NASA/TM-2011-216302

.

N~~ /. ~".,

Low Force Icy Regolith Penetration

Technology

Philip T. Metzger, Gregory M. Galloway, and James G. Mantovani

NASA Kennedy Space Center

Kris Zacny and Jack Craft

Honeybee Robotics, Inc., New York City, New York

July 11, 2011
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NASA/TM-2011-216302

. .

.. . .

Low Force Icy Regolith Penetration

Technology

Philip T. Metzger, Greg M. Galloway, and James G. Mantovani

NASA Kennedy Space Center

Kris Zacny and Jack Craft

Honeybee Robotics Space Mechanisms Corporation

New York, New York

National Aeronautics and

Space Administration

Kennedy Space Center

July 11, 2011
Acknowledgments

This work was supported by the 2010 NASA Innovation Fund from NASA's Innovative

Partnerships Program and by cost sharing by Honeybee Robotics Space Mechanisms

Corporation. The NASA contract with Honeybee for this project was NNK10EA98P. Honeybee

provided to NASA a final contract report HBR Doc No. 249.RPT.001 dated September 2,2010.

Portions ofthat Honeybee report have been incorporated in this document with permission ofthe

authors.

Available from:

NASA Center for AeroSpace Information (CAS!)

7121 Standard Drive

Hanover, MD 21076-1320

(301) 621-0390

National Technical Information Service (NTIS)

5285 Port Royal Road

Springfield, VA 22161-2171

(703) 605-6000

This report is also available in electronic form at URL http://www.sti.nasa.gov/ and

http://ntrs.nasa.gov/search.jsp.

11
1-------------------------------------

Contents

ACKNOWLEDGMENTS II

FIGURES IV

TABLES V

PREFACE 7

INTRODUCTION 8

EXPERIMENTS 8

Percussive Cone Penetrometer 8

Ice/Soil Mixtures 9

Procedure 11

RESULTS 12

DISCUSSION 17

Ice Content 17

Penetration Rate 18

Retracting the Rod 19

SUMMARY OF FINDINGS 19

CONCLUSIONS 20

REFERENCES 21

111
Figures

Figure 1. Honeybee Robotics percussive cone penetrometer. 9

Figure 2. (Left) Ice/soil can. (Right) I-meter column 10

Figure 3. One-meter icy/soil column with final position of penetrometer. 11

Figure 4. Penetration into sample can 12

Figure 5. Penetration depth versus time for sample can #3 13

Figure 6. Downforce versus time for sample can #3 13

Figure 7. Penetration depth versus time for sample can #4 14

Figure 8. Downforce versus time for sample can #4 14

Figure 9. Fractured surface of can #4. Shaft demonstrates depth of penetration 15

Figure 10. Fractured surface of can #5 with 100% water ice 15

Figure 11. Depth of penetration and downforce versus time for I-meter column 16

Figure 12. Top surface of I-meter column with embedded penetrometer rod 17

IV
Tables

Table 1: SoillIce Sample Cans 10

v
This page intentionally left blank.

VI
Preface

Recent data from the Moon, including LCROSS data, indicate large quantities of water ice and other

volatiles frozen into the soil in the permanently shadowed craters near the poles. If verified and

exploited, these volatiles will revolutionize spaceflight as an inexpensive source of propellants and other

consumables outside Earth's gravity well. This report discusses a preliminary investigation of a method

to insert a sensor through such a soil/ice mixture to verify the presence, nature, and concentration of the

ice. It uses percussion to deliver mechanical energy into the frozen mixture, breaking up the ice and

decompacting the soil so that only low reaction forces are required from a rover or spacecraft to push the

sensor downward. The tests demonstrate that this method may be ideal for a small platform in lunar

gravity. However, there are some cases where the system may not be able to penetrate the icy soil, and

there is some risk of the sensor becoming stuck so that it cannot be retracted, so further work is needed.

A companion project (lSDS for Water Detection on the Lunar Surface) has performed preliminary

investigation of a dielectric/thermal sensor for use with this system.

7
Introduction

Data from remote sensing and from the LCROSS mission indicate the existence of vast quantities of

water ice and other volatiles in the lunar regolith, frozen into the permanently shadowed craters near the

poles. This will be game-changing because of the magnitude and importance of such a resource outside

Earth's gravity well. It will be important to ground-truth these findings by putting an instrument into the

lunar regolith to measure the ice content directly. This will be difficult to do with a small-class or

medium-class rover in the low lunar gravity because these platforms will not have adequate weight to

provide the necessary downforce. In the Apollo program, astronauts found it extremely difficult to push

tubes into the dense, frictional lunar soil in 1/6 G. It will be even worse as we take core samples, anchor

onto, and mine asteroids and small moons like Phobos, or mine icy soil on the Moon. Low-force

penetration systems will be mandatory in all these situations.

Prior work by Honeybee Robotics Spacecraft Mechanisms Corporation has shown that percussive

cone penetrometers are capable of penetrating lunar regolith with only a small fraction of the force of an

ordinary penetrometer. This study asks the question whether percussion is a suitable method to insert

instruments into that regolith when it contains various quantities of water ice. We performed preliminary

experiments to measure penetration resistance in lunar soil simulant with varying quantities of water ice.

We also performed a demonstration of percussive penetration into a I-meter deep column of ice and soil

mixtures in layers of varying proportions. One meter is the expected depth to reach the ice beneath the

desiccated upper layers of lunar soil. A companion study (lSDS for Water Detection on the Lunar

Surface) has performed preliminary investigation of a dielectric/thermal sensor that may be inserted into

the regolith by this percussive penetration met~ to positively identify lunar ice. This system combining

the sensor with percussive penetration ha~otential to provide the first-ever ground truth of vast

quantities of dense ice layers in the lunar regolith.

Experiments

The experiments were performed jointly by Honeybee and NASA at the Kennedy Space Center

(KSC). The percussive penetrator was provided and operated by Honeybee Robotics. The mixtures of

lunar soil simulant and water ice were prepared by NASA/KSC. Descriptions of the hardware and

experiments are provided below.

Percussive Cone Penetrometer

Originally we had planned to use both percussion and gas pulsing in the cone penetrometer. Further

analysis ofthe icy soil mixtures indicated that gas pulsing was not an appropriate approach due to the low

permeability of ice-impregnated lunar soil and due to its extremely high mechanical strength. Therefore,

the gas pulsing approach was abandoned. For this effort, we used a percussive dynamic cone

penetrometer originally developed under a separate Honeybee SBIR Phase 1 effort. In the configuration

tested, this device delivers 2.6 Joules of percussive energy per blow at a frequency of approximately

1500-1750 blows per minute. This device was originally designed as a geotechnical instrument: By

driving a cone into soil using a known percussive energy and recording the rate of penetration, soil

strength can be derived. This device is shown in Figure 1.

8
Figure 1. Honeybee Robotics percussive cone penetrometer.

Ice/Soil Mixtures

Lunar soil simulant JSC-1 A was used in this project to represent lunar soil. Carrier et al [1991] have

summarized the geotechnical properties of actual lunar soil without ice. The mechanics of JSC-1A

without ice have been studied by Alshibli and Hasan [2009] and Zeng et al [2010]. The mechanics ofthe

original version ofthis simulant, JSC-1, was reported by Klosky et al [2000]. No data have been returned

from the Moon to indicate the mechanics of the soil with or without ice as it may be found in the

permanently shadowed craters. Gertsch et al [2006] used JSC-1A in ice/simulant mixtures to

experimentally study the resistance to a surface indentor (chipping the surface) and found that resistance

is a strong function of ice content. They reported that ice concentrations of 0.6 to 1.5% by mass behave

like weak shale or mudstone, whereas concentrations of 10.6% behave like strong limestone or sandstone

and thus would be very difficult to excavate. Gamsky and Metzger [2010] used JSC-I A without ice on

shake tables and in ovens and report that iceless regolith in the permanently shadowed craters may be less

compacted than elsewhere on the Moon due to the lack of the strong, localized, diurnal quakes to shake

down the soil and due to the lack of thermal cycling to directly compact it [Chen et ai, 2006]. We are

unaware of any other studies addressing soil mechanics in the permanently shadowed craters. The JSC1A in this study was dried thoroughly in an oven and massed then monitored as it cooled and re-adsorbed

humidity in the laboratory environment. The percent mass of adsorbed water was not significant, so predrying was not performed for further sample preparation. JSC-IA was mixed with water in percentages

ranging between 0% and 8% by mass in 1% increments. The water/simulant mixtures were placed in

layers into six I-gallon cans (paint cans) as shown in Fig. 2 (left). Each can had three layers, the layer

with the greatest moisture content at the bottom. Each layer was tamped to compact it as it was laid

down. The moisture did not migrate significantly from their original layers to the adjacent layers due to

the relative impermeability ofJSC-1A and because they were quickly frozen. Freezing was performed to600 C overnight. The cans were removed from the freezer for testing, and although some warming may

have occurred, it should have been small relative to the freezing point of water due to the large bulk of

frozen material. The cans are described in Table 1. A I-meter tall column, shown in Fig. 2 (right), was

prepared in a similar manner with ten layers. The first and every other layer were dry (0% ice). The

interleaving layers were (from top to bottom) 2%, 4%, 6%, 8% and 10% water ice by mass, as shown in

Fig. 3. It was frozen at -600 C overnight.

9
Figure 2. (Left) Ice/soil can. (Right) I-meter column.

Table 1: SoiVIce Sample Cans.

ID Description Result

Can #1 Three layers oficy regolith, each layer approximately Penetrated all three layers.

6 cm thick, 0%, 1%, and 2% water by weight from

top to bottom.

Can #2 Three layers oficy regolith, each layer approximately Penetrated all three layers, but

6 cm thick, 2%, 3%, and 4% water by weight from more slowly than can #1.

top to bottom.

Can #3 Three layers oficy regolith, each layer approximately Penetrated the 4% layer and

6 cm thick, 4%, 5%, and 6% water by weight from halfway through the 5% layer.

top to bottom. Increased frequency did not

renew progress.

Can #4 Three layers oficy regolith, each layer approximately Penetrated the 6% layer and

6 cm thick, 6%, 7%, and 8% water by weight from halfway through the 7% layer.

top to bottom. Increased frequency did not

renew progress.

Can #5 Pure water ice. Penetrated very quickly.

Can #6 Three layers oficy regolith, each layer approximately Penetrated approximately 5

6 cm thick, 8%, 9%, and 10% water by weight from cm into the 8% layer.

top to bottom.

10
dry

dry

2% Ice

dry

dry

dry

6% Ice

4% Ice

8% Ice

10% Ice

Final rod loc: @5.5cm from edge @5 deg angle

toward center (cone & rod progress toward tube

inside sidewall). Rod chuck end sticking 4 em

above top surface. Contact with side wall at 67cm

depth. Data valid only thru 6% water ice layer.

Oem tube top

no regolith

---- 8.6 + 1.2cm Top of JSC-la

} 7.7cm thick layer JSC-1a

,---- 16.3 + 1.2cm

} 9.6cm thick: 5.5kg JSC-1a+O.llkg H20

---- 25.9 + 1.2cm

} 7.9cm thick layer JSC-1a

---- 33.8 + 1.2cm

} 1O.7cm thick: 5.5kgJSC-1a+O.22kg H20

---- 44.5 + 1.2cm

} 9.1cm thick layer JSC-1a

---- 53.6 + 1.2cm

} 1O.9cm thick: 5.5kgJSC-1a+O.33kg H20

---- 64.5 + 1.2cm

} 8.7em thick layer JSC-1a

---- 73.2 + 1.2em

} 10.4cm thick: 5.5kg JSC-1a+o.44kg H20

---- 83.6 + 1.2em

} 8.2cm thick layer JSC-1a

---- 91.8 + 1.2cm

} Hem thick: 5.5kg JSC-1a+0.55kg H20

l04cm inside -- Bottom of JSC-1a

~p 3.5cm from bottom

---.::L.

4cm

rtI_

.- ..c. "0 u

E.::

u

'-"00

O_. I

N

Figure 3. One-meter icy/soil column with fmal position of penetrometer.

Procedure

The cone penetrometer was held as shown in Fig. 4 with the cone tip touching the sample can. On

some occasions, an effort was made to push it into the icy regolith without percussion but with moderate

downforce provided by the operator. For all samples, percussion was activated, providing 2.6 Joules per

blow at about a 15 Hz repetition rate. Each can was penetrated using only the 61.7 N weight of the

penetrator for downforce or sometimes using additional downforce provided by the operator pushing

down on the penetrometer's handles. In each case the can was sitting on an Acculab electronic mass

scale, which provided a measurement ofthe downforce. Each penetration event, including the reading of

the mass balance, was video recorded. The rate of penetration was obtained post-test by observing the

length indicators on the shaft ofthe penetrator as they entered the ice/simulant mixture.

11
Figure 4. Penetration into sample can

Results

Penetration into cans #1 and #2, which had ice contents between 0% and 5% by mass, was not

difficult. The percussive penetrator made progress under its own weight. The speed of penetration

decreased as the percent water content increased.

In the case of can #3, the percussive penetrator acting under its own weight achieved a maximum

depth of 7.5 cm, passing through the top layer and some portion of the second layer before progress

halted. The top few centimeters of icy regolith was broken into chunks as the cone passed through it.

Increasing down force was then applied by the operator. No further progress beyond this was possible

with only operator applied weight. Video shows that the sheet metal top surface of the mass scale was

vibrating in response to the sample can. It is possible that this motion rendered the percussive cone less

effective by absorbing some ofthe percussive energy. To investigate this, the can was moved to the floor

next to the scale. The percussive cone was operated with a large down force applied from 2 people

amounting to about 750 N. There was a small, barely perceptible additional penetration. This was also

tried with the can back on the scale to measure the load with no further cone penetration noted.

Penetration into the third layer, 6% ice, was not achieved. Figure 5 shows the depth versus time profile

for can #3, obtained from post-test video analysis. Figure 6 shows the downforce versus time profile.

12
--------------

Percussive Cone 4,5,6% Ice JSC-la

a

-1

-2

E

-3

-4 c

·5 o

u

-6

-7

-8

20 40 60 80 10

\.

------ -

o

-ConeDepth

-4%lceJSC-1a

- S%lceJSC-1a

TIme to Depth (sec)

Figure 5. Penetration depth versus time for sample can #3.

Down Force (kg @lG)

::4 + +-.::~~::.::_-_-_-_-_~_c _

t---~ o 20 40 60 80 100

Figure 6. Downforce versus time for sample can #3.

Can #4 performed similarly to can #3. The cone acting only under its own weight penetrated the first

layer at 6% ice and a portion of the second layer at 7% ice. Additional down force was applied

momentarily at ~300 seconds to see if further progress could be made. Minor additional penetration was

achieved. After this the percussor frequency was increased to maximum without significant added

penetration progress. Video shows that the sheet metal top surface of the mass scale was vibrating in

reaction to the sample can. It is possible that this motion rendered the percussive cone less effective by

absorbing some of the percussive energy. Figure 7 shows the penetration depth versus time for can #4,

and fig. 8 shows the downforce versus time. Figure 9 shows the fracturing ofthe sample's surface.

13
Percussive Cone 6,7,8% Ice JSC-la

0-.-------,--,-----,-------,--,------,--,---,

-1 .-_~c._&_n-~'n'*l',nl___--1-<>'C'G-lOO 25 n '00 350-400

-2 +--------------------

E -3 ~I\<------------------

-4 -t-'lr-------------------

'5 '-....

-5 +--""""''''______.=-----------------

-6 +----------""....... ,-------------

u -7 -1--------''''''----===;;;;;:=-----

-8 +----------------.........--=-_=-- - -9 +--------------------

-10 .1.- _

TIme to Depth (sec)

Figure 7. Penetration depth versus time for sample can #4.

-Cone Depth

-6%lceJSC·la

-7%lceJSC-la

Down Force (kg @lG)

:: j

a so 100 150 200 250 300 350 400

Figure 8. Downforce versus time for sample can #4.

14
-------------------------------------- - --------------------

Figure 9. Fractured surface of can #4. Shaft demonstrates depth of penetration.

In the case of can #5 with 100% water ice (no simulant), the penetrator fractured the ice, and the

resulting large pieces moved apart or slid past each other as the cone moved deeper into the target. The

cone penetrated to the bottom of the can much more quickly than it had penetrated the different mixtures

that contained lunar soil simulant. Figure 10 shows the fractured surface of can #5.

Figure 10. Fractured surface of can #5 with 100% water ice.

15
------------

In the case of can #6 with 8% and higher water ice, the cone penetrated the surface but it did not do so

by fracturing the top layer of icy regolith into chunks as before. The hole that the cone created in the icy

regolith had very clean sides. Powdered material was observed on top ofthe target's original surface, and

this powdered material could be brushed aside to reveal the original surface. From this, we infer that the

cone was pulverizing icy regolith and ejecting it from the resulting borehole though the force of its own

vibration. When the borehole became too deep for the pulverized material to be ejected, progress came to

a halt.

For the I-meter column, the cone penetrated its entire length to a depth of 90.7 cm. The rate of

penetration varied, and was observed to correspond with the layering as shown in Fig. II, where the

slopes ofthe fitted linear segments are the penetration rates. The 8% slope is not valid since the cone was

on the container sidewall and the container was splitting, relieving the soil's stress. However, the

penetrator did not maintain a straight vertical path, and struck the side of the column 67.2 cm below the

surface, or 2.6 cm into the 8% layer. We were unable to extract the penetrator from the frozen soil after

driving it in to its full depth. Figure 12 shows the top surface (unfractured) with the rod still embedded in

the icy regolith after the percussive penetrometer was de-attached.

-1 -Cone Penetration

--Layer-1 (Drf JSC-1a) y = -U.3~ IIx - lS.~ 114

-Layer-2 (2%lce JSC-1a)

-I <'lypr-~ (Dry JSC-1 <1)

-Layer-4(4%lce JSC-Ia)

y= -O.1343x-19.434

-Layer-5(Drf JSC-Ia) III

u

.::::.. -Layer-6 (6%lce JSC-1a) III

....

v --Layer-7(Dry JSC-1a) III

.~- --Layer-8 (8%lce JSC-1a)

E y = -0.0463x - 38.04 u -Layer-9(Drf JSC-Ia)

-

Co -Layer-IO (lO%lce JSC-la) III

0

III -Down Load Kg@ IG c

0

u -4%lceSlope

--6%lceS ope

--8%lccS ope

-2%lceSope

--Linear (4%lceSlope)

--Linear (6%lceSlope)

--Linear (8%lceSlope)

Time to Depth (Seconds)

Figure 11. Depth of penetration and downforce versus time for I-meter column.

16
Figure 12. Top surface of I-meter column with embedded penetrometer rod.

Discussion

Ice Content

In general we find as expected that, in the range of 0% to 10% ice content by mass, the greater ice

content is more resistant to penetration. However, it is interesting that the top layer of can #4 with 6% ice

could be penetrated, whereas the second layer of can #3 with only 5% ice could not be penetrated. Thus,

we found that it is not simply the percentage of ice that matters, but whether the fracturing ice has room to

move into the surrounding volume. In the case of top layers, there was always room at the free surface

for fractured chunks of ice to move upward. In the second and deeper layers ofthe cans, the ice could not

always fracture and move. Thus, a lower percentage of ice at depth could resist penetration whereas a

higher percentage of ice at the surface could not.

The mechanics are apparently different than the case of penetration into dry regolith. Dry regolith is

free to rearrange at the grain-scale to make room for the penetrator. The strain field of cone penetration

into ordinary, terrestrial sands and soils has been studied in detail (see for example [Tumay at aI, 1985]

and [Acar and Tumay, 1986]), indicating soil motion (of decreasing amplitude) at long distances from the

cone. Furthermore, comminution of the individual grains allows their material to move into the pore

spaces between other grains, increasing the bulk density of the material around the penetrometer to make

the room. For frozen soils, however, the grains cannot move individually, and comminuted material may

not be able to move into pore spaces between neighboring grains. Therefore, to make room for a cone

and rod, the frozen soil must exhibit a combination of pulverization with powder removal and fracturing

with relative motion ofthe fractured domains. As long as the cone is near the surface of the icy regolith,

powder could exit the downshaft around the sides of the rod, and likewise near the surface the fractured

domains could move upward above the free surface ofthe sample.

17
-- ---------

For the small sample cans with three layers of icy/soil mixture, when the ice content was sufficiently

high the cone could not penetrate through the second layer because it was trapped between the overlying

and underlying frozen layers. For sample cans #1 and #2 this was not a problem. Presumably the low ice

content did not stop the soil from deforming at the grain scale to densify within each layer, or to push into

the neighboring layers that then deformed at the grain scale to absorb the additional volume of material.

Therefore, it appears that the transition in penetration mechanics occurs somewhere in the range of 3% to

5% ice content by mass.

For sample can #5 with 100% water ice, the soil did fracture but was able to rearrange all the way to

the bottom of the can, permitting the penetrator to reach the bottom. Apparently, the ice has less friction

than an ice/regolith mixture, and thus the fractured chunks even deep in the can are able to push the

fractured chunks above them out ofthe way.

For the case of the I-meter column, the fractured domains could make room by expanding into the

interleaving dry layers of regolith. A fractured domain expanding into neighboring space would

presumably experience more resistance if it were moving into dry regolith than if it were moving into

empty space above the free surface of the sample, as was the case with the top layers of the smaller

sample cans. However, the dry regolith did not produce enough resistance to stop this penetration as

evidenced by the cone passing successfully through layers of up to 10% ice. To make room for adjacent

fractured domains, the dry regolith layers must have densified through the ordinary processes discussed

above for cone penetration. However, in this experiment only half the volume of the column was dry

regolith whereas the other half was icy. Half the domain must have been adequate to absorb the full

volume ofthe penetrating cone and rod.

Based on these results, it is likely that bulk volumes of greater than 4-6% ice (by mass) will be

resistant to percussive cone penetrometers unless a method is developed to remove pulverized material.

Fortunately, the instrument that will go onto the cone, which is being developed in the companion project,

is capable of detecting and measuring ice content at concentrations less than these values. Also, since the

percussive penetrometer can always penetrate at least the top few centimeters of material higher than 4-

6% (since the fractures can expand upward into the material that has less ice), the system is guaranteed to

enter at least that concentration of ice even if no modifications are made. If the lunar ice lies beneath a

meter of desiccated soil, or soil that contains less than 4-6% ice, or layers less than a few centimeters

thick of any concentration interleaved by layers less than 4-6% ice, then the system will successfully pass

through it to the bulk quantities of more concentrated ice. In any case, when it finds the bulk ofthe more

concentrated ice, it should penetrate several centimeters. Therefore, the delivery method appears to be

successful but with room for increased performance.

Penetration Rate

The penetration rate was not a strong function of downforce. In most cases it was a strong function

only of the ice content. Therefore, penetration rate may serve as a useful secondary measurement of ice

content to corroborate what is measured by the primary instrument. By comparing the primary

instrument's [mdings with the penetration rate, it may also be possible to back out information about the

compaction of the soil and thus the volume of pore space not occupied by frozen volatiles. This may

support analysis of the permeability of the regolith and modeling of ice stability and transport

mechanisms.

It makes sense that penetration rate would be dependent on ice content. The ice must be fractured or

pulverized to permit movement of material to admit the cone. The more volume ice there is bonding the

soil grains together, the more energy that must be expended to break those grains apart. Thus, more

percussive blows are needed to free equivalent volumes of regolith when there is more ice. Penetration

could be sped up by increasing the percussion rate, but (as seen with can #4) ifthe blows are incapable of

moving material, then increasing their frequency will not restore motion.

18
On the other hand, toward the bottom of the I-meter column, increased downforce did help

penetration (see "Download" curve on Fig. 11). This might be because the fracturing ice layers deep in

the column needed to be mechanically pushed into the neighboring volumes of dry regolith. Because the

large chunks would be moving dry regolith far away from the percussing cone, their motion relied upon

the direct downforce. Thus, there is additional information available by analyzing both downforce and

penetration rate together that may indicate the structure of ice layers beneath the surface.

Retracting the Rod

In the one test with the I-meter column, the rod could not be retracted. This may have been due to

the fact that the rod became bent as it struck the wall of the column, but other factors may have

contributed. For example, the base diameter of the cone is larger than the diameter of the rod, and

compacted JSC-I a can exert high friction on a rod that has been driven into it. There is also some

concern that ice could freeze to the cone or shaft. The instrument on the cone will have a heater element

to enable volatilization ofthe ice as a part of measuring its concentration. The heater element could serve

a secondary function of de-icing the regolith around the cone or shaft to help free it. Also, the team has

indentified mechanical changes to the design ofthe system to enable easier retraction.

Summary of Findings

1. A percussive cone can penetrate icy regolith at ice concentration layers that a static cone cannot

penetrate. The percussive penetrator was able to penetrate material under 65 N of downforce

that the static cone could not penetrate under full body weight.

2. The percussive cone could penetrate:

a. 100% water ice (-60 C);

b. dry soil that is compacted and cold (-60 C);

c. ice/soil mixtures up to 4-6% ice by weight (note that 5% ice is more resistant than 100%

ice) with much less resistance than non-percussive;

d. mixtures with 6% and 8% ice as long as there is a free surface above the layer to allow

the icy chips room to move;

e. a little more than a cone-length into the top surface of mixtures that have 8% or more ice;

f. completely through layers of 8% ice as long as they are interleaved with dry layers to

allow the icy chips room to move.

3. These percentages of ice are within the range that can be detected by the sensor developed in the

companion project, "ISDS for Water Detection on the Lunar Surface." Therefore, the system

is capable of penetrating deeply enough into the regolith to detect ice.

4. The ability of a percussive cone to displace material affects its ability to penetrate material. The

device proved capable of penetrating material with 8% ice, but did not penetrate very far

because it could not displace the resulting chip. A certain amount of material must be displaced

for the cone to advance.

5. Increased downforce on the percussive system did not result in increased penetration capability.

In hard material, the percussive penetrator made no more progress under 750 N than it did

under 65 N. This suggests that increasing the energy delivered in each percussive blow would

be a more effective than increasing downforce for penetrating stronger materials. When the ice

19
is too dense, pushing harder will not make it penetrate. The percussive system either

penetrates or doesn't.

6. There may be cases with layers of ice interleaved by dry regolith in which increased downforce

helps move the fractured ice and thus increases penetration rate, but this condition is not the

baseline expectation for lunar regolith. If such a condition does exist on the Moon, then it can

be detected by measuring both penetration rate and downforce to corroborate other instruments

on the cone.

7. A percussive cone can become stuck in frozen regolith. For anchoring, this is beneficial. A rod

driven in under 65N (15 Ibs) of downforce could not be pulled out with at least that much

force. For repeated probing, this must be addressed.

Conclusions

This investigation successfully demonstrated percussive penetration of regolith with varying ice

concentrations. It demonstrated that percussive penetration is feasible in situations where non-percussive

is not. It successfully demonstrated penetration to a meter in depth, which is the expected depth to lunar

ice. It demonstrated that the device is capable of entering ice concentrations that are easily within the

measurement range of instruments that will go on the cone. This serves as experimental proof-of-concept

ofthe critical function, and so percussive insertion of lunar ice instruments has now achieved Technology

Readiness Level 3.

The experiments developed preliminary correlation data between penetration rate and ice content, and

thus the data from the penetration process can be used to corroborate the findings of another sensor. This

project also produced insights into the mechanics ofthe penetration resistance of ice and ice/soil mixtures.

It provided an opportunity to develop and test methods to prepare ice/soil mixtures for mechanical testing.

It provided insights into how to improve the test stands and hardware. It also indicated a number of

modifications that may be made to improve the penetration system, which will be the subject of on-going

projects.

20
References

Acar, Yalcin B., and Mehmet T. Tumay (1986). "Strain Field around Cones in Steady Penetration," J.

Geotech Eng 112 (2), 207 - 13.

Alshibli, Khalid A., and Alsidqi Hasan (2009), "Strength Properties ofJSC-IA Lunar Regolith Simulant,"

J. Geotech. and Geoenvir. Engrg. 135 (5),673-679.

Carrier, W. David, III, Gary R. Olhoeft and Wendell Mendell, "Physical Properties ofthe Lunar Surface,"

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

eds., (Cambridge University Press, Melbourne, Australia, 1991), pp. 475 - 594.

Chen, K., J. Cole, C. Conger, J. Draskovic, M. Lohr, K. Klein, T. Scheidemantel and P. Schiffer

(2006), "Granular materials: Packing grains by thermal cycling," Nature 442, 257.

Gamsky, Jacob N., and Philip T. Metzger (2010), "The Physical State of Lunar Soil in the Permanently

Shadowed Craters ofthe Moon," paper presented at Earth and Space 2010, 12th Biennial ASCE

Aerospace Division International Conference on Engineering, Construction and Operations in

Challenging Environments, Honolulu, HI, Mar. 14-17,2010.

Gertsch, Leslie, Robert Gustafson, Richard Gertsch (2006), "Effect of water ice content on excavatability

of lunar regolith," paper presented at Space Technology and Applications International ForumSTAIF 2006, AlP Conference Proceedings, vol. 813 (AlP, Melville, NY), pp. 1093-1100.

Klosky, J.L., S. Sture, H.-Y. Ko, and F. Barnes (2000), "Geotechnical behavior ofJSC-l lunar soil

simulant," J. Aerospace Eng. 13 (4), 133-138.

Tumay, Mehmet T., Yalcin B. Acar, Murat H. Cekirge, and Narayanan Ramesh (1985), "Flow Field

Around Cones in Steady Penetration," J. Geotech Eng 111 (2), 193 - 204.

Zeng, Xiangwu, Chunmei He, Heather Oravec, Allen Wilkinson, Juan Agui, and Vivake Asnani (2010),

"Geotechnical Properties ofJSC-l A Lunar Soil Simulant," J. Aerosp. Engrg. 23 (2), 111-116.

21
REPORT DOCUMENTATION PAGE

1

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1. REPORT DATE (DD-MM-YYYY) 12. REPORT TYPE 13. DATES COVERED (From- To)

Final June 2010 - Sept. 2010

4. TITLE AND SUBTITLE Sa. CONTRACT NUMBER

Low Force Icy Regolith Penetration Technology N/A

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S) 5d. PROJECT NUMBER

P. T. Metzger, G. M. Galloway, and J. G. Mantovani (1) 5e. TASK NUMBER

K. Zacny and J. Craft (2)

Sf. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION

(1) NASA Kennedy Space Center, FL 32899 REPORT NUMBER

(2) Honeybee Robotics, Inc., 460 W. 34th Street, New York City, New

York 10001

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Unclassified - Unlimited Distribution: Standard

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Availability: Publicly Available STI

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14. ABSTRACT Recent data from the Moon, including LCROSS data, indicate large quantities of water ice and other volatiles

frozen into the soil in the permanently shadowed craters near the poles. If verified and exploited, these volatiles will

revolutionize spaceflight as an inexpensive source of propellants and other consumables outside Earth's gravity well. This

report discusses a preliminary investigation of a method to insert a sensor through such a soiVice mixture to verify the

presence, nature, and concentration ofthe ice. It uses percussion to deliver mechanical energy into the frozen mixture,

breaking up the ice and decompacting the soil so that only low reaction forces are required from a rover or spacecraft to push

the sensor downward. The tests demonstrate that this method may be ideal for a small platform in lunar gravity. However,

there are some cases where the system may not be able to penetrate the icy soil, and there is some risk ofthe sensor becoming

stuck so that it cannot be retracted, so further work is needed. A companion project (ISDS for Water Detection on the Lunar

Surface) has performed preliminary investigation of a dielectric/thermal sensor for use with this system.

15. SUBJECT TERMS

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