2396.7 2115.8 1744.8 29.5 26 452.9 446.7 452.9 446.2 0.8854 2340.9 2,564.0 31.0 28.4 9.1 8.9 449.1 449.6 43.6 42.6 31.3 31.4 1660.8 1430.1 1454.7 29.7 

26B 452.3 447.4 452.5 447.1 0.9028 1909.9 2,096.7 32.1 28.9 8.1 8.0 449.5 450.1 41.6 40.8 31.2 31.0 1373.6 1157.0 1219.2 30.4 

28 454.2 447.0 453.9 446.3 0.7769 2412.6 2,537.7 29.7 28.3 10.1 9.9 449.3 449.9 84.6 83.8 72.0 71.6 2055.2 1949.3 1433.8 29.0 29 453.8 447.9 453.5 447.5 0.7815 1978.7 2,021.1 31.1 29.5 9.1 8.9 450.0 450.7 81.9 81.1 71.5 71.2 1783.2 1618.6 1212.7 30.3 30 454.5 445.9 454.2 445.4 0.7777 2863.9 2,949.2 28.1 27.2 11.1 10.9 448.6 449.3 87.0 85.7 72.2 71.9 2595.8 2438.6 1607.1 27.6 31 404.4 396.6 404.2 397.1 0.7842 2568.8 2,365.6 25.0 29.0 10.1 9.8 399.7 400.1 67.3 65.9 51.7 51.4 1836.4 2003.0 1328.7 26.9 32 404.0 397.6 403.9 398.1 0.7801 2124.9 1,935.1 27.1 31.2 9.1 8.9 400.3 400.6 64.8 64.0 51.3 51.2 1335.1 1737.8 1179.4 29.0 

32B 403.7 398.4 403.6 399.0 0.7716 1729.4 1,492.7 28.2 33.8 8.1 8.0 400.7 401.0 62.4 61.8 51.1 51.0 1192.5 1256.1 991.9 30.8 

NASA/TM—2011-216266 49
STEADY STATE (PHASE I—FACILITY AND STIRLING CONVERTOR DATA).—Concluded. 

Test 

Pt. 

E1 

NaK Inlet 

Temp 

(°C) 

E1 

NaK 

Outlet 

Temp 

(°C) 

E2 

NaK 

Inlet 

Temp 

(°C) 

E2 

NaK 

Outlet 

Temp 

(°C) 

E1 & 

E2 

NaK 

Flow 

(kg/s) 

E1 

Q in 

(W) 

E2 

Q in 

(W) 

E1 

Eff 

(%) 

E2 

Eff 

(%) 

E1 

Piston 

Amp 

(mm) 

E2 

Piston 

Amp 

(mm) 

AVG E1

NaK 

Head T 

(°C) 

AVG E2 

NaK 

Head T 

(°C) 

AVG E1

PV T 

(°C) 

AVG E2

PV T 

(°C) 

Avg E1

Cool 

H2O T 

(°C) 

Avg E2

Cool 

H2O T

(°C) 

E1 

Qout 

(W) 

E2 

Qout 

(W) 

Total 

Elec 

Power 

(We) 

Combined 

Efficiency 

(%) 

35 403.6 397.2 403.4 397.7 0.7537 2030.5 1,849.9 29.9 35.2 9.0 8.9 399.8 400.0 45.8 44.8 30.5 30.8 1063.5 1472.8 1257.4 32.4 

35B 403.1 397.9 402.9 398.4 0.7577 1672.8 1,468.5 31.1 37.3 8.1 7.9 400.1 400.3 43.7 42.9 30.5 30.9 914.2 1193.8 1068.2 34.0 

37 403.5 396.1 403.9 397.1 0.8333 2607.3 2,413.1 22.6 24.4 10.1 9.9 399.5 400.0 85.0 84.2 72.0 71.4 2066.5 1869.0 1176.5 23.4 38 403.5 397.3 403.7 398.2 0.8223 2149.6 1,906.1 24.0 26.7 9.1 8.9 400.1 400.7 83.4 82.7 72.0 71.5 1896.7 1728.5 1023.7 25.2 39 404.3 395.4 404.5 396.1 0.8080 3052.3 2,885.9 21.1 23.1 11.1 10.9 398.9 399.4 87.6 86.7 72.3 72.0 2621.4 2320.2 1309.9 22.1 

NASA/TM—2011-216266 50
STEADY STATE (PHASE I—FACILITY DATA) 

Test 

Pt. 

DP-02 

(psid) 

DP-03 

(psid) 

VG-02 

(torr) 

T-018 

(°C) 

T-019 

(°C) 

T-020 

(°C) 

T-021 

(°C) 

D-FM-01-C 

(kg/s) 

D-Qse1 

(W) 

D-Qse2 

(W) 

1* 0.564 0.407 0.0040 555.0 554.6 545.8 545.9 0.7877 3,188.0 3,078.9 2* 0.566 0.417 0.0040 555.9 555.4 544.8 545.0 0.7690 3,710.7 3,637.1 3* 0.553 0.393 0.0041 553.8 553.4 545.9 546.2 0.8048 2,705.5 2,678.6 4* 0.550 0.395 0.0044 552.7 552.4 546.4 546.6 0.8419 2,271.0 2,262.3 5* 0.534 0.398 0.0049 552.1 552.0 547.2 547.4 0.8704 1,816.2 1,843.0 7* 0.510 0.419 0.0031 555.3 555.6 546.6 546.0 0.8284 3,395.3 3,294.9 8* 0.501 0.425 0.0033 553.4 554.4 547.2 546.3 0.8518 2,692.4 2,735.8 

10* 0.550 0.425 0.0042 555.2 554.6 546.1 545.9 0.7172 2,952.0 2,697.4 11* 0.550 0.414 0.0041 554.4 553.9 546.6 546.7 0.7312 2,494.4 2,339.9 12* 0.550 0.432 0.0042 556.4 555.8 545.6 545.6 0.7009 3,351.8 3,176.5 

13 0.553 0.427 0.0043 504.1 504.0 495.4 495.8 0.7839 2,822.6 2,953.7 14 0.553 0.423 0.0044 503.8 503.7 496.5 496.9 0.7992 2,377.6 2,514.0 15 0.552 0.431 0.0042 504.4 504.4 494.1 494.6 0.7737 3,315.8 3,440.1 17 0.539 0.414 0.0048 503.9 503.8 496.5 497.1 0.8319 2,458.3 2,651.1 

17B 0.535 0.419 0.0049 503.2 503.3 497.6 497.6 0.8556 2,081.6 2,143.6 

19* 0.551 0.443 0.0024 503.9 504.2 495.8 495.9 0.7813 2,725.4 2,831.8 20* 0.554 0.445 0.0024 503.5 503.7 496.9 497.1 0.7709 2,157.6 2,286.3 21* 0.553 0.453 0.0025 504.1 504.3 494.5 494.8 0.7574 3,079.3 3,224.7 

22 0.557 0.440 0.0042 453.1 452.6 445.0 445.7 0.8041 2,532.5 2,626.5 23 0.562 0.442 0.0042 452.8 452.2 446.0 446.8 0.8167 2,104.8 2,190.6 24 0.559 0.443 0.0041 454.3 453.9 445.1 445.8 0.7978 2,907.5 3,015.1 26 0.542 0.437 0.0049 452.9 452.9 446.2 446.7 0.8854 2,340.9 2,564.0 

26B 0.536 0.442 0.0051 452.3 452.5 447.1 447.4 0.9028 1,909.9 2,096.7 

28 0.556 0.453 0.0040 454.2 453.9 446.3 447.0 0.7769 2,412.6 2,537.7 29 0.555 0.449 0.0040 453.8 453.5 447.5 447.9 0.7815 1,978.7 2,021.1 30 0.558 0.459 0.0040 454.5 454.2 445.4 445.9 0.7777 2,863.9 2,949.2 31 0.537 0.421 0.0064 404.4 404.2 397.1 396.6 0.7842 2,568.8 2,365.6 32 0.538 0.426 0.0065 404.0 403.9 398.1 397.6 0.7801 2,124.9 1,935.1 

32B 0.533 0.426 0.0063 403.7 403.6 399.0 398.4 0.7716 1,729.4 1,492.7 

NASA/TM—2011-216266 51
STEADY STATE (PHASE I—FACILITY DATA).—Concluded. 

Test 

Pt. 

DP-02 

(psid) 

DP-03 

(psid) 

VG-02 

(torr) 

T-018 

(°C) 

T-019 

(°C) 

T-020 

(°C) 

T-021 

(°C) 

D-FM-01-C 

(kg/s) 

D-Qse1 

(W) 

D-Qse2 

(W) 

35 0.525 0.422 0.0061 403.6 403.4 397.7 397.2 0.7537 2,030.5 1,849.9 

35B 0.531 0.430 0.0061 403.1 402.9 398.4 397.9 0.7577 1,672.8 1,468.5 

37 0.542 0.418 0.0065 403.5 403.9 397.1 396.1 0.8333 2,607.3 2,413.1 38 0.545 0.418 0.0066 403.5 403.7 398.2 397.3 0.8223 2,149.6 1,906.1 39 0.545 0.419 0.0066 404.3 404.5 396.1 395.4 0.8080 3,052.3 2,885.9 

STEADY STATE (PHASE I—NAK MASS FLOW SENSITIVITY) 

Test 

Pt. 

Piston 

Amplitude 

(mm) 

Engine 

Pressure 

(psig) 

Avg Hot-End 

Temp 

(°C) 

Stirling 

Power Out 

(W) 

NaK Flow 

Rate 

(kg/s) 

NaK Pump 

Power 

(W) 

40 10.0 433.2 550.5 1988.2 0.8386 3412.7 

40B 10.0 434.8 550.0 1976.8 0.7066 2361.5 40B 10.0 440.4 550.0 1966.7 0.7083 3514.7 43B 10.0 439.4 275.4 1989.9 0.5215 1837.2 41B 9.0 434.1 550.5 1668.2 0.7094 2591.7 

44 9.0 434.0 549.5 1642.8 0.5150 1362.6 

42B 8.0 432.3 550.4 1329.3 0.7120 3187.6 

45 8.0 432.0 550.2 1328.2 0.5137 1546.4 45 8.0 431.8 549.1 1320.4 0.5071 1552.2 

NASA/TM—2011-216266 52
NASA/TM—2011-216266 53 

Parameter Definitions—Engine 1 

TCE1HOT1 NaK Jacket Inlet—A (°C) (Eng 1) 

TCE1HOT2 NaK Jacket Inlet—B (°C) (Eng 1) 

TCE1HOT3 NaK Jacket Inlet—C (°C) (Eng 1) 

TCE1HOT4 NaK Jacket Inlet—D (°C) (Eng 1) 

TCE1HOT5 NaK Jacket Torus—E (°C) (Eng 1) 

TCE1HOT6 NaK Jacket Torus—F (°C) (Eng 1) 

TCE1HOT7 NaK Jacket Torus—G (°C) (Eng 1) 

TCE1HOT8 NaK Jacket Torus—H (°C) (Eng 1) 

TCE1PRVSL1 Press Vessel Temp (°C) (Eng 1) 

TCE1PRVSL2 Press Vessel Temp 2 (°C) (Eng 1) 

TCE1PRVSL3 Press Vessel Temp 3 (°C) (Eng 1) 

TCE1H2OIN Cooler Water Inlet Temp (°C) (Eng 1) 

TCE1H2OUT Cooler Water Exit Temp (°C) (Eng 1) 

TCE1LAGAS Linear Alternator Gas Temp (°C) (Eng 1) 

TCE1PVH2OUT PV Coolant Water Exit Temp (°C) (Eng 1) 

XPE1POS Piston Position (mm) (Eng 1) 

XDE1POS Displacer Position (mm) (Eng 1) 

LAE1VOLT Linear Alternator Voltage (V) (Eng 1) 

LAE1CUR Linear Alternator Current (A) (Eng 1) 

LAE1POW Linear Alternator Power (We) (Eng 1) 

PRE1CHRG Engine Mean Charge Pressure (psig) (Eng 1) 

FME1COOL Coolant Flow Rate (L/min) (Eng 1) 

FME1PVCOOL PV Coolant Flow Rate (L/min) (Eng 1) 
NASA/TM—2011-216266 54 

NaK Heater Head Thermocouple Locations—Engine 1 
NASA/TM—2011-216266 55 

Parameter Definitions—Engine 2 

TCE2HOT1 NaK Jacket Inlet—I (°C) (Eng 2) 

TCE2HOT2 NaK Jacket Inlet—J (°C) (Eng 2) 

TCE2HOT3 NaK Jacket Inlet—K (°C) (Eng 2) 

TCE2HOT4 NaK Jacket Inlet—L (°C) (Eng 2) 

TCE2HOT5 NaK Jacket Torus—M (°C) (Eng 2) 

TCE2HOT6 NaK Jacket Torus—N (°C) (Eng 2) 

TCE2HOT7 NaK Jacket Torus—O (°C) (Eng 2) 

TCE2HOT8 NaK Jacket Torus—P (°C) (Eng 2) 

TCE2PRVSL1 Press Vessel Temp (°C) (Eng 2) 

TCE2PRVSL2 Press Vessel Temp 2 (°C) (Eng 2) 

TCE2PRVSL3 Press Vessel Temp 3 (°C) (Eng 2) 

TCE2H2OIN Cooler Water Inlet Temp (°C) (Eng 2) 

TCE2H2OUT Cooler Water Exit Temp (°C) (Eng 2) 

TCE2LAGAS Linear Alternator Gas Temp (°C) (Eng 2) 

TCE2PVH2OUT PV Coolant Water Exit Temp (°C) (Eng 2) 

XPE2POS Piston Position (mm) (Eng 2) 

XDE2POS Displacer Position (mm) (Eng 2) 

LAE2VOLT Linear Alternator Voltage (V) (Eng 2) 

LAE2CUR Linear Alternator Current (A) (Eng 2) 

LAE2POW Linear Alternator Power (We) (Eng 2) 

PRE2CHRG Engine Mean Charge Pressure (psig) (Eng 2) 

FME2COOL Coolant Flow Rate (L/min) (Eng 2) 

FME2PVCOOL PV Coolant Flow Rate (L/min) (Eng 2) 
NASA/TM—2011-216266 56 

NaK Heater Head Thermocouple Locations—Engine 2 
NASA/TM—2011-216266 57 

Parameter Definitions—Convertor Pair 

TCPVH2OIN PV Coolant Water Inlet Temp (°C) (Eng 1and 2) 

TCCABLETRAY Cable Tray Temperature (°C) 

OVRSTRK Overstroke Protection Circuit (V) 

ACCELX Vibration in the Vertical Direction (g) 

ACCELY Vibration in the Axial Direction (g) 

ACCELZ Vibration in the Radial Direction (g) 

Parameter Definitions—Calculations 

FreqE1 Frequency (Hz) (Eng 1) 

FreqE2 Frequency (Hz) (Eng 2) 

PhaseXpXdE1 Piston/Displacer Phase (°) (Eng 1) 

PhaseXpXdE2 Piston/Displacer Phase (°) (Eng 2) 

QWE1OUT Heat Transfer to Cooling Water (W) (Eng 1) 

QWE2OUT Heat Transfer to Cooling Water (W) (Eng 2) 

PlossE1I2R I2

R Power Loss in Alternator Cables (W) (Eng 1) 

PlossE2I2R I2

R Power Loss in Alternator Cables (W) (Eng 2) 

VdropE1IR Voltage Drop in Alternator Cables (V) (Eng 1) 

VdropE2IR Voltage Drop in Alternator Cables (V) (Eng 2) 

Parameter Definitions—Facility 

DP-02 Stirling Engine 1 Diff Press (psid) 

DP-03 Stirling Engine 2 Diff Press (psid) 

VG-02 Chamber Press 1 (Torr) 

T-018 Stirling Engine 1 Inlet Temperature (°C) 

T-019 Stirling Engine 2 Inlet Temperature (°C) 

T-020 Stirling Engine 1 Outlet Temperature (°C) 

T-021 Stirling Engine 2 Outlet Temperature (°C) 

D-FM-01-C NaK Flow Meter (filtered) (kg/s) 

D-Qse1 Heat extracted from NaK by Stirling Engine 1 (W) 

D-Qse2 Heat extracted from NaK by Stirling Engine 2 (W) 

Appendix C.—NaK Heat Exchanger Drawing 

NASA/TM—2011-216266 59
NASA/TM—2011-216266 60 

References 

1. Kim, S.Y.; Huth, J.; and Wood, J.G.: Performance Characterization of Sunpower Free-Piston Stirling 

Engines. AIAA 2005–5540, 2005. 

2. Dhar, M.: Stirling Space Engine Program. Final Report, NASA CR/1999—209164/VOL1, 1999. 

3. Garber, A.E.: Capabilities and Testing of the Fission Surface Power Primary Test Circuit (FSP–PTC). 

Proceedings of Space Nuclear Conference 2007, paper 2030, American Nuclear Society, La Grange 

Park, IL, 2007. 

4. Mason, L.S.: A Comparison of Fission Power System Options for Lunar and Mars Surface 

Applications. Proceedings of Space Technology and Applications International Forum (STAIF–2006) 

(NASA/TM—2006-214120), M.S. El-Genk, ed., American Institute of Physics, Melville, New York, 

2006, pp. 270–280. 

5. Mason, L.S.: A Practical Approach to Starting Fission Surface Power Development. Proceedings of 

International Congress on Advances in Nuclear Power Plants (ICAPP’06) (NASA/TM—2006-

214366), paper 6297, American Nuclear Society, La Grange Park, IL, 2006. 
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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY)

01-03-2011 

2. REPORT TYPE

Technical Memorandum 

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Test Results From a Pair of 1-kWe Dual-Opposed Free-Piston Stirling Power Convertors 

Integrated With a Pumped NaK Loop 

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Geng, Steven, M.; Briggs, Maxwell, H.; Penswick, L., Barry; Pearson, J., Boise; Godfroy, 

Thomas, J. 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

WBS 463169.04.03.04.01.01 

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-17256 

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-2011-216266 

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited 

Subject Category: 44 

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

As a step towards development of Stirling power conversion for potential use in Fission Surface Power (FSP) systems, a pair of 

commercially available 1-kW-class free-piston Stirling convertors were modified to operate with a NaK (sodium (Na) and potassium (K)) 

liquid metal pumped loop for thermal energy input. This was the first-ever attempt at powering a free-piston Stirling engine with a pumped 

liquid metal heat source and is a major FSP project milestone towards demonstrating technical feasibility. The convertors were successfully 

tested at the Marshall Space Flight Center (MSFC) from June 6 through July 14, 2009. The convertors were operated for a total test time of 

66 hr and 16 min. The tests included (a) performance mapping the convertors over various hot- and cold-end temperatures, piston

amplitudes, and NaK flow rates and (b) transient test conditions to simulate various startup (i.e., low-, medium-, and high-temperature 

startups) and fault scenarios (i.e., loss of heat source, loss of NaK pump, convertor stall, etc.). This report documents the results of this 

testing. 

15. SUBJECT TERMS

Stirling engines; Stirling cycle; Fission surface power 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

 ABSTRACT

UU 

18. NUMBER

 OF 

 PAGES

66 

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