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Acta Astronautica Vol. 17, No. 7, pp. 675-690, 1988 0094-5765/88 $3.00 + 0.00 Printed in Great Britain Pergamon Press plc
SCIENTIFIC INVESTIGATIONS AT A LUNAR BASE
Michael B. Duke and Wendell W. Mendell
National Aeronautics and Space Administration
Lyndon B. Johnson Space Center
Houston, Texas, U.S.A.
Abstract
Scientific investigations to be carried out at a lunar base can have significant impact on the location, extent, and complexity of lunar surface facilities. Among the potential research activities to be carried out are: (1) Lunar Science: Studies of the origin and history of the Moon and early solar system, based on lunar field investigations, operation of networks of seismic and other instruments, and collection and analysis of materials; (2) Space Plasma Physics: Studies of the time variation of the charged particles of the solar wind, solar flares and cosmic rays that impact the Moon as it moves in and out of the magnetotail of the Earth; (3) Astronomy: Utilizing the lunar environment and stability of the surface to emplace arrays of astronomical instruments across the electromagnetic spectrum to improve spectral and spatial resolution by several orders of magnitude beyond the Hubble Space Telescope and other space observatories; (4) Fundamental physics and chemistry: Research that takes advantage of the lunar environment, such as high vacuum, low magnetic field, and thermal properties to carry out new investigations in chemistry and physics. This includes material sciences and applications; (5) Life Sciences: Experiments, such as those that require extreme isolation, highly sterile conditions, or very low natural background of organic materials may be possible; and (6) Lunar environmental science: Because many of the experiments proposed for the lunar surface depend on the special environment of the Moon, it will be necessary to understand the mechanisms that are active and which determine the major aspects of that environment, particu- lar3y the maintenance of high-vacuum conditions.
From a large range of experiments, investigations and facilities that have been suggested, three specific classes of investigations are described in greater detail to show how site selection and base complexity may be affected: (1) Extended geological investigation of a complex region up to 250 kilometers from the base requires long range mobility, with trans- portable life support systems and laboratory facilities for the analysis of rocks and soil. Selection of an optimum base site would depend heavily on an evaluation of the degree to which science objectives could be met. These objectives could include lunar cratering, volcanism, resource surveys or other investigations; (2) An astronomical observatory initially in- strumented with a VLF radio telescope, but later expanding to include other instruments, requires site preparation capability, "line shack" life support systems, instrument maintenance and storage facilities, and sortie mode transportation. A site perpetually shielded from Earth is optimum for the advanced stages of a lunar observatory; (3) an experimental physics laboratory conducting studies requiring high vacuum facilities and heavily instrumented experiments, is not highly dependent on lunar location, but will require much more flexibility in experiment operation and EVA capa- bility, and more scphisticated instrument maintenance and fabrication facilities.
I ~ A - 8 6 - 5 0 9 p r e s e n t e d a t the 37 th Congress of the I n t e r n a t i o n a l srPaper A s t r o n a u t i c a l F e d e r a t i o n , I n n s b r u c k , A u s t r l a , 4 -11 October 1986.
*.A. n/7--C 675
676 Michael B. Duke and Wendell W. Mendell
Introduction
During the past several years, a series of workshops and
symposia have been held which have begun to identify the rationale
for and characteristics of a permanent base on the Moon (Keaton
and Duke, 1984; Mendell, 1986; Burns, 1986; Keaton and Duke,
1986). In space exploration plans, new emphasis has been given
to the role of lunar bases (Duke et al, 1985; Koelle, 1986;
National Commission on Space, 1986). These reports have
generally described the uses of a base on the Moon in terms of
its usefulness for scientific research, resource (commercial)
development, and expansion of horizons for the human race. We
suspect that the initial impetus for establishment of a lunar
base will come from politically motivated decisions, either space
competition or space cooperation. An alternative scenario, in
which economic reasons related to the use of lunar resources for
major space projects is the driver, is also a possibility. In
either of these cases, significant scientific research could be
accomplished and science would probably form a part of the public
rationale for the undertaking. With this in mind, we have
considered the scientific research that might be undertaken
relatively early in a lunar base program, in an effort to initiate
discussion at a more detailed level than has previously been
explored and to begin to specify the manner in which science
facilities and requirements would affect decisions of architecture
or location of a lunar base.
Origin and History of the Moon
The Moon is a small planetary body, probably intimately
related to the Earth in its origin, and apparently relatively
simple in its evolutionary history. Although it has been studied
locally in more detail than any other planet except Earth, major
questions about its origin and history remain (LGO Science
Workshop, 1986). The most promising current hypothesis involves
the Moon's origin through collision of a Mars-sized planet with
the young Earth, following separation of the Earth's core
(Hartmann, 1986; Hartmann and Davis, 1975). If this explanation
Scientific investigations at a lunar base 677
is correct, the origin of the Earth and Moon are intimately tied,
and the later history of the Earth can only be understood in the
light of this early, intense event. However, because the early
history of the Earth is no longer directly accessible through
rocks, which have been recycled by geological activity,
understanding the Moon offers the only possibility to test the
hypothesis.
The Moon itself is a somewhat evolved planet. During the
first 200-400 million years of its history, the outer regions
became largely molten and segregated into a less dense crust, rich
in feldspathic rocks and now represented by the lunar highlands.
Major impacts bombarded this crust, creating huge basins, up to
about 3900 million years ago. At this point, the large basins
began to be filled with dark volcanic basaltic rocks of the lunar
maria. This episode continued to perhaps 2000 million years ago,
after which the lunar surface has been struck occasionally by
large meteoroids, such as the ones that produced the rayed
craters Copernicus and Tycho, and by a myriad of smaller
meteoroids that have ground the surface layer to form the lunar
regolith. Current efforts are concentrating on understanding the
earliest history, through the study of rock fragments excavated by
the major basin impacts which have survived the later events.
These are typically small fragments in the lunar regolith "soil"
and in breccias, fragmental rocks created in impact events, which
are still large enough for modern techniques to determine
composition and age.
The Lunar Environment
Taylor (1986) has reviewed the beneficial and detrimental
attributes of the lunar environment as it applies to activities at
the lunar surface. The melting of the exterior regions of the
Moon apparently thoroughly outgassed the planet, and these gases
have been lost due to the Moon's 1/6 gravity. The results are
rocks that contain virtually no residual gases or combined
volatiles (water of crystallization) and virtually no atmosphere.
678 Michael B. Duke and Wendell W. Mendell
The nighttime atmosphere is a collisionless gas with a density of
approximately 2x105 atoms per cubic centimeter, most of which
atoms are from solar wind gases weakly implanted in the lunar
soil. The surface diurnal temperature ranges from 100 - 385 K at
the lunar equator, but is constant at about 253 K below a few
centimeters depth. The slow rotation of the Moon yields days and
nights that are 14 Earth days long at the lunar equator, but some
points near the lunar poles may be in permanent light (hot) or
shadow (cold) as the rotational axis is nearly perpendicular to
the plane of the ecliptic. The lunar magnetic field is 10 -2 to
10 -4 smaller than that of the Earth at its equator, and the
release of seismic energy is 109 smaller than that of Earth; the
maximum moonquake magnitude would be in the background noise on
Earth. External fluxes of micrometeoroids and charged particle
radiation are inevitably present.
Lunar Science
Many questions remain about the origin and history of the
Moon. These have been summarized in the LGO Science Workshop
Report (1986), which has documented the contributions expected
from a satellite in polar orbit around the Moon (Lunar Geoscience
Observer). They include: (i) What is the origin of the Moon?;
(2) How did the lunar crust and mantle evolve?; (3) What is the
magmatic history of the Moon?; (4) What is the history and nature
of impact processes on the Moon?; (5) Is there an iron-rich
core?; (6) What is the Moon's thermal history?; (7) What is the
origin of lunar paleomagnetism?; and (8) what is the nature of
the lunar regolith? Most of these questions can be finally
resolved only with intensive study of the Moon at several sites
and by the probing of its interior utilizing geophysical
techniques operated over long periods of time. The first lunar
base, if properly sited, can make contributions to all of the
questions.
Cintala, et al (1986) have described the geological
investigation possible with a lunar surface traverse of some 4000
km and 29 sites across Mare Imbrium. We describe here a more
constrained set of observations, consistent with a lunar base
Scientific investigations at a lunar base 679
which serves as a base camp for extended surface explorations, but
requiring less intensive long-range traverse capability. The base
site chosen is the Apollo 15 landing site; however, many excellent
alternatives could be illustrated, with somewhat different science
emphases. The advantage of choosing one of the Apollo sites for
an initial base is that the general geological aspects of the
landing site are known from the Apollo samples and previous
studies (Spudis and Ryder, 1985).
Examples of investigations to be undertaken from this base
include: (i) Studies of a major basin-forming event (e.g., the
Imbrium event); (2) Characterization of the latest (youngest)
lunar volcanic activity; and (3) Deciphering the history of
cometary and asteroidal impact on the Moon's surface.
i. Detailed Exploration of the Imbrium Basin
The Imbrium Basin was a major impact event that occurred
about 4000 million years ago, excavating a crater 700 km in
diameter and perhaps 20 km deep. Subsequently, the floor probably
rebounded and then later was filled with basaltic lavas. Within a
distance of 250 km of the Apollo 15 site it will be possible to
investigate a sequence of basin ejecta deposits that were
excavated from the lunar mantle and crust by the Imbrium event.
It may be possible to derive information on the vertical structure
of the pre-mare crust as the farther from the original crater rim,
the deeper the excavation depth of samples. Melt sheets and pools
resulting from the impact can be reached from which accurate ages
for the impact event can be determined and mechanisms of melt
formation to be studied. Topographic and structural features
resulting from the impact can be sampled and studied using
geophysical techniques. Using deep drilling techniques, the rocks
underlying the later mare volcanic fill can be sampled. Possibly
pre-mare volcanic rocks, exposed in the Apennine Bench, can be
investigated. These rocks are believed to be rich in elements
potassium, rare-earth elements and phosphorous (KREEP) and may
contain interesting mineral deposits.
680 Michael B. Duke and Wendell W. Mendell
The base elements required to support detailed investigation
are shown in Table i. It is anticipated that studies will proceed
from reconnaissance, in which instruments are emplaced and samples
collected at various locations, then more detailed study, as
Tab. ICharacteristics for Lunar Base 'to Support Geological
Investigations
Base Camp (includes habitats, life support, etc.)
Laboratory Facilities
Sample preparation (thin section)
Sample analysis (scanning electron microscope,
microscope, x-ray fluorescence)
Sample storage (soils, rocks, cores)
Sample documentation/data facility
Map preparation facility (computer system)
Geophysical Instrumentation
Main station
Seismic station
Neutral ion mass spectrometer
Remote station / Traverse vehicle
Seismic stations (remote emplacement)
Traverse gravimeter
Active seismic
Magnetometer
Traverse Vehicle
250 km range
Capability to carry drop tanks to remote sites
I0 kw power
Remote Shelters
Unpressurized solar flare "huts"
Scientific investigations at a lunar base 681
samples are analyzed and questions refined. This will require
that remote stations be reoccupied from time to time. Also,
shelters are required for quick occupancy in the event of solar
flares.
2. Volcanic History
Three distinctive epochs of volcanism can be studied at the
Hadley Base Site. These include pre-mare volcanism, the
mare-filling volcanics and late-mare or post-mare volcanism. The
mare-filling period produced the feature known as Hadley Rille,
apparently a collapsed lava tube which could have base development
implications if open sections remain. The Apollo 15 samples
included evidence of volcanic fire fountains that produced
deposits of volcanic glass in the form of tiny spheres, which
commonly contain thin volatile-rich surface coatings. Location of
the source of these glasses is of considerable interest for
volcanic mechanism and resource-related studies. The later
volcanism is of interest because it can yield information of the
thermal history of the Moon, and may contain fragments of crustal
materials as inclusions, from which information on the underlying
mantle can be gained. Dark deposits which may mark volcanic
vents, and features which may represent volcanic cones are present
in the vicinity of Hadley Base. Field locations to study each of
these features can be reached with modest surface traverse
capability. Here also, it will be desirable to set up
local shelters for field crews, for protection from solar flares,
to provide support while detailed local investigation is underway.
3. Impact History
A unique record which possibly can only be read on the Moon
is the historical abundance of comets and Earth-crossing
asteroids, which can be sampled through the intensive study of
impact craters. The experiment would involve sampling all impact
craters in a given area (say 20 km square). By studying the
features of the craters, the compositional glass formed by the
impact, and the distribution of fragments of the impacting object,
it should be possible to distinguish primary from secondary
682 Michael B. Duke and Wendell W. Mendell
craters, the compositional characteristics of the impacting
object, and the age of each crater. The capability of trenching
the regolith to up to 10 meters depth would allow older craters to
studied in a similar manner, allowing the impactor flux to be
documented as a function of time.
Lunar Astronomical Observatories
Several unique aspects of the lunar environment characterize it
and distinguish it from other locations on Earth or in
space(Smith, 1986). The high vacuum of the lunar surface offers
diffraction-limited imagery utilizing sensors and arrays that are
particularly sensitive and will not suffer from significant decay
due to molecular contamination. The vacuum, absence of magnetic
field and low ion density in the lunar ionosphere should lead to a
lunar sky that is even darker than that seen from Earth orbit, due
to the very high terrestrial airglow. The Moon's stability as a
base for instruments, including an absence of seismic noise, will
allow instruments to remain in fixed position and orientation for
extended periods of time, and the slow rotational rate of the Moon
will allow long exposures for very faint sources or variable
objects. The lower gravity and lack of winds will eventually allow
the construction of very large instruments with very precise
positions. Some of these instruments may be adapted to natural
lunar landforms, such as craters, which may allow Arecibo-like
antennas to be utilized. If ways are found to utilize lunar
materials in construction, many of the transportation costs for
such large antennas may be offset by using local materials.
Finally, the far side of the Moon is permanently shielded from the
natural and artificial noise of the Earth.
The advantages of the Moon as an observatory site must be compared
to that of other potential sites for space observatories. For
UV-optical observatories, Stockman(1986) has made the comparison
shown in Table i.
The types of astronomical facilities that have been proposed and
their characteristics are presented in Table 2.
Scientific investigations at a lunar base 683
The requirements for a lunar astronomical observatory are varied,
depending on the instruments to be established. One important
characteristic of modern astronomy is the strategy of constructing
telescopes which provide the signal-gathering capability, but
changing out the detectors/instruments at the focus to introduce
new analytical capability as technology advances. This is expected
to be the case for lunar telescopes as well, making an
observatory's association with a manned base a valuable asset. By
locating the observatory within easy transportation distance from
a base (5-50km), servicing and instrument replacement capability,
supported by shops and laboratories at the base, can provide
considerable flexibility to observatory operations. Instruments
not currently in use can be stored in a controlled high vacuum
environment at the main base.
Isolation of sensor systems from the inhabited base also must be
considered. Potential sources of contamination include volatiles
outgassed from habitats and suited astronauts; dust raised by
surface activities, traveling along ballistic trajectories;
vibrations and displacements related to movement of people and
equipment at the base. Location of communications antennas on the
surface or in space may interfere with some sensors. In general,
it appears that separation of the observatory from the base
activity by distance of a few kilometers should be satisfactory.
Placing the observatories at higher elevation than the base
facility should be effective, as could siting the instruments
behind ridges or mountains from the base. Attention should be paid
to preparation of the observatory site to minimize contamination
problems that might arise during observatory servicing.
Instrumentation for astronomical observatories will be fabricated
on Earth and transported to the Moon in the early stages of a
lunar base. Preparation of the site will be an important step in
observatory emplacement, depending on the type of installation.
Transportation routes from the base to the observatory site must
be established and stabilized, in order to support routine visits
by vehicles carrying people and replacement instruments. It will
probably be desirable to establish "lineshack" shelter capability
684 MichaelB. Dukeand Wendell W. Mendell
Tab ,2 : ADVANTAGES FOR ASTRONOMICAL FACILITIES IN VARIOUS ORBITS
LEO GEO MOON
LAUNCH COSTS LOW HIGH HIGH
MAINTENANCE PLATFORM STS/SS* SS/LB LB
MAINTAINABILITY VERY GOOD POOR VERY GOOD
SCIENCE OPS. COMPLEX SIMPLE SIMPLE
SCIENCE EFF. 35% 90% 45%
OPTICAL BACKGROUND EARTH/ZODIACAL ZODIACAL ZODIACAL
THERM. STAB. POOR VERY GOOD VERY GOOD
MAX. EXP. 45 MIN 17 H 14 DAYS
LARGE APERTURES LIMITED LIMITED GOOD
POTENTIAL
UPGRADING GOOD POOR EXCELLENT
CONFIGURATION RIGID RIGID FLEXIBLE
*STS = SPACE SHUTTLE; SS = SPACE STATION; LB = LUNAR BASE
at the observatory site, in order to provide protection from solar
flares. As the capability of a lunar establishment increases, it
may be possible to manufacture more and more of the components,
particularly structural components (supports, insulation, light
shields, etc.) from lunar materials, thereby decreasing the
transportation costs associated with expansion of lunar astronomy.
Scientificinvestigationsatalunarba~
TYPICAL LUNAR ASTRONOMICAL OBSERVATORY INSTRUMENTS
685
INSTRUMENT CHARACTERISTIC REFERENCE
OPTICAL INTERFEROMETER MICROARCSECOND RESO-
LUTION AT OPTICAL
WAVELENGTHS
BURKE(1985)
MOON-EARTH RADIO
INTERFEROMETER
<30 MICROARCSECOND
RESOLUTION AT <6CM
WAVELENGTH
BURNS(1985)
VERY LOW FREQUENCY
RADIOASTRONOMY
OPENS 10-100M WAVE-
LENGTH REGION TO STUDY
DOUGLAS &
SMITH(1985)
LARGE RADIOTELESCOPE
(SETI)
FAR-SIDE EMPLACEMENT OLIVER(1985)
Some instruments may benefit from emplacement out of line of sight
from Earth. At an early stage in lunar development, however, much
can be done within a few tens of kilometers of any base site
chosen. Selection of a lunar base site near the lunar limb may
provide an optimum way to provide an initial frontside facility
with ready access to a more extensive future far-side observatory,
perhaps a few hundred kilometers distant.
Physics / Chemistry Laboratory
The lunar environment is characterized by high vacuum with
arbitrarily high pumping capacity, excellent access to insolation,
and the virtual absence of an internal magnetic field. At the
lunar surface there is a constant flux of energetic radiation, but
a few meters below the surface, all radiation is absent except for
neutrinos and radioactive decay products from naturally occurring
potassium, uranium, and thorium. The latter could, in principle,
be made arbitrarily low by selecting natural lunar materials that
are depleted in radioactive species. By suitable thermal
686 Michael B. Duke and Wendell W. Mendell
management, it should be possible to develop sustained very high
(several thousand degrees Centigrade) or very low (<5 K)
temperatures.
Fundamental physics investigations could be undertaken when
very low radiation backgrounds are necessary, e.g., for detecting
neutrinos (Shapiro, 1985; Petschek, 1985; Cherry and Lande, 1985)
or studying the electric dipole moment of the neutron (Keaton and
Duke, 1986). The stability of the lunar surface may make possible
the detection of gravity waves predicted by the theory of
relativity. Experiments at low temperatures might include
research on properties of matter near absolute zero. Techniques
for the isotopic separation of 3He from 4He or hydrogen from
deuterium might be developed. Hypervelocity electromagnetic mass
accelerators could be used to investigate impact phenomena and
material properties under very high shock pressures.
The nature of the facilities required for a fundamental
physics facility are are not now known in specific detail.
However, based on the speculation above, such a facility would
seem to be characterized by the following attributes:
i. Large volumes which are maintained at high vacuum should
be provided with structures to allow for experiment emplacement,
sensor positioning and remote observation, these may be shielded
or unshielded, depending on requirements for radiation and
temperature control. Access to the facility would be through
telerobotics or space-suited technicians.
2. Adequate power (tens of kilowatts) are necessary in order
to provide thermal control and stable high voltage power supplies
for experiments.
3. Underground, heavily radiation-shielded tunnels may be
required.
4. Provision must be made for adequate support of
experimentation. This includes data processing as well as shops
for fabrication of experiment and equipment maintenance.
The location of these facilities is probably not dependent on
intrinsic properties of the Moon and can be established at any
Scientific investigations at a lunar base 687
base site. There will be a need to isolate the facilities from
certain types of interaction with other activities, particularly
those which would affect the high vacuum conditions. The physics
facility will also be distinguished from other facilities by a
relatively large staff of scientists, technicians, and supporting
crew, in order to maintain a suitable pace of experimentation.
Conclusion
Scientific uses of the Moon will require three distinct
classes of support capability. Geological exploration will
require emphasis on long range mobility, emplaced instruments,
coring and trenching apparatus, and analytical apparatus in order
to provide for rapid progress in field geological characterization
and selection of samples to return to Earth for detailed
investigation. Field crews will have to supported for extended
stays away from the base camp in order to take advantage of
mobility.
Astronomical facilities will generally require significant
emplacement of facilities, probably by human crews, but may not
require permanent crews on-site. Maintenance can be provided by
crews form the base, which will probably be separated from the
observatory 25 - 500 km. Rapid, reliable long-range
transportation will be required. The base camp will require
maintenance facilities and will provide a data processing
facility. However, much analysis may still be accomplished by
astronomers on Earth.
A physics laboratory will be characterized by extensive
surface and subsurface structures, complex sensor/data systems
requirements, and real time operations by scientists and
technicians. Shop facilities for experiment modification and
fabrication will be desirable and provision made for substantial
on-site staff (20 persons).
688 Michael B. Duke and Wendell W. Mendell
Site selection for a base that will support geological
exploration will be determined primarily by the science
requirements. Capabilities for extended exploration may be
developed either by emplacing additional bases or expanding
traverse capability. Site selection for astronomical
observatories may be dominated by ability to access the lunar
farside and by the local characteristics of the site (engineering
considerations). Site selection is probably not a major
consideration for a lunar physics facility, although special
characteristics of the site (engineering properties, access to
craters) may be important.
The establishment of lunar base characteristics and optimal
sites should be investigated further, as requirements are
developed more completely.
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690 Michael B. Duke and Wendell W. Mendell
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