Julie Kleinhenz and Diane Linne

Glenn Research Center, Cleveland, Ohio

Preparation of a Frozen Regolith Simulant Bed for 

ISRU Component Testing in a Vacuum Chamber 

NASA/TM—2013-217833

January 2013

AIAA–2013–0732
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Julie Kleinhenz and Diane Linne

Glenn Research Center, Cleveland, Ohio

Preparation of a Frozen Regolith Simulant Bed for 

ISRU Component Testing in a Vacuum Chamber 

NASA/TM—2013-217833

January 2013

AIAA–2013–0732

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

51st Aerospace Science Conference

sponsored by the American Institute of Aeronautics and Astronautics

Grapevine, Texas, January 7–19, 2013
Acknowledgments

This work is supported by the Regolith and Environment Science and Oxygen and Lunar Volatile Extraction (RESOLVE) project 

under the Advanced Exploration Systems (AES) program and the ISRU Project under the Game Changing Technology Division 

of the Space Technology Program.

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NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

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

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2013-217833 1

Preparation of a Frozen Regolith Simulant Bed for ISRU 

Component Testing in a Vacuum Chamber 

Julie Kleinhenz and Diane Linne

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Abstract

In-Situ Resource Utilization (ISRU) systems and components have undergone extensive laboratory 

and field tests to expose hardware to relevant soil environments. The next step is to combine these soil

environments with relevant pressure and temperature conditions. Previous testing has demonstrated how 

to incorporate large bins of unconsolidated lunar regolith into sufficiently sized vacuum chambers. In 

order to create appropriate depth dependent soil characteristics that are needed to test drilling operations 

for the lunar surface, the regolith simulant bed must by properly compacted and frozen. While small 

cryogenic simulant beds have been created for laboratory tests, this scale effort will allow testing of a full 

1m drill which has been developed for a potential lunar prospector mission. Compacted bulk densities 

were measured at various moisture contents for GRC-3 and Chenobi regolith simulants. Vibrational 

compaction methods were compared with the previously used hammer compaction, or “Proctor”, method. 

All testing was done per ASTM standard methods. A full 6.13 m3 simulant bed with 6 percent moisture 

by weight was prepared, compacted in layers, and frozen in a commercial freezer. Temperature and 

desiccation data was collected to determine logistics for preparation and transport of the simulant bed for 

thermal vacuum testing. Once in the vacuum facility, the simulant bed will be cryogenically frozen with 

liquid nitrogen. These cryogenic vacuum tests are underway, but results will not be included in this 

manuscript.

Nomenclature

ASTM American Society for Testing and Materials

ISRU In-Situ Resource Utilization

LCROSS Lunar Crater Observation and Sensing Satellite

LRO Lunar Reconnaissance Orbiter

RESOLVE Regolith and Environment Science, Oxygen and Lunar Volatiles Extraction

VF Vacuum Facility

Introduction

Exploration of extraterrestrial environments will require rugged hardware that can withstand a variety 

of unique environmental conditions. These environments include extreme pressure and temperature 

conditions, but for In-Situ Resource Utilization (ISRU) this also includes heavy exposure to surface 

material, or regolith. ISRU systems can consist of drills, excavators, reactors, and sensitive science 

equipment that must withstand direct interaction with the abrasive regolith. Earth-based testing of 

hardware in relevant environments is key to understanding these interactions and developing appropriate 

hardware. 

The Regolith and Environment Science, Oxygen and Lunar Volatiles Extraction (RESOLVE) project

is a prospective ISRU mission that will prospect for volatile resources in the cold regions near the lunar 

poles. Potential instruments included in the RESOLVE payload are a coring drill and auger designed to 

obtain samples down to 1m depth. The project has undergone several hardware iterations including 

breadboard and field demonstrations. These tests examined operational and integration methods using 
NASA/TM—2013-217833 2

various lunar regolith simulants. RESOLVE is now preparing for environmental testing in a lunarrelevant thermal vacuum environment, which must necessarily include lunar regolith simulant.

When exposed to vacuum, gas trapped in and adsorbed onto earth-based granular media (such as 

lunar regolith simulant) is released. This gas release can occur violently, which loosens and weakens the 

simulant, altering the consolidation state. Previous studies (Ref. 1) using a 1-ton bin of lunar regolith 

simulant LHT-3M in a vacuum chamber have identified operational procedures to avoid this violent gas 

release and maintain the soil state. This study is the largest simulant bin tested in a vacuum chamber to 

date, and serves as the spring-board for future component and hardware systems tests.

Testing of the RESOLVE drill and auger requires a simulant bed prepared to a controlled moisture 

content and density to mimic expected, and worst-case, lunar surface conditions for the drill subsystem.

The prepared simulant bed will also be cryogenically frozen using liquid nitrogen within the vacuum 

chamber. These tests will be performed in the same vacuum chamber and with the same procedural 

techniques as Ref. 1. However, the size of the simulant bin will be altered to better accommodate the 

hardware and facilitate freezing. Instead of the 1- by 1- by 0.7-m (depth) square bin from Reference 1, a 

0.278 m diameter, 1.2 m tall cylindrical bin will be used.

In preparation for the RESOLVE vacuum component testing, simulant bed preparation and initial 

vacuum tests are underway. This document describes procedures for the soil preparation up to the point of 

vacuum testing.

Objectives

The first critical objective for the simulant bed preparation was to find a way to compact the soil to 

obtain a repeatable bulk densities that are representative of the lunar regolith. While returned core sample 

density measurements from the Luna and Apollo missions ranged from 1.1 to 2.3 g/cm3

, the most 

common values were in the range of the 1.5 to 1.9 g/cm3 (see Ref. 2, table 9.4). Prior to flight it is 

desirable to test the hardware at conditions that meet or exceed the most challenging conditions expected 

on the Moon to ensure mission success. Therefore, one objective was to compact to maximum density. 

However, lower densities might also present a challenge in maintaining and transferring core samples and 

should also be tested prior to flight.

Smaller scale drill tests (Ref. 3) utilized the ASTM D698 “Proctor” compaction method, (Ref. 4) in 

which a weight is repeatedly dropped on the surface of the material. According to the ASTM standard, 

this method accommodates a soil bed 11.4 cm (4.5 in.) deep, 15.2 cm (6 in.) in diameter and requires 56 

drops of the 2.5 kg rammer weight from a height of 12 in. When considering a layered fill of a 1 m tall 

simulant bed, and performing this procedure on each layer, this is a time consuming prospect. The moist 

simulant would also be exposed to room air during the compaction process, giving it the opportunity to 

desiccate. A more timely way of soil compaction is the vibration method described in ASTM D4253

(Ref. 5). In this method, a surcharge weight (2 lb/in2

) is placed on the surface of the soil while the entire 

soil bed is vibrated. The vibration compaction standard also specifies a soil depth of 20.3 cm (8 in) with a 

27.9 cm (11 in) diameter. This larger diameter is better suited to the drill/auger tests since multiple drill 

holes are feasible within the simulant bed. Considering the preparation time of the simulant and the time 

needed to achieve desired vacuum conditions (up to a week based on Ref. 1), the possibility of multiple 

drill points was highly desired. However, a layered compaction would still be required to achieve the 

appropriate simulant bed depth, and it had to be demonstrated that the vibration would not disturb 

previously compacted layers.

The second objective in the simulant bed preparation was to add a known amount of moisture to the 

simulant. Based on LCROSS and LRO data (Ref. 6), the moisture content in the near permanently 

shadowed regions of the moon is expected to be around 5 percent by mass. To challenge the drill 

hardware, the simulant bed should be at its maximum bulk density at each moisture condition. Baseline 

tests were performed with the ASTM vibration method to determine the moisture-dependent bulk 

densities. Compaction tests were done with lunar regolith simulants GRC-3 and Chenobi. The GRC-3 
NASA/TM—2013-217833 3

was used for initial tests to determine procedures, since it is less expensive and more available. The 

RESOLVE drill hardware tests will use Chenobi. 

The final simulant bed preparation objective is to study how to cryogenically freeze the simulant bed 

in a vacuum chamber. This involves monitoring the temperature and pressure profile to determine the 

time scales and temperature uniformity. The condition of the simulant bed will also be examined during 

and after the pump down for evidence of gas release effects. Moisture content will also be examined at 

the end of the test to look for desiccation. 

Equipment and Facilities

All simulant handling and preparation work was performed in the Simulated Lunar OPErations 

(SLOPE) laboratory at NASA Glenn Research Center. The primary feature of the SLOPE lab is the 

mobility and traction test bed with an adjustable tilt angle up to 45°. Since the lab has safety features to 

allow safe handling of large quantities of lunar regolith simulants, it is also used for soil preparation and 

soil mechanics tests. A variety of equipment is available for this purpose. For the current test program this 

equipment included an oven, a cement mixer, a vibration table, and a commercial upright freezer 

(Figure 1). The oven was used for desiccating the simulant. It can accommodate three baking trays of 

simulant, each of which can hold 1.5 kg of simulant. The cement mixer was used for moisture addition. 

Water was added as the simulant was mixed to ensure uniform distribution. The vibration table, used for 

compaction, has a fixed vibration frequency of 60Hz and adjustable amplitude, which meets the 

requirements of the ASTM D4253 for compaction (Ref. 5). Finally, the upright freezer was used to chill 

the simulant prior to transport to the vacuum chamber facility where it will be cryogenically cooled. This 

initial freeze solidified the soil state to prevent disturbance of the simulant bed during transport. The 

freezer can maintain a temperature of –20 °C.

Figure 1.—Simulant preparation equipment in the 

SLOPE lab.
NASA/TM—2013-217833 4

Figure 2.—The apparatus for the ASTM 

D4253 vibration compaction tests. A) The 

0.5 ft3 mold filled with GRC3 simulant. B) 

The guide sleeve is attached to the top of 

the mold, and the weight is lowered.

Figure 3.—The cylindrical 

simulant bin shown with the 

coolant loops clamped on.

The baseline compaction tests were performed in the apparatus in Figure 2 which was designed 

according to ASTM vibration standard D4253 (Ref. 4). This 14200 cm3 (0.5 ft3

) mold (Figure 2A) has an 

internal diameter of 27.94 cm (11in). A baseplate (not shown) sits atop the simulant and supports the 

79.4 kg (175 lb) surcharge weight. A guide sleeve is attached to the top of the mold to contain the 

surcharge weight during vibration (Figure 2B). The assembly is then strapped securely to a 60 Hz 

vibration table and vibrated. This apparatus was used to map the maximum bulk densities of the simulants 

at the different moisture contents. These densities were then used to develop the compaction procedures 

for the taller cylindrical bin.

The simulant bed for the vacuum chamber tests was a 1.2 m (48 in.) cylinder (Figure 3). The inner 

diameter was 0.278 m (11 in.), which is identical to the ASTM apparatus so that procedures and

equipment (surcharge weight, baseplate) from the smaller ASTM apparatus could be used. Three feedthrough ports at various heights along the drill tube accommodated thermocouple probes. Each probe had 

five type T thermocouples which were embedded in the soil at different radial positions, as shown in 

Figure 4. These probes were embedded as the bin was filled with simulant, and the simulant was 

compacted on top of them.

The vacuum facility that will be used, VF-13, is a vertical, cylindrical chamber with an internal 

volume of 6.35 m3 (Figure 5). The bulk of the volume is within the removable 2.52 m tall by 1.5 m 

diameter lid (the white portion in Figure 5). The fixed base is 1.08 m deep and accommodates all the 

electrical, mechanical, and gas feed-throughs. Four different types of pumps can be used to achieve a 

pressure of 10–6Torr. Liquid nitrogen is plumbed to the facility to accomplish cryogenic cooling of the 

simulant bin. Coolant loops (Figure 3) are clamped to the bin and the simulant bed is chilled as a vacuum 

is pulled. A cryogenic shroud (liquid nitrogen) will be available in the lid portion of VF13 during 

RESOLVE component testing.
NASA/TM—2013-217833 5

Figure 4.—The position of the thermocouples in the simulant bed. At left, 

the radial positions of the thermocouple rake. At right, the axial position of 

each thermocouple rake.

Figure 5.—The VF13

vacuum facility, shown 

sealed.

Results and Discussion

The following sections describe the different aspects of soil preparation. In the case of moisture 

addition and compaction, these are methods to scale-up the procedures set forth in the ASTM standards. 

Simulant specific data for GRC-3 and Chenobi simulants include bulk densities versus moisture content.

Rudimentary data regarding time dependent desiccation and moisture absorption in room conditions

helped determine logistics for simulant handling. Moist simulant was frozen in a commercial freezer, and 

then thawed, to determine temperature uniformity over time. Simulant preparation up to the point of 

vacuum testing will be covered. Thermal vacuum data is left for a later publication. 

Simulant Moisture Addition

One of the goals of the RESOLVE project is to determine the volatile water content of the lunar 

regolith (water ice, or loosely bound). Validation testing must therefore address a range of possible 

moisture contents that may exist on the lunar surface. The cylindrical bin holds over 150 kg of lunar 

regolith simulant, so procedures were developed to prepare a large quantity of simulant to a known 

moisture state. This involved adding, and uniformly distributing, a known amount of water into the 

simulant. To do so, it was also important to understand the moisture content of the simulant at room 

conditions and how quickly the moist simulant would desiccate when exposed to room conditions. As 

mentioned, two types of lunar soil simulant were used. GRC-3 is a lower cost, lower fidelity physical 

simulant that was used for check out tests. Chenobi simulant is a higher fidelity lunar highlands simulant 

that will ultimately be used for RESOLVE drill hardware tests. Moisture tests were performed on both.

To determine the water content of the simulant, small samples (~40 g) were baked in an oven as per 

ASTM D2216 (Ref. 7). The samples were baked at 100 ± 5 °C overnight, though mass loss typically 
NASA/TM—2013-217833 6

stopped after 4 hr. The samples were weighed before and after oven exposure and were kept sealed when 

outside of the oven. At laboratory room conditions (typically 20 percent relative humidity) the GRC-3 

simulant held approximately 0.5 percent moisture while the Chenobi held less than 0.1 percent. Dry 

samples were then allowed to reabsorb moisture, and regained 0.1 percent within 30 min.

Increasing the moisture content of the simulant was done on a mass basis. Simulant was mixed in 

batches of 20 to 25 kg, or a single 5 gal bucket. The mass of water to be added for a desired mass fraction

was determined by Equation (1) where ms is the total simulant mass, fw is the water fraction desired, and 

mw is the mass of water added. Tap water was used for the GRC-3 test while distilled water was used with 

the Chenobi.

( )

( f )

f m

m w

w s w − = 1 (1)

A hand pump sprayer was used to spray the water into the cement mixer as simulant was added. This

method achieved a uniform distribution of the water without the simulant ‘clumping’. Once mixing was 

complete the moist simulant was allowed to cure in a sealed bucket overnight (as per Ref. 4). To verify 

the water content, two 40 g samples from each soil bucket were baked out using the procedures described 

above. Moisture contents were generally within 1 percent of the target when the simulant was not oven 

dried prior to moisture addition. One would expect that without drying, the moisture contents would be 

consistently higher than the target, but from Table 1, that is not the case. Even multiple samples from the 

same simulant batch had as much as 0.5 percent (average 0.3 percent) variation moisture content. Other 

sources of error that could cause moisture variations include attrition of water and simulant during 

mixing, resolution of the scale (0.01 kg), and desiccation. When choosing moisture conditions for 

RESOLVE validation testing, a resolution of 1 percent should be used.

TABLE 1.—THE TARGET WATER CONTENT IS SHOWN WITH 

THE ACTUAL WATER CONTENT, AS MEASURED BY ASTM D2216

Test designation Target 

water

Measured

water

Deviation 

from target

GRC-3 room.1 -------- 0.42 --------

GRC-3 6.1

6.00 5.84 –0.16

6.00 5.72 –0.28

GRC-3 6.2 6.00 6.34 0.34

GRC-3, 8.1

8.00 9.39 1.39

8.00 9.79 1.79

GRC-3 11.1

11.00 11.90 0.90

11.00 11.59 0.59

Chenobi room.1 -------- 0.05 --------

Chenobi room.2 -------- 0.05 --------

Chenobi, 2.1

*oven dry

2.00 2.02 0.02

2.00 1.78 –0.22

Chenobi 5.1 5.00 4.74 –0.26

5.00 4.54 –0.46

Chenobi 8.1 8.00 8.68 0.68

8.00 8.81 0.81

Chenobi 10.1 10.00 10.54 0.54

10.00 11.08 1.08
NASA/TM—2013-217833 7

0.00%

1.00%

2.00%

3.00%

4.00%

5.00%

6.00%

7.00%

0.01 0.1 1 10 100 1000

Moisture, % by mass

Time, hour

GRC3 

Drying in Room Air

21kg in Bucket

50g in Jar

30g mounded

Figure 6.—Desiccation of GRC-3 in room air.

Figure 6 is an indication of how quickly the simulant desiccates when exposed to room conditions.

This data gives an idea of how long GRC-3 simulant may be handled in room conditions during 

compaction, transfer, etc. Three different configurations are shown; 21 kg of simulant in a 5 gal bucket 

(30 cm diameter at the soil surface), a 50 g sample in a 3 cm tall by 5 cm diameter jar (8 oz), and 30 g of 

simulant in a fully exposed pile. All samples start at ~6 percent water by mass. The relative humidity of 

the room was typically 20 percent. The jar, in which only the surface is exposed, reduces by 1 percent

within the first 5 hr, while the mounded simulant only takes 15 min due to the increased surface area. The 

simulant is generally prepared in batches of 20 to 25 kg, so the 21 kg test shown here is the most relevant 

to test logistics. It takes nearly three days for the bucket to lose 1 percent of its moisture. While the 

simulant on the surface of the bucket visibly dries with a few hours, the soil beneath the surface is damp.

Generally compaction procedures with a simulant batch take 1 to 2 hr. Based on the results shown in 

Figure 6, this amount of time should not represent a significant desiccation.

When dry samples were desired, the simulant was placed on baking sheet trays, which could hold 

about 1.5 kg simulant each. Three trays could be baked simultaneously in the oven at 110 °C. With the 

high surface area, the samples dried (no further mass loss) within 30 min. 

Simulant Compacted Densities

Once the simulant was prepared to the desired moisture content, it was compacted to achieve a 

maximum bulk density. These compactions were done with procedures and apparatus listed in ASTM 

D4253 for vibrational compaction (Ref. 5). The 14200 cm3 (0.5 ft3

) mold was filled with the simulant and 

the 79.4 kg (175 lb) surcharge weight was placed on the surface. The apparatus was then strapped 

securely to the vibration table. For tests with added moisture, the mold was filled with simulant as it was 

vibrated at a low level. This was not done with dry simulant since the airborne particulate would have 

created a hazard. As per the standard, the simulant was vibrated for 8 min at 60 Hz. The amplitude of the 

vibration was controlled via a rheostat. The standard specifies an acceleration of 14 m/s2 (1.5 g) to 

45 m/s2 (4.8 g). An accelerometer was used in several tests to determine the necessary rheostat setting to 

achieve this. Generally, a setting of 12 percent resulted in an acceleration of 20 to 24 m/s2 and resulted in 

the best compaction. The sound of the vibration was generally a good indicator of appropriate rheostat 

setting. As the rheostat was increased to 12 percent, the sound would go from a low level ‘buzz’ to a loud 

rumble. At this transition point the surcharge weight visibly rotated and bounced slightly. The change in 

height of soil bed was also measured at 1 min intervals during vibration. To achieve the best results, the 

rheostat was set at 12 percent for the first 5 min of vibration. At this point, simulant height had stabilized. 
NASA/TM—2013-217833 8

Figure 7.—Compaction as a function of vibration time. A range of test conditions are shown, 

lines link points from a single test condition.

By ramping the rheostat between 0 and 40 percent for the remaining 3 min an additional few millimeters 

of compaction could be achieved. Figure 7 shows bed height measurements during vibration with an 

accuracy of ± 2 mm. (The last data point was always taken after vibration stopped, which explains the 

additional few millimeters of compaction). The majority of the compaction occurs with in the first 2 min

of vibration, with only a few millimeters change after. This result agrees with Reference 8. However, the 

full 8 min vibration was performed for traceability to the ASTM standard and to ensure the last few 

millimeters of compaction could be achieved. The simulant mass was measured after vibration and after 

the surcharge weight and baseplate were removed from the simulant surface. The density was then 

determined using this mass and the final simulant height within the mold.

The resulting wet densities are shown in Figure 8. For the GRC-3 simulant, several repeat tests were 

conducted at water fractions below 6 percent, which are most expected in the lunar regolith. These tests 

demonstrated that densities were very repeatable using the vibration compaction method. For both the

GRC-3 and Chenobi, the compacted bulk density initially decreases as water is added to the simulant. 

This was also seen in other simulants like JSC-1A (Ref. 10) and LHT-2M (Ref. 11).

Results from previous studies (Ref. 9)

1 that used the Proctor compaction method (ASTM D698) are 

also plotted in Figure 8. Note that the goal of these previous tests, and the goal of the ASTM standard

D698, was to determine the moisture content that produced the maximum dry bulk density. Thus, results 

from these Proctor method studies were reported as equivalent dry bulk density and were converted to wet 

bulk densities using Equation (2) where ρ is density and fwater is the water fraction of the simulant by 

mass.

water

wet

dry 1+ f

ρ ρ = (2)

All densities in Figure 8 are wet densities (ρwet). In the present work, the goal was to find the maximum 

bulk density at moisture contents in the range of 0 to 8 percent water by mass. However, the Proctor 

method tests typically miss the dip in bulk density at these lower moisture contents based on the advice in 

 1

The data for Chenobi compaction tests using Proctor method were obtained from NORCAT (NOrthern Center for 

Advanced Technologies) via personal communication.
NASA/TM—2013-217833 9

Figure 8.—Wet compacted densities for GRC-3 and Chenobi simulants at different moisture contents.

ASTM D698 (Ref. 4), “Typically soils at the optimum water content can be squeezed into a lump that 

sticks together when hand pressure is released...” The optimum water content in this context refers to the 

maximum dry bulk density. Simulant of this consistency tends to happen at water contents greater than 

5 percent. While higher densities were achieved in the previous studies, the Proctor method is not 

necessarily superior for this situation. The Proctor method specifies a diameter smaller than what was 

required for the simulant bed, and it is unknown how effective the method would be with a larger 

diameter bed. Given that the densities obtained using the vibration method were within the range of the 

lunar surface measurements (Ref. 2), and that the logistics are better suited to the simulant bed 

preparation, the vibration results were a good match to the objectives of the RESOLVE project. 

Simulant Test Bed Preparation

The next step was to determine if the bulk densities determined in the ASTM mold could be achieved 

in the larger cylindrical bin. Since the height of the simulant bed would be five times greater than that of 

the ASTM apparatus, the effectiveness of vibration may be different. The simulant for the cylindrical bin

tests was prepared in batches of ~25 kg (5 gal buckets). A layered fill was then performed whereby the 

bin underwent vibration compaction after each successive layer. The compaction procedures established 

with the smaller ASTM apparatus were used. With the additional mass of the bin, vibration was adjusted 

with a higher rheostat setting. This setting was gauged by the sound and visible motion of the surcharge 

weight, as observed in the ASTM apparatus tests. The bin was also strapped securely to the vibration 

table during each compaction, as was done in the ASTM tests. The bulk density of the total simulant bed

was measured after each layer was added (the bulk density listed for layer 2 includes layers 1 and 2, and 

layer 5 is the bulk density of all the layers combined). The results of two of these tests are shown in Table 

2. In the first test, GRC-3 at room ‘dry’ conditions (no moisture added) was used. The bulk density after 

each layer was very consistent for all but the last (top) layer. A larger mass of soil was added in this final 

layer to top off the bin and resulted in a less effective compaction. 
NASA/TM—2013-217833 10

TABLE 2.—THE BULK DENSITIES DURING LAYERED FILL AND COMPACTION 

OF THE SIMULANT BED. LAYER 5 REPRESENTS A FILLED BED

Layer GRC-3 room dry GRC-3 6 moisture

Layer mass, 

kg

Compacted density, 

g/cm3

Layer mass, 

kg

Compacted density, 

g/cm3

Moisture content, 

%

1 25.7 1.85 24.4 1.59 5.72

2 24.5 1.85 25.0 1.57 6.21

3 25.3 1.85 21.4 1.58 6.13

4 20.8 1.85 21.2 1.57 6.31

5 32.5 1.83 17.3 1.57 6.64

For the next test, GRC-3 with 6 percent moisture content, all layers were 25 kg or less. While the first 

layer achieved a slightly higher compaction, the bulk density with subsequent layers was constant. This

consistency suggests that the vibration was not altering the state of the previously compacted (lower) 

layers. However, all of these densities were lower than those achieved in the earlier ASTM tests 

(Figure 8). Given that the cross section area, surcharge weight, etc. matched those of the smaller 

apparatus, it is surprising that at least the first layer did not match the ASTM results. Additional tests have 

not yet been performed to resolve this, but one difference was the fill method of the simulant. The 

cylindrical bin could not be vibrated during fill like the ASTM apparatus. Also, the layering in the bin

was done on a mass basis whereas the ASTM apparatus was done by volume (e.g. the mold was entirely 

filled for each test). A higher mass, or deeper simulant layer, could have decreased the effectiveness of 

the vibration. For comparison, a single compaction was attempted with a single 116 kg room-dry simulant 

bed. The resulting bulk density for this room condition GRC-3 simulant was 1.74 g/cm3

, considerably less 

than the layered compaction test.

Another difference with the 6 percent moisture test was the addition of thermocouples in the simulant.

These were used to monitor the thermal profile of the simulant during the subsequent freezing process.

These thermocouple probes were embedded in the simulant during the fill process. Simulant was added 

until the level reached the feed through port. The thermocouple probe was then inserted (see Figure 4), 

the rest of the simulant layer was added, and then compacted. It was expected that the probes would be 

bent to some degree while the simulant was compacted atop them. 

The filled bin was then inserted into a commercial upright freezer for an initial freeze prior to full 

cryogenic exposure. The vacuum facility with the cryogenic cooling capability is housed separate from 

the soils laboratory. Thus, freezing the simulant bed prior to transport would help solidify the soil state, 

maintaining the prepared density and preventing spills or material loss. The initial freeze would also 

reduce the degree of thermal shock that may occur when exposed to the liquid nitrogen. Temperatures 

were monitored during freezing, and then thawing to determine the logistics of the transport. The data 

acquisition system was configured to monitor 8 of the 15 thermocouples. The results of the freeze and 

thaw tests are shown in Figure 9, along with graphic to identify which thermocouples were monitored. As 

expected, the temperature rate leveled at 0 °C while the phase change occurred. The simulant nearest the 

wall (position 5) froze in 3 hr, and by 8 hr the most insulated position, B1, was frozen. After 18 hr the full 

simulant bed had reached equilibrium with the freezer temperature, –20 °C. When exposed to room 

conditions (22 °C), the thaw process followed a similar timeline. The simulant nearest the wall thawed in 

2 hr while the full simulant bed (gauged by B1) thawed within 8 hr. The simulant at the bottom of the bed 

(probe A) was the most sensitive to temperature change. This sensitivity is likely due to the large thermal 

mass of the bottom flange, which has a higher thermal conductivity than the simulant. Note that the 

simulant bin was entirely uninsulated during these tests as a worst-case. 
NASA/TM—2013-217833 11

Figure 9.—The temperature traces of the filled simulant bed during freezing (left) and thaw (right). Eight thermocouple 

traces are shown, with positions indicated by the graphic.

Desiccation of the simulant bed in the freezer was also examined. While surface desiccation of the 

simulant bed would mimic lunar surface conditions, a uniform moisture profile would be more 

challenging to the drill hardware. In the upright freezer, a plug lid was inserted into the top of the bin and 

sealed using foam weather-stripping tape. This lid is not intended for the cryogenic freezing in the 

vacuum facility since there would be no way to remove it at vacuum. After the bin was removed from the 

freezer, a sample of the frozen simulant was chipped from the surface. The moisture content of this 

sample was 3 percent. With the lid in place, the simulant bed was allowed to thaw. Once it reached room 

temperature, another sample was removed from the surface. This had a moisture content of 5.9 percent.

This indicates that the sample surface had desiccated in the freezer, but that the moisture was still trapped 

within the bin. Ice crystals were observed along the inner surface of the bin and on the bottom of the lid.

A 3 percent moisture loss in the top 1 cm of the simulant translates to 29 ml of water, which qualitatively 

is reasonable for the condensation observed. The thaw process took 24 hr, during which time at least 

some of this condensate would return to the simulant bed. The moisture in depth of the simulant bed 

would also have an opportunity to diffuse into the drier surface. Recall that the procedures for moisture 

addition described earlier include a cure period for this reason. 

To illustrate this reabsorption process, a test was done with the air desiccated bucket discussed earlier

(Figure 6). At the end of the desiccation test the bucket of soil had a moisture content of 5 percent with a 

visibly dry surface. A core sample was removed from the bucket using a 10 cm long scoop. The simulant 

was divided up into four sections to fill 8 oz jars and then baked out to determine moisture. The bucket 

was then sealed and allowed to cure for 2.5 days. The same core sample method was used to collect depth 

samples. Table 3 shows the results. Even with a dry lid (no condensation dripping back into the sample) 

some moisture diffused into the surface.
NASA/TM—2013-217833 12

TABLE 3.—DEPTH DEPENDENT MOISTURE MEASUREMENTS 

TAKEN AFTER DESICCATION IN ROOM CONDITIONS 

AND SUBSEQUENT 2.5 DAY SEALED CURE

Depth beneath 

surface, 

cm

After room desiccation, 

%

After cure 2.5 day, 

%

0, surface 0.6 1.9

4 to 7 5.0 4.7

7 to 10 5.1 5.2

Figure 10.—The simulant bed in the VF13 chamber prior to 

vacuum testing.

Vacuum Test

A simulant bed has been prepared and is currently installed in the vacuum chamber (Figure 10). The 

final facility check-out tests are underway. The frozen simulant bed was transported to the vacuum

chamber in under 1 hr, and is expected to take closer to 30 min now that transport procedures are known.

The time from vacuum chamber installation until the start of liquid nitrogen flow is not yet known.

Insulation may be added to the simulant bin to prevent thawing if this time is significant. 

Conclusions

A simulant bed has been prepared to accommodate thermal vacuum testing of RESOLVE component 

hardware. This 0.278 m diameter, 1.2 m tall cylindrical simulant bin can accommodate drill subsystem 

test to full depth. Simulant preparation methods have been developed to obtain moisture levels expected 

on the lunar surface. Baseline compaction tests were performed at a range of moisture levels to determine 

maximum achievable bulk densities. This was done for GRC-3 and Chenobi lunar regolith simulants.

Vibration compaction was the most viable method to accommodate a simulant bed of this size. It 
NASA/TM—2013-217833 13

produced densities within the range of those measured on the lunar surface (returned core samples) and 

accommodated a larger diameter simulant bed that could support multiple drill holes. A layered fill 

procedure was used to compact the 1.2 m simulant bed. Vibration compaction on each successive layer 

resulted in a consistent bulk as layers were added. This suggests that the vibration did not undo the 

compaction of previous layers, so a layered vibrational compaction is viable. However, the bin had lower 

bulk densities than those achieved in a smaller vessel. Smaller layers, not to exceed the height of the 

ASTM vibration apparatus, will be used in future bed preparations to better correlate the densities.

During vacuum testing, the simulant bin will be wrapped in liquid nitrogen coolant tubes to achieve 

cryogenic temperatures expected on the lunar surface. However, an initial freeze of the simulant bed 

using a commercial upright freezer was used solidify the simulant bed prior to transport into the vacuum 

facility. Thermocouples embedded in the simulant indicated that the entire bed was frozen within 8 hr 

inside the –20 °C freezer. Once removed from the freezer, the most exposed locations of the simulant bed 

began to thaw in 2 hr. Transport of the simulant bed to the vacuum facility has been demonstrated in 

under 1 hr.

References

1. Kleinhenz, J.E. and Wilkinson, A., 2012, “ISRU Soil Mechanics Vacuum Facility: Soil Bin 

Preparation and Simulant Strength Characterization,” 50th Aerospace Sciences Meeting and Exhibit,

American Institute for Aeronautics and Astronautics, AIAA-2012-0359.

2. LSB, G. H. Heiken, D. T. Vaniman, and B. M. French, Lunar Sourcebook: A User's Guide to the 

Moon, New York, Cambridge University Press, 1991.

3. Lakanen, G., Sigurdson, L., Boucher, D., and Timusk, M., 2012. “Development of an Intelligent 

Measure while Drilling System for Planetary Drills,” 50th Aerospace Sciences Meeting and Exhibit,

American Institute for Aeronautics and Astronautics, AIAA-2012-0518.

4. ASTM Standard D698-07, “Standard Test Methods for Laboratory Compaction Characteristics of 

Soil Using Standard Effort (12 400ft-lbf/ft3 (600 kN-m/m3

)),” ASTM International, West 

Conshohocken, PA.

5. ASTM Standard D4253-00, “Standard Test Methods for Maximum Index Density and Unit Weight 

of Soils Using a Vibratory Table,” ASTM International, West Conshohocken, PA.

6. Colaprete, A., et al, 2010, “Detection of Water in the LCROSS Ejecta Plume,” Science, 22, 463-468.

7. ASTM Standard D2216-05, “Standard Test Methods for Laboratory Determination of Water 

(moisture) Content of Soil and Rock by Mass,” ASTM International, West Conshohocken, PA.

8. Gustafson, R., Grzesiak, B., Gertsch, L., and Rostami, J., 2009, “Low-Energy Planetary Excavator,” 

NASA Phase 2 SBIR 2009 Final Report.

9. He, C., Zeng, X., and Wilkinson, A., “Geotechnical Properties of GRC3 Lunar Simulant,” J. Aerosp. 

Eng., doi: 10.1061/(ASCE)AS.1943-5525.0000162.

10. Zeng, X., He, C., Oravec, H., Wilkinson, A., Agui, J., and Asnani, V. (2010). ”Geotechnical 

Properties of JSC-1A Lunar Soil Simulant,” J. Aerosp. Eng., 23(2), 111–116. 

11. Zeng, X., He, C., and Wilkinson, A., 2010, “Geotechnical Properties of NT-LHT-2M Lunar 

Highland Simulant,” J. Aerosp. Eng., 23(4), 213–218.
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Preparation of a Frozen Regolith Simulant Bed for ISRU Component Testing in a Vacuum 

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Kleinhenz, Julie; Linne, Diane 

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14. ABSTRACT

In-Situ Resource Utilization (ISRU) systems and components have undergone extensive laboratory and field tests to expose hardware to 

relevant soil environments. The next step is to combine these soil environments with relevant pressure and temperature conditions. Previous 

testing has demonstrated how to incorporate large bins of unconsolidated lunar regolith into sufficiently sized vacuum chambers. In order to 

create appropriate depth dependent soil characteristics that are needed to test drilling operations for the lunar surface, the regolith simulant 

bed must by properly compacted and frozen. While small cryogenic simulant beds have been created for laboratory tests, this scale effort 

will allow testing of a full 1m drill which has been developed for a potential lunar prospector mission. Compacted bulk densities were 

measured at various moisture contents for GRC-3 and Chenobi regolith simulants. Vibrational compaction methods were compared with the 

previously used hammer compaction, or “Proctor”, method. All testing was done per ASTM standard methods. A full 6.13 m3 simulant bed 

with 6 percent moisture by weight was prepared, compacted in layers, and frozen in a commercial freezer. Temperature and desiccation data 

was collected to determine logistics for preparation and transport of the simulant bed for thermal vacuum testing. Once in the vacuum 

facility, the simulant bed will be cryogenically frozen with liquid nitrogen. These cryogenic vacuum tests are underway, but results will not 

be included in this manuscript. 

15. SUBJECT TERMS

Lunar regolith; Granular materials; In situ resource utilization 

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