advanced radioisotope thermoelectric generator (artg...

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


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


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


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


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


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)


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


ARTGCase 1: 18-GPHS Modules, Thj=1000°C

Select System Plots


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


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


ARTG

T fin root(deg C)

Generatorefficiency

Mass(kg)

Power Output

(W)


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



Select System Plots


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



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



Number of Couples

Mass(kg)


Power Output

(W)


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


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



209.8 W210.2 W

210.6 W211.0 W

211.2 W211.4 W212.1 W


T fin root(deg C)

Generatorefficiency

Mass(kg)

Power Output

(W)


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



System Plots


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



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


Number of

Couples

Mass(kg)


Power Output

(W)


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


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



190.3 W190.5 W

190.7 W190.9 W

191.1 W191.3 W191.5 W


T fin root(deg C)

Generatorefficiency

Mass(kg)

Power Output

(W)


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


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%


Case 1-3 SummaryCouple Comparisons: TE height = 1.27 cm

Case 2:8-GPHS Modules

1000°C/225°C


1000°C/225°C


850°C/225°CJPL Test Couple:1000°C/200°C

Thermoelectric couple sizes required are within the range of those already fabricated at JPL


Concept 4 - Modular


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


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


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


advanced radioisotope thermoelectric generator (artg...

Documents