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1Strauch – General Atomics
Radioisotope TPV Power Systems for SpaceGeneral Atomics Technology Information - Business Sensitive
General Atomics Thermo-Photovoltaic (TPV) Power Sources
Presented By:
Jason Strauch
(858)-999-5239
Presented To
Nuclear and Emerging
Technologies for Space
Albuquerque, NM
Feb 23-25, 2015
Milli-Watts to 10s of Watts for 20 years
2 W Power Source
2Strauch – General Atomics
Radioisotope TPV Power Systems for Space
History and Acknowledgements
TPV Power Source Overview
Heat Source
TPV Cells
Optical System
System Performance
NASA Specific Designs
Path Forward
Overview of GA Radioisotope Power System
3Strauch – General Atomics
Radioisotope TPV Power Systems for Space
TPV History
TPV Technology developed over 10 year period under
Naval Reactors program: highly funded competition
between KAPL and Bettis National Labs, ~$100M from later
‘90s to early 2000s
DARPA RIMS program had first fueled TPV test, heat source
and cells decoupled, ~$1.5M from 2004 to 2006
DARPA MIPS program resulted in integrated design and
long term fueled testing, ~$3.5M from 2006 to 2012
GA IRAD scales design up to current level, with other
support, ~$1.5M from 2012 to 2014
NASA TPV programs achieve 15-19% efficiency in GPHS
electrically heated system at much larger scale, 2007-2012
History and Acknowledgments
4Strauch – General Atomics
Radioisotope TPV Power Systems for Space
TPV Power Source for NASA
~2x the efficiency of traditional thermoelectric RTGs
- Reduced fuel loading = lower weight
and fuel cost
Scalable from 1 mW to >50 W
- Higher efficiency than direct conversion such as
alpha or betavoltaics or chemical batteries
- Design allows varying isotope fuel loading / power
source size
20+ year life
- Proven minimal neutron TPV cell degradation
Solid State – no moving partsGA 2 We TPV battery
next to a standard D-cell
Ideal for outer planetary exploration (beyond solar)
or deep space missions.
5Strauch – General Atomics
Radioisotope TPV Power Systems for Space
Heat Source - Isotope Selection
Isotope candidates for 2 We/Long Life Power Source
Study of ~3000 total isotopes results in just 3 reasonable
candidates
Critical is the Specific Power and Half Life
Also important is the semiconductor lattice damage due to
neutron flux; Cm-244 used to study neutron degradation
Isotope parameters after 20 years:
PU-238 best for NASA missions
IsotopeHalf Life (Years)
Thermalpower
[W]
Specific Power (W/g)
Fuel mass[gm]
Fuel Volume[cm^3]
Eff.[%]
BatteryVolume
[cm3]
Radiation Dose
[mrem/hr]
PEOL[W]
EOL/BOLThermal Power
EOL/BOL Output
NeutronDamage
Factor
Sr-90 28.7 25.5 0.92 34.00 13.08 8 80 42,000.0 1.61 19.2% 81.5% 0.5%
Pu-238 87.7 25 0.56 63.25 12.53 8 78 1.5 1.81 6.5% 90.5% 3.2%
Am-241 432 30 0.11 365.00 33.22 6.8 140 14.9 1.92 1.3% 96.2% 2.5%
6Strauch – General Atomics
Radioisotope TPV Power Systems for Space
Safe Heat Source - Pellet Containment
All tests were performed cumulatively on a single sample. The standard allows 2 samples per test.
Double e-beam welded, 90Ta/10W MIPS
pellet and analysis
General Atomics has developed safe fuel pellet designs for terrestrial use at 2 scales
Passed tests include, among others: 800C for > 30 min 1000 kg crush test 500C at 13,800 psi internal
pressure (33 yr battery operation equivalent at 627C)
70 MPa external pressure
Temperature cycling: -40C (20 min) to 600C (1 h) and thermal shock 600C to 20C
The 2 We/ 20 year pellet
will be encapsulated to
meet safety standards
by LANL and tested by
arc-jet at NASA Ames
LANL-GA designed 20 W Heat
Source Pellet
Potential heat source design using NASA GPHS have been developed
For DARPA MIPS a pellet design has been developed to pass ANSI class 5,
49 CFR173.469 and Pacemaker Interim Guidance standards
7Strauch – General Atomics
Radioisotope TPV Power Systems for Space
Four Critical Areas are Needed for Successful Device Development
TPV Design
Epitaxial Growth
Cell Processing1.Back Contact Etch
2.Isolation Etch
3.Dielectric Etch
4.Metallization
Electrical
Testing
With shunting defects
Without shunting defects
Defect density
= 9E4 / cm2
Defect density
< 100 / cm2
TPV Devices Fabrication
TPV cells are difficult to make and the capability exists at GA
1 2
3 4
8Strauch – General Atomics
Radioisotope TPV Power Systems for Space
0
5
10
15
20
25
30
600 800 1000 1200 1400 1600 1800
De
vic
e E
ffic
ien
cy
Hot-Side Temperature (K)
Eg=0.50 eV
Eg=0.55 eV
Eg=0.60 eV
Eg=0.65 eV
Eg=0.70 eV
Optimization of TPV Cells Power Conversion
InGaAs TPV devices are the best for
NASA applications
Bandgap at 0.6 eV (2.07 micron)
has highest conversion efficiency
for ~1000 K
Produce 0.25 to 1 W/cm2 at >20%
device efficiency
0
0.5
1
1.5
2
2.5
300 500 700 900 1100 1300 1500 1700 1900 2100 2300 2500Wavelength (nm)
Irra
dia
nce, W
/m2-n
m..
.
0
20
40
60
80
100
120
140
160
180
Irra
dia
nce, W
/m2-n
m..
.
Increasing Energy of Photons
InGaP
GaAsSi
GeInGaAs
1050K
Blackbody
Solar
Space
Solar
Earth
0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3 2.5Wavelength (microns)
Band edge of
convertible
photons for
different PV
material
systems
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
1000 1100 1200 1300 1400 1500 1600
Po
we
r D
en
sit
y (W
/cm
2)
Hot-Side Temperature (K)
Eg=0.50 eV
Eg=0.55 eV
Eg=0.60 eV
Eg=0.65 eV
Eg=0.70 eV
Eg=0.74 eV
InGaAs TPV Cell Power Density Best across wide range of temperatures
InGaAs TPV Cell Efficiency best overall
Conversion range
9Strauch – General Atomics
Radioisotope TPV Power Systems for Space
TPV Cells – Tunable Voltage and Load Matching
TOP FIELD
EMITTER
BASE
BACK FIELD
INSULATING SUBSTRATE
Back
Surface
Reflector
Insulating
InP
Substrate
- Busbar
(device
contact)
InGaAs/InP MIM Structure (not to scale)
Epitaxial
MIM
Structure
Dielectric
insulator
AR
coating
+ Busbar
(device
contact)
Cell
interconnects
TOP FIELD
EMITTER
BASE
BACK FIELD
INSULATING SUBSTRATE
TOP FIELD
EMITTER
BASE
BACK FIELD
INSULATING SUBSTRATE
Back
Surface
Reflector
Insulating
InP
Substrate
- Busbar
(device
contact)
InGaAs/InP MIM Structure (not to scale)
Epitaxial
MIM
Structure
Dielectric
insulator
AR
coating
+ Busbar
(device
contact)
Cell
interconnects
Monolithically Integrated Module (MIM)
TPV cell voltage can be tailored for
specific applications
Diodes are series-connected on-chip
Reduced I2R (resistive) losses
Same power source can deliver multiple
voltages, for instance 12 V and 24 V from a
single power source
0
5
10
15
20
25
30
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
Forward Voltage (V)O
utp
ut C
urr
ent (m
A)
0
5
10
15
20
25
Outp
ut P
ow
er
(mW
)
himp = 99.0%
himp = 99.9%
4 junction TPV cell
@ Temit = 1100K
2 junction TPV cell
@ Temit = 900K
50 W load line
6-Junction MIM
Load matching efficiencies up to 99% by optimizing
number of junctions
10Strauch – General Atomics
Radioisotope TPV Power Systems for Space
TPV Cell Fabrication Sustained at GA
General Atomics Clean Room
All process steps are performed in house
Epi wafers are supplied by Sandia National Lab
In-house material characterization used to
determine material quality
TPV Cells
Before Dicing
General Atomics has the facilities and capabilities to
deliver TPV cells and systems
11Strauch – General Atomics
Radioisotope TPV Power Systems for Space
2 arrays fabricated by General Atomics
Contain 4 strings of 4 MIMs in BeO
30 junction 0.6 eV InGaAs
VOC = 12V
ISC = 0.24 A
FF = 70-72
String VMP = 37.9 V
String PMP MIN = 8.0 W
Performance exceeded 26% larger legacy array
From Dave Wolford, Overview and Status of Radioisotope Thermophotovoltaic (RTPV) Power System Development
for Space Exploration Missions TPV-9 World Conference, 2010
NASA GRC RTPV Test Panel Built by GA
GA built the best panel tested by NASA and maintains that capability
12Strauch – General Atomics
Radioisotope TPV Power Systems for Space
The pellet container design conforms as
closely to the NASA GPHS design as is
possible, working from publicly
available information.
GPHS Design Based on Current NASA Heat Sources
Carbon Fiber Sleeve
Iridium
Cladding
Graphite Impact Shell
Aeroshell
Pu-238 Pellet
GPHS GA
Iridium Cladding 0.55 mm(minimum)
0.55 mm
Graphite Impact Shell
~5 mm 5 mm
Carbon Fiber Sleeve
~2 mm 2.4 mm
Aeroshell ~5 mm 6 mm
Total shielding
thickness
12.7 mm 14.4
mm
CSNR’s cermet fuel would be an enabling technology for much
higher-performing TPV systems as it requires little-to-no additional packaging (pressure containers, etc)
Slide 12 of 19
13Strauch – General Atomics
Radioisotope TPV Power Systems for Space
TPV Power Source for Space Power
~2x the efficiency of traditional thermoelectric RTGs
- Reduced fuel loading = lower weight and fuel cost
Scalable from 1 mW to >50 W
- Higher efficiency than competing technologies
20+ year life
- Proven minimal neutron TPV cell degradation
Solid State – no moving parts
GA 2 We TPV
battery next to
a standard D-cell
Ideal for outer
planetary exploration
or deep space
missions.
Launch 1 Year EOL 2 Year EOL 10 Year EOL
20 Year EOL
P0 61.502W
T BOL 986.653K
hsysB 10.946 %
PB 6.732 W
mf 141.216 gm
H_bat 7.372 cm
D_bat 6.13 cm
V_bat 217.566 cm3
mission_duration 1 yr
Pti 61.078W
T EOL 985.362K
hsysE 10.528 %
PE 6.43 W
mission_duration 2 yr
Pti 60.656W
T EOL 984.071K
hsysE 10.153 %
PE 6.159 W
mission_duration 10 yr
Pti 56.987W
T EOL 972.455K
hsysE 7.86 %
PE 4.479 W
mission_duration 20 yr
Pti 52.621W
T EOL 957.612K
hsysE 6.161 %
PE 3.242 W
14Strauch – General Atomics
Radioisotope TPV Power Systems for Space
Electric Power Out
Thermal Power
EfficiencyFuel Mass
Thermal Density
mWe per gm fuel
Flight-Launched NASA/Aerodyne MMRTG
120 W 2000 W 6% 4800 gm 1.09 W/cm^2 25 mW/gm
NASA GPHS brick TPV withGA built panels
38 W 250 W 15% 570 gm 0.64 W/cm^2 66 mW/gm
GA new GPHS Design 6.7 W 62 W 11% 140 gm 0.54 W/cm^2 50 mW/gm
GA TAPS 3.0 W 30 W 10% 69 gm 0.58 W/cm^2 43 mW/gm
TAPS pellet cavity filled 21.68 W 51 gm 0.50 W/cm^2
TAPS form factor with 1.5mm Iridium clad
cermet43.98 W 100 gm 1.01 w/cm^2
LANL pellet cavity filled 30.7 W 70 gm 0.57 W/cm^2
LANL form factor with 1.5mm Iridium clad
cermet58.81W 140 gm 1.09 W/cm^2
GPHS pellet with cladding
44.363 W 100 gm 1.25 W/cm^2
NASA Power Source Comparison
Thermal power per unit surface area is a major driver of performance in TPV systems
-Increased emitter temperature
-Higher cell performance and efficiency
-Increased thermal power
-Reduced pellet surface area
Strauch et al., Radioisotope Fueled TPV Power Systems for Space Applications
15Strauch – General Atomics
Radioisotope TPV Power Systems for Space
TPV Power Conversion – Optical Considerations
Emitter Filter and TPV CellHeat Source
radiativelyor
conductively coupled
Considerations: Radioisotope Power density Radiation leakage
Considerations: Selective photon
emission Mechanical properties Long term operation Evaporation rate Surface Quality
Considerations: Long-term operation Radiation degradation Minimized absorption Transmission of convertible light Reflectance of non-convertible light Surface Quality
Convertible photons
Non-convertible photons
TPV System Components
Photonic cavity and thermal control is critical for high system efficiency
16Strauch – General Atomics
Radioisotope TPV Power Systems for Space
Power increases as temperature to the 7th
power
With selective emitter (SE) a given source operates at a higher temperature
2 We battery operates currently at ~1050K
System Efficiencies
Without SE With SE
950K 4.7% 5.6 %
1050K 7.2% 8.5%
1100K 8.4% 10.1%
1200K 10.3% 10.9%
Selective Emitter and Temperature Dependence
InGaAs Cell
Quantum Efficiency
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
wavelength in micron
Emitter Temperatures: 1100 K
1050 K
950 K
Heat radiation with
Selective Emitter
Heat radiation without
Selective Emitter
The selective emitter is instrumental for high system efficiency
17Strauch – General Atomics
Radioisotope TPV Power Systems for Space
Front Side Filter Increases Efficiency by
Reducing Cell Temperature
Wavelength (m)
Re
fle
ctivity,4
5
AO
I
0 5 10 150
10
20
30
40
50
60
70
80
90
100
Interference Stack
Tandem Filter
Plasma Layer
Me
asu
red
Re
fle
ctivity, 45 o
AO
I (%
)
BAD (2-6 µm)
Interference Filter
InP Substrate
InPAs Plasma Layer
Glue
TPV Cell
Heat Source
Photon Emission
Anti-Reflection Coating
BAD (6- ∞ µm)
Anti-Reflection Coating
GOOD
(1-2 µm)
TPV Cell and filter stack and Layers
Non convertible photons in the TPV device become phonons in the cell
Phonons increase cell temperature & reduced voltage, power & efficiency
Spectral measurements of filter and stack
Tandem Filter Combines Performance of Interference Filter & Plasma Filter
Resulting in Increased Source Temperature & Higher System Efficiency
Front side filters fabricated by Rugate Technologies
18Strauch – General Atomics
Radioisotope TPV Power Systems for Space
Control box
TPV Power Source Testing
High Power Battery with Passive Cooling Fins
Hermetically sealed high power battery package
Demonstration of TAPS battery in a laboratory environment shows true performance and efficiency
GA has performed fueled tests for MIPS and electrically heated tests
at both the MIPS scale (5-50 mW) and 2 W Power Source scale
19Strauch – General Atomics
Radioisotope TPV Power Systems for Space
2 W TPV Power Source Performance - Output Power
Extensive system testing has
been performed and data gathered
System testing with legacy 10+ year old
TPV cells and filters
Measured pellet power conditions
correspond to fuel density and loading
for terrestrial application with pressure
containment
Cell development 90% of legacy best
System and design highly optimized and
ready for qualification testing-0.2
-0.15
-0.1
-0.05
0
0.05
0 5 10 15 20 25 30 35 40
Cu
rre
nt (
A)
Voltage (V)
Clamshell 1
Clamshell 2
Battery, clamshells connected in series
6 times better hex chip
Prediction based on prior data
Pmax = 2.7 W (h = 9.0%)Pmax = 2.3 W
(h = 7.6%)
30 W Pellet, Thot = 1069K
Pmax = 3.0 W (h = 10.1%)
Power Source performance demonstrated with a clear path to >10% efficiency
Pellet
Power,
Watts
Pellet
Temp,
K
Measured
Power
Output, W
Measured
Efficiency,
%
Efficiency with
Best Cells and
Filters, %
20 977K 1.5 4.9% 6.8%
25 1026K 2.3 6.3% 8.5%
30 1069K 3.0 7.6% 10.1%
34 1106K 3.6 NA 11.1%
20Strauch – General Atomics
Radioisotope TPV Power Systems for Space
TPV Power Source Scalability Modeled and
Demonstrated at Different Scales
Fuel
Density,
gram/cc
Pu238
Mass,
gram
Pellet
Power,
Watts
Power
Source
Output, W
5.9 35.7 20 1.5
7.3 44.6 25 2.3
8.6 53.6 30 3.0
9.6 60.5 34 3.6
Power
Level
Pu238 Mass
needed, grams
1 mW 1.2 gm
10 mW 1.8 gm
1.5 W 35.7 gm
3.6 W 60.5 gm
7.0 W 158 gm
Verified Scalability: Model predictions match test data
0.01
0.1
1
10
100
1000
10000
0 10 20 30 40 50 60 70 80 90 100 110
Elec
tric
Po
wer
Ou
tpu
t (m
We)
Battery Volume (cc)
DARPA MIPS program
Operating for over 414 days
Data using
electric heater
Predictions of
performance using LANL fuel pellet for various
fuel densities
Modelled data
1 to 2 We window
Model accurately predicts electrically
heated and isotope fueled systems
TPV Power Source
Power Levels and
Fuel Loadings
The 7 W version
includes full
impact shell and
aeroshell based
on GPHS design
Power source
performance
depends on fuel
density, purity
and mass. NASA
system will have
more fuel.
• 1-100 mW – AA cell size• 100 mW-2 W – D cell size• 2W – 20 W – Soda can size
Hardware developed, modeled and tested
21Strauch – General Atomics
Radioisotope TPV Power Systems for Space
TPV Power System Long Term Neutron Testing
0
10
20
30
40
50
60
70
80
0 10 20 30 40 50
Spec
ific
Po
wer
(We/
g-23
8Pu
)
Estimated Time with PuO2 (years)
TAPS - 2W
NASA - Voyager
NASA - MMRTG Mars RoverGA - 2 W RTPV
NASA -Voyager
MIPS program - fueled testing
140 days of Cu244 testing equivalent to
160 yrs with Pu238
414 days of continuous testing with Pu238
Cell degradation less than 1%/year
RIMS program had NRL perform Monte
Carlo analysis and e-beam neutron cell
testing showing <1%/year damage
0
0.05
0.1
0.15
0.2
0.25
0.3
0 50 100 150 200 250 300 350 400 450
Ma
xim
um
Po
we
r (m
W)
Time (days)
Curium Pellet
Plutonium Pellet
Predicted Output Power
244Cm 238Pu
Neutrons per spontaneous fission 2.72 2.22
Spontaneous fission branching ratio 1.37x10-4 % 1.85x10-7 %
Activity per gram of isotope 2.99x1012 dis/s-g 5.94x1011 dis/s-g
Neutrons emitted per sec per gram 1.12x107 n/s-g 3.81x103 n/s-g (1)
Fuel loading 0.2 g 1.4 g
Neutrons per sec 2.23x106 n/s 5.55x103 n/s
Acceleration factor at beginning of life 1 420
Curium fuel used to measure
neutron degradation of TPV cells
GA RTPV
Proven minimal TPV device degradation
22Strauch – General Atomics
Radioisotope TPV Power Systems for Space
FuelElectric
Power Out [W]
Efficiency [%]
Fuel Mass [gm]
Gamma Radiation [mrem/hr]
Neutron Radiation [mrem/hr]
Battery Volume [cm^3]
Battery Mass [gm]
Pu-238 Battery to Test Pu-238 1.55 7.8 50.6 0.382 0.825 69 665
Americium Same Output
Am-241 1.55 6.0 316 11.5 1.39 130 1380
Americium Same Battery Mass
Am-241 0.164 2.2 91.4 3.43 0.415 62 653
Americium Same Battery Volume
Am-241 0.248 2.8 110 4.10 0.496 69 723
238Pu and 241Am NASA Power Source Comparison
Two isotope designs for NASA applications developed
Modeled performance for ~1.5 W battery based on current tested design
23Strauch – General Atomics
Radioisotope TPV Power Systems for Space
What: Deliver long lived power sources for NASA Applications
Why: Best current solution for less than 100 W applications
requiring high efficiency long life power
Impact: New missions/operations possible, conserves limited fuel reserves while enabling NASA’s Space Science continuing missions
Parallel Testing and Development for fast track to flight missions
- LANL Pellet test: low cost and provides data while cermet fuel is developed and tested, ~$1.5M
- INL Am241 cermet development and arcjet testing
- Full qualification of balance of system components, ~$12-15M
More Missions are enabled by low fuel need and available scaling
- ISS flight test w Am241 cermet source – low power demo
- Cubesat, small landers, sensors, Europa mission
Path Forward – Enabling Continued NASA Missions
Through Efficient Use of Pu Fuel and Small Scales
24Strauch – General Atomics
Radioisotope TPV Power Systems for Space
Partners and Resources to Succeed for NASA’s Mission
Idaho National Laboratory (INL)
Battery assembly and CSNR
Oak Ridge National Laboratory (ORNL)
Fuel development and cladding
Los Alamos National Laboratory (LANL)
Pellet isotope preparation and assembly
(sealed source)
Sandia National Laboratory (SNL)
Wafer growth and testing
• Contact Information
• Jason Strauch: [email protected], (858)-999-5239
Partners to Form NASA Team
25Strauch – General Atomics
Radioisotope TPV Power Systems for SpaceGeneral Atomics Proprietary Information
Back Up Slides
26Strauch – General Atomics
Radioisotope TPV Power Systems for Space
Special Form Testing Status
Note: ANSI class 4 impact test and 49CFR173.469 percussion test are very similar; the more stringent ANSI
class 4 test will be performed. The Pacemaker Interim Guidance is 25% more energy impact than ANSI
Class 4 (equivalent of 2.6 kg mass from 1 m). Green has been completed, blue are ongoing efforts.
All tests are followed by leak tests meeting the ISO 9978 standard.
• Double E-beam welded,
90Ta/10W
• Er2O3 fuel surrogate
• Cumulative testing
Test ANSI Class 4 ANSI Class 5 49CFR173.469 Pacemaker Interim
Guidance
Temperature -40oC (20 min)
+400oC (1h) and thermal
shock 400oC to 20
oC
-40oC (20 min)
+600oC (1h) and thermal
shock 600oC to 20
oC
800oC (10 min) 800
oC (30 min)
External Pressure 25 kPa abs. (3.6 psi) to 7
MPa (1,105 psi)
25 kPa abs. (3.6 psi) to
70 MPa (10,153 psi)
1000 kg crush test
Impact
2 kg (4.4 lb) from 1 m
(3.28 ft.)
5 kg (11.0 lb) from 1 m
(3.28 ft.) Drop from 9 m (30 ft.)
onto target specified in
49CFR173.465
50 m/sec
Percussion Test Place on a sheet of lead,
struck by a steel billet 1.4
kg (3 lb) from 1 m (3.3
ft.), see Note 1
Vibration 3 times 30 min 25 to 80
Hz at 1.5 mm amplitude
peak to peak and 80 to
2000 Hz at 196 m/sec2
(20 g)
Not used
Puncture 50 g (1.76 oz) from 1 m
(3.28 ft.)
300 g (10.6 oz) from 1 m
(3.28 ft.)
Leaching
/Corrosion
7 days in water at RT, pH
6-8, 10 micromho/cm at
20oC. Dist. water at 50
oC
for 4 h
Seawater linear
corrosion less than 1
m/year
Temperature then
crush
800oC (30 min) then
1000 kg
Temperature at
pressure
500oC (30 min) at
pressure (33 yr.
equivalent at 627oC)
Temperature at
pressure -
cremation
1300oC (30 min) at
pressure (10 yr.
equivalent)
826K at 13,800 psi
27Strauch – General Atomics
Radioisotope TPV Power Systems for Space
b-
T1/2 = 2.6a
T1/2 = 138.4d
n
T1/2 = 87.7a
n
T1/2 = 18.1a
b-
T1/2 = 128.6d
Phase II & Phase IIIA testing and battery life testing
Not available, need to develop production pathway
Non-domestic source with high toxicity and low melting temperature
Non-domestic source, high radiation due to impurities
Phase IIIB source with oxygen exchange
b-
T1/2 = 2.6a
T1/2 = 138.4d
n
T1/2 = 87.7a
n
T1/2 = 18.1a
b-
T1/2 = 128.6d
Phase II & Phase IIIA testing and battery life testing
Not available, need to develop production pathway
Non-domestic source with high toxicity and low melting temperature
Non-domestic source, high radiation due to impurities
Phase IIIB source with oxygen exchange
(1) Includes neutrons due to <a,n> reactions with oxygen assuming 90% 16O enrichment (1,400 n/s-g)
244Cm 238Pu
Neutrons per spontaneous fission 2.72 2.22
Spontaneous fission branching ratio 1.37x10-4 % 1.85x10-7 %
Activity per gram of isotope 2.99x1012 dis/s-g 5.94x1011 dis/s-g
Neutrons emitted per sec per gram 1.12x107 n/s-g 3.81x103 n/s-g (1)
Fuel loading 0.2 g 1.4 g
Neutrons per sec 2.23x106 n/s 5.55x103 n/s
Acceleration factor at beginning of life 1 420
Using 244Cm for Neutron Degradation Acceleration Testing
28Strauch – General Atomics
Radioisotope TPV Power Systems for Space
0
50
100
150
200
250
300
350
400
450
0 20 40 60 80 100 120
Pre
dic
ted
Tim
e U
sin
g 2
38P
u (
years
)
Measurement Time Using 244Cm (days)
Using 244Cm for Neutron Degradation Acceleration Testing
244Cm 238Pu
Neutrons per spontaneous fission 2.72 2.22
Spontaneous fission branching ratio 1.37x10-4 % 1.85x10-7 %
Activity per gram of isotope 2.99x1012 dis/s-g 5.94x1011 dis/s-g
Neutrons emitted per sec per gram 1.12x107 n/s-g 3.81x103 n/s-g (1)
Fuel loading 0.2 g 1.4 g
Neutrons per sec 2.23x106 n/s 5.55x103 n/s
Acceleration factor at beginning of life 1 420
130 days of testing with 244Cm have been completed
26 yrs
57 yrs
100 yrs
29Strauch – General Atomics
Radioisotope TPV Power Systems for Space
GA Cleanroom Facility
In 2012, GA opened a state-of-the-art 1000 sq. ft. class 100/1000
cleanroom facility for semi-conductor materials engineering, photonics,
and electronic material fabrication.
Nanoscale Fabrication: Optical lithography,
Advanced dry etching
Thin-film deposition
Wet chemical processing
Thermal processing
Metrology
Back-End Processing
30Strauch – General Atomics
Radioisotope TPV Power Systems for Space
Cleanroom Full Equipment Capability
Oerlikon Leybold Univex
450B E-Beam Evaporator
Oxford Instruments PlasmaPro800+ Plasma Enhanced
Chemical Vapor Deposition (PECVD)
Reynolds Tech
Wet Process Hood
Karl Suss MA6 Mask Aligner and
Laurell Spin Coater
Oxford Instruments NGP 80 Reactive Ion Etch (RIE)Keyence VHX-1000E Digital Microscope
and Bruker Dektak xA
31Strauch – General Atomics
Radioisotope TPV Power Systems for Space
Characterization and Testing
Device Characterization and back end
processing equipment, including: FTIR, probe
stations, UV-VIS spectrometer, vacuum
chambers for a variety of tests, as well as in
house SEM and (in fall 2013) ellipsometry.