JOURNAL OF GEOPHYSICAL RESEARCH VOL. 74, NO. 25, NOVEMBER 15, 1969 Soil Mechanics Surface Sampler 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 tem- peratures from +180øF to --167øF. The motor current was sampled during lunar bearing and trenchingtests, and these data, togetherwith prefiight calibrationsenabled us to calcu- late the forces involved in these tests. After minimal lunar surface testing, the surface sam- pler 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 ex- tension/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 con- sistedof 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 ...............½--....*:.• ....•.,•:•::,.• •:. - . : :.:..?::•½g.z•;.•5)½•½:•4•,..•.:•.•..:•:•:.:::•:::•::4:• ..........:: :::• •;{?•*•"' .:::::;:4•?,:................. -•.•.:.•)•:;.•:• .•½i•:: *:"::2:•X•'" ..... .......... ..., '::2;-•?" •..•4......... 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-scatter- ing 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 sur- face 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