Stephen Berkebile, Kenneth W. Street, Jr., and James R. Gaier

Glenn Research Center, Cleveland, Ohio

Adhesion Between Volcanic Glass and Spacecraft 

Materials in an Airless Body Environment

NASA/TM—2012-217221

January 2012

AIAA–2011–3675
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Stephen Berkebile, Kenneth W. Street, Jr., and James R. Gaier

Glenn Research Center, Cleveland, Ohio

Adhesion Between Volcanic Glass and Spacecraft 

Materials in an Airless Body Environment

NASA/TM—2012-217221

January 2012

AIAA–2011–3675

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 thank Mike Weinstein of Zybek Advanced Products for supplying the synthetic noritic glass, Dave Hull for

glass sample cutting, Joy Buehler for glass polishing, and Scott Panko and Rick Mondry for support in the laboratory.

Financial support was provided by NASA ETDP Thermal Control and Dust Mitigation Projects through the

NASA Postdoctoral Program (administered by Oak Ridge Associated Universities).

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

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

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

either expressed or implied, by the National Aeronautics and 

Space Administration.

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2012-217221 1 

Adhesion Between Volcanic Glass and Spacecraft Materials 

in an Airless Body Environment 

Stephen Berkebile, Kenneth W. Street, Jr., and James R. Gaier 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

The successful exploration of airless bodies, such as the Earth’s moon, many smaller moons of the 

outer planets (including those of Mars) and asteroids, will depend on the development and 

implementation of effective dust mitigation strategies. The ultrahigh vacuum environment (UHV) on the 

surfaces of these bodies, coupled with constant ion and photon bombardment from the Sun and 

micrometeorite impacts (space weathering), makes dust adhesion to critical spacecraft systems a severe 

problem. As a result, the performance of thermal control surfaces, photovoltaics and mechanical systems 

can be seriously degraded even to the point of failure. The severe dust adhesion experienced in these 

environments is thought to be primarily due to two physical mechanisms, electrostatic attraction and high 

surface energies, but the dominant of these has yet to be determined. The experiments presented here aim 

to address which of these two mechanisms is dominant by quantifying the adhesion between common 

spacecraft materials (polycarbonate, FEP and PTFE Teflon (DuPont), Ti-6-4) and a synthetic noritic 

volcanic glass, as a function of surface cleanliness and triboelectric charge transfer in a UHV 

environment. Adhesion force has been measured between pins of spacecraft materials and a plate of 

synthetic volcanic glass by determining the pull-off force with a torsion balance. Although no significant 

adhesion is observed directly as a result of high surface energies, the adhesion due to induced electrostatic 

charge is observed to increase with spacecraft material cleanliness, in some cases by over a factor of 10, 

although the increase is dependent on the particular material pair. The knowledge gained by these studies 

is envisioned to aid the development of new dust mitigation strategies and improve existing strategies by 

helping to identify and characterize mechanisms of glass to spacecraft adhesion for norite volcanic glass 

particles. Furthermore, the experience of the Apollo missions revealed that dust mitigation strategies must 

be subjected to high fidelity tests. To facilitate the effectiveness of ground-based testing of mitigation 

strategies, the issue of a pressure limit for high fidelity tests will be addressed. 

Nomenclature 

θ torsion balance deflection angle 

κ torsion spring constant 

τ torque 

U potential energy 

1.0 Introduction 

The development of dust mitigation strategies is important for the exploration of airless bodies in the 

Solar System, such as the lunar surface and the surfaces of asteroids, Mercury and the moons of Mars. 

This is because many critical spacecraft systems are sensitive to dust accumulation. When exposed to dust 

in vacuum, the performance of thermal control surfaces is seriously degraded (Ref. 1), photovoltaic 
NASA/TM—2012-217221 2 

efficiency is decreased (Refs. 2 and 3), mechanical systems are compromised through abrasion (Ref. 4) 

and optical elements of cameras and telescopes are scratched or occluded (Ref. 5). As a result, these and 

other systems may fail when operating in a dusty vacuum environment if effective mitigation strategies 

are not developed and implemented. 

Under the conditions of ultrahigh vacuum (UHV, 10–9 torr) found at the surfaces of airless bodies, 

dust behaves very differently than in our atmosphere (Refs. 1 and 4). Dust adhesion properties are thought 

to be enhanced by two classes of mechanisms, increased surface energy and electrostatic attraction. 

Firstly, particles of dust are made more reactive through “space weathering” processes caused by their 

exposure to high energy electromagnetic radiation and atomic or subatomic particle impacts, mainly from 

the Sun, as well as micrometeorite impacts (Refs. 1, 6, and 7). Micrometeorite impacts create small dust 

particles and freshly fractured surfaces, whereas radiation and particle impacts create free radicals via 

electron ejection and dangling bonds at material lattice defect sites. These processes are referred to as dust 

“activation”. In UHV environments, the atomic cleanliness of freshly fractured surfaces is maintained and 

the population of chemically reactive surface species remains significant due to the scarcity of molecules 

in the gas phase colliding with the surface of the dust. The particle bombardment of the dust (and, with 

exposure time, the spacecraft materials) in the UHV environment results in the absence of a thin film of 

hydrocarbons and water that exists on surfaces in our atmosphere. As a result, the adhesion of dust is 

enhanced up to two orders of magnitude, primarily due to van der Waals interactions (Refs. 7 to 9). Both 

chemical reactivity and cleanliness of the surfaces lead to an increased effective surface energy and can 

lead to increased adhesion. For example, between sapphire and aluminum, adhesion force was seen to be 

13 times greater when cleaned in a UHV environment through ion bombardment than in ambient 

laboratory conditions (Ref. 10). 

The second mechanism which can enhance dust adhesion arises from electrostatic forces. For 

example, most lunar particles are composed of nonconductive minerals and glasses and will build up a 

static charge under constant ion and photon bombardment (Ref. 11). The surface of the moon is positively 

charged on the side of the body facing the Sun (photoelectric effect) and negatively charged on the dark 

side (electrons from the solar wind) (Ref. 12). 

It is unclear whether surface energy or electrostatic forces dominate for different particle sizes and for 

different types of dust, but both can lead to a strongly increased adhesion in UHV conditions. In order to 

develop the most effective mitigation strategies, the nature and strength of the adhesive forces must first 

be determined. 

As a result of space weathering under UHV conditions, dust mitigation strategies which work under 

atmospheric conditions cannot be assumed to work on the surfaces of airless bodies, due to the 

mechanisms listed above which lead to an increased adhesion. As the Apollo missions have shown, even 

tests in low to high vacuum environments can lead to misleading results which do not accurately simulate 

the lunar environment (Ref. 1). An accurate pressure limit for high fidelity tests has still not been 

determined. Through the characterization of the mechanisms of adhesion in airless environments, such a 

pressure limit can be found and rigorously tested. 

In this study we address the issues of adhesion on airless bodies by using well-defined conditions 

which attempt to simulate a lunar environment combined with simple model systems of lunar and 

spacecraft materials to determine which mechanism above causes the greatest adhesion. To this end, the 

adhesion between pins of spacecraft materials and a plate of lunar simulant glassy material has been 

investigated in a UHV environment. The materials can be tested with control of their surface atomic 

cleanliness and “activation” state, as well as their electrostatic charge. This study includes measurements 

of adhesion due to both van der Waals forces and electrostatic charging induced by triboelectric charging 

and electron beam irradiation. The dependence of adhesion forces on time and background pressure will 

also be addressed. 
NASA/TM—2012-217221 3 

2.0 Experimental Details 

2.1 Materials 

2.1.1 Ex situ Preparation 

A synthetic noritic volcanic glass (Zybek Advanced Products) was cut, mechanically polished and 

fashioned to a plate approximately 1 cm across. Rods of spacecraft materials—a titanium alloy (Ti-6V4Al), polytetrafluoroethylene (PTFE) Teflon, fluorinated ethylene propylene (FEP) Teflon, polycarbonate 

(PC)—were machined in the form of a pin 2 cm long with rounded ends (radius 1.6 mm). The pin ends 

were spindle polished as described below and cleaned with high purity ethanol before introduction to a 

UHV chamber. 

Polycarbonate (PC) was wet polished (deionized water) with 9, 3, 1, and 0.3 μm AlOx paper. 

Following the mechanical polishing, a vapor polishing procedure was used (Refs. 13 and 14). A 

dichloromethane vapor was created in a bubbler, which was carried by N2 to the PC pin in a separate 

flask. Both the bubbler and flask with the PC pin were immersed in a water bath at 30 °C (pDCM = 

520 torr at 30 °C). The PC pin was exposed to the vapor for 140 sec. After 5 min in air, the pin was baked 

in an oven at 115 °C for 10 min. The baking prevented crazing of the PC pin under stress. PTFE Teflon 

was mechanically polished with PTFE Teflon tape. FEP Teflon was mechanically polished with a FEP 

sheet. Ti-6-4 was mechanically polished with diamond sheets and paste. 

The roughnesses of the volcanic glass plate and the ends of the pins were measured using a Wyko 

NT1000 optical profiler from Veeco Metrology Group in VSI mode. The approximate root mean square 

(RMS) roughnesses of the materials before and after adhesion measurement in the UHV chamber are 

given in Table 1. 

2.1.2 In Situ Preparation and Characterization 

The surfaces of the materials were cleaned by bombardment with Argon ions accelerated to 2 keV 

from a Varian 981-2043 ion gun. This process removed atmospheric contamination due to water and 

organic compounds from mineral surfaces and created a number of broken bonds, both of which leave the 

surface in a state similar to that which dust particles have in an airless body environment. Ti-6-4 was 

sputtered until no improvement in the C and O surface contamination could be discerned using a built-in 

Auger electron spectrometer before each measurement, unless stated otherwise. Plastic materials were 

sputtered in 5 min cycles before measurements, when stated in the text. The synthetic volcanic glass was 

cleaned through ion bombardment prior to all measurements, unless explicitly stated. 

TABLE 1.—APPROXIMATE RMS ROUGH-NESSES 

OF PLATE AND PIN SURFACES BEFORE AND 

AFTER ADHESION MEASUREMENTS 

IN THE UHV CHAMBER 

Material RMS roughness, 

nm 

Before After 

Glass --- 30 

PC 90 150 

PTFE 130 180 

FEP 250 --- 

Ti-6-4 --- 300 
NASA/TM—2012-217221 4 

TABLE 2.—SURFACE ATOMIC COMPOSITION (IN PERCENT) OF SYNTHETIC VOLCANIC GLASS AND 

TI-6-4 PIN AS MEASURED BY AES. TI-6-4 PRODUCTION VALUES FOR THE BULK ALLOY ARE INCLUDED 

Material: % Mg % Ca % Al % Si % O 

Synthetic glass 6.10.8 16.40.7 20.91.7 16.20.8 40.40.9 

% Ti % Al % V % C % O 

Ti-6-4 (typical) 70.03.1 7.50.7 6.50.6 11.82.8 4.21.1 

Ti-6-4 (best attained) 74.9 7.1 6.1 8.0 3.9 

Ti-6-4 bulk values 90 5.5-6.75 3.5-4.5 ---------- ---------- 

Sample surface composition was monitored using Auger electron spectroscopy (AES) both to define 

sample cleanliness before adhesion measurement and to determine if any material had been transferred 

after contact has been broken. AES allows a quantitative analysis of the chemical composition within the 

first few atomic layers of the surface. Since the investigated minerals and glasses are insulating, the 

energy of the impinging electron beam was selected so that equilibrium was obtained between impinging 

and emitted electrons. An electron beam energy of 1.2 keV allowed relevant peaks to be observed but 

precluded glass sample charging. The plastic pins could not be measured with a beam energy exceeding 

550 eV without severe charging effects. Several atomic species, such as Al, Mg, Si, and Ca, have Auger 

electron emission peaks at low energies observable with this primary beam energy. An electron beam 

energy of 3 keV was used for the Ti-6-4 pin. 

The surface composition of the synthetic volcanic glass and Ti-6-4 pin after Ar+

 ion sputtering are 

found in Table 2. Oxygen and carbon-containing adsorbates were seen to accumulate within an hour on 

the Ti-6-4 pin, even in UHV. The volcanic glass accumulated adsorbates at a much lower rate with a few 

percent C accumulation over several days. 

The plastic materials (PTFE, FEP, PC) displayed a C peak at emission energies around 270 to 285 eV. 

Only trace amounts of Cl were observed in the PC pin, with no Al contamination apparent around 65 eV. 

Otherwise no other atomic species were seen for any of the plastics. Note, however, that fluorine features 

are beyond the observable spectrum range using a primary electron beam energy of 550 eV. 

Surface composition of both the pin and glass plate was measured with AES after adhesion 

measurements, and no transfer of material was observed. 

2.2 Measurement Apparatus 

The measurements were conducted in an oil-free UHV chamber with a base pressure of 10–10 torr, 

allowing experiments to be made on a time scale which prevented significant contamination of the 

cleaned surfaces. The chamber was equipped with a PHI 15-110A Auger electron spectrometer. A 

PHI/Perkin-Elmer sputtergun was used for Argon ion bombardment for sample cleaning at an Ar pressure 

of 5×10–5 torr and an acceleration voltage of 2 kV. Argon bombardment removed hydrocarbons and water 

adsorbed from the atmosphere on the sample surfaces and simulated the effects of space weathering, 

leaving the surface in an activated state. 

The force of adhesion was measured using a sensitive UHV-compatible torsion balance (Refs. 15 and 

16). The balance, shown in Figure 1, provided a direct measure of the pull-off force (referred to as 

adhesion force) required to separate the synthetic volcanic glass plate from a pin of spacecraft material 

with a defined radius after they have been brought into contact with a defined force (referred to as load). 

The load was applied by an approach of the pin towards the glass plate, while the pull-off force was 

measured through retraction of the pin from the glass plate. The balance was constructed of an arm, 

approximately 10 cm long, suspended in the center from a taut wire. The force exerted on the glass plate 

mounted on one side of the balance arm is directly proportional to the torque on the wire. The torque τ

depends, in turn, on the angle θ of the arm from its equilibrium position and the spring constant κ of the 

wire as 

  . (1) 
NASA/TM—2012-217221 5 

Figure 1.—Torsion balance in UHV chamber with glass plate and PC pin shown magnified in the inset. 

The spring constant was calculated from the moment of inertia of the balance arm and the resonant 

frequency of the balance. The angle was measured by the displacement of a DVRT magnetic reluctance 

transducer (Microstrain, Inc.) from a copper block mounted on the other side of the balance arm. For 

more details on the torsion balance, see Reference 10. The lower limit on the pull-off force/adhesion force 

which could be effectively measured by the torsion balance was about 1 N, due to sensor system noise 

and vibrations (which corresponds to a real balance deflection of 0.0002 or a displacement of 0.2 m at 

the glass sample position). The convention used here is to assign positive values for the load the pin 

exerts on the glass and negative values for the adhesion force observed when pulling the pin away from 

the glass. 

The pins were mounted on the end of a step-motor-driven manipulator with one rotational and three 

translational degrees of freedom. Two types of mechanical movements were used, slow movement to 

measure adhesion forces and mechanical striking. Mechanical striking was accomplished by moving the 

pin to a position 50 m away from the surface, and then quickly approaching and retracting. An example 

of the displacement of the glass sample on the balance arm during a strike can be seen in Figure 2, panel 

(a). The kinetic energy of the strike used later in Figure 4 is the kinetic energy gained by the balance as a 

result of the strike, which, ignoring losses, is equal to the potential energy of the balance at maximum 

deflection. The potential energy stored in the spring depends on the deflection as 

2

2 U   1  (2) 
NASA/TM—2012-217221 6 

Figure 2.—Displacement of the glass sample on the arm of the torsion balance from the equilibrium 

position during adhesion measurements. 

2.3 Adhesion Force Measurements 

To measure adhesion forces, slow mechanical movement was used with an approach and retraction 

speed of 9.3 m/s. Two types of adhesion forces could be observed, electrostatic and van der Waals. 

Discriminating between the two was simply a matter of watching the position of the balance during 

approach. Figure 2, panels (b) and (c) demonstrate the differences seen in the movement of the balance. 

When the pin approached the glass on the balance, the balance would be pulled from equilibrium over a 

distance of up to several m in the case of electrostatic forces [panel (b)], whereas a movement of the 

balance was not observed during approach for van der Waals attraction [panel (c)]. Van der Waals 

attraction was likely not observed during approach due to its short range nature and the 200-nm limit of 

balance displacement measurement. Measurements of the adhesion force were made under different 

loads. Where the magnitude of the load is important, it will be made clear in the text, otherwise a load of 

around 0.1 to 0.5 mN was used for electrostatic adhesion measurements. The duration of the loads was 

30 sec for the van der Waals measurements in Figure 3 whereas the loads were typically maintained 

15 sec for cases of electrostatic adhesion. No dependence on the load duration or magnitude was seen for 

electrostatic adhesion. The adhesion force values given throughout this report are generally the average of 

three or more contacts with the standard deviation calculated and shown as error bars. 
NASA/TM—2012-217221 7 

Figure 3.—Adhesion force due to van der Waals interactions as a function 

of load for a PTFE pin on synthetic volcanic glass. Measurements of 

different loads at any particular contact position are connected by lines. 

3.0 Results 

An adhesion force due to van der Waals interactions was below the apparatus detection limits for both 

unsputtered and sputtered glass and pin sample pairs up to a load of at least 10 mN except in the case of the 

PTFE pin. The van der Waals adhesion force of the PTFE pin on the glass plate for various loads maintained 

for 30 sec is shown in Figure 3. Data are shown for several particular positions on samples which are 

unsputtered, on samples for which only the glass has been sputtered, and on samples for which both the 

PTFE pin and the glass have been sputtered, as indicated by the legend. It can be seen in Figure 3 that the 

adhesion force depended on the magnitude of the load in a roughly linear fashion for any particular contact 

position. However, the amount of adhesion varied widely between contact positions, even for similarly 

treated samples. Leaving the pin attached to the glass at a load of 1.9 mN for a period of 2 hr resulted in an 

increase in the adhesion force by a factor of 5 to 10 over 30-second-long loads. 

Figure 4 displays the electrostatic adhesion force induced between the glass plate and the pins of 

spacecraft materials by a mechanical strike as a function of the kinetic energy of that strike (as determined 

from balance deflection). In panel (a), it can be seen that sputtered FEP achieves the greatest electrostatic 

adhesion forces of greater than –3 mN, even for strike energies on the lower end of the scale. After FEP, 

sputtered PTFE has the largest resulting electrostatic adhesion from striking, increasing fairly linearly 

with strike energy from –0.5 mN for small strike energies to –5 or 6 mN for larger strike energies. 

Adhesion force values after pin-glass striking for a PTFE sample which was left for two weeks in vacuum 

(at 10–10 torr) are found slightly below the values of sputtered PTFE. Below PTFE, sputtered PC has the 

next strongest induced adhesion force. In panel (b) the adhesion force induced for strikes with PC 

increased roughly linearly from –0.1 to –0.7 mN. For unsputtered PC, PTFE and FEP samples, little 

relationship to the strike energy was seen, and all adhesion values remain below –0.15 mN. Each data 

point displayed in Figure 4 is the average of five or more measurements immediately after the strike at the 

strike position. Note that although the adhesion force values vary widely for different strikes, the value 

measured for any particular strike is fairly precise. 
NASA/TM—2012-217221 8 

Figure 4.—Electrostatic adhesion achieved as a function of kinetic energy 

transferred during pin-glass strike. Panel (b) shows an expanded ordinate 

(adhesion scale) for the data of panel (a). 

Ti-6-4 displayed no induced electrostatic adhesion for any mechanical strike energy both in sputtered 

and unsputtered states (the Ti-6-4 pin is grounded). Electrostatic adhesion could, however, be induced 

between the Ti-6-4 pin and glass plate by irradiating the glass plate with a 5 keV electron beam from the 

Auger spectrometry system. (The electron beam was rastered over a 2 by 3 mm area and had a nominal 

beam current of 1.2 mA. No change in the surface composition was observed with AES after electron 

beam irradiation.) Figure 5 shows the adhesion force versus irradiation time of the glass for both pins 

which have been sputtered less than an hour previously as well as pins which had been allowed to 

accumulate adsorbates (AES showed carbon and oxygen accumulation). It is apparent from the figure that 

the adhesion force attained through electron beam irradiation varied over two orders of magnitude and did 

not depend on the total electron dose. Electron beam energies of 500 eV to 4 keV were also used, but did 

not induce measureable adhesion. 
NASA/TM—2012-217221 9 

Figure 5.—Adhesion force induced between Ti-6-4 pin and volcanic glass 

by electron beam bombardment of glass as a function of bombardment 

time. 

Figure 6.—Adhesion dependence on time for different spacecraft materials and different electrostatic adhesion 

values. Panel (a) shows an expanded abscissa (time scale) for the data of panel (b), which, in turn, is an expansion 

of panel (c). Values measured after any particular strike are connected by lines. 

The persistence with time of the electrostatic adhesion force induced by strikes in UHV was measured 

for many individual strikes over periods ranging from hours to days. Figure 6 contains a summary of the 

time dependence found for electrostatic adhesion between the glass and different materials starting from 

various initial adhesion force values. In panels (a) and (b), it can be seen that the adhesion force measured 

for the different materials dropped quickly in the first few minutes to hours. This drop was roughly 

exponential for all materials and strengths of adhesion force. In panel (c), it can be seen that the adhesion 

values dropped less quickly after the first hours and remained significant over a period of days. 
NASA/TM—2012-217221 10 

Figure 7.—FEP adhesion as a function of time during an increase of Argon pressure. 

To test the robustness of the electrostatic adhesion with variation of background pressure, Argon gas 

was leaked into the UHV chamber while measuring the adhesion force of an FEP pin to the glass after 

striking. Figure 7 displays the adhesion force and the Ar pressure as a function of time. The adhesion 

force remained around –3.5 mN until an Ar pressure of 5×10–6 torr was reached, at which point the 

adhesion force dropped quickly. Another drop was seen as the Ar pressure was increased to 5×10–5 torr. 

This drop appeared as a discontinuity due to the inability to measure adhesion force when further opening 

the Ar valve. At a pressure of 1×10–4 torr, the limit of the ionization gauge, the adhesion force had 

dropped by an order of magnitude from its original value. 

4.0 Discussion 

The results above show that non-electrostatic adhesion forces between synthetic volcanic glass and 

pins of spacecraft materials are below 1 N for this contact geometry regardless of the atomic cleanliness 

of the pins and glass, except in the case of PTFE. PTFE is known to have a small surface free energy. 

Therefore, the small adhesion seen in the PTFE due to van der Waals forces presumably occurs due to 

deformation of the asperities and curvature of the PTFE pin to create a larger contact surface with the 

glass, as evidenced by the increase in adhesion force with load and time. The behavior of these materials 

is in stark contrast to results obtained by Miyoshi et al., for silicon carbide/aluminum and sapphire/ 

aluminum material pairs, where a strong adhesion force was observed for sputtered, atomically clean 

surfaces (Refs. 10 and 17). In the case of silicon carbide with aluminum, the chemical bond formed 

between the two materials was sufficient to cause a transfer of aluminum to the silicon carbide surface. 

Significant electrostatic adhesion was, however, observed between the spacecraft materials and the 

volcanic glass. In the case of the plastics (PC, PTFE, FEP), triboelectric charge transfer occurred through 

a mechanical strike of the pin against the volcanic glass. The magnitude of this charge transfer for any 

particular material depended to a great extent on the atomic cleanliness of the surface. The electrostatic 

adhesion induced by striking was seen to increase by one to two orders of magnitude for pins which had 

been sputtered for 5 min or more. 
NASA/TM—2012-217221 11 

The electrostatic adhesion induced per strike energy on sputtered pins was roughly an order of 

magnitude greater for the Teflon pins than for the PC pin, with FEP slightly greater than PTFE. Consultation 

of triboelectric tables, which indicate rough charge transfer expected for two materials in mechanical 

contact, show that soda-lime glass (presumably similar to the synthetic volcanic glass) lies towards the 

positive side of the triboelectric series, whereas PC lies on the negative side of the series. Teflon is generally 

found at the far most end of the negative side as a result of the strong electron affinity of the fluorine it 

contains. In light of the triboelectric expectations, the Teflon and PC pins are presumably negatively 

charged after striking, with a greater transfer of electrons to the Teflon than to the PC. 

The strike energies used in this study correspond roughly to the kinetic energy a 2-mm or larger 

particle has after a drop of 1 m on the lunar surface. The resulting electrostatic adhesion force expected is 

then 1000 times the gravitational force acting on that 2-mm particle. In the range measured here, the 

adhesion force apparently scales linearly with the strike energy. Lee has stated that particle adhesion will 

involve electrostatic interaction on the lunar surface if the particles are pre-charged (e.g., through the 

photoelectric effect) (Ref. 18). If the triboelectric scaling behavior persists down to smaller orders of 

magnitude, then electrostatic adhesion due to triboelectric charge transfer by dust particle impact will also 

present a significant source of adhesion. 

The electrostatic adhesion induced by charging the glass plate through electron beam irradiation 

likely resulted in a positive charge on the glass due to more secondary electrons being ejected from the 

material than the impinging electron beam provides. Oechsner observed secondary electron yields greater 

than 1 for silica glass at comparable electron beam energies (Ref. 19). The mechanism of attraction of the 

Ti-6-4 pin to the charged glass will be due to the image charge induced in the metallic pin. Due to 

asperities on the surface of the Ti-6-4 pin, the glass was not discharged through contact with the pin. 

Considering the expectation of a positive charge generally present on the illuminated side of an airless 

body due to the photoelectric effect, electrostatic adhesion of glassy regolith materials to metallic surfaces 

can be expected. Further, Walton has postulated that the charge on individual dust particles is distributed 

in inhomogeneous patches of charge (Ref. 8), which, coupled with the uneven surfaces of many dust 

particles, will lead to little chance of discharge through contact with a conductive material. 

Surface cleanliness has been shown to be an important factor for the triboelectric charge transfer. 

After the initial Ar+

 ion sputter cleaning of the surfaces used in this study, the cleanliness will depend on 

the quality of the vacuum environment. Likewise, once the charge transfer has taken place, the persistence 

of the charge on the surface and, hence, the electrostatic adhesion depends on the quality of the vacuum 

environment. Strong electrostatic adhesion was observed here to persist for a period of at least several 

days with no significant degradation in a vacuum of 10–10 torr. Once the charged pin has been exposed to 

Argon gas at pressures around 10–5 torr, a drastic drop in the adhesion force occurs. In a typical unbaked 

vacuum system, the largest constituent of the remaining gas is water, which will likely discharge any 

charged surfaces at lower pressures than Argon. Considering that the surfaces of airless bodies are in a 

UHV environment under conditions which result in atomically clean materials, high fidelity tests of dust 

adhesion should be made with the best pressure possible, but at least 10–6 torr, and should also include a 

cleaning step of any exposed surfaces. 

5.0 Conclusion 

We have found that van der Waals forces between a synthetic volcanic glass plate and pins of Ti-6-4, 

polycarbonate (PC), and FEP are negligible, and very small for PTFE, even for atomically clean samples. 

However, large adhesion forces are obtained if the pin or plate materials are charged. Triboelectric charge 

transfer occurs when the plastic pin materials (PC, PTFE, and FEP) are struck against the glass plate. On 

striking, electrons flow presumably from the glass to the plastic. The charge transfer is much higher when 

the surfaces have been activated by cleaning the surface of the pin of the contaminant layer by sputtering 

with Ar+

 ions. We expect that material surfaces on the moon, and other airless bodies, will be in this 

atomically clean and active state because of the constant bombardment by the solar wind and the 

extremely high vacuum. 
NASA/TM—2012-217221 12 

Triboelectric charge transfer is greater to the Teflon than to the polycarbonate because of the fluorine 

in the Teflon, which has a very high affinity for electrons. The greater charge transfer to Teflon implies 

that on the surface of the moon, Teflon surfaces will tend to accumulate dust at a higher rate than 

polycarbonate surfaces and a much higher rate than metallic surfaces. In addition, once they get dust on 

them we can expect that Teflon surfaces will be harder to clean. 

The implication of these results is that dust mitigation techniques should be targeted at electrostatic 

interactions, particularly when plastic materials must be used. The results may explain, for example, why 

workfunction matching coatings (which lower charge transfer) were more effective than textured coatings 

(which lower surface area and, hence, van der Waals forces) at lowering the adhesion of dust to the 

surfaces of silver-backed FEP sheets (AgFEP) in a recent study (Ref. 20). 

Furthermore, tests of materials and spacecraft systems to determine their performance and endurance 

in dusty lunar and airless body environments should presume that the atomic cleanliness of the materials 

and the pressure of the test system will play an important role in the fidelity of the results. 

References 

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

Prospects,” NASA/TM—2007-214814, 2007. 

2. O’Brien, B.J., Freden, S.C., and Bates, J.R., “Degradation of Apollo 11 Deployed Instruments 

Because of Lunar Module Ascent Effects,” Journal of Applied Physics, Vol. 41, No. 11, 1970, 

pp. 4538-4541. 

3. Katzan, C.M., Brinker, D.J., and Kress, R., “The Effects of Lunar Dust Accumulation on the 

Performance of Photovoltaic Arrays,” NASA Glenn Research Center, Document ID 19910020924, 

Brook Park, OH, 1991. 

4. Gaier, J.R., “The Effects of Lunar Dust on EVA Systems During the Apollo Missions,” 

NASA/TM—2005-213610/REV1, 2005. 

5. Murphy Jr., T.W., Adelberger, E.G., Battat, J.B.R., Hoyle, C.D., McMillan, R.J., Michelsen, E.L., 

Samad, R.L., Stubbs, C.W., and Swanson, H.E., “Long-Term Degradation of Optical Devices on 

the Moon,” Icarus, Vol. 208, No. 1, 2010, pp. 31-35. 

6. Vander Wal, R.L., “Lunar Dust Chemical, Electrical, and Mechanical Reactivity: Simulation and 

Characterization,” The National Center for Space Exploration Research, NASA/CR—2008-215431, 

Cleveland, OH, Oct. 2008. 

7. Gaier, J.R., “Regolith Activation on the Lunar Surface and Its Ground Test Simulation,” 

NASA/TM—2009-215648, 2009. 

8. Walton, O.R., “Adhesion of Lunar Dust,” Grainflow Dynamics, Inc., NASA/CR—2007-214685, 

Livermore, CA, Apr. 2007. 

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

NASA/TM—2007-214704, 2007. 

10. Miyoshi, K., Pohlchuck, B., Whitle, N.C., Hector, L.G., Jr., and Adams, J., “Properties Data for 

Adhesion and Surace Chemistry of Aluminum,” NASA TM-1998-206638, 1998. 

11. Katzan, C.M., and Edwards, J.L., “Lunar Dust Transport and Potential Interactions with Power 

System Components,” NASA, Document ID 19920002733, NASA CR-4404, Brook Park, OH, 

Nov. 1991. 

12. Sickafoose, A.A., Colwell, J.E., Horányi, M., and Robertson, S., “Photoelectric Charging of Dust 

Particles in Vacuum,” Physical Review Letters, Vol. 84, No. 26, 2000, pp. 6034-6037. 

13. McGinniss, V.D., “Vaporous Solvent Treatment of Thermoplastic Substrates,” U.S. Patent No. 

4,529,563, July 1985. 

14. Lee, K. S.-K., “Large Core Polymer Optical Backplanes for Fluorescence Detection,” Master’s 

Thesis, Dept. of Electrical Engineering and Computer Science, Massachusetts Institute of 

Technology, Cambridge, MA, 2006. 
NASA/TM—2012-217221 13 

15. Miyoshi, K., “Design, Development, and Applications of Novel Techniques for Studying Surface 

Mechanical Properties,” NASA TM-101959, 1989. 

16. Miyoshi, K., Maeda, C., and Masuo, R., “Development of a Torsion Balance for Adhesion 

Measurements,” NASA TM-100799, 1988. 

17. Miyoshi, K., “Uses of Auger and X-ray Photoelectron Spectroscopy in the Study of Adhesion and 

Friction,” NASA TM-103266, 1991. 

18. Lee, L.-H., “Adhesion and Cohesion Mechanisms of Lunar Dust on the Moon’s Surface,” 

Fundamentals of Adhesion and Interfaces, edited by D.S. Rimai, L.P. DeMejo and K.L. Mittal, VSP 

BV, Utrecht, Netherlands, 1995, pp. 73-94. 

19. Oechsner, H., “Analysis of Electrically Non-conducting Sample Structures with Electron and Mass 

Spectroscopic Methods,” Thin Solid Films, Vol. 341, No. 1-2, 1999, pp. 105-108. 

20. Gaier, J.R., Waters, D.L., Misconin, R.M., Banks, B.A., and Crowder, M., “Evaluation of Surface 

Modification as a Lunar Mitigation Strategy for Thermal Control Surfaces,” 41st International 

Conference on Environmental Systems, American Institute of Aeronautics and Astronautics, 

Reston, VA 2011, AIAA-2011-5183. 
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Adhesion Between Volcanic Glass and Spacecraft Materials in an Airless Body Environment 

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Berkebile, Stephen; Street, Kenneth, W., Jr.; Gaier, James, R. 

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WBS 780896.04.06.02.03 

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National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

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14. ABSTRACT

The successful exploration of airless bodies, such as the Earth’s moon, many smaller moons of the outer planets (including those of Mars) 

and asteroids, will depend on the development and implementation of effective dust mitigation strategies. The ultrahigh vacuum 

environment (UHV) on the surfaces of these bodies, coupled with constant ion and photon bombardment from the Sun and micrometeorite 

impacts (space weathering), makes dust adhesion to critical spacecraft systems a severe problem. As a result, the performance of thermal 

control surfaces, photovoltaics and mechanical systems can be seriously degraded even to the point of failure. The severe dust adhesion 

experienced in these environments is thought to be primarily due to two physical mechanisms, electrostatic attraction and high surface 

energies, but the dominant of these has yet to be determined. The experiments presented here aim to address which of these two mechanisms 

is dominant by quantifying the adhesion between common spacecraft materials (polycarbonate, FEP and PTFE Teflon, (DuPont) Ti-6-4) and 

a synthetic noritic volcanic glass, as a function of surface cleanliness and triboelectric charge transfer in a UHV environment. Adhesion 

force has been measured between pins of spacecraft materials and a plate of synthetic volcanic glass by determining the pull-off force with a 

torsion balance. Although no significant adhesion is observed directly as a result of high surface energies, the adhesion due to induced 

electrostatic charge is observed to increase with spacecraft material cleanliness, in some cases by over a factor of 10, although the increase is 

dependent on the particular material pair. The knowledge gained by these studies is envisioned to aid the development of new dust 

mitigation strategies and improve existing strategies by helping to identify and characterize mechanisms of glass to spacecraft adhesion for 

norite volcanic glass particles. Furthermore, the experience of the Apollo missions revealed that dust mitigation strategies must be subjected 

to high fidelity tests. To facilitate the effectiveness of ground-based testing of mitigation strategies, the issue of a pressure limit for high 

fidelity tests will be addressed. 

15. SUBJECT TERMS

Thermal control; Surface properties; Adhesion; Particles; Dust; Minerals; Surface properties; Surface energy 

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