Reports/Apollo 17/Mission report/4.0 Lunar Surface Science
The Apollo lunar surface experiments package for this mission consisted of the heat flow experiment, the lunar seismic profiling experiment, the lunar atmospheric composition experiment, the lunar ejecta and meteorites experiment, and the lunar surface gravimeter experiment. Other lunar surface experiments included the traverse gravimeter experiment, the surface electrical properties experiment, the lunar neutron probe experiment, the cosmic ray detector experiment, the lunar geological investigation, and the soil mechanics experiment.
Descriptions of the experiment equipment or references to documents in which the descriptions may be found are contained in Appendix A. A comprehensive discussion of the preliminary scientific results of the mission are contained in reference 1.
[edit] 4.1 Summary of lunar surface activities
The landing point was in a cratered valley between two massifs. Figure 4-1 is a panoramic camera photograph of the Taurus-Littrow landing site. The variety of topographic features at the Taurus-Littrow landing site provided a valuable asset in the exploration of the lunar surface. The crew completed three periods of extravehicular activity during the 75 hours on the surface. The events of each of the three periods are summarized in table 4-I and the routes traversed are shown in figure 4-2. The arrangement of the experiment equipment is shown in figure 4-3. More detailed descriptions of the lunar surface activities are provided in sections 4.12 and 10.8.
[edit] 4.2 Apollo Lunar Surface Experiments Package central station
The site selected for deployment of the Apollo lunar surface experiments package was located approximately 185 meters west northwest (bearing of 287°) of the lunar module (fig. 4-3). During preparations for the traverse, the Lunar Module Pilot had difficulty removing the dome from the fuel cask where the fuel capsule is stowed. Insertion of the dome-removal tool and dome rotation to the unlocked position went smoothly; however, the tool extraction pull resulted in a separation of the tool from the dome. Using the chisel end of the geological hammer, the dome was pried from the cask. (Section 15.4.4 contains a discussion of this anomaly.) Removal of the fuel capsule from the cask and installation in the generator was completed normally. During the traverse to the deployment site, one of the two central station levelling blocks was knocked off; however, this did not adversely affect the deployment.
During the antenna alignment, centering of the east/west bubble level was difficult, and near the end of the third extravehicular activity, the antenna level settings were rechecked. The east/west bubble was against the east edge and the north/south bubble was centered, and no changes were made. This amount of misalignment causes a somewhat greater variation in signal strength during the lunar libation cycle, but it will not impact system commands or the transmission and reception of telemetry data.
Initial data were received at 0254 G.m.t. on December 12 and the received signal strength, radioisotope thermoelectric generator power, reserve power, and temperature status were all near the pre-mission predictions. The power output stabilized at 75.8 watts during the first lunar day and increased to 77.2 watts during the first lunar night. The automatic power management circuit is maintaining the average thermal plate temperature of the central station between 270.1° K and 324.8° K.
The telemetry signal power level, as received at various Spaceflight Tracking and Data Network sites, varied ±1.5 dBm in a sinusoidal manner around the normal level and this had no affect on the data. This variation was probably caused by a multipath phenomena produced by an antenna side-lobe reflection from the South Massif.
[edit] 4.3 Heat flow experiment
Two heat flow experiment (S-037) bore stems were drilled into the lunar surface to the planned depth of 254 centimeters and the probes were inserted during the first extravehicular activity (fig. 4-4).
The total power-on time required to drill bore stem 1 into the soil was 3 minutes 46 seconds. The penetration rate was variable with a particularly low penetration rate (40 centimeters per minute) occurring at a depth of about 80 to 100 centimeters. Between 120 and 200 centimeters depth, the penetration rate was 84 centimeters per minute, and in the final 50 centimeters, the rate slowed to about 6e centimeters per minute. Based on crew comments and televised visible sudden torques on the drill handles, some rock fragments were probably encountered during the drilling operations. The first meter of probe hole 2 was drilled more rapidly than that of probe 1 and below 200 centimeters, a resistant layer was encountered which slowed progress to about 60 centimeters per minute. Rock fragments were frequently encountered during the drilling of probe hole 2 which required a total power-on time of approximately 3 minutes.
The heat flow experiment was turned on at 0302 G.m.t. on December 12 and valid temperature data were received from all sensors. The operation of the experiment has been satisfactory. Probe 2 was operating before being inserted into the bore stem and a bore stem-and-probe temperature of about 300° K was indicated immediately after insertion. From December 12 to January 3, the experiment was operated in the normal gradient mode, which samples each sensor every 7.2 minutes. Between January 3 and January 24, eight low-conductivity experiments were conducted with a heater power of 0.002 watt. One high-conductivity experiment was performed on January 26.
The reference thermometer attached to the experiment electronics package radiator plate indicates that the package reaches a maximum temperature of 328° K at lunar noon, and remains at 290° K throughout the lunar night.
[edit] 4.4 Lunar seismic profiling experiment
The lunar seismic profiling experiment (S-203) geophone array was deployed at the lunar surface experiments site (fig. 4-3). The experiment was commanded on to verify instrument operation at 0358 G.m.t. on December 12.
The explosive packages were deployed as shown in figure 4-2 during the three extravehicular activity periods. All of the explosive charges were detonated by command and each of the geophones responded to the detonations. The detonation of explosive package 7 was observed through the television camera.
The central station was commanded to the high-bit-rate mode at 2229 G.m.t. on December 14 to record the impulse produced by the lunar module ascent. A strong seismic signal response from the geophone array was recorded.
The lunar seismic profiling experiment was again commanded to the high-bit-rate mode at 0636 G.m.t. on December 15 to record the lunar module ascent stage impact. The impact occurred at 19 degrees 59 minutes 24 seconds north and 30 degrees 30 minutes 36 seconds east at 0650 G.m.t. on December 15. The impact point was on the south slope of South Massif, about 8.4 kilometers southwest of the Apollo 17 landing site.
The recording of the seismic signals produced by the detonation of the eight explosive packages, together with the signal from the lunar module ascent stage impact, have enhanced the knowledge of the lunar structure. At the Taurus-Littrow site, the lunar near-surface material has an average seismic velocity of 250 meters per second to a depth of 248 meters. There is an indication of increased apparent velocities within the lunar near-surface material, suggesting the presence of possible inter-stratified material, perhaps thin lava flow. Beneath the 250 meters per second material, the seismic velocity increases to 1200 meters per second, characteristic of a competent lava flow. The thickness of the 1200 meters per second material is about 925 meters. Underlying the 1200 meters per second layer is material of an undetermined thickness which possesses a seismic velocity of about 4000 meters per second.
When the Apollo 17 data are combined with data from the earlier missions, it should be possible to determine the structure of the lunar crust to a depth of approximately 10 kilometers.
[edit] 4.5 Lunar atmospheric composition experiment
The lunar atmospheric composition experiment (S-205) deployment is shown in figure 4-3. All activities associated with the deployment were completed as planned. The dust cover was opened on December 18 at approximately 0420 G.m.t. after the last lunar seismic profiling experiment explosive package was detonated. After allowing the radiator temperature to decrease from a peak of 340.8° K (before cover removal), to 327.5° K, nine hours of ion source outgassing was accomplished the following day with a temperature of 523° K having been reached.
The first activation of the experiment occurred on December 27 at approximately 1800 G.m.t. The instrument responded well to commands and was operating normally except for a background count ramp in the low- and mid-mass channels. The presence of this interference will not cause the loss of data, but it will increase the difficulty in reducing the data from this portion of the spectrum. This anomaly is discussed in section 15.4.5.
Operation throughout the first lunation was characterized by good performance of the instrument except for two occasions during lunar sunrise when the instrument switched into the high-voltage-lock mode, which stopped the stepping of the sweep voltage. Two logic system noise bursts, which occurred just after sunrise, may have caused the sweep high voltage to be commanded into lock. On both occasions, the situation was properly rectified by commanding the sweep high voltage back on.
Many residual peaks were observed in the spectrum, but only the helium peak is clearly native to the moon. The remainder are at least partially due to outgassing of the instrument, the lunar module, and the Apollo lunar surface experiments package, as evidenced by the peaks decreasing in amplitude throughout the lunar night.
Sunrise brought a large increase in all peaks in the spectrum except helium which decreased as would be expected if it were a native noncondensible gas. Operation was curtailed 24 hours after sunrise because of the very high gas densities in the ion source chamber (approximately 109 molecules per cubic centimeter) from material outgassing. A 15-minute period of operation was performed at lunar noon. Full-time operation was begun again a few hours before sunset on January 23. There was a marked decrease in gas densities about the time of sunset.
Daytime operation will be limited to those times when the outgassing levels are tolerable. As indicated by the data from previous missions, the instrument, site, and other artifacts will eventually be sufficiently free of outgassing contaminants to enable the lunar atmospheric composition experiment to produce high quality data.
[edit] 4.6 Lunar ejecta and meteorites experiment
The lunar ejecta and meteorites experiment (S-202) deployment is shown in figure 4-3. The radiator mirror was uncovered at 0957 G.m.t. on December 21, after detonation of the last explosive package and when the internal structural temperature had decreased to 344° K. The experiment was operated for about 15 hours on December 22 but was turned off because of rising temperatures. The experiment was turned on again on December 23 to record the background noise rate for the instrument. The sensor covers were not removed until December 28, after completion of continuous operation which encompassed about 60 hours of lunar day and about 50 hours of lunar night. The instrument data indicate that the background noise rate was essentially zero.
The instrument is in the full operating mode from sun angles of 20° before sunset through 20° after sunrise because of a thermal control problem during the lunar day. Section 15.4.3 contains a discussion of this anomaly. Fortunately, the instrument measurements of ejecta are best performed during the lunar night when the primary particle impact rates are near zero. The instrument will remain off during most of the lunar day until the science objectives which can be achieved during lunar night are fulfilled or until satisfactory thermal control can be attained.
The measurements indicate that the detected number of lunar ejecta particles compare within an order of magnitude to the number of primary particles. The measurements are verifying that the bulk of cosmic dust material comes from the general direction of the sun which agrees with the results obtained from similar instruments carried on Pioneer 8 and 9.
[edit] 4.7 Lunar surface gravimeter experiment
The lunar surface gravimeter experiment (5-207) (fig. 4-3) was activated at 0523 G.m.t. on December 12, and following activation, the data (science and engineering) indicated normal operations. However, the addition of all masses apparently set the sensor beam against the lower stop and removal of one mass apparently moved the beam against the upper stop. Operation of the adjustment screws failed to null the beam and the second adding of all masses failed to move the beam to the lower stop. This anomaly is discussed in section 15.4.1.
On January 3, 1973, the experiment was re-configured, and the sensor beam was centered by adjusting the mass change mechanism to obtain longterm seismic and free-mode science data. In this revised configuration, tidal data are not being obtained, but the experiment is collecting longterm seismic and free mode information.
The lunar surface gravimeter experiment sensor's initial on-scale temperature of 321.5° K occurred at about 2054 G.m.t., December 14, some 63 hours after initial turn-on. The experiments sensor temperature now remains stabilized at 322.323° K. The instruments subsystem components continue to operate normally providing engineering status data.
[edit] 4.8 Traverse gravimeter experiment
The traverse gravimeter experiment (S-199) made an earth-moon gravity tie and obtained the value of gravity at various stops along the traverses, relative to the value of gravity at the landing site. Using absolute gravity measurements on the Earth, a preliminary value of 162 694 (±5) milligals was obtained at the Taurus-Littrow landing site. The number of stations (12) at which discrete gravity measurements were made (fig. 4-2 and table 4-I) was about as planned with an extra measurement being made at station 2A and no measurements taken at station because of time constraints.
The hardware performed satisfactorily except for differences between measurements made on the lunar roving vehicle and measurements made with the experiment resting on the surface at the same sites. The values measured on the surface were always lower. The difference in the gravity measurement at the landing point was 4.6 milligals, at station 8 it was 6.9 milligals, and at station 9 it was 6.2 milligals. The reason for this discrepancy is not known. In initial postflight calculations, an empirical correction of -6 milligal was established for all values measured when the experiment was mounted on the lunar roving vehicle.
A preliminary analysis of the data has been made by projecting it to a northwest-southeast profile and by making two dimensional approximations for all the reductions and interpretations. Free-air and Bouguer corrections were applied to the data. The resultant Bouguer corrections shows values at stations 2A and 8, near the South and North Massifs, respectively, which are more than 20 milligals lower than the value at the landing site. The variation of Bouguer values in the central part of the valley are relatively small, although the value at station 4 is a few milligals higher and the value at station 5 is a few milligals lower than the value at the landing site. A preliminary interpretation of the gross features of the gravity profile is a model with basalt flows having a positive density contrast of 0.8 gram per cubic centimeter and a thickness of 1 kilometer buried under the valley floor.
[edit] 4.9 Surface electrical properties experiment
The surface electrical properties experiment (S-204) was deployed as shown in figure 4-2, and was utilized during portions of both the second and third extravehicular activity periods. During the transmitter deployment, a problem was encountered in keeping the solar panel open because of memory in the solar panel wiring harness. The crew resolved the problem by taping the panel fully open. Also, during the deployment of the transmitter antennas, the two sets of dipoles were reversed from the planned orientation. The effect of the reversal was corrected in the data reduction process with no loss of data.
A thermal control problem with the surface electrical properties receiver caused the premature termination of the experiment. This problem is discussed in detail in section 15.4.2.
Despite these problems, when the surface electrical properties experiment recorder was returned to earth, 1 hour and 42 minutes of data had been obtained.
[edit] 4.10 Lunar neutron probe experiment
The lunar neutron probe experiment (S-229) was deployed as shown in figure 4-3 and emplaced in the deep drill core hole during the first extravehicular activity period. The 2-meter probe was retrieved and deactivated at the end of the third extravehicular activity period, accruing 49 hours of exposure. The site was approximately 38 meters north of the Apollo lunar surface experiments package radioisotope thermoelectric generator (fig. 4-3). Corrections required because of the proximity of the generator, which is a strong source of neutrons, should be small; although experimentation is necessary to determine the size of the correction.
The probe was returned, disassembled, and the targets and detectors were in excellent condition.
The background due to the direct interaction of the fast neutrons from the radioisotope thermoelectric generator with the plastic was measured, and appears to be negligible.
Only the mica detectors have been completely examined. Analysis of the remaining detectors and data is continuing and will be completed after postflight calibration of the probe. Although the calibration data have not been completely processed, the track densities are in the expected range. The neutron capture rates appear to be within a factor of two of those estimated from the theoretical calculations.
[edit] 4.11 Cosmic ray detector experiment
The cosmic ray detector experiment (S-152) was deployed by pulling the slide cover open and hanging the cover in the shade while the box was in the sun on the lunar module. In both cases, the nuclear particle detectors faced outward from the lunar module. The detectors were exposed to the lunar environment for approximately 45.5 hours. No degradation of any of the detector surfaces was found. Microscopic examination of the detector surfaces showed very little dust. The maximum temperature of approximately 4000 K (as shown by temperature labels) was well below the critical limit.
The tracks of heavy solar wind ions are clearly visible, as are the tracks of intermediate-energy heavy particles. The flux of the latter is surprisingly high (approximately 6 x 103 tracks per square centimeter) and indicate that the sun emits an appreciable flux of particles in the range of 10 keV per nucleon to 10 meV per nucleon, even at times of quiet sun. These particles were found in both the shade and sun detectors and thus are not directly associated with the solar wind. The tracks have been seen in the mica, glass, and plastic detectors. The energy spectrum is similar to that of solar flares. This intermediate energy component is possibly associated with a visually active sun spot area that was present during the entire Apollo 17 mission. This experiment is the first flown that could have detected the presence of the intermediate-energy particles. The presence of the intermediate-energy particles will limit the degree to which the radon atmosphere can be established at the Apollo 17 site, but this constitutes no degradation of the basic experiment.
Edits and errors by Eric Hartwell are licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 license. The original NASA material is copyright-free.