Many questions of lunar science remain unanswered because of a lack of specific data. With the potential for returning humans to the Moon and establishing a long-term presence there, a new realm of exploration is possible. Numerous plans have been outlined for orbital and surface missions. The capabilities and objectives of a small class of rovers to be deployed on the lunar surface are described. The objective of these small rovers is to collect detailed in situ information about the composition and distribution of materials on the lunar surface. Those data, in turn, would be applied to a variety of lunar geoscience questions and form a basis for planning human activities on the lunar surface

Lane, A. L.

Miller, D.

Plescia, J. B.

English

NASA Technical Reports Server

44 New Technologies for Lunar Resource Assessment
Radar backscatter. The surface and subsurface scattering prop-
erties of the Moon can be analyzed using radar backscatter imaging.
The radiation is both transmitted and received by Earth-based
radar antennae. Two-dimensional backscatter images are derived
using a delay-doppler technique developed in the 1960s and 1970s.
The returned signal is directly related to the geometry of the
measurements, the number of scatterers encountered on the scale
of the wavelength, and the dielectric properties of surface mate-
rials. Surfaces that are smooth on the scale of the wavelength
reflect the radiation in a specular manner. Surfaces containing
abundant scattering elements on the scale of the wavelength
return a higher signal. Since the lunar surface is anhydrous,
subsurface block population can also be detected with longer
wavelengths.
As summarized in Table 2, radar measurements of the Moon
have also had a long history with several important milestones.
First was simply the detection of the Moon with Earth-based
instruments. As technology advanced during the 1960s and 1970s,
the techniques for measurement of radar backscatter of the Moon
were perfected and two-dimensional images of the radar back-
scatter properties were produced at relatively low spatial re-
solution. Analyses of dual-polarization radar data confirmed the
sensitivity to block population on the surface. The last several
years have seen dramatic improvement of radar measurements
possible. These include an improvement in both sensitivity and,
more important for lunar measurements, an improvement in the
spatial resolution that can be obtained with Earth-based telescopes.
Current technical capabilities indicate that a spatial resolution
of 30-300 m is possible for lunar nearside targets (optical telescopes
can achieve 1-km resolution; Lunar Orbiter IV obtained ~IOO-m
resolution for the lunar nearside from orbit). Several tests of these
new radar capabilities have already been made. In order to achieve
the desired resolution and science analysis return, a modest upgrade
to current radar telescopes is required to allow dual polarization
at three wavelengths and more extensive data analyses (informa-
tion extraction) capabilities need to be developed for lunar specific
LUNAR SURFACE ROVERS. J. B. Plescia, A. L. Lane, and
D. Miller, Jet Propulsion Laboratory, California Institute of Tech-
nology, Pasadena CA 91109, USA.
Despite the Ranger, Lunar Orbiter, Surveyor, Apollo, Luna, and
Lunokhod programs, many questions of lunar science remain
unanswered because of a lack of specific data. With the potential
for returning humans to the Moon and establishing a long-term
presence there, a new realm of exploration is possible. Numerous
plans have been outlined for orbital and surface missions. Here
we describe the capabilities and objectives of a smallclass of rovers
to be deployed on the lunar surface. The objective of these small
rovers is to collect detailed in situ information about the com-
position and distribution of materials on the lunar surface. Those
data, in turn, would be applied to a variety of lunat geoscience
questions and form a basis for planning human activities on the
lunar surface.
The initial rover design has been scoped for a small Artemis
lander payload (about 60 kg). It consists of a four- or six-wheeled,
solar-powered rover with a mass of 28 kg. Two rovers would be
deployed from a single Artemis lander. Rover lifetime would be
at least 3 lunar days and hopefully 7-10; at least tens of kilometers
of range are possible (depending upon the amount of time devoted
to moving vs. sampling and analysis). During the lunar night, the
rover would hibernate. About II kg of the total 28 kg is available
for science payload and sampling equipment, which allows for a
variety of capabilities that capitalize on microtechnology. Rover
speed would be 0.5-1.0 km/hr depending upon the tetrain. Power
(60-200 W) is provided by solar panels (0.3 m2) that also serve
to shield the rover from high thermal loads during the day.
IZOWhr of AgZn batteries provide capability for short-period,
high-load demands; these batteries are capable of withstanding
the lunar night. Nominal data rate would be about 30 kbps at
20 W RF; rates as high as 150 kbps would be possible for limited
periods. Control of the rover mobility would be in two modes:
behavioral control dtivingand teleoperation dtiving. In the behav-
ior control mode, a series of way points would be selected and
the rover would navigate along the predetermined path, to a site,
invoking autonomous obstacle avoidance if necessary. In the tel-
eoperation driving mode, mobility would-be controlled in a real-
time sense from the Earth using slow-scan video for viewing.
Sampling and deployment would all be done autonomously once
a specific action and position had been selected from the ground.
The system would not make autonomous decisions about meas-
urement or sampling.
Two types of payloads are envisioned for such a small rover:
a geoscience payload and a physical properties payload. The nom-
inal geoscience payload is aimed at addressing the chemical and
mineralogic properties of the regolith and tocks, the composition
of absorbed and adsorbed gases in the regolith, and the morphology
of the surface to millimeter scale. The payload includes stereo
imaging, field lens camera, infrared imaging spectrometer, evolved
gas analysis, and alpha/proton/X-tay fluorescence instruments, as
well as a scoop and an auger drill to obtain samples of the upper
meter of regolith. Using these data, several questions can be
addressed: geochemical and petrological processes; regolith stra-
tigraphy and development; history of the solar-wind-implanted
gases; lunar resources; small-scale surface morphology; and site
evaluation.
Steteo imaging is achieved through two mast-mounted CCD
framing cameras (800 X 1000 pixels) with a separation of about
25 cm. Mast mounting allows 360° horizontal viewing and 120°
of vertical viewing. The field lens camera is the same type of camera
but mounted on the rover body with optics that allow imaging
at a resolution of a few millimeters in the near field. The infrared
imaging spectrometer covers the spectral range of 0.7 to 2.5 /jm
and focuses on the portion of the spectrum sensitive to pyroxenes,
olivines, FeO content, and soil composition. A spatial resolution
of <2 mm at 30 cm is possible. The alpha/proton/X-ray fluores-
cence instrument is aimed at obtaining elemental composition.
The alpha/proton mode measures low Z elements, whereas the
X-ray fluorescence mode is sensitive to higher Z elements. Curium-
244 is used as the source for the alpha particles; l09Cd or I44Cm
would be used for the X-ray excitation. The evolved gas analysis
system would be used to heat the samples to drive off gases that
would then be analyzed by a mass specttometer or other system.
Target gases include H2,3He, SO2, CO, CO2, H,S, H2O, and N,.
Two types of sample acquistion equipment are planned: a scoop
and a drill. The scoop is a clamshell mounted on a 4 degree-of-
freedom arm and would collect samples for analysis to depths of
a few centimeters with a sample volume of a few cubic centi-
metets; it could also be used for shallow trenching. This same
arm would also deploy the alpha/proton/X-ray device to the
surface. The drill is an auger drill mounted to the rover body that
https://ntrs.nasa.gov/search.jsp?R=19930008073 2020-03-24T07:24:08+00:00Z
LP1 Technical Report 92-06 45
could penetrate to depths of about 1 m. Sample volume of a few
cubic centimeters from depth intervals of a few centimeters would
be obtained. The auger would be housed in a tube such that samples
from a given depth remain isolated from regolith material at other
depths.
A physical properties payload would be intended to study the
geotechnical properties of the surface and subsurface. Those data
would be aimed primarily at engineering objectives but would also
be applicable to geoscience problems. Parameters of interest
include particle size and shape, density and porosity, compressi-
bility, shear strength, bearing capacity, trafficability, electrical
conductivity, and charging/discharging of the surface. The com-
plete payload is under study and has not yet been determined.
However, it is anticipated that an electron-magnetic sounding
system would be used to determine the thickness, stratigraphy,
and boulder content of the regolith. This system would be mounted
on the rover body such that long distance or areally extensive
traverses could be obtained.
Later Artemis landers have a larger payload capability, about
200 kg or larger. Additional studies are underway that consider
the possibility of building larger rovers that have more capability,
particularly with respect to lifetime, range, and drilling. Alterna-
tively, the larger payload capacity could be used to deploy more
of the_small rovers outlined above.
uyto-73
COMBINED GAMMA R£Y/5lEUTRON SPECTROSCOPY
FOR MAPPING LUNAR RESOURCES. R. C. Reedy, R. C.
Byrd, D. M. Drake, W. C. Feldman, }. Masarik, and C. E. Moss,
Space Science and Technology Division, Los Alamos National
Laboratory, Los Alamos, NM 87545.
Some elements in the Moon can be resources, such as hydrogen
and oxygen. Other elements, like Ti or the minerals in which
they occur, such as ilmenite, could be used in processing lunar
materials. Certain elements can also be used as tracers for other
elements or lunar processes, such as hydrogen for mature regoliths
with other solar-wind-implanted elements like helium, carbon, and
nitrogen. A complete knowledge of the elemental composition of
a lunar region is desirable both in identifying lunar resources and
in lunar geochemical studies, which aiso helps in identifying and
using lunar resources. Discussed here is the use of gamma ray and
neutron spectroscopy together to determine abundances of many
elements in the top few tens of centimeters of the lunar surface.
To date, very few discussions of elemental mapping of planetary
surfaces considered measurements of both gamma rays and the
full range of neutron energies.
The concepts of using gamma rays or neutrons escaping from.
the Moon to determine lunar elemental composition date back
over 30 years (e.g., [ 1 1). In 1 97 1 and 1 97 2, gamma ray spectrometers
(GRS) on Apollos 15 and 16 mapped =22% of the lunar surface
but only could determine the abundances of several elements (Th,
Fe, Ti, K, and Mg) because of the use of low-resolution Nal(Tl)
scintillator detectors and the short durations of the missions. A
high-resolution germanium GRS is on the Mars Observer sche-
duled to be launched in late September 1992 [2). Such a spec-
trometer is much more sensitive for determining lunar elemental
abundances and for identifying surface components than was the
Apollo GRS [3]. Neutron spectroscopy of another planet has not
been done yet, although the Mars Observer GRS is capable of
detecting thermal andepithermal neutrons [2]. A germanium GRS
can also detect neutrons >0.6 MeV by triangular-shaped peaks
in the spectrum made by neutron-induced inelastic-scattering
reactions in the detector [4]. The inclusion of a detector specifically
designed to measure fast (E,, ~ 0.1-10 MeV) neutrons improves
the sensitivity of detecting hydrogen in the lunar surface [5).
Spectrometers to measure the fluxes of garnma rays and neutrons
escaping from the Moon are discussed elsewhere in this volume
[6]. A gamma ray spectrometer can also be used to detect thermal
and epithermal neutrons using coatings of thermal-neutron-
absorbing materials [3], although not with the sensitivity of detec-
tors designed specifically for such neutrons. The theories for
gamma ray and neutron spectroscopy of the Moon and calculations
of leakage fluxes are presented here with emphasis on why com-
bined gamma ray/neutron spectroscopy is much more powerful
than measuring either radiation alone.
Sources of Neutrons and Gamma Rays: Most gamma ray
lines made by the decay of excited states in nuclei are produced
by several types of nuclear reactions, mainly neutron nonelastic
scattering and neutron capture [7-9]. The main exceptions are
the gamma rays made by the decay of the naturally radioactive
elements (K, Th, and U). The neutrons are made by the interaction
of the energetic particles in the galactic cosmic rays (GCR) with
the lunar surface [10]. Neutrons are produced mainly with energies
of —0.1-10 MeV, with some made with higher energies. The rates
for the production of these fast neutrons depends on the intensity
of the GCR particles, which can vary by a factor of =3 over an
11-year solar cycle [11] , and is slightly (~5%) dependent on the
surface composition [12]. The transport and interactions of these
fast neutrons are also dependent on the surface composition.
Neutrons in the Moon can be slowed by scattering reactions to
epithermal (£„ ~ 0.5-103 eV) and thermal (E,, - 0.01-0.5 eVj
energies. The flux of epithermal neutrons is mainly dependent
on the hydrogen content of the surface, while the flux of thermal
neutrons depends both on the amounts of neutron moderators
like H and of thermal-neutron absorbers like Fe, Ti, Sm, and Gd
[ 1,5,12,13). Many neutrons escape from the lunar surface and can
be detected in orbit. The gravitational field of the Moon affects
slightly the flux at orbit of the lowest-energy neutrons [14].
The reaction of these neutrons with atomic nuclei in the lunar
surface produces most of the gamma rays used for elemental
mapping. Fast neutrons make gamma rays by a large variety of
nonelastic-scattering reactions. Many elements (e.g., O, Mg, Si,
and Fe) are mapped by neutron inelastic-scattering reactions mak-
ing excited states in the target nucleus, such as 24Mg(n,n y)'4Mg
exciting the 1.369-MeV state of 24Mg (which almost immediately,
~1 ps, decays to the ground state). Neutrons with energies of
~0.5-10MeVmake most of these inelastic-scattering gamma rays.
Neutrons with higher energies can induce many types of reactions,
such as the 28Si(n,n or y)24Mg reaction, which also can make the
1.369-MeV gamma ray. Many thermal and some epithermal neu-
trons produce gamma rays by neutron-capture reactions, such as
the 28Si(n,y)29Si reaction, which makes a cascade of gamma rays.
The cross sections for neutron-capture reactions vary by orders
of magnitude, and the elements mapped by gamma rays made by
such reactions (e.g., Ti, Fe, and possibly Cl, Sm, and Gd) are those
with high cross sections for (n,y) reactions and that emit one
or more gamma ray with a high yield per captured neutron.
Calculations of Neutron and Gamma Ray Fluxes: The ulti-
mate sources of lunar neutrons and most lunar gamma rays are
from interactions of the high-energy (E ~ 0.1-10 GeV) particles
in the galactic cosmic rays. The Los Alamos high-energy transport


Lunar Surface Rovers

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