James R. Gaier, Khrissaundra Journey, Steven Christopher, and Shanon Davis

Glenn Research Center, Cleveland, Ohio

Evaluation of Brushing as a Lunar Dust Mitigation 

Strategy for Thermal Control Surfaces

NASA/TM—2011-217231

December 2011

AIAA–2011–5182
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James R. Gaier, Khrissaundra Journey, Steven Christopher, and Shanon Davis

Glenn Research Center, Cleveland, Ohio

Evaluation of Brushing as a Lunar Dust Mitigation 

Strategy for Thermal Control Surfaces

NASA/TM—2011-217231

December 2011

AIAA–2011–5182

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

41st International Conference on Environmental Systems

sponsored by the American Institute of Aeronautics and Astronautics

Portland, Oregon, July 17–21, 2011
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 financial support 

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

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

Available from

NASA Center for Aerospace Information

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Hanover, MD 21076–1320

National Technical Information Service

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Alexandria, VA 22312

Available electronically at http://www.sti.nasa.gov

Trade names and trademarks are used in this report for identification 

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—2011-217231 1

Evaluation of Brushing as a Lunar Dust Mitigation Strategy for 

Thermal Control Surfaces

James R. Gaier, Khrissaundra Journey,

* Steven Christopher,† and Shanon Davis*

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Abstract

Evaluation of brushing to remove lunar simulant dust from thermal control surfaces is described. First, 

strip brushes made with nylon, PTFE, or Thunderon (Nihon Sanmo Dyeing Company Ltd.) bristles were 

used to remove JSC-1AF dust from AZ93 thermal control paint or aluminized FEP (AlFEP) thermal control 

surface under ambient laboratory conditions. Nylon and PTFE bristles removed a promising amount of dust 

from AZ93, and nylon and Thunderon bristles from AlFEP. But when these were tested under simulated 

lunar conditions in the lunar dust adhesion bell jar (LDAB), they were not effective. In a third effort, seven 

brushes made up of three different materials, two different geometries, and different bristle lengths and 

thicknesses were tested under laboratory conditions against AZ93 and AlFEP. Two of these brushes, the 

Zephyr fiberglass fingerprint brush and the Escoda nylon fan brush, removed over 90 percent of the dust, 

and so were tested in the fourth effort in the LDAB. They also performed well under these conditions 

recovering 80 percent or more of the original thermal performance (solar absorptance/thermal emittance) of 

both AZ93 and AgFEP after 20 strokes, and 90 or more percent after 200 strokes.

Nomenclature

AgFEP 0.25 mm (0.010 in.) thick fluorinated ethylene propylene (FEP) film with a silver reflecting 

surface 

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

AxFEP either AgFEP or AlFEP

AZ93 a white thermal control paint formulated by AZ Technologies similar to Z93

α absorptivity over the solar spectrum

ε emissivity over thermal range (100 to 400 K)

1.0 Introduction

During the Apollo program, lunar surface operations were hampered by the effects of a fine, 

pervasive, highly adhesive dust. The mission records contain references to challenges involving 

obscuration of vision, clogging of equipment, coating of surfaces, abrasion of surfaces, degradation of 

seal performance, degradation of thermal performance, and minor health issues (Ref. 1). Some of the 

potentially most serious consequences were due to lunar dust on thermal control surfaces, which caused 

overheating in several of the science experiments and the batteries of the lunar roving vehicle (LRV)

(Ref. 2). Recent studies using lunar simulant dusts sprinkled onto thermal control surface samples in a 

simulated lunar environment suggest that, depending on the nature of the dust, the degradation of 

performance, as measured by the ratio of the solar absorptance (α) to the thermal emittance (ε), will be 

substantial, perhaps by as much as a factor of 3.5 (Ref. 3), and unpublished data with other simulants 

suggest as high as 7. Increasing the thermal control surface area by such a factor is not a realistic option.

It seems clear that before extensive lunar exploration efforts can continue, strategies must be developed to 

mitigate the effects of dust.

 *

NSTI Summer Interns

†

LERCIP Summer Intern
NASA/TM—2011-217231 2

A wide variety of approaches have been suggested to mitigate the effects of dust. There are three 

principal approaches. The thermal control surface can somehow be made more dust tolerant, technology 

can be developed to decrease the chances of dust attaching to the surface, or technology can be developed 

to remove the dust from the surfaces. The technology development has generally followed one of two 

philosophies, active removal of the dust or prevention of its accumulation, and passive surfaces that keep 

the dust from adhering to the surfaces.

Concern was raised during the Apollo program about the effect that lunar dust would have on thermal 

control surfaces, particularly with regard to the radiators on the LRVs which were used on the last three 

missions. A study was published that evaluated the effectiveness of different types of brushes in removing 

lunar soil and dust (Ref. 4). Using soil returned from Apollo 12, they concluded that a nylon bristle brush 

would be effective to remove dust from the LRV radiator, and return it to nominal function. But when the 

brushing was used on the LRV radiators on the lunar surface during Apollo 15, 16, and 17, it was found 

to be almost wholly ineffective (Ref. 2). Exactly why there was a discrepancy between the brushing 

effectiveness during the ground tests and the lunar surface was never explained. It is presumed that the 

lunar environment simulation conditions during the tests were not of sufficient fidelity.

One of the priority projects of the NASA’s Exploration Technology Development Program has been 

to develop dust mitigation technologies to remove dust from thermal control surfaces. A logical starting 

place is with the technology used on Apollo, the nylon bristle brush, but using the highest fidelity lunar 

simulation chamber available, the lunar dust adhesion bell jar (LDAB) (Ref. 5). The goal of this study 

was to quantify the effectiveness of the nylon bristle brush to remove dust from thermal control surfaces 

in the LDAB as a baseline. Five different nylon bristle brushes were tested that varied in bristle diameter, 

bristle length, brush configuration, and bristle packing density. In addition, four other bristle materials, 

PTFE Teflon, Thunderon, fiberglass, and carbon fiber were tested for comparison. These also varied in 

bristle diameter, bristle length, brush configuration, and bristle packing density. Preliminary brushing 

effectiveness tests were run under bench-top conditions, and the most promising candidates were tested in 

the LDAB.

2.0 Methods and Materials

The brushing effectiveness tests were run as four series of experiments, which will be referred to as 

Stages 1 to 4. In Stage 1 initial (ex situ) brushing tests were carried out under ambient laboratory conditions, 

and the best performing brushes were tested under simulated lunar conditions (in situ) in the LDAB in Stage 

2. The ex situ tests enabled a much faster turn-around, since there was no waiting to establish the vacuum 

and activate the dust between runs. Lessons learned during Stages 1 and 2 were applied to a second set of 

candidate brushes in Stage 3 ex situ tests. Those that performed best in Stage 3 were then tested in situ

during Stage 4. Brushing effectiveness in the ex situ tests was characterized by the amount of dust removed 

by measuring the fraction of the thermal control surface covered by dust before and after brushing. Brushing 

effectiveness in the in situ measurements was characterized by the thermal performance, as measured by 

changes in the ratio of the solar absorptance (α) to the thermal emittance (ε).

Three types of thermal control surfaces were applied to 2.54 cm (1.00 in.) diameter, 0.64 cm 

(0.25 in.) thick aluminum substrates. The surfaces included aluminum-backed 130 μm (0.005 in.) thick 

FEP, 250 μm (0.010 in.) thick FEP backed with silver and an Inconel oxidation protection layer (both 

from Sheldahl), and AZ93 thermal control paint (AZ Technologies). In order to minimize heat losses, the 

substrates were suspended from the edges in the sample holder by two layers of 250 μm thick layers of 

Kapton (DuPont), and temperature was measured using 130 μm diameter(AWG 36) type K calibrated

thermocouples affixed to the back of each sample. 

The fractional dust coverage before and after the Series 1 and 3 brushing tests was determined by 

particle counting. Nine 1 mm2 regions spaced about 6.3 mm apart arranged in a “+” shaped pattern, 

parallel and perpendicular to the brushing direction, were photographed at 100× using an optical 

microscope equipped with a digital camera. Each pixel was about 0.5 μm in size. This image was 
NASA/TM—2011-217231 3

analyzed using ImagePro (Media Cybernetics, Inc.) software, sorting on color. The Series 2 and Series 4 

evaluations depended not on particle counting but on thermal performance, that is, changes in α/ε. To 

optically determine α, The total reflectivity (ρ) of AZ93 and AxFEP samples was measured over the

wavelengths of 250 to 2500 nm (where nearly all solar intensity is emitted) using either a Lambda-19 

with an integrating sphere (Series 2 samples) or a Cary 5000 with an integrating sphere (Series 4 

samples). The α of the AZ93 was calculated from the convolution of the ρ spectrum and the ASTM air 

mass zero solar spectrum. The ε of AZ93 as well as both the α and ε of the AxFEP were determined 

thermally from the heating and cooling curves as described below. These values are shown in Table 1.

Data reported for the effectiveness of mitigation in this report is relative to these values.

TABLE 1.—MEASURED VALUES FOR THE α AND ε OF PRISTINE THERMAL CONTROL SAMPLES

α Stage 2 α Stage 4 ε Stage 2 ε Stage 4

AZ93 0.13 ± 0.01 0.171 ± 0.006 0.73 ± 0.02 0.79 ± 0.04

AlFEP 0.13 ± 0.02 ----------------- 0.68 ± 0.06 ---------------

AgFEP --------------- 0.095 ± 0.004 -------------- 0.78 ± 0.05

The initial series of ex situ tests used the NASA/USGS developed lunar highlands type simulant, NULHT-1D. This was chosen over the more commonly used JSC-1A lunar simulant because it contains 

smaller particles and in handling the two lunar dust simulants it appeared that the NU-LHT-1D has higher 

adhesion, and so would provide a more rigorous test. Although the original test plan called for the testing 

of both simulants in the in situ LDAB tests, late in the year funding cuts shortened the tests to using one 

simulant. Since the in situ tests had already been initiated with JSC-1A, they were continued. So there is 

an unfortunate situation that the ex situ tests of Series 1 and the in situ tests of Series 2 to 4 were run with 

different lunar simulants. Although the absolute performance of the brushes is probably dependent on the 

lunar simulant used, it is thought that the relative performance of the brushes, and so the general 

conclusions of the study, are not strongly simulant dependant.

Strip brushes utilizing one of three types of bristles were used for the Stage 1 and State 2 tests, shown 

in Figure 1(a). All of them were standard 0.95 cm (3/8 in.) wide brushes with a bristle length of 2.54 cm 

(1 in.). Nylon bristles were the baseline test, because these were judged to be effective in previous 

simulations, but proved to be ineffective on the lunar surface (Ref. 4). It should be pointed out, however, 

that both the ground simulations and the lunar environment performance was on a silica second surface 

mirror, which is considerably harder than either the AlFEP second surface mirror or the AZ93 white paint 

samples that were used in these tests.

The second type of bristle was made of polytetrafluroethylene (PTFE). Part of the rationale for this 

type of bristle was that the top surface of the AlFEP is chemically similar fluoroethylenepropylene (FEP)

and both the Apollo suits and the current Shuttle and ISS suits have FEP outer layers. The result is that 

the brush and the brushing surface have the same work function, and thus electrons would not tend to 

flow either towards or away from the bristles. This should reduce tribocharging of the surface, which in 

turn would reduce the electrostatic forces which cause the dust to adhere to the surface. (This, of course, 

would not necessarily be the case when brushing AZ93 paint.) One complication was that the only 

commercially available Teflon brushes had bristles that were 1.3 mm (0.050 in.) diameter, so the brushes 

were very stiff.

The third type of bristle was made up of Thunderon fibers. A brush was desired that was electrically 

conductive and so could drain charge from the surface. The Jacobs study (Ref. 4) had tried metallic bristle 

brushes and found them to be too stiff and too hard. There was concern that if a metal-coated-polymer 

bristle brush was used that the metal coating might come off and contaminate the thermal control surface.

Although the formulation of Thunderon is proprietary, it is a soft, conducting acrylic bristle, with no 

metallic coating to abrade off.

Seven different brushes were included in Stage 3 of the study. Since nylon brushes were the most 

effective in the initial study, a Dynasty Black Gold Fan #2 brush (FM Brushes) was selected as a nylon 

brush with a lower bristle packing density, and longer, thinner, more pliable bristles. A Dynasty Black 
NASA/TM—2011-217231 4

Gold Fan #6 brush was selected because it has the same characteristics as the #2, but with still longer 

bristles. The Princeton Synthetic Watercolor Brush Series 6150 Fan #4 (Princeton Synthetic) was 

included because it was similar to the Gold Fan brushes, but the bristles are held into a more rigid shape 

by surface texture. The Escoda Toray White Synthetic Fan #6 brush was chosen because it has a variable 

bristle diameter, which was thought might be more effective in removing a variety of particles sizes.

In addition to the four fan brushes, three round brushes designed for fingerprint imaging were tested as 

well. Two Brush-N-Burnish brushes with twisted bristle packing were selected. One had carbon fibers 

(Brush-n-Burnish Carbosmoove II Brush) and the other glass fibers (Brush-n-Burnish Twisted Fiberglass 

Brush). The last fingerprint brush, Lightning Powder Fingerprint Brush (Zephyr) has fiberglass fibers that 

are bundled. Table 2 describes the characteristics of the brushes tested, and Figure 1(b) shows them in a 

photograph.

A rotational motion was used in all of the brushing tests. Figure 2 shows the samples and both the ex 

situ and in situ brushing apparati. The initial tests used a rotational speed of 2 strokes/s, but brushes used 

in Stages 3 and 4 were physically larger which lead to an increased torque resistance. For the ex situ trials 

only, the rotation frequency was doubled to 2 cycles/s (4 strokes/s) to enable the motor to run smoother.

The faster rate in combination with the longer lever arm resulted in a tangential velocity of the brush that 

was a factor of 4× to 8× greater than that of the previous tests. However, a parameterization study found 

that dust removal was insensitive to the speed of the brushing, at least through a factor of 10, so the 

results of the two test series should be comparable. For the Stage 1 trials, ex situ trials were carried out for 

20, 60, 200, 600, and 2000 strokes at 2 strokes/s, and the Stage 2 in situ trials for 1000 strokes at 2 

strokes/s. But the Stage 3 test series, ex situ trials were carried out for 40, 120, 400, 1200, and 4000

strokes at 4 strokes/s, and for the Stage 4 in situ trials for 20 and 200 strokes at 2 strokes/s.

Figure 1.—Brushes used in the Stage 1 study (left): (a) nylon, (b) PTFE, and (c) Thunderon. Brushes used in the 

Stage 3 study (right): (d) B&B Carbon, (e) Black Gold Fan #2, (f) B&B Glass, (g) Black Gold Fan #6, (h) Locked Fan 

#4, (i) Zephyr Lightning, (j) Escoda Fan #6.

TABLE 2.—CHARACTERISTICS OF BRUSHES USED IN THIS STUDY

Brush Material Geometry Length, 

cm

Bristle diameter, 

μm

Bristle packing

Nylon strip Nylon Strip 2.5 300 Twisted

PTFE strip PTFE Strip 2.5 1300 Straight

Thunderon strip Thunderon Strip 2.5 30 Straight

Black Gold #2 Nylon Fan 1.5 35 to 50 with taper to 5 Straight

Black Gold #6 Nylon Fan 2.5 35 to 50 with taper to 6 Straight

Locked Fan #4 Nylon Fan 2.8 32 - 45 Locked

Escoda Fan #6 Nylon Fan 2.6 35 Straight

B&B Carbon Carbon Round 6.0 10 Twisted

B&B Glass Fiberglass Round 5.0 35 - 40 Twisted

Zephyr Lightning Fiberglass Round 5.7 15 Bundled
NASA/TM—2011-217231 5

Figure 2.—Photographs of the (a) ex situ brushing test and (b) in situ brushing test apparati.

The in situ tests were conducted in the LDAB. To start, the JSC-1AF, with a maximum particle size 

of 20 μm, was placed in the LDAB and treated with an air plasma to remove organic residue from the 

grains. It was subsequently dried by heating to 200 °C in vacuo for 12 to 24 hr, and then treated with a 

hydrogen-helium plasma to chemically reduce their surfaces. Heating and cooling curves were obtained 

by shining a 10-sun xenon arc lamp on each sample individually and then letting them cool in a 30 K 

cold-box. The heating and cooling curves for each sample was measured in the pristine state, after being 

dusted, and after being brushed. The curves were then analyzed using Thermal Desktop (Cullimore and 

Ring Technologies) to extract the α and ε. Particle counting was carried out on 50 of 641 randomly 

chosen non-overlapping viewing frames in an optical microscope at a magnification of 100× and analyzed 

using ImagePro software. The procedures are described in detail elsewhere (Ref. 6).

3.0 Results and Discussion

3.1 Stage 1: Initial Bench Top Testing

3.1.1 Nylon Bristle Brush Tests

The first test was to determine if, for a given number of brush strokes, the speed of the brushing was 

an important variable. Tests were conducted on the AZ93 sample, with the assumption that the AxFEP 

behavior would be similar. Two different speeds were used, about 3.8 strokes/s and about 38.7 strokes/s.

Each of these was carried out for three different time intervals to give 385, 3850, and 38,500 strokes.

Within these limits, brushing speed was found to not affect the amount of dust removed.

Figure 3 shows the fraction of 1 mm2 sampling area covered by NU-LHT-1D lunar simulant dust in 

the line across the sample perpendicular to the brushing direction. Data parallel to the brushing direction 

were similar except at the extremes where the brush did not make full contact with the sample. Each data 

point is the average of 20, 60, 200, 600, and 2000 strokes by the nylon strip bristle brush. There was no 

particular trend of the dust removal over time, indicating that after 20 strokes under ambient conditions 

steady state between dust removal and deposition by the brush had been established. (As will be seen 

later, this was not the case under simulated lunar conditions.) The error bars on Figure 3 represent 1σ in 

the spread of 4 to 8 data points. Comparison with Figure 3(a) and (b) shows that the nylon brush was 

more effective at removing the dust from the AZ93 paint than the AlFEP. In the case of AZ93 taking the 

total data set gave an average of 0.084 ± 0.089 of the surface still covered with dust. But it can be seen 

that the edges of the brush were not as effective, probably due to the distortion of the shape as the bristle 

moves across the surface. Bristles near the center of the brush are constrained to flex in the direction of 

motion by neighboring bristles, but those near the ends can also flex outward, and so apply less force to 
NASA/TM—2011-217231 6

the surface. On average 0.33 ± 0.17 of the AgFEP surface was covered with dust after brushing. There is 

no discernable rise in the amount of dust remaining on this sample near the edges, perhaps because the 

brush embedded dust grains into the surface rather than flicking them off. In both the AZ93 and the 

AlFEP most of the dust that remained on the surface was left in streaks. It was also noted that both the 

FEP and AZ93 paint surface was rather deeply scratched after this test (Figure 4). Since nylon is 

relatively soft, particularly compared to the AZ93, these were probably caused by dust adhering to the 

bristles and then gouging into the surface.

Figure 3.—The mean and standard deviation of fraction of dust remaining on the surface of the (a) AZ93 paint

and (b) AlFEP after being brushed in the ex situ bench-top test with the nylon bristle brush.

Figure 4.—Abrasion lines are clearly visible in this 100× photomicrograph 

of AZ93 that has been brushed with a nylon bristle brush.
NASA/TM—2011-217231 7

3.1.2 PTFE Bristle Brush Tests

Figure 5 shows the fraction of the sampling area covered by dust after brushing the AZ93 and AlFEP 

samples with the PTFE brush. The dust coverage on the AZ93 was reduced to 0.25 ± 0.14. But 2 of the 36 

data points, the 20 stroke data from position-4, and the 200 stroke data at position 0, appear to be 

anomalously high, apparently skewing the results. If those two points are dropped from the analysis then 

the dust coverage on the AZ93 was reduced to 0.22 ± 0.07, which is probably more indicative of the 

PTFE effectiveness. In contrast, the PTFE brush left 0.86 ± 0.18 of the AlFEP surface covered with dust. 

In this case nearly two-thirds of the sampling regions had dust coverage greater than 0.9, indicating very 

limited effectiveness in the ability to remove dust from the FEP surface with this brush. Owing to the 

large diameter of the PTFE bristles, they had little flexibility. This caused them to damage the surface 

more, and be less effective in removing the dust. Instead, this brush just embedded the dust into the soft 

FEP surface.

3.1.3 Thunderon Bristle Brush Tests

The effectiveness of the Thunderon brushes to remove dust from the thermal control surfaces is shown 

in Figure 6. The brush left 0.39 ± 0.11 of the AZ93 surface covered with dust. In addition, at the end of the 

test there were many bristle fragments on the paint, which visibly darkened the surface. The brush was also 

visibly damaged, with the bristle length being shorter and many of the bristles were curled. This abrasion 

would make the Thunderon unsuitable for use with the AZ93 paint. However, the Thunderon brush worked 

well to remove dust from the AlFEP. The brush left just 0.13 ± 0.11 of the surface covered with dust, with 

over half of the sample areas being less than 0.1 covered in dust. Although the soft bristles still seemed to 

scratch the surface of the AlFEP, dust did not get embedded into the scratches. Thunderon was the only 

brush tested in Stage 1 that effectively removed dust from the AlFEP in the ex situ bench-top tests.

Figure 5.—The fraction of dust remaining on the surface of the (a) AZ93 paint, and (b) AlFEP after being brushed in 

the ex situ bench-top test with the PTFE bristle brush.

Figure 6.—The fraction of dust remaining on the surface of the (a) AZ93 paint, and (b) AlFEP after being brushed in 

the ex situ bench-top test with the Thunderon bristle brush.
NASA/TM—2011-217231 8

3.2 Stage 2: Initial LDAB Testing

For these tests there was an attempt to apply relatively heavy dust coverage to more fully test the 

brushing. Although the fractional dust coverage was not measured directly, the α and ε of the JSC-1AF 

dusted samples were measured. Using previous results, the value of α/ε could then be used to calculate 

the approximate fractional dust coverage before brushing using the equation of the least squares fit from

our previous work (Ref. 3).

One measure of effectiveness of a cleaning technique compares the ratio of the integrated solar 

absorptance to the integrated thermal emittance (α/ε) of the surface after it has been brushed off (α/ε)b to 

the α/ε of the dusted surface (α/ε)d in terms of the that of the pristine surface (α/ε)p. A new term, the dust 

removal efficiency, ξ, is defined in Equation (1) as: 

( ) ( )

( ) ( ) d p

d b

α ε − α ε

α ε − α ε ξ ≡ (1)

Inspection of this equation reveals that if no dust is removed, that is (α/ε)b = (α/ε)d then ξ = 0. If all of the 

dust has been removed, (α/ε)b = (α/ε)p then ξ = 1. Previous studies have shown that a complete monolayer 

of JSC-1AF lunar simulant increases the α/ε of a thermal control surface by about a factor of 3.5 (Ref. 3).

The effect of brushing JSC-1A from AZ93 by the nylon and PTFE brushes on the α and ε of the 

surface, as expressed by ξ is shown in Figure 7(a). Dust deposition raised the α of the AZ93 substantially, 

by about a factor of 3. Brushing with either nylon or PTFE lowered the α slightly. So even though both 

brushes were very effective in removing dust from the AZ93 under ambient conditions, under simulated 

lunar conditions they lost their effectiveness. Neither of the brushes in these tests would be effective at 

removing enough dust to substantially lower the α once dusted.

Figure 7(b) shows the effects of dusting and brushing on the ξ of the AlFEP surface. The JSC-1A dust 

increased the α of the AlFEP by about a factor of 2. As with the AZ93, the nylon bristle brush restored 

about half of the thermal performance. Two of the samples showed a similar clearing by the Thunderon

bristle brush, and the third was not cleared. As with the AZ93, brushes that were effective at removing 

dust under ambient conditions were ineffective at restoring thermal performance under simulated lunar 

conditions. Neither of these brushes was judged to be effective enough to warrant further investigation. 

Figure 7.—Dust clearing parameter, ξ, as a function of initial fraction of the thermal control surfaces covered with 

JSC-1A lunar simulant dust for (a) AZ93, and (b) AlFEP.
NASA/TM—2011-217231 9

Even though the results of the brushing tests under simulated lunar conditions were not promising, and 

despite the fact that the nylon bristle brush used during Apollo were almost totally ineffective when used 

on the LRV radiators, brushing is such a simple solution that further trials seemed warranted. Evidence of 

abrasion of the thermal control surfaces lead to the consideration that perhaps more flexible bristles would 

be more effective. This lead to the decision to conduct a second round of testing with a variety of bristle 

materials, lengths, diameters, and packing geometries.

3.3 Stage 3: Advanced Benchtop Brushing

Fractional coverage diagrams such as those shown in Figures 3, 5, and 6 were generated for each of 

the seven brushes selected for the advanced brushing study. Since the samples were not uniformly 

covered with dust at the start of the tests, the total dust remaining after the test is not indicative of brush 

performance. Instead a dust clearing parameter (Ξ) was used to judge brush performance, defined in 

Equation (2) as:

( ) ( )

( )before

before after

%dust coverage

%dust coverage − %dust coverage Ξ =

(2)

The average Ξ for AlFEP samples brushed with each of the seven brush types are plotted in Figure 8.

Two brushes, the Escoda Fan and the Zephyr Round met the success criteria of cleaning off 90 percent of 

the dust (Ξ = 0.9) and three others were effective enough (Ξ > 0.8) to warrant future consideration, 

especially considering the spread in the measurements. The bars shown in white were fan brushes and 

those shown in black were round brushes. It appears that either geometry can make for an effective brush.

Two new bristle materials were introduced in this study that were not included in the initial study, 

fiberglass and carbon. Figure 9 shows Ξ for the brushes sorted by bristle material. Although there was 

only one carbon bristle brush tested, it had by far the poorest performance. The fiberglass bristles, on the 

other hand, had performance comparable to the nylon bristles. Fiberglass is also likely to be more durable 

in the high radiation environment of the lunar surfaces than nylon. All of the brushes used in this study 

had longer bristles than those used in the initial study, and since they also performed better, it is worth 

exploring how important bristle length is. This relationship is also shown in Figure 9, which shows a plot 

of Ξ as a function of bristle length. This reveals that bristle length is certainly not an overriding factor in 

that the longest bristles were on the least effective brush, and the shortest on the second least effective.

However, within similar brushes, length appears to play a role. This is seen most directly by comparing 

the Gold Fan #2 and the Gold Fan #6 performance (Fig. 8). These two brushes were identical except for 

bristle length and the #6 had an average Ξ of 0.88 compared to the #2 average Ξ of 0.65 (see Fig. 4).

There may also be an upward trend in Ξ with bristle length within the nylon fan brushes and within the 

fiberglass round brushes.

There were only four AZ93 painted samples available for these tests, so they were tested with only 

the top two performing brushes, the nylon bristled Escoda fan brush and the fiberglass bristled Zephyr 

round brush. They were tested at 30 s and 300 s intervals (120 and 1200 strokes). Both brushes were very 

effective at removing the dust, leaving less that 0.5 percent of the surface covered (Ξ > 0.995).
NASA/TM—2011-217231 10

Figure 8.—Average values of Ξ for each of the seven brush types. Error bars 

represent ± 1σ. Bars shown in white were fan brushes and those found in 

black were round brushes.

Figure 9.—Average values of Ξ as a function of bristle 

length for each of the seven brush types. Bristle material 

is indicated by color.

3.4 Stage 4: Advanced LDAB Brushing

By particle counting, both the Zephyr and the Escoda brushes were more effective at removing dust 

from the AZ93 painted surfaces than from the AgFEP surfaces. Although there was a wide variation, the 

AZ93 surfaces brushed 200 strokes with a Zephyr brush had an average of 3 percent of its surface covered 

with dust and with the Escoda had 10 percent covered. The AgFEP surface on the other hand was on 

average 29 percent covered when brushed by the Zephyr and 31 percent covered when brushed by the 

Escoda. Thus, they removed dust from AgFEP with equal efficiency, but the Zephyr brushed removed 

dust from the AZ93 surface more efficiently.

Figure 10 shows ξ as a function of the relative α/ε of the samples after they were dusted but before 

they were brushed, where (α/ε)rel = (α/ε)dust/(α/ε)pris. For AZ93 samples brushed with the Zephyr brush 
NASA/TM—2011-217231 11

and the Escoda brush, the spread in the data is wide, about a factor of 2. But the mean ξ values for the two 

brushes are statistically indistinguishable, 0.8 for 20 brush strokes and 0.9 for 200 brush strokes. With the 

Zephyr brush there is no trend in ξ with the initial amount of dust. That means that on average enough 

dust is removed in 20 strokes to increase the α/ε to 80 percent of its pristine value regardless of whether 

the initial α/ε was degraded by a factor of 2 or a factor of 4. There appears to be a trend with the Escoda 

brush that ξ increases with the initial amount of dust. That is to say, the Escoda brush returns the α/ε

towards pristine values more rapidly if there is more dust initially on the AZ93.

Figure 11 shows ξ as a function of the relative α/ε of the samples after they were dusted but before 

they were brushed for AgFEP samples brushed with the Zephyr brush and the Escoda brush. The Zephyr 

brush data look similar to the AZ93 data. The spread in ξ is about a factor of 2, with the average after 20 

strokes being about 0.8 and after 200 strokes about 0.9. But the ξ values for the Escoda brush data are 

considerably different. The spread is only about 10 percent, and the average ξ after 20 strokes is 0.92 and 

after 200 strokes is 0.95. But it is also worth noting that the Escoda-brushed AgFEP samples started with 

a heavier coating of dust. The α/ε after dusting ranged from 4.4 to 7.4, whereas that which was Zephyr 

brushed ranged from 2.5 to 4.2. As noted above, heavier dust loads are removed relatively more quickly 

with the Escoda brush.

Although ξ is a useful parameter to judge the relative effectiveness of brushes, ultimately what is 

important is the final value of the thermal control surface after the dust layer has been cleaned from it.

Table 3 shows the actual mean α/ε values for the pristine samples used in a particular series of tests and 

those of the dusted and cleaned samples. Even though there was much more dust left on the AgFEP 

samples in the end the thermal performance of the dusted and brushed sample still out performed the 

AZ93 samples by a factor of 1.6 to 1.9.

Figure 10.—The values of dust removal efficiency, ξ, as a function of relative α/ε for the (a) Zephyr and (b) Escoda 

brushes for JSC-1AF simulant on AZ93.
NASA/TM—2011-217231 12

Figure 11.—The values of dust removal efficiency, ξ, as a function of relative α/ε for the (a) Zephyr and (b) Escoda 

brushes for JSC-1AF simulant on AgFEP.

TABLE 3.—VALUES OF α/ε FOR THERMAL CONTROL SURFACES IN THE 

PRISTINE STATE, DUSTED, AND DUSTED THEN BRUSHED 20 OR 

200 STROKES BY EITHER THE ZEPHYR OR ESCODA BRUSH

(α/ε)pris (α/ε)dust (α/ε)B20 (α/ε)B200

Zephyr brushed AZ93 0.22 0.65 0.30 0.26

Escoda brushed AZ93 0.21 0.70 0.29 0.24

Zephyr brushed AgFEP 0.12 0.40 0.21 0.15

Escoda brushed AgFEP 0.10 0.61 0.14 0.13

4.0 Conclusions

A four stage investigation into the effectiveness of brushing of thermal control surfaces was 

undertaken. In Stage 1, strip brushes of three bristle types were used to remove NU-LHT-1D lunar 

simulant from AZ93 and AgFEP thermal control surfaces under ambient laboratory conditions. The nylon 

bristle removed more than 90 percent of the dust and PTFE bristle removed nearly 80 percent of the dust 

from AZ93, as determined by particle counting. The Thunderon bristle brush was ineffective. On the 

AlFEP surface, the Thunderon bristle brush removed more than 90 percent of the dust, and the nylon 

bristle removed two-thirds of the dust, and the PTFE bristle brush was ineffective. In Stage 2, none of the 

brushes proved to be effective under simulated lunar conditions. A nylon bristle brush was not very 

effective in restoring the α of thermal control surface on the Apollo LRV, so perhaps it is a validation of 

the fidelity of our lunar simulation facility and protocol that the brushing was not effective, as opposed to 

the study of Jacobs (Ref. 4) that indicated it was effective.

In Stage 3 of the investigation seven additional brushes made up of three materials, two brush 

designs, and seven bristle lengths were tested for their effectiveness to remove dust from thermal control 

surfaces under ambient laboratory conditions. The carbon bristle brush was found to be ineffective, but 

fiberglass and nylon brushes were found to be equally effective. Both the fan brush and round brush 

designs proved to be more effective than the strip brushes tested in the first stage. Longer bristles were 
NASA/TM—2011-217231 13

found to be more effective at removing dust than shorter bristles, though the effect seems less important 

than brush material. Two brushes, the nylon Escoda fan brush and the round fiberglass Zephyr brush 

removed more than 90 percent of the dust from AlFEP surfaces under ambient conditions, with a few as 

40 strokes. Both brushes were also able to remove more than 99.5 percent of the dust from AZ-93 thermal 

control paint with as few as 120 strokes.

In Stage 4 the Zephyr and Escoda brushes were tested for their effectiveness at removing lunar 

simulant dust from thermal control surface materials under simulated lunar conditions. Both proved 

effective, restoring more than 80 percent of the pristine α/ε for both thermal control surfaces after 20 

strokes, and more than 90 percent after 200 strokes. The Escoda brush performed slightly better than the 

Zephyr on AgFEP, though perhaps within the error of the experiment. Although the brushes removed 

more dust from the AZ93 surfaces than from the AgFEP surfaces, the dusted-then-brushed AgFEP 

surfaces still out performed the dusted-then-brushed AZ93 surfaces, when judged by α/ε. Both brushes 

were judged effective at removing dust and restoring optical properties.

References

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

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

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

Prospects,” Space Technologies and Applications International Forum 2007. See also NASA/TM—

2007-214814.

3. J. R. Gaier, "Effect of Lunar Simulant Type on the Absorptivity and Emissivity of Dusted Thermal 

Control Surfaces in a Simulated Lunar Environment,” International Conference on Environmental 

Systems 2010, AIAA–2010–6111. See also NASA/TM—2010-216786.

4. S. Jacobs, R. E. Durkee, and R.S. Harris, Jr., “Lunar Dust Deposition Effects on the Solar 

Absorptance of Thermal Control Materials,” in the proceedings of AIAA 6th Thermophysics 

Conference, AIAA, Reston ,VA, AIAA Paper 71–459. 

5. J. R. Gaier and E. A. Sechkar, “Lunar Simulation in the Lunar Dust Adhesion Bell Jar,” Proceedings 

of the 45th AIAA Aerospace Sciences Meeting (2007). See also NASA/TM—2007-214704.

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

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

214164. See also NASA/TM—2010-216828.
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Evaluation of Brushing as a Lunar Dust Mitigation Strategy for Thermal Control Surfaces 

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14. ABSTRACT

Evaluation of brushing to remove lunar simulant dust from thermal control surfaces is described. First, strip brushes made with nylon, 

PTFE, or Thunderon (Nihon Sanmo Dyeing Company Ltd.) bristles were used to remove JSC-1AF dust from AZ93 thermal control paint or 

aluminized FEP (AlFEP) thermal control surface under ambient laboratory conditions. Nylon and PTFE bristles removed a promising 

amount of dust from AZ93, and nylon and Thunderon bristles from AlFEP. But when these were tested under simulated lunar conditions in 

the lunar dust adhesion bell jar (LDAB), they were not effective. In a third effort, seven brushes made up of three different materials, two 

different geometries, and different bristle lengths and thicknesses were tested under laboratory conditions against AZ93 and AlFEP. Two of 

these brushes, the Zephyr fiberglass fingerprint brush and the Escoda nylon fan brush, removed over 90 percent of the dust, and so were 

tested in the fourth effort in the LDAB. They also performed well under these conditions recovering 80 percent or more of the original 

thermal performance (solar absorptance/thermal emittance) of both AZ93 and AgFEP after 20 strokes, and 90 or more percent after 200 

strokes. 

15. SUBJECT TERMS

Lunar soil; Lunar dust; Thermal control 

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