Gibson, Marc A.

Maxwell, Briggs

Sanzi, James L.

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Two Phase Titanium Water Heat Pipe for Space 
Rated Stirling Power Conversion
Ninth International Conference on Two-Phase 
Systems for Ground and Space Applications 
Baltimore, MD Sept. 22-26, 2014
Marc Gibson, Jim Sanzi, Max Briggs
https://ntrs.nasa.gov/search.jsp?R=20150002092 2019-08-31T14:09:24+00:00Z
National Aeronautics and Space Administration
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Background 
• Radioisotope Power System (RPS) options that use Pu238 
General Purpose Heat Sources (GPHS):
– Multi-Mission Radioisotope Thermoelectric Generator (MMRTG)
– Advanced Stirling Radioisotope Generator (ASRG)
MMRTG (8 GPHS)
ASRTG (2 GPHS)
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ASRG Thermal Control
• GPHS provides approx. 250Wt
• Convertor Accepts approx. 200Wt
• Conversion of 200Wt to 70We
• Rejects approx. 130Wt from convertor 
to radiator housing
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Radioisotope Power Systems
110 We Multi-Mission 
Radioisotope Thermalelectric
Generator  (MMRTG)
8 GPHS Plutonium Fuel 
Modules
140 We Advanced Stirling
Radioisotope Generator (ASRG)
2 GPHS Plutonium Fuel 
Modules
500-1000 We ASRG
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Conduction vs. Two-Phase 
• Conduction fins become too heavy as 
rejection power levels increase
• Two-phase heat pipe uses working 
fluid vapor to transfer heat
• Hollow design for vapor path 
creates much lighter design
CSAF
RCHS
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Technology Derived Design Requirements
• Thermal 
– Reject 130Wt from Stirling Convertor (RCHS ID) to 
generator housing (RCHS OD) DURING LAUNCH
– Operational Temperature Range: 50-150C
– Temperature Delta <30C
• Environment
– Assembly Test and Launch 
• Accelerations: Specific to Launch Vehicle (Peregrine)
• Horizontal and Vertical Orientations: Specific to Spacecraft
– Atmospheric and Vacuum Environment
• Atmospheric during ground, launch
• Vacuum or Atmospheric during transit and science return 
depending on mission
Structural
– Survive Thermal and Environmental requirements
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RCHS Design
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RCHS Design
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RCHS Design Continued
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Testing
• Ground
– 1g Environment
– Wick Capillary Performance
– Thermal Vacuum
– Power Capacity
– Vibration
• Parabolic
– 0-2g Gravitational Performance 
• Microgravity, Lunar, and Martian Environments 
• Sounding Rocket
– Peregrine Specific Launch Accelerations
– 6+ minutes of microgravity  
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Ground Testing; Wick Performance
-100 Titanium Powder
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Ground Testing, Thermal Performance Cont.
T1 T2
T3 T4 T5
T0
T0 T1
T2
T3 T4 T5
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Ground Testing; Thermal Performance 
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Parabolic Testing
• 200+parabolas 0-2g
• Multiple power levels
• Multiple Orientations
Thermal Performance was 
unaffected by 0-2g gravity levels!
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Sounding Rocket Experiment
• Radioisotope Power systems are fueled at launch 
pad and must perform thermal management before, 
during, and after launch scenarios
• RCHS must be able to:
1. Reject 130Wt from the Stirling convertor to the 
radiator housing  in any spatial configuration 
during 1g, hyper-gravity, negative gravity, and 
microgravity. (For this experiment, the Stirling convertor has 
been replaced with an electrical heater and the radiator housing 
with an air/PCM heat exchanger)
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Peregrine Rocket
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RCHS Experiment 
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Vibration Testing
15
 Vehicle Level One Vehicle Level Two 
 
 
 
 
S 
I 
N 
E 
 
Sweep Rate: 4 oct./min. 
 
Test Profile: 
3.0 in./s        10-144 Hz 
7.0 g         144-2000Hz 
 
 
 
 
THRUST AXIS ONLY 
Sweep Rate: 4 oct./min. 
 
Test Profile: 
3.84 in./s              5-24 Hz 
1.53 g              24-110 Hz 
3.50 g            110-800 Hz 
10.0 g          800-2000 Hz 
 
 
THRUST AXIS ONLY 
 
 
 
R 
A 
N 
D 
O 
M 
Duration: 20 sec./axis 
 
Thrust Axis Spectrum: 
10.0 grms 
0.051 g2/Hz 20-2000 Hz 
 
Lateral Axis Spectrum: 
7.60 grms 
0.029 g2/Hz 20-2000 Hz 
 
Duration: 10 sec./axis 
 
Spectrum: 
12.7 grms 
0.01 g2/Hz               20 Hz 
0.10 g2/Hz           1000 Hz 
(on 1.8 db/oct. slope) 
0.10 g2/Hz 1000-2000 Hz 
 
SAME IN ALL AXES 
 
T 
E 
S 
T 
 
I 
N 
F 
O 
 
LEVEL 1 VEHICLES 
 
Terrier-Orion 
Terrier-Malemute 
Single Stage Improved-
Orion 
Terrier-Lynx 
LEVEL 2 VEHICLES 
 
Black Brant V 
Black Brant VIII 
Black Brant IX 
Black Brant X 
Black Brant XI 
Black Brant XII 
Table 8 Limiting Bending Moments * 
Vehicle Moment (in.-lb.) 
Orion 100,000 
Malemute 200,000 
Black Brant 300,000 
Limit Model 1830 TEAM table to a max. of 240,000 in.-lb. overturn moment. 
Input to payload during 1/2g sinusoidal vibration must be limited during first 
bending mode via dual control accelerometer at CG of the payload. This is done 
to avoid exceeding the maximum bending moment at the base of the payload.  
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Comparison Data 
RCHS CSAF
Mass 175g 750g
Delta T @ 130W Heat Rejection 12 10
Max. Thermal Conductance >1000 W/K <20 W/K
Temperature Range 50-250C -200 to 250C
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Conclusion
• RCHS heat pipe technology provides a passive 
thermal control option for current and higher power 
Radioisotope Stirling Generators 
• Current 130W heat rejection application using the 
RCHS provided a 4:1 decrease in mass over current 
state of the art with similar thermal performance
• Ground and flight testing of the RCHS has validated 
the thermal performance over a wide range of 
environments applicable to TRL5
• Peregrine sounding rocket experiment will validate 
the RCHS performance through launch and 
microgravity operations


Two Phase Titanium Water Heat Pipe for Space Rated Stirling Power Conversion

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