In an effort to examine the feasibility of applying dynamic compaction techniques to fabricate construction materials from lunar regolith, preliminary explosive shock-loading experiments on lunar soil simulants were carried out. 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 abundance: lunar regolith

Bernold, Leonhard E.

Boslough, Mark B.

Horie, Yasuyuki

English

NASA Technical Reports Server

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
https://ntrs.nasa.gov/search.jsp?R=19930008049 2020-03-24T07:24:51+00:00Z
LPJ Technical Report 92-06 15
250
Impression Testing Results eds.), 423-424, North Holland, Amsterdam. (4) Graham R. A.
and Webb D. M. (1986) In Shock Waves in Condensed Matter (Y. M.
Gupta, ed.), 719-724, Plenum, New York. [5] Weiblen P. W. et
al. (1990) In-Proceedings of Space 90, 98-106, ASCE.
N9 9 -iv n
0.000 0'.025 0.050 0.075 0.100 0.125
True Strain
Fig. 1. Results of impression tests. 2-1, 2-2, and 2-3 are samples from
experiment 1 3B917 without binder. 2/Al is from experiment 14B917 with
aluminum binder.
There are two noteworthy features that are evident from optical
microscopy:
1. Compact densities are strongly influenced by the addition
of aluminum particles. The metal appears to have acted as a
lubricant to enhance densification through interparticle sliding
and rotation.
2. Aluminum particles are well dispersed as thin boundary layers
between simulant particles. This type of mixing cannot be easily
achieved by conventional mixing methods. Also, thinly dispersed
layers may be exploited to enhance postshock processing of shock-
compacted materials by acting as an agent for dynamic reaction
sintering of lunar materials.
Impression Testing: Stress vs. strain curves were determined
with a WC indentor (diameter — 1 mm, cross-head speed =
0.002 in/min). Material recovered from experiment 13B917 (no
binder) was sampled from three different locations (2-1, 2-2, and
2-3). One sample (2/AI) was taken from experiment 14B917 (Al
binder). Stress-strain data for these four samples are summarized
in Table 1, and plotted in Fig. 1. The following is a brief summary
of impression testing results for the two recovery experiments.
I3B917(no binder): Samples 2-2 and 2-3 yielded nearly identical
values for strengths, but the strains were not consistent. When
the samples were crushed, there was not enough strain energy
to cause them to fly.
14B917 (Al binder): Sample IIAl was much stronger (see Fig. 1).
Moreover, the failure mode was quite different from the other
samples. The resistance to impression was very large, higher by
a factor of about 3. The elastic modulus was higher by a factor
of about 6. Strain energy caused the sample to shatter under
maximum load, launching fragments at high velocity.
This work was supported by the U.S. Dept. of Energy under
contract DE-AC0476DP00789.
References: [1) Murr L. E. et al. (1986) Metallurgical Appli-
cations of Shock-Wave and High-Strain-Rate Phenomena, Marcel
Dekker, New York, 1120 pp. [2] Graham R. A. and Sawaoka
A. B., High Pressure Explosive Processing of Ceramics, Trans. Tech.,
Switzerland, 404 pp. [3] Graham R. A. and Webb D. M. (1984)
In Shock Waves in Condensed Matter—(983 (J. R. Asay et al.,
?289
A LUNAR PENETRATOR TO DETERMINE SOLAR-
WIND-IMPLANTED RESOURCES AT DEPTH EN THE
LUNAR REGOLITH. W. Boynton1, W. Feldman2, and T.
Swindle1, 'University of Arizona, Tucson AZ 85718, USA, 2Los
Alamos National Laboratory, Los Alamos NM 87454, USA.
Introduction: Several volatiles implanted into the lunar rego-
lith by the solar wind are potentially important lunar resources.
3He might be mined as a fuel for lunar nuclear fusion reactors
(1 ]. Even if the mining of 3He turns out not to be feasible, several
other elements commonly implanted by the solar wind (H, C, and
N) could be important for life support and for propellant or fuel
production for lunar bases (2). We propose a simple penetrator-
borne instrument package to measure the abundance of H at
depth. Since solar-wind-implanted volatiles tend to correlate with
one another, this can be used to estimate global inventories and
to design extraction strategies for all of these species.
Current Knowledge: A considerable amount is known about
the distribution of solar-wind-implanted volatiles from analyses
of Apollo and Luna samples. Since the energy of the solar wind
is only sufficient to implant ions to depths of less than a micro-
meter into grains, these volatiles are only found on grain surfaces
that were once exposed to the solar wind. However, the regolith
is constantly gardened by impacts, so volatiles are mixed to depths
of order several meters. Models predict that the hydrogen abun-
dance of formerly exposed grains will fall off with depth in the
lunar regolith (e.g., the model of [3] predicts an exponential fall-
off with an e-folding distance of about 3 m). The Apollo drill
cores are not much help in testing this because their lengths are
short compared to the scales of interest (only one is longer than
2 m, and that one is only 3 m). In fact, the Apollo cores do not
clearly show that there is any systematic decrease in volatile
abundance with depth for the first 2-3 m 14]. This uncertainty
could have a large impact on resource evaluation [4|: assuming
that volatiles are uniformly distributed throughout the regolith
(8-15 m deep) leads to a factor, of 10 higher estimated global
inventory than does assuming the distribution derived from the
model of [3). Furthermore, mining strategies for a resource found
throughout the top 10 m or so of the regolith might be substantially
different from ones for a resource found only in the top 2 or
3m.
In the Apollo samples, most of the solar-wind-implanted vol-
atiles correlate with one another and with other measures of soil
"maturity" (extent of exposure to the solar wind) [5]. The excep-
tions are He and Ne, whose abundances show a strong dependence
on the amount of the mineral ilmenite (and hence the Ti content).
However, He and Ne also correlate with maturity if the Ti
abundance is factored out [6]. Although the correlation of H
content with maturity is not as strong as for some other elements
in the Apollo samples (perhaps reflecting the difficulty in elim-
inating H contamination of the dry lunar soils), measurements
of H with depth in the regolith should be indicative of all solar-
wind-implanted species.
Basis of the Technique: Simple neutron counters have been
shown to provide high sensitivity for the detection of low H


Shock-treated Lunar Soil Simulant: Preliminary Assessment as a Construction Material

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