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.


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 panoramic camera.



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.


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 functional changes.

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 limits.

Figure 4-3.-Apollo lunar surface experiment deployment


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


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.


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.


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 (see fig. 4-6).

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 lost.


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 sunset.


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 outgassing.

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 (approximately 85 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.


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.


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.


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. 4-6).


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 craters.

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 lenses. Figure 4-8 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 constraints.

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 front.

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 centimeter long.

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 sequence.

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.

4.12.4 Equipment

The equipment used during the geology portion of the extravehicular activities performed well with the following exceptions:

4.12.5 Photography

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.


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. Figure 4-9 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, performed satisfactorily.


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.