**SIMULANT MATERIALS OF LUNAR DUST: REQUIREMENTS AND FEASIBILITY.**

Laurent Sibille, BAE Systems Analytical and Ordnance Solutions, NASA
Marshall Space Flight Center, XD42, Huntsville, AL, 35812,
Laurent.Sibille@msfc.nasa.gov.

**Introduction:** As NASA turns its exploration ambitions towards the
Moon once again, the research and development of new technologies for
lunar operations face the challenge of meeting the milestones of a
fast-pace schedule, reminiscent of the 1960's Apollo program. While the
lunar samples returned by the Apollo and Luna missions have revealed
much about the Moon, these priceless materials exist in too scarce
quantities to be used for technology development and testing. The need
for mineral materials chosen to simulate the characteristics of lunar
regoliths is a pressing issue that must be addressed today through the
collaboration of scientists, engineers and program managers. While the
larger size fraction of the lunar regolith has been reproduced in
several simulants in the past, little attention has been paid to the
'fines' fraction, commonly refered to as lunar dust. As reported by
McKay and Carrier, this fraction of the lunar regolith below 20 microns
can represent up to 30% by mass of the total regolith \[1\]. The issue
of reproducing the properties of these fines for research and technology
development purposes was addressed by the recently held Workshop on
Lunar Regolith Simulant Materials at Marshall Space Flight Center.
Preliminary conclusions from the workshop and considerations concerning
the feasibility of producing such materials will be presented here.

**Present Status of Lunar Simulant Materials:** No coordinated program
currently exists in the U.S.A. to define reference materials to be used
as analogs of lunar materials. Such coordinated efforts have existed at
different times in the past to either provide these materials to
specific technology development programs such as the Apollo Landing
Module and Lunar Rover or when NASA policies showed a renewed interest
in lunar missions as was the case in 1989 and the early 1990's. While no
Apollo lunar simulants remain today, the more recent efforts led to the
development and distribution of materials such as MLS-1 \[2\], a
titanium-rich basalt from Minnesota and JSC-1 \[3\], a glass-rich
basaltic ash from the volcanic fields of the San Francisco mountains of
Arizona. Both of these simulant materials were successful in the sense
that they provided known source materials for researchers and engineers
but were only adequate for certain applications. These deficiencies led
to efforts to ameliorate their characteristics, particularly to better
duplicate the content of glassy agglutinates in lunar regoliths (MLS-2).
The lack of funding and the waning interest from NASA in the 1990's
resulted in disappearing stocks and the resurgence of a variety of
'home-made' lunar simulants and independent commercial materials. Today,
neither of the simulants mentioned above are available from their
manufacturers. In parallel to NASA-funded simulants, the Japanese space
agency NASDA, which is now the Japan Aerospace Exploration Agency, has
funded a development program for lunar simulant materials for the past
decade. As a result, simulants such as FJS-1, MKS-1 are used in Japan,
but are not well known or used in the USA \[4\]. These materials have
been characterized extensively in terms of bulk chemical composition,
mineralogy, geotechnical properties and are available in modest
quantities.

**Requirements for Lunar Dust Simulants:** The previous simulant
materials outlined above contained a portion of fines although the
fraction below 20 microns was not specifically characterized. Multiple
direct observations of the behavior of lunar dust were made by the
Apollo astronauts and reveal a potentially serious threat to crew health
and mission hardware. The study of the interactions of lunar dust with
humans and hardware will require the use of some of the actual lunar
samples available but also the elaboration of specific materials that
reproduce several properties of lunar dust at a time. One major obstacle
to this task is the strong dependence of these properties on the lunar
environment itself. Surface properties such as adsorption, adhesion,
chemical reactivity, and electrocharging are defined by the absence of
oxidation, the ambient vacuum and the illumination by the full solar
light spectrum. The reproduction of complex grain shapes and surfaces
created by micrometeoritic bombardments and aggregation of charged
grains is indeed difficult at best. While many techniques of particle
synthesis can be used to create nano- and micro-particles of varying
shapes and compositions, the feasibility of producing simulant materials
depends strongly on the actual requirements imposed by the researchers
who will use these dust particles. In fact, one should consider
carefully the problems raised by the accumulation of requirements such
as mineral chemistry, crystallinity, glass content, aspect ratios and
surface properties. The combination of these very varied properties into
a single processed material is doubtful from a technical point of view
and may be unfeasible economically. The choice of which properties to be
simulated are critical and in what combinations must be made by the user
community while keeping these factors in mind. The chaotic situation
concerning lunar simulant materials calls for a focused and coordinated
development of large quantities of simulant materials in the near future
to meet the needs of present and future efforts to develop technologies
and test new hardwares for lunar precursor missions and lunar base
development.

**References:** \[1\] D.S. McKay et al. (1991) "The Lunar Regolith", Ch.
7 in Lunar Sourcebook, Eds. G. Heiken, D. Vaniman, B.M. French; and W.D.
Carrier et al. (1991) "Physical Properties of The lunar Surface", Ch. 9
in Lunar Sourcebook, Eds. G. Heiken, D. Vaniman, B.M. French; \[2\]
Weiblen P.W., Murawa M.J., and Reid K.J. (1990) "Preparation of
simulants for lunar surface materials" *Engineering, Construction and
Operations in Space II*, ASCE, 428-435; \[3\] D.S. McKay, J.L. Carter,
W.W. Boles, C.C. Allen & J.H. Allton (1997) "JSC-1: A new Lunar Regolith
Simulant", *Lunar and Planetary Science* XXIV, 963; \[4\] Kanamori, H.,
Udagawa, S., Yoshida, T., Matsumoto S., and Takagi, K. (1998)
\'Properties of Lunar Soil Simulant Manufactured in Japan\', Space98,
ASCE, 462-468.