4.0 LUNAR SURFACE SCIENCE
The following experiments associated with the Apollo lunar surface
experiment package are discussed in this section: suprathermal ion
detector, cold cathode gage, passive seismometer, lunar surface
magnetometer, solar wind spectrometer, heat flow, and lunar dust detector.
Other experiments and activities discussed consist of a laser ranging retro-reflector
experiment, a solar wind composition experiment, lunar geology,
soil mechanics, and lunar gravity measurement. Additionally, the operation
of the lunar drill, used in conjunction with the heat flow experiment and
to obtain a deep core sample, is described. A comprehensive discussion of
the preliminary scientific results of this mission are contained in
reference 2. References to descriptions of the experiment equipment are
contained in Appendix A.
4.1 SUMMARY OF LUNAR SURFACE ACTIVITIES
Because of the variety of surface features, the Hadley-Apennine landing
site permitted extensive diversified geologic exploration and sampling.
During the approximately 67 hours on the surface, the crew conducted a 33-
minute standup extravehicular activity as well as three extravehicular
activities for experiment operations and lunar roving vehicle traverses. The
timelines for the three extravehicular activity periods are contained in
table 4-1. The actual and planned traverse routes are shown in figures 4.1
and 4-2, which are actual photographs of the lunar surface taken with the
TABLE 4-1.- EXTRAVEHICULAR TRAVERSE EVENTS
TABLE 4-1.- EXTRAVEHICULAR TRAVERSE EVENTS - Concluded
The outbound route of the first extravehicular traverse was southwest
across the mare to the edge of Hadley Rille, south along the edge of the
rille to Elbow Crater (station 1, fig. 4-1); then along the edge of the
rille to an area near St. George Crater (station 2). The return route was
past Elbow Crater and directly across the mare to the lunar module. After
returning to the lunar module, the crew deployed the Apollo lunar surface
experiment package, the laser ranging retro-reflector, and the solar wind
composition experiment (fig. 4-3). The extravehicular activity was
approximately 6 hours 33 minutes in duration and the traverse covered a
distance of 10.3 kilometers (5.6 miles).
The second extravehicular activity was southeast across the mare to the
Apennine front (stations 6 and 6a) northwest to Spur Crater (station 7) and
north to the area of Dune Crater (station 4). The return was north across
the mare to the Apollo lunar surface experiment package site (station 8) and
then to the lunar module. The duration of the second extravehicular activity
was approximately 7 hours 12 minutes, and the distance traveled was 12.5
kilometers (6.8 miles).
The third extravehicular activity included a 5.1-kilometer (2.8-mile)
traverse. The outbound trip was west to Scarp Crater (stations 9
and 9a) and
northwest along the edge of the rille (station 10). The return was east
across the mare to the lunar module. The duration of the third
extravehicular activity was approximately 4 hours and 50 minutes.
Figure 4-1.-Actual lunar surface traverse routes
Figure 4-2.-Planned lunar surface traverse routes.
4.2 APOLLO LUNAR SURFACE EXPERIMENTS PACKAGE CENTRAL STATION
The site selected for emplacement of the central station was
approximately 110 meters (360 feet) west-northwest of the lunar module.
During erection of the central station, the rear-curtain-retainer removal
lanyard broke, requiring the Lunar Module Pilot to remove the pins by hand.
(See section 14.4.2 for further discussion.)
Initial acquisition of a downlink signal from the Apollo lunar surface
experiment package was reported by the Canary Island station prior to
antenna installation. Initial data were received in the Mission Control
Center at 1850 G.M.T. (125:18:00) on July 31 and, within 1 hour, all
instruments were turned on and operationally checked out. (The initial
acquisition of data was earlier than expected because the shorting plug was
inadvertently activated.) The radioisotope thermoelectric power source is
providing 74.5 watts, the highest output of any Apollo lunar surface
experiment package, and sufficient to operate the large complement of
instruments. During the first lunar-night operation, the system reserve
power registered as low as 1 watt. The solid-state timer, used
for the first time on an Apollo lunar surface experiments package has
generated all scheduled 18-hour pulses to initiate certain automatic
Six days after startup, on August 6, the experiment package was
subjected to its first lunar eclipse. This was a total eclipse and the
package was closer to the center of the umbra than any previous Apollo lunar
surface experiments package during any previous eclipse. During the eclipse,
sun shield temperature of the central station dropped from plus 140 F to
minus 143 F with accompanying rates of change of temperatures up to
260 F per
hour. The central station engineering measurements provided data on the
varying solar intensity throughout the eclipse. The instrument measured a
lunar surface temperature change of 330 F during the eclipse. There was no
indication of significant dust collection on the instrument's solar cells as
a result of the lunar module ascent.
The system continues to exhibit normal performance. Equipment
temperatures during both lunar day and lunar night are within design
Figure 4-3.-Apollo lunar surface experiment deployment
4.3 PASSIVE SEISMIC EXPERIMENT
The passive seismic experiment was deployed approximately 2.7 meters
(9 feet) west of the experiment package central station and has functioned well
since its initial activation on July 31, 1971. One deviation from nominal
operation has occurred. The instrument internal temperature fell below the
predicted 126 F as the Apollo 15 site entered the first lunar night. This will
not detrimentally affect the operation of the instrument except that
degradation of gravity tidal data from the experiment is expected.
Photographs of the instrument show the shroud skirt to be raised up at
several places (fig. 4-4). Heat loss due to the uneven shroud accounts for the
low night temperature.
Figure 4-4.- Passive seismic experiment deployment
The installation of this experiment at Hadley Rille provides a widely
spaced network of seismic stations on the lunar surface which is essential for
the location of natural lunar events. The first event to be recorded on all
three Apollo Lunar surface experiment package stations was the impact of the
lunar module ascent stage approximately 93
kilometers (50 miles) west of the Apollo 15
station. The signal generated by this impact spread slowly outward,
reaching the Apollo 15 station in 28 seconds, and reaching the
Apollo 12 and 14
stations, located to the southwest at distances of 1130 kilometers
(610 miles) and 1049 kilometers (566 miles), respectively, in about 7 minutes (fig. 4-5).
The fact that this small source of energy was detected at such great range
strongly supports the hypothesis that meteoroid impacts are being detected
from the entire lunar surface.
Two moonquakes were detected at all three stations during the moon's
travel through its first perigee following activation of the Apollo 15 station.
Preliminary analysis places the focus of one of these moonquakes 400
kilometers (216 miles) southwest of the Apollo 15
station. It is believed that the second moonquake was 1000 kilometers
(540 miles) southwest of the Apollo 12 and 14 stations and was 800 kilometers
(432 miles) deep.
The S-IVB impact extended the depth to which lunar structure can be
determined by seismic methods to nearly 100 kilometers (54
miles). From this
and previous data from impacts of spent vehicles, it now appears that a
change in composition occurs at a depth of 25 kilometers (13.5 miles) beneath
the surface. This implies that the lunar crust is equivalent to the crust
of the earth, and about the same thickness.
Two meteoroid impacts were recorded at the Apollo 15 station during
the first 2 weeks of its operation. One of these impacts was recorded
at all three stations and was located by triangulation. Fourteen impact
events were recorded by the Apollo 12 and 14 stations during this period.
Signals were also recorded that were caused by events and activities
associated with lunar surface operations, particularly the movements of
the lunar roving vehicle and the ascent from the lunar surface. The lunar
roving vehicle was detected at ranges up to 5 kilometers (2-7 miles) with
an accuracy within approximately 0.5 kilometer (0.27 mile). As in
previous missions, numerous signals were also recorded from venting of
gases and thermal "popping" within the lunar module.
Figure 4-5.- Apollo landing sites and impact locations on the lunar surface
4.4 LUNAR SURFACE MAGNETOMETER EXPERIMENT
The lunar surface magnetometer was deployed approximately
15 meters (48 feet) west-northwest of the Apollo lunar surface experiment package central
station. The experiment was initially commanded on near the end of the first
extravehicular activity. A-11 operations of the experiment have been nominal.
The electronics temperature has reached a high of 157 F at lunar noon, and a
low of 41 F during lunar night. The instrument is routinely commanded into
a calibration mode every 18 hours by the central station timer. The one-time
site survey was successfully-completed on August 6. The remanent magnetic
field at the site is lower than that measured at the Apollo 12 and 14 sites.
The eddy current produced by the interaction of the solar wind with the lunar
surface has been measured.
4.5 SOLAR WIND SPECTROMETER EXPERIMENT
The solar wind spectrometer was deployed
4 meters (13 feet) north of
the Apollo lunar surface experiment package central station and was
activated near the end of the first extravehicular activity. The
instrument recorded engineering and background data for approximately
2 earth days before the seven dust covers were removed.
The instrument recorded normal magnetospheric plasma data until the
instrument passed into the geomagnetic tail of the earth. As expected, the
plasma level in the geomagnetic tail was below the measurement threshold of
the instrument (and essentially no solar wind plasma was detected) Upon
emerging from the geomagnetic tail, the instrument was switched to the
extended-range mode with no operational problems. The instrument will be
left in this mode for correlation of data with the Apollo 12 solar wind
spectrometer which is also operating in the same mode. A comparison of
samples of simultaneous data from the two instruments has already
demonstrated differences in the electron and proton components of the solar
wind plasma that strikes the surface of the moon at the two stations. The
solar plasma levels during the lunar night, as expected, were below the
measurement threshold of the instrument.
4.6 HEAT FLOW EXPERIMENT
Deployment of the heat flow experiment was started on the first
extravehicular activity and completed on the second extravehicular activity.
A minor problem was experienced in removing two Boyd bolts that fasten the
heat flow experiment components to the subpallet and problems were
encountered in drilling the holes for two probes and emplacing the second
probe. Refer to sections 4.11 and 14.4.1 for further discussion. The
electronics box was placed about 9 meters (30 feet) north-northeast of the
central station. The first probe hole was drilled about 4 meters (12 feet)
east of the electronics box and the second, about 4.5 meters (15 feet) west
of the box. The first hole was drilled to a depth of about 172 centimeters
(70 inches) and probe 1 was emplaced during the first extravehicular
activity, but the drilling of the second hole and emplacement of probe 2 was
deferred because of time constraints. Drilling was resumed at the second
hole during the second extravehicular activity and a hole depth of about 172
centimeters (70 inches) was again achieved; however, damage to a bore stem
section (sec. 14.4.1) prevented probe 2 from reaching the bottom of the
hole. The first heat flow experiment probe extends from a point 47 centimeters (19
inches) below the surface to a point 152 centimeters (62
inches) below the surface. Because of the damage to the bore stem in the
other hole, the second probe extends from the surface to 105 centimeters (43
inches) below the surface
The experiment was turned on at 1947 G.m.t., July 31, and valid
temperature data were received from all sensors. Because of the shallow
emplacement of probe 2, high near-surface temperature gradients will keep the
differential thermometers on the upper section off-scale during most of a
lunar day-night cycle. The lower section of probe 2 and both the upper and
lower sections of probe 1 are returning valid data on subsurface
temperatures. Sensors on these sections that are shallower than 80
centimeters (32 inches) are seeing the effects of the diurnal cycle of
surface temperature, but these variations are well within the range of
measurement. Lunar surface temperatures are being obtained from five of the
eight thermocouples in the probe cables that are just above or on the lunar
surface because of the shallow emplacement.
Data for the reference thermometer sampled with the probe 2
thermocouple measurement went off-scale high at 1027 G.m.t. August 7;
however, the data from this reference thermometer is also sampled with the
probe 1 thermocouple measurement, and is valid. Therefore, no data have been
4.7 SUPRATHERMAL ION DETECTOR EXPERIMENT
The suprathermal ion detector experiment was deployed and aligned
approximately 17 meters (55 feet) east-northeast of the Apollo lunar surface
experiment package central station. Some difficulty was encountered during
deployment when the universal handling tool did not properly interface with
the experiment receptacle and, as a result, the instrument was dropped. The
instrument was initially turned on near the end of the first extravehicular
activity and operated normally, returning good scientific data. After about
30 minutes of operation the instrument was commanded to "standby" to allow
outgassing. The dust cover was removed by ground command prior to the second
extravehicular activity. Subsequently, the instrument was commanded on for
five periods of approximately 30 minutes each to observe the effects of: (1)
depressurization for the second extravehicular activity, (2)
depressurization for the third extravehicular activity, (3) depressurization
for equipment jettisoning, (4) ascent, and (5) lunar module ascent stage
impact. During some of this time simultaneous observations of intense
magnetosheath ion fluxes were made by all three suprathermal ion detector
instruments now on the moon. The high voltage was commanded off prior to
the hotter part of the first lunar day
to allow further outgassing and was commanded back on shortly before lunar
4.8 COLD CATHODE GAGE EXPERIMENT
The cold cathode gage experiment was deployed about 0.3 meter (1 foot)
northeast of the suprathermal ion detector experiment. The instrument was
turned on and the seal was commanded open 3 minutes prior to the end of the
first extravehicular activity. Upon initial turn-on, the gage indicated full-
scale, and during the first half hour, the output became slightly less than
full-scale. Subsequently, the high voltage was commanded off to allow
The experiment was operated five more times simultaneously with the
suprathermal ion detector experiment for periods of approximately 30
minutes each. The purpose of the operations was to observe the effects of
the lunar module depressurizations for the second and third extravehicular
activities and equipment jettison, the effects of the lunar module ascent
from the lunar surface, and lunar module ascent stage impact. In each of
the three depressurizations, the output of the experiment was driven to
full-scale for approximately 30 seconds. The response to the lunar module
depressurizations was very similar to that obtained during the Apollo 14
mission. The lunar module ascent resulted in the longest full-scale output
seconds). The exhaust from the lunar module ascent was
detected for approximately 17 minutes.
The high voltage was turned off until just prior to the first lunar
sunset to permit additional instrument outgassing. As the instrument and the
lunar surface cooled during lunar night, the output of the gage gradually
decreased to 10E-12 torr. This value is very near that observed on the Apollo
14 gage during lunar night. Two gas clouds of unknown origin were observed
at the Apollo 15 site at 0400 and 1930 G.m.t. on August 15; these may be
associated with Apollo 15 hardware left on the lunar surface.
4.9 LASER RANGING RETRO-REFLECTOR EXPERIMENT
The laser ranging retro-reflector was deployed during the first
extravehicular activity approximately 43 meters (140 feet) west-southwest of
the Apollo lunar surface experiment package central station. Leveling and
alignment were accomplished with no difficulty. The McDonald Observatory
team initially acquired a return signal from the Apollo 15 instrument August
3, 1971, when atmospheric conditions first permitted ranging. Based on
successful acquisition on every attempt, and the receipt of four
to five consecutive returns during a number of operations, the return signal
strength appears higher than returns from the Apollo 11 and 14
retroreflectors (fig. 4-5). No degradation of the retro-reflector appears to
have resulted from lunar module ascent engine firing.
4.10 SOLAR WIND COMPOSITION EXPERIMENT
The solar wind composition experiment, a specially prepared aluminum
foil designed to entrap noble gas particles, was deployed at the end of the
first extravehicular period and retrieved near the end of the third
extravehicular period. The experiment was deployed approximately 15
meters (50 feet) southwest of the lunar module for a total foil exposure time of
41 hours and 8 minutes. Upon retrieval, the foil could not readily be rolled up
mechanically and had to be rolled manually. This problem has been
experienced on previous missions but does not affect the experiment. The
returned hardware showed that the edge of the foil had rolled onto the reel-
handle, which caused enough friction to stop the mechanical wind-up. Good
data on the abundance of the isotopes of helium and neon in the solar wind
have already been obtained.
4.11 LUNAR SURFACE DRILL OPERATION
The lunar surface drill, used for the first time on the lunar surface,
provided a means for one crewman to emplace the heat flow experiment probes
below the lunar surface and collect a subsurface core. For the heat flow
experiment, the bore stems used in drilling remained in position in the
lunar soil and functioned as an encasement to preclude cave-in of
unconsolidated material. The subsurface core was obtained by drilling six
core stems into the lunar soil. The stems were then removed and capped for
return to earth.
The performance of the drill power-head and the core stem was good.
However, full depth penetration with the bore stems was a problem and
extraction of the core stems from the hole was difficult (see sec. 14.4.1).
The two bore stem holes were drilled to a depth of about 172 centimeters (70
inches) instead of the desired 294 centimeters (120 inches), with one of the
bore stem strings probably sustaining damage at a point slightly above the
first joint [about 105 centimeters (43 inches) below the surface] (see fig.
4.12 LUNAR GEOLOGY
4.12.1 Landing Site
The lunar module landed on an undulating cratered plain adjacent to
the high and steep-sloped Apennine Mountains
( fig. 4-7).
Most of the
craters in the vicinity of the landing site are subdued and are rimless
or have low raised rims. Rock fragments and boulders are abundant along
the rim of Hadley Rille and around a few of the fresher craters.
4.12.2 Extravehicular Traverses
Areas visited during the extravehicular activities that are defined
on photogeologic maps were the mare surface of Palus Putredinis; the
Apennine Mountain Front; Hadley Rille; and a cluster of secondary
The standup extravehicular activity provided the geologic and terrain
setting for later traverse updating, and allowed the crew to familiarize
themselves with landmarks. Good photographs were obtained of the landing
site and the Hadley Delta area by using the 60-mm and 500-mm focal-length
is typical of the photographs obtained.
On the first extravehicular traverse, station 1 and 2 tasks were
performed as planned. Refer to figures 4-1 and 4-2 for locations of stations
on actual and planned traverse routes. The radial sample was collected at
Elbow crater (station 1). Documented samples and a comprehensive sample,
including a double-core, were collected near St. George crater (station 2).
Station 3 on the planned traverse was not visited because of time
The traverse time allowed during the second extravehicular activity was
shortened because of the time required to complete the Apollo lunar surface
experiment package site tasks that were not completed during the first
extravehicular activity. Therefore, the planned traverse to the east along
the front was shortened and only three stations along the front, 6, 6a, and 7
(Spur Crater), were visited. Several documented samples were collected at
stations 6 and 6a, and a single core was collected at station 6.
Documented samples and a comprehensive sample were collected at station 7.
The planned stop at station 4 (Dune crater) was accomplished on the return from the
The start of the third extravehicular activity was delayed and, as a
result, was shortened from 6 to 4 1/2 hours. The shortening of the
extravehicular period, plus the time required to remove the deep core
sample from its hole, required that the traverse to the North Complex and
mare station 14 be omitted. However, the premission-planned traverse to
stations 9 and 10 at Hadley Rille was made. A sample was collected from the
upper portion of a bedrock ledge exposed near station 9a. Documented
samples were collected at stations 9 and 9a, and a rake sample and a double
core were collected at station 9a.
4.12.3 Summary of Geology
Samples were collected that appear to be representative of the
Apennine Front, the mare in the vicinity of the landing site, bedrock from
the rim of Hadley Rille, and a possible ray associated with Aristillus or
Autolycus. Some breccias were collected that appear similar to those
collected on Apollo 14; others appear to be indurated regolith. Abundant
glass, found as coatings on the rock surfaces and in fractures, is
associated with the breccias. Also collected were basaltic rocks ranging
from vesicular and scoriaceous to dense with phenocrysts greater than a
Layered bedrock ledges are exposed in the upper parts of Hadley Rille.
These are probably a cross-section of mare flows and possibly bedded
pyroclastic materials. At least some of the samples from station 9a (fig. 4-
1) are probably representative of the upper part of the mare stratigraphic
Planar structures in the Apennine Front occur in different
orientations from one mountain to the next, which suggests rotation of
large blocks along the faults that are shown on the premission maps. The
faults and associated rotation were probably caused by the impact event
that produced the Imbrium Basin.
The equipment used during the geology portion of the extravehicular
activities performed well with the following exceptions:
a. Excessive time was required for the gnomon to damp.
b. Sample return container 2 did not seal properly because part of
a collection bag was caught in the seal area between the knife edge and
the indium seal.
c. The Lunar Module Pilot's camera did not advance film properly
near the end of the second extravehicular activity. The camera failed
again during the third extravehicular activity after six pictures had
been taken. (See section 14-5.4 for further discussion.)
d. Problems with the drilling were experienced as described in
e. The polarizing filter for the Hasselblad electric data camera
could not be installed because of excessive dust in the bayonet fitting.
f. Both retractable tethers (Yo-yo's) failed (sec. 14.5.7).
g. The tongs were difficult to operate during the third
extravehicular activity; however, a backup pair was supplied for such a
contingency and these operated satisfactorily.
A total of 1152 photographs was taken on the lunar surface with the 60-
mm and 500-mm focal-length cameras. At least one 360-degree 60-mm panorama
was taken at every station except stations 3 and 4. Apollo 15 was the first
mission using the 500-mm focal length lens mounted on the 70-mm Hasselblad
electric data camera hand-held by a crewman. Good photography was obtained
of distant photographic targets such as the Apennine Front and across and
inside Had-ley Rille.
4.13 SOIL MECHANICS EXPERIMENT
The soil mechanics experiment provided data on the physical
characteristics and Mechanical properties of the lunar surface and subsurface
soil. Activities during Apollo 15 unique to the soil mechanics experiment
were performed during a compressed timeline at station 8 (fig. 4-1) near the
end of the second extravehicular activity with only one crewmember available
to do the work instead of two as scheduled. The Lunar Module Pilot excavated
the soil mechanics trench, exposing a Vertical face to an estimated depth of
a little more than 1 foot without apparent difficulty. The vertical face
exposed a fine-grained, cohesive, gray material with small white fragments
and larger fragments of glass. Stratification was not observed. Digging of
the trench was followed by six of seven planned measurements using the self-
recording penetrometer. These tests consisted of four cone penetration
resistance tests and two plate load tests. No time was available for the
detailed planned photographic documentation of these activities, nor was the
television camera on the lunar roving vehicle in a suitable position to
provide a high degree of detail.
Data from the penetrometer tests were intended to provide
quantitative information on the physical properties of the lunar soil to
depths up to 74 centimeters (30 inches). The data, now under study, will
probably not provide the quantitative detail on physical properties
originally anticipated because of the following reasons: (1) The soil
structure at the site had greater penetration resistance than had been
anticipated (2) A particularly resistant layer was encountered at a depth
of only a few centimeters; (3) The lunar surface plate on the penetrometer
failed to stay in the proper position during four of the tests because the
friction between the reference plate bushing and the shaft was less than
had been anticipated.
The average depth of lunar roving vehicle tracks was on the order of 1
centimeter (1/2 inch), in agreement with predictions based on terrestrial
wheel/soil interaction tests performed on simulated lunar soil.
illustrates vehicle tracks, footprints, and excavated areas.
The large number of photographs and the numerous observations made by
the crew concerning the interactions between the lunar surface and (1) the
crew, (2) the lunar module, (3) the lunar roving vehicle, and (4) the
experiment packages and handtools will be of value to the soil mechanics
experiment. The core tubes, which were modified for this mission,
4.14 LUNAR GRAVITY MEASUREMENT
Accelerometer data telemetered to earth between lunar module
touchdown and inertial measurement unit powerdown were obtained to
determine the observed lunar gravity. Nineteen measurements were taken
during four operating periods. The time spans and sequence of the periods
were: 658 seconds, 240 seconds, 12 seconds, and 269 seconds. Lunar gravity
at the landing site will be calculated from the reduced data.