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MARS PATHFINDER BATTERYPERFORMANCE

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B. OTZINGER, D. PERRONE, S. DAWSON, T. VALDEZ

S. SURAMPUDI , R. EWELL, M. SHIRBACHEH,

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NASA BATTERY WORKSHOP

HUNTSVILLE, ALABAMA

NOVEMBER 18-20, 1997

ELECTROCHEMICAL TECHNOLOGIES GROUP

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https://ntrs.nasa.gov/search.jsp?R=19990017678 2020-06-18T00:45:23+00:00Z

JPL

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OUTLINE

° MISSION REQUIREMENTS

° BATTERY DESIGN FEATURES

" BATTERY OPERATIONAL OVERVIEW

• BATTERY PERFORMANCE- PRELAUNCH

- CRUISE

- EDL

- MARS OPERATIONS

° SUMMARY AND CONCLUSIONS

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MISSION REQUIREMENTS

• PRE LAUNCH 4 MONTH ACTIVE INVERTED STORAGE

• LAUNCH INVERTED BATTERY LAUNCH

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• CRUISE

• EDL

7 MONTH ACTIVE STORAGE

40 AH, 1080 WH

• MARS OPR. CYCLES 30 CYCLES(1CYCLE/DAY, 8HOUR CHARGE 16 HOURDISCHARGE) 50% DOD

• WEIGHT 15 KG

• DIMENSIONS 9.8" x 7.4" x 7.4"

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• VOLTAGE 27 V

• CAPACITY 40 Ah

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• RATE CAPABILITY 1-5 A

PULSE CAPABILITY 40 A FOR 40 MSEC

• CYCLE LIFE 40

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• WET LIFE 14 MONTHS

• WEIGHT 15 KG

• DIMENSIONS 9.8" x 7.4" x 7.4"

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KEY CELL DESIGN FEATURES

• Robust separator system - 5 layers of cellophane and 2 layers of polymer membrane.To achmevelong calendar and cycle hfe

_ • Triple redundant case-to-cover seal including basic ultrasonic seal.To prevent electrolyte leakageTo improve safety

• Large cell plate area - approximately 200 square inches.Low temperature operatmon"

For enhanced pyro-firing

• Unique leak-free cell vent valves.

For inverted battery operation

allow gas venting under off-limit operation

• Minimal free electrolyte

For inverted battery operation

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KEY BATTERY DESIGNFEATURES

& PROCESS

• Titanium fabricated battery case with sealable cover and gasket.Light weight constructiongas and electrolyte containment

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• Battery vent valve and pressurization port.

Redundant valve to protect cells from electrolyte loss

• Battery heater and two temperature sensors.

Thermal management for charge control

• Over-pot of cells,, surface conformal coating, connector back side pottingelectrolyte absorptmn system.

Prevent ionic conductive pathsImprove safety

and

•Cell Matching and selectionExtend cycle life

ELECTROCHEMICAL TECHNOLOGIES GROUP

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"I KEY BATTERY OPERATING STRATEGIES

• Battery was mounted inverted and maintained at 12 C during pre-launch andlaunch Phases

•Battery was partially dischar ed to o,, . _ g _ 80 YoSOC and on open circuit stand, at -5 tou aegrees C, during 7 Month cruise period.

• Battery was charged at end of cruise through 1.2 Ohm resistor to 0.2 A cut-offand 1.95 V I cell Ave.

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• Battery was heated to 15 to 20 degrees C prior to all charges.

• Battery was charged during Mars operations without resistor to a selectiveshunt limiter controlled maximum volta,-,- o: .... ,- ....

......... . . _. o,x vu_tage settings were availablew=tn 1.95 v / cell Ave.., the nom,nal full charge selection.

• Battery was taper charged !o a constant shunt limiter voltage, 1.95 V /Ave.. well below the 2 V. I,m,t e'----' .... .,. ..... cellfull charge result. ,,,_,,uy=u i, constant current charging with same

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BATTERY CAPACITY VS CHARGE VOLTAGE

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MARS PATHFINDER - 16 8ST Ag-Zn CELLS WITH 2+5 SEPARATOR SYSTEM

CONSTANT VOLTAGE CHARGE CHARACTERISTIC FOR NEW CELLS WITH 4.5 AMPERE INRUSH AT

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VOLTAGE

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, MARS Pathfinder Power System Configuration Relays

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Deadface

Main B_Relay

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SUMMARY AND CONCLUSIONS

• The first use of a silver-zinc battery in a spacecraft application thatcalled for extensive rechargeable operation after 12 months of activestand hasproven to be very successful.

BST has developed a silver-zinc battery with unique design featuresfor the Mars Pathfinder mission.

• JPL has developed battery management strategies to meet the MarsPathfinder mission requirements.

- Partial SOC at low temperature and open circuit stand was found to bethe most effective method for insuring extensive cycle life following along period of active storage

- Silver-zinc battery charging at a reduced constant voltage was shownto provide full charge and a capability of supporting a large number ofcycles.

- Launch of an inverted silver-zinc battery was shown to be possiblewhen a leak free cell vent valve is employed.

- The use of a silver-zinc battery and shunt limiter in a direct energytransfer power system resulted in a very energy efficient designapproach.

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ACKNOWLEDGMENT

The work described here was carried out at the Jet Propulsion Laboratory,

California Institute of Technology, under contract with the

National Aeronautics and Space Administration.

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