The arrangement of an apparatus designed to measure the mechanical properties of the lunar surface from the Surveyor spacecraft is described. The experiments that may be made with this device are discussed and examples are given

Scott, Ronald F.

Caltech Authors - Main

JOURNAL OF GEOPHYSICAL RESEARCH VOL. •2, NO. 2 JANUARY 15. 1967 
Soil Mechanics Surface Sampler Experiment for Surveyor 
t•ONALD F. SCOTT 
Division o.f Engineering and Applied Science 
California Institute o• Technology, Pasadena 
The arrangement of an apparatus designed to measure the mechanical properties of the 
lunar surface from the Surveyor spacecraft is described. The experiments that may be made 
with this device are discussed and examples are given. 
INTRODUCTION 
One of the experimental devices that may 
be carried on the Surveyor spacecraft will 
measure the mechanical properties of the lunar 
surface in the vicinity of the spacecraft. The 
apparatus and the experiment. to be performed 
are discussed, in addition to the interpretation 
of the results of the experiment. From the ap- 
pearance and behavior of the lunar surface in 
the vicinity of Surveyor 1 [Jaffe et al., 1966], 
the experiment would be potentially fruitful in 
similar lunar areas. 
APPARATUS 
The original 'surface sampler' was designed 
to obtain only samples of lunar surface material 
in the vicinity of the spacecraft. At a later 
stage in the development of Surveyor, the de- 
sign of the surfbee sampler was revised to 
provide an instrument, for measuring the me- 
chanical properties of the lunar surface ma- 
terial. 
The apparatus consists of an articulated 
mechanism (Figure 1) that is capable of ex- 
tending, contracting, swinging to the right or 
left in azimuth, and moving up or down in 
elevation. At the end of the mechanism is a 
scoop or bucket with a movable door. The 
door may be opened or closed, but it is not 
possible to select intermediate positions. The 
attitude of the apparatus is monitored by po- 
tentiometers attached to the shafts of the 
motors that control the motions of extension, 
azimuth, and elevation. Extension is powered 
by pretensioned springs mounted near the 
support of the sampler; they are arranged to 
drive the bucket outward. To draw it back, 
a retraction motor winds up a thin metal tape 
attached to the bucket. 
In operation, the sampler arm may be 
raised and, by the actuation of a clutch, re- 
leased to allow the bucket to fall on the lunar 
surface to break up any hard material or to 
reduce small rocks to more usable fragments. 
To increase the eftieaey of the blow under 
lunar gravity, the downward motion is strength- 
ened by means of a pretensioned torque spring 
attached to the elevation axis of the apparatus. 
Two separate modes of command are pro- 
vided, one to control with some precision the 
position of the surface sampler, and the other 
to permit relatively rapid movement of the 
sampler from one location to another. In the . 
first mode, each motor is run for 0.1 see; and, 
in the second mode, for 2 see. The actual dis- 
tanee moved during each time interval depends 
on the motor employed and the load on it, but 
control is such that the bucket can be brought 
to within a few tenths of an inch of a selected 
position. 
To make the apparatus capable of measuring 
the forces it applies to the lunar surface, three 
sensors were added: (1) a strain gage was 
bonded to one of the arms of the trellis to 
measure essentially the vertical component of 
force acting on the surface sampler; (2) 
another strain gage, attached near the bucket 
on a small cantilever arm to which the con- 
traction tape is eormeeted, measures the con- 
traction force applied to the mechanism; and 
(3) an aeeelerometer was attached rigidly to 
the cutting edge of the bucket (Figure 2) to 
record the decelerations of the bucket on im- 
pact with the lunar surface. 
The door of the bucket was also modified 
(Figure 2) to present, in the dosed position at 
maximum extension, an area of about 13 
(2 in.') to the lunar surface. In the open posi- 
827 
828 RONALD F SCOTT 
Fig. 1. The deployed surface sampler mounted 
on a mockup of the Surveyor spacecraft, one leg 
of which is seen in the background. 
Fig. 2. The scoop or bucket and trap door. 
The accelerometer is mounted on the knife blade 
attached to the scoop. 
tion, the lower edge of the bucket, which may 
be placed in contact with the surface, has an 
area of about 0.5 cm •' (0.1 in.•) '. 
This instrumentation gives the surface sam- 
pler a very wide range of discrimination of the 
material properties of the lunar surface and 
permits quantitative determinations to better 
than I order of magnitude within a range of 6 
orders of magnitude [Scott, 1965]. 
The instrumented surface sampler can per- 
form the following surficial quantitative ex- 
periments: 
1. Static vertical bearing or penetration 
test. The surface sampler is extended above 
the surface to a selected radius and the bucket 
is lowered by 0.1-sec increments until it makes 
contact with the lunar surface. On continuing 
the descent, the tip of the bucket is forced into 
the lunar soil. Throughout this sequence, the 
outputs of the vertical force strain gage and 
the elevation potentiometer are recorded. This 
information together with television pictures of 
the position of the surface sampler make it 
possible to obtain the force versus penetration 
record of the bucket as it is pushed into the 
surface. With a maximum downward force 
capability of about 1350 grams weight (3 lb) 
at maximum extension, the maximum pressure 
that can be applied to the surface varies from 
a minimum of 100 g?cm •' (1• psi), with the 
trap door closed, to about 2700 g/cm' (30 psi), 
with the door open. 
2. Static drag or horizontal load test. After 
a vertical loading •est has been performed, the 
bucket may be pulled in toward the spacecraft 
on or through the surface material, and a meas- 
urement of the force exerted on the bucket can 
be made by means of the horizontal force 
strain gage output (Figure 3). This force in- 
cludes both the force being applied to the 
lunar surface and the force required to con- 
tract the articulated mechanism itself. It will 
be necessary, therefore, to calibrate the con- 
traction strain gage at the lunar surface by 
contracting the arm near the surface, but not 
in contact with it, while monitoring the force 
recorded by the strain gage. This will be done 
periodically during the Surveyor's life. 
Sdccessive drag tests at the same location 
can be employed to dig a trench. The surface 
sampier's geometrical arrangement and posi- 
tion on the spacecraft is such that theoretically 
$.64 (8) 
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b. 0.91 (2) 
• 76.5 cm (50 in.) EXTENSION 
/ 
, , 
152.6 cm (60 in.) EXTENSION 
i,.I r I (o) 
0 5 I0 15 20 25 30 
TIME, sec 
Fig. 3. The horizontal force measured during a 
surface sampler drag test in sand. 
SURVEYOR PROJECT--FUTURE EXPERIMENTS 829 
a trench can be dug to a depth of about 45 cm 
(18 in.). Actually, the size of the trench will 
depend on the lunar surface properties and the 
power and time available for the trenching op- 
eration. At various stages in a trenching opera- 
tion, vertical lead penetration tests could be 
conducted to determine vertical inhomogeneity 
of the material. 
Further information on the mechanical prop- 
erties of the lunar surface will be obtained by 
photographic observation of the material's be- 
havior during trenching and by study of the 
stability of the trench walls. 
3. Impact deceleration test. When the sur- 
face sampler is dropped on the surface, the 
output of the accelerometer at the bucket end 
of the device can be obtained. This deceleration 
contains information on the lunar surface and 
on the vibration properties of the surface sam- 
pler arm itself. The interpretation of the record 
requires both studies of deceleration in various 
soils (Figures 4 and 5) and an examination of 
the vibration behavior of the surface sampler. 
Experiments [McCatry et al., 1964] have 
shown that the deceleration of an object hitting 
various materials has a characteristic form of 
deceleration as a function of time; this form 
is frequently called the deceleration 'signature.' 
The peak deceleration reached and the time for 
the deceleration to reach this peak are both 
dependent on the strength of the material im- 
pacted and the velocity of impact. In the case 
of the surface sampler, the velocity depends on 
the height from which it drops to the lunar sur- 
face. The high-frequency vibrations that are 
superimposed on the deceleration curve (Figure 
4) are in themselves characteristic of the grain 
size or the vesicular structure of the material 
on which the impact occurs. Information on 
0 5 I0 1520 
eo 
40' 
2o 
o 
TIME, ms 
Fig. 4. The record of decleration obtained from 
an impact test 20.3-cm (8 in.) drop in sand. 
• 600 
n,' 
"' $00 
"' 0 
TIME, ms 
Fig. 5. The record of deceleration obtained from 
an impact test 5.1-cm (2 in.) drop on basalt. 
these properties can be obtained from the ac- 
celeration record by passing the record through 
filters of different frequencies following the ex- 
periment. 
In addition to the deceleration measurements, 
an impact experiment can give empirical infor- 
mation on the amount of force necessary to 
break small rocks or boulders on the surface, 
should any be accessible. The characteristics of 
the spring, surface sampler, and bucket are 
such that it is possible to break material of the 
hardness of a conventional building brick. 
4. Weighing experiment. Since the vertical 
lead can be monitored, it is possible to pick up 
and weigh a suitably sized pebble or rock frag- 
ment. If a television picture of the pebble is 
also possible, the dimensions of the pebble can 
be estimated by comparison with the scal• 
painted on the side of the surface sampler 
(Figure 2); a value for the density of the 
pebble then can be computed to within 20 to 
30% of its actual density. Although this is not 
sufficient to distinguish among many common 
rock materials on earth, it should be enough 
to determine whether the rock is solid or rela- 
tively porous. The distinction between the den- 
sity of pumice and the density of an aggregate 
of grains would not, of course, be possible from 
this test. 
5. Use in connection with a-scattering ex- 
periment. The positions of the surface sampler 
and the deployed a-scattering device [Turke- 
vich et al., 1967] will be such that the surface 
sampler can pick up the a-scattering device and 
place it in a new location on the lunar surface 
to provide more information on the atomic 
properties of the surface. The surface sampler 
also can clear off an area to a given depth to 
permit sensing of the subsurface material by 
the a-scattering device. 
830 RONALD F. SCOTT 
MODE OF OPERATION 
The surface sampler Should be capable of 
certain standard sequences of events in order 
to carry out the tests described above. For ex- 
ample, a normal sequence of events might con- 
sist of lowering the surface sampler bucket to 
the lunar surface at a preselected number of 
points and driving the bucket vertically down- 
ward through the surface to the limit of the 
apparatus's capability at each of these points. 
From the subsequent record, the 'mechanical 
surface' (the surface at which the sensitivity of 
the device first indicated a load) could be de- 
termined for comparison with the visual surface 
at the same point. In addition, a vertical load 
penetration test would have been carried out 
at each of these points. Following this, a drag 
test could be performed at selected cross sec- 
tions, followed by a trenching operation to give 
information on the material below the surface. 
Other standard sequences including, for ex- 
ample, drop tests, have been formulated and 
programmed. In practice, it may be desirable 
to select a program after television views of the 
actual surface in the vicinity of the spacecraft 
have been studied. After some preliminary 
tests, for example, an attempt to pick up, weigh, 
or break a rock may be of greater value than 
further standard tests. 
Acknowledgments. The author is indebted to 
Mr. F. Roberson of the Jet Propulsion Laboratory 
of the California Institute of Technology for his 
assistance in formulating the experiments and 
carrying out the laboratory tests described in this 
paper. 
The work described herein is performed under 
contract JPL-CIT 69811 with the Jet Propulsion 
Laboratory. The surface sampler was designed and 
is constructed by Hughes Aircraft Company, E1 
Segundo, California. 
I•EFERENCES 
Jaffe, L. D., et al., Surveyor 1: preliminary results, 
Science, 152, 1737-1750, June 24, 1966. 
McCatry, J. L., A. G. Beswick, and G. W. Brooks, 
Application of penetrometers to the study of 
the physical properties of lunar and planetary 
surface, NASA Tech. Note D-2413, 1964. 
Scott, R. F., Lunar problems in soil engineering, 
Proc. Am. Soc. Civil Engrs., J. Soil Mech. Found. 
Div., 91, SM1, January 1965. 
Turkevich, A. L., K. Knolle, E. Franzgrote, and 
J. H. Patterson, Chemical analysis experiment 
for the surveyor lunar mission, J. Geophys. Res., 
72 (2), 1967. 
(Received November 17, 1966.) 


Soil mechanics surface sampler experiment for Surveyor

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Soil mechanics surface sampler experiment for Surveyor

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