This paper summarizes an effort by Gates Aerospace Batteries (GAB) and the Reliability Analysis Center (RAC) to analyze survivability data for both General Electric and GAB NiCd cells utilized in various spacecraft. For simplicity sake, all mission environments are described as either low Earth orbital (LEO) or geosynchronous Earth orbit (GEO). 'Extreme value statistical methods' are applied to this database because of the longevity of the numerous missions while encountering relatively few failures. Every attempt was made to include all known instances of cell-induced-failures of the battery and to exclude battery-induced-failures of the cell. While this distinction may be somewhat limited due to availability of in-flight data, we have accepted the learned opinion of the specific customer contacts to ensure integrity of the common databases. This paper advances the preliminary analysis reported upon at the 1991 NASA Battery Workshop. That prior analysis was concerned with an estimated 278 million cell-hours of operation encompassing 183 satellites. The paper also cited 'no reported failures to date.' This analysis reports on 428 million cell hours of operation emcompassing 212 satellites. This analysis also reports on seven 'cell-induced-failures.

Denson, William K.

Klein, Glenn C.

English

NASA Technical Reports Server

N93-20510
NiCd CELL RELIABILITY IN THE MISSION ENVIRONMENT
William K. Denson; Reliability Analysis Center, Rome, IVY
Glenn C. Klein; Gates Aerospace Batteries, GainesvilIe, FL
INTRODUCTION
This paper summarizes an effort by Gates Aerospace Batteries (GAB) and the
Reliability Analysis Center (RAC) to analyze survivability data for both General
Electric and GAB NiCd cells utilized in various spacecraft. For simplicity sake, all
mission environments are described as either LEO or GEO. "Extreme value
statistical methods" are applied to this database because of the longevity of the
numerous missions while encountering relatively few failures. Every attempt has
been made to include all known instances of cell-induced-failures of the battery and
to exclude battery-induced-failures of the cell. While this distinction may be
somewhat limited due to availability of in-flight data, we have accepted the learned
opinion of the specific customer contacts to ensure integrity of the common
databases.
This paper advances the preliminary analysis reported upon at the 1991 NASA
Battery Workshop. That prior analysis was concerned with an estimated 278
million cell-hours of operation encompassing 183 satellites. That paper also cited
"no reported failures to date" [see Reference 1]. This analysis reports on 428 million
cell hours of operation encompassing 212 satellites. This analysis also reports on
seven "ceil-induced-failures."
MISSION ENVIRONMENT
Several assumptions have been made concerning both the mission
environment and the overall population of cells by which the numbers of cell-
hours or cell-cycles are estimated. First for simplicity sake, all mission
environments are described as either LEO (predominantly rapid and repetitive
cycling) or GEO (predominantly long periods of overcharge followed by brief duty
cycles). Generally Polar Orbits are incorporated into the LEO analysis, and Highly
Elliptical orbits are incorporated into the GEO analysis. LEO is considered to
1992 NASA Aerospace Battery Workshop -437- Nickel-Cadmium Technolo_es Session
https://ntrs.nasa.gov/search.jsp?R=19930011321 2020-03-17T08:11:24+00:00Z
experience sixteen cycles per day. Second, the analysis assumes twenty-two cells per
battery and two batteries per satellite.
The third area of assumption becomes more an area of definition and
discrimination. Defining the words failure, termination, and deterioration can lead
to both endless discussion and endless dissension. For purposes of this analysis,
failures is defined as: outright failure or termination of a cell and/or a battery.
Deterioration is defined as: expected performance had deteriorated or degraded to
the point that the original mission intention has been significantly limited or
compromised either by manifestation of immediate performance deterioration or
the limiting of expected life. Discriminating between cell-induced battery failures
and battery-induced cell failures encounters the same discussion and dissension.
Both definition and discrimination are hampered by different levels of telemetry
sophistication for receiving in-flight performance data. This analysis unilaterally
accepts both definition and discrimination as proffered by the responsible technical
personnel.
It should also be noted that the analysis is being performed at the complete
satellite battery level and not the individual cell level, since this is the level for
which the data was collected.
MISSION PERFORMANCE
Table 1 contains the detail and arithmetical summary of the 212 satellites
reported in this analysis. Details include cell capacity rating, mission environment,
launch date and years of operation. Neither customer, program or reason for
satellite termination is identified in this listing. Note that four specific indicators of
operational life were used since this information was extracted from several sources.
They are final or total years of operation, data as of December 1987, data as of January
1991, and data as of April 1992. Total LEI Mission Years reported are 331.7 years; total
GEO Mission Years reported are 777.9 years. Note that specific failure data is not
included in Table 1.
1992 NASA Aerospace Battery Workshop -438- Nickel-Cadmium Technologies Session
MISSION SUMMARY
The last page of Table 1 provides the total Mission Summary, the LEO Mission
Summary, and the GEO Mission Summary. For 212 spacecraft analyzed, 1109.5 Total
Mission Years have accumulated. This equivalent 428 million cell-hours is
considerably greater than the 278 million cell-hours reported on last year [Reference
1]. In addition, the previous report did not differentiate between the various
mission environments.
For the LEO Mission Environment, 74 spacecraft or satellites were analyzed.
Accumulated are 332 Total Mission Years or 85 million Total Cell-Cycles. For the
GEO Mission Environment, 138 spacecraft or satellites were analyzed. Accumulated
are 778 Total Mission Years or 300 million Total Cell-Hours.
As previously stated, cell-induced failures are not cited or summarized in Table
1. Neither will these failures be tabulated separately due to their sensitive nature.
In brief summary, one "long term" GEO has occurred, and six LEO failures have
occurred ranging from approximately four thousand to thirty-two thousand cycles.
Again note that a cell-induced performance failure does not necessarily imply a
mission termination.
STATISTICAL ANALYSIS OF RELIABILITY DATA
A simple method of analyzing reliability data is to determine a failure rate by
dividing the number of observed failures by the number of operating hours or
cycles. The use of a failure rate inherently assumes that the rate of failures are
occurring in a time independent random manner.
Since it is known that batteries typically exhibit wearout characteristics, or an
increasing failure rate in time, a failure rate is too simplistic of a metric describing
the reliability of the battery.
Weibull analysis is often used to quantify, from empirical time (or cycle) to
failures data, the rate of occurrence of failure as a function of time. A complete
Weibull analysis usually consists of plotting the cumulative percentage of failures
against time on Weibull probability paper when a large percentage of the population
1992 NASA Aerospace Battery Workshop -439- Nickel-Cadmium Technologies Session
has failed. This methodology, however, looses its usefulness when the population
contains few or no failures. Since there have been a relatively small percentage of
the population failing, alternative analysis methods were required.
The appropriate analysis methodology under these circumstances is the use of
confidence limits in conjunction with the Weibull distribution. Nelson [Reference
2] has proposed such a methodology which will be used in this analysis.
Background on the Weibull distribution and Nelson's methodology is given in the
following paragraphs.
The probability density function fit) of the Weibull time to failure distribution
is;
f(t) =-0_ It_ -1 e "(t) _
where
=
t =
characteristic life, time to 63% population failure
Weibull shape parameter
time
The reliability (probability of survival to a time t) is;
And the hazard rate h(t) (or instantaneous failure rate), given the part has
survived until time t is;
1992 NASA Aerospace Battery Workshop -440- Nickel-Cadmium Technologies Session
To estimate the value of the characteristic life in the Weibull distribution, the
following maximum likelihood estimator is typically used;
1I 1i_1 Ti_ / r
where
T i = Time to fail of the i th part or survival time of the i th part if it has not
failed
r = Number of failures
n = Total population of parts
Since the database contains few failures, the characteristic life implied by this
estimate is suspect. As stated previously, the appropriate analysis methodology to
use under these conditions is to apply confidence limits to derive worst case
reliability values. From this, lower bound estimates of lifetimes can be made within
a given confidence level. To accomplish this, the Chi-square distribution can be
utilized. The lower confidence limit for the Weibull distribution is:
1
[i=_lTi _ / rl_ [2r / X2 (C; 2r+2)]_
where
X2 = the chi-square percentile at C% confidence and r failures
This value of characteristic life was then calculated for various values of betas
and various confidence levels for both LEO and GEO. Table 1 summarizes the data
used. The sum of the individual survival times raised to the power beta, as a
function of beta, are as follows:
1992 NASA Aerospace Battery Workshop -441- Nickel-Cadmiurn Technologies Session
LEO
1 331.9
2
Z Til3
i=1
GEO
777.9
2,911 6,220
3 38,182 57,977
4 624,847 588,803
5 11,472,255 6,357,012
6 2.236 x 108 7.215 x 107
The values of the Chi-square percentiles are given as follows:
C Confidence Level
.25
.50
.75
.90
.95
.975
.990
.995
.999
Chi-Square Percentile
LEO (6 failures)
14 Degrees of Freedom
10.17
GEO (1 failures)
4 De_grees of Freedom
1.923
13.34 3.357
17.12 5.385
21.06 7.779
23.68 9.488
26.12 11.14
29.14 13.68
31.32
36.12
14.86
18.47
1992 NASA Aerospace Battery Workshop -442- Nickel-Cadmium Technologies Session
The resulting lower limit characteristic life estimates as a function of confidence
(C) and beta value are summarized in the following table for both LEO and GEO
applications.
O_ FOR LEO APPLICATIONS
1
2
3
4
5
6
.25 .50
65.3 49.8
23.9 20.9
19.6 17.9
18.7 17.5
18.6 17.7
18.8 17.9
.75
38.8
18.4
16.5
16.4
16.8
17.2
C
.90 .95 .975
31.5 28.0 25.4
16.6 15.7 14.9
15.4 14.8 14.3
15.6 15.2 14.8
16.1 15.7 15.4
16.6 16.3 16.1
.990
22.8
14.1
13.8
14.4
15.1
15.8
.995
21.2
13.6
13.5
14.1
14.9
15.6
.999
18.4
12.7
12.8
13.6
14.5
15.2
O_ FOR GEO APPLICATIONS
1
2
3
4
5
6
.25
809
80.4
39.2
28.0
23.1
20.5
.50
463
60.9
32.6
24.3
20.7
18.7
C
.75 .90 .95
289 200 164
48.1 40.0 36.2
27.8 24.6 23.0
21.6 19.7 18.8
18.8 17.5 16.8
17.3 16.3 15.7
.975
139
33.4
21.8
18.0
16.2
15.3
.990
117
30.6
20.6
17.2
15.7
14.9
.995 .999
105 84
28.9 25.9
19.8 18.4
16.8 15.9
15.4 14.7
14.7 14.1
As an example, if a beta value of 4 is assumed, one can be 90% confident that the
characteristic life for LEO applications is a minimum of 15.6 years.
If it is desired to calculate the time (t) to the P percentile failure of the
population, the following can be used;
1
t= ot [-ln (1 - 1_---_)1_
1992 NASA Aerospace Battery Workshop -443- Nickel-Cadrtffum Technologies Session
If the characteristic life is the lower confidence limit as tabulated previously, the
time to P percent failure will also be the lower confidence limit. For example, using
the characteristic life of 15.6 years for beta = 4 and 90% confidence, the worst case
time (at 90% confidence) to reach 1% failure is;
1
t = 15.6 -In 1- = 4.94 years
In this example, there is 90% confidence that the time to 1% failure will be
greater than 4.94 years.
DISCUSSION ON LONGEVITY OF LEO MISSIONS
Let us assume that five years in LEO environment (29,200 cycles) is a typical
mission life time requirement. Then several superlatives can be shown. First, 24 of
the 74 LEO missions analyzed were operated beyond that benchmark including one
mission for 22 years. Second, testing of a four-cell pack of 26.5 Amp-Hour cells has
recently achieved 11.7 years (68,110 cycles) in a LEO test regime. This cell pack (Pack
No. 0026G) is currently under test at Crane-NSWC at 10°C and 20% DOD.
SUMMARY AND RECOMMENDATIONS
This database contains substantial updating and upgrading from our previous
report. The previous report cited 183 satellites operating for 278 million cell-hours
and "no reported failures." This report contains 212 satellites operating for 428
million cell-hours and seven reported failures. We continue to use the extreme
value statistical methods of Wayne Nelson as the most viable analysis technique
due to relatively few failures.
Predictions of the Characteristic Life and times to percentile failures based upon
assumed [3 values has shown a small decrease in the "predicted life" due to the
observance of failures. However, these estimates appear more realistic because any
failure improves the estimation of Confidence Intervals; and because the total base
of survivability increased 54%.
1992 NASA Aerospace Battery Workshop -444- Nickel-Cadmium Technologies Session
TABLE 1"GAB NiCd PERFORMANC5 IN M!SSION ENVIRONMENT
STATUS AS OF JULY, 1992 ( ) FINAL
unmarked as of 4/92
* as of 12/87
**as of 1/91
RATING MISSION LAUNCH YEARS OF LEO GEO
A-H DATES OPERATION YEARS YEARS
4 LEO 66/02
4 LEO 66/02
4 LEO 66/10
4 LEO 66/12
4 LEO 67/01
4 LEO 67/03
4 LEO 67/04
12 LEO 67/04
4 LEO 67/11
4 LEO 67/11
4 LEO 68/08
4 LEO 68/08
4 LEO 68/12
4 LEO 69/02
6 LEO 69/04
4 LEO 70/01
4 LEO 70/12
6 LEO 70/12
15 GEO 71/01
15 GEO 71/12
15 GEO 72/01
15 GEO 72/06
6 LEO 72/07
6 LEO 72/10
7 GEO 72/11
6 LEO 72112
7 GEO 73/04
15 GEO 73/08
6 LEO 73/11
6 LEO 73/12
7 GEO 74104
7 GEO 74/10
24 GEO 74/11
6 LEO 75/01
7 GEO 75/05
24 GEO 75/05
6 LEO 75/06
12 LEO 75/06
24 GEO 75/09
6 LEO 75/10
6 LEO 75/11
6 LEO 75/?
24 GEO 76/01
(1.25) 1,3
(4.5) 4.5
(2.0) 2.0
(20) 20.0
(0.9) 0.9
(2.4) 2.4
(2,8) 2.8
[22.0] 22.0
17.8" 17.8
(2) 2.0
(0.2) 0.2
(0.9) 0,9
(7.2) 7.2
(4,8) 4.8
(1.75) 1.8
(1.4) 1.4
(0.7) 0.7
(0.8) 0.8
14,6"
(11.5)
3.6"
4.0*
5.75) 5.8
2.2) 2.2
10.6)
7.25) 7.3
10,2)
9.8)
(2.6} 2.6
(5.0) 5.0
(9.0)
[9.8]
10.8"
(5.0l 5.0
[9.5]
10.2"
(4.5) 4.5
[3.0] 3.0
9.9"
(0.4) O.4
(5.6) 5.6
(1.01 1.0
9.6*
14.6
11.5
13.6
14.0
10.6
10,2
9.8
9.0
9.8
10.8
9.5
10.2
9,9
9.6
1992 NASA Aerospace Battery Workshop -445- Nickel-Cadmium Technologies Session
TABLE 1 :Cont'd.
STATUS AS OF JULY, 1992 ( ) FINAL
unmarked as of 4/92
* as of 12/87
*°as of 1/91
RATING MISSION LAUNCH
A-H DATES
YEARS OF LEO GEO
OPERATION YEARS YEARS
2 LEO
2 LEO
10 GEO
6 LEO
24 GEO
7 GEO
24 GEO
7 GEO
24 GEO
6 GEO
6 LEO
6 LEO
6 GEO
24 GEO
15 GEO
24 GEO
6 LEO
24 GEO
4 GEO
7 GEO
15 GEO
24 GEO
7 GEO
6 LEO
15 GEO
15 GEO
15 GEO
17 GEO
7 GEO
15 GEO
6 LEO
15 GEO
24 LEO
15 GEO
6 LEO
6 GEO
22 GEO
35 GEO
24 GEO
6 GEO
12 GEO
35 GEO
6 LEO
5 GEO
76/03
76/03
76/03
76/04
76/05
76/07
76/07
77/03
77105
77/06
77108
77/12
78101
78/01
78/02
78/02
78/03
78/03
78/04
78/05
78105
78/06
78108
78/10
78/10
78111
78/12
78/12
79/08
79/09
79/10
80102
80/02
80/04
80/05
80/09
80111
8(] '12
81 '02
81 '05
81 '05
81 '05
81 '07
81 '08
(4.0} 4.0
(1.0) 1.0
(3.0) 3.0
(3.0) 3.O
[8.5] 8.5
[9.1] 9.1
9.1 9.1
8.4* 8.4
8.2" 8.2
(7) 7.0
[13] 13.0
(3.0) 3.0
7.7* 7.7
7.6* 7.6
(0.6) 0.6
14.2 14.2
(5.5) 5.5
7.4* 7.4
(3.8) 3.8
7.2** 7.2
[6.0] 6.0
[7.2] 7.2
(0.3) 0.3
12.2"* 12.2
11.2"* 11.2
12.2"* 12.2
[2.8] 2.8
6.7* 6.7
6.0* 6.0
10.5 10.5
[10] 10.0
(4.4) 4.4
[9.8] 9.8
9.7** 9.7
(1.0) 1.0
(2.8) 2.8
4.8* 4.8
11.3 11.3
(4.5) 4.5
(3.6) 3.6
8.6** 8.6
10.9 10.9
11.0 11.0
4.0* 4.0
1992 NASA Aerospace Battery Workshop -446- Nickel-Cadmium Technologies Session
TABLE 1 :Cont'd.
STATUS AS OF JULY, 1992 ( ) FINAL
unmarked as of 4/92
* as of 12/87
**as of 1/91
RATING MISSION LAUNCH
A-H DATES
YEARS OF LEO GEO
OPERATION YEARS YEARS
22 GEO 81/09
17 GEO 81/11
35 GEO 81/12
17 GEO 82/01
17 GEO 82/02
24 LEO 82/02
35 GEO 82/03
12 GEO 82/04
17 GEO 82/06
50 LEO 82/07
17 GEO 82/08
35 GEO 82/09
24 GEO 82/10
35 GEO 82/10
17 GEO 82/11
22 GEO 82/11
15 GEO 83/02
15 GEO 83/02
30 LEO 83/03
6 GEO 83/04
30 LEO 83/05
12 LEO 83/06
17 GEO 83/06
24 GEO 83/06
24 GEO 83/06
6 LEO 83/07
21 GEO 83/07
12 GEO 83108
12 GEO 83/08
40 GEO 83/08
24 GEO 83/09
4 GEO 84/01
6 LEO 84/02
50 LEO 84/03
12 LEO 84/04
15 GEO 84106
4 LEO 84/08
5 GEO 84/08
21 GEO 84/08
25 GEO 84/08
15 GEO 84/09
12 GEO 84/10
17 GEO 84/10
50 LEO 84/10
4.1" 4.1
4.0 * 4.0
10.4 10.4
3.85 ° 3.9
10.2 10.2
0.8 0.8
10.1 10.1
(.8) 0.8
9.9 9.9
8.5"" 8.5
9.7 9.7
9.6 9.6
9.5 9.5
9.5 9.5
2.8" 2.8
9.4 9.4
9.2 9.2
2.5" 2.5
9.1 9.1
7.8 * 7.8
1.0 1.0
4.2 4.2
2.2* 2.2
8.8 8.8
8.8 8.8
9.0 9.0
2.1" 2.1
8.6 8.6
4.0** 4.0
8.5 8.5
8.5 8.5
(1.6) 1.6
8.5 8.5
6.8** 6.8
5.5 5.5
7.8 7.8
3.0** 3.0
1.0" 1.0
1.0" 1.0
7.7 7.7
7.6 7.6
5.0 5.0
2.6* 2.6
6.2* 6.2
1992 NASA Aerospace Battery Workshop -447- Nickel-Cadmium Technologies Session
TABLE 1 :Cont'd.
STATUS AS OF JULY, 1992 ( ) FINAL
unmarked as of 4/92
RATING MISSION LAUNCH YEARS OF LEO
A-H DATES OPERATION YEARS
• as of 12/87
• •asof 1/91
GEO
YEARS
15 GEO 84/11 .8"
17 GEO 84/11 7.6
25 GEO 84/11 7.6
24 GEO 85/02 7.2
35 GEO 85/02 [0.6]
24 GEO 85/03 2.5* •
25 GEO 85/04 7.0
21 GEO 85/06 2.8 ••
21 GEO 85/06 0.2 • •
35 GEO 85/06 [4.5]
50 GEO 85/07 7.0
12 LEO 85/08 [6.0]
25 GEO 85/08 6.7
27 GEO 85/08 6.7
15 GEO 85/10 6.5
35 GEO 85/10 6.5
4 GEO 86/02 [4.0]
24 G EO 86/03 6.9
6 LEO 86/09 5.8
30 LEO 86/10 5.7
12 LEO 86/11 3.1 • •
35 GEO 86/12 6.3
6 GEO 87/02 5.2
30 LEO 87/06 4.8
50 GEO 87/07 5.0
12 LEO 87/09 2.2 ••
12 LEO 87/09 2.2 ° •
27 GEO 87/09 5.3
40 GEO 87/11 5.4
35 GEO 88102 3.0" °
6 GEO 88/03 (0.8)
30 LEO 88/03 4.1
12 LEO 88104 1.7
12 LEO 88/06 1.5
12 LEO 88106 1.5
24 LEO 88/07 4.0
12 GEO 88/07 3.7
12 LEO 88/08 1.3* *
30 GEO 88/09 3.6
40 GEO 88/09 3.5
35 GEO 88/12 3.3
35 GEO 89/02 3.1
40 GEO 89/03 3.0
30 GEO 89/05 2.9
6.0
5.8
5.7
3.1
4.8
2.2
2.2
4.1
1.7
1.5
1.5
4.0
1.3
3.6
0.8
7.6
7.6
7.2
0.6
2.5
7.0
2.8
0.2
4.5
7.0
6.7
6.7
6.5
6.5
4.0
6.9
6.3
5.2
5.0
5.3
5.4
3.0
0.8
3.7
3.5
3.3
3.1
3.0
2.9
1992 NASA Aerospace Battery Workshop -448- Nickel-Cadmium Technologies Session
TABLE 1 "Cont'd.
STATUS AS OF JULY, 1992
RATING MISSION LAUNCH
A-H DATES
( ) FINAL " as of 12/87
unmarked as of 4/92 **as of 1/91
YEARS OF LEO GEO
OPERATION YEARS YEARS
35 GEO 89/06
35 GEO 89/06
40 GEO 89/06
21 GEO 89/08
35 GEO 89/08
5 GEO 89/09
35 GEO 89/09
35 GEO 89/10
24 LEO 89/11
35 GEO 89/12
35 GEO 89/12
35 G EO 90/01
10 LEO 90/02
35 LEO 90/02
35 GEO 90/03
18 GEO 90/06
15 LEO 90/07
35 GEO 90/07
17 GEO 90/08
21 GEO 90/08
35 GEO 90/08
35 GEO 90/08
32 GEO 90/10
35 GEO 90/10
35 GEO 90/11
40 GEO 90/11
30 LEO 90/12
35 GEO 91/01
32 GEO 91/03
50 LEO 91/04
30 LEO 91/05
35 GEO 91/07
17 GEO 91/08
40 GEO 91/08
50 LEO 91/09
40 GEO 91/11
50 LEO 91/11
2.8 2.8
2.8 2.8
2.8 2.8
2.6 2.6
2.6 2.6
2.5 2.5
2.5 2.5
2.4 2.4
2.4 2.4
2.3 2.3
2.3 2.3
2.1 2.1
2.1 2.1
2.1 2.1
2.0 2.0
1.8 1.8
1.7 1.7
1.7 1.7
1.7 1.7
1.7 1.7
1.7 1.7
1.7 1.7
1.5 1.5
1.5 1.5
1.4 1,4
1.4 1.4
1.3 1.3
1.2 1.2
1.1 1.1
1.0 1.0
0.9 0.9
0.8 0.8
0.7 0,8
0.7 0.7
0.6 0.6
0.3 0.3
0.3 0.3
TOTAL LEO MISSION YEARS
TOTAL GEO MISSION YEARS
331.7
777.9
1992 NASA Aerospace Battery Workshop -449- Nickel-Cadmium Technologies Session
TABLE 1 :Cont'd.
STATUS AS OF JULY,1992
MISSION SUMMARY:
TOTAL MISSION YEARS
TOTAL MISSION DAYS
TOTAL MISSION HOURS
TOTAL BATTERY HOURS
TOTAL CELL HOURS
TOTAL SPACECRAFT ANALYZED
LEO MISSION SUMMARY:
TOTAL MISSION YEARS
TOTAL MISSION DAYS
TOTAL MISSION CYCLES
TOTAL BATTERY CYCLES
TOTAL CELL CYCLES
TOTAL SPACECRAFT ANALYZED
GEO MISSION SUMMARY:
TOTAL MISSION YEARS
TOTAL MISSION DAYS
TOTAL MISSION HOURS
TOTAL BATTERY HOURS
TOTAL CELL HOURS
TOTAL SPACECRAFT ANALYZED
1109.5
0.40 Million
9.72 Million
19.44 Million
427.65 Million
212
331.7
0.12 Million
1.94 Million
3.87 Million
85.22 Million
74
777.9
0.28 Million
6.81 Million
13.63 Million
299.81 Million
138
1992 NASA Aerospace Battery Workshop -450- Nickel-Cadmium Technologies Session
This reporting format and analysis technique were the pathfinder for similar
databases anticipated for the NiH2 and NiMH Product Lines. We find this format to
be sufficiently stable and mature to apply to those product lines. Our expectations
are to update on a bi-annual basis and report on the database every four to five years.
REFERENCES
[1] Denson, William K. and Klein, Glenn C., "Analysis of Nickel-Cadmium Battery
Reliability Data Containing Zero Failures," Proceedings of the I99I NASA
Battery Workshop.
[2] Nelson, W., "Weibull Analysis of Reliability Data With Few or No Failures,"
Journal of Quality Technology, Vol. 17, No. 3, July 1985.
1992 NASA Aerospace Battery Workshop -451- Nickel-Cadmium Technologies Session



NiCd cell reliability in the mission environment

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