Chromic acid anodize was used as the exterior coating for aluminum surfaces on LDEF to provide passive thermal control. Chromic acid anodized aluminum was also used as test specimens in thermal control coatings experiments. The following is a compilation and analysis of the data obtained thus far

Golden, Johnny L.

English

NASA Technical Reports Server

N93"12779
ANODIZED ALUMINUM ON LDEF
A Current Status Of Measurements On
Chromic Acid Anodized Aluminum
_lohnnv L. Golden
Boeing Defense & Space Group
Seattle, WA 98124-2499
Phone: 206/7"/3-2055, FAX: 206/773-4946
Chromic acid anodize was used as the exterior coating for aluminum
surfaces on LDEF to provide passive thermal control. Chromic acid
anodized aluminum was also used as test specimens in thermal control
coatings experiments. The following is a compilation and analysis of
the data obtained thus far.
Solar absorptance and thermal emittance data for this summary was
graciously provided by the following people.
SOURCES OF INFORMATION
• Measurements Of ¢xAnd g From
• T. R. Sampair, NASA LaRC / Lockheed
LDEF Structure, Longerons, And Intercostals
• W. L. Plagemann, Boeing Defense & Space Group
LDEF Tray Clamps
• W. S. Slemp, NASA LaRC
Test Specimens
• D. R. Wilkes, AZ Technology, Inc.
J. M. Zwlener, NASA MSFC
Test Specimens
PRIEC_DING PAGE BLANK r¢OT FILMED
211
https://ntrs.nasa.gov/search.jsp?R=19930003591 2020-03-17T10:35:49+00:00Z
Measurements reported by Tom Sampair for the solar absorptance and
thermal emittance of chromic acid anodize on LDEF intercostals and
Iongerons are shown in figures 1-4. During deintegration, readings were
made on both exposed and unexposed areas of these structures (where
covered by tray lips). Comparison is made in these figures to the Quality
Assurance logs of 1978, made during LDEF part fabrication. Absorptance
readings show significant variability from row to row. Absorptance
measurements taken for leading edge surfaces are relatively unchanged,
within the exhibited data scatteK However, trailing edge surfaces show
significant increases in absorptance. Emittance readings for all exposed
surfaces are not changed when compared to the QA logs. Unexposed
surfaces, however, have a consistent increase in emittance compared to
exposed surfaces.
LDEF INTERCOSTALS: AVERAGE ABSORPTIVITY Vs ROW LOCATION
|
" 212
i
t
|
i
i
i
o QA LOG 1 978
.- " KSC UNEXPOSED 1 990
0._ A KSC EXPOSED 1 990
O.4O
-
0
co
m
<C 0.30
0.25
1 2 3 4. 5 6 7 8, 9 10 11 12
LDEF ROW
Figure 1.
LDEF LONGERONS: AVERAGEABSORPTIVITYVs ROWLOCATION
o QA LOG 1 978
o KSC UNEXPOSED 1 990
0.45
0.40
_0.35
o
m
"< 0.:30
0.25 [ i _m?e
1 2 3 4
i ,, --¢ ,|
5 6 7
LDEF ROW
8 9 10 11 12
Figure 2.
213
LDEF' INTERCOSTALS: AVERAGE EMISSIVITY Vs ROW LOCATON
!
214
o QA LOG 1 978
0.30 " KSC UNEXPOSED 1990
•'- KSC EXPOSED 1 990
0.25
0.20
0.1 5
0.10
1 2 3 4. 5 6 7 8 9 10 11 12
LDEF ROW
Figure 3.
LDEF LONGERONS: AVERAGE EMISSIVITY Vs ROW LOCATON
0.30
0.25
0
0
QA LOG 1 978
KSC UNEXPOSED 1 990
KSC EXPOSED 1 990
0.20
0.15
0.1 0
1 2 3 4 5 6 7 8 9 10 11 12
LDEF ROW
Figure 4.
Measurements reported by Wally Plagemann for optical properties of LDEF
tray clamps are summarized in Table 1. When treated as averages, the
anodize has suffered very little degradation as a result of space environmental
effects.
Details of the tray clamp measurements are presented in various forms as
figures 5 - 9. Figure 5 compares the absorptance readings for the exposed
(front) and unexposed (back) surfaces of clamps as a function of LDEF
location. A slight increase in absorptance for trailing edge surfaces is apparent.
A similar plot of emittance is shown in figure 6. Although there is a 0.04
emittance unit spread to the readings, there is no difference apparent between
leading and trailing edge clamps. There is, however, a slightly lower emittance
for exposed surfaces than for unexposed surfaces, consistent with the readings
reported for LDEF structure.
Solar absorptance versus UV exposure for LDEF side tray clamps is shown
in figure 7. It appears that trailing edge specimens, as described previously,
have higher absorptances than their counterparts on the leading edge. But
there is no trend in absorptance change with UV exposure. A similar plot,
figure 8, includes the readings for the earth and space end tray clamps. Finally,
a plot of absorptance versus atomic oxygen fluence is shown in figure 9. Again
the only change is a slight absorptance increase moving from high AO fluence
(leading edge) to low AO fluence (trailing edge).
TABLE 1.
Averages Of Measurements From Groups Of Tray Clamps
As Compared To Control Data
Measurements On Flisht Tray Clamps Data From
Unexposed Exposed- Exposed- Exposed- Exposed- AIAA-
Leadin_ Trailin_ S_ace Earth 8_- 1492
a - 0.34 a = 0.33 ot = 0.35 a o 0.35 a = 0.35 a - 0.32
0.01 0.01 0.02 0,02 0.01
c- 0.16 ¢- 0,]5 ¢=0,15 e-0.16 ¢=0.17 e- 0,16
0.01 0,01 0.0! 0.02 0,01
we = 21 We = 2.2 (we = 2._ we = 2.2 we - 2,1 _e = 2.0
Measurements
On Unused
Clamps
a - 0.36
215
I,LI
O
Z
I--
13.
n"
O
03
CO
n-
/
O
03
0.5
0.4
0.3
0.2
0.1
SOLAR ABSORPTANCE VERSUS ROW POSITION
FOR ANODIZED LDEF TRAY CLAMPS
ii """ !i" !!-;'. 'i"'!'i= :
_ -- • ABSORPTANCE - BACK --
UNANODIZED CLAMP ]
1 2 3 4 S 6 7 8 9 10 11 12
L
o
ROW
Figure 5.
216 j
THERMAL EMITTANCE VERSUS ROW POSITION
FOR ANODIZED LDEF TRAY CLAMPS
---
o.=o_?'",°'sI I I I .________
_ D j •
el ! • i •
,--.--.-......._ u nDt
0.10 "-_- -*-'--" -+-_
°
: _,,g_c,_c_
0.05 - - P-"--+
0 1 2 3 4 S 6 7 8 9 10 11 12
ROW
Figure 6.
|
=
t|
0.44
SOLAR ABSORPTANCE VERSUS UV EXPOSURE
FOR RAM (LEADING EDGE) AND WAKE (TRAILING EDGE)
ANODIZED LDEF TRAY CLAMPS
LLI
C.)
Z
,<I-
n
n-
O
(/)
m
,<
n-
,<
,_1
O
(/)
0.42 ...........................................
[] ABS-WAKE
• ABS-RAM
0.40' --
El
0.38 o
[] rl rl
0.36 o o.--o
$ [] mo [] ¢i
0.34 : []---_-* : =
m• [] $ eo • •
0.32 = c :
0.30 l
6000 7O00
[] = []
O O
[] .4 • "+
[] • II • [] 6
i l ! i
8000 9000 1 0000 1 1 000
UV EXPOSURE (ESH)
Figure 7
12000
0.5
U,,l
0 0.4
Z
,4
I..-
11.
n-
O
U'J 0.3
m
,<
n-
,<
O 0.2'
cn
[]
[]
SOLAR ABSORPTANCE VERSUS UV EXPOSURE
FOR ANODIZED LDEF TRAY CLAMPS
0.1
4000 6000
[] []
r4 B
Go B
D[][]m mm []_
[][] [] Bm _
[]
[]
[] []
rJ
-g--N--
_[] _[]
0000 10000 12000
UV EXPOSURE (ESH)
[]
B
B
[]
[]
[]
• .L
14000 16000
Figure 8
217
0.5 "
I11
0 o.4
Z
i-
a.
n-
O
(n 0.3
m
.<
n-
<
--I
0
(n 0.2'
0.1
SOLAR ABSORPTANCE VERSUS A• FLUENCE
FOR ANODIZED LDEF TRAY CLAMPS
N u
nv,n
B
U B B II 8
B B 8 m []
B m= N m r,_ [] []lamb
[] H IB B [] [] []B rm
[] [] 8_
' ....... 0_11012_11 .... 1.591691791 '801.9[)20021''03104105106107108109101 . 30140
A• FLUENCE (atoms / sq cm)
(THIS IS A VERY COMPRESSED LOG SCALE)
Figure 9.
22
218
.=
Measurements reported by Wayne Slemp for chromic acid anodize on
experiment S0010 are summarized in Table 2. Coatings of relatively
constant absorptance (~10%) and varying emittance received two
exposure levels at tray position B9 (8.7x10E21 oxygen atoms/sq, cm and
11,200 ESH). Both absorptance and emittance readings at either
exposure level are consistent with preflight measurements.
TABLE 2.
NASA LaRC Experiment S0010 On
Chromic Acid Anodize (CAA)
Preflight I0 Month Exposure 5.8 Year Exposure
Coating a ¢ a _. a (:
Thin CAA 0.29_ 0.16 0.299 0.17 ....
0.288 0.J8 .... 0.296 0.19
Medium CAA 0,292 0.4,_ 0287 0.43 ....
0.306 0,45 .... 0.3 l 1 0.46
Thick CAA 0.33 0,71 0.337 ,071 ....
0.341 0.75 .... 0:354 0.75
219
Measurements reported by Don Wilkes and__Jim Zwiener for chromic acid
anodize on experiment S0069 are summarized in Table 3. This experiment
was located at tray position A9 (8.7x10E21 oxygen atoms/sq, cm and
11,200 ESH). Two specimens of comparable absorptance anti emittance
were periodically measured for absorptance on this active experiment during
the flrst 19.5 months of the L_- flight. _u_i_ttime, _lhe absorptance of
the anodize specimens increased significantiy ancfconsi_stently. One of the
specimens was left exposed for the entire mission and recovered slightly
(decreased) in absorptance. Emittance of the two specimens was not
affected.
TABLE 3.
22O
NASA MSFC And AZI"EK Experiment S0069
Chromic Acid Anodize Specimens
Specimen Preflight 12 Months 19.5 Months Postfiigbt
(69.2 Months}
C6 1 a - 0,50 - -a= 0.41
e - 0.84
C63 ot - 0.40 a = 0.49 _ - 0.54
e = 0.84 e- 0.84
There are several points that can be made in summary. First, there was
some variability inherent in the absorptance and emittance measurements for
LDEF chromic acid anodize coatings, due to both the anodizing process, and
due to the differences in equipment and analysts used to make the
measurements over the years. Data from tray clamps (and from LDEF
structures) indicates this variability within one standard deviation is 0.02 for
absorptance and 0.01 for emittance.
Next, absorptance changes for leading edge surfaces was minimal, with the
exception being the results from Experiment S0069. The absorptance on trailing
edge surfaces increased in general when compared to available control
measurements.
Emittance changes were complex in that emittance appears to have slightly
increased for unexposed surfaces, when compared to exposed surface or QA
logs. However, these changes are of minimal significance when compared to
inherent emittance variability or when treated relatively.
Based on the analyses thus far, indications are that chromic acid anodize is
quite stable in the LEO environment, but that contamination did effect
absorptance increases. Most leading edge surfaces were cleaned of this
contamination by atomic oxygen.
• SUMMARY
• Variability Inherent In CAA Process From Tray Clamp
Measurements Is + 0.02 - 0.03 In Both Absorptance
And Emlttance
• Emissivity Of Shielded Anodize Is Greater Than That
Measured For Exposed Anodize
• Absorptance Change On Leading Edge Surfaces Is
Minimal, With Exception
• Absorptance Increased on Trailing Edge Surfaces Com-
pared to Unexposed Surfaces or to 1978 QA data
• Results Indicate Absorptance Increases Are Due To
Contamination Early In The LDEF Mission,
Subsequently Removed From Leading Edge
Surfaces By Atomic Oxygen
221



Anodized aluminum on LDEF: A current status of measurements on chromic acid anodized aluminum

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