Table Of ContentTHE
LUNAR
SURFACE
LAYER
Materials and Characteristics
EDITED BY
JOHN W. SALISBURY
AIR FORCE CAMBRIDGE RESEARCH LABORATORIES
BEDFORD, MASSACHUSETTS
PETER E. GLASER
ARTHUR D. UTTLE, INC.
CAMBRIDGE, MASSACHUSETTS
I964
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LIST OF CONTRIBUTORS
Burns, Eugene A. , Space Technology Laboratories, Inc. ,
Redondo Beach, Calif 469
Charters, A. C. , General Motors Corporation,
Santa Barbara, Calif 215
Dobar, W. I. , Bendix Systems Division, Ann Arbor, Mich. . . . 381
Dubin, Maurice, National Aeronautics and Space Adminis
tration, Washington, D. C 179
Gault, Donald E., Space Sciences Division, Ames Research
Center, Moffett Field, Calif 151
Gehring, J. W., General Motors Corporation, Santa Barbara,
Calif 215
Glaser, Peter E., Arthur D. Little, Inc., Cambridge, Mass. . . 389
Gold, Thomas, Center for Radiophysics and Space Research,
Cornell University, Ithaca, N. Y 345
Green, Jack, Space Sciences Laboratory, North American
Aviation, Inc. , Downey, Calif 135
Halajian, J. D., Grumman Aircraft Engineering Corporation,
Bethpage, Long Island, N. Y 67
Hapke, Bruce, Center for Radiophysics and Space Research,
Cornell University, Ithaca, N. Y 323
Heitowit, Ezra D., Space Sciences Division, Ames Research
Center, Moffett Field, Calif 151
Jaffe, L. D. , Jet Propulsion Laboratory, California Institute
of Technology, Pasadena, Calif 355
Johnson, P. C. , Arthur D. Little, Inc. , Cambridge, Mass. ... 93
Johnson, Rodney W., Lunar and Planetary Systems Develop
ment, Missile and Space Division, General Electric
Company, Philadelphia, Pa 491
Liu, Nora C., Bendix Systems Division, Ann Arbor, Mich. . . . 381
Lyon, R. J. P., Stanford Research Institute, Menlo Park, Calif.. 469
Martin, R. Torrence, Civil Engineering Department,
Massachusetts Institute of Technology, Cambridge, Mass. ... Ill
McCracken, Curtis W., NASA Goddard Space Flight Center,
Greenbelt, Md 179
v
Moore, Henry J. , U. S. Geological Survey, Menlo Park,
Calif 151
Osgood, J. H., Space Sciences Laboratory, North American
Aviation, Inc., Calif 135
Ryan, J. A. , Douglas Missile and Space Systems Division,
Santa Monica, Calif 265
Salisbury, John W. , Lunar-Planetary Research Branch,
Air Force Cambridge Research Laboratories,
Bedford, Mass 411
Scott, Ronald F., California Institute of Technology,
Pasadena, Calif 1
Simon, Ivan, Arthur D. Little, Inc. , Cambridge, Mass 445
Sjaastad, Captain Gerald D. , Air Force Weapons Laboratory,
Kirkland Air Force Base, New Mexico 23
Smalley, Vern G. , Lunar-Planetary Research Branch,
Air Force Cambridge Research Laboratories,
Bedford, Mass 411
Stein, B. A. , Arthur D. Little, Inc., Cambridge, M ass 93
#
Van Tassel, Roger A. , Lunar-Planetary Research Branch,
Air Force Cambridge Research Laboratories,
Bedford, Mass 445
Warnica, R. L., General Motors Corporation,
Santa Barbara, Calif 215
Wechsler, Alfred E. , Arthur D. Little, Inc. , Cambridge,
Mass 389
Wehner, G. K. , Electronics Division of General Mills, Inc. ,
Minneapolis, Minn 313
Winterkorn, Hans F. , Princeton University, Princeton, N. J. . . 491
VI
FOREWORD
The papers collected in these Proceedings are representa
tive of the state of knowledge on lunar surface materials and
their characteristics. We hope that the information presented
here will be a benchmark for the continuing efforts to predict
more completely the conditions to be encountered during a
lunar landing. The acid test of whether these predictions
are valid is scheduled to occur within the next decade.
Rarely has an opportunity presented itself for such complete
verification or refutation of the different hypotheses pre
sented in this book.
We wish to express our appreciation to the authors for
their efforts and contributions. We thank Ralph B. Baldwin,
Charles P. Sonnett, and Zdenek Kopal for assuming major bur
dens in the development and conduct of the conference. Our
special acknowledgements go to John P. Donaldson and Carol
Maclver who contributed at every stage in the organization of
the conference and the publication of the Proceedings. We
are grateful to Air Force Cambridge Research Laboratories
and Arthur D. Little, Inc., for the financial support of
the conference.
John W. Salisbury
Air Force Cambridge Research
Laboratories
Peter E. Glaser
Arthur D, Little, Inc.
vii
PREFACE
We know sufficient facts concerning the moon to give us
only an approximation of the lunar surface environment· We
have reasonable approximations to the surface and near-surface
temperatures and their variations. We have certain ideas con
cerning the flux of incident light of different wavelengths
including x-rays from the sun. We know that cosmic rays are
continually "bombarding the moon. In addition, the solar wind
and flare gusts will affect the lunar materials. Approxima
tions can "be made of the flux of meteoritic materials of all
sizes striking the moon. The lunar air has been shown to be
so rare that only a few laboratories can simulate it. We do
not know its composition.
Each factor, taken by itself, can be analyzed to give a
reasonable picture of its effect on the outer layers of the
moon. Taken all together, however, the interactions of the
various processes, the aeons through which they have operated,
the unknown variations in the rates of activity in the past,
coupled with the uncertain chemical nature of lunar materials,
complicate the understanding of the lunar surface properties.
In spite of, or perhaps because of these limitations in
our knowledge, the tremendous surge of interest in the moon
which has developed in the last few years was ample justifica
tion for holding the Lunar Surface Materials Conference.
The Conference Co-chairmen, John W. Salisbury and Peter
E. Glaser, are both active in studies simulating possible
lunar surface conditions under high vacuum. From their work
and related study, they came to appreciate the tremendous
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THE LUNAR SURFACE LAYER
number of variables involved in the lunar environment and
therefore brought together recognized authorities so that
diverse views could be presented.
The concept of the Conference was masterful. The need
for it was evident, but sufficient knowledge to yield defini
tive and final conclusions about the lunar surface materials
simply does not exist as yet. The many important papers pre
sented have merely served to restrict the range of possible
solutions. A scientist today, in effect, has a problem which
may be stated, "The moon is covered by an unknown substance
or substances to an unknown depth. Its physical nature has
been found to be different from terrestrial substances. You
are to describe it; tell its composition, origins, behavior,
history, structure, and strength and how it may best be
studied."
Ralph B Baldwin
Oliver Machinery Company
Grand Rapids, Michigan
x
INTRODUCTION
Zdenek Kopal
The University
Manchester, England
We now should take stock of what we think we know of the
surface of the moon so far, ponder over the new information
presented by many colleagues at this meeting, and try to fore
see how to go about the tasks remaining for the future.
First, a few words concerning the methods by which the
lunar environment can be observed from the earth at a distance.
Direct telescopic observations at optical frequencies—visual
or photographic--can provide first-hand information concerning
lunar topographic relief down to details of a fraction of the
kilometer in size. A 2l·-inch refractor should, under ideal
seeing conditions, resolve on the lunar surface details
approximately 400 yards in size; and a 40-inch telescope—the
largest apperture used so far for systematic lunar studies—
may depress this limit down to somewhat more than 200 yards.
Below this limit, the outlines of individual lunar objects
become blurred in a haze arising from the contribution of dif
fraction phenomena, unsteadiness of seeing conditions, and
photographic plate grain. When the sun stands very low above
the lunar horizon, long shadows cast in its rays may enable us,
to be sure, to establish the presence of surface unevenness on
a scale 10-100 times smaller than that necessary for direct
resolution; but few results of such studies have been reported
so far.
Actual measurements of local deformations of the lunar
surface from the shadows cast by such unevenness on the
xi
THE LUNAR SURFACE LAYER
surrounding landscape—carried out in recent years on a large
scale—have revealed that the overwhelming part of the lunar
surface is smooth and gently sloping, its average inclination
to the horizontal does not seem to amount to more than a few
degrees. This appears to be true not only in the maria, but true
also in regions which are ordinarily called "mountainous";
former notions of great ruggedness of the lunar surface,
based on telescopic inspection of the shadows along the termi
nator, failed to take proper account of the low altitude of
the illuminating source. This statement does not, to be sure,
intend to rule out possible presence of slopes considerably
steeper than average, on a small scale. For instance, the
inner rims of small craters and crater pits may be considerably
more inclined to the horizontal. However—and this should be
emphasized—the total area occupied by such slopes represents
only a tiny fraction (certainly less than one percent) of the
entire lunar surface—so that, on the whole, the macroscopic
character of the lunar surface must be accepted as smooth.
This, on the face of it, does not perhaps seem very unusual;
for very much the same is true of our earth. However, the
principal leveling factors operating on the earth—air and
water—are totally absent on the moon and have been so from
time immemorial; so that the reason why the moon appears to
be so similar to the earth in this respect today must be sought
along different lines.
Below the limit of direct optical resolution, studies of
the microstructure of the lunar surface must rely entirely on
indirect methods, based on the measurement and interpretation
of the lunar radiation (in the widest range of the spectrum)
which remains the sole link between us and the object of our
inquiry. With a quite insignificant exception (i.e., thermal
radiation of the moon due to its internal radiogenic heat),
xii
THE LUNAR SURFACE LAYER
all moonlight derives its origin from the sun—whether this be
sunlight falling directly on the moon, or sunlight scattered
towards it through the intermediary of our earth ("earth shine")—
and is absorbed or scattered by the lunar surface in accordance
with its local optical properties. A small part of the solar
radiation (both electromagnetic and corpuscular) may be absorbed
and re-emitted by cascade processes to give rise to fluores
cence. Energetic corpuscles of the solar wind may even induce
the lunar surface to emit an x-ray "brems-Strahlung" the
analysis of which could reveal to a terrestrial observer above
the atmosphere the atomic chemical composition of the outer
lunar crust—just as the studies of lunar luminescent spectra
could provide some information about its molecular structure.
At optical frequencies and in the near infrared (up to
4-5 M) scattered sunlight dominates the lunar spectrum; while
above ^—i.e., in the deep infrared and in the domain of
radio frequencies—lunar radiation is essentially due to ther
mal emission of its globe. The energy sent out as thermal
radiation is much greater than that of scattered light—for
out of the total incident flux of illuminating sunlight, only
about 7$ gets scattered by the lunar surface, the balance
being absorbed and re-emitted.
Even so large a balance of incident flux is insufficient
to maintain the outermost layer of the lunar surface at a
temperature higher than approximately 400 K at noontime, and
about 100 K at night. This means that much of the thermal
radiation emitted by it will be absorbed by our^ own terres
trial atmosphere. Fortunately, our atmosphere is fairly
transparent in the 8-12γ- band—which should include the maxi
mum of the lunar radiation curve at daylight—but the second
atmospheric window through which the thermal radiation of the
moon can be observed—between 1 mm and 1 meter—is already so
xiii
