National Aeronautics and

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IS20

George C. Marshall Space Flight Center

Marshall Space Flight Center, Alabama

35812
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i

NASA/TM—2010–216443

Figure of Merit Characteristics Compared 

to Engineering Parameters

C.M. Schrader

BAE Systems, Huntsville, Alabama

D.L. Rickman

Marshall Space Flight Center, Marshall Space Flight Center, Alabama

September 2010

National Aeronautics and

Space Administration

Marshall Space Flight Center • MSFC, Alabama 35812
ii

Available from:

NASA Center for AeroSpace Information

7115 Standard Drive

Hanover, MD 21076 –1320

443–757–5802

This report is also available in electronic form at

<https://www2.sti.nasa.gov>
iii

TABLE OF CONTENTS

1. INTRODUCTION ............................................................................................................. 1

1.1 2005 Regolith Simulant Workshop ................................................................................ 1

1.2 Development of Figures of Merit ................................................................................. 1

1.3 Explanation of the 2005 Workshop Rankings With the Figure of Merit ...................... 2

2. FIGURE OF MERIT ......................................................................................................... 3

2.1 Objective of Figure of Merit ......................................................................................... 3

2.2 Parameters .................................................................................................................... 3

3. EVALUATION OF RECOMMENDED PROPERTIES 

VERSUS FIGURE OF MERIT ......................................................................................... 5

3.1 Geomechanical (Mechanical Strength Properties) ........................................................ 7

3.2 Physical ......................................................................................................................... 8

3.3 Grain Specific ............................................................................................................... 9

3.4 Chemical ....................................................................................................................... 10

3.5 Mineralogical ................................................................................................................ 11

3.6 Multicategory ............................................................................................................... 12

4. CONCLUSION .................................................................................................................. 13

REFERENCES ....................................................................................................................... 15
iv
v

LIST OF TABLES

1. Properties from the 2005 Lunar Simulant Workshop, from table 2 in Sibille et al. ....... 5

2. Properties from 2005 workshop correlated to FoM properties by which they 

are directly addressed or from which they are derived .................................................. 6
vi
vii

LIST OF ACRONYMS

Br bromine

Cl chlorine

CO2 carbon dioxide

F fluorine

Fe0 iron metal

FoM figure of merit

H2O water

I iodine

ISRU in situ resource utilization

MSFC Marshall Space Flight Center

nFe0 nanophase iron metal

OH hydroxyl

P phosphorous

TM Technical Memorandum
viii
1

TECHNICAL MEMORANDUM

FIGURE OF MERIT CHARACTERISTICS COMPARED 

TO ENGINEERING PARAMETERS

1. INTRODUCTION

Current NASA lunar architecture calls for permanent human habitation of the Moon by 

the year 2020. Due to the expense of delivering materials into orbit, technologies are being developed to use lunar regolith for building and as a material resource for fabrication, oxygen production, and other needs. Additionally, constant exposure to the finest size fraction of lunar regolith 

may present hazards to human health. Towards developing these technologies and mitigating 

hazards, lunar regolith simulants are becoming an increasingly important part of the development 

paradigm.

1.1 2005 Regolith Simulant Workshop

In January 2005, Marshall Space Flight Center (MSFC) hosted a workshop in Huntsville, 

AL, to discuss the future development of lunar regolith simulants. This meeting brought together 

geoscientists including some major figures in lunar geology, project managers, engineers, and simulant users from NASA centers, academia, and private enterprise. In addition to 2 days of presentations (content is available at < http://est.msfc.nasa.gov/workshops/lrsm2005_program.html >), 

sessions were held to identify characteristics necessary for a lunar regolith simulant to sufficiently 

serve the community. Regolith characteristics were discussed and votes were taken with regard to 

perceived importance. Following the 2005 workshop, Sibille et al. published a technical paper ranking these properties.1

1.2 Development of Figures of Merit

Between 2005 and 2007, the lunar regolith simulant project advanced considerably. Much 

of the progress and development is evident in presentations of the October 2007 MSFC-hosted 

Huntsville workshop < http://isru.msfc.nasa.gov/2007wksp_docs.html >. Part of the evolution was 

the establishment of the figure of merit (FoM) mathematics and algorithm for formal, quantitative 

comparison of two particulate materials composed of geologic components.2,3 Although normally 

the comparison will be between a particular sample of lunar regolith and a simulant, the FoM can 

also be used to compare two simulants or two regolith samples. 
2

1.3 Explanation of the 2005 Workshop Rankings With the Figure of Merit

The primary motivation for this document is to define the relationship between the four 

FoM measurements and other characteristics of interest. For the most part, it is shown that the 

characteristics of interest from the 2005 conference are either directly contained within one of the 

four attributes measured for and evaluated by the FoM, or they are derivative characteristics resulting from one or a combination of the FoM attributes. This information is presented along with a 

brief explanation in cases where the ranked characteristics from the 2005 workshop are not measurable, technically undefined, or not addressed by the FoM.
3

2. FIGURE OF MERIT

2.1 Objective of Figure of Merit

The FoM was designed as a practical and efficient way to characterize and compare materials. Towards this end, the parameters for evaluation are chosen to have the following characteristics: 

•	 Definable: Many characteristics of materials are not rigorously defined. This is true even of 

some important physical characteristics like surface activation.

•	 Measurable: Parameters were chosen that could be measured economically, in a timely fashion, 

and with results reproducible across laboratories.

•	 Useful: For simplicity of design, parameters were chosen that correlate to properties important 

to the functioning of simulant under expected conditions.

•	 Primary versus derivative: This concept recurs throughout the FoM logic. Some characteristics 

are inherent to a material, like the composition of its constituents, be they minerals or glass. All 

else being equal, other properties, like the behavior of a material during heating, are derivative 

of the composition.

These are positive attributes desirable in any standard. 

Expressed in the negative, if something cannot be rigorously defined and measured reproducibly by multiple people, it has little value in a standard. If it cannot be practically known, a 

problem common with lunar materials for a host of reasons, it is not of functional utility within a 

standard. If a variable cannot be realistically measured in a way suitable for controlling the manufacture and the use of simulants, it has little place in a standard. If a parameter does not discriminate between materials, it has limited function to a quantitative standard. 

2.2 Parameters

The FoM requires four types of measurements from both the reference material and the 

simulant: Particle type, particle size, particle shape, and density. These four material attributes were 

chosen to comply with the above objectives and because they are measurable quantities from which 

almost all of the 31 characteristics ranked during the 2005 conference are derived. They also are 

functionally useful to anyone seeking materials to make simulant, to those trying to manufacture 

simulant, and to those trying to use the simulant. Refer to reference 3 for a formal definition of the 

four characteristics.

2.2.1 Particle Type/Composition

Composition describes attributes of a particle that exist without regard to size or shape. 

Here, the term particle is used to mean a piece of solid matter mechanically separable from others, such as by use of a sieve. The 2005 report uses the term grain for several basic concepts. This 
4

is common practice for geologists who, by training and experience, understand the meaning by 

context. Because the majority of simulant users and developers are not geologists, the simulant 

development project explicitly decided to restrict grain to mean a discrete subset of a particle. All 

particles in lunar regolith or simulant will be comprised of glass and/or mineral grains, but particles may be amalgams of grains that result in lithic fragments (rock particles) or agglutinates.

Therefore, the first order of classification of constituents includes mineral grains, glass 

grains, lithic fragments, and agglutinates. Measuring proportions of particle types by volume is 

known in geologic science as a modal analysis and is usually reported in modal percent by each 

constituent. Although it is not required by the FoM, it is ideal that modal analyses be obtained 

for a material in several different size fractions. This is because the percentages of constituents of 

any bulk material will tend to vary by size due to differential susceptibility to grinding and crushing. Modal analyses for lunar highlands regolith have been published (e.g., reference 4). These data 

serve as the basis for the regolith simulant team’s reference material in the FoM algorithm, but 

more precise data are being gathered to augment them.

2.2.2 Particle Size Distribution

For the FoM, particle size is measured on a particle-by-particle basis and reported as a 

distribution. The number of bins and the size of the bins are defined by the user, but a more precise 

FoM evaluation is rendered by an approximation to the lunar regolith dataset. For instance, these 

data can be found in The Lunar Soils Grain Size Catalog.5

2.2.3 Particle Shape Distribution

Particle shape is a crucial parameter in determining many geotechnical properties such as 

abrasiveness and bulk shear strength. The FoM calls for measurement of shape on a particle-byparticle basis, which is then reported as a distribution. Shape is described by two parameters, 

aspect ratio and sphericity. The specific algorithms for measuring these characteristics are being 

determined.

2.2.4 Density

Density as an FoM parameter refers to bulk density, and it is the only parameter that is not 

measured by the particle but as a bulk characteristic. The measurements that comprise the density 

FoM are minimum bulk density, maximum bulk density, and specific gravity. Measured as such, the 

bulk density FoM conveys information as to the specific gravity of the constituent particles and on 

the packing (i.e., the bulk relationship of the particles to one another). It is the FoM 

property most easily affected by handling of the simulant.
5

3. EVALUATION OF RECOMMENDED PROPERTIES 

VERSUS FIGURE OF MERIT

Table 1 contains the ranked properties from the 2005 workshop. It should be noted that 

neither rigorous definitions of these properties nor suggested measurement protocols or standards 

were provided.

Table 1. Properties from the 2005 Lunar Simulant Workshop, from table 2 in Sibille et al.1

Category

Category Properties Listing

Regolith Property Rank

Geochemical (metered strength properties)

 Total number of ranked properties

 Number of properties in top 10

11

1

Compressive strength

Coefficient of friction

Shear strength

Hardness

Rheology

Angle of repose

Tensile strength

Fracture behavior

Impact resistance

10

12

18

23

24

25

27

28

32

Physical

 Total number of ranked properties

 Number of properties in top 10

7

2

Particle density

Bulk density

Porosity

Thermal properties

Surface area

Friability

Permeability

3

5

13

20

21

22

26

Grain specific

 Total number of ranked properties

 Number of properties in top 10

6

4

Grain size

Grain size distribution

Grain shape

Magnetic grain properties

Grain shape distribution

Electrostatic charging

1

2

7

9

16

17

Chemical

 Total number of ranked properties

 Number of properties in top 10

6

4

Glass composition

Bulk chemistry

Reactivity as volatile/soluble minerals

Surface reactivity (including damage)

4

8

14

29

Mineralogical

 Total number of ranked properties

 Number of properties in top 10

4

2

Mineralogical composition as function of grain size

Modal mineralogical composition

Soil texture

6

11

30

Multicategory

 Total number of ranked properties

 Number of properties in top 10

2

0

Implanted solar particles

Agglutinates with nanophase iron metal (nFe0)

15

31

The 2005 report uses the term grain for several basic concepts. The simulant development 

project has subsequently decided to explicitly restrict grain to mean a discrete subset of a particle. 
6

In concept, a particle is a physically isolatable mass not chemically bonded to anything else. The 

grain commonly is a crystal of a mineral, but it can also be a piece of glass.

Table 2 presents relationships of properties to the FoM. Comments are provided for each 

parameter that is not explicitly a part of the FoM standard. In most cases the comments indicate 

the basic science explaining how the property is a derivative property. Also, where there are limitations to the assumptions or assertions made, some consideration of the limitations is given.

Table 2. Properties from 2005 workshop correlated to FoM properties by which

they are directly addressed or from which they are derived.

Category Properties Listing 

Regolith Property

Particle 

Type 

Particle Size 

Distribution 

Particle Shape 

Distribution Density 

Not Addressed 

or Undefined 

Compressive strength 

Coefficient of friction 

Shear strength 

Hardness 

Rheology 

Angle of repose 

Tensile strength X

Fracture behavior 

Impact resistance 

Particle density

Bulk density

Porosity

Thermal properties

Surface area

Friability

Permeability

Grain size

Grain size distribution

Grain shape

Grain shape distribution

Magnetic grain properties

Electrostatic charging

Glass composition

Bulk chemistry

Reactivity as volatile/soluble minerals X

Surface reactivity X

Mineralogical composition as function

 of grain size

Modal mineralogical composition

Soil texture X

Implanted solar particles X

Agglutinates with nFe0

Notes:

Property directly addressed by FoM

Property derivative of FoM property

Property partially dependent on environment
7

3.1 Geomechanical (Mechanical Strength Properties)

3.1.1 Compressive Strength

This is a derivative property. It is a function of the particles’ composition, size, shape, and 

how they are packed together. To the limit the FoM parameters can be measured in both the 

simulant and the lunar material, this property is tightly constrained by the FoM.

3.1.2 Coefficient of Friction

This is a derivative property. It is a function of the particles’ composition, size, shape, and 

packing. To the limit the FoM parameters can be measured in both the simulant and the lunar 

material, this property is tightly constrained by the FoM.

3.1.3 Shear Strength

This is a derivative property. It is a function of the particles’ composition, size, shape, and 

how they are packed together. To the limit the FoM parameters can be measured in both the 

simulant and the lunar material, this property is tightly constrained by the FoM.

3.1.4 Hardness

Hardness, as a geomechanical property, is ambiguous or undefined at best. In the 2005 

workshop report, the context of usage is always with respect to a single particle. In the report, the 

usage is also with either the explicit statement or the assumption of mineral hardness as used by 

geologists. Assuming this is the intention of the term, the FoM particle type very tightly constrains 

this property. The limitation is the mechanical strength of lithic fragments and shattered particles. 

For this small minority of particles, the basic concept breaks down. In engineering, applications 

terms such as abrasiveness are substituted.

3.1.5 Rheology

Rheology is the branch of physics that deals with the deformation and flow of matter, 

especially the non-Newtonian flow of liquids and the plastic flow of solids. As used in the 2005 

workshop report, “The rheological behavior (flow properties) of the regolith is a key property of 

the bulk material during excavation.” The particle size and shape distribution and the bulk density 

largely determine the flow properties of a material.

3.1.6 Angle of Repose

The rheological behavior (flow properties) of the regolith is a key property of the bulk material during excavation. As an example, it manifests itself in the angle of repose of a regolith slope 

forming a trench or an erected berm. See section 3.1.5 of this Technical Memorandum (TM).
8

3.1.7 Tensile Strength

The varying types of tensile strength describe a material’s reaction to stress and are defined 

as the maximum stress before rupture (breaking strength) or deformation (yield strength). The 

tensile strength of an individual particle is entirely constrained by the composition of the particle, 

although the properties may not have been adequately measured for some composite particles like 

breccias and agglutinates. Tensile strength of the bulk material is less well defined, but it should be 

a derivative of all of the four FoM characteristics.

3.1.8 Fracture Behavior

Fracture behavior of particles is driven by the particle type, specifically the hardness, cleavage, and fracture properties inherent in mineral and glass. These are addressed by the FoM and to 

some extent by particle shape. Whether and how particles fracture in bulk material, as a response 

to stress, is dependent on their size and packing.

3.1.9 Impact Resistance

Impact resistance should be akin to fracture behavior (section 3.1.8 of this TM).

3.2 Physical

3.2.1 Particle Density

If the particle type is known, this can be directly computed to high or very high precision. 

The limitation is for particles with large amounts of internal voids such as agglutinates and, to a 

lesser extent, shattered particles. The significance of this error for a bulk sample is estimated to be 

much less than 1%. For individual particles, it is estimated to be as high as 20%. 

3.2.2 Bulk Density

This is an explicit part of the FoM standard. However, it is not rigorously defined in the 

2005 recommendations.

3.2.3 Porosity

Porosity is a function of the particle type (due to vugs and voids in particles), shape and size 

distribution, and bulk density. It may not be uniquely constrained by these characteristics.

3.2.4 Thermal Properties

Thermal properties are derivatives of the particle type, size and shape distribution, and bulk 

density. Particles will have distinct conductive/insulating properties and the contact relationships 

between them will depend on size, shape, and bulk density.
9

3.2.5 Surface Area

Surface area is a function of particle size and shape distribution, and its bulk density will 

determine the surface area exposed in a given volume of material. Surface area is uniquely constrained by these parameters, but effective surface area defined as surface area available for contact 

is more largely dependent on the type of packing that may not be uniquely described by the bulk 

density parameter.

3.2.6 Friability

Most simulants are expected to be unconsolidated on the bulk scale and thus friability, 

defined as the tendency to reduce to finer particles under stress, is not applicable. Individual particles in a simulant or regolith such as breccias may be friable. Although friability and other measurements of mechanical strength are important considerations in simulant production, these 

properties of lunar regolith have not been measured adequately enough to simulate them.

3.2.7 Permeability

Permeability is a function of the particle shape and size distribution and bulk density. It 

may not be uniquely constrained by these characteristics.

3.3 Grain Specific

Size and shape are not defined by the 2005 workshop report. These concepts can only be 

given physical meaning by defining a specific method of measurement. Many of the measurement 

methods have physical meaning or are only applied to assemblies of particles.

3.3.1 Grain Size

This is an explicit part of the FoM standard.

3.3.2 Grain Size Distribution

This is an explicit part of the FoM standard.

3.3.3 Grain Shape

This is an explicit part of the FoM standard.

3.3.4 Magnetic Grain Properties

Magnetic properties derive from the mineralogy, grain or particle size, and environmental 

history of the particle. For example, heating above a material specific temperature will cause a 

radical change in magnetic response. Subsequent cooling will change it yet again. In lunar materials, particle composition should determine most of the magnetism of the bulk material, but 
10

this is complicated by the presence of nanophase iron metal (nFe0) in the lunar regolith. At this 

time, nFe0 is normally considered as a distinct solid phase independent of the commonly present 

Fe0 derived from meteoritic sources. Nanophase Fe0 is present in the agglutinates and in vapordeposited nanoscale rims on particles. As of now, the nFe0 in the agglutinates can only be partially 

reproduced, and that is at significant cost. The rims cannot be reproduced. 

The FoM incorporates the mineral phase Fe0. This was done to address both the meteoritic 

derived iron and the nFe0. The FoM also explicitly incorporates the particle type agglutinate. It is 

concluded that when fully implemented, these two measures, with the other FoM characteristics, 

will reasonably cover the performance of lunar material and simulants. This is almost certainly true 

for first order and probably most second order measurements. It is acknowledged that this may not 

be the case for very high quality measurements due to the role of particle history. As there is so 

little applicable information of any kind on this topic for actual lunar material, inclusion of such 

a parameter in the current FoM would violate basic characteristics of a standard, being neither 

measurable nor known.

3.3.5 Grain Shape Distribution

This is an explicit part of the FoM standard.

3.3.6 Electrostatic Charging

This is not part of the FoM standard. There is little data on this parameter for lunar 

material. It is almost certainly dominated by the composition and size of the particles, which is 

addressed by the particle type and size FoM. The limitation on this is the effect of the vapor-deposited rims.

3.4 Chemical

3.4.1 Glass Composition

Glass composition is important to many applications like in situ resource utilization (ISRU) 

and fabrication. Theoretically, the particle type FoM measures abundance and composition of 

particles. The diverse populations of glass compositions in lunar regolith pose a unique problem 

for evaluation. In the first FoM software release, only glass abundance is included in the algorithm, 

though there are entry spaces for subclasses of glass. This allows the user to define populations of 

glass (basaltic glass, Ti-rich basaltic glass, etc.) in the reference and simulant. Future revisions to 

the FoM software will include a routine to compare the chemical composition of glass in the 

materials and the abundance of the glass.

3.4.2 Bulk Chemistry

This is an implicit part of the FoM standard. If the composition of the particles is known, 

the bulk chemistry of the particles is known. The limitation to this is a question of precision. The 

standardized list of minerals does not cover all possible minerals, nor does it attempt to specify 
11

glass composition other than to restrict it by normative mineralogy. The minor element (<1 wt. %) 

and trace element (<0.1 wt. %) chemistry of a material is less well determined by particle type 

composition, except for cases like phosphorous (P), which is specifically addressed by reporting the 

modal percent of phosphates—the only minerals in which it is likely to occur.

3.4.3 Reactivity as Volatile/Soluble Minerals

Although the meaning of this entry is not entirely clear in the 2005 workshop document, 

it seems to refer to volatile (e.g., hydroxyl (OH), water (H2O), and carbon dioxide (CO2))-bearing 

materials and halogen (fluorine (F), chlorine (Cl), bromine (Br), and iodine (I))-bearing materials. 

3.4.3.1 Volatile-Bearing Materials. The presence of volatile-bearing materials in a simulant 

invokes a penalty to the composition FoM because correlative materials do not occur in lunar regolith. Furthermore, in revision 1 of the FoM software, these volatile-bearing minerals will populate 

their own subclass under the nonlunar minerals heading, and their presence will be weighted more 

than other nonlunar minerals due to their adverse affects on many ISRU processes.

3.4.3.2 Halogen-Bearing Materials. For halogen-bearing materials, the primary F- and 

Cl-bearing mineral in lunar regolith is the phosphate apatite. There is an entry for fluoroapatite 

on the FoM composition sheet; therefore, its presence, or lack thereof, will be assessed.

3.4.5 Surface Reactivity (Including Damage)

Surface reactivity is dependent on particle type (for reasons of chemistry) and on surface 

area (see section 3.2.5 of this TM). It is also dependent on the activation of a particle surface, a 

variable condition determined by particle lattice damage, lack or presence of adsorbates, and other 

characteristics. No general, measurable parameter correlates to this condition. Furthermore, it 

would seem to be a dynamic condition that would be difficult to impart to a bulk material by the 

manufacturer.

3.5 Mineralogical

3.5.1 Mineralogical Composition as Function of Grain Size

This is an explicit part of the FoM standard.

3.5.2 Modal Mineralogical Composition

This is an explicit part of the FoM standard.

3.5.3 Soil Texture

This is not defined and has many, many meanings. Some of the possible meanings are 

directly related to size and shape distribution and to material density.
12

3.6 Multicategory

3.6.1 Implanted Solar Particles

This is not addressed by the FoM as of this date. It is not considered practical or useful to 

add during simulant production. Reproduction of the process or result would likely be very expensive, and it seems best for the investigator to carry out treatment to replicate this property. This 

may change in the future.

3.6.2 Agglutinates With Nanophase Iron

The particle type FoM can address the presence of nFe0 in the agglutinates. In version 1 of 

the software, data on the distributions of agglutinates are required. A subclass could be added of 

those agglutinates containing nFe0 after this property is defined in the requirements document. 
13

4. CONCLUSION

The FoM is considered to be a work in progress, both conceptually and in terms of algorithm and software development. It provides a reasonable and practical means to compare materials by addressing fundamental, inherent, measurable characteristics.
14
15

REFERENCES

1. Sibille, L.; Carpenter, P.; Schlagheck, R.; and French, R.A.: “Lunar Regolith Simulant Materials: Recommendations for Standardaization, Production, and Usage,” NASA/TP—2006–

214605, 118 p, 2006.

2. Rickman, D.; Hoelzer, H.; Carpenter, P.; et al.: “A Quantitative Method for Evaluating Regolith Simulants,” Space Technology And Applications International Forum, Albuquerque, NM, 

February 11–15, 2007.

3. Rickman, D.: Lunar Regolith Simulant Requirements, Pre-Decisional Draft, MSFC–RQMT–

3503, 90 p, August 31, 2006.

4. Houck, K.J.: “Modal Petrology of Six Soils From Apollo 16 Double Drive Tube 64002,” Proceedings of the 13th Lunar and Planetary Science Conference, Part 1, J. Geophy. Res., Vol. 87, 

Sup., pp. A210–A220, 1982.

5. Graf, J.C.: Lunar Grain Size Catalog, NASA Reference Publication 1265, 464 p, 1993.
16

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Figure of Merit Characteristics Compared 

to Engineering Parameters

C.M. Schrader,* and D.L. Rickman

George C. Marshall Space Flight Center

Marshall Space Flight Center, AL 35812

National Aeronautics and Space Administration

Washington, DC 20546–0001

Unclassified-Unlimited

Subject Category 91

Availability: NASA CASI (443–757–5802)

Prepared by the Earth Sciences Office

*BAE Systems, Huntsville, Alabama

M–1292

Technical Memorandum

NASA/TM—2010–216443

lunar simulant, figure of merit, engineering, particle composition, particle shape, particle size, bulk 

density

01–09–2010

UU 24

NASA

U U U

A workshop held in 2005 defined a large number of parameters of interest for users of lunar simulants. The need 

for formal requirements and standards in the manufacture and use of simulants necessitates certain features of 

measurements. They must be definable, measureable, useful, and primary rather than derived. There are also 

certain features that must be avoided. Analysis of the total parameter list led to the realization that almost all of 

the parameters could be tightly constrained, though not predicted, if only four properties were measured: Particle 

composition, particle size distribution, particle shape distribution, and bulk density. These four are collectively 

referred to as figures of merit (FoMs). An evaluation of how each of the parameters identified in 2005 is controlled 

by the four FoMs is given.

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