The incorporation of nickel-hydrogen technology for low-Earth-orbit spacecraft applications requires the establishment of a data base. An extensive test program was established to provide this data base. The test program is outlined and the preliminary test programs is presented

Mcdermott, J. K.

English

NASA Technical Reports Server

N87-11098
NICKEL-HYDROGEN LOW-EARTH-ORBIT
TEST PROGRAM
Joseph K. McDermott
Martin Marietta Denver Aerospace
Denver, Colorado
ABSTRACT
The incorporation of nickel-hydrogen technology for low-earth-orbit (LEO)
spacecraft applications require the establishment of a data base. An
extensive test program has been established to provide this data base. This
paper outlines the test program and presents preliminary test results.
INTRODUCTION
The vast majority of spacecraft secondary energy storage systems flown in
the last two decades were nickel-cadmium batteries. Such applications took
advantage of the inherently long cycle life, a good specific energy and high
reliability. The hermetically-sealed nickel-cadmium system required a
sophisticated charge control system, however, and as a result of temperature
sensitivity required operation under close environmental control. Increasing
spacecraft power requirements dictated the need toward a higher performance
battery system capable of a I0 year mission life with deeper
depths-of-discharge (DOD's) and variable load profiles. In the past, the
extensive data base for nickel-cadmium systems had restrained aerospace
contractors from investigating alternative energy storage systems. However,
the limitations of nickel-cadmium batteries, particularly usable energy
density, have provided strong economic incentives for a new system, and led
to the recent development in nickel-hydrogen cell technology.
Nickel-hydrogen cell and battery technology has matured to the point
where a viable choice now exists for current and future aerospace energy
storage applications. The nickel-hydrogen system offers a true hermetically
sealed design capable of thousands of maintenance free cycles without need
for complex charge control circuitry or close environmental control. The
real potential of nickel-hydrogen systems has aroused aerospace contractors
to conduct in-house studies and investigate the feasibility of
nickel-hydrogen implementation. Nickel-hydrogen cell technology represents
the best engineering choice for numerous power storage systems, and with the
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establishment and expansion in its data base, which is presently insufficient
(ref. i), the nickel-hydrogen system will become the practical choice.
Nickel-hydrogen battery cell technology has been successfully
demonstrated for geosynchronous (GEO) orbit applications, both by ground
testing and in-flight performance. The GEO data base cannot, however, be
extrapolated to provide pertinent LEO data. Applications of nickel-hydrogen
technology in LEO require the development of a cycle life data base with
DOD's in the 40% to 60% range. A nickel-hydrogen test program was thus
established to provide this LEO data base.
TEST PLAN
Table 1 identifies the suppliers and numbers of cells procured for
nickel-hydrogen LEO testing. Eagle-Picher and General Electric were selected
for the procurement of 36 Air Force designed nickel-hydrogen cells. Six (6)
Yardney cells were also procured. Four cells from Eagle-Picher are
identified on Table i as COMSAT designed cells. Eagle-Picher provided these
cells to Martin Marietta for LEO testing. The general concensus by the
aerospace industry is that the COMSAT cell is not adequately designed for LEO
application. The addition of the four COMSAT cells to the test program will
possibly provide evidence to either support or negate this assumption.
The matrix for the nickel-hydrogen testing is summarized in Table 2. The
primary area of interest is 40% DOD. This would translate into appreciable
weight savings when compared to nickel-cadmium systems (ref. 2). It is also
assumed that 40% DOD is a conservative test parameter. The test temperature
of 10°C is based on the present thermal design capabilities of typical
spacecraft (ref. 3). Vendors predict that 20,000 cycles at 40% DOD and 10°C
is attainable with their nickel-hydrogen cells. The 60% DOD test will serve
two main purposes: first accelerate the testing and provide early failure
rate data; and second, characterize cell performance at a higher DOD. The
added temperature of 20°C is of interest because further weight and cost
savings could be possible if the requirement for maintaining battery
temperature was less stringent. All testing conducted under this matrix will
be a 90 minute LEO regime consisting of a 55 minute charge and a 35 minute
discharge. The 90 minute LEO is generic, and also accelerates testing to an
extent. The charge control parameter was considered to be a significant
factor with regard to LEO testing. Analysis of test equipment capabilites
and the results of preliminary testing support charge control utilizing a
current integrator. Charge control is therefore maintained by ending the
charge and discharge phase after a predetermined capacity is achieved. A
recharge fraction roughly between 1.05 and I.I0 (dependent upon test
temperature and cell life) will be maintained for all testing.
362
TEST PROCEDURE
All the nickel-hydrogen cells subjected to Life Cycle Tests have aluminum
collars. The collars provide cell support to the test fixture and aid in
thermal management. All cells are tested in the horizontal position.
Possible problems have been identified with testing in the vertical position,
therefore the horizontal testing requirement was imposed. It is also the
general concensus that testing the cells in the horizontal position will aid
electrolyte distribution within the cell. The test fixture for mounting and
thermal management consists of copper tubing pressure-fitted between two
aluminum plates. Each test fixture has mounting provisions for four cells.
The test fixtures are then mounted in an environmental test chamber. The
test fixture temperature is controlled by a circulator bath. The chamber
temperature is set to match the test fixture. Preliminary test data shown in
Figure I indicates the delta temperature between cell case and test fixture
is less than 5°C during LEO testing.
Nearly all the nickel-hydrogen cells tested have strain gages. The
strain gages allow the cell pressure to be monitored during LEO testing.
Possible charge control utilizing cell pressure data has been proposed for
nickel-hydrogen cells, but for our test program the pressure data is for
characterization purposes only. It has been shown that a direct relationship
exists between the state-of-charge and the pressure of a nickel-hydrogen cell
(ref. 4, 5).
Table 3 outlines the actual test parameters for nickel-hydrogen LEO
testing. The discharge capacity for the 40% DOD testing is set at 20.0
ampere-hours. This translates into a discharge current of 34.4 amperes. The
charge current for the 40% DOD testing is set between 22.9 amperes and 24
amperes. Depending upon cell test temperature and life, the recharge
fraction is set between 1.05 and i. I0 by adjusting the charge current. The
end of a discharge phase is when 20.0 ampere-hours has been removed. The end
of a charge phase is when 21 to 22 ampere-hours (dependent upon test
temperature and life) has been returned. The 60% DOD testing follows the
same recharge fraction control scenario as the 40% DOD testing. The
discharge current for 60% DOD testing is set at 51.5 amperes while the charge
current is set between 34.3 amperes and 36.0 amperes.
For each test group, a representative cell will be temperature monitored
to thermally characterize the cell and test fixture (equipment). The coolant
plate will also contain thermocouple(s) to ensure test temperature is held as
close to 10°C or 20°C as possible. Cell pressure will be monitored by strain
gages. This data will be utilized for characterization purposes only and
will be reported in the future. Due to safety concerns, all testing was
conducted in an enclosed environmental chamber equipped with a nitrogen purge
system.
363
The definition of a cell failure during life cycle tests is the inability
of a cell to support an end-of-discharge voltage of 1.0 volt. At the
discretion of the test engineer, an attempt may be made to recondition the
cell. Cells which cannot support a 1.0 volt end-of-discharge voltage will be
removed from the test group. Life cycling will then continue on the
remaining cells. Analysis of the data from a failed cell will determine
final cell disposition.
A capacity test will be conducted every 1,000 cycles starting with cycle
0. The capacity test will consist of a cell discharge to 1.0 volt, followed
by a 16 hour charge at 5.0 amperes, followed Dy a 25.0 ampere discharge to
1.0 volt per cell. The objective of the capacity test is to characterize
cell degradation in relationship to LEO cycling. The capacity check may also
be in effect a reconditioning cycle, due to the fact the cell is fully
recharged. The data from the capacity test may also indicate possible
electrochemical changes within the cell associated with LEO cycling.
TEST RESULTS
Test results to date are primarily focused around the first delivery of
12 Air Force designed nickel-hydrogen cells and the four COMSAT cells. The
Acceptance Test Procedure (ATP) conducted at the vendor on the twelve Air
Force designed nickel-hydrogen cells during late May 1985 revealed a capacity
range of 59.8 to 63.2 ampere-hours (10°C test, 34.4 ampere discharge to 1.0
volt per cell). Final ATP testing at the vendor was completed in June 1985.
The cells were first tested in the Power Sources Laboratory in late July
1985. Initial capacity checks (five continuous cycles) consisting of a 5.0
ampere charge for 16 hours followed by a 25.0 ampere discharge to 1.0 volt
per cell revealed a fourth cycle capacity range of 45.0 to 48.2
ampere-hours. Table 4 lists the capacities for both the vendor ATP data and
the fourth cycle capacity check conducted in-house. The in-house capacity
discharge was continued to an end-of-discharge voltage of 0.5 volt.
Significant residual capacity was noted in the cells as shown in Table 4. A
typical capacity discharge cycle is depicted in Figure 2. A second, distinct
voltage plateau can be seen at 0.7 volt. All twelve nickel-hydrogen cells
shared this second plateau characteristic.
The first twelve vendor cells were divided into two groups. The first
test group consisted of eight series-connected cells tested at 10°C and 60%
DOD. The initial capacity (25.0 A to 1.0 V/cell) of this cell/battery test
group was 55.1 ampere-hours. Figure 3 depicts the end-of-discharge voltage
and recharge fraction plots for this test to date. The remaining four cells
were series-connected and placed on tests at 20°C and 60% DOD. The initial
capacity of this cell/battery test group was 44.0 ampere-hours. Figure 4
depicts the end-of-discharge voltage and recharge fraction plots for this
four cell test group to date.
364
The four COMSAT cells were series-connected and placed on tests at 10°C
and 40% DOD. The initial capacity of this four-cell test group was 62.5
ampere-hours. Figure 5 depicts the end-of-discharge voltage and recharge
fraction plots for this four-ceil test group to date.
Testing has not been initiated to date on the 24 recently received vendor
cells nor the 6 Yardney cells. LEO testing on these cells will be underway
by December 1985. The addition of 36 more cells to the test program in 1986
will be the final group of cells procured for this test plan.
CONCLUSIONS
The significant loss of capacity observed in the first group of
nickel-hydrogen cells from ATP testing to our initial capacity testing has
several possible causes. The activation procedure for these cells followed
Rev F of the "Product Specification Nickel-Hydrogen Battery Cell" (ref. 6).
A hydrogen precharge of 40 psig is completed immediately prior to the
conditioning cycles and ATP testing. The hydrogen precharge has recently
been deleted from the specification, and nickel-hydrogen manufacturers have
suggested that the hydrogen pr_charge of 40 psig may have caused the noted
capacity degradation and resultant double-knee or second plateau discharge.
The twelve cells were in a stored , shorted condition for approximately six
weeks, and it has been postulated that during this period the hydrogen
precharge reacted with and changed the positive plate. At the present time,
extensive studies are underway by the vendor to characterize this positive
plate change. It was decided that for the second cell build of 24 cells a
revised cell activation procedure would be utilized. The 40 psig precharge
was reduced to a one atmosphere precharge, or approximately 16 psig.
Hopefully, this change will minimize the capacity loss observed on the first
twelve cells. The twenty-four cells recently received will undergo the same
receiving, inspection and initial capacity tests as the first twelve to
ensure an accurate evaluation of the revised activation procedure. No other
parameters in the manufacturing of the cell have been revised. Tests are
scheduled for November 1985 on the second build of twenty-four cells.
Cells under LEO cycling have nearly i000 cycles to date, therefore it is
too early yet to draw any conclusions regarding nickel-hydrogen performance.
Test control parameters were initially identified as major items for an
accurate and reliable test program. Early tests have shown the most reliable
method for charge control is ampere-hour integration. The coolant fixtures
have been shown to provide excellent thermal conductivity for the removal of
heat from the cells. Test control parameters have been optimized, and
hopefully cells under the LEO test program will meet the goal of 20,000
cycles.
365
REFERENCES
io
"An Industry and Government Survey: A Nickel-Hydrogen Testing Data Base",
Charles Badcock and Martin Milden, The 1984 Goddard Space Flight Center
Battery Workshop, p. 583.
o
"Nickel-Hydrogen Spacecraft Module Configurations Study",
William B. Collins, Joseph K. McDermott and Owen B. Smith,
The 1984 Goddard Space Flight Center Battery Workshop, p. 459.
o "In-Flight Performance of a Six Ampere-Hour Nickel-Cadmium Battery in
Low-Earth-Orbit", Joseph K. McDermott, The 1983 Goddard Space Flight
Center Battery Workshop, p. 325.
.
e
So
"The Open Circuit Stand Behavior INTELSAT VI Nickel-Hydrogen Batteries
and Its Relationship to Charge Rates and Temperature", P. F. Ritterman
and A. M. King, Proceedings of the 20th Intersociety Energy Conversion
Engineering Conference, p. 1.176.
"The GSTAR and SPACENET Nickel-Hydrogen Batteries for Geosynchronous
Orbit Applications", Stephen J. Gaston, Proceedings of the 19th
Intersociety Energy Conversion Engineering Conference, p. 259.
"Product Specification Nickel-Hydrogen Battery Ceil, PS 32014-031 Re£ F",
Hughes Aircraft Company, 23 June 1980.
366
TABLE 1. CELL SUPPLIERS FOR LEO TEST PROGRAM
CELL CELL NUMBER OF
TYPE
EAGLE-PICHER AIR FORCE 36
STATUS
12 CELLS RECEIVED 07/85
/
24 CELLS RECEIVED 10/85
EAGLE-PICHER COMSAT 04 04 CELLS RECEIVED 08/85
GENERAL ELECTRIC AIR FORCE 36 20 CELLS SCHEDULED
FOR DELIVERY 01/86
16 CELLS SCHEDULED
FOR DELIVERY 02/86
YARDNEY MAN-TECH 06 06 CELLS RECEIVED 10/85
TABLE 2. NICKEL-HYDROGEN LEO TEST MATRIX
DEPTH-OF-
ARGE
lO'C
20"C
40%
16 EP CELLS
16 GE CELLS
6 YARDNEY CELLS
4 EP COMSAT CELLS
60%
8 EP CELLS
8 GE CELLS
8 EP CELLS
8 GE CELLS
4 EP CELLS
4 GE CELLS
367
TABLE 3, NICKEL-HYDROGEN LEO TEST PARAMETERS
TEST
TEMPERATURE
10"C
20"C
DOD
40%
60%
40%
60%
DISCHARGE
RATE
34.3 A
51.5 A
34.3 A
51.5 A
CHARGE
RATE
22.9 A
34.3 A
22.9-24.0 A
34,3-36.0 A
RECHARGE
FRACTION
1.05
1.05
1.05 TO 1,10
1.05 TO 1.10
TABLE 4. EAGLE-PICHERATP CAPACITY VERSUS IN-HQV_ q_PACITY TESTS
S/N
1
2
3
4
5
6
7
8
9
i0
ii
12
EAGLE-PICHER
ATP CAPACITY (05/29/85)
34,3 A D/C TO 1,0 VOLT
62.8
63.2
61.1
64.5
60.6
62.9
60.7
59.9
63.4
60.3
60,4
59.8
A-HR
A-HR
A-HR
A-HR
A-HR
A-HR
A-HR
A-HR
A-HR
A-HR
A-HR
A-HR
MARTIN MARIETTA CAPACITY TEST (07/31/85)
25,0 A D/C To
1.0 VOLT 0,5 VOLT
46.9
46.5
48.2
47.1
46.9
45,0
47.3
46.3
48.0
46.1
46.3
45.9
55.6
57.1
57.7
57.7
55.8
55.2
57.1
56,0
57.3
57,3
57.1
55.2
368
ORIGINAL PAGE IS
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FIGURE 1
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FIGURE 2
369
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:.3
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FIGURE 3
EP TEST GROUP(4 CELLS) 20"C, 60Z DOD LEO TEST DATA
_.0
4.0
3.0
_._L
l..c.. ......... , ......... , ......... , ......... . ................... . ....... , ......... , ......... , ....... 1..':
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HUM_E_' OF C'r'CLES
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FIGURE 4
37O
ORIGINAL PAGE IS
OF POeR QUALITY
EP COMSAT TEST GROUP (4 CELLS) 10"C, 40% DOD LEO TEST DATA
6.0
5.0
bJ
(I 4.L,_
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0 I O0 200 300 400 gO0 G00 700 '300 900 1000
NUMDER OF CYCLEST
FIGURE 5
371


Nickel-hydrogen low-Earth-orbit test program

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