Soil Mechanics Surface Sampler

JOURNAL OF GEOPHYSICAL RESEARCH VOL. 74, NO. 25, NOVEMBER 15, 1969

R. F. SCOTT1 AND F. I. ROBERSON2

A lunar surfacesampler essentially identical to that operatedfrom Surveyor 3 was mounted on Surveyor 7 and performed flawlessly on the moon throughout a range of operating temperatures from +180øF to --167øF. The motor current was sampled during lunar bearing and trenchingtests, and these data, togetherwith prefiight calibrationsenabled us to calculate the forces involved in these tests. After minimal lunar surface testing, the surface sampler was employedto releasethe sensorhead of the s-scatteringinstrument, which had jammed in its backgroundposition. Subsequently, the sensorhead was relocatedto analyze a rock and, still later, to analyzesome subsurface lunar material.The mechanicaltests of the surfacein the vicinity of Tycho indicated that the surfacebehaved in a manner that was quantitativelysimilar to the behaviorof the material closeto Surveyor3, but the surface near Tycho appeared qualitatively to be more deformable and less brittle. A rock was weighedand foundto have a densitybetween 2.4 and 3.1 g/cm8 (earth basis).Another rock was brokenby a moderatelyhard blow from the sampler.The soil varied in depth from I to at least severalinches over underlyingrock fragmentsnear Surveyor7. Little adhesionof lunar soil to the mirror surfaceof the s-scatteringexperiment sensor head was observedover a 24-hour period.

SUBSYSTE1VfDESCRIPTION unit, the elevationand retractionmotors have a sensorattached to each motor housing (Fig- The physicaldesign of the surface-sampler mechanismand its auxiliary electronicsunit is ure 1). the sameas that of Surveyor3 [Scott and Rob- Mountingsubstructure. The surfacesampler is mounted below the survey televisioncamera erson,1967]. The subsystem,as discussedhere, includes the mechanism,its auxiliary, wiring and to the right of the a-scatteringinstrument, as viewed from the positionof the television harness,and mounting substructure. camera.The relative positionsof the surface Mechanism,motors, and electronics. The extension/retractionmechanism, the motors, and sampler,television camera, and a-scatteringin- strumentbetween footpads 2 and 3 of the Sur- auxiliary electronicsunit are describedby Scott and Roberson[1967] and Rouze .et al. [1968]; veyor7 spacecraftare shownin FigureI of Choate et al. in this report (page 6150). The the primary changemade on Surveyor7 consistedof an increasein the capacityof the elec- mountingsubstructure was designed to provide the surfacesampler with the capabilityof reach- tronic auxiliary heater to 7.5 watts. Scoop. The surface-samplerscoop is attached ing the sensorhead of the a-scatteringinstru- to the end of the extension/retraction mecha- ment in its normally deployedposition on the lunar surfaceand redeployingit to anotherse- nism (Figure 1). On Surveyor7, the fiat foot lectedlocation. The designof the azimuth drive of the scoopdoor incorporatedtwo embedded rectangularhorseshoe magnets. In Figure2 these preventsthe surfacesampler from reaching footpad2. The areasof surface-sampleropera- magnetsare shownoutlined by fine-grainedma- tions and a-scatteringinstrument redeployment terial after they made contact with the lunar surface. capabilityare shownin Figure3. Temperaturesensors. In additionto the tem- FUNCTIONAL AND OPERATIONAL I)ESCRIPTION peraturesensor within the auxiliaryelectronics The surface sampler, through the azimuth, elevation,and extensionmotors, can be driven • California Institute of Technology, Pasadena, in 0.1- or 2.0-secondsteps left and right, up and California 91109. down,and radially in extensionand retraction. 2 Jet PropulsionLaboratory, California Institute of Technology, Pasadena, California 91103. Figure 3 showsthe area that canbe reachedon a nominal surface. Copyright ¸ 1969 by the American GeophysicalUnion. Commands. Spacecraft commandslisted in

6175 6176 SCOTT AND ROBERSON

Fig. 1. Surface sampler on test stand, partially extended.

Table I provide all surface-samplersubsystem original telemetry mode, and repeating the en- operations. The heater commands are self-ex- tire sequence.Figure 4 presentsa force-versus- planatory, as are the power on and off com- penetration plot of such a bearing test. mands.The zero- and one-levelinput commands Telemetry and data display. During surface- are usedto generatefunctional commandswithin sampler lunar operations, telemetry from the the auxiliary electronicsunit. Table 2 provides spacecraftis displayedin several ways. A com- a dictionary of functional commandsso gen- puter (Univac 1219) processesspacecraft telem- erated. To commanda single surface-sampler etry and provides a cathode-ray tube display. motion requiresa minimum of five commands; Selectionof the proper format causesdata per- a seriesof any given motions requiresmultiple tinent to the surface-sampleroperations to be commands[Rouze et al., 1968]. For operational displayed.Teletype outputs provide command convenience,as well as for reducingthe chances confirmation,and computer line printers provide of operational error, command tapes are used hard copy data, again on a selectable format to transmit the correct sequenceof spacecraft basis. commands. The motor current is assignedfive symmet- A special-purposecommand tape was used in rically positioned commutator frames; other the performanceof severalbearing tests during pertinent data (voltage, temperature,etc.) are Surveyor 7 lunar operations.The commandtape assigneda single frame. This provides motor- designated907, first sets the 2.0-secondtiming current data at 50-msec intervals and other mode and loads the command to lower the sur- data at 250-msecintervals at the highestspace- face sampler. Then, the executeand power off craft telemetry bit rate (4400 bits/see). For a commands,separated by exactly 0.5 second,are 2-secondmotor command, nominally 40 motor- transmitted; this provides the surface sampler current samplesare received; this samplingin- with the capability of applying loadsto the sur- terval is apparent in the plot of Figure 5. face for 0.5 second. Command tape 907 con- A multichannel strip chart recorder' (Brush tinues, changingthe spacecrafttelemetry mode, recorder) provides real-time plots of motor cur- taking a televisionpicture, changingback to the rent for evaluation of surface-sampleperform- SURVEYOR 7--SOIL MECHANICS SURFACE SAMPLER 6177 ance. The commandregister status and power- average of the motor current in which the first on/power-off status are also displayed on this four samplesin a given burst are ignored.These recorder. first four samples indicate a motor starting To assistin post-missionanalyses of surface- transient. sampler performance, the motor-current data Calibration. Shortly before launch, the sur- are further processedand plotted (after the face-sampler subsystem calibration was per- mission) for comparisonwith calibration data. formed at Cape Kennedy, Florida..At a normal An exampleof sucha plot is shownin Figure 5. voltage of 22 volts the motor current required In addition to plotting the motor-current val- to drive the surface sampler against a seriesof ues,this output includestemperatures, bus volt- forces was recorded for this calibration. The age, average value of motor current, and an opposingforce was varied in controlledsteps

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Fig. 2. Surface-samplerscoop holding rock A. Note that the rock is slightly larger than the width of the scoop. 6178 SCOTT AND ROBERSON

-)• SPACECI•AFT • TABLE 2. Command Glossary AXIS + STOWEDPOSITION-• Digital Input Function

0111 Set fine timing (0.1 see) 0000 Set coarsetiming (2.0 sec) 1101 Enable squib firing 0101 Enable squib firing (backup) 0011 Release mechanism (fires squib) 1111 Disable squib firing (protection of circuits) 1001 Open scoop 1110 Close scoop 1000 Release clutch 1010 All motors off 0001 Extend 0110 Retract 1011 Left azimuth 1100 Right azimuth Fig. 3. Plan view of surface-samplerarea of 0010 Lower operationsfor a nominal surface.The crosshatch- 0100 Elevate ing indicates the area within which the a-scattering instrument sensorhead can be manipulated by the surface sampler. corded by a Univac 1219 computer, and print- outs were provided in the same format as the from zero up to a force that stalled the drive flight data. Plots of the current pulseswere also motor. Both retraction,or trenchingmode, and processed.For quick-look analysisin real time, lowering, or bearing mode, calibrations were a plot of average motor current versus force performed, each at extensiondistances of 106 was used.A typical plot of a bearingcalibration and 148 cm. The motor-current data were re- test at full extensionis given in Figure 6. Operations. The basic operationsof the surface sampler are bearing, trenching, picking, TABLE 1. SurfaceSampler SubsystemCommands and lifting of objects. A bearing test can be performedwith the scoopdoor open,thus pre- Spacecraft sentinga narrow blade edgeto bear on the sur- Command Designation Function Performed face, or with the scoop closed,to present a 2.5- by 5.1-em bearingplate. Bearing tests are 0131 Power on/ Turns subsystem power execute on; if power is on, performedby selectinga test site from the tele- executes the command visionpictures, positioning the scoopabove the standing in the register. point of interest,and commandingthe lowering 0132 Digital Enters a one-levelinput of the scoop.This sequencecan be accomplished one input to the command de- with several 2.0-second commands until a stall coder shift register. 0133 Digital Enters a zero-levelinput conditionis reached,or by using the special zero input to the command de- commandtape 907 describedabove to providea coder shift register. If series of 0.5-second commands. A 0.1-second the register is full, a commandis not used in a sequentialbearing zero-level input clears the register. test because the motor-current readout occurs 0134 Power off Turns subsystem power at 50-msee intervals at the highest spacecraft off. Turning power telemetrybit rate available.The 0.1-second off automatically re- command thus does not afford sufficient current sets the register and sets fine-timing mode. or force samplesfor a meaningfultest. 0616 Heater off Turns off power to aux- A trenchingtest is performedby driving the iliary thermal control. scoopinto the surface(normally, but not neces- 0614 Heater on Turns on power to aux- sarily, with the scoopdoor open) in the same iliary thermal control. manner as in a bearingtest. After the elevation SURVEYOR 7--SOIL MECHANICS SURFACE SAMPLER 6179

SURVEYOR-?SURFACE SAMPLER NOTOR CURR•NTS FOR •,•,.•, I•TRACT ... COHHANO motor is stalled, a seriesof retraction commands 16 pulls the scoopback through the soil, digging It a trenchthe width of the scoop(5.1 cm). Motor-- currentdata yield informationabout the strength of the soil; current measurementsduring suc- cessivepasses through a trench provide information about the variation of strength with .depth. 0.8 A picking, or impact, test is performedby positioningthe scoop above a desired surface point or rock and releasingthe solenoid-operated •o4 elevation drive clutch. This allows the mechanism to rotate freely at the elevation axis, so 02 that a torque spring and gravitational accelera- O0 tion cause the scoop to strike the surface.

Manipulating, grasping,or lifting objectswith -0.2 2.5 :5.0 3.5 4.0 4.5 50 the surface sampler is the most time-consuming DELTA TIME (SEC), START TIME=OIl DAYS 01 HRS :50 MINS type of operation. Such an effort requires care- -0 SEC 432 MS ful study of televisionpictures before and after Fig. 5. Typical computer output plot of post- any commandsequence to evaluate the surface- mission processedsurface-sampler motor current. sampler responseand to select further commands to achieve the desired result. face-sampler subsystem was flawless under a Figure 7, which is intendedas an operational wide range of operating conditions. Figure 8 aid, is a plot of the surface-samplerarea of op- showsthe temperaturesof the elevation and re- erations, with a diagram of the surface areas traction motors and of the auxiliary electronics viewed by the television camera at various cam- unit throughoutthe first lunar day. During the era azimuth and elevations. From the television critical period around lunar noon (days 015 data, the positionof a selectedobject within the through 018), the surfacesampler was operated surface-samplerarea can be plotted, and the to provide shade for the thermal-control sur- commandsrequired to move the surfacesampler faces of the a-scattering instrument's sensor to the object may be chosen. head. Without this shade,it is possiblethat the MISSION DESCRIPTION temperature of the sensorhead would have ex- ceeded its survival limits. Engineering per/ormance. During Surveyor Several of the shadingoperations were per- 7 lunar operations,the performanceof the sur- formed when the auxiliary electronics unit of the surfacesampler was above its upper operat- FORCE,dynes X 106 ing limit. In these operations,the motors op- 0 I 2 $ 4 I I I erated normally at temperaturesup to 180øF.

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ß Fig. 6. Calibration curve produced from pre- ß flight calibration performed at Cape Kennedy, 4 Florida. This curve shows force versus current for Force versus penetration curve for bear- the bearing test mode with the surfacesampler at ing test 2. 147-cm extension. 6180 SCOTT AND ROBERSON

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GMT DATE, 1968

Fig. 8. First lunar day surface-samplertemperatures. Periods of operation are noted by the bars at the bottom of the figure. SURVEYOR 7--SOIL MECHANICS SURFACE SAMPLER 6181 On the other hand, at one stageduring post- Day 011. Surveyor 7 surface-sampleropera- sunsetoperations, retraction forces were applied tions started with the initial power-on com- to the lunar surface at a time when the retrac- mand at 01h 00m 28s GMT; after four 2.0- tion motor temperaturewas --167øF. secondextend commands, the first televisionpic- Throughout the mission the command decod- ture verifying proper responsewas receivedat ing and telemetryoutputs of the auxiliaryelec- 0lb 22m 35s GMT. This initial checkoutpro- tronics unit performed as designed.Table 3 cedure continued with motor current and video givesthe total commandsand operatingdura- verification that the azimuth, elevation,and ex- tions for the subsystemduring the first lunar tensiondrive systemswere functioningproperly. day. Of the 36 hoursand 21 minutesof opera- Initial contact with the lunar surface occurred tion time, a total of 8 hours and 45 minutes was at bearing point 1, shownin Figures 10 and 11. usedin deployingor redeployingthe a-scatter- This bearing test was accomplishedby driving ing instrument. the scoopdown two 2.0-secondsteps. Bearing point 2, located to the left of bearing point 1 Lunar Operations:First Lunar Day and at a greater extensiondistance (Figure 10), Initial operationsfor the surfacesampler were was the first test to use command tape 907. not scheduledto begin until the a-scattering This test is shownin Figure 12a. instrumenthad been deployedto the lunar sur- After these initial bearing tests, the first at- face, thus ensuringan undisturbedlunar surface tempt was made to free the sensorhead from as the first sample.This delay would also pro- its backgroundposition. In the hope that the vide adequate television coverageof the area problemwas a minor frictional one, the attempt for planning tests before initiation of activities. consistedof light taps applied to the circular This preliminary television coverageis shown plate of the sensor head. Although television in Figure 9. The attempt to deploy the sensor pictures did show that the a-scatteringinstru- head of the a-scatteringinstrument to the lunar ment moved and swayed at the end of its nylon surfaceby normal meanswas unsuccessful.This cord, the instrument did not lower. failure led to decisionsto start surface-sampler Day 012. Surface-sampleroperations on day activities and, after certain minimal data were 012 started with bearing point 3 (Figure 10). acquired, to attempt to free the a-scattering This test consisted of a 2.0-second down com- instrument. mand in which surface contact was made during

TABLE 3. Surface-SamplerSubsystem Performance Summary for First Lunar Day

Number of Commands Number of Surface- Number of Surface- Day of Addressedto Surface Sampler Functions Sampler Mechanism 1968 Power on Time Sampler Performed* Motions Commanded

011 03h 59m 806 371 184 012 06h 30m 1,581 766 426 013 03h 29m 1,499 853 561 014 03h 43m 2,008 1,190 828 015 00h 09m 73 38 22 016 00h 00m 0 0 0 017 00h 10m 42 18 6 018 00h 03m 21 9 3 019 03h 07m 1,364 898 590 020 05h 35m 2,006 1,022 596 021 04h 37m 1,289 713 463 022 04h 01m 1,830 1,017 685 023 00h 58m 120 61 33

Tot.•,l 36h 21m 12,639 6,956 4,397

* Functionsperformed include such operationsas set timing mode, clear register, etc.; they did not necessarilyresult in surface-samplermotions. 6182 SCOTT AND ROBERSON

Fig. 9. Mosaic of Surveyor ? pictures showingthe surface-samplerarea of operationsbefore activities began. the last one-third of the travel. The elevation Bearing test 5 was performed by moving left motor was not stalled, thereby giving data on and locating at the position noted in Figure 10. the initial penetrationonly. This bearing test was performedby using a sin- Bearing point 4 followed at the sameazimuth gle 2.0-secondlower commandand by attempt- position at a greater extension (Figure 10). ing to contactthe surfaceduring the steady-state Again, commandtape 907 and eight 0.5-second part of the travel. This contact was achieved, stepswere used.Bearing point 4 is seenin Fig- and the result is shown in Figure 12c. ure 12b. The initial pickup of rock A (Figure 12d)

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Fig 10. Plan view of surface-sampleroperations showing location of bearingand impact tests performed. ß - SURVEYOR 7--SOIL MECHANICS SURFACE SAMPLER 6183 followed bearing test 5. The rock was lifted and ure 13) it appearedthat the a-scatteringinstru- motor-current data taken to give weight infor- ment was wedgedbetween the helium tank, the mation. The rock was dropped after this first surface-samplerscoop, and some part of the a- pickup, and it landed at position A' shown in scatteringinstrument's standard-sample bracket. Figure 16. Figure 2 showsthe rock in the scoop Under this condition, surface-sampler lower before it was dropped. commandsapplied a downward force to the a- In the Surveyor Experiment Test Laboratory, scattering instrument, which came free and an analysisof the a-scattering instrument'sposi- moved down several centimeters. This allowed tion led to a plan for further attempts to free the scoopto be placed on top of the a-scatter- the sensorhead. The surface sampler was posi- ing instrument and a direct downward force to tioned near the right side of the sensorhead, be applied to it. The thermal mirror on the sen- and by a seriesof extendand left azimuth steps sor head was an aid in positioning the scoop the sampler gradually rotated the sensorhead and, as can be seen in Figure 14, afforded a and moved it left until it was in contact with view of the scoopinterior. The a-scattering in- the helium tank. In this position (shownin Fig- strument was lowered to a point at which it

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Fig. 12a. Results of surface-samplerbearing test 2. appeared to be on the surface,but a short test revealed that rock C had landed at location C' of the instrument counting rate showed that it in Figure 16. was not. The surface sampler was again posi- Because the sun azimuth was progressing tioned above the sensor head and continued to acrossthe surface-samplerarea, the first trench- force it down until it was on the surface in the ing operation was performed at the extreme positionshown in Figure 15. right azimuth position. The position choicewas Day 013. The first activity on day 013 was also influencedby a desirenot to disurb the sur- an attempt to reach rock B (Figure 16) and lift face near the sensorhead of the a-scatteringin- it. Two attempts were made, and verified that strument and by the operational convenienceof the rock was beyond the maximum extension azimuth positioning accuracy for possiblefur- distance for the surface sampler. In further at- ther passesthrough the trench. Trench 1, shown tempts to weigh another rock (in addition to in Figure 17, was dug by going to the right rock A), rock C was picked up (Figure 17), but stop, applying two 2.0-secondlower steps, at in the course of being elevated for weighing it which point the surface sampler was stalled, slipped out of the scoop. Though it was not and retracting six 2.0-secondsteps. The scoop immediately apparent, later television surveys was then lifted clear of the surface and extended SURVEYOR ?--SOIL MECHANICS SURFACE SAMPLER 6185 back to the head of the trench. A secondpass working with rock D (Figure 16 and 18a). At through the trench required a singlelower com- this time in the mission, television camera and mand, and after four 2.0-secondretract com- spacecraftbattery temperatureswere high and, mands, the surface sampler stalled. Two addi- in fact, dictated low-duty-cycle operations.The tional retract commands failed to break it loose. surface-sampleroperations consisted of extend- The surfacesampler was extendedand lifted ing to the maximum distance at rock D and clear of the trench. Positioningthe scoopto cast closingthe scoopon the rock. The rock was dis- a shadow on the sensorhead completed opera- lodged, as shown in Figure 18b, and attempts tions for day 013. to lift it resultedin its slipping from the scoop. Day 01•. In a further attempt to obtain a Over a total period of 7 hoursattempts to move large rock for weighing, (an attempt that was the rock closer for a better grip were unsuc- reinforcedby a desire to make a rock available cessful. for analysisby the a-scatteringinstrument), the Operationsfor the day were concludedwith operations for day 014 consistedentirely of the repositioningof the scoop shadow on the

Fig. 12b. Results of surface-sampler bearing test, 4. 6186 SCOTT AND ROBERSON

Fig. 12c. Resulis of surface-samlderbearing test 5. thermal-control surfacesof the a-scattering in- Day 018. On day 01t•, spacecraft tempera- strument.. tures still precluded effective surface-sampler Day 015. Althoughthe surface-samplertem- operation, and activity was again limited to peratureswere high, the instrumentwas turned shadingthe sensorhead. on and moved to provide continuedthermal re- Day 019. With camera duty cyclesincreas- lief for the sensorhead. Surface-sampleropera- ing and general spacecraft temperatures im- tions were not effective under the severelylimit- proving, surface-sampleroperations were re- ing duty cyclesimposed by cameratemperature. sumed, starting with further weighing of rock Day 016'. No surface-sampleroperations were A. The rock, at position A' in Figure 16, was performed. lifted, the motor current was recordedfor weight Day 017 The surface-samplerscoop was data, and 'the rock was subsequentlymoved •noved twice to shade the sensor head. A total into the area of stereoview, by usingthe auxil- of six surface-samplermotions were commanded iary mirror for stereocoverage. for this effort.(Table 3). Om'e in this area, the rock was viewed di- SURVEYOR 7--SOIL MECHANICS SURFACE SAMPLER 6187 rectly by the television camera and was viewed chosenfor its proximity to the sensorhead. The through the stereo mirror. Subsequently,the surface-samplerscoop was lowered to the rock rock was picked up in the surface-sampler at its new location, and a series of lower com- scoop,and stereo pictureswere obtained.After mands used to perform a bearing test on the dropping the rock, additional pictures were rock. taken at the identical camera positions,to pro- From this position, the surface sampler was vide before and after coverage.Analysis of these extended to its maximum distance; the scoop pictures provided the information on surface- opened,and a 2.0-second-commandbearing test samplerdeflection caused by the weight of the was performed at bearing point 6 (Figure 10). rock. After the scoopwas driven into the surface in After the weighing exercise, the rock was this bearing test, a seriesof nine.2 O-secondre- again pickedup and transportedto a.third loca- tract commandscompleted the first passthrough tion, point A" in Figure 16. This positionwas trench 2 (Figure 16). At the end of operations

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Fig. 12d. Surface-sampler bearing test 6 in progress. 6188 SCOTT AND ROBERSON

Fig. 13. The surface sampler is shown forcing the •ensor head against the helium tank, preparatory to applying a downward force to free the sensor head. on day 019, the surface sampler was left in it, four 2.0-secondretract commandsresulted in place at the foot of trench 2. a stalled retraction drive. A fifth retract com- Day 020. At the start of day 020 operations, mand failed to. break it free, and some maneu- the surface sampler was lifted clear of its posi- vering of the scoopby extendingand elevating tion at the foot of trench 2, extended,and low- slightly before continuing the retraction was ered into the head of the trench for a second necessaryto clear the subsurfaceobject causing pass through the trench. After five 2.0-second the stall. After twice stalling on the object, the retract commands,a secondlower commandwas trench was lengthened to its maximum dimen- given to maintain the scoop bearing force on sion. The third pass was completedafter thir- the bottom of the trench. Three additional teen coarse retract steps, three of which were coarse(2.0 second)retract commandscompleted executed under stall conditions. the secondpass through the trench. At the beginningof the fourth pass,near the After again extending to the head of the head of trench 2, after the first two retract trench and lowering for the third pass through commands (2.0-secondtiming mode), a slight SURVEYOR 7--SOIL MECHANICS SURFACE SAMPLER 6189 increase in resistance was indicated by the second commands completed bearing test 7. motor-current data, and the scoopwas observed Bearing tests 8 and 9 were performed at the to be forced laterally to the left, widening the same site, just left of bearing point 7, as can be trench as though the scoopwere going around seenin Figure 10. Bearing test $ was performed a buried obstruction. The remaining retraction with the scoop closedby using command tape Inet little resistance, and a total of seven 2.0- 907 for a total of four 0.5-second lower com- second retract steps completed the effort in mands.Figures 19a and 19b showbearing test $ trench 2. in progressand after removal of the scoop,re- After completingtrench 2, the scoopwas ex- spectively. tended and moved right to the point noted as Bearing test 9 was performed at the same bearing point 7 in Figure 10. With the scoop location, after opening the scoopdoor. The test, still open, a bearing test was performedby use shown in Figure 19c and 19d, consistedof two of command tape 907. A series of seven 0.5- 2.0-second lower commands.After the scoop

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Fig. 14. The thermal radiating mirror of the sensor head affords an excellent view of the surface-samplerscoop interior when the scoopis positionedabove it. 6190 SCOTT AND ROBERSON

Fig. 15. The sensor head is shown on the hmar surface in position for its first am•lvsis after the surface sampler has forced it down. w:ts lifted clear of bearing point 9 for examina- in six 0.5-secondlower •teI)s. This test was fol- tion, it was again lowered,and three 2.0-second lowed by bea.ring test 11, performed with the retract commandswere executed,which resulted scoopopen; again command tape 907 was used, in trench 3, located as shown in Figure 16..At which resulted in six lower commands. the completion of the trench, the scoop was Trench 4 was dug by retracting three 2.0 closed,and two 2.0-secondelevate commands second steps from bearing point 11. The area were executed,with motor-current data to de- noted in Figure 16 as the magnet scrapetrench termine the weight of the soil in the scoop. was the location of operationsfollowing trench The scoopwas extendedto the maximumdis- 4. The scoop was lowered to the surface with tance and moved right in preparation for bear- the door closed and, by a series of 2.0-second ing point 10, as located in Figure 10. As in retract commands,was dragged across the sur- bearing tests 8 and 9, bearing test 10 was con- face in a trenching mode. After three such com- ducted by use of commandtape 907, resulting mands, the scoopwas lifted clear of the surface SURVEYOR 7--SOIL MECHANICS SURFACE SAMPLER 6191 and the •coop door was opened. A rock frag- and right azimuth commands, was positioned •nent was observed,apparently adheringto the abovepoint A (Figure 16). scoopdoor. To afford • closer television view, Two 2.0-second elevate commands were exe- the scoop was elevated two 2.0-secondsteps.. cuted with the sensorhead held by the scoop. and • narrow-angletelevision picture was taken The motor current provided a calibration by (Figure 20). Subsequentattempts to move the lifting a known weight to assist in the analysis scoopinto the stereo view area for closertele- of similar data received while rock A was lifted vision study of the fragment resulted in its loss at the sameposition. before the stereo view was achieved. The continuation of extend and left azimuth To completeoperations for day 020, the scoop commandsled to the position shownin Figure was again positionedto shadethe sensorhead. 21, in which the target rock sample is seen at Day 021. Operations for day 021 started the lower-left corner of the sensor head. Con- with the performanceof 2.0-secondelevate com- tinued maneuveringled to the positioningof the mands at the final position of rock A, noted as sensor head viewing port over this rock, as positionA" in Figure 16. These commandswere noted in Figure 16. In Figure 22 the ring around executed to gather no-load motor-current data the rock showsthe final position achieved. before later lift tests with the sensor head at the Bearing point 12 (Figure 10) was the next same position. site of operations; at this point, a bearing test Operations then proceededwith the position was executed,by means of commandtape 907. of the scoopabove the sensorhead and the clos- A total of six 0.5-second lower commands was ing of the scoopon the knob, or eye bolt, pro- executed.At the completionof the bearing test truding at the center of the thermal mirror of sequence,trench 5 (Figure 16) was dug; this the a-scattering-instrument.After grasping the operation required five 2.0-secondretract com- knob, the sensor head was lifted clear of the mands. surface and, after a series of elevate, extend, After the scoopwas closed,extend and right

20 ø qO o

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-40 +41 ø /

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1.0

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Fig. 16. Plan view of surface-sampleroperations showing trenches,rocks, and the a-scattering instrument. 6192 SCOTT AND ROBERSON

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Fig. 17. Mosaic of trench 1. Note the irregular shapeand shallow depth of the.trench. azimuth commandspositioned the surface sam- No magnetic fragments were observedat this pler t•orbearing point 13. This bearingtest and time. trenching operationwere executedin the same To provide a large area of disturbed subsur- manner as bearing test 12 and trench 5. Com- face material as a third sample for the e•-scat- mand tape 907 was used to executefive 0.5- tering instrument, the decisionwas made to dig second lower commands,followed by four 2.0- a trench between trenches 5 and 6,. To achieve second retract commands.The surface sampler this, bearingpoint 14 was contacted,and a bear- remained in contact with the surface at the foot ing test consistingof two 2.0-secondlower com- of trench 6 at the end of operationson day 021. mands was executed.The scoopwas closeddur- Day 022. Operationsstarted by carefully ing this bearing test and during the subsequent completingtrench 6, in the procedureused when retract commands,which produced trench 7. the magneticobject was pickedup on day 020. The debris at the foot of trenches 5, 6, and 7 '?i? ....

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Fig. 18o. Undisturbed view, showing exposed smooth face of rock D.

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. .,•...... Fig. 18b. View of roc'k D after moving, showing angular, fragmented underside. 6194 SCOTT AND ROBERSON

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Fig. 19a. Bearing tests 8 and 9 in sequence. provided the third •-aml)lefor chemicalanalysis, head and commanding 0.1-secondleft azimuth and efforts to redcploy the sensorhead to this steps. The final position is shownin Figure 16. samplefollowed the completionof trench 7. Re- After positioningthe sensorhead on its third deployment again required the positioningof sample, impact tests i and 2 were performed. the scoopabove the sensorhead and the grasp- These tests consistedof positioningthe. scoop ing of the knob. Figure 22 showsthe sensorhead above the points noted in Figure 16, elevating after it had been lifted and moved part way to to the desired height, and releasingthe eleva- the third sampleposition. tion drive clutch. Following the impact tests, The sensorhead was placed on the debris at bearing lest 15 was performed, by using com- the foot of the trenches.The analysis of televi- mand tape 907. Figures 10 and 16, show that sion pictures indicatedthat the viewing port bearing point 15 is very near trench 2. This test was directly above trench 7. A slight lateral was performed by taking pictures of the trench movement of the sensor head was effected by wall between each of the bearing commandsin placingthe scoopagainst the sideof the sensor order to observe the behavior of the wall. SURVEYOR 7---SOIL MECHANICS SURFACE SAMPLER 6195 Bearing test 16 made use of commandtape i (Figures 16 and 17). After two 2.0-second 907, and, after each 0.5-second bearing com- elevate commands,the clutch was released,and ma.nd, the scoopwas lifted clear of the surface the scoop blade struck the rock. As discussed for television coverage. Low sun angles made below, the rock fractured under this blow. interior views of the bearing point difficult; After careful television coverage.of the frac- after three such 0.5-secondattempts, the bear- tured rock, including polarizing filter surveys, ing test was completed by executing two 2.0- the scoopwas extended and lowered into. trench second commands,which resulted in a. stalled 2. Two 2.0-secondlower commands,followed by condition. two 2.0-second retract commands, resulted in By using 0.1-secondright azimuth commands, the surface sampier's being stalled against the the surface sampler was driven against the right subsurface rock previously encountered. The azimuth stop, thus locating it above trench 1. surface sampler was left in this position in an- The scoop was opened and positionedso that ticipation of post-sunse;operations. the bbde was ,above rock E at the foot of trench Day 023. Sunset occurred somewhat earlier

Fig. 19b. Bearing tests 8 and 9 in sequence. 6196 SCOTT AND ROBERSON

Fig. 19c. Bearing tests 8 and 9 in sequence. than expected (becauseof the elevationof the was again stalled against the rock in an attempt western horizon), and so the decisionwas made to dislodgeit or to move the spacecraft. to operate the surface sampler after sunset while the spacecraftwas being commandedby Lunar Operations: SecondLunar Day the Deep SpaceStation at Robiedo,Spain (DSS Day 0•5. To verify that the surface-sampler 61). Without benefit of televisioncoverage, the subsystemhad survived the lunar night, a single trench 1 operation of the previousday was re- 2.0-second extend command was executed. Both peated, and the sampler again stalled against motor-current telemetry and emergency mode the subsurface rock. Motor current was trans- television verified normal response. mitted and, at the lower motor temperature, Day 051. Two 0.1-secondextend commands was high, as expected. verified surface-samplerperformance by motor- After Goldstone, California. (DSS 11), ac- current telemetry. An attempt at one elevate quired spacecraftcontrol, the surfacesampler and two left azimuth commands (all 2.0-second SURVEYOR 7--SOIL MECHANICS SURFACE SAMPLER 6197 commands)verified that the surface sampler ing instrumentin the backgroundposition, from seemed normal, but that the power system which it could not be successfullydeployed to couldnot supportoperations. the surface by normal operations.There were more rocky fragmentson the lunar surfacein DISCUSSION OF TESTS the area of Tycho than at the Surveyor3 land- Many testsof the mechanicalproperties of ing site. Some of the fragmentsvisible in the the lunar surfacewere conductedby the surface picture are 6 to 10 cm across.Several of these sampler,in additionto other manipulatoryop- fragmentswere moved during surface-sampler erations. This section contains a discussion of operations;one of them was weighedand one these tests. was broken. Description of area. Shortly after touch- Figure 23 showsthe accomplishmentsof the down,a seriesof pictureswas taken of the area surfacesampler by day 021, toward the end of of surface-sampleroperations (see Figure 9). the first lunar day. In this mosaic,the a-scatter- This narrow-angle mosaic showsthe a-scattering instrument can be seen in its secondde-

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Fig. 19d. Bearin• tests8 and 9 in sequence. 6198 SCOTT AND ROBERSON

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Fig. 20. Fragment adhering to surface-sampler magnets after lunar surface was contacted. ployed position at the left-hand side of the pic- Someshorter trenchesare visible on the right- ture; the surface sampler is in the processof hand side of Figure 23; on the extreme right- excavatingsubsurface soil to provide the third hand edge lies a shallow trench, which was the samplefor analysis.Some ,of the surface-sampler first trench attempted. This trench could be ex- tests, identified in F'igures10 and 16, may also cavated to a depth of only 2.5 to 5 cm because be seenin Figure '23. In particular, just to the of the presenceof rock immediately below the right of the position of the surface sampler, a surface. At the foot of this trench is a small fairly large rock (rock B) is seen at the outer rock fragment (rock E), which was broken by edge of the surface-sampler area. On the near the surface sampler into two fragments after side of the rock, two small trenchesdemonstrate the picture was taken. On the left-hand side of that the rock was just outside the surface sam- the figure, just to the right of the shadow cast pier's reach. To the right o.f the rock is a long, by the sensorhead is a •omewhat rounded rock 15- to lg-cm-deep trench, identified as trench 2 (rock A), which was weighed. Many surfacein Figure 10. sampler operations involved this rock, which SURVEYOR 7--SOIL MECHANICS SURFACE SAMPLER 6199 was finally positionedas shown in Figure 23 to Bearing tests. There were 16 bearing tests permit analysisby the a-scatteringinstrument. of various kinds conductedby the surface sam- However, an undisturbed rock, better suited to 'pier before and after deploymere of the a-scat- analysis, was located at the position of the a- tering instrument. Some of these bearing tests scattering instrument in Figure 23; the instru- are described here. ment, as shown, is located on top of this rock. Figure 24 show• a view of the result of bear- In the lower left of Figure 23, at the very edge ing test 1, which was performed by means of of the sensor-headshadow, is a rounded mark two 2.0-second down commands in which the or indentation in the lunar soil. This was the motor current was recorded. The disturbed soil position of the sensorhead at its first sampling showsa remarkableresemblance to the appear- site, and it was to this location that the surface ance of the lunar surface at the Surveyor 3 site sampler deployedthe sensorhead following its following the first bearing test performed at release. that location [Scott and Roberson,196.7]. The

Fig. 21. Surface sampler nearing final position in deploying sensorhead to secondsample on the lunar surface. 6200 SCOTT AND ROBERSON

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Fig. 22. Surface sampler.in processof moving sensorhead from secondto •hird lunar sample. Note ring around target rock at second sample location. total depth of penetration of the surface sam- face material, a certain amount of minor crack- pler into the lunar soil in Figure 23 was about ing appears, together with an obvious general 5 c•n in this test. The test was apparently lo- bulging of the area. cated on the edge of • small surfacedepression, Since bearing test 1 and the previous calibra- which became obviousin pictures taken later in tion tests of the surface sampler on the moon the lunar day. Consequently,the surface sub- indicated that the sampler was in good opera- jected to the test (Figure 24) slopesdownward tional conditionand, in particular, that the mo- to the right, which accountsfor the unsymmet- tor currents appeared reliable, it was decided rical appearanceof the deformed soil. At this to perform a secondbearing test to. the left of location, the surface sampler was at. an exten- bearing test 1 and at greater extension, using sion distanceof about 103 cm from the space- command tape 907. Bearing test 2 was conse- craft (see Figure 23), and consequentlyapplied quently performed; the appearanceof this test its force at an angle to the surface rather than is somewhatdifferent from that of bearing test directly downward. In the disturbed lunar sur- 1, althoughsome bulging of the surfacematerial SURVEYOR 7--SOIL MECHANICS SURFACE SAMPLER 6201 in the vicinity of the bearing test was also evi- was attained, and the soil was disturbed to a dent. distance of approximately 8 cm from the near It is felt that the differencebetween bearing edgeof the surfacesampler. In this test, a piece tests I and 2 probably results from the differ- of rock (or a rock fragment.) seems to have ent angle of penetration of the surface-sampler been encountered near the surface at the left- scoopinto the lunar soil; in bearing test I the hand top corner of the surface-samplerimpres- positionof the scooptended to drag the surface sion (Figure 12b), sincethere is somesoil crack- material toward the spacecraft. In addition, ing, and the surfaceappears somewhatbulged bearingtest 2 appearedto have beenperformed beyond the surface-samplerimpression. It ap- on a level surface. Once again, in Figure 12a, it pearsthat the surfacesampler may have pressed can be seen that the disturbed material cracks down on one corner of the rock fragment that to some extent and exhibits displacementto was sligh.•]ybelow t•.e surface,and that this some distance from the point of application of fragment '•ilted upward, thereby cracking the the force. surface. Careful analysis and comparisonof the pic- Bearing test 5 is shown in Figure 12c; bear- tures of the soil in the area of bearing test 2 ing test 6, conductedwith an open scoop, is show that it appearsto have been disturbedby shown in Figure 12d. In bearing test 5, only the bearing test to a distanceof at least 9 cm a relatively minor amount of surface disturb- from the near edge of the surface sampler. The ance in the vicinity of the surface-samplerscoop maximum depth of penetrationin this test was tip appears obvious, although some displace- in the vicinity of 4 cm. A preliminary analysis ment_:i'0fthe surfaceand somebulging have oc- of force-versus-penetrationdata from bearing curred.The amountof penetrationin thistest test 2 has been made from the motor-current was about i cm, which is considerablyless than data and pictures; the force-versus-penetration on the previous tests. Bearing test 6. was per- relationship is shownin Figure 4. formed with the scoopdoor open; the test shows Another test (bearing test 4), also made with that the scoop at maximum force has pene- commandtape 907 and exhibiting a somewhat trated a distance of about 6 to 7 cm into the similar appearanceto bearing test 2, is shown soil. after completionin Figure 12b. Once again, in Because there are indications that somewhat this test, a depth of penetration of about 2 cm different surface disturbancesand penetrations

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Fig. 23. Mosaic of area of operations. 62O2 SCOTT AND ROBERSON

Fig. 24. Results of bearing test 1. were being obtainedfrom test to test during penetrationwas limited by an underlyingrock, Surveyor7 surface-sampleroperations, two spe- it was decidedto open the scoopand perform cial tests were performedto study this effect anotherbearing test in preciselythe sameloca- (seeFigure 19). Figure 19a showsbearing test tion. Figure19c shows the resultof drivingthe 8, whichresulted in an extremelysmall amount open scoopdown into the surface.This was of penetrationinto the surface.In thistest, the bearingtest 9, and it can be seenthat the scoop far edgeof the surface-samplerscoop penetrated haspenetrated a distanceof 5 to 8 cm without perhapsI cm, whereasthe near edgeof the c•usingany markedsurface disturbance, which scooppenetrated approximately 0.5 cm,and ex- would indicate the presenceof an underlying t.remclylittle surfacedisturbance was mani- rock. fested on the near side of the scoop.The im- In Figure 19d,the lunar surfaceis shownin pressionleft by the surfacesampler is smooth the vicinity of bearingtests 8 and 9 following and distinct (Figure 19b), and the variousfea- the removalof the scoopfrom the surface;it tures of the scooptip ca•nbe seenclearly. Be- can be seenthat. only a minimal amount of sur- causeof the possibilitythat in this test the face disturbance has occurred. The right-hand SURVEYOR 7--SOIL MECHANICS SURFACE SAMPI,ER 6203 side of Figure 19d showsthe surface at bearing had been obtained (Figure 25b). It is seenthat, test 7, which was a test performed with the as a result of draggingthe scoopbackward, the scoop full of soil from trench 2. The mass of penetration of the scoopinto the lunar soil has soil, which appears on the spacecraft side of been greatly increasedbecause of the additional that test mark in Figure 19d, is, in fact, ma- shearingstresses applied to the surface. terial that had been compressedin the scoop, Trenching operations. Trenching operations but remained on the surface (still retaining the during the Surveyor 7 missionwere made for a shape of the inside of the scoop) after the sur- variety of purposes. The first trench (Figure face samplerhad beenwithdrawn. 16) was dug at the extreme right-hand end of Bearing test 13, which was performed with the surface-sampleroperations area.. This area the scoop closed,is shown in Figure 25a; one was selectedbecause it was possibleto bring the retract command was given after the maximum surfacesampler to the extreme right-hand stop downwardforce on the scoopin the bearing test very readily after moving it away from the

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Fig. 25a. Bearing test 13. 6204 SCOTT AND ROBERSON

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Fig. 25b. Trench 6, performed in sequenceat the sample point. trench. When trenching was attempted at this again at a motor temperature of about --167øF position, however, it was found that rock ma- in order to exert a very large retraction force terial (or a large rock) lay under the trench, at on the rock. No movement of the rock was ap- a depth of only about 2.5 cm, so that deeper parent in the pictures taken, although somede- penetrations could not be obtained. The rock flectionof the leg 2 shockabsorber was achieved. had an irregular upper surface,and subsequent Consideringthe retraction force of 1.8 to 2.0 x drag tests with the simultaneousrecording of 10* dynes that can be generated at very low retraction motor current indicated fluctuations motor temperatures, it would seem that the in current as the surface sampler rode over the rock must have been a. •ubstantial fragment. underlying rock material. Trench 1 is shown in Figure 17. Shortly after sunsetof the first lunar day, the Following deployment of the sensorhead of surfacesampler, which had been left in a stalled the a-scattering-instrument,another trench was positionon the rock underlyingthe near end of attempted in approximately the middle of the trench 1, wss operated in the retraction mode surface-sampleroperations area (seeFigure 16): 6205 SURVEYOR7 ß¾•OIL , MECHANICS SURFACE SAMPLER

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Fig. 27a. Direct view of rock A after it was moved.

Several trenching passes were made through ance of t,'cnch 2 at several stages in its con- this trench, which w•ls eventreallyenlarged to a struction is shown in Figure 26. In depth and lengthof approximately75 cm, a depth of about. general appearance, the trench is not dissimilar 15 cm, and a width of 5 cm. Two obstructions to trenches excavated by the surface sampler were observed in this trench, Olle at the head on Surveyor 3 [Scott and Roberso•, 1967]. of the trench, where the surface sampler was Three trenchin• operations were performed deflected to the left. :•round •ome subsurface ob- at the left side of the surface-s.•,mplerarea in ject, •nd one •pproximately two-thirds of the order to provide subsurfacematerials for the way down the trench toward the spacecraft, third sample to be analyzed by the a-scattering where • small protuberanceagain interrupted instrument. The sensorhead was subsequently surface-sampleroperations. The retraction mo- positionedin this area. Other trencheswere dug tor stalled on the object, which could not be with the scoopclosed (see Figures 25a and 25b) extracted from the surface,and was thereupon in order to examine the change in the amount avoided in trenching operations. The appear- of penetrationof the surfacesampler by apply- SURVEYOR 7--SOIL MECHANICS SURFACE SAMPLER 6207 ing lateral shearing stressesafter a drag test; rock, was measured.On one occasion,the rock a short trench was made for the purpose of was picked up in the surface-samplerscoop; a locating a possiblefragment on the surface. pair of ifictures was taken, both directly and Rock weighing. Early on the first lunar day, indirectly through the auxiliary mirror on the a rock (rock A) was observed that was in a spacecraf[ mast, to provide stereoscopicim- position convenient for the surface sampler to agery; the rock was dropped and another pair reach, and that was of suitable dimensionsto be of stereo pictures was taken. From these pie- enclosedin the. surface-samplerscoop. This rock tures, the deflectionof the surface sampler can was moved on a number of occasionsto present be measuredso that., with the known force-de- its various surfaces to the camera for observa- flectionrelationship of the surfacesampler, the tion and to provide a possiblealternate rock for weight of the rock can be obtained. From chemical analysis. In the course of picking up the stereo pairs of pictures taken, the size of the rock, the motor current required to. elevate the rock can be measured,and the densityof the the surfacesampler, both with and without the rock can be calculated.At present, the volume

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Fig. 27b. View through the stereo mirror. Rock A after it was moved. 6208 SCOTT AND ROBERSON

Fig. 28a. Rock E before breaking. of the rock has only been estimated from its that an attempt was made to pick it up also. over-all dimensions;its density will be discussed The rock, on excavation,revealed a substantial in a following section.The pictures of rock A surface underlying the soil of a much more an- used in the measurementsare shown in Figures gular appeh.rance than the surface projection, 27a and 27b. indicatingi.hat an erosionprocess had occurred An attempt was made to pick up another on the exposedpart of the rock (Figure 18b). rock (rock C), but it apparently was flipped Unfortunateli, this rock was slightly too large out of the jaws of the surface sampler by the for the surface sampler to grasp and conse- coil spring in the scoopdoor, and it landed at. quently coiild not be picked up. The attempt to the extreme edge of the surface-sampleropera- weigh it was abandonedbecause of the time- tions area. A third rock (rock D), which ap- consumingnkture of the effortrequired. pears at the extremeleft edgeof the area, had Becauseof the presenceof polarizing filters a rounded protuberanceabove the surface (see on the Surveyor 7 televisioncamera, it was con- Figure 18a). This rock was of such dimensions sideredof value to attempt to break one of the SURVEYOR 7--SOIL MECHANICS SURFACE SAMPLER 6209 lunar rocks so that a polarizing sequenceof off (Figures 28b and 28c); Figure 28c affords pictures could be taken on any fresh surface a slightly better view of the broken fragment. that might be revealed. For this purpose, an- After this operation,a polarimetric study of the other rock (rock E), lying at the foot.of trench rock was made. l, was selectedbecause of the suitable viewing Other operations. When the sensor head of angle and the nearnessof the rock for pictures. the a-scattering instrument was being moved •o Figure 28a is a picture of rock E before it was its secondlocation, a certain amount of soil that broken by the surface sampler. After the open had adhered to the surface-samplerscoop was scoop was located appropriately on the rock's dropped on top of the mirror surface,giving il surface, the surface sampler was elevated to a the appearance shown in Figure 29a. When the height of about 35 to 40 cm above the rock and sensor head had been in its second sampling the clutch was operated.After the impact, the position for approximately 24 hours, it. was rock had moved slightly toward the spacecraft, moved by the surface sampler to its third loca- and a fragment of the rock had been broken tion. The sequenceof operationsinvolved first

Fig. 28b. Rock E after breaking. 6210 SCOTT AND ROBERSON ...... ß::.-/ ....'. ',. • •..i-'--'"'•'•'•.... '..-.-;',- .•'.•-,'i..--'•:• ...... •

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Fig. 25a. Bearing test 13. picking up the sensorhead and then making a Careful photographic studies were made of series of movementsto the right. in 0.1-second the two small horseshoemagnets, located in the steps.This type of motion is quite jerky, and base of the scoop door, both before lunar sur- the appearanceof the sensorhead after two of face operationsand at various times during'the theseright stepsis shownin Figure 29b. It can first lunar day. The magnetsapp:•rently picked be seen that some of the soil on the s-scattering up a coating of magnetic material from the instrument has slid to one side during the mo- lunar surface. In addition, the surface sampler tion, leaving a fairly clean surface with only a was dragged through the surface at a selected fine coating of dust. Since the mirror surface is locatio.n in order to. determine if a small frag- made of Vyco.r glass, a comparisonof Figures ment of lunar surface had magnetic character- 29a and 29b would seem to. indicate that., over istics. A fragment was, in fact, found adhering a 24-hour period, strong adherenceof the lunar to the surface sampler, which was elevated for surface material to the surface of the mirror better inspection of the fragment (see Figure did not develop. 20). SURVEYOR 7--SOIL MECHANICS SURFACE SAMPLER 621'1 •)RELIMINARY ANALYSES AND RESIn,LTS sampler at the Surveyor 7 site, in contrast to a Soil properties. In general, it appears that relatively uniform depth of material within the the bearing tests performed from Surveyor 7 capabilitiesof the surface sampler at the Sur- exerted forces on the lunar surface similar in veyor 3 site. Consequently,the variation in be- magnitude to those of the tests performed dur- havior of the bearing tests may have been ing the Surveyor 3 mission,although the retrac- caused by a varying depth of hmar material tion forces on Surveyor 7 were considerably over underlying rocks or a rock surface.In gen- larger than those on Surveyor 3. However, the eral, however, the material behavior was not consequencesto the lunar surface varied con- substantiallydifferent from tha,t exhibited in the siderably from place to place as can be seenin Surveyor 3 surface-sampler operations; as a Figures 12, 19, and 24. It appeared from the first estimate, it is consideredthat essentially trenching tests that a varying depth of lunar the same density, friction, and cohesionvalues soil ranging from perhaps i to at least 15 cm can be consideredrepresentative of the soil in existedover the operationalarea of the surface the Tycho area.

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Fig. 29a. Lunar soil dropped on the sensor-headthermal mirror. 6212 SCOTT AND ROBERSON :•½•::•":.... .•.

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...

•. 298. After redeployment of sensor head, showing soil movement.

To some slight extent, the soil around Tycho exhibit the degreeof cementingand brittle frac- appears strongeror denserthan the material in turing evidencedby the first few centimetersof the maria. In general, the soil in the bearing the lunar surface in the mare area.. The con- tests and trenching operations in the Tycho trasting behavior of the soils on the moon may area did not crack or split to the same extent be related to the differencein agesof the Tycho as the soil in the Surveyor 3 mare area. During blanket (younger) and mare materials (older), trenching operations, it appeared to yield or or to the slight chemicaldifference observed by deform without breaking up into large individ- means of the a-scattering experiment. ual chunks or fragments of aggregatedmaterial, To date, only a preliminary analysishas been as did the soil near Surveyor 3 [Scott and Rob- made with commandtape 907 and motor-cur- erson,1967]. It is concluded,therefore, that the rent information. Bearing test 2 has been soil at the Surveyor 7 landing site, althoughco- analyzed in this way by using motor currents hesive,as evidencedby the smoothvertical walls in the form shownin Figures5 and 6, together of trench 2 and by other operations, did not with the step-by-step motions of the surface- SURVEYOR 7--SOIL MECHANICS SURFACE SAMPI,ER 6213 samplerscoop, given by the sequentialpictures that the individualparticles composing the soil to give the force-versus-penetrationcurve of are, in themselves,not highly porous.This de- Figure 4. In Figure 4, it can be seenthat some termination would appear to reinforcethe con- amount of penetration occurred at relatively clusionsobtained from the Surveyor 3 surface- low load. This initial part of the curve, which sampler operationsthat, in fact, the strength is commonly referred to in soil mechanics as and deformation characteristics of the lunar 'seating,'is due to the initial wedge indentation surface granular material can be explained by of the sampler during a bearing test (see Fig- the presenceof a material with a density com- ure 3 of Scott and Roberson [1967]), and it parable to that of commonterrestrial soils,that may also develop either from the irregular is, in the range 1.5 g/cm3 and greater. Bear- nature of the surface or from a layer of softer ing test data, such as shown in Figure 4, and soil above underlying denser material. It will other tests do appear to indicate the presence be seen from the curve that there is a tendency in some locations of a surface layer, possibly for the rate of penetration to increase at ap- several millimeters thick, that is softer or more proximately 3.0 X 106 dynes of force. This easily compressiblethan the underlying ma- value may be interpreted as a bearing capacity terial. However, the material appears to gain for this size of footing. After this point, how- in strength or density comparatively quickly as ever, the rate of penetration again decreases, a function of depth in the first 1 or 2 cm. The and it seemslikely that the increaseis caused increasewith depth will be evaluated to greater by an increasingstrength or density of the depths from the motor-currentdata obtained material below a depth of a few centimeters. during variouspasses through trench 2. A more detailed interpretation of a number of Observations. The lunar soil at the surveyor bearing tests must be made before more general 7 landing site appears to be irregular in depth conclusions can be drawn. and relatively shallow, ranging in the surface- Rock density. Based on measurements of samplerarea of operationsfrom depths of less the deflectionof the surface sampler before and than 2.5 cm to a depth of at least.more than after dropping the rock, a preliminary estimate 15 cm. The soil is underlain by substantial rock of the weight of rock A has been made. From fragments. It is estimated that, on the first the dimensions of the rock on the lunar sur- earth day following lunar sunset, the drag face,by comparisonwith the dimensionsof the tests performed in trench 1 exerted a force of surface sampler, its volume has been estimated. at least 180 newtons on the subsurface frag- The w•ight appears at this time to be accurate ment underlying that trench. An individual to within 4-7 or 8%; at best, the volume can rock fragment resisting a lateral force of this be obtained within about 30%. Since stereo order of magnitudeon the moon would have pairs of pictures of the rock have been ob- a very substantial size:•In none of the trench- tained, a more accurate calculation of its vol- ing operationsin the lunar surfacewere other ume should be possible at a later date. By soil fragments brought up that were com- using the extremes of weight and volume ob- parable in size to the pieceslying about on the tained for the rock, it is estimated that its surface. A distinct impression is gained from density lies within the range of 2.4 to 3.1 the surface-samplerwork that the surface rocks g/cm3. Although such a determination is not lie on a relatively.•fine,grainedgranular material, of sufficient accuracy to be used in an evalua- and that this material does not contain rocks tion of the rock type, if does indicate that the of comparablesize to the fragmentson the material of which the rock is composedis not surface. However, the surface is underlain with substantially porous, since the density lies substantiallylarger fragments. One normally within the range of common terrestrial rocks. expects in a granular material a gradation of If it can be assumed that this rock was char- fragments of all sizes distributed both hori- acteristic of many of the other fragments zontallyand yerticallythrough the material. around the Surveyor 7 landing site and that the The rounded surface shape of rock D and its soil tested by the surface sampler in the same angular subsurfaceshape appear to be indica- area was derived by meteoritic bombardment tive of some process of erosion, probably of these rock fragments, it must be concluded meteoritic bombardment at the surface. A1- 6214 SCOTT AND ROBERSON though the undersidesof some of the rocks There was lessgeneral cracking, and tests and excavated from the lunar surface were darker trenching operationsprovided smaller lumps or than the above-surfaceside of the rock, it ap- aggregatesof lunar soil. peared that this differencewas due to a coating Rock material (or a rock) was encountered of fine-grained granular soil on the underside. at two locations below the lunar surface, but It has not been possible,to the present time, it was too large or firmly embedded to be to calculate a value for the strength of the moved. No movable subsurfacerock fragments rock broken by the surface-sampler impact; were excavated. however,the impact deliveredwas not the most The density of a single rock, which was violent that the surface sampler was capable picked up and weighed,was in the range 2.4 to of delivering, and the implication is that the 3.1 g/cm•. rock was relatively weak, either intrinsically or The excavation of one partially buried rock as a result of an existing fracture in it. revealed that the subsurfaceportion was angu- As on Surveyor 3, little soilmaterial appeared lar in contrast to the rounded visible portion. to adhere to the scoopearly in the operations, One apparently intact rock was broken by a but, as the lunar day proceeded,the soil showed blow from the surface sampler. a greater tendency to adherence.It was, how- The adhesion of lunar soil to the surface- ever, comparatively easily dislodged,as, for sampler scoop appeared to increase with time example, during the processof picking up the on the lunar surface. sensorhead to move it to its secondposition. Little adhesion of lunar soil to the mirrored surface on top of the sensor head occurred in SUMSMARY a 24-hour period. The lunar surfaceat the Surveyor 7 landing Acknowledgments. The assistance and advice site is covered with a fine-grained soil whose of M. C. Clary in the analysis of the performance depth over rock or rock fragmentsvaries from of the mechanism and auxiliary, especially under 1 or 2 cm to at least 15 cm. Many rock frag- critical temperature conditions during the mis- ments ranging in size up to 10 cm lie on the sion, contributed materially to the successof the surface within the surface-sampleroperations operation. The work described herein was performed by area. the senior author under contract JPL-CIT 69811 The surface soil exhibits properties similar with the Jet Propulsion Laboratory. The surface to the properties of the soil at the Surveyor 3 sampler was designed and built by the Hughes landing site. The behavior of the soil at a Aircraft Company, E1 Segundo, California. depth of several centimeters is therefore con- sistent with the behavior a material possessing a cohesion of the order of 0.35 to 0.7 X 104 Rouze, E. R., M. C. Clary, D. H. LeCroissette, C. C. Porter, and J. W. Fortenberry, Surveyor dynes/cm2, an angle of friction of 37ø to 39ø, surface sampler instrument, Jet. Propul. Lab. and a density of about 1.5 g/em•. Tech. Rep. 32-1223, Pasadena, Calif., Feb. 1, To a depth of several millimeters at the lunar 1968. surface,the soil appearsless dense, softer, and Scott, R. F., and F. I. Roberson, Soil mechanics more compressiblethan the underlyingmaterial. surface sampler: Lunar surface tests, results, and analyses, Surveyor 3 Mission Report, Part The bearing capacity of the lunar soil to the 2, Scientific Results, Jet Propul. Lab. Tech. 2.54-cm-wide area of the closed scoop of the Rep. 32-1177, 69-110, Pasadena, Calif., June 1, surfacesampler was about 2.1 X 105dynes/cm •', 1967. at a maximum penetration of about 3 cm. Qualitatively, the soil at the Surveyor 7 site was less brittle than at the Surveyor 3 site. (Received July 17, 1969.)