James R. Gaier

Glenn Research Center, Cleveland, Ohio

Effect of Simulant Type on the Absorptance and 

Emittance of Dusted Thermal Control Surfaces 

in a Simulated Lunar Environment

NASA/TM—2010-216786

August 2010

AIAA–2010–6111
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James R. Gaier

Glenn Research Center, Cleveland, Ohio

Effect of Simulant Type on the Absorptance and 

Emittance of Dusted Thermal Control Surfaces 

in a Simulated Lunar Environment

NASA/TM—2010-216786

August 2010

AIAA–2010–6111

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

40th International Conference on Environmental Systems

cosponsored by AIAA, AIChE, ASME, SAE Environmental Systems Committee, and 

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Acknowledgments

This work is the result of a great deal of effort by a sizable team of dedicated professionals from many organizations, all of whom 

the author would like to thank. E.A. Sechkar (Arctic Slope Regional Corporation) and F.P. Lam (Jacobs Sverdrup) provided 

engineering and technical support of the LDAB facility. S.R. Panko (Arctic Slope Regional Corporation) provided both electrical

engineering and test engineering support for the LDAB. The thermal modeling was a team effort involving several people from the

NASA Glenn Research Center (GRC) Thermal Systems Branch. D.A. Jaworske (GRC) oversaw the fabrication of the test samples 

and acted as a general resource on the behavior of thermal control coatings. Technical, programmatic, and fi nancial support was 

provided by the Exploration Technology Development Program’s Dust Mitigation Project (M.J. Hyatt from GRC) and Advanced 

Thermal Control Project (R.A. Stephan from the NASA Johnson Space Center).

Available from

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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. 
NASA/TM—2010-216786 1

Effect of Simulant Type on the Absorptance and Emittance 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

During the Apollo program the effects of lunar dust on thermal control surfaces was found to be more 

significant than anticipated, with several systems overheating due to deposition of dust on them. In an 

effort to reduce risk to future missions, a series of tests has been initiated to characterize the effects of 

dust on these surfaces, and then to develop technologies to mitigate that risk. Given the variations in 

albedo across the lunar surface, one variable that may be important is the darkness of the lunar dust, and 

this study was undertaken to address that concern. Three thermal control surfaces, AZ–93 white paint and 

AgFEP and AlFEP second surface mirrors were dusted with three different lunar dust simulants in a 

simulated lunar environment, and their integrated solar absorptance (α) and thermal emittance (ε) values 

determined experimentally. The three simulants included JSC–1AF, a darker mare simulant, NU–LHT–

1D, a light highlands simulant, and 1:1 mixture of the two. The response of AZ–93 was found to be 

slightly more pronounced than that of AgFEP. The α increased with fractional dust coverage in both types 

of samples by a factor of 1.7 to 3.3, depending on the type of thermal control surface and the type of dust. 

The ε of the AZ–93 decreased by about 10 percent when fully covered by dust, while that of AgFEP 

increased by about 10 percent. It was found that α/ε varied by more than a factor of two depending on the 

thermal control surface and the darkness of the dust. Given that the darkest simulant used in this study 

may be lighter than the darkest dust that could be encountered on the lunar surface, it becomes apparent 

that the performance degradation of thermal control surfaces due to dust on the Moon will be strongly 

dependent on the α and ε of the dust in the specific locality. 

Nomenclature

AgFEP 0.13 mm thick fluorinated ethylene propylene (FEP) with a silver reflecting surface on the 

back

AlFEP 0.13 mm (0.005 in.) thick FEP with an aluminum reflecting surface on the back

AxFEP both AgFEP and AlFEP

AZ–93 a white thermal control paint formulated by AZ Technologies similar to Z–93

α absorptivity over the solar spectrum

αrel α/α of pristine surface

ε emissivity over thermal range (100 to 400 K)

εrel ε/ε of pristine surface

f fractional of surface covered by dust

Introduction

As part of the plans to return humans to the Moon, NASA is evaluating the threats that the lunar 

environment may pose to astronaut health and mission success. These threats are numerous and serious, 

but the one singled out by Apollo astronauts as being the most worrisome is the effects of lunar dust

(Ref. 1). One of the most serious system effects was the overheating caused when dust contaminated 
NASA/TM—2010-216786 2

thermal control surfaces. For example, the batteries on the lunar roving vehicle ran hotter than anticipated, 

and in fact hotter than their rated operating temperature for part of the time, even though they were 

equipped with dust covers and were brushed off at regular intervals (Ref. 2

Since only a limited amount of fine lunar particles were returned during the Apollo missions, 

characterization of dust effects has been carried out with lunar simulants. Results reported to date have 

been limited to measurements of effects of the sub-monolayers of the lunar simulant JSC–1A on the 

integrated solar absorptance (α) and thermal emittance (ε) of white thermal control paints (AZ–93) and 

second surface mirrors (AgFEP). It was found that the α/ε of both types the thermal control surfaces 

increased by a factor of about 3.5 when fully covered by JSC–1A dust (Ref.

). In anticipation of the much 

longer stays for lunar surface systems to operate on the lunar surface, a joint task has been developed by 

NASA’s Exploration Technology Development Program’s Dust Mitigation Project and Advanced 

Thermal Control Project to quantify the effects of lunar dust accumulation on thermal control surfaces 

and to develop mitigation strategies.

3

But dust on the surface of the Moon is not uniform in its thermal optical properties. The lightest crater 

rays have an α of about 0.50, and the darkest portions of the mare have an α of about 0.93. It is 

reasonable to expect that the effects of the dust on the α and ε of the dusty thermal control surfaces would 

depend on the α and ε of the dust itself. JSC–1A has a measured α of about 0.77 (Ref. 

).

4), about the same 

as expected from the average albedo of the soils on the near side lunar surface (Ref. 5

Methods and Materials

). A recently 

developed lunar simulant designated NU–LHT–1D has a measured α of about 0.51 (Ref. 4), nearly the 

same as the lightest soils on the lunar surface. The purpose of this study was to determine what 

quantitative effect varying the darkness of the dust has on the α and ε of dusted thermal control surfaces.

This report can be thought of as a follow-on to the report by Gaier (Ref. 3). The methods and 

materials were only slightly modified from that report. Three lunar simulants were used in the study. The 

first, JSC–1A, is the same simulant used in the previous study, and in fact all of the data found in this 

paper using JSC–1A comes from the previous study. The second simulant, NU–LHT–1D, is much lighter 

in color, and corresponds to a freshly excavated, or highly immature, highlands soil. Soil that is exposed 

to space weathering is thought to darken as more metallic iron is generated (Ref. 6

Approximately 15 grams of lunar simulant was placed in the activation bowl of the Lunar Dust 

Adhesion Beljar (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 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.

), so this simulant 

might be thought of as a light end-member, because all soils found on the lunar surface are expected to be 

at least this dark. A third simulant was created by the 1:1 mixing of the JSC–1A and the NU–LHT–1D. 

As expected, it was intermediate in color. However, it would be a mistake to think of this simulant as a 

mixture of light NU–LHT–1D particles and dark JSC–1A particles. Both of the root simulants are 

themselves mixtures of nearly colorless plagioclase and dark pyroxenes, as well as some intermediate 

color minerals. 
NASA/TM—2010-216786 3

One AZ93 painted aluminum disk, and one aluminum disk with a 0.13 mm (5 mil) thick FEP 

appliqué coated either with a few nm of aluminum or silver with an Inconel oxidation protection layer 

applied to the back was mounted in the sample holder for each experimental run. They were suspended in 

the sample holder by two layers of 0.13 mm Kapton, to minimize thermal losses. Temperature was 

measured by an AWG 36 Type K thermocouple fastened to the back of each sample. 

The intensity of the Xe arc lamp was monitored by a photodiode placed directly beneath the lamp. It 

was found that the intensity of the lamp gradually increased over the first 3 to 5 min, and then leveled off 

and was constant over the remaining time, up to 40 min. The total reflectance of several of the AZ–93 

samples was measured in either a Lambda 19, a Lambda 950, or a Cary 5000 spectrophotometer over 250 

to 2500 nm wavelengths. The average α calculated from these values, corrected for the air mass zero solar 

spectrum, was then used in the analysis to calibrate the lamp intensity for each run.

After the lamp intensity stabilized, one of the samples was positioned under the Xe arc lamp. 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 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 until the temperature of both samples was below 20 °C. 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, the sample was positioned under a sieve filled with 

activated dust. A Kimball Physics (Wilton, NH) model FRA–2X1–2 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. The sample was then translated under the 

Xe arc lamp, and heated and cooled using the procedure described above for the pristine samples.

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. 7

The α and ε values were derived from thermal modeling which was done using Thermal Desktop 

(Cullimore & Ring Technologies) using a model that has been described previously (Ref. 7). Because 

there were concerns that the intensity of the Xe arc lamp might be changing over time, it was calibrated 

for each AZ–93 as described above. In the calculation, 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 AZ–93 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 AZ–93 data was considered more reliable because of 

the unknown effects of the light on AgFEP being reflected back up onto the lamp. 

). The mean of 50 measurements was calculated for each sample, as was the 

95 percent confidence interval.

Results and Discussion

Effect on White Thermal Control Paint

White thermal control paints are diffuse reflectors that have relatively higher values of α and higher 

values of ε. AZ–93, which was used in this study has a solar α = 0.13 and a thermal ε = 0.92. The overall 

performance of a thermal control surface is dependent on both the α and the ε, and so the ratio α/ε is 

typically used, with a smaller value yielding a higher efficiency radiator. The thermal performance of this 

paint, α/ε = 0.14.
NASA/TM—2010-216786 4

The effects of the different simulant types on the relative α (αrel = αdusted / αpristine) of AZ–93 are 

shown in Figure 1(a). Although there is a wide scattering in the data, there is an unmistakable trend 

upwards as the fraction of the surface covered by the dust increases. Least squares fits to the three 

different populations of data in the figure yielded values for αrel at full monolayer coverage of 2.2, 2.6, 

and 3.0 by the lighter, middle, and darker simulants respectively. Previously reported data for the JSC–

1AF (darker simulant) have yielded similar values. So it appears that the darkness of the dust does affect 

the α of a dusted AZ–93 white paint thermal control surface.

The effects of the different simulant types on the relative ε (εrel = εdusted / εpristine) of AZ–93 are shown 

in Figure 1(b). The εrel values are much more tightly grouped, and there is an unmistakable downward 

trend as the fraction of the AZ–93 surface covered by dust increases. But perhaps surprisingly, the 

darkness of the dust has no measurable effect, with the least squares lines for all three simulants yielding 

a εrel of about 0.9 at full dust coverage. This would indicate that despite their different darkness in the 

visible part of the spectrum, these simulants have similar darkness in the thermal infrared. 

Because the effect of dust on the ε of AZ–93 is slight, the relative thermal performance, (α/ε)rel of the 

dusted thermal control surfaces is dominated by the α. Thus the plot of (α/ε)rel as a function of dust coverage 

(Fig. 1(c)) looks very similar to that of the αrel (Fig. 1(a)). Least squares fits to the three different 

populations of data yielded values for (α/ε)rel at full monolayer coverage are summarized in Table 1. 

TABLE 1.—α/ε EXTRAPOLATED TO FULL MONOLAYER COVERAGE

Pristine NU–LHT–1D 1:1 JSC–1A

α/ε (α/ε)rel (α/ε)rel (α/ε)rel

AZ93 0.14 2.6 3.0 3.4

AgFEP 0.14 1.5 2.2* 3.0

*Mixture of three AgFEP and 4 AlFEP samples.

Effects on Second Surface Mirrors

Unlike white thermal control paints, second surface mirrors are specular reflectors that have lower 

values of both α and ε than white paints. AgFEP used in this study has an α = 0.10 and an ε = 0.70. The 

overall performance of a thermal control surface was similar, α/ε = 0.14. The JSC-NULHT data set 

contains four AlFEP samples. Although the α/ε is slightly higher, 0.16, the relative trends are expected to 

be the same as the AgFEP, since it is the FEP surface that is exposed to the dust, though this is difficult to 

verify with such a small number of samples.

The effects of the different simulant types on αrel of AgFEP are shown in Figure 2(a). Again there is a 

wide scattering in the data, and again an unmistakable trend upwards as the fraction of the surface 

covered by the dust increases. Least squares fits to the three different populations of data in the figure 

yielded values for αrel at full monolayer coverage of 1.7, 2.3, and 4.2 by the lighter, middle, and darker 

simulants respectively. It appears that the darkness of the dust affects the α of dusted AgFEP surfaces 

more strongly than the Z–93 white paint thermal control surface.

The effects of the different simulant types on the εrel of AgFEP are shown in Figure 2(b). Interestingly, 

the εrel values trend upward as the fraction of the AgFEP surface covered by dust increases, contrary to 

what was observed in AZ–93. Again, the darkness of the dust has no measurable effect, with the least 

squares lines for all three simulants yielding a εrel of about 1.1 at full dust coverage. This reinforces the 

idea that these simulants have similar darkness in the thermal infrared. 

Again small dependencies on the effect of dust on the emissivity means that the relative thermal 

performance, (α/ε)rel of the dusted thermal control surfaces is dominated by the α. So again the plot of 

(α/ε)rel as a function of dust coverage (Fig. 2(c)) looks very similar to that of the αrel (Fig. 2(a)). Least 

squares fits to the three different populations of data yielded values for (α/ε)rel at full monolayer coverage 

summarized in Table 1. So although the (α/ε)rel of the pristine AZ–93 and AgFEP are the same, the 

AgFEP was slightly less affected by the dust. 
NASA/TM—2010-216786 5

Figure 2.—Thermal optical properties of AgFEP second surface 

mirror thermal control surface as a function of fractional coverage 

by three lunar simulant dusts, (a) αrel, (b) εrel, and (c) (α/ε)rel.

Figure 1.—Thermal optical properties of AZ–93 thermal control paint 

as a function of fractional coverage by three lunar simulant dusts, 

(a) αrel, (b) εrel, and (c) (α/ε)rel.
NASA/TM—2010-216786 6

Rule of Mixtures Calculations of α

A comparison can be made between the measured α and that which might be expected. A reasonable 

model to use is the rule of mixtures model which assumes that there are no interactions between the dust 

particles and the thermal control surface. Thus, if a surface is one-quarter covered with dust, the α of that 

one-quarter should have the α of bulk dust, and the α of the remaining three-quarters of the surface 

should be unaffected. The definition of αrel can be written in terms of the rule of mixtures as Equation (1):

( ( ) )

pris

dust dust dust pris

rel

1

α

α + − α

α = f f (1)

Values of αdust for each of the test dust have been recently calculated from their total reflectance spectra

(Ref. 4). Table 2 shows the comparison between the optical constants as measured spectrophotometrically, 

and those measured thermally in the LDAB for a thermal control surface that has been fully covered with 

dust. It can be seen that the rule of mixtures overestimates the effect of the dust on AZ–93 by a factor of 1.8 

to 2.0, and on AgFEP by a factor of 2.4 to 3.1. 

TABLE 2.—COMPARISON OF THE αrel OF FULL DUST COVERED THERMAL CONTROL 

SURFACES FROM OPTICAL MEASUREMENTS USING THE RULE OF MIXTURES 

MODEL (Opt) WITH THOSE FROM THERMAL MEASUREMENTS IN LDAB (Th)

AZ–93–Opt AZ–93–Th AgFEP–Opt AgFEP–Th

Pristine α 0.132 --- --- 0.098

NU–LHT–1D 3.9 2.2 5.3 1.7

NULHT–JSC 4.9 2.6 6.5 2.3

JSC–1AF 5.9 3.0 7.9 3.3

This may be due to differences in the optical depth of the dust in the two cases. The 

spectrophotometric measurement uses a dust layer about 4 mm thick. This corresponds to 160 layers of 

25 μm particles. In most cases, the dust layer on the thermal control surfaces was a single layer, and not 

fully covered. This becomes particularly important because most dust particles are colorless and 

transparent plagioclase crystals, with a relatively small fraction of dark pyroxene or glass particles. In 160 

layers most light will encounter one of the dark particles, but in a single layer most light will not. 

Conclusions

A study of the effects of the darkness of lunar simulants on the α and ε of dusted thermal control 

surfaces was undertaken. The response of the white thermal control paint, AZ–93 was found to be slightly 

more pronounced than that of the second surface mirror thermal control surface, AgFEP or AlFEP. The α

increased with fractional dust coverage in both types of samples by a factor of 1.7 to 3.3, depending on 

the type of thermal control surface and the type of dust. The ε of the AZ–93 decrease by about 10 percent 

when fully covered by dust, while that of AgFEP increased by about 10 percent. The thermal 

performance, α/ε, each thermal control surface covered by a full monolayer for each of the thermal 

control surfaces by each type of dust varied by a factor of 1.5 to 3.4. So the effect of dust itself varies by 

more than a factor of two depending on the thermal control surface and the darkness of the dust. Given 

that the darkest simulant used in this study is probably significantly lighter than the darkest dust that 

could be encountered on the lunar surface, it becomes apparent that the performance degradation of 

thermal control surfaces due to dust on the Moon will be strongly dependent on the α and ε of the dust in 

the specific locality. A simple rule of mixtures calculation overestimates the effect of dust by a factor of 

1.8 to 3.1, depending on the surface and the dust. It is suggested that this is due to the compositional 

heterogeneity of the dust, with the particle number being dominated by particles with low α, but the 

optical properties dominated by the relatively few high α particles.
NASA/TM—2010-216786 7

References

1. Gaier, J.R., “The Effect of Lunar Dust on EVA Systems During the Apollo Missions,” NASA 

Technical Memorandum, NASA/TM—2005-213610/REV1, (2007).

2. Gaier, J.R. and Jaworske, D.A., “Lunar Dust on Heat Rejection System Surfaces: Problems and 

Prospects,” Space Technologies and Applications International Forum 2007.

3. Gaier, J.R., “Effect of Illumination Angle on the Performance of Dusted Thermal Control Surfaces in 

a Simulated Lunar Environment,” International Conference on Environmental Systems, paper 2009–

01–2420 (SAE, 2009).

4. Gaier, J.R., and Gustafson, R.J., “Measurement of the Solar Absorptivity and Thermal Emissivity of 

Lunar Simulants,” International Conference on Environmental Systems, AIAA–2010–6025. 

5. NASA SP–315, Apollo 16 Preliminary Science Report, Chapters 6 and 19, (NASA, 1972).

6. Noble, S.K., et al., “The Optical Properties of the Finest Fraction of Lunar Soil: Implications for 

Space Weathering,” Meteoritics & Planetary Science ,Vol. 36, 2001, pp. 31–42.

7. Gaier, J.R., Siamidis, J., and Larkin, E.M.G., “Extraction of Thermal Performance Values from 

Samples in the Lunar Dust Adhesion Bell Jar,” 25th Space Simulation Conference, NASA/CP—2008-

214164, 2008.
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14. ABSTRACT

During the Apollo program the effects of lunar dust on thermal control surfaces was found to be more significant than anticipated, with several systems overheating due to 

deposition of dust on them. In an effort to reduce risk to future missions, a series of tests has been initiated to characterize the effects of dust on these surfaces, and then to 

develop technologies to mitigate that risk. Given the variations in albedo across the lunar surface, one variable that may be important is the darkness of the lunar dust, and this 

study was undertaken to address that concern. Three thermal control surfaces, AZ-93 white paint and AgFEP and AlFEP second surface mirrors were dusted with three 

different lunar dust simulants in a simulated lunar environment, and their integrated solar absorptance (α) and thermal emittance (ε) values determined experimentally. The 

three simulants included JSC-1AF, a darker mare simulant, NU-LHT-1D, a light highlands simulant, and 1:1 mixture of the two. The response of AZ-93 was found to be 

slightly more pronounced than that of AgFEP. The α increased with fractional dust coverage in both types of samples by a factor of 1.7 to 3.3, depending on the type of thermal 

control surface and the type of dust. The ε of the AZ-93 decreased by about 10 percent when fully covered by dust, while that of AgFEP increased by about 10 percent. It was 

found that α/ε varied by more than a factor of two depending on the thermal control surface and the darkness of the dust. Given that the darkest simulant used in this study may 

be lighter than the darkest dust that could be encountered on the lunar surface, it becomes apparent that the performance degradation of thermal control surfaces due to dust on 

the Moon will be strongly dependent on the α and ε of the dust in the specific locality. 

15. SUBJECT TERMS

Lunar soil; Lunar dust; Thermal control 

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