Movement of Surveyor 3 Spacecraft

VOl,. 76, NO. 14 JOURNAL OF GEOPHYSICAL RESEARCH MAY 10, 1971

BriefReport

Movementof Surveyor3 Spacecraft

R. F. $corrrr,T.-D. Lu, .aNDK. A. Ztrcxcga•tAN

Division o• Engineeringand Applied Science California Institute of Technology, Pasadena 91109

An examinationof the positionof the Surveyor3 spacecraftas it appearedin the photographs taken by astronautsC. Conrad and A. Bean of the Apollo 12 lunar mission in Novem- ber 1969 suggestedthat some changeshad occurred in the spacecraft'sattitude since the Surveyoroperation of April 1967.A detailedstudy was made by simulatingin the laboratory the position of one of the Surveyor spacecraft'sfootpads and its imprints in the lunar surface. Photographswere taken both from the location of the original Surveyor television camera and from the estimated position of the astronauts.It was found to be impossibleto match the footpad and imprint positionsand attitude in picturestaken from the two points of view. Consequently,it is tentatively concludedthat the Surveyor spacecraft moved a few inches at some time between May, 1967 and November 1969. It seemsmost likely that this movement occurred as a result of a relatively sudden failure of one or two of the shock absorbers on Surveyor'slanding gear, since2 out of the 3 shock absorberswere collapsedat the time of the astronauts' visit.

The Surveyor 3 spacecraft landed on the served; the footpad had plowed downhill moon on April 20, 1967, and was operateduntil throughthe soil, and in its final positionthe May 3, 1967. The scientific and engineering visible part of its top surfacewas a few inches results of its sojourn on the lunar surfacehave above the soil level. been reported [Surveyor 3 Mission Report, On November 19, 1969, the Lunar Module 1967]; thosepertinent to this discussionwill be of the Apollo 12 spacecraftcarrying astronauts repeated briefly here. C. Conradand A. Beanlanded near Surveyor 3, No communication was returned from the and in the second of their two excursions on spacecraft after its first lunar night. At the the lunar surface the two astronauts visited their termination of its multiple impact touchdown, precursor.They took a numberof photographs the spacecraftcame to rest on the inner eastern of Surveyor and removed several spacecraft slope of a 200-meter-diameter crater. The components for return to earth. Some of the ground slope was approximately 10ø to 12ø , photographs,when comparedwith the original and the inclination of the spacecraft'svertical Surveyor pictures,suggest that, at sometime axis from lunar vertical was determined to be betweenSurveyor 3 shutdownon May 3, 1967, 12.4ø. One of the vehicle'sfootpads (number 2) and the time the photographswere taken by was within the field of view of the television Conrad and Bean, the Surveyor spacecraft camera;another (number3) was partly visible; moved a few inches. and the third was obscuredby spacecraftcom- ponents.In the last stagesof landing, footpad MOVEMENT STUDY 2 left an impressionon the lunar surfacea few On their way toward Surveyor3, Conrad inches from its final location. The appearance and Bean took the photographshown here as of this apparently penultimatecontact and the Figure 2. If the mast anglein this pictureis footpad itself from the point of view of the measured with respect to the visible lunar Surveyortelevision camera is shownin Figure 1. horizon,it is found to be about 15ø , in the Only the right sideof footpad3 couldbe ob- planeof the picture.The maximumdownslope angleof tilt wouldbe somewhatgreater. If the Copyright ¸ 1971 by the American GeophysicalUnion. lunar horizon differs from the true horizontal

3414 BRIEF REPORT 3415 in this picture by less than 2.5ø, it would shock absorber of leg 3 in Figure 4 showed appear that the spacecraft has increasedits that the latter shock absorber is also collapsed inclination downslopesince 1967. More positive All the shock absorberswere extended during evidencefor this is apparent in Figures3 and 4 the landing and communicationlife of Surveyor of legs I and 3, respectively,also taken by the 3 in 1967. The shock absorbers contained helium astronauts.In this picture, the shock absorbers gas at high pressure;the gas was retained by of legs I and 3 are seento have collapsed.Their seals that can fail. It is concluded that the normally extended position can be seen from shockabsorbers on legs I and 3 of Surveyor 3 the position of the leg 2 shock absorber in collapsed at some time after the terminalion Figure 2. Here the extended shock absorber of communicationwith the spacecraft. and its supportingstrut form a straight line, in An indication that the failure of the shock comparisonwith the angle visible in Figure 3 absorber on leg 3, at least, may have been of leg 1. Study of the positionof the leg 2 shock suddenis seen in Figure 4, taken by the astro- absorber in Figure 2 and comparisonwith the nauts and showingfootpad 3. This picture indi-

... Fig. 1. Picture of footpad 2 from Surveyor 3 television camera, April 21, 1967. The imageis hazy becausea film of lunar dust was depositedon the mirror of the cameraduring the landing (GMT day 111, 07h 43m 38s). 3416 SCOTT,Lu, AND ZUCKERMAN caresthat the edge of footpad 3 not visible to white were a light tan color at the time of the Surveyor 3 camera dug into the lunar soil their visit. This observation was subsequently so that its upper surfacebecame covered with confirmedby examinationof the returnedspace- soil. However, a lighter shadingappears around craft parts [Benson et al., 1970]. It is con- the edgeof the pile of soil on the footpad.This jectured, therefore, that the footpad receiveda was at first interpreted [Scott et al., 1970], it partial coveringof soil in the landing in April is now thought erroneously,as being lunar soil 1967; this soil protected the underlying foot- of a lighter color. pad surfacefrom a processthat either coated However, the astronauts reported that the or, more probably, altered the white surfaceto exposedspacecraft parts Ihat were originally tan in an unknown length of time. When the

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•... Fig. 3. Astronaut photograph showing detail of collapsed shock absorber connection on leg 1, to left, partly in shadow (AS. 12-48-7118.). footpad was jerked by the hypothetical shock strongly than to the spacecraft, under lunar absorber collapse,the soil on the pad moved, conditions,an impulsesuch as that of the postu- and the protected white footpad surface was lated sudden shock absorber collapsegenerated revealed in contrast to the tanned surface. An footpad accelerations high enough to cause argument against this explanation is that the shearing at the soil/footpad interface rather lunar soil has repeatedlydemonstrated the prop- than through the soil. erty of adhering to spacecraft surfaces.Thus, In Figure 1, the spacecraft'sview of footpad it is not clear that the soil on the footpad could 2 shows an impact mark a few inches uphill have slid sidewaysto reveal a relatively white, of the footpad's final resting place. The same rather than a soil-covered surface. However, footpad as viewed by the astronauts' camera is the appearanceof the footpad in Figure 4 is shown in Figure 5, in which a secondimprint difficult to account for by another explanation. can be seen between the previously observed The explanation would have to be that, since mark and the footpad. The clarity of this second the lunar soil probably adheresto itself more imprint was somewhatsurprising, since it is not 3418 SCOTT,LU, AND ZUCKERMAN apparent in Figure 1, althoughits presencewas at the correct angle. A slide of Figure I was suggestedin the Surveyor 3 report. From this inserted in the projector, and the full-scale unexpected result and the consideration dis- footpad and imprint were adjusted until the cussedabove, the questionarose: Was footpad2 projected'image overlay them correctly.The as observed by Conrad and Bean (Figure result of this operation is shown in Figures 6a 5) in the same position as it had been 31 and b. Figure 6a is a photographof the final months earlier (Figure 1)? It was decidedto arrangement taken by a camera in the Sur- attempt an answerby simulatingthe geometri- veyor 3 television camera position. For Figure cal arrangementof footpad 2, lunar soil im- 6b, the projector was set up at the Surveyor3 prints, and both Surveyor and Apollo 12 cam- camera position and projected an image of eras. It was not difficult to arrange a Surveyor Figure I on the footpad and soil. A camerawas footpad, and the Surveyor 3 camera position positionedas nearly as possiblein the line of correctly, becausethe location and orientation sight of the projector and took the photograph of the spacecraftparts was known. To obtain shown as Figure 6b using the illumination of the first imprint position,a slide pro•ectorwas the projected image. It can be seen that the set up at the Surveyor cameralocation and set overlap of the projected Surveyor 3 image on

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Fig. 4. Astronaut photograph of footpad 3 and part of leg 3. The collapsedshock absorber is the upper tubular member. On the footpad some soil can be seen, with adjacent lighter- colored areas. (AS 12-48-7124.) BmEF R•rom • 3419

Fig. 5. Enlargement of part of astronaut photograph showing pad 2 of Surveyor 3 and lunar surface imprints. (AS 12-48-7110.) the laboratorymodel is reasonablygood except orientation. The closestreproduction is shown at the left edge of the pad. The slight mis- in Figure 7. The footpad was then adjusted match there does not affect the conclusion. It until • photograph was obtained that was a was found that the appearanceof the footpad close duplication of Figure 5. This required a as viewed from the Surveyor 3 camer• position footpad translation of approximately 3 inches, was extremely sensitiveto the angle of footpad in effect obtained by a lateral rotation of the tilt. It is consideredthat the angle in the simu- spacecraftabout footpad I and • footpad tilt lation is within ___1ø of the angle in the Sur- of approximately 5 ø in the counterclockwise veyor photographs. direction when viewed from the astronaut posi- A collimatedlight sourcewas directedto light tion of Figure 5. The resultant photograph,to the scene at the sun angle of the Apollo 12 be comparedwith Figures 5 and 7, is Figure 8. photograph (Figure 5), and the position and A view of this arrangement from the Sur- orientation of the footpad imprints in that veyor3 cameraposition is sccn in Figure9• In photographwere duplicated.The footpad was this picture the second imprint is clearly ob- maintained at the position and orientation of servable, in contrast with Figures I and 6a. In the Surveyor 3 pictures (Figures I and 6). Figure 6a the secondimprint was present in With this arrangementit was found to be im- the correct position with respect to the first possibleto obtain a photographthat matched imprint accordingto the Apollo 12 photograph Figure 5 with respectto footpad positionand of Figure 5. In addition, the appearanceof the 3420 SCOTT,LU• ANDZUCKERMAN footpad,because of its changeof tilt, is entirely would have showed a less-obvioussecond im- differentin Figure9 from that in Figure6a or print, and a footpadat a differentangle. Figure 1. A further,minor piece of evidencefor space- It appears,therefore, from this simulation craft rotationis that the originalSurveyor pic- study,that a televisionpicture of footpad2 on tures appearto showthe insideedge of footpad a Surveyor3 spacecraftin the sameposition as 2 resting on an essentiallylevel soil surface. observedby the astronautswould have clearly Picturestaken by the astronautsshow a ridge showedthe secondimprint. It would also have of soil alongthis edgealmost to the top of the showeda footpadtilt angledifferent from that conicalportion of the pad. However,the view- in the originalSurveyor 3 picture (Figure 1). ing anglesare so.different in the Surveyor3 Alternatively,an astronautpicture of footpad and Apollo 12 pictures that it is difficult to 2 on a Surveyor3 in its April 1967 position be surethat the samearea is beingobserved.

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Fig. 6a. Laboratoryphotograph simulating position of Surveyor3 œootpad2 axed lunar soilimprints. Pict. ure taken œrom Surveyor 3. cameraposition for comparisonwith Figure 1. In thispicture both imprints visible in the astronautpicture (Figure 5) arepresent in their correctpositions relative to eachother, but the secondimprint is concealedfrom the camera by the œootpad. BRIEF REPORT 3421

Fig. 6b. Photograph of projection of Figure 1 on footpad and soil arrangement of Figure 6a in the laboratory.

CONCLUSIONS astronauts. Post-missionquestioning of Conrad It is tentatively concludedthat the Surveyor and Bean indicated that this was not the case. 3 spacecraftmoved, probably as a result of a The time at which the movement occurred suddenfailure of the leg 3 shockabsorber, be- can only be estimatedfrom the comparisonof tween May 1967 and November 1969. The the shieldedand unshieldedparts of footpad 3 movement at footpad 2 was in the amount of and a knowledgeof the mechanismand rate 5 ø of tilt and 3 inches of lateral translation in of the processthat tans the painted surface. the form of a rotation about footpad 1, which is imbedded in the lunar soil. The nature and magnitude of the spacecraft Becausea number of fairly closeviews of the movementare pertinent to studiesof the pos- Surveyor spacecraftand surfacesampler appear sible movement of lunar surface particles ad- on the Apollo 12 roll of film before the photo- jacent to Surveyor3 [Ja.ffe,1970]. They also graph of Figure 6 appears,the possibilityarose have significancefor any spacecraftexamina- that the spacecraftmay havebeen moved by the tions in which its orientation is important. 3422 SCOTT,Lu, A•D ZUCKERMAI•?

.. •.-..•c::..: '..?'• ß

ß . .

-:...... :; •:.

.;...... •.. . . •:.•:•:•...... Fig. 7. Laboratory photograph of footpa& 2 in original Surveyor 3 location. Compare with Figure 5.

Fig. 8. Laborato.ry photograph of footpad 2 and imprints in position best matching astronauts' photograph (Figure, 5). BRIEF REPORT 3423

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Fig. 9. Laboratory photograph from Surveyor camera position of footpad 2 and imprints in position best matching astronaut picture. The second imprin5 is clearly visible. Compare with Figures I and 6a.

Acknowledgments. Part of the work described Jaffe, L. D., Lunar surface: Changesin 31 months here was supported under NASA grant NGR-05- and micrometeoroid flux, Science, 170, 1092- 002-118. 1094, 1970. Scott, R. F., W. D. Carrier, N. C. C0stes, and REFERENCES J. K. Mitchell, Mechanical properties of the Lunar Regolith, part C, Chap. 10, Apollo 12 Benson,R. E., B. G. Cour-Palais,L. E. Giddings, Prelim. Sci. R ep., NASA SP-235, 1970. Jr., Stephen Jacobs, P. I-I. Johnson, J. R. Mar- Surveyor 3 Mission Report, 2, Scientific results, tin, F. J. Mitchell, and K. A. Richardson, Pre- JPL Tech. Rep. 32-1177, June 1, 1967. liminary results from Surveyor 3 analysis, chap. 13, Apollo 12 Prelim. Sci. Rep., NASA SP-235, 19'70. (Received October 20, 1970.)