James R. Gaier

Glenn Research Center, Cleveland, Ohio

Effect of Illumination Angle on the Performance 

of Dusted Thermal Control Surfaces in a 

Simulated Lunar Environment

NASA/TM—2009-215647

October 2009

2009–01–2420
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James R. Gaier

Glenn Research Center, Cleveland, Ohio

Effect of Illumination Angle on the Performance 

of Dusted Thermal Control Surfaces in a 

Simulated Lunar Environment

NASA/TM—2009-215647

October 2009

2009–01–2420

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

39th International Conference on Environmental Systems (ICES)

sponsored by the Society of Automotive Engineers International

Savannah, Georgia, July 12–16, 2009
Acknowledgments

This work is the result of a great deal of effort by a sizable team of dedicated professionals from many organizations. Edward 

A. Sechkar (Arctic Slope Research Corporation) and Frank P. Lam (TFOME) provided engineering and technical support of the 

LDAB facility. Scott R. Panko (Arctic Slope Research Corporation) provided both electrical engineering and test engineering 

support for the LDAB. Michael C. Hicks (GRC) did the thermal modeling. Don Jaworske (GRC) oversaw the fabrication of the 

test samples and acted as a general resource on the behavior of thermal control coatings. Funding for this work was provided by

the Dust Mitigation Project and the Thermal Control Project of NASA Exploration Technology Development Program.

Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

5285 Port Royal Road

Springfi eld, VA 22161

Available electronically at http://gltrs.grc.nasa.gov

Trade names and trademarks are used in this report for identifi cation 

only. Their usage does not constitute an offi cial endorsement, 

either expressed or implied, by the National Aeronautics and 

Space Administration.

Level of Review: This material has been technically reviewed by technical management. 
Effect of Illumination Angle on the Performance of Dusted Thermal 

Control Surfaces in a Simulated Lunar Environment 

James R. Gaier 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

JSC-1A lunar simulant has been applied to AZ93 and 

AgFEP thermal control surfaces on aluminum substrates in a 

simulated lunar environment. The temperature of these 

surfaces was monitored as they were heated with a solar 

simulator using varying angles of incidence and cooled in a 

30 K coldbox. Thermal modeling was used to determine the 

solar absorptivity (α) and infrared emissivity (ε) of the thermal 

control surfaces in both their clean and dusted states. It was 

found that even a sub-monolayer of dust can significantly raise 

the α of either type of surface. A full monolayer can increase 

the α/ε ratio by a factor of 3 to 4 over a clean surface. Little 

angular dependence of the α of pristine thermal control 

surfaces for both AZ93 and AgFEP was observed, at least 

until 30° from the surface. The dusted surfaces showed the 

most angular dependence of α when the incidence angle was 

in the range of 25° to 35°. Samples with a full monolayer, like 

those with no dust, showed little angular dependence in α. The 

ε of the dusted thermal control surfaces was within the spread 

of clean surfaces, with the exception of high dust coverage, 

where a small increase was observed at shallow angles. 

Introduction 

National Space Policy calls for NASA to return humans to 

the Moon by 2020. Largely due to the lack of an appreciable 

atmosphere, the lunar surface environment is hostile. In 

addition to being at ultrahigh vacuum (10–12 Torr during the 

day at 10–14 Torr during the night), there are thermal extremes 

(100 to 400 K), unshielded solar electromagnetic and particle 

radiation, cosmic radiation, and an unceasing bombardment of 

meteoroids. But of all of the environmental threats on the 

Moon, the one singled out by Apollo astronauts as being the 

most worrisome is lunar dust. They were particularly surprised 

by how much the thermal control surfaces were affected. For 

example, even though they were equipped with dust covers 

and were brushed off at regular intervals, the batteries for the 

lunar roving vehicle ran hotter than anticipated, and in fact 

hotter than their rated operating temperature for part of the 

time (Ref. 1). Since the new lunar architecture calls for the 

next generation of surface systems to operate on the lunar 

surface for years rather than the days required of Apollo 

systems, a joint task has been developed by the Dust 

Mitigation Project and the Advanced Thermal Control Project 

to quantify the effects of lunar dust on thermal control 

surfaces and to develop mitigation strategies. 

The current lunar exploration architecture calls for 

exploring the lunar poles. Since the radiators will likely be 

facing up into space to radiate to the lowest temperature, solar 

radiation will be striking these surfaces at low angles. This 

study sought to determine the effect of solar incidence angle 

on the absorptivity (α) of pristine thermal control surfaces. 

The second objective was to continue the investigation into the 

effect of dust on the α of the thermal control surfaces. The 

third objective was to determine the effect of dust on the 

angular dependence of α of these surfaces. 

Methods and Materials 

This study utilized a white thermal control paint (AZ93) and 

a second surface mirror (Ag coated FEP Teflon, Dupont) as 

the thermal control surfaces. The thermal control surfaces 

were applied to 2.54 cm (1 in.) diameter aluminum substrates. 

The AZ-93 paint was applied by AZ Technology (Huntsville, 

Alabama). The AgFEP appliqués were fabricated by Sheldahl 

(Northfield, Minnesota) from 12.7 μm (5 mil) thick FEP 

Teflon which was coated with a few tens of nm of silver and a 

few tens of nm of Inconel as a sealing layer to prevent 

oxidation. They were hand-applied to the substrates using a 

film adhesive. 

The tests were carried out using the NASA Lunar Dust 

Adhesion Bell jar (LDAB). The lunar simulation facility 

enables the simulated lunar dust to be heated, dried, plasmacleaned, chemically reduced, and sieved onto samples in situ. 

It operates at a pressure of 10–5 Pa(10–8 Torr). The sample, 

pristine or dusted, can be heated using a 20-Sun xenon arc 

lamp solar simulator, and radiatively cooled in a 30 K coldbox. Details of the LDAB are available elsewhere (Ref. 2). 

One AZ-93 coated sample and one AgFEP sample were 

exposed during each test in a single sample holder. Figure 1 

shows two samples mounted in the LDAB sample holder. 

Approximately 15 g of JSC-1AF lunar simulant was placed 

in the activation bowl of the LDAB where it was stirred as a 

vacuum was pulled down to about 13 Pa (100 mTorr). At this 

pressure it was exposed to a radio frequency air plasma for 

1 hr, with intermittent stirring, to remove organic 

contaminants. The chamber was then pumped down to about 

10–4 Pa (10–6 Torr) and the simulant was heated at least 16 hr 

to at least 200 °C, with stirring, to remove water. After cooling 

to room temperature, the chamber was backfilled with a 

NASA/TM—2009-215647 1 
5 percent H2 in He gas to a pressure of 13 Pa and the dust was 

exposed to a radio frequency plasma for 1 hr, with intermittent 

stirring, to chemically reduce and to add hydrogen to the dust 

particle surfaces. This was to mimic the effects of solar wind. 

The H2-He mixture was pumped out and the pressure again 

dropped to 10–4 Pa. Then a recirculating He refrigerator was 

used to cool a cold box within the chamber to about 30 K. The 

resulting condensation of gases onto the surface of the cold 

box lowered the pressure in the chamber to about 10–5 Pa. This 

was the level of vacuum under which most of the testing was 

carried out. The dust was transferred from the activation bowl 

to a 3 in. standard, 38 μm stainless steel sieve for application 

to the samples. 

One of the samples was positioned under a 20-Sun Xe arc 

lamp (Luxtel), and tilted to the desired incidence angle using a 

bubble-level type angle indicator. Incidence angles of 90°, 

45°, 30°, and 10° were used. After the temperature recording 

software was started, the arc lamp was ignited. The sample 

was exposed for 800 sec, or until the temperature approached 

200 °C, whichever came first. Then the second sample was 

positioned under the lamp and exposed for a similar duration. 

Then the lamp was extinguished, the angle returned to 90°, 

and the sample holder was translated into the cold box, which 

is lined with an absorbing material (Vel-Black) and 

maintained at about 30 K with a recycling helium refrigerator. 

The samples were allowed to cool for at least 20 min, or until 

the temperature of both samples was below 15 °C, whichever 

took the longest. The sample was then pulled out of the cold 

box, though still in the vacuum chamber, and allowed to come 

to near equilibrium temperature before the next test was 

started. 

After heating and cooling data had been collected at all four 

angles, the sample was positioned under a 25 μm sieve filled 

Figure 1.—Aluminum substrate coated with AZ-93 (left) and 

Ag/FEP (right) thermal control surfaces. The thin brown 

wires in the photo are two thermocouples, one connected 

to each sample. 

with activated dust. Dust was sieved onto the sample at an 

angle of 90° in all cases. The sample was then translated under 

the Xe arc lamp, and heated at incidence angles of 90°, 45°, 

30°, and 10°, and cooled using the procedure described above 

for the pristine samples. 

In some cases a Kimball Physics (Wilton, NH) model FRA2X1-2 electron flood gun sprayed electrons onto the dust as it 

dropped from the sieve onto the samples. The electron energy 

was set at 1000 V, and the emission current was about 

200 μA. It should be noted that this was a rather narrow beam, 

so only some fraction of the falling dust was directly exposed 

to the electrons. 

Fractional dust coverage was determined from images 

obtained with an optical microscope at 100× using image 

analysis software and a rigorous statistical procedure. The 

process has been described in detail elsewhere 

(Ref. 3). The mean of 50 measurements was calculated for 

each sample, as was the 95 percent confidence interval. 

Figure 2.—Picture of the thermal model and parameters used in its construction. 

Material Material cond.

W/mK

Material cp,

J/KgK

Material

finish

Material finish,

a/e

Chamber SS 316 16.3 504 SS polished 0.42/0.11

Blend copper Copper 406.4 380 Buffed copper 0.30/0.03

Copper box Copper 406.4 380 Buffed copper 0.30/0.03

Vel‐black layer

inside copper box

Carbon

fiber 360 628 Black paint 0.95/0.95

Sample  

holder Al 6061‐T8

f(t)=43.3 at

32 K

to 175.6 at  

743.9 K

f(t)=64.6 at  

34.6 K

to 1126.8 at

810.9 K

Al polished 0.15/0.05

Aluminum  

sample Al 6061‐T8

f(t)=43.3 at

32 K

to 175.6 at  

743.9 K

f(t)=64.6 at  

34.6 K

to 1126.8 at

810.9 K

Z‐93 Initial 0.20/0.91

then varied

Composite

sample

Three layer

composite

Varies by layer

First layer: 1100

Second and  

third: 5

~1000 AgFEP Initial 0.08/0.81

then varied

Sample  

holder rod SS 304 16.3 500 SS machined 0.47/0.14

NASA/TM—2009-215647 2 
The thermal modeling was done using Thermal Desktop 

(Cullimore & Ring Technologies), a PC based design 

environment for generating thermal models of electronics and 

vehicles. Thermal Desktop incorporates both parameter based 

finite difference surfaces with finite elements and CAD 

technology to model thermal problems. Thermal Desktop 

develops the capacitance and conductance network for input to 

SINDA/Fluint which is a comprehensive finite-difference, 

lumped parameter (circuit or network analogy) tool for heat 

transfer design analysis and fluid flow analysis in complex 

systems. Thermal Desktop 5.1 Patch 3 was used to generate 

the thermal model, which consists of 743 nodes and 1840 

linear conductors. A visualization of the model and the 

material parameters used in it are shown in Figure 2. 

Because there were concerns that the intensity of the Xe arc 

lamp might be changing over time, it was calibrated for each 

sample assuming that the absorptivity (α) of the AZ-93 

sample at 90° was the same as the literature value (0.200). The 

emissivity (ε) was determined from the measured cooling 

curve. The lamp intensity was then varied until the calculated 

heating curve fit the experimental data within 0.5 percent. 

That lamp intensity was used for the rest of the pristine and 

dusted heating curves for that sample, and α was varied until 

the model matched the heating curve data to within 0.5 

percent. This process was repeated for each of the AZ93 

samples. This same lamp intensity was also used for the 

corresponding AgFEP analysis. The data were collected for 

both types of surfaces at the same time and the AZ93 data was 

considered more reliable because of the unknown effects of 

the light on the 90° AgFEP being reflected back up onto the 

lamp. 

Results and Discussion 

90° Test Results 

The data collected at 90° is in every way equivalent to the 

thermal control surfaces on data taken in a previous study 

(FY08) (Ref. 4). Figure 3 compares the optical constants 

calculated in this study (FY09) with those calculated 

previously and the literature values. Since the α of the 90°

AZ93 samples was constrained to be 0.20, and the 

experimentally determined ε was found to be the same in three 

of the four AZ93 samples, three of those points are 

superimposed in the plot at ε = 0.89 and α = 0.20. This is not 

the case for the AZ93 samples from FY08 where the α from 

the first sample was used to set the lamp intensity, and the α

was allowed to vary for the other three. The α for the AgFEP 

in the FY09 data set was very consistent, 0.104±0.001, but 

somewhat higher than the FY08 sample α of 0.074±0.002. 

The average ε of the AZ93 was found to be 0.895, close to 

the literature values of 0.90 to 0.92. The high precision in the 

value of ε compared to the FY08 study draws from more 

Pristine Thermal Control Surfaces 

Figure 3.—Plot of the α and ε calculated for the eight pristine 

90° samples (open), the eight calculated from the 2008 

study (filled), and the literature values (+) for AZ93 and 

AgFEP. 

Thermal Control Surface Degradation Due to Dust 

Figure 4.—The relationship between α/ε as a function of 

percent JSC-1A lunar simulant dust coverage for all of the 

90° data collected during FY08 (filled) and this study 

(open). A least squares line through the data indicates a 

monolayer of dust coverage increases the α/ε by a factor 

of 3.5. 

consistent cooling curves. It is tempting to attribute this to the 

new sample holder arrangement that holds the sample in a 

more reproducible position within the cold box, however, as 

can be seen in Figure 3 the ε for the AgFEP had essentially the 

same spread in the FY09 data as in the FY08 data. 

0.00

0.05

0.10

0.15

0.20

0.25

0.60 0.70 0.80 0.90 1.00

Emissivity

Absorptivity 

AZ93-08

AZ93-09

AgFEP-08

AgFEP-09

AZ93 Lit

AgFEP Lit

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0 20 40 60 80 100

Percent Dust Coverage

Change in A/E 

AZ93Al

AZ93C

AgFEPAl

AgFEPC

Extrap

AZ93-9

AfFEP-9

NASA/TM—2009-215647 3 
The results from the dusted 90° samples were also 

consistent with the FY08 data. Although direct comparisons 

were not available because the samples cannot be dusted 

reproducibly, the trends appear to be the same. This is evident 

in Figure 4 which shows the α/ε ratio as a function of percent 

dust coverage. The FY09 data fall along nearly the same line 

as the FY08 data. The least squares line indicates that a 

thermal control surface covered with a monolayer of JSC-1A 

lunar simulant dust has a α/ε ratio 3.5 times greater than a 

clean surface. If the apparently anomalous point at 48 percent 

coverage and α/ε of 3.7 is deleted the intercept drops to 3.3. 

But the empirical α/ε measured for the completely dust 

covered AgFEP-903 sample was 4.1. It is concluded that the 

value of α/ε for a complete monolayer of dust is increased by 

a factor of 3-4 over pristine surfaces, and appears to be 

independent of thermal control surface type or substrate. 

Angular Dependence of α For Pristine Surfaces 

Figure 5 shows the relative α (α/α90°) of three pristine AZ93 

surfaces as a function of incidence angle. (No pristine AZ93-

902 angular data were available.) Recall that the 90° case was 

constrained to have the same α, 0.20. What is probably the 

most striking characteristic about these data is that the spread 

in the data increased as the angle becomes more shallow. This 

may, at least in part, be an artifact of the sample holder. The 

sample holder was not designed to hold the samples at high 

angle. In fact, a geometric analysis shows that there was 

enough play in the way that the samples were held by the 

Kapton (Dupont) clamshell that there could be a deviation of 

as much as 6° from the set angle for AZ93-901, and 4° for 

AZ93-903 and AZ93-904. With the sin θ dependency this 

deviation has much more impact on the α calculated when the 

modeled θ = 10° than when the modeled θ = 90°. So while the 

AZ93-903 and AZ93-904 samples show essentially no angular 

dependence of α, the AZ93-901 sample shows a marked 

dependence, with the α at 10° varying by 35 percent from that 

of the 90°. Modifications have been made in the sample and 

sample holder to eliminate this source of error in the future, 

and more data will be taken to clarify this issue, but the 

tentative conclusion is that pristine AZ93 has no appreciable 

angular dependence in α at angles as shallow as 30°. The 

spread in the data at 10° leaves any conclusions about it in 

doubt. But these data are consistent with the finding of 

Jaworske who measured the reflectance of Z-93-P thermal 

control paint as a function of angle (Ref. 5). He found only 

very small changes in the reflectance as a function of angle 

down to 30° for light in the 3 to 40 μm range. However, at 

angles of 10° to 20° there was significant increases in 

reflectance. Since light impinging on an opaque surface must 

either be reflected of absorbed, this would imply little change 

in α over that range as well. 

Relative Absorptivity of Dusted AZ93 

Figure 5.—The α/α90 for pristine AZ-93 as a function of 

incidence angle. 

Relative Absorptivity of Pristine AgFEP 

Figure 6.—The α/α90 for pristine AgFEP as a function of 

incidence angle. 

The α as a function of incidence angle for pristine AgFEP is 

shown in Figure 6. Only 90° data are available for the AgFEP902 samples. Unlike the AZ93 samples, the AgFEP-903 and 

AgFEP-904 samples utilized the new sample substrate and 

holder that maintains the angle very well. So for those two the 

increase in spread in the data as the angle becomes more 

shallow is not due to angular error. The relative α for the 

AgFEP-904 climbs markedly while that for AgFEP-903 

actually dips. More trials will be required before conclusions 

can be drawn. 

Angular Dependence of α For Dusted Surfaces 

Figure 7 shows the relative α of AZ93 surfaces dusted to 

four different levels as a function of incidence angle. It 

appears that at coverage as high as 26 percent there is no 

0.0

0.5

1.0

1.5

2.0

0 15 30 45 60 75 90

Incidence Angle

Relative Absorptivity 

903

901

904

1

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 15 30 45 60 75 90

Incidence Angle

Relative Absorptivity 

903

901

904

1

NASA/TM—2009-215647 4 
significant angular dependence until the angle becomes very 

shallow (10°). At these shallow angles the relative α increases 

as the dust coverage decreases. Though as noted above, this 

may be at least in part, an artifact of the sample holder. 

The corresponding plot of the relative α of AgFEP surfaces 

dusted to four different levels as a function of incidence angle 

is shown in Figure 8. Note that the levels of dust coverage are 

higher than in the AZ-93 case, and in fact the AgFEP-903 

samples were completely covered with dust. The AgFEP-901 

samples were 74 percent covered, more than twice the dust on 

the dustiest AZ-93 sample. This plot indicates that if the 

AgFEP is totally, or even mostly covered by dust, there is no 

angular dependence to angles as shallow as 10°. But, like the 

AZ93 case, if the dust coverage is in the 10 to 

34 percent range, there is an increase in the relative α at the 

very shallow angles.

Emissivity of Pristine and Dusted Samples 

It has been the conventional wisdom that since the lunar 

regolith is so dark that dust on a thermal control surface will 

have no appreciable effect on the ε. The FY08 data seemed to 

call that into question, with ε of the AZ93 samples apparently 

decreasing with dust coverage and the ε of AgFEP increasing 

with dust coverage, given the data on both aluminum and 

composite substrates. The FY08 data have been combined 

with the 90° FY09 data in Figure 9. The combined data calls 

for a reconsideration of the original contention. Although the ε

of the most heavily dusted AZ93 samples tend to fall below 

the range of undusted, and the most heavily dusted AgFEP 

samples tend to fall above the range of the undusted, most of 

the ε values of the dusted samples fall within the range of the 

pristine samples. This will only be resolved by taking 

additional data. But from a technology development 

perspective, the effect is not pronounced. 

Conclusions 

There are four major conclusions that can be drawn from 

this study. The first is confirmation that even a sub-monolayer 

of simulated lunar dust can significantly degrade the 

performance of both white paint and second-surface mirror 

type radiators under simulated lunar conditions. If anything, 

the results of this study point to a slightly higher degradation 

in the α/ε value, increasing to a factor of 3 to 4 for the case of 

full monolayer coverage. 

The second conclusion is that there is little angular 

dependence of the α of pristine thermal control surfaces in 

both AZ93 and AgFEP. Although there may be an effect at 

angles as shallow as 10°, the experimental error in the angle 

Relative Absorptivity of Dusted AZ93 

Figure 7.—The α/α90 for AZ-93 dusted to four different levels 

as a function of incidence angle. 

Relative Absorptivity of Dusted AgFEP 

Figure 8.—The α/α90 for AgFEP dusted to four different levels 

as a function of incidence angle. 

Emissivity of Thermal Control Surfaces 

Figure 9.—Plot of ε as a function of fractional dust coverage for 

all of the thermal control samples characterized to date. 

 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 15 30 45 60 75 90

Incidence Angle

Absorptivity Dusted/Prist

26%

18%

9%

8%

1

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 15 30 45 60 75 90

Incidence Angle

Absorptivity Dusted/Prist

100%

74%

34%

10%

1

0.50

0.60

0.70

0.80

0.90

1.00

0.0 0.2 0.4 0.6 0.8 1.0

Fractional Dust Coverage

Emissivity

AZ93-08

AZ93-09

AgFEP-08

AgFEP-09

AZ93-C

AgFEP-C

NASA/TM—2009-215647 5 
NASA/TM—2009-215647 6 

measurement may be as large as 6°, and this can perhaps 

explain the increasing spread in the data with shallower angle. 

The sample holder has been redesigned to improve the 

precision and it is hoped that this issue will be resolved by 

future tests. 

The third conclusion, which is tentative, is that there is little 

angular dependence of sub-monolayer coatings of dust, 

particularly at very low and very high dust coverage. In the 25 

to 35 percent coverage range the α may be enhanced at 

shallow angles, perhaps by as much as a factor of 3. More 

precise angle control and additional data are required to 

confirm this. 

The fourth conclusion is actually a backing away from the 

idea that at high loading the ε of the thermal control surfaces 

is significantly affected. More data will be required to confirm 

whether this effect is real.

References 

1. J.R. Gaier and D.A. Jaworske, “Lunar Dust on Heat Rejection 

System Surfaces: Problems and Prospects,” STAIF07, Paper 26, 

and NASA/TM—2007-214814. 

2. J.R. Gaier and E.A. Sechkar, “Lunar Simulation in the Lunar 

Dust Adhesion Bell Jar,” Presented at the 45th AIAA Technical 

Conference as AIAA–2007–0963, and NASA/TM—2007-

214704. 

3. J.R. Gaier, J. Siamidis, and E.M.G. Larkin, NASA/CP—2008-

214164, 25th Space Simulation Conference (2008). 

4. J.R. Gaier et al., “The Effect of Simulated Lunar Dust on the 

Absorptivity, Emissivity, and Operating Temperature of AZ-93 

and Ag/FEP Thermal Control Surfaces,” NASA/TM—2008-

215492. 

5. D.A. Jaworske, “Optical and Calorimetric Evaluation of Z-93-P 

and Other Thermal Control Coatings, Thin Solid Films,” (1996) 

pp. 278–282.
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Effect of Illumination Angle on the Performance of Dusted Thermal Control Surfaces in a 

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11. SPONSORING/MONITORING

 REPORT NUMBER

NASA/TM-2009-215647 

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited 

Subject Category: 91 

Available electronically at http://gltrs.grc.nasa.gov 

This publication is available from the NASA Center for AeroSpace Information, 443-757-5802

13. SUPPLEMENTARY NOTES

14. ABSTRACT

JSC-1A lunar simulant has been applied to AZ93 and AgFEP thermal control surfaces on aluminum substrates in a simulated lunar 

environment. The temperature of these surfaces was monitored as they were heated with a solar simulator using varying angles of incidence 

and cooled in a 30 K coldbox. Thermal modeling was used to determine the solar absorptivity (a) and infrared emissivity (e) of the thermal 

control surfaces in both their clean and dusted states. It was found that even a sub-monolayer of dust can significantly raise the a of either 

type of surface. A full monolayer can increase the a/e ratio by a factor of 3 to 4 over a clean surface. Little angular dependence of the a of 

pristine thermal control surfaces for both AZ93 and AgFEP was observed, at least until 30° from the surface. The dusted surfaces showed 

the most angular dependence of a when the incidence angle was in the range of 25° to 35°. Samples with a full monolayer, like those with no 

dust, showed little angular dependence in a. The e of the dusted thermal control surfaces was within the spread of clean surfaces, with the 

exception of high dust coverage, where a small increase was observed at shallow angles. 

15. SUBJECT TERMS

Lunar soil; Lunar dust; Thermal control 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

 ABSTRACT

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18. NUMBER

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 PAGES

11 

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email:help@sti.nasa.gov) 

a. REPORT

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b. ABSTRACT

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c. THIS 

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19b. TELEPHONE NUMBER (include area code)

443-757-5802 

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