The theme of this workshop is lunar resource assessment. Topics include identification, quantification, and location of useful elements on and below the lunar surface. The objective of this paper is to look at another side of the issue--how to remove soil from the stiff lunar-soil matrix once useful deposits are located. The goal of this paper is to cause those who think that digging or excavating on the Moon is a trivial problem to rethink the reasons for their opinions. Another goal is to encourage them to view total reliance upon terrestrial heuristics with suspicion. This paper will focus primarily upon digging

Boles, Walter W.

English

NASA Technical Reports Server

12 Netu Technologies for Lunar Resource Assessment
cures. The LIBS pulses may impart sufficienc energy inco the ground
to also serve as seismic sources. The following table summarizes
the estimated instrument gross specifications.
TABLE 1. Instrument summary.
LIBS XRF/XRD MS Geophys Total
Mass (kg)
Average regu-
lated power (W)
Data rate (bits/s)
30
i
1 M
10
10
10k
20
35
40k
20
20
50k
80
72
1.1 M
The TOPLEX operates in a mobile, exploration-and-sample
acquisition mode during the lunar day and in a stationary, sample-
analysis mode during the lunar night. The rover vehicle that carries
the instruments is estimated to mass 100 kg and require 25 W
of average power. Vehicle requirements/specifications include the
following: Range - 200 km; maximum speed - 500 m/hr; com-
munications - high-gain antenna and data rate consistent with
teleoperation; endurance - 4 to 6 months; and must be self-
deploying from the lunar lander. In addition, the rover will have
stereoscopic vision with zoom and selectable band filtering, and
a robotic arm for sample acquisition, preparation (i.e., powdering),
and conveyance to appropriate instruments.
References: [ 1 ] Cremers D.
 and Kane K. (1992) LPSC XXIII;
this workshop. |2] Vaniman D. et al. (1991) LPSC XX//, 1429-
1430; this workshop. [3)Perrin R. (1992) personal communication.
|4] Becker A. et al. (1992) personal communication.
N 9 3 - 1 7 2
DRILLING AND DIGGING TECHNIQUES FOR THE
EARLY LUNAR OUTPOST. Walter W. Boles, Department
of Civil Engineering, Texas A&.M University, CoHege Station TX
77843-3136, USA.
Introduction: The theme of this workshop is lunar resource
assessment. Topics include identification, quantification, and loca-
tion of useful elements on and below the lunar surface. The
objective of this paper is to look at another side of the issue—
how to remove soil from the stiff lunar-soil matrix once useful
deposits are located.
The author has been involved with the study of digging and
excavating on the Moon for several years. During that time he
has overheard some disturbing comments such as the following:
"We know what works best here [on the Earth). Just make the
systems such as power and thermal control work in the lunar
environment and the machine will work well on the Moon."
"Just send something up there that looks like a front-end loader
with a back hoe. It will work. Don't worry about it."
Comments such as these are disquieting, to say the least, because
even if a machine's subsystems- are designed to operate well in
the lunar environment, it may still perform its tasks poorly. Also,
one cannot assume that the operational characteristics of terres-
trial machines, based upon terrestrial heuristics, will be similar
to machines operating on the Moon. Finally, due to the suspect
accuracy of terrestrial soil-tool interaction theories, one cannot
justifiably argue that these theories can be used along with ter-
restrial heuristics to make accurate predictions of the performance
of various excavating methods on the Moon. The need is great,
therefore, for quantitative and verifiable evidence of the perfor-
mance of various digging methods. This evidence is necessary for
the confident selection of appropriate methods for further research
and development.
The goal of this paper is to challenge comments such as those
mentioned above and to cause those who think that digging or
excavating on the Moon is a trivial problem to rethink the reasons
for their opinions. Another goal is to encourage them to view
total teliance upon terrestrial heuristics with suspicion. This paper
will focus primarily upon digging since another paper will focus
primarily upon drilling.
Lunar Soil: Much is known about the lunar soil. The char-
acteristics of interest here, however, are those that tend to make
the soil difficult to excavate. The soil is composed of very angular,
abrasive, fine-grained particles that have re-entrant corners. As
a result, they tend to cling to each other. The soil matrix is very
loose (lov> density) at the surface and is very hard (high density)
at relatively shallow depth. It is believed that the soil approaches
90% to 100% relative density at a depth of approximately 0.7 m.
Additionally, it is reasonable to assume that rocks and boulders
will be encountered in any digging activities. The regolith has been
described as a dense, interlocking soil matrix [ 1 ].
The lunar soil, therefore, will be very difficult to penetrate below
about 0.5 m. Penetration of blades, scoops, and cutters will require
crushing and shearing of many soil particles since the soil nears
100% relative density at shallow depth. This crushing and shearing
action requires high forces. Encounters with rocks and boulders
will serve to make a difficult situation worse. Expected perfor-
mance of traditional terrestrial methods, therefore, is low.
Lunar Experience: During the Apollo missions, hollow stems
were augered into the lunar soil. The first attempts were only
able to drill to about 1.5 m. This was due to discontinuous auger
flights at splice locations on the stem. It is assumed that the soil
particles seized the stem at the joint and caused the stem to fail.
On later missions the stem was redesigned with continuous auger
flights and depths of approximately 3 m were reached. The rate
of penetration, however, had to be kept low since the stem would
tend to screw itself into the soil and was difficult to remove 11) .
There are two major problems regarding drilling. The first one
is the removal of cuttings. The second one is cooling of the drill
bit. Both these problems are usually solved on the Earth with
fluids. The use of fluid to remove cuttings and cool the bit is
obviously a problem on the Moon.
Shoveling on the Moon was relatively easy in. the top 10 to
I 5 cm. Below this depth the shoveling became very difficult. Also,
hammer tubes were driven to a depth of approximately 0.7 m
before the resistance became too great [1). It is interesting that
this depth corresponds well with the depth at which the regolith
is assumed to approach 90% to 100% relative density. In summary,
these limited data tend to verify data in the previous section. It
also tends to confirm that digging in the lunar regolith will be
very difficult.
Excavation Methods: Typical terrestrial excavation methods
include bulldozers, hoes, shovels, scrapers, draglinesr bucket-wheel
excavators, and continuous miners with rotating cutting heads.
All these methods depend heavily upon gravity to generate down-
ward and horizontal fotces. These forces are necessary for the
machines to perform well. With the gravity of the Moon approx-
imately one-sixth that of the Eatth's, one can expect a corre-
sponding decrease of the machines' performance. For example,
the maximum productivity of a 15,000-lb bulldozer on Earth, over
a 100-ft haul distance, is approximately 100 ydVh. On the Moon,
https://ntrs.nasa.gov/search.jsp?R=19930008048 2020-03-24T07:24:53+00:00Z
LPI Technical Refxm 92-06 13
TOTAL FORCE
Fig. 1. Balovnev's model.
however, with appropriate efficiency factors (2) and an assumed
one-sixth reduction due to the reduced gravity, the output may
plummet to only 2 or 3 yd3/h. This seems ridiculously low for
a 15,000-lb machine. Compounding this problem of low produc-
tivity is a size and power constraint. Machines that will actually
be in use on the Moon will probably have about as much capability
and mass as the average riding lawn mower.
Every suggested method the author has seen in print is based
upon terrestrial methods. It is the author's opinion that these
methods will prove to be very limited in performance and ca-
pability. This implies that total reliance upon terrestrial methods
is unwise, and innovative methods must be found that will perform
well on the Moon.
Soil-Tool Interaction Theories: Most soil-tool interaction
theories were developed for soil-tillage applications and focus upon
draft or drawbar-pull forces. They do not consider penetration
or vertical forces. Verification testing was typically conducted in
soft soils. The models were developed assuming the soil to be
uniform with fluid properties. The models were also developed
for small tools such as tines [3-6).
One often-quoted reference of a bulldozer model is by Balovnev
17). This model looks only at drawbar forces and attributes the
total drawbar force required to four factors—dragging of the soil
prism in front of the blade, friction between the blade and soil,
bending of the soil layer, and break-out of the soil at the cutting
edge. Bending of the soil layer is assumed to be negligible. These
forces are as indicated in Fig. 1. There is no gravity factor in the
model. Soil weight is a factor, however. If one reduces the soil
weight appropriately and uses reasonable estimates of other factors
such as an angle of internal friction of 45°, one sees that ap-
proximately 90% of the total force required is due to break-out
forces while other frictional forces represent only about 10% of
the total force required. This result is quite revealing because it
again tends to verify that penetration of blades or cutting devices
into the lunar soil will require high forces.
Current Research: The author is aware of research con-
ducted at several universities. Studies at the University of Mary-
land found that the compacted lunar soil simulant was very difficult
to penetrate [8]. The difficulty was so great with the testing
equipment available that explosive methods were investigated in
order to loosen the soil so that excavation coulckbe performed.
Research is currently underway at the University of Colorado.
The author has not seen published results of this research. He
believes, however, that this research involves the use of vibration
to reduce penetration forces.
Research at Texas A&.M University is focusing on small-scale
experiments to enable more accurate predictions of excavating
forces and productivities to be encountered on the Moon for
various digging methods. The objective of the testing is to compare
traditional as well as innovative methods in terms of certain
measures of merit such as low forces, high productivities, and low
power. The testing device, as depicted in Fig. 2, will be small so
that verification testing can be conducted on board NASA's KC-
135 airplane to simulate the Moon's gravitational field. Once
testing is complete, a better understanding of the expected per-
formance of different digging methods will promote the selection
of promising methods for further development.
One particularly interesting method that is being investigated
involves the use of a rotary wire (or wirelike) brush for excavation.
The concept was first proposed by the Army Corps of Engineers
(9). It was intended to sweep up loose regolith that was assumed
to lie on top of a smooth rock surface. The importance of this
concept, however, lies in its ability to excavate the dense lunar
soil matrix and it may prove to have advantages over methods
that require penetration of an implement into the stiff lunar soil
matrix.
High penetration forces, for example, will not be required since
the bristles will remove soil particles from the surface. As soil
particles are removed, other particles are exposed and removed
by subsequent bristles. This may be a major advantage since, as
indicated previously, break-out forces may represent 90% of the
forces required. The method may also prove to be relatively rock
tolerant since the bristles will deflect over rocks and not become
immobile when rocks are encountered. This may make the device
relatively easy to automate. The device may also be designed to
collect soil particles up to a certain size depending upon stiffness
of the bristles. This has obvious advantages for subsequent pro-
cesses that would otherwise require sifting or crushing to achieve
a small grain-size distribution. Preliminary indications are that the
wire-brush method will also be much more productive than tra-
ditional methods. Disadvantages of the method may include high
rates of wear, high power consumption, and difficulties in collecting
the ejected soil particles. The generation of dust may also be a
problem to overcome.
Rotation Capability c=c>
Implement c=>
Fig. 2. Test apparatus.
14 New Technologies for Lunar Resource Assessment
Conclusions: It is the author's opinion that there has been
too much dependence upon terrestrial heuristics in suggesting
digging methods for the Moon and not enough attention to basic
forces, required mass, required power, and expected production
rates. Progress toward more basic research is being made, however.
Results of work at the University of Colorado and Texas A&.M
University will prove important for the selection of efficient
metltods. Short-term results at Texas A&.M University are
expected to reveal quantitative and verifiable evidence as to which
methods are more promising. Long-term results are expected to
include candidate methods for prototype development and testing.
Acknowledgments: This research is funded by a grant from
the Texas Higher Education Coordinating Board's Advanced
Research Program.
References: [1] Carrier W. D. Ill et al. (1991) In Lunar
SmiTcebook (G. H. Heiken et a!., eds.), Cambridge Univ., New
York. (2) Caterpillar Tractor Co. (1991) Caterpillar Performance
Handbook, 22nd edition, Caterpillar Tractor Co., Peoria. [3] Het-
tiaratchi D. R. P. and Reece A. R. (1966) J. Ag. Eng. Res., I),
89-107. 14] Godwin R. J. and Spoor G. (1977) J. Ag. Eng. Res.,
22, 2 1 3-228. [5] McKyes E. and Ali O. S. (1977)7. Terramecfianics.
14, 43-58. |6] Perumpral J. V. et al. (1983) Trans. ASAE, 26, 991-
995. |7J Balovnev V. I. (1983) New Methods for Calculating Resist-
ance to Cwting of Soil, Amerind Publishing, New Delhi, India.
[8] Bernold L. and Sundareswarean S. (1989) Proceedings of
One-Day Seminar on Planetary Excavation, Univ. of Maryland.
[9J Department of the Army Corps of Engineers (1963) Lunar
Construction, Vol. 2. NASA DPR W-l 1430, Washington, DC.
N 9 3 - 1 7 ^
SHOCK-TREATED LUNAR SOIL SIMULANT: PRELIMI-
NARY ASSESSMENT AS A CONSTRUCTION MATE-
RIAL. Mark B. Boslough1, Leonhard E. Bernold2, and Yasuyuki
Horie2, 'Sandia National Laboratories, Albuquerque NM 87185,
USA, 2North Carolina State University, Raleigh NC 27695, USA.
In an effort to examine the feasibility of applying dynamic
compaction techniques to fabricate construction materials from
lunar regolith, we have carried out preliminary explosive shock-
loading experiments on lunar soil simulants. Analysis of our shock-
treated samples suggests that binding additives, such as metallic
aluminum powder, may provide the necessary characteristics to
fabricate a strong and durable building material ("lunar adobe")
that takes advantage of a cheap base material available in abun-
dance: lunar regolith.
Introduction: Because of transport cost considerations, it is
clear that the vast majority of construction material for lunar
structures must be indigenous. The most readily attainable material
on the Moon is regolith, so an obvious question is: What is the
easiest method of converting lunar regolith to a construction
material?
One technology that has been used to modify materials involves
the use of shock treatment |1,2). The principal concept relies on
exerting an extremely high dynamic force on a certain base
material that is mixed with an agent and thus changes its prop-
erties. If such a process could be emulated on the Moon, new
soil-based "lunar adobe" construction materials could be created.
Although this technology has been proven on Earth, research is
needed to study the feasibility of such an approach under lunar
conditions and to evaluate the consequences on the design, engi-
neering, and construction of lunar bases.
Experimental: We have performed two shock recovery exper-
iments on samples of a lunar soil simulant. These experiments
made use of the Sandia "Momma Bear" explosive loading fixtures
to achieve well-characterized shock states. These recovery fixtures
allow samples to be shocked in a controlled, reproducible manner.
A planar shock wave is generated by detonating a high-explosive
lens next to an explosive pad. The shock wave passes through
an iron pulse-forming plate and into the copper fixture, which
contains the 5 cm3 powder sample. The entire assembly has
cylindrical symmetry. Because of the large impedance difference
between the sample and copper, and the finite lateral extent of
the sample, the shock loading is not a simple, one-step uniaxial
process. On the contrary, the initial loading is due to a radially
converging shock wave, and the final shock state at a given position
is reached by a series of shocks.
Shock pressure and temperature histories were determined
numerically by two-dimensional computer simulations [3,41- These
calculations are based on the geometry of the sample holder, the
type of explosive, and the initial packing density of the powder
(in general, the lower the packing density, the higher the shock
temperature as long as nothing else is changed). The two exper-
iments for the present study made use of the explosive Baratol,
and the peak shock pressure range was 510 GPa, with the peak
pressure a function of position within the sample.
For the first experiment (13B917) the sample was "Minnesota
Simulant" Lot 2, with particle size between 50 and 100 mesh,
and a mean initial powder density of 1.896 g/cm3. The second
experiment (14B917) made use of the same, simulant, with an
admixture of aluminum metal; CERAC A-1189, 99.99% pure with
a particle size less than 325 mesh. The mean initial powder density
of the mixture was 2.051 g/cm'. The material used in these
experiments was intended to simulate the crystalline fraction of
basaltic lunat regolith. The simulant was taken from the fine-
grained basalt of the Duluth Complex, Minnesota, and was pro-
vided by P. W. Weiblen [5].
Results: Macrocracking was only observed in the sample with
aluminum binder. It is possible that the cracking was created during
the postshock handling of the compacts. The samples appear to
have been compacted to densities in the range from 70 to 85%,
but they had very little mechanical strength. However, strong
metallurgical bonding of nonmetallic powders by weak shock in
the peak pressure range of 5-10 GPa cannot be expected. A rough
estimate of the threshold pressure required for shock consolidation
is twice the Vickers microhardness of the solid materials. Thus,
without the use of binding additives, several tens of GPa are
required to consolidate lunar simulants.
TABLE I. Impression tests of lunar material.
Sample
Lunar
#2-1
Lunar
#2-2
Lunar
#2-3
#2/Al
Binder
dec
"I
IMPaj 1C n'
|MPa)
 02% 0.5% UYP LYP [MPa| (MPa)
1057 37.5 36.5 38 36.7 54.9 0.077 494 0.945
1078 58.2 60.3 58.2 58.2 73.8 0.093 396 0.904
1329 54.3 52.5 56.4 52.4 67.2 0.064 388 0.810
8957 175 207 - — 210.6 0.032 5021 0.971


Drilling and Digging Techniques for the Early Lunar Outpost

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