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Advanced Radioisotope Thermoelectric Generator (ARTG)
Leverages Segmented Thermoelectric Technology
NETS 2015William Otting – Aerojet Rocketdyne
Tom Hammel – Teledyne Energy Systems
David Woerner – Jet Propulsion Laboratory
Jean-Pierre Fleurial – Jet Propulsion Laboratory
Abstract 5079National Aeronautics and Space Administration
Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena, California
Pre-Decisional Information -- For Planning and Discussion Purposes Only
Agenda
Background Design Study Objectives Advanced Thermoelectric Materials System Parametric Model Select Results Summary
Pre-Decisional Information -- For Planning and Discussion Purposes Only
eMMRTG
Background Advanced thermoelectric materials and couple technologies are being successfully
developed at JPL under the NASA sponsored Radioisotope Power Systems’ Thermoelectric Technology Development Project (TTDP) Advanced Thermoelectric Materials
– Skutterudite (SKD) materials for temperatures up to ~600°C (873 K)– La3-xTe4/Yb14MnSb11 Zintl materials extend temperature range to 1000°C (1273 K)
when segmented with the SKD materials
MMRTG:PbTe &TAGS
eMMRTG:Skutterudite (SKD)
Technology Status: – SKD technology is now developed and is being
transferred to industry (Teledyne Energy Systems) for production under the TTDP’s Advanced Thermoelectric Couple (ATEC) Task
Near Term Technology Infusion– Implementing SKD couples results in an
enhanced MMRTG (eMMRTG) providing a sizable 25% power boost at Beginning of Life and > 50% at End of Design Life
– Technology insertion into the existing MMRTG platform provides a low risk path to a high performing multi-mission generator
Pre-Decisional Information -- For Planning and Discussion Purposes Only
Background
Next Steps: Segmented Thermoelectric Technology insertion into a GPHS-RTG like platform
– Transition the n-type La3-xTe4 and p-type Yb14MnSb11 Zintl technologies to production
– Segmenting with the SKDs results in a high temperature couple suitable for deep space vacuum generators
– The segmented couples have demonstrated more than 15% thermal-to-electric efficiency across a 1000°C to 200°C ∆T
– Current ATEC technology work focuses on achieving low power degradation rates over the targeted design life (17 years)
The present design study was performed to evaluate options for implementing advanced segmented thermoelectric
technology into a deep space generator
Pre-Decisional Information -- For Planning and Discussion Purposes Only
ARTG Design Study
Objective: • Understand the first order design tradeoffs between mass, power, and efficiency
for a deep space generator implementing the segmented thermoelectric materialsApproach: • Integrate generator sizing and thermoelectric sizing into a single model to allow
parametric evaluation of the system considering a range of hot and cold junction temperatures.
– Use ATEC-ARTG deep space generator concept as a point of departure– Use measured thermoelectric material properties for thermoelectric sizing
and layout• Evaluate point design vacuum systems and a modular system
– Case 1: 18-GPHS modules, Thj = 1000°C– Case 2: 8-GPHS modules, Thj = 1000°C– Case 3: 8- GPHS modules, Thj = 850°C– Case 4: Modular; 4-to-16 GPHS modules, Thj =1000°C
Pre-Decisional Information -- For Planning and Discussion Purposes Only
Point of Departure Design: ATEC - ARTG
Advanced RTG• Advanced RTG – deep
space (vacuum only)• Incorporates Step-2
GPHS• Designed to withstand
EELV loads• Cantilevered ATEC
thermoelectric couples• Incorporates MFI/aerogel
insulation• Based on 12-GPHS
modules• Thj - 1273 K (1000°C)• Tcj - 569 K (296°C)• Mass – 38 kg
Pre-Decisional Information -- For Planning and Discussion Purposes Only
Advanced Thermoelectric Couple Technology
2x increase in ZTave over SOA Si-Ge alloys (1275 to 475 K DT) when combined through segmentation
Segmented Couple
x2 Efficiency of Heritage RTG Couples
Higher Performance Materials15% Conversion Efficiency at
Beginning of Life (BOL)
Pre-Decisional Information -- For Planning and Discussion Purposes Only
Trade Study Overview
TE SizingModel
Generator Sizing Model
System Parametric Performance Model
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
200 300 400 500 600 700 800 900 1000 1100 1200 1300
ZT
T (K)
LTP6‐3LTP6‐4LTP12‐3LTP13‐3LTP18‐2
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400
ZT
T(K)
AZH05-1
AZH06-1
AZH07-1
AZH08-1
100 g Baseline
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400
ZT
T(K)
Average Yb14MnSb11 ball-milled YMS233 after 720hrs at 1273K YMS234 after 720 hrs at 1273K YMS236 after 720hrs at 1273K YMS240 after 720hrs at 1323K YMS241 after 720hrs at 1323K YMS244 after 720hrs at 1323K YMS998-3 after 6 months at 1273K YMS998-4 after 6 months at 1273K YMS1002-3 after 6 months at 1273K YMS1660 after 6 months at 1273K YMS1666 after 6 months at 1323K YMS1660 after 12 months at 1273K YMS1666 after 12 months at 1323K YMS 1660 after 24 months at 1273K YMS1666 after 24 months at 1323K
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400
ZT
T(K)
ALT16-1 1500hr at 1273K
ALT16-1 after 6 months at 1273K
ALT16-1 after 12 months at 1273K
ALT22 BOL
ALT22 1500hr at 1323K
ALT22 after 6month at 1323K
ALT22 after 12 months at 1323K
ALT35 after 1500hrs at 1273K
ALT35 after 1500hrs at 1323K
TE properties
Point of DepartureGenerator Design
Leg HeightTE Height
TE Height
TE Gap
Key input variables # GPHS: Q input Tsink THJ/TCJ Load voltage (32.8 Vdc) T/E length
Key Outputs: Power output Number of T/E couples N and P leg: bit widths N and P leg: segment lengths T/E efficiency Open circuit voltage Generator efficiency Heat rejection sizing Generator dimensions/weight
Series/parallel circuit 3% Electrical losses Square cross-section legs Optimum shape factor
Pre-Decisional Information -- For Planning and Discussion Purposes Only
ARTGCase 1: 18-GPHS Modules, Thj=1000°C
Select System Plots
Pre-Decisional Information -- For Planning and Discussion Purposes Only
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
100 125 150 175 200 225 250 275 300 325
Specific Po
wer, W
e/kg
Cold Junction Temperature, deg C
Case 1: Fin Root Temperature Design ParametricThj=1000°C, 18-GPHS Modules
Case 1:Power Target – 500 WT hot junction – 1000°C (1273 K)TE length – 1.27 cm
442.3 W461.9 W481.4 W
499.1 W
516.8 W
535.8 W
Specific Power near Maximum at Tcj=250°C
Q inv = 244 W/GPHSPower @ 32.8 VPower includes 3% lead loss
T cold junction(deg C)
Mass(kg)
Number of Couples
Generator efficiency
Power Output
(W)
Specific Power(W/kg)
175 101.7 394 12.2% 535.8 5.27200 71.7 404 11.8% 516.8 7.20225 60.3 415 11.4% 499.1 8.28250 55.7 427 11.0% 481.4 8.64275 54.0 441 10.5% 461.9 8.56300 53.5 456 10.1% 442.3 8.27
Pre-Decisional Information -- For Planning and Discussion Purposes Only
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75
Specific Po
wer, W
e/kg
TE Length, cm
Case 1 – TE Height Design ParametricThj=1000°C, 18-GPHS Modules
Case 1:Power Target – 500 WT hot junction – 1000°C (1273 K)T cold junction – 250°C (523 K)Number of couples - 427
478.8 W
479.3 W479.8 W
480.3 W480.8 W
481.4 W482.1 W
GPHS RTGInsulation Thickness
Q inv = 244 W/GPHSPower @ 32.8 VPower includes 3% lead loss
ARTG
T fin root(deg C)
Generatorefficiency
Mass(kg)
Power Output
(W)
Specific Power(W/kg)
217 11.0% 55.0 482.1 8.76226 11.0% 55.7 481.4 8.64230 10.9% 57.0 480.8 8.44233 10.9% 58.7 480.3 8.19235 10.9% 60.7 479.8 7.90237 10.9% 63.0 479.3 7.60238 10.9% 65.7 478.8 7.29
Pre-Decisional Information -- For Planning and Discussion Purposes Only
ARTGCase 2: 8-GPHS Modules, Thj=1000°C
Select System Plots
Pre-Decisional Information -- For Planning and Discussion Purposes Only
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
100 125 150 175 200 225 250 275 300 325
Specific Po
wer, W
e/kg
Cold Junction Temperature, deg C
Case 2: Fin Root Temperature Design ParametricThj=1000°C, 8-GPHS Modules
Case 2:Power Target – 200 W T hot junction – 1000°C (1273 K)TE length – 1.27 cm
187.6 W195.8 W
203.9 W211.4 W
219.1 W
226.8 W
Specific Power near Maximum at Tcj = 240°C
Q inv = 244 W/GPHSPower @ 32.8 VPower includes 3% lead loss
T cold junction(deg C)
Number of Couples
Mass(kg)
Generator efficiency
Power Output
(W)
Specific Power(W/kg)
175 394 45.3 11.6% 226.8 5.01200 404 33.6 11.2% 219.1 6.52225 415 29.2 10.8% 211.4 7.23250 427 27.6 10.4% 203.9 7.39275 441 27.0 10.0% 195.8 7.25300 456 26.9 9.6% 187.6 6.97
Pre-Decisional Information -- For Planning and Discussion Purposes Only
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75
Specific Po
wer, W
e/kg
TE Length, cm
Case 2 – TE Height Design ParametricThj=1000°C, 8-GPHS Modules
Case 2:Power Target – 200 WT hot junction – 1000°C (1273 K)T cold junction – 225°C (498 K)Number of couples - 415
209.8 W210.2 W
210.6 W211.0 W
211.2 W211.4 W212.1 W
Q inv = 244 W/GPHSPower @ 32.8 VPower includes 3% lead loss
T fin root(deg C)
Generatorefficiency
Mass(kg)
Power Output
(W)
Specific Power(W/kg)
189 10.9% 29.7 212.1 7.13199 10.8% 29.2 211.4 7.23203 10.8% 29.5 211.2 7.16206 10.8% 30.0 211.0 7.03208 10.8% 30.8 210.6 6.84210 10.8% 31.7 210.2 6.63212 10.7% 32.7 209.8 6.41
Pre-Decisional Information -- For Planning and Discussion Purposes Only
ARTGCase 3: 8-GPHS Modules, Thj=850°C
System Plots
Pre-Decisional Information -- For Planning and Discussion Purposes Only
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
100 125 150 175 200 225 250 275 300 325
Specific Po
wer, W
e/kg
Cold Junction Temperature, deg C
Case 3: Fin Root Temperature Design ParametricThj=850°C, 8-GPHS Modules
Case 3:Power Target – 200 W T hot junction – 850°C (1123 K)TE length – 1.27 cm
Specific Power near Maximum at Tcj = 235°C
164.9 W173.6 W
183.2 W191.3 W
200.2 W
207.9 WQ inv = 244 W/GPHSPower @ 32.8 VPower includes 3% lead loss
T cold junction(deg C)
Number of
Couples
Mass(kg)
Generator efficiency
Power Output
(W)
Specific Power(W/kg)
175 502 43.7 10.7% 207.9 4.8200 516 33.4 10.3% 200.2 6.0225 535 29.5 9.8% 191.3 6.5250 554 28.0 9.4% 183.2 6.6275 579 27.5 8.9% 173.6 6.3300 604 27.4 8.4% 164.9 6.0
Pre-Decisional Information -- For Planning and Discussion Purposes Only
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75
Specific Po
wer, W
e/kg
TE Length, cm
Case 3 – TE Height Design ParametricThj=850°C, 8-GPHS Modules
Case 3:Power Target – 200 WT hot junction – 850°C (1123 K)T cold junction – 225°C (498 K)Number of couples - 535
190.3 W190.5 W
190.7 W190.9 W
191.1 W191.3 W191.5 W
Q inv = 244 W/GPHSPower @ 32.8 VPower includes 3% lead loss
T fin root(deg C)
Generatorefficiency
Mass(kg)
Power Output
(W)
Specific Power(W/kg)
194 9.8% 29.6 191.5 6.47202 9.8% 29.5 191.3 6.49206 9.8% 29.9 191.1 6.39209 9.8% 30.6 190.9 6.23211 9.8% 31.5 190.7 6.05212 9.8% 32.6 190.5 5.85213 9.8% 33.7 190.3 5.64
Pre-Decisional Information -- For Planning and Discussion Purposes Only
Case 1-3 Summary Results and Observations
• The 18-GPHS ARTG provides 60-70% higher performance when compared to the previous SiGe GPHS RTG (300 W and 5.3 W/kg)
• The 8-GPHS ARTG shows a modest penalty for scaling down from 18-to-8 GPHS modules: about 12% lower on specific power and 5% lower on efficiency
• Design and operation at Thj = 850°C vs 1000°C reduces power and specific power by about 10% and reduces efficiency by about 8%
The ARTG has the potential to provide power levels and specific power levels60-70% above the SiGe GPHS RTG
Case 1:18‐GPHS (Step‐2)
Thj = 1000°C
Case 2:8‐GPHS (Step‐2)Thj = 1000°C
Case 3:8‐GPHS (Step‐2)
Thj = 850°C
Power @ 32.8 V 480 ‐ 515 W 205 ‐ 220 W 187 ‐ 200 W
Specific Power 7.2 ‐ 8.6 W/kg 6.5 ‐ 7.4 W/kg 6.0 ‐ 6.5 W/kg
Generator Efficiency 11.0 ‐ 11.8% 10.4 ‐ 11.2% 9.6 ‐ 10.3%
Pre-Decisional Information -- For Planning and Discussion Purposes Only
Case 1-3 SummaryCouple Comparisons: TE height = 1.27 cm
Case 2:8-GPHS Modules
1000°C/225°C
Case 1:18-GPHS Modules
1000°C/225°C
Case 3:8-GPHS Modules
850°C/225°CJPL Test Couple:1000°C/200°C
Thermoelectric couple sizes required are within the range of those already fabricated at JPL
Pre-Decisional Information -- For Planning and Discussion Purposes Only
Concept 4 - Modular
Pre-Decisional Information -- For Planning and Discussion Purposes Only
Design Concept 4 – ModularARTG in 4-GPHS Building Block
Module 14-GPHSs
VL
32.8 V
- +
Module 14-GPHSs
VL
32.8 V
- +
Module 24-GPHSs
Module 14-GPHSs
VL
32.8 V
- +
Module 24-GPHSs
Module 34-GPHSs
Module 14-GPHSs
VL
32.8 V
- +
Module 24-GPHSs
Module 34-GPHSs
Module 44-GPHSs
4-GPHS Modules 8-GPHS Modules 12-GPHS Modules 16-GPHS Modules
Pre-Decisional Information -- For Planning and Discussion Purposes Only
Design Concept 4 – ModularARTG in 4-GPHS Building Block
4‐GPHS Modules 8‐GPHS Modules 12‐GPHS Modules 16‐GPHS Modules
Power @32.8 V 93.2 W 204.8 W 313.6 W 425.2 W
Specific Power 5.7 W/kg 7.3 W/kg 7.7 W/kg 8.1 W/kg
Generator Efficiency 9.5% 10.5% 10.7% 10.9%
• Q inv = 244 W/GPHS• Thj = 1000°C• Tcj = 250°C• Vload = 32.8 V
All systems utilize the same thermoelectric module as a common building block
The 32.8 V is generated in a 4-GPHS module array
Segmented Module
Pre-Decisional Information -- For Planning and Discussion Purposes Only
Summary and Conclusions• Study findings:
– Advanced segmented thermoelectric technology has the potential to provide a significant performance boost for deep space generators … about 60-70% over SiGe deep space generator
– Advanced segmented thermoelectric couples operate over the same temperature range as SiGe deep space generators … pushing the generator technology is not required
• Benefits of a modular generator:– A modular RTG based on a common multi-couple thermoelectric module
design has broad application for future missions while leveraging nonrecurring engineering and development costs
– Provides missions the flexibility to select the optimum power system size for their mission and helps NASA best manage its fuel inventory
An ARTG based on the segmented thermoelectric couples has the potential to provide power levels and specific power levels much higher than ever before making missions
more capable, cost effective, and potentially enabling new classes of missions
Pre-Decisional Information -- For Planning and Discussion Purposes Only