James R. Gaier, Shaneise Ellis, and Nichole Hanks

Glenn Research Center, Cleveland, Ohio

Thermal Optical Properties of Lunar 

Dust Simulants and Their Constituents

NASA/TM—2011-217232

December 2011

AIAA–2011–3673
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James R. Gaier, Shaneise Ellis, and Nichole Hanks

Glenn Research Center, Cleveland, Ohio

Thermal Optical Properties of Lunar 

Dust Simulants and Their Constituents

NASA/TM—2011-217232

December 2011

AIAA–2011–3673

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

3rd Atmospheric and Space Environments Conference

sponsored by the American Institute of Aeronautics and Astronautics

Honolulu, Hawaii, June 27–30, 2011
Acknowledgments

The authors gladly acknowledges the contributions of K. Street, S.K.R. Miller and D.A. Jaworske of the NASA Glenn Research 

Center (GRC), D. Rickman of the NASA Marshall Spaceflight Center, and D. Stoesser of the U.S. Geological Survey for their 

many helpful discussions about the properties of the lunar regolith and lunar simulants. S. Wilson of the U.S. Geological Survey 

and R.J. Gustafson of Orbital Technologies kindly provided simulant samples. Assistance with the x-ray diffraction data collection 

and analysis was provided by R. Rogers and M. Cox of GRC. Programmatic and financial support from the NASA Exploration 

Technology Development Program came through the Dust Mitigation Project (M.J. Hyatt at GRC) and the Advanced Thermal 

Control Project (R.A. Stephan, NASA Johnson Space Center.)

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only. Their usage does not constitute an official 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—2011-217232 1

Thermal Optical Properties of Lunar Dust Simulants 

and Their Constituents

James R. Gaier, Shaneise Ellis,

* and Nichole Hanks†

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Abstract

The total reflectance spectra of lunar simulant dusts (< 20 μm particles) were measured in order to 

determine their integrated solar absorptance (α) and their thermal emittance (ε) for the purpose of 

analyzing the effect of dust on the performance of thermal control surfaces. All of the simulants except 

one had a wavelength-dependant reflectivity (ρ(λ)) near 0.10 over the wavelength range of 8 to 25 μm, 

and so are highly emitting at room temperature and lower. The 300 K emittance (ε) of all the lunar 

simulants except one ranged from 0.78 to 0.92. The exception was Minnesota Lunar Simulant 1 (MLS-1), 

which has little or no glassy component. In all cases the ε was lower for the < 20 μm particles than for 

larger particles reported earlier. There was considerably more variation in the lunar simulant reflectance 

in the solar spectral range (250 to 2500 nm) than in the thermal infrared. As expected, the lunar highlands 

simulants were more reflective in this wavelength range than the lunar mare simulants. The integrated 

solar absorptance (α) of the simulants ranged from 0.39 to 0.75. This is lower than values reported earlier 

for larger particles of the same simulants (0.41 to 0.82), and for representative mare and highlands lunar 

soils (0.74 to 0.91). Since the α of some mare simulants more closely matched that of highlands lunar 

soils, it is recommended that α and ε values be the criteria for choosing a simulant for assessing the 

effects of dust on thermal control surfaces, rather than whether a simulant has been formulated as a 

highlands or a mare simulant.

1.0 Introduction

As NASA prepares to return humans to the Moon, extensive efforts are under way to design the 

thermal control systems that will protect future lunar landers and surface system elements from the harsh

thermal environment. Part of this effort is to determine the effects of dust deposited on thermal control 

surfaces. But even a casual glance at the Moon reveals that the lunar surface is not uniform in brightness. 

The albedo of specific areas of the Moon varies from 0.50 for the brightest features to 0.07 for the darkest

(Ref. 1). If the dust is darker, then more light will be absorbed by it, resulting in increased heating both of 

the dust and, through conduction and radiation, any thermal control surface it may land on. To quantify 

these effects, lunar simulants must be developed that have a variety of reflectance properties. 

There are several characteristics of the albedo which limit its usefulness when assessing the effects of 

radiant energy on thermal control systems. First, as these measurements are typically made either from 

Earth-based instruments or from lunar orbit, the topographical features within the measurement frame will 

affect the measurement. Any shadowed areas will skew the albedo to a lower value. And even for those 

areas lit, the fraction of light reflected is dependent on the angle of incidence. The bidirectional 

reflectance function of the lunar surfaces is known to be decidedly non-Lambertian. In addition, the 

albedo is typically measured in the visible region of the spectrum (400 to 700 nm wavelength), and the 

solar radiation is principally emitted over a wider spectral region, 250 to 2500 nm (Fig. 1) (Ref. 2).

 *

Summer Intern, UNCFSP/NASA Science and Technology Institute for Minority Institutions

†

Summer Intern, Lewis Educational Research Collaborative Internship Program
NASA/TM—2011-217232 2

Figure 1.—The solar spectrum measured at 1 AU from the 

Sun above the Earth’s atmosphere (Air Mass Zero 

spectrum). The visible spectrum is the region between 

the dotted lines.

More useful measures for most analyses are intrinsic material properties such as the wavelength 

dependant absorptivity (α(λ)), reflectivity (ρ(λ)) and transmissivity (T(λ)). These three properties are 

related through conservation of energy, since a photon must either be absorbed, reflected, or transmitted 

as described by Eq. (1):

α(λ) + ρ(λ) + T(λ) = 1 (1)

Under the usual condition for the lunar surface where the surface is opaque (T = 0), Eq. (1) can be 

expressed as:

α(λ) = 1 – ρ(λ) (2)

Another useful relationship is Kirchhoff's Law, which states that for a given wavelength of light the 

emissivity (ε(λ)) of a surface is equal to its α(λ), or:

ε(λ) = α(λ) (3)

In thermal analysis the quantity usually required is the total integrated absorptance (α) and total integrated 

emittance (ε). As illustrate in Figure 1, convolving the α(λ) of a material over the 250 to 2500 nm range 

with the AM0 solar spectrum yields a very good approximation of α, since there is little solar intensity 

outside this spectral range.

The intensity of ε(λ) is temperature dependant. Temperatures of interest range from the hottest 

surfaces of a nuclear reactor (perhaps 800 K) to the coldest of the permanently shadowed craters (perhaps 

25 K), though the daily lunar temperature swing of 100 to 400 K will encompass the temperatures most 

thermal control surfaces will be exposed to. The relationship between wavelength and temperature can be 

approximated by the Raleigh-Jeans law, which determines the wavelength at which the intensity for a 

blackbody radiation curve at a given temperature is maximum. Temperatures of interest and their 

corresponding wavelengths are shown in Table 1. 
NASA/TM—2011-217232 3

TABLE 1.—TEMPERATURES OF INTEREST AND THEIR CORRESPONDING

WAVELENGTHS ACCORDING TO THE RALEIGH-JEANS LAW

Feature Temperature, 

K

Wavelength max, 

μm

Permanently shadowed craters 25 115

Lunar night 100 29

Lunar polar regions 200 14

Lunar habitat temperature 300 10

Lunar equator at noon 400 7

Nuclear reactor radiator 800 4

Lunar simulant development is a rapidly evolving field. Although thermal optical properties of the 

lunar regolith are critical to designing systems that will survive the challenging lunar thermal 

environment, there has been little work to characterize the thermal optical properties of lunar simulants.

The spectra of many of these simulants were reported earlier by Gaier, et al. (Ref. 3), but the results were 

confounded by a large variation in particles size. 

The effects of particle size on the ρ(λ) of lunar dust particles is illustrated in Figure 2, which shows 

bidirectional reflectance spectra measured of a mare soil (12001) and a highlands soil (64801) returned by 

Apollo 12 and 16, respectively as reported by the Lunar Soil Characterization Consortium on their 

website.4 Note that the ρ(λ) increases as the particle size decreases. The authors attributed this, at least in 

part, to their observation that the finer fraction contained more feldspar, which is lighter in color than the 

more mafic pyroxenes. 

But the Gaier et al., study found that, with a single exception, all of the large grained simulants had 

higher α values than all of the small grained simulants. The composition of the simulants was nearly 

invariant between the larger and smaller components because the fine fractions were produced from 

grinding the coarser fractions. The present study was undertaken with the aim of eliminating particle size 

as a factor in the α and ε determination by grinding and sieving the simulants to a common size range, < 

20 μm. It was recognized that the grinding and sieving process has its own perils, such as the creation of 

more glassy phase and the possibility that softer minerals would be over-represented in the sieved 

fraction. Long grinding times were used to minimize the selective removal of the harder minerals, at the 

risk of increasing the glassy phase content. X-ray diffraction of the simulants before and after sieving was 

used to judge whether there was selected removal of major mineral components. The reflectance spectra 

in the 250 nm to 25 μm range, the integrated solar α, and the 300 K ε values are reported herein for a 

variety of ground and sieved lunar simulants.

2.0 Methods and Materials

2.1 Spectroscopic Methods

In order to determine the α of a simulant powder, the α(λ) over the solar spectrum must be 

determined. The easiest way to do that is to measure its ρ(λ) and apply Eq. (2). Since on the lunar surface 

sunlight will impinge on the dust particles both directly and from many different reflected directions, the 

total ρ(λ), including the specular and diffuse components is the quantity of interest. This is best 

accomplished using a spectrophotometer equipped with an integrating sphere. The reflectance spectra 

reported here were collected on a Cary 5000 spectrophotometer (Varian) equipped with a DRA 2500, 150 

mm diameter integrating sphere over the wavelength range of 250 to 2500 nm. 
NASA/TM—2011-217232 4

Figure 2.—The bidirectional reflectance spectra (a) Apollo 12001 mare and (b) Apollo 64801 highland lunar 

soils (Ref. 2).

Great care must also be taken in the preparation of the sample. How tightly the powder is packed will 

make a difference in this wavelength range, with lose powders reflecting less. In this study a Varian 

powder attachment was used. A sample is trapped in a compression cell, one side of which is a quartz 

window. The cell is tightened to the point where the powder makes a smooth and uniform surface, and the 

grains do not move when the cell is tipped or rotated. The Varian powder attachment was filled with 

about 10 grams of sample which resulted in a sample about 4 mm thick, rendering all of the samples 

opaque.

Determining the scale factors to put the ρ(λ) measurement on an absolute must be done thoughtfully 

as well. The 100 percent reflectance must be set with a powdered standard, which in turn must be 

calibrated against a NIST-traceable standard. Ideally, this calibration should be against a suite of NISTtraceable standards of varying ρ(λ) to determine the response function of the detector. In this study a 

second, manufacture-provided powder attachment filled with powdered Spectralon (Labsphere, Inc.), the 

same material that coated the inside of the integrating sphere, and a quartz window matched with the 

sample holder was used for the baseline. A set of eight NIST traceable diffuse reflectance standards 

(Labsphere) with ρ ranging from 0.02 to 0.99 was measured through the quartz window as well. A 

correction factor was applied to the averaged ρ for each sample to place it on an absolute scale.

Data were collected from 250 to 2500 nm in increments of 1 nm, at a scan rate of 600 nm/min. A 

deuterium lamp was used to measure the 250 to 350 nm data, and a halogen lamp to measure the 350 to 

2500 nm data. Immediately prior to running each sample, a spectrum of the Spectralon was collected as a 

sample, to determine whether the baseline was still valid. In all instances the deviations in the baseline 

were less than 1 percent. Three spectra of each sample were collected consecutively. The sample holder 

was rotated between each spectrum so that the beam sampled a different area of the sample. If the three 

spectra were determined to be similar enough, the three spectra were averaged, point by point, and 

multiplied by the ratio of blank to baseline.
NASA/TM—2011-217232 5

The integrated solar α of each sample was determined by calculating the convolution of the scaled 

ρ(λ) of the simulant with the ASTM air mass zero solar spectrum E–490–00 and expressed as a fraction 

of the solar spectrum. 

In order to determine the thermal ε, a similar procedure is required in the thermal infrared part of the 

spectrum. The ε(λ) was determined from the α(λ) using Eq. (3), which in turn was determined from the 

ρ(λ) using Eq. (2). Ideally the thermal infrared ρ(λ) spectra should overlap with the solar ρ(λ) spectrum 

(i.e., starting at less than 2.5 μm) and extend up to the wavelength that corresponds to the lowest 

temperature expected (i.e., 115 μm). But due to practical instrument considerations, it is difficult to 

measure infrared ρ(λ) at wavelengths longer than about 25 μm.

Ambient laboratory air contains enough carbon dioxide and water to absorb the infrared in the light 

path, and distort the ρ(λ) spectrum. So the integrating sphere was flooded with dry nitrogen gas to reduce 

absorption enough that the ρ(λ) signal of the simulant could dominate. For this study reflectance spectra 

in the 2.5 to 25 μm range were collected on a Magna-IR 760 (Nicolet) equipped with a Labsphere RSA–

NI–550ID 76 mm Infragold (Labsphere, Inc.) integrating sphere using a deuterated triglycidyl sulfate 

detector. This is a Fourier transform instrument and 80 scans with a data point spacing of 7.714 cm–1 were 

collected for each sample. A gold background spectrum was measured prior to each scan. Powder 

samples of 4 to 6 mm thickness were place in a Fluoroware dish which was placed at the sample port at 

the bottom of the integrating sphere. No window was necessary in this configuration. None of the 

Fluoroware spectral peaks were visible in any of the spectra, indicating that the samples were optically 

opaque. During the course of the data collection two NIST traceable standards of similar reflectivity 

(SRS–10–010 and SRS–20–010) were measured as well. 

There are subtle differences between the ways the data were collected on the two spectrophotometers. 

In the Cary, the sample was physically substituted for the reference on the surface of the integrating 

sphere. But in the Nicolet, the sample was measured by alternating a mirror between reference and sample 

positions. So in the case of the Nicolet, some small fraction of the integrating sphere when the reference 

was being measured was covered with the sample, whereas in the Cary it was not. This correction factor 

is dependent on the reflectance of the sample. Both instruments measured the samples at 1600 to 

2500 nm, so the average ρ(λ) over this region was used to scale the Nicolet data to the Cary data. A plot 

of the Cary data as a function of the Nicolet data revealed that the ρ(λ) varied linearly with an R2 of 0.97. 

This correction factor was applied to all of the Nicolet data. The integrated thermal ε was determined over 

the full temperature range expected on the lunar surface, 100 to 400 K. This was calculated by 

convoluting the 2.5 to 25 μm wavelength ε(λ) data with blackbody curves over the temperature range in 

5 K increments (Ref. 5). The temperature dependence was small, so only the ε at 300 K is reported here.

2.2 Lunar Simulants

The basic spectra of six of the most common lunar simulants were measured, three mare type and 

three highlands type. The first of these was JSC–1A, a mare-type simulant that is a remake of the JSC–1 

simulant that has been the de facto NASA simulant since it was introduced in 1994 (Ref. 6). The second 

was a simulant developed by researchers at the University of Minnesota in 1988 approximating the bulk 

chemistry of Apollo 11 soil sample 10084, Minnesota Lunar Simulant #1 (MLS–1) (Ref. 7). The third 

was developed in Japan in 1995 from the volcanic soils on Fujisan called FJS–1 (Ref. 8). The fourth was 

a lunar highlands type simulant produced through a current joint effort of NASA and the U.S. Geological 

Survey, NU–LHT-2M (Ref. 9). Two recently developed simulants from Canada were tested as well, the 

OB-1 and the Chenobi highlands simulants (Ref. 10).

In addition to those simulants, four simulant variants were measured to determine the general effects 

of adding minor constituents to the simulants. Since JSC-1A is a remake of JSC-1, their spectra should be 

identical. This was examined. MLS–1P is a variant of MLS-1 produced by dropping the MLS–1 through 

a 6000 °C plasma in an in-flight sustained shockwave plasma reactor, 10 m tall. MLS-1 itself has 

essentially no glass content, but glass content from 10 to 30 percent was achieved with feed rates of 40 to 
NASA/TM—2011-217232 6

50 kg/hr. Although no agglutinate-like materials were produced, part of the simulant was melted into 

glassy spheroids, some as large a 2 mm. ORBITEC, under a Phase I SBIR contract, used a proprietary 

process to create a mature lunar regolith simulant designated JSC–1A–5000–2X that contains a high 

proportion of agglutinate-like particles and glass spherules, both of which contain metallic iron globules 

(including nanophase Fe0

). They also processed NU-LHT-2M in a similar manner to create a highlands 

simulant, designated NU–LHT–2M–700–1X containing simulated agglutinates with iron globules

(Ref. 11).

Finally, the spectra of five minerals from which lunar simulants may be fabricated, anorthosite,

norite, ilmenite, chromite, and harzburgite were measured as well. The hope is that models can be 

developed from these spectra that will enable the mimicking of various lunar dust spectra by the physical 

combination of these constituents.

2.3 Processing the Lunar Simulants

Particle size is known to affect the ρ(λ) of powdered rock and mineral samples. This was dramatically 

shown in the case of lunar regolith in the data reported by the Lunar Soil Characterization Consortium, 

who measured the ρ(λ) of sieved fractions of lunar samples returned during Apollo.4 They found that 

smaller particles were both more reflective and showed fewer spectral features. Since the simulants were 

acquired with a wide variety of particle sizes, they were processed to remove particle size as an important 

factor. Each of the samples was dry ground in a Micronizer (McCone) vibrating mill for 90 min, and then 

sieved through a 25 μm sieve (no 450). After both sets of spectral measurements were taken, x-ray 

diffraction analysis was performed on both the ground samples and the ground-and-sieved samples to 

make sure that the sieving was not systematically removing individual components from the samples.

X-ray diffraction (XRD) analysis was carried out on a Bruker D8 Advance diffractometer equipped 

with a sample spinner and a linear position-sensitive detector using Cu Kα radiation. The micronized 

materials were sampled before and after being sieved. A thin layer of each sample was dispersed with 

alcohol onto a silicon “zero background” holder and allowed to dry. Each sample was scanned over the 

range of 10 to 130° 2θ with a step size of 0.02° and a scan rate of 1 step/s.

None of the samples showed differences in the major phases induced by sieving greater than 

1 percent except for MLS-1P, which showed an increase of pyroxene over plagioclase by about 5 percent 

on sieving. This sample differed from the others in that the initial material contained glassy spheres up to 

2 mm in diameter, much larger than the grain size. The mirconizing did not appear to significantly 

increase the size fraction of the glassy phase for any of the samples, as determined by XRD.

3.0 Results and Discussion

3.1 Reflectivity Measurements

The reflectance spectra of Chenobi, NU–LHT–2M, MLS–1, JSC–1AF, FJS–1, and OB-1 sieved to 

below 25 μm particles are shown in Figure 3. Large differences are noted among the six basic simulants 

in the ρ(λ) in the 250 to 2500 nm range, where the solar spectrum is the most intense. Even before a 

quantitative analysis, it is apparent from these spectra that there will be substantial variations in the solar 

α among the simulants. As expected, two of the highlands type simulants, Chenobi and NU-LHT-2M are 

more reflective than the mare types. OB-1, despite the fact that it was intended to be a highlands type 

simulant, proved to be among the darkest of the simulants.

It is clear that there was little difference in the ρ(λ) among the simulants at wavelengths greater than 

about 8 μm, except for the case of MLS–1. Further, the infrared ρ(λ) for those simulants is about 0.10 for 

wavelengths longer than 8 μm. Using the Raleigh-Jeans law this corresponds to temperatures of 360 K 

and lower, so for the temperatures at which the thermal control surfaces are expected to operate under 
NASA/TM—2011-217232 7

lunar conditions, the ε’s are all about the same. This implies that the thermal emission properties all over 

the lunar surface are likely to be similar, and in the range of 0.9. 

It can be seen in Figure 3(b) that MLS–1 is much more reflecting than the other simulants in the 10 to 

25 μm wavelength range. This is thought to be because MLS-1 contained almost no glass or agglutinates. 

Glasses are known to dramatically increase absorption over crystalline materials in this portion of the 

spectrum. In addition, the other simulants all had high glass content, as does the lunar soil. So MLS–1 

would probably not be a good simulant to use if the ε properties are important to the test. But MLS–1P is 

a variant of this material that has been exposed to a high temperature plasma, in which part of the MLS-1 

is melted, and quickly cooled to increase its glass content. Figure 4 shows the darkening that this 

produces over the entire spectral range.

Figure 3.—Reflectance spectra of the six baseline simulants measured in this study in the solar 

absorptance region (a), and for the emittance regions (b).

Figure 4.—Reflectance spectra of the MLS-1 and MLS-1P in the solar absorptance region (a), and 

for the absorptance and emittance regions (b).
NASA/TM—2011-217232 8

The participants at the Lunar Regolith Simulant Materials Workshop convened by NASA in 2005 

agreed that engineering large quantities of lunar simulants would be required to support NASA’s 

Exploration program. Since quantities of the mare simulant JSC-1 were largely depleted, it was decided to 

recreate that simulant, with the designation JSC-1A. Although the goal was an exact reproduction of JSC-1, 

it can be seen in Figure 5 that the reflectance spectrum, particularly in the 250 to 2500 nm range, differs 

appreciably. This illustrates an important lesson about the variability of natural materials. Even if the source 

material is taken from the same region and processed using the same techniques, there will be differences. 

So too will it be on the Moon. It will be more useful to consider the range of material properties the lunar 

regolith will have than to try to duplicate one particular sample exactly.

Unlike the lunar simulants in Figure 3(a), the ρ(λ) of lunar soils increases almost monotonically over 

the range from 300 to 2500 nm (Fig. 2). This is often attributed to agglutinitic glass, and the nanophase 

iron it contains. So the addition of synthetic agglutinates, which also contain small metallic iron particles 

would be expected also to increase the ρ(λ) over the base simulant in a similar way. Figure 6 shows ρ(λ) 

for JSC–1A and its variant JSC–1A–5000–2X, which had synthetic agglutinate particles added to it. 

Although there was an appreciable increase in theρ(λ) for this variant in the 250 to 2500 nm range, there 

was little effect on the reflectivity at wavelengths greater than 8 μm. Figure 7 shows ρ(λ) for NU–LHT 

and its variant NU–LHT–2M–700-1X which has agglutinates added using the same method as JSC–1A–

5000–2X. Here, there was even a smaller effect of the synthetic agglutinates, if any at all, on the 

reflectance spectrum. 

There are at least two possible explanations why the spectra of the simulants did not change as 

expected when the agglutinates were added. The first is that the synthetic agglutinates do not reproduce 

the key characteristics of the lunar agglutinates in sufficient fidelity. The most difficult part of the lunar 

agglutinate to reproduce is the nanophase iron which is found primarily in the amorphous “rind” around

each grain, but also to a lesser extent on the grain surface. Even though nanophase iron has been observed 

in the transmission electron microscope, the particle size and distribution of the nanophase may be critical 

in some manner that is not as yet understood. The second explanation is that the effect in lunar materials 

may be caused by factors in addition to agglutinate and nanophase iron that are not as yet understood.

Like most lunar soils, the lunar simulants fall into two broad categories, the darker mare simulants and 

the lighter highlands simulants. In order to determine whether the effects on thermal control systems vary 

linearly with the darkness of the soil, a simulant of intermediate α was desired. To accomplish this a 1:1 

mixture of the light highlands simulant NU–LHT–1D and the dark mare simulant JSC–1AF was prepared.

Figure 5.—Reflectance spectra of the JSC-1 and JSC-1A in the solar absorptance region (a), and 

for the thermal emittance region (b).
NASA/TM—2011-217232 9

Figure 6.—Reflectance spectra of the JSC-1A and the synthetic agglutinate variant JSC-1A-5000-

2X in the solar absorptance region (a), and for the thermal emittance region (b).

Figure 7.—Reflectance spectra of the NU-LHT-2M and the synthetic agglutinate variant NU-LHT2M-700-1X in the solar absorptance region (a), and for the thermal emittance region (b).

This also provided an opportunity to see how additive the α and ε of these multicomponent mixtures are. 

The results are shown in Figure 8, which shows the mixed simulant spectrum along with those of its 

constituents. Also shown is a point by point average of the two. It can be seen that the point-by-point 

average lies nearly on top of the 1:1 mixture, showing that the ρ(λ) is additive. 

Many lunar simulants are not simply a similar mineral composition that is dug out of the ground, but 

a mixture of minerals which may come from a variety of sources and geographic locations. This is 

entirely appropriate since the soils returned during the Apollo missions were composed of a variety of 

granular materials including single crystal grains, volcanic and impact glasses, multi-mineral grains, and 

agglutinates. Figure 9 shows the spectra of four components that have been found in lunar materials and 

could be used to develop lunar simulants. Anorthosite and norite are plagioclase feldspars of the type that 

make up the bulk of the lunar regolith. Harzbergite is made up of pyoxenes and olivine, the principal 

minerals that darken the regolith. Ilmenite and chromite are representative of very dark minor 

constituents. Since the thermal optical spectra are additive, the spectra of combinations of lunar separates
NASA/TM—2011-217232 10

Figure 8. The reflectance spectra of JSC–1AF, NU–LHT–1D and a 1:1 mixture of the two in the solar absorptance 

region (a), and for the absorptance and emittance regions (b). The dotted line shows the point by point average of 

JSC–1AF and NU–LHT–1D in the solar absorptance region (a), and for the absorptance and emittance regions (b).

Figure 9. Reflectance spectra of the constituent minerals anorthosite, norite, chromite, ilmenite, and harzburgite in the 

solar absorptance region (a), and in the thermal emittance region (b).

can be predicted. So if a target spectrum of a region of the lunar surface can be determined, in principal 

that spectrum can be duplicated by combinations of mineral and glassy separates. However, it is noted 

that none of these components have the characteristic rising ρ(λ) with λ which is characteristic of lunar 

soils (see Fig. 2). It is thought that perhaps it is the agglutinates and associated nanophase iron that give 

rise to this type of spectrum, but to date no material with rising ρ(λ) has been duplicated in the laboratory. 
NASA/TM—2011-217232 11

3.2 Thermal Optical Property Calculations

Since the goal for this series of tests is to characterize the thermal properties of the simulant dust, the 

ρ(λ) for each must be used to calculate the α and ε. The 250 to 2500 nm data were used to calculate the α, 

and the 2.5 to 25 μm data were used to calculate the ε. The α and ε300 (ε at 300 K) for each of the 

simulants are listed in Table 2.

The α ranged from 0.39 to 0.75 for the simulants. Albedo measurements suggest a range of α for the 

Moon of 0.50 to 0.93. As discussed above, the albedo measurements tend to indicate α values that are 

somewhat higher than expected from measuring the intrinsic α of the dust. In addition, these simulants 

would compare to the smallest fraction of the regolith, and for that reason would tend to be high. An 

appreciation for the impact of the particle size effect for these materials can be gained by comparing these 

α values to those of the samples in their as-received sizes, as reported by Gaier, et al. (Ref. 3), which are 

also shown in the table for comparison.

Although no lunar dust samples were available for analysis in this study, the α of the mare soil 12001 

and the highlands soil 64801 were estimated using the spectra displayed in Figure 2. These are 

bidirectional reflectance data, so the ρ will be somewhat lower and the α somewhat higher than what 

would be measured from total reflectance data, which includes the diffuse component as well. 

With these limitations in mind, the finest fraction of the mare soil 12001 has an α ≈ 0.89, and the 

coarsest fraction about 0.91, within the ranges of the coarser mare simulants tested here, but darker than 

the simulant fine fraction. The α of the highland soil 64801 varies from about 0.74 for the finest fraction 

to about 0.80 for the coarsest fraction, considerably darker than the range of the mare simulants tested. It 

is expected that the NU-LHT-2M would be lighter than typical highlands samples because the particles do 

not have any of the characteristics of space weathering, and thus represent fresh, rather than matured 

soils. The NU-LHT-2M-700-1X has had synthetic agglutinate glass and iron particles added, and thus is 

somewhat darker, at least for the larger particle sizes. However, the micronizing and sieving appears to 

have resulted in a simulant that is no darker in the fine fraction. However, some of the mare simulants, 

most notably JSC-1A, appear to mimic the optical properties of the highlands soil quite well. So when 

simulating the effects of dust and soil on thermal control surfaces, matching the simulants to the optical 

properties is a better strategy than merely using a highlands simulant for the highlands region, or a mare 

simulant for a mare region.

TABLE 2.—INTEGRATED SOLAR ABSORPTANCE (α) CALCULATED FROM 250 TO 2500 nm 

TOTAL REFLECTIVITY AND INTEGRATED THERMAL EMITTANCE (ε) AT 300 K CALCULATED 

FROM 2.5 TO 25 μm TOTAL REFLECTIVITY. VALUES FOR < 20 μm SAMPLES ARE FROM THIS 

STUDY, AND THOSE FOR > 20 μm SAMPLES FROM THE WORK OF GAIER, ET AL. (REF. 3)

VALUES FROM LUNAR SOIL SAMPLES (*) CALCULATED 300 TO 2500 nm USING 

BIDIRECTIONAL REFLECTANCE SPECTRA FROM LSCC (REF. 4).

Simulant < 20 μm α > 20 μm α < 20 μm ε > 20 μm ε

Chenobi 0.39 --- 0.86 ---

NU-LHT-2M 0.45 0.56 0.78 0.88

NU-LHT-2M-700-1X 0.46 0.67 0.82 0.90

MLS-1 0.54 0.82 0.73 0.70

MLS-1P 0.75 0.85 0.84 0.90

JSC-1 0.64 --- 0.84 ---

JSC-1A 0.75 0.82 0.83 0.90

JSC-1A-5000-2X 0.66 0.92 0.83 0.91

FJS-1 0.65 0.81 0.84 0.90

OB-1 0.73 --- 0.92 ---

Mare soil 12001* 0.89 0.91 --- ---

Highlands 64801* 0.74 0.80 --- ---
NASA/TM—2011-217232 12

The ε at 300 K for each of the simulants is given in Table 2. If MLS–1 is excluded, the ε’s of the fine 

fraction of the lunar simulants ranged from 0.78 to 0.92 with an estimated error of ±0.005. This is about 

0.1 lower than was found with the larger particles sizes. The higher value for the ρ(λ) in MLS-1 is 

probably due to a lower level of glassy material, which is known to decrease the ρ(λ) in the infrared. The 

fact that MLS-1 with smaller particle sizes actually had a higher ε may be an indication that a glassy 

phase is generated upon milling. Since the lunar dust contains a very high fraction of impact glasses, the ε

of the lunar dust would be expected to be high, and has been found to be about 0.95. The ε of the dust will 

also be somewhat higher than that of the thermal control surfaces, and so the blocking of emitted heat will 

probably not play a major role in thermal performance degradation. Nearly all of the dust degradation of 

thermal control surfaces will be due to increased α, that is, the dust will keep the solar incident light from 

reflecting off of the thermal control surface. This is consistent with what was observed on the Apollo 

LRV radiators when they were dust covered.

4.0 Conclusions 

A comparative study of the reflectance spectra of lunar simulants is presented. All of the simulants 

except one had a wavelength-dependant reflectivity (ρ(λ)) near 0.10 over the wavelength range of 8 to 25 

μm, so they are highly emitting at room temperature and lower. The 300 K emittance (ε) of all the lunar 

simulants except one ranged from 0.78 to 0.92. There was considerably more variation in the lunar 

simulant reflectance in the solar spectral range (250 to 2500 nm) than in the thermal infrared. As 

expected, the lunar highlands simulants were more reflective in this wavelength range than the lunar mare 

simulants. The integrated solar absorptances (α) of the simulants ranged from 0.39 to 0.75. This is lower 

than the values reported earlier for larger particles of the same simulants, and for representative mare and 

highlands lunar soils. It is recommended that α and ε values be the criteria for choosing a simulant for 

assessing the effects of dust on thermal control surfaces, rather than whether a simulant has been 

formulated as a highlands or a mare simulant.

References

1. “Apollo 16 Preliminary Science Report,” NASA SP–131. (Bret R., England A. W., Calkins J. E., et 

al.). Washington D.C.: NASA; 1972.

2. 2000 ASTM Standard Extraterrestrial Spectrum Reference E-490-00. 2000. Available at 

http://rredc.nrel.gov/solar/spectra/AM0. 

3. James R. Gaier, Kenneth W. Street, and Robert J. Gustafson, “Measurement of the Solar Absorptance 

and Thermal Emittance of Lunar Simulants,” International Conference on Environmental Systems 

2010, AIAA-2010-6025. Also NASA/TM—2010-216788.

4. Lunar Soil Characterization Consortium. Bidirectional reflectance spectra for lunar soils. Available at 

http://www.planetary.brown.edu/relabdocs/LSCCsoil.html, accessed April 2010.

5. Jaworske D, Skowronski T., “Portable Infrared Reflectometer for Evaluating Emittance,” Space 

Technology and Applications Forum, Ed., M.S. El-Genk, American Institute of Physics 2000:CP-504. 

6. McKay D., et al., “JSC-1: A New Lunar Soil Simulant,” Engineering, Construction, and Operations 

in Space IV, American Society of Civil Engineers; 1994: 857-866.

7. Weiblen P, Gordon K., “Characteristics of a Simulant for Lunar Surface Materials,” Second 

Conference on Lunar Bases and Space Activities in the 21st Century, Lunar and Planetary Institute; 

1988:652.

8. Kanamori H, et al., “Properties of Lunar Soil Simulant Manufactured in Japan,” Proceeding of the 6th

International Conference and Exposition on Engineering, Construction, and Operations in Space.

Albuquerque: ASCE; 1998.

9. Stoesser D, et al., “Development of Lunar Highlands Type Simulants, NU-LHT-1M. -2M,” 

Geochemica et Cosmochemica Acta. 72(12):A902.
NASA/TM—2011-217232 13

10. Battler M. M., Spray J. G., “The Shawmere Anorthosite and OB1 as Lunar Highlands Regolith 

Simulants,” Planetary and Space Science. 2009: 57(15-15):2128-2131.

11. Gustafson R, White B. “Development of a Lunar Dust Simulant,” International Conference on 

Environmental Systems Proceedings. Society of Automotive Engineers; 2009:09ICES-0125.
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Thermal Optical Properties of Lunar Dust Simulants and Their Constituents 

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14. ABSTRACT

The total reflectance spectra of lunar simulant dusts (< 20 mm particles) were measured in order to determine their integrated solar 

absorptance (α) and their thermal emittance (ε) for the purpose of analyzing the effect of dust on the performance of thermal control 

surfaces. All of the simulants except one had a wavelength-dependant reflectivity (ρ(λ)) near 0.10 over the wavelength range of 8 to 25 μm, 

and so are highly emitting at room temperature and lower. The 300 K emittance (ε) of all the lunar simulants except one ranged from 0.78 to 

0.92. The exception was Minnesota Lunar Simulant 1 (MLS-1), which has little or no glassy component. In all cases the ε was lower for the 

< 20 μm particles than for larger particles reported earlier. There was considerably more variation in the lunar simulant reflectance in the 

solar spectral range (250 to 2500 nm) than in the thermal infrared. As expected, the lunar highlands simulants were more reflective in this 

wavelength range than the lunar mare simulants. The integrated solar absorptance (α) of the simulants ranged from 0.39 to 0.75. This is 

lower than values reported earlier for larger particles of the same simulants (0.41 to 0.82), and for representative mare and highlands lunar 

soils (0.74 to 0.91). Since the α of some mare simulants more closely matched that of highlands lunar soils, it is recommended that α and ε

values be the criteria for choosing a simulant for assessing the effects of dust on thermal control surfaces, rather than whether a simulant has 

been formulated as a highlands or a mare simulant. 

15. SUBJECT TERMS

Lunar soil; Lunar dust; Thermal control 

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