Introduction The Aerospace Corporation

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					          Overview of Vibration Testing
              of Stirling Convertors
      at the NASA Glenn Research Center
                            Presented at
The 2001 Spacecraft & Launch Vehicle Dynamic Environments Workshop
                      The Aerospace Corporation
                        El Segundo, California
                           June 26-28, 2001

                                by
                        William O. Hughes
                       Thomas W. Goodnight
                         Anne M. McNelis

                  Structural Systems Dynamics Branch
                     NASA Glenn Research Center
                          Cleveland, Ohio USA




                     Introduction
  • NASA’s Mars Surface and Deep-Space Missions requires
  radioisotope spacecraft power systems. Historically, RTGs
  (Radioisotope Thermoelectric Generators) have been
  successfully utilized for NASA missions such as Galileo,
  Ulysses, and Cassini.

  • NASA Glenn Research Center (GRC), in conjunction with
  the Department of Energy (DOE) and Stirling Technology
  Company (STC), are currently developing a Stirling convertor
  to supply spacecraft on-board electric power for NASA’s
  Mars Surface and Deep-Space Missions.




                                           The 55We Technology
                                  2        Demonstration Convertor




                                                                     1
                                         The Stirling Story
                       The Revolution in Space Power is About to Happen !


                     • Well over 4000 satellites have been launched into Earth orbit
                     • Approximately 200 deep space science missions have been launched

    1957 - Sputnik        >>> ALL have used static power systems <<<

    Deep space missions beyond Mars generally require radioisotope power systems

Plutonium 238 supplies heat to the power system
with an 88 year half life, however:
 • It is a precious resource in very limited supply
 • It is extremely expensive
 • It raises environmental concerns

A Stirling Radioisotope Power System reduces the
isotope inventory required by more than a factor of 4




                                                      3




                                   GRC History with Stirling


 Kinematic Stirling existed since 1816

 Stirling Research initiated at NASA LeRC in mid 1970s

 Areas of Stirling Engine Expertise Developed at GRC
                                                                                             Early Stirling
                                                                                               Engine
     •   Stirling cycle thermodynamics & losses
     •   Materials issues
     •   Structural analysis
     •   Tribology & bearing technology
     •   Controls
     •   Design & Fabrication
     •   System integration                               Automotive Stirling Engine
                                                          installed in an AMC Spirit




                 LeRC/GRC recognized as the center
                  LeRC/GRC recognized as the center
                  of excellence in Stirling technology
                  of excellence in Stirling technology
                 by the energy conversion community
                 by the energy conversion community
                                                                                       P-40 Stirling Engine being
                                                                                         tested in ERB SE-13
                                                      4




                                                                                                                    2
                                      Recent Stirling Radioisotope
                                        Power System Activities

1997 Multi-Agency team reviews potential power sources for NASA deep space missions
           • Stirling considered to be available technology with relatively high payoff

10/97 Launch of Cassini mission to Saturn
1998 DOE funds effort to develop the 55 watt Technology
     Demonstration Convertor (TDC)
                                                                                                        55 watt Technology
6/99 NASA HQ initiates funding of Stirling effort at GRC                                              Demonstration Convertor


8/99 DOE informs NASA HQ & JPL that AMTEC will not be ready
     for Europa Orbiter (2003) or Pluto Kuiper Express (2004)

9/99 DOE reviews power system options with NASA & JPL
           • DOE proposes use of RTGs, small RTGs, and consideration for Stirling option
                                                                                                        The Radioisotope fueled
10/99 DOE forms team to determine the readiness of the Stirling option                                    Cassini Spacecraft

       • Seven critical areas were identified

1/00   DOE Team presents findings to NASA HQ
           •   Spacecraft power requirements are growing
           •   Missions are being replanned
           •   Satisfactory results shown for all critical areas            TDC Stirling Convertor met Europa &
                                                                                 Pluto EMI requirements
           •   Focus future efforts on Stirling
                                                                5




                                    Recent Stirling Radioisotope
                                  Power System Activities (continued)


  • NASA HQ & JPL has revised the launch dates & mission requirements
       – Work has stopped on Pluto Kuiper Express
       – Europa Orbiter launch date changing (was planned for 2006)
       – Solar Probe launch date changing (was planned for 2007)

  • Current DOE procurement for a Stirling system integrator
       – Announced in January 2000 by DOE
       – Boeing, Lockheed Martin, and Teledyne Brown
                                                                                                  LMA configuration design
       – Down select late 2001 for potential mission

  • GRC is the government agent for Stirling efforts
       – NASA HQ looks to GRC for experience & expertise
       – DOE heavily dependent on GRC for technical expertise
       – Expertise in Stirling, and also in a wide range of supporting fields
                                                                                OSC configuration design

  • There are a multitude of applications now being seriously considered
       –       Mars surface (Rover) application, baselined for 2007
       –       Outer Planets/Solar Probe missions
       –       Venus mission
       –       Spin Offs, terrestrial & space, commercial                                                  Solar Probe Spacecraft




                                                               6
                                                                          Europa Orbiter Spacecraft




                                                                                                                                    3
                                            General Free-Piston
                                      Stirling Convertor Schematic


                                                                                   Linear
                                                     Piston Stroke                Alternator
                                                                                   Mover

                               Displacer                  Power
                                                          Piston




                       Th

                                                                                                Linear
                                                                                               Alternator
                                                                                                 Stator
                       Heater               Cooler

                              Regenerator
                                     Figure 1. General Free-Piston Stirling Convertor Schematic


                                                                      7




                              Major Components & Functions of
                                    the Stirling Convertor

                                    Piston Flexures - support                                          Displacer Flexures -
                                    and spring Piston /Alternator                                      support and spring the
Linear Alternator                   assembly                          Close Clearance Seals -          displacer
Magnets, Stator & Coils -                                             isolates gas working spaces
remain stationary and
produce electric power                                                                                          Displacer - reciprocates,
                                                                                                                shuttling working fluid
                                                                                                                between expansion and
                                                                                                                compression spaces




 STC 55 We
  STC 55 We
  Stirling
   Stirling
 Convertor
  Convertor




                                                                                                                        Heater - heats
                                                                                                                        the working gas
Linear Alternator Mover,
reciprocates with piston to
produce power                                                 Displacer Rod - drives                      Regenerator - improves
                                                              the displacer                               engine cycle efficiency
                                Power Piston -
                                reciprocates and drives
                                the alternator                                         Cooler - rejects heat
                                                                                       from the working gas
                                                                      8




                                                                                                                                            4
            Dynamic Testing at NASA GRC

• To help advance the continuing development of the
  Stirling Technology, GRC Structural Dynamics
  Laboratory (SDL) has embarked upon a series of dynamic
  tests of the Stirling Technology Demonstration Convertor
  (TDC) Engineering Units.

• (1) Vibration Test of a single TDC Unit
   – November 29 - December 2, 1999
• (2) “Microgravity” Emission Test (MEL) of two TDC Units
   – January 3-16, 2001
• (3) Modal Test of a single TDC Unit
   – February 1-9, 2001 & May 25-30, 2001
• (4) Vibration Transmissibility Test of two TDC Units
   – May 2001

                                     9




                     Test 1. Vibration Test

  •This testing was done as part of the technical readiness evaluation
  performed to evaluate critical areas. One of several key issues of the
  evaluation was to demonstrate that the Stirling convertor can withstand
  the harsh liftoff random vibration environment.

  •Testing was performed to characterize the Stirling Technology
  Demonstration Convertor’s (TDC’s) structural integrity and power
  performance under random and sinusoidal vibration excitation.

  •To accomplish this objective an operating Stirling TDC was vibration
  tested at NASA GRC’s SDL from November 29-December 2, 1999.




                                     10




                                                                            5
       Stirling TDC and
     Vibration Test Fixture



                                      Alternator




                                      Fixture
Heater
                                  X
                                            Y



                       11




    Stirling TDC Vibration Test
        at NASA Glenn SDL




                            C210 Shaker



                  le
               Tab              TDC
            ip
         Sl




                       12




                                                   6
                                                  Overview of Test Levels

                            •       The Stirling TDC’s most severe test was the JPL’s “Qualification”
                                    Random Vibration test levels:
                                     – 12.3 Grms overall (20 - 2000 Hz)
                                     – 0.2 g2/Hz from 50 - 250 Hz
                                     – Test duration of 3 minutes per axes
                                     – Tested in axial and lateral directions
                                     – Stirling TDC was exposed to vibration levels significantly greater
                                        than qualification levels used for Galileo/Ulysses/Cassini RTGs

                            •       In addition to the above JPL’s Qualification test levels, the Stirling TDC
                                    also was tested to the following dynamic environments:
                                     – Random vibration to JPL’s Flight Acceptance (8.7 Grms) levels
                                     – Random vibration to NASA’s workmanship (6.8 Grms) levels
                                     – Numerous low level sine sweeps (to compare pre versus post
                                        dynamic signatures and for checks of linearity)

                            •       Functionality checkout tests were conducted after each dynamic test.



                                                                              13




                                                     Stirling TDC
                                               Random Vibration Test Levels

                                1

                                                                                                        Design/Qual
                                                                                                         12.3 grms
Vibration Level (g2/Hz)




                            0.1
                                                                                                                Flight Acceptance
                                                                                                                     8.7 grms




                                                                 Workmanship
                           0.01                                   6.8 grms


                                                                 Modified Workmanship
                                                                        6.8 grms



                                                        Test Range 20 to 2000 Hz per Test Plan

                          0.001
                                    10                       100                                 1000                               10000
                                                                    Frequency (Hz)
                                                                              14




                                                                                                                                            7
                                            Structural Response of TDC
• All vibration tests in both axes (sine sweeps, modified workmanship, JPL’s
Flight and JPL’s Qualification random vibration levels) were completed
without any Stirling TDC structural failures.

•The pre and post sine testing showed no significant changes in dynamic
characteristics of measurements, due to the exposure to the random
environments.

•The Lateral sine sweep testing indicates that the structure responds
reasonably linearly (Q = 5 - 8), with an engine casing structural resonance at
1030 Hz.

• The Axial sine sweep testing indicates that the structure responds
reasonably linearly (Q =2 - 5), with possible engine casing/fixture structural
resonances at 1470 and 1730 Hz.

•The Stirling TDC test structure is dynamically well-behaved and linear, with
reasonable damping. Its structural casing resonances are high enough in
frequency to avoid dynamically coupling problems.
                                                                        15




                     Comparison of Force Gauge (105Y) Data
                  from Axial Pre and Post Qual Sine Sweep Tests

            2.0E+00


            1.0E+00
                                                                79 Hz, Piston Stroke Frequency
                  Reaction Force (lbsrms)




                                                                       158 Hz, First Harmonic
            1.0E-01




            1.0E-02

                                                                  Frequency (Hz)
            4.0E-03
                                    55                 100                                        1000   1600
                                            59 :105Y+ 105Y+ 3                        60 :105Y+ 105Y+ 4
                             Post Qual Test ____
                                Bolt_strain-gauge
                              PPAx_PostQualSine_RMS
                                                                             Pre Qual Test ____
                                                                                    Bolt_strain-gauge
                                                                                  PPAx_PreQualSine_RMS


                                            Figure 6. Comparison of Force Gauge (105Y) Data
                                              from Axial Pre and Post Qual Sine Sweep Tests
                                                                        16




                                                                                                                8
                                    Comparison of Test Input Versus TDC Response
                                    for Lateral Random Vibration Qualification Test


                                     1.0E+00

                                                                                      Accelerometer 11X (20.1 Grms),
                                                                                      at End of Alternator


                                     1.0E-01
                                          PSD (g2/Hz)


                                                                              Test Specification                             Test Input
                                                                              (12.3 Grms)                                    (12.2 Grms)
                                     1.0E-02




                                     2.0E-03
                                                        20                                          100                                         1000         1600
                                          2 :1X+ 1X+ 2
                                                                                                        Frequency (Hz)
                                                                                                     2 :1X+ 1X+ 1                          12 :11X+ 11X+ 1
                                       Control Average                                        Control Specification                               M11X+
                                StEng_Lat-FA+3dB_HBW_rms_u                                    05-Apr-00 14:50:45                    StEng_Lat-FA+3dB_HBW_rms_u



                                               Figure 7. Comparison of Test Input versus TDC Response
                                                    for Lateral Random Vibration Qualification Test


                                                                                                              17




                                                Comparison of Output Power versus
                                             Level of Input Vibration in Lateral Direction



                                                                                              Stirling Lateral Testing
                                                                                        Stirling TDCTDC Lateral Testing
                               70
Average Output Power (Watts)




                               60      Nominal 55 Watts
  Average Output Watts




                               50
                               40
                                                                                                                                                                          Steady State = 56.8
                                                        Steady State = 54.0




                               30
                                                                                          Mean = 50.0




                                                                                                                      Mean = 44.5




                                                                                                                                               Mean = 37.7
                                                                                          Sigma = 1.0




                                                                                                                      Sigma = 1.6




                                                                                                                                               Sigma = 3.0




                               20
                               10
                               0
                                          Pre Test                                     Qual - 6dB                Qual - 3dB                    Qual                   Post Test
                                        (no excitation)                               ( 6.2 Grms )              ( 8.7 Grms )              ( 12.3 Grms )             (no excitation)

                                                                                                            Level of Excitation                      Mean +/- 2 Sigma
                                                                                                        Level of Excitation

                                                                               Figure 5. Comparison of Output Power versus
                                                                               Level of Input Vibration in Lateral Direction.


                                                                                                              18




                                                                                                                                                                                                9
                                         Comparison of Output Power versus
                                       Level of Input Vibration in Axial Direction



                                                                               Stirling Axial Testing
                                                                        Stirling TDC TDC Axial Testing
                               70
Average Output Power (Watts)

                               60   Nominal 55 Watts
  Average Output Watts



                               50
                               40




                                                                                                                                              Steady State = 54.3
                                          Steady State = 54.0
                               30




                                                                          Mean = 54.2




                                                                                                    Mean = 54.7




                                                                                                                     Mean = 53.8
                                                                          Sigma = 2.2




                                                                                                    Sigma = 3.2




                                                                                                                     Sigma = 5.3
                               20
                               10
                                0
                                      Pre Test                         Qual - 6dB                Qual - 3dB           Qual                Post Test
                                    (no excitation)                   ( 6.2 Grms )              ( 8.7 Grms )      ( 12.3 Grms )         (no excitation)
                                                                                            Level of Excitation            Mean +/- 2 Sigma
                                                                                        Level of Excitation

                                                                Figure 6. Comparison of Output Power versus
                                                                 Level of Input Vibration in Axial Direction.



                                                                                              19




                               Summary of Stirling TDC Vibration Test # 1


•                              An operating Stirling TDC was exposed to significant
                               (greater than expected launch) vibration test levels and
                               survived with no structural or performance problems.
                                – The most severe test was at the JPL “Qualification”
                                  random vibration levels of 12.3 Grms for 3
                                  minutes/axes.

•                              The Stirling TDC operated at full-stroke and continued to
                               produce power during all vibration testing.
                                – The TDC produced full power at the end of each
                                  vibration test.

•                              This testing provided, to the Stirling Assessment Team
                               and NASA Headquarters, extreme confidence that the
                               Stirling convertor will dynamically survive the expected
                               launch environment of a Mars Surface or Deep-Space
                               Mission spacecraft.
                                                                                              20




                                                                                                                                                                    10
            Test 2. “Microgravity” Emission Laboratory
                 Test of Tandem Stirling TDC Units
    •     Current spacecraft power systems are considered passive.
    •     The Stirling Convertor is a dynamic power system destined for Mars
          Surface and Deep Space Power Applications.
    •     Supplying Satellite power requires vibratory compatibility (“Good
          Neighbor Policy”) with other spacecraft components.
    •     Current System Integrators are in Preliminary Design and must
          manage complex system drivers including;
           – Design choices which drive power system tolerances
           – Lift-off environment durability
           – Spacecraft science requirements which dictate µg management
               scheme.
    •     NASA GRC’s Microgravity Emissions Laboratory (MEL) facility was
          utilized to characterize the effects of manufacturing tolerances on
          the structureborne disturbances produced by the operation of an
          opposed pair of Stirling convertors.
           – The MEL facility is typically utilized to determine the forces and
               moments produced by the operation of various Space
               Experiments in order to determine their impact on ISS
               microgravity levels.         21




                        MEL Facility Description

•   The Microgravity Emissions Laboratory (MEL) was
    established in November 1999 in the Structural Dynamics
    Laboratory (SDL) at the Glenn Research Center.
•   MEL is an 6 DOF inertial force measurement system.
     – Inertial forcing functions are measured from 0.5-315 Hz
        using the system mass and 6 DOF acceleration vector.
     – System is capable of measuring down to tenths of µg.
     – The “rigid body” acceleration vector is measured and
        normalized with the test unit’s diagonal mass matrix.
     – The apparatus is “isolated” using a 34 foot pendulum
        length and a “zero spring rate mechanism”to suppress
        vertical modes.


              FOR MORE INFO...
        For Microgravity Emissions Laboratory information call (216) 433-8880
            http://www.grc.nasa.gov/WWW/MEL/ or Anne McNelis@grc.nasa.gov


                                                 22




                                                                                  11
                  Dual Opposed Stirling Convertors
                        MEL Test Assembly

 T D C #6                      Stirling Convertor and
                               MEL Axes Designations       T D C #5



                                                                      -Z




                                                       X
                                                                           -Y
                                  M EL Test D ata
                                 A xes D esignations




                                            23




                          Stirling Convertors with
                         MEL Accelerometer Platform

           MEL Test
       Platform with
    Accelerometers
(4 pairs of 5 visible)


                                                                 Z




                                                       X                   Y




                                            24




                                                                                12
                      MEL Testing of the Tandem
                         Stirling Convertors

•   The Stirling Convertors were rigidly
    mounted. A thick wall tube was used
    to mount & to allow centerline
    misalignment in the XZ plane & angular
    changes about the Convertor large
    flange at one end. This simulated
    effects of manufacturing tolerances.
•   Limited centerline and angular
    misalignment were studied.
      – The centerline lateral misalignment
         was varied from + 0.1 inch.
      – The centerline angularity was
         changed from 0 to 4 degrees, along
         with a combined 1.5 degree rotation
         along both lateral axis.
•   The effects of the power system
    interface stiffness was also tested by
    utilizing various isolation bases (53 Hz,                                                             ZX
    113 Hz, “rigid”).
                                                                                                           Y
                                                         25




             Tandem Stirling Convertor
      Rigid Body Force (Baseline Configuration)
                                     Stirling Convertor MEL Test Results
                          Force (X Translation) Narrowband (deltaf=.078 Hz)
       1.0E+02



       1.0E+01



       1.0E+00



       1.0E-01



       1.0E-02



       1.0E-03



       1.0E-04



       1.0E-05
                 0               100               200               300           400              500
                                                    Frequency (Hz)
                   19 :60XT+ 60XT+ 3                                           19 :60XT+ 60XT+ 3
           X AXIS FORCE AT COMBINED CG                                X AXIS FORCE AT COMBINED CG
         Stirling_Config-1_Op2_Baseline                               Stirling_Conf-1_Op1_Ambient


                     Tandem Stirling Convertor Centerline Force Misalignment Effects -
                           Hanning Broad Window; ∆f=.078 Hz; Force X- (lbf)



                                                         26




                                                                                                               13
                            Tandem Stirling Convertor
                    Rigid Body Moment (Baseline Configuration)


                                            Stirling Convertor MEL Test Results
                                    Force (Y Rotation) Narrowband (deltaf=.078 Hz)
1.0E+02



1.0E+01



1.0E+00



1.0E-01



1.0E-02



1.0E-03



1.0E-04



1.0E-05
               0                         100               200               300            400              500
                                                            Frequency (Hz)
             26 :60YR+ 60YR+ 6                                                         26 :60YR+ 60YR+ 6
       Y AXIS MOMENT AT UUT'S CG                                                 Y AXIS MOMENT AT UUT'S CG
   Stirling_Config1_Op2_Baseline                                             Stirling_Config-1_Op1_Ambient



                                      Tandem Stirling Convertor Centerline Force Misalignment Effects -
                                           Hanning Broad Window; ∆ f=.078 Hz; Moment Y- (in lb)
                                                                        27




                            Tandem Stirling Convertor Force
                            Centerline Misalignment Effects

                                           Tandem Stirling Convertors MEL Test
                                                Lateral Force in X direction
                                            due to Misalignment in Z direction
                                    5
                                  4.9
           Force in X (lbf rms)




                                  4.8
                                  4.7
                                  4.6
                                  4.5
                                  4.4
                                  4.3
                                  4.2
                                  4.1
                                    4
                                    -0.15         -0.1         -0.05               0      0.05         0.1         0.15
                                                           Misalignment in Z (inches)
                                  Fundamental Frequency at 82.5 Hz                                 Total (0-500 Hz)

          Tandem Stirling Convertor Centerline Force Misalignment Effects -
                Hanning Broad Window; ∆f=.078 Hz; rms force (lbf)

                                                                        28




                                                                                                                          14
          Tandem Stirling Convertor Moment
            Centerline Misalignment Effects

                                 Tandem Stirling Convertors MEL Test
                                        Moment about Y axis
                                  due to Misalignm ent in Z direction
                            50
           Moment about Y
                            49
             (in-lb rms)
                            48

                            47

                            46

                            45
                             -0.15   -0.1      -0.05      0        0.05   0.1    0.15
                                            Misalignm ent in Z (inches)
                   Fundamental Frequency at 82.5 Hz                 Total (0-500 Hz)
            Tandem Stirling Convertor Misalignment Moment Comparison -
               Hanning Broad Window; ∆f=.078 Hz; rms moment (in-lbf)

                                                     29




        Summary of Stirling Emission Test # 2

•   The Tandem Stirling Convertors did emit relatively benign tonal
    forces at it’s operational frequency and associated harmonics.
     – The rms responses are dominated by the fundamental 82.5 Hz
        operating forcing function.
•   An “optimum” alignment condition was observed at 0.050 inches
    above centerline, although within the + 0.100 in tolerance, the
    variation was small. (This may be due to the lack of “true zero”.)
•   Angular misalignment is a larger driver than centerline misalignment.
•   The resultant forcing functions are attenuated by representative
    mounting conditions.
•   The Stirling Convertors should be a non-disturber to Spacecraft
    Science with appropriate mounting efforts.
     – No extra effort was made to test a matched pair of TDC units.
         • Piston stroke of these 2 units were measured to be different.
     – A previous STC study measured much lower vibration emissions
        for a matched pair of units.
     – The tonal content of the emissions allows for further vibration
        reduction by using adaptive vibration reduction systems.

                                                     30




                                                                                        15
    Test 3. Modal Test of a single TDC Unit

•   Vibration tests were performed for modal
    characterization of the Stirling TDC
     – Particular interest is in measurement of deflection
       of the linear alternator when subject to random
       vibration excitation.
        • The alternator pressure shell was removed to
          allow access to the alternator shaft.
        • A fiberoptic probes used to measure the shaft
          deflection.
     – Testing was performed for both sine (0.25 G) and
       random (1/4 “flight” level, 2.17 Grms) excitation in
       both axial and lateral directions.
     – Testing performed for two different piston strokes.
     – Low level impact hammer tests were also
       performed.
•   Test data is currently being analyzed.
                             31




     Sample FRF from Modal Test of TDC




                             32




                                                              16
               Test 4. Vibration Transmissibility
                     Test of two TDC Units

•   Attempt made to study effect of possible prototypical launch
    configurations, by varying convertor package interface stiffness,
    approximately +/- 40%(50 Hz - 115 Hz) about fundamental
    frequency.
    – Actual interface test resonances occurred at 18 Hz (lateral
      test) and 36 Hz (axial test), and at 90 Hz (lateral test) and 104
      Hz (axial test).
•   Two Stirling TDC (with Heater ends facing and structurally
    mounted off major diameter of piston housing) were tested under
    vibration load:
    – Sine (0.25 G), Random (1/4 “flight 2.17 Grms & flat 2.0 Grms)
•   Transmissibility between power system interface and convertors
    will be studied.
•   Test data is currently being analyzed.
                                   33




               Test 4. Tandem Vibration
           Transmissibility Test Configuration




                                   34




                                                                          17
                                 Summary

         •   Stirling convertors are a viable alternative for
             spacecraft power systems and are currently being
             sereiously considered for various NASA missions.
         •   Testing performed to date at NASA GRC has shown
             that the engineering Stirling TDC units:
              – are capable (structurally and functional power
                 performance) of withstanding the launch liftoff
                 random vibration environments
              – are capable of meeting “good neighbor” vibratory
                 emissions requirements
              – further analysis currently being performed to
                 research modal characteristics and transmissibility
                 effects of Stirling TDC units for future system
                 integrator benefit
         •   Additional future dynamic testing of Stirling convertors
             at NASA GRC is planned.
                                      35




                   Acknowledgement & References

•   The authors would like to thank and acknowledge the numerous
    people &organizations that have contributed to the success of the
    Stirling dynamic test program. They include but are not limited to the
    following:
     – NASA GRC Power and On-Board Propulsion Technology Division
        (Thermo-Mechanical Systems Branch):
         • R. Shaltens, J. Schreiber, L. Thieme, S. Geng, R. Skupinski
     – NASA GRC Engineering Design and Analysis Division:
         • Structural Systems Dynamics Branch
            – M. McNelis, V. Suarez, S. Cutlip
         • Structural Dynamics Laboratory
            – S. Samorezov, P. Steve, R. Shaw, M. Houston, J. Szelagowski
     – DOE - R. Furlong; JPL - K. Chang; STC - M. White
•   References: NASA/TM-2000-210526 & 2000-210527

                                      36




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