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 photo- graphs 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 Geophysical Union. 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 ..•:.... :.4... .:. 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