Gina M. Dugala

Glenn Research Center, Cleveland, Ohio

Test Rack Development for Extended

Operation of Advanced Stirling Convertors

at NASA Glenn Research Center

NASA/TM—2010-216232

March 2010
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Gina M. Dugala

Glenn Research Center, Cleveland, Ohio

Test Rack Development for Extended

Operation of Advanced Stirling Convertors

at NASA Glenn Research Center

NASA/TM—2010-216232

March 2010

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

Seventh International Energy Conversion Engineering Conference (IECEC)

sponsored by the American Institute of Aeronautics and Astronautics

Denver, Colorado, August 2–5, 2009
Acknowledgments

The work described in this paper was performed for the Science Mission Directorate

and the Radioisotope Power System Program, which funded these projects. 

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

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

either expressed or implied, by the National Aeronautics and 

Space Administration.
NASA/TM—2010-216232 1 

Test Rack Development for Extended Operation of Advanced 

Stirling Convertors at NASA Glenn Research Center 

Gina M. Dugala 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

The U.S. Department of Energy, Lockheed Martin Space Systems Company, Sunpower Inc., and 

NASA Glenn Research Center (GRC) have been developing an Advanced Stirling Radioisotope 

Generator (ASRG) for use as a power system on space science missions. This generator will make use of 

free-piston Stirling convertors to achieve higher conversion efficiency than with currently available 

alternatives. One part of NASA GRC’s support of ASRG development includes extended operation 

testing of Advanced Stirling Convertors (ASCs) developed by Sunpower Inc. and GRC. The ASC 

consists of a free-piston Stirling engine integrated with a linear alternator. NASA GRC has been building 

test facilities to support extended operation of the ASCs for several years. Operation of the convertors in 

the test facility provides convertor performance data over an extended period of time. One part of the test 

facility is the test rack, which provides a means for data collection, convertor control, and safe operation. 

Over the years, the test rack requirements have changed. The initial ASC test rack utilized an alternatingcurrent (AC) bus for convertor control; the ASRG Engineering Unit (EU) test rack can operate with AC 

bus control or with an ASC Control Unit (ACU). A new test rack is being developed to support extended 

operation of the ASC–E2s with higher standards of documentation, component selection, and assembly 

practices. This paper discusses the differences among the ASC, ASRG EU, and ASC–E2 test racks. 

I. Introduction 

Extended operation of Advanced Stirling Convertors (ASCs) has been an ongoing effort at the NASA 

Glenn Research Center (GRC) since 2006. This effort was initiated to demonstrate the life and reliability 

of Stirling convertors. Extended operation involves continuous, unattended convertor operation over a 

period of thousands of hours. The test rack provides the means for measuring and collecting data for 

observing operating trends. In addition, it provides convertor control and safe operation. Figure 1 shows 

test racks in GRC’s Stirling Research Laboratory. 

Sections II, III, and IV of this paper describe the three test rack designs used at GRC. The first test 

rack was designed for operating ASCs with AC bus control. Figure 2 shows a pair of ASC test articles on 

a test stand. The second test rack was designed for operating an Advanced Stirling Radioisotope 

Generator Engineering Unit (ASRG EU) with AC bus control or with an ASC Control Unit (ACU). 

Figure 3 shows a cutaway drawing of the ASRG EU. The third test rack was designed for operating 

ASC–E2 convertors with the intent of improving the quality of the test rack. The ASC–E2 is a second 

generation of the engineering-level Stirling convertor development. This test article will resemble the one 

shown in Figure 2. Each test rack allows the adjustment of operating conditions, including hot-end 

temperature, rejection temperature, and piston amplitude. Each test article was instrumented to measure 

these parameters in addition to output characteristics such as alternator voltage, current, power, and 

operating frequency. The test racks differ primarily in the instrumentation used to accomplish these 

measurements, to implement safe operation, and to control the convertor. 
NASA/TM—2010-216232 2 

Figure 1.—Test racks in the Stirling Research Laboratory. 

Figure 2.—Standard ASC test article (Ref. 2). 

Figure 3.—ASRG–EU test article (Ref. 2). 

Gas Management 

Valve 

Controller 

ASC (2) 

ASC Interconnect 

Tube 

Radiator Fins 

Pressure Relief 

Device 

Electric Heat 

Source (2) Thermal Insulation 

Instrumentation 

End Enclosure (2) 

Inboard 

Housing 

Outboard 

Housing 

Space Vehicle 

Interface (4) 

Cold-Side 

Adapter 

Flange (2) 

Heat Source 

Support (2) 
NASA/TM—2010-216232 3 

All test articles described in this paper consist of a pair of convertors mounted in the dual-opposed 

configuration, with the heater heads facing outward and the pressure vessel sections rigidly attached to 

each other. This configuration permits operation that is dynamically balanced because the piston motions 

are equal but opposite in direction. The hot end of each convertor is heated with electric cartridge heaters. 

The cold end of the standard ASCs and the ASC–E2s is maintained with a water/glycol bath, and that of 

the ASRG EU is air-cooled. Table 1 shows the approximate hot-end and cold-end temperatures of the 

convertors as well as the approximate alternator voltage and current of each of the convertors. 

TABLE 1.—ASC, ASRG–EU, AND ASC–E2 TEST ARTICLE 

OPERATING CONDITIONS (REF. 1). 

Convertors Nominal operating 

temperature 

Alternator 

voltage, 

Vrms

Alternator 

current, 

T A hot, 

°C 

Tcold, 

°C 

Standard ASC 

ASC–0 #1 and #2 645 72 24 3.5 

ASC–0 #3 and #4 650 90 24 3.5 

ASC–1 #3 and #4 850 90 10.9 8 

ASC–1HS #1 and #2 850 90 24 3.5 

ASC–E #1 and #4 650 90 10.9 8 

ASRG–EU 

ASC–E #2 and #3 640 90 10.9 8 

ASC–E2 

ASC–E2 #1 and #2 850 90 10.9 8 

ASC–E2 #3 and #4 850 90 10.9 8 

ASC–E2 #5 and #6 850 90 10.9 8 

ASC–E2 #7 and #8 850 90 10.9 8 

Nomenclature 

AC alternating current 

ASC Advanced Stirling Convertor 

ASRG Advanced Stirling Radioisotope Generator 

ACU ASC Control Unit 

DAQ data acquisition 

DC direct current 

E engineering-level Stirling convertor 

E2 second generation of the engineering-level Stirling convertor 

EU Engineering Unit 

FLDT fast linear displacement transducer 

FPC failsafe protection circuit 

GPHS General Purpose Heat Source 

GRC Glenn Research Center 

LED light-emitting diode 

PID proportional integral derivative 

RMS root mean square 

RTD resistance temperature detector 

UPS uninterruptible power supply 
NASA/TM—2010-216232 4 

II. Standard ASC Test Rack 

The standard ASC test rack is the basis for the development of all other test racks (Refs. 2 and 3). 

Each test rack discussed in this paper has the features of this test rack unless otherwise noted in its 

individual sections (Sections II, III, and IV). 

A. Data Acquisition System 

The data system utilizes National Instruments’s LabVIEW-based data acquisition (DAQ) hardware 

and software to acquire data and monitor the test. It displays and records data on a computer, collects and 

saves data in various time frames, calculates parameters with received data, and provides safety to the 

convertors. The DAQ software, which was developed to operate in unattended mode, can control the 

support systems without user intervention. 

Data collection allows for detailed analysis of convertor operation. To achieve this, LabVIEW 

collects and displays several parameters, including 

 Heater voltage and current 

 Heat-source temperature 

 Hot-end temperature 

 Cold-end temperature 

 Cold-end coolant inlet and outlet temperatures 

 Ambient temperature 

 Cold-end coolant flow rates 

 Pressure vessel temperature 

 Alternator root mean square (RMS) voltage, RMS current, and power 

 Piston amplitudes 

 Operating frequency 

 AC bus controller voltage and current 

A complete data record of these parameters is stored every hour. In addition, the DAQ system 

maintains a buffer of data recorded over the last 24 hr at a 2-sec scan rate, records an average of the data 

over the last 5 min of every hour, and allows these data to be stored manually as needed for detailed 

analysis. From the stored data, numerous parameters are calculated, including 

 Heater resistance and power 

 System efficiency 

 Power factor 

 Average hot-end temperature 

 Cold-end temperature 

 Piston amplitude 

 Net heat input 

 Alternator motor constant 

LabVIEW safety features are discussed in Section V, Subsection A. 

B. Control Systems 

The test rack provides two control systems: convertor and hot-end temperature control. Convertor 

control is performed by an AC bus that simulates the convertors being connected to an AC grid. The AC 

bus controller fixes the convertor frequency independent of changes in convertor dynamics. The operating 
NASA/TM—2010-216232 5 

frequency cannot deviate significantly from the intended convertor operating frequency. The power factor 

of each alternator indicates if the operating frequency deviates significantly from the natural frequency of 

each convertor. The AC bus controller controls piston amplitude by varying the AC voltage and, 

therefore, the load on the convertors. Increasing the AC voltage increases the piston amplitudes. 

The controller dissipates power generated by the convertors in a load resistor, which is connected 

across the alternator output. The electrical load is sized for the maximum power output of the convertor. 

For convertors with low-voltage, high-current alternators, a transformer is used between the AC power 

supply output and the load resistor to enable the use of a more standard power supply. In addition the 

alternator is connected to tuning capacitors that compensate for the alternator inductance. 

Hot-end temperature control is controlled with a heat-source controller. This controller regulates the 

power into the cartridge heaters that provide heat to the heat collectors of the convertors, thereby 

achieving constant-temperature control. Two independent heat-source controllers are capable of sourcing 

between 0 and 400 W. The controller regulates electrical power to the heaters by means of two 

proportional integral derivative (PID) temperature controllers. These are programmed to limit the rate of 

change in power to 1 C/sec. Programmable direct-current (DC) power supplies are driven by the PID 

controllers. Each hot-end temperature is controlled individually. 

C. Measurement 

The test rack receives signals from transducers, piston signal processors and accelerometer 

processors, and thermocouples. Alternator output is measured using voltage, current, and power 

transducers, which provide output signals ranging from 0 to 5 V to the DAQ system. Two sets of 

transducers are mounted in the test rack, where one panel measures heater voltage and current as well as 

AC bus controller voltage and current and the other panel measures alternator voltage, current, and power. 

Obtaining an accurate position signal is desirable for observing trends in data. A Fast Linear 

Displacement Transducer (FLDT) integrated in the convertor senses piston position. The FLDT consists 

of a single coil and an Aluminum core. As the core moves in and out of the coil, the coil inductance 

changes with position. A processor calibrated with the FLDT produces the output signal. It processes and 

scales the signal into a usable form for the DAQ and safety interfaces in the test rack. In addition it allows 

the zero, polarity, and span of the signal to be adjusted. 

An accelerometer measures any exported dynamics created by the convertors during operation. This 

information can be used to estimate net dynamic forces generated by the convertor pair and to monitor 

changes over time. Accelerometer signals connected to an amplifier provide a means to collect data from 

the accelerometer. These data are collected every 1,000 hr of operation through a separate data system. 

Thermocouples are used to measure the ambient temperature as well as temperatures of the heaterhead, cold-side adapter flange, pressure vessel, heat source, and coolant. These thermocouples are 

monitored by the DAQ and are used to trigger a shutdown of the convertors. Shutdown conditions are 

discussed in Section V, Subsection A. 

Two steps are taken to verify measurements collected by the data system: calibration and testing. 

Measurement instruments—such as transducers, flow rate and pressure sensors, and the DAQ system—

are calibrated yearly. Data are collected and analyzed on a regular basis to determine convertor 

performance, making the calibration of the equipment necessary to ensure accurate data. A test procedure 

is used to verify the measurements received by the DAQ system from instrumentation in the rack: 

transducer, piston, and pressure signals. This procedure is also executed when instrumentation that has 

been removed from the rack for calibration is reinstalled. 

D. Interface 

Several panels were designed to provide a means to interface the convertors and instrumentation in the 

test rack. These panels include a power, pressure, load, and flow meter signal conditioner interface. Interface 

panels used to implement safe operation of the convertors are discussed in Section V, Subsection B. 
NASA/TM—2010-216232 6 

The power panel serves as an interface for the AC power flow. Tuning capacitors, alternator output, 

convertor controller, and transducers interface to this panel. The pressure panel serves as an interface for 

pressure and position signals to the DAQ and protection devices. The load panel interfaces the electrical 

load, transformer, and AC bus controller. The flow meter signal-conditioner panel provides power to the 

flow meters. The flow meter signal is received and processed by LabVIEW. The flow meter signal 

conditioner is mounted and connected to allow for removal while the convertors are operating. The flow 

meter signal conditioner must be removed from the test rack for calibration. 

III. ASRG EU Test Rack 

The ASRG EU test rack can use either the AC bus controller or the ACU. Additional instrumentation, 

measurement, and calculations are needed to meet this requirement. The following sections describe 

either a change or addition to the standard ASC test rack. 

A. Data Acquisition System 

The DAQ for the ASRG EU test rack includes all parameters on a standard ASC rack with the 

addition of several others for operating with an ACU and for cooling system and temperature monitoring. 

The ACU provides data through analog and serial telemetry: 

 DC bus voltage and current 

 Analog piston position 

 Analog alternator current 

Cooling system monitoring for the ASRG EU is more detailed because it is air-cooled, whereas the 

standard ASC test setups provide cooling with a water/glycol mixture (Ref. 4). 

Cooled air is circulated through the protective cover by fans. Figure 4 shows the ASRG EU cooling 

system. Additional parameters are measured for cooling system monitoring: 

 ASRG EU housing temperatures 

 Fan speed 

 Upstream and downstream fan air temperatures 

 Protective cover temperatures 

 Argon pressure (Ref. 2) 

Figure 4.—ASRG–EU cooling system. 
NASA/TM—2010-216232 7 

The ASRG EU is instrumented with additional temperature-detection devices, including resistance 

temperature detectors (RTDs) and thermistors. 

The DAQ also performs the following calculations: 

 Controller efficiency 

 Generator system efficiency 

 Generator power 

 Average housing temperature 

 FLDT temperature 

 Alternator current 

 Piston amplitude 

B. Control Systems 

The test rack provides for two hot-end temperature-control systems and two convertor-control 

systems: constant heater temperature and fixed-heat input for temperature control, and AC bus and ACU 

for convertor control. Only one convertor control and one hot-end temperature control system are used in 

the test rack at one time. The ASRG EU test rack utilizes constant-temperature control for heat input 

when the convertor is operating with the AC bus controller, and it utilizes fixed-heat input control when 

the convertor is operating with the ACU. Fixed-heat input mimics operation with the General Purpose 

Heat Source (GPHS) module. The GPHS thermal output is independent of temperature. This value will 

slowly decrease from the time that it is assembled until the end of the mission, but at any one moment in 

time, it can be treated as a constant heat source. Constant-temperature operation is more straightforward 

to implement, but it may not be representative of the flight operation. Fixed-heat input is implemented 

with a microcontroller, with two independent heat-source controllers that are capable of sourcing between 

0 and 300 W by regulating electrical power to the heaters. 

Electronics in the ACU place requirements on the power path line resistance. The test rack was modified 

in two ways to accommodate this requirement. First, the power panel was moved from the back of the test rack 

to as close to the convertor as possible to reduce the length of wire in the power flow path. Second, external 

current sensors were used for current measurements. These modifications allow measurements to be taken 

close to the convertor rather than via a long cable from the convertor to the test rack. 

AC bus control dissipates power in resistors. ASRG EU control relies on a DC electronic load to sink 

power. The ASRG EU output voltage is between 22 and 34 Vdc and is determined by the end user. The 

ASRG EU will track to this voltage, providing power as a constant-power source, and will sense a bus 

overvoltage condition. The ASRG EU will provide constant power as long as the end user is in the 

required voltage range, but it will internally shunt power and disconnect itself from the bus if the voltage 

range is exceeded. Shunt resistors sized for maximum output power of the convertors are mounted on the 

load panel in the test rack for this purpose. The bus is connected to a capacitor bank for transient energy 

storage. This capacitor needs to be in the range of 10,000 to 100,000 μF. 

C. Measurement 

This ASRG–EU test rack allows for three measurements that were not available on the standard ASC 

test rack: thermistors and RTDs for temperature measurement and load cells for force measurement. Four 

thermistors measure pressure vessel and cold-end temperature. Six RTDs measure hot-end temperature. 

Four load cells measure the vertical, horizontal, and lateral loads at the interface between the test stand 

and the mechanical hardware. The signal is processed through an amplifier to allow data to be collected 

 
NASA/TM—2010-216232 8 

with a spectrum analyzer. The load cell readings are summed into single readings of force in the x, y, and 

z directions. The DAQ system monitors the load cell signal in the z direction; this signal is also monitored 

by safety protection devices, which are discussed in Section V. 

IV. ASC–E2 Test Rack 

The ASC–E2 test racks are in the process of being designed and built. The first of four racks is 

scheduled to be complete in the fall of 2009. Because of the high value of the hardware to be tested, these 

test racks are being built to a higher quality standard than previous test racks. This effort includes 

updating documentation, purchasing instrumentation with greater accuracy, and following procedures for 

fabrication and inspection to ensure that each rack is built identically. 

A. Measurement 

Currently, two measurement techniques that are different from the standard ASC and ASRG–EU test 

racks will be implemented on the ASC–E2 test rack. The existing test racks at GRC measure alternator 

and heater voltage, current, and power with transducers. First, a power meter was selected that would 

improve the accuracy of and simplify the rack wiring and calibration process. Table 2 compares the fullscale accuracy of the transducer and power meter. Second, external current sensors will be used to 

measure current. This will minimize the line resistance in the power path of the convertors, which affects 

the operation of high-current, low-voltage convertors. 

TABLE 2.—FULL-SCALE ACCURACY OF TRANSDUCERS AND POWER METERS 

Voltage 

transducer, 

percent 

Current 

transducer, 

percent 

Power 

transducer, 

percent 

Power meter 

voltage, 

percent 

Power meter 

current, 

percent 

Power meter 

power, 

percent 

0.25 0.25 to 0.5 0.5 0.2 0.2 0.1 

B. Documentation 

Developers have several goals for improving the documentation of the ASC–E2 racks. One goal is to 

improve the quality of the schematics. In the past, schematics were drawn in OrCAD and were not as 

detailed as should be used for test equipment for flight-like hardware. Work is underway to control the 

configuration by adding details such as parts lists, references, notes, wire sizes, lengths, and colors to the 

schematics. A second goal is to create schematics of circuits that were previously not documented. A third 

goal is to have all OrCAD schematics drawn in AutoCAD and filed in the Glenn Adept System. The 

quality of the test rack will be further improved through a design review with NASA senior engineers 

from outside of the organization. A fourth goal is to write a procedure to guide the assembly and checkout 

of the test racks to ensure that each rack is identical. This procedure will include steps needed to test each 

interface, control system, and measurement device; the order for installing each panel; and the wire length 

and routing for interfaces between the instrumentation and the convertors. 

V. Safety

Safety systems on the test racks are implemented through the DAQ system and through hard-wired 

circuitry. The following subsections outline the unique safety systems on each test rack. 

A. LabVIEW DAQ Shutdown Sequence 

The user may specify upper and lower bounds for any parameter monitored by the DAQ system. The 

DAQ software will safely shut down operation of the test article when an out-of-bound condition is sensed. 
NASA/TM—2010-216232 9 

Parameters that trigger the shutdown of a standard ASC include low or high hot-end temperatures, 

low or high rejection temperatures, high pressure-vessel temperature, high piston amplitude, and loss of 

building power. If a shutdown is initiated, the DAQ commands the hot-end temperature to 10 °C and 

circulator temperature to 25 °C, and it turns off the heater power supplies and AC bus controller. A 

shutdown is initiated for loss of building power after 5 min of operating on an uninterruptible power 

supply (UPS) system. 

Parameters that trigger a shutdown of the ASRG–EU or ASC–E2 include low or high hot-end 

temperatures, high rejection temperatures, high pressure-vessel temperature, high piston amplitude, loss 

of building power, and high housing temperature. Both thermistors and thermocouples are used to detect 

shutdown conditions. If a shutdown is initiated, the DAQ commands the hot-end temperature to 10 °C 

and the circulator temperature to 25 °C, and it turns off the heater power supplies. The convertors 

continue to be motored with the AC bus controller until the average hot-end temperature reaches 575 °C, 

with the nominal hot-end temperature being 625 °C. During the shutdown of a standard ASC, the piston 

motion is stopped, which prevents the transfer of heat. The change to continue to motor the convertor was 

implemented to allow the convertor to cool down more quickly. 

Another safety feature in the software notifies the end user when a shutdown to prevent heat soak 

from the heat source occurs, logs the fault via the DAQ, and records the data. The end user is notified by a 

cell phone text message that indicates the fault code of the shutdown. 

The DAQ shutdown functionality is tested via an unattended DAQ test rack checkout, which verifies 

that the sequence of each shutdown is correct. The shutdown scenarios are simulated with either a 

thermocouple calibrator or voltage reference. 

B. Hard-Wired Protection 

Three hard-wired protection devices installed in the operations rack function independently of the 

software-based protection (Refs. 2 and 3): temperature limit, protection circuit, and emergency push button. 

Three panels and a DC power supply are used to initiate the temperature limit shutdown. The fault 

panel serves as an interlock for the heater power supplies. If a fault is registered by the temperature limit 

device, the DAQ, or an optional third source, the heater power supplies are disabled and a fault is 

indicated by a light-emitting diode (LED). A temperature panel houses the PID temperature controller and 

the temperature limit device. A thermocouple interface is provided between the DAQ and the temperature 

control panel. Feedback is provided to both the PID and the temperature limit device by two individual 

hot-end thermocouples. If the hot-end temperature of either convertor exceeds the user-defined limit, the 

limit controller removes the heater power from both convertors via a relay. 

A failsafe protection circuit (FPC) was implemented to prevent piston overstroke. The FPC can monitor 

up to four input signals. Each input has an associated, user-adjustable setpoint. When any signal exceeds its 

setpoint, the convertor controller is disconnected, and an emergency load is applied across both alternators 

and a signal is sent to the DAQ. Piston-position sensor signals are the primary input on the standard ASC 

test rack, whereas the ASRG EU test rack has an additional input from the load cells. This input was added 

because it is independent of the piston signal from the ASRG EU controller. If the controller fails, the piston 

position signal would no longer be available to trigger a shutdown. The increased vibration from an 

overstroke of the piston would increase the load cell signal and trigger a shutdown. 

A protection circuit interface panel provides a means for the user to be notified via LEDs when a 

piston amplitude limit is exceeded. The user can reset the protection circuit after the fault and can stall the 

convertors by a switch on this panel. The user also can disconnect the protection circuit and select 

between AC bus control and an external controller. 

Several steps are required in the event of an emergency shutdown during convertor operation. These 

steps include removing power from the heaters, loading the convertor, and turning off the controller. An 

emergency shutdown button was created to simplify this process. This button initiates all of these steps 

with one action. This safety feature is being considered for integration in the ASC–E2 test rack; it is not 

available on either the ASC or ASRG EU test rack. 
NASA/TM—2010-216232 10 

Conclusions 

The Stirling Research Laboratory can support various types of Advanced Stirling Convertor (ASC) 

operation in continuous, unattended mode. Three ASC test racks at NASA were presented. The standard 

ASC test rack provides alternating-current (AC) bus control and constant-temperature hot-end 

temperature control. The Advanced Stirling Radioisotope Generator Engineering Unit (ASRG EU) test 

rack supports both AC bus and ASC Control Unit (ACU) convertor control. In addition it supports both 

constant-temperature and fixed-heat input control. The ASC–E2 rack supports AC bus convertor control 

and constant-temperature hot-end temperature control. In addition, the quality of the documentation, 

procedures, and rack build are being improved. Table 3 summarizes the Stirling Research Laboratory test 

racks. The first ASC–E2 test rack is scheduled to be complete in the fall of 2009. 

TABLE 3.—SUMMARY OF STIRLING RESEARCH LABORATORY TEST RACK DEVELOPMENT 

Standard ASC ASRG–EU ASC–E2 

Measurement instrumentation 

Thermocouples 

Transducers 

Fast linear displacement transducer 

(FLDT) processor 

Accelerometers 

Thermistors 

Resistance temperature devices (RTDs) 

Thermocouples 

Transducers 

FLDT processor 

Accelerometers 

Load cells 

Thermocouples 

Power meter 

Accelerometers 

Convertor control 

Alternating-current (AC) 

bus power supply 

AC bus power supply 

ACU 

AC bus power supply 

Temperature control 

Constant temperature 

Water/glycol bath 

Fixed-heat input 

Constant temperature 

Air-cooled 

Constant temperature 

Water/glycol bath 

Miscellaneous 

 Line resistance 

Direct-current (DC) bus 

Line resistance 

Documentation 

Safety 

Piston overstroke 

LabVIEW 

Hot-end temperature 

Load cells 

Piston overstroke 

LabVIEW 

Hot-end temperature 

Emergency shutdown button 

Piston overstroke 

LabVIEW 

Hot-end temperature 

References 

1. Cornell, P.A., Lewandowski, E.J., Oriti, S.M., and Wilson, S.D., “Stirling Convertor Extended 

Operation Testing and Data Analysis,” Proceedings of the Seventh International Energy Conversion 

Engineering Conference (IECEC 2009), American Institute for Aeronautics and Astronautics, 2009. 

2. Oriti, S.M., and Blaze, G.M., “Advanced Stirling Convertor Testing at NASA Glenn Research 

Center,” Proceedings of the Fifth International Energy Conversion Engineering Conference (IECEC 

2007), American Institute for Aeronautics and Astronautics, 2007. 

3. Lewandowski, E.J., Schreiber, J.G., Wilson, S.D., Oriti, S.M., and Cornell, P.A., “Extended 

Operation Testing of Stirling Convertors in Support of Stirling Radioisotope Power System 

Development,” Proceedings of the Sixth International Energy Conversion Engineering Conference 

(IECEC 2008), American Institute for Aeronautics and Astronautics, 2008. 

4. Lewandowski, E.J., Schreiber, J.G., Oriti, S.O., Meer, D.W., and Dugala, G.M., “Design of a Facility 

to Test the Advanced Stirling Radioisotope Generator Engineering Unit,” Proceedings of the Seventh 

International Energy Conversion Engineering Conference (IECEC 2009), American Institute for 

Aeronautics and Astronautics, 2009. 
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1. REPORT DATE (DD-MM-YYYY)

01-03-2010 

2. REPORT TYPE

Technical Memorandum 

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Test Rack Development for Extended Operation of Advanced Stirling Convertors at NASA 

Glenn Research Center 

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Dugala, Gina, M. 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

WBS 138494.04.01.01 

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-17219 

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

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

10. SPONSORING/MONITOR'S

 ACRONYM(S)

NASA 

11. SPONSORING/MONITORING

 REPORT NUMBER

NASA/TM-2010-216232 

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited 

Subject Category: 20 

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

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

13. SUPPLEMENTARY NOTES

14. ABSTRACT

The U.S. Department of Energy, Lockheed Martin Space Systems Company, Sunpower Inc., and NASA Glenn Research Center (GRC) have 

been developing an Advanced Stirling Radioisotope Generator (ASRG) for use as a power system on space science missions. This generator 

will make use of free-piston Stirling convertors to achieve higher conversion efficiency than with currently available alternatives. One part 

of NASA GRC’s support of ASRG development includes extended operation testing of Advanced Stirling Convertors (ASCs) developed by 

Sunpower Inc. and GRC. The ASC consists of a free-piston Stirling engine integrated with a linear alternator. NASA GRC has been

building test facilities to support extended operation of the ASCs for several years. Operation of the convertors in the test facility provides 

convertor performance data over an extended period of time. One part of the test facility is the test rack, which provides a means for data 

collection, convertor control, and safe operation. Over the years, the test rack requirements have changed. The initial ASC test rack utilized 

an alternating-current (AC) bus for convertor control; the ASRG Engineering Unit (EU) test rack can operate with AC bus control or with an 

ASC Control Unit (ACU). A new test rack is being developed to support extended operation of the ASC-E2s with higher standards of 

documentation, component selection, and assembly practices. This paper discusses the differences among the ASC, ASRG EU, and ASC-E2 

test racks. 

15. SUBJECT TERMS

Advanced Stirling radioisotope generator; Power systems; Stirling convertors 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

 ABSTRACT

UU 

18. NUMBER

 OF 

 PAGES

16 

19a. NAME OF RESPONSIBLE PERSON

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

a. REPORT

U 

b. ABSTRACT

U 

c. THIS 

PAGE

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19b. TELEPHONE NUMBER (include area code)

443-757-5802 

Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. Z39-18