Lunar Orbiter 1, Preliminary Results - Lunar Terrain Assessment and Selenodesy Micro Meteoroid, And Radiation Measurements

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    NASA SP-197

    Lunar Orbiter IPreliminary ResultsLUNAR TERRAIN ASSESSMENT AND

    SELENODESY, MICROMETEOROID, A N DRAD IATI ON MEASUREMENTS

    Compiled byJ. KENRICKHUGHES nd GERALDW. BREWERN A S A Langley Research CenterLangley Station, Hampton. Virginia

    Scient@ and Technical Information DivisionOFFICE OF TECHNOLOGY UTILIZATION 1969NATIONAL AERONAUTICS AN D SPACE ADM INISTRATIO NWashington, D.C.

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    PREFACEIn March 1964, the National Aeronautics and Space Administration initiated the

    Lunar Orbiter Program, a program which involved the des ign, development, and util iza-tion of a complex spacec raft to acquire detailed photographs of t he lunar s urf ace fromlow-altitude orbi ts about the moon. Five miss ions with launch inte rva ls of 3 months wer eplanned, the overall objectives being to obtain, prim aril y, information on the nature ofthe lunar surf ace and, secondarily , information on the gravitational, micrometeoroid,and radia tion fie lds of the moon.

    The first of the se spacecraf t, Lunar Orbiter I, w a s launched August 10, 1966, only28 months after contract go-ahead. It achieved the distinction of being the first UnitedStates spacecra ft to orb it the moon, to obtain detailed photographic coverage of extendedareas of the near and far si de s of the moon, and to photograph the ea rt h from th e vicinityof the moon.

    The Lunar Orbiter I photographic mission w a s designed to examine selected areasnea r the equator on the moon's visible face. These area s, on the basis of what could besee n by telescopic observation fro m ear th, appeared to be suitable as manned landingsites in the Apollo Pro gr am .

    These sites, as well as other s of scientif ic int ere st , wer e photographed duringAugust 1966. The mission w a s not an unqualified succ ess . A malfunction i n the high-resolut ion ca me ra resul ted in smeared and unusable high-resolution photographs. How-ever , of the 413 fr am es exposed and transmitted to ea rth, 220 were perfectly usable.

    It is the purpose of th is r epo rt to presen t the preliminary scient ific informationobtained by Lunar Orbiter I. This covers an assessmen t of lunar terra in, and the res ult sof the secondary experiments in selenodesy, micrometeoro ids, and radiation. For furtherinformation concerning Lunar Orbiter photographs, the reader should contact the NationalSpace Science Data Center, Goddard Space Flight Center, Greenbelt, Maryland 20771.

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    CONTENTSPage

    PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iiiS U M M A R Y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1I N T R O D U C T I O N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2M S S IO N O BJECTIVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

    PRIMARY OBJECTIVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3SECONDARY OBJECTIVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

    M I S S I O N D ES IG N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3DESIGN CRITERIA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

    PHOTOGRAPHIC-SYSTEM CONSTRAINTS . . . . . . . . . . . . . . . . . . . 4OTHER MISSION CONSTRAINTS . . . . . . . . . . . . . . . . . . . . . . . . . 5ORBIT DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

    SITE SELECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7LUNAR ORBITER SPACECRAFT . . . . . . . . . . . . . . . . . . . . . . . . .PHOTOGRAPHIC COVERAGE . . . . . . . . . . . . . . . . . . . . . . . . . . .

    S C I E N T I F I C R E S U L T S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .LUNAR SURFACE CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . .

    TERRAIN ASSESSMENT APPROACH . . . . . . . . . . . . . . . . . . . . . .Selection of Te rr ai n Units . . . . . . . . . . . . . . . . . . . . . . . . . . .Effect of Conditions of Photography . . . . . . . . . . . . . . . . . . . . . .Photographic Proc essing . . . . . . . . . . . . . . . . . . . . . . . . . . . .Photographic Supporting Data . . . . . . . . . . . . . . . . . . . . . . . . .Crater-Diameter Determination . . . . . . . . . . . . . . . . . . . . . . . .

    8151920202021222323

    Delineation of Rough Ter ra in . . . . . . . . . . . . . . . . . . . . . . . . . 23Cr ate r Counts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

    ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25SiteA-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25SiteA-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27SiteA-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28SiteA-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34SiteA-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37SiteA-6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43SiteA-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

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    PageSiteA.8.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Site A-9.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

    RANKING OF SITES I N ORDER OF RELATIVE ROUGHNESS . . . . . . . . . . 61COMMENTARY ON LUNAR TERRAIN FEATURES SHOWN INSELECTED PHOTOGRAPHS . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

    INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62GEOLOGICINTERPRETATIONOFSITEA-9.2PHOTOGRAPHY . . . . . . . 62CRATER EJECTA PATTERNS AND VOLCANISM . . . . . . . . . . . . . . . . 63EAFtTH-MOON PHOTOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . 63

    SELENODESY EXPERIMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9393

    By Will iam H. Michael. Jr., Robert H . Tolson. and John P.GapcynskiGeneral Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93Related Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

    TRACKING DATA STUDIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100By J . Lorell and Warren L. MartinForeword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100Ranging and Time Synchronization Methods . . . . . . . . . . . . . . . . . . 100

    103By W. L.SjogrenReferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

    107By John F . Newcomb, William R.Wells. and G. Calvin BroomeINTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107V/H SENSOR DESCRIPTION. OPERATION, AND VALIDATION . . . . . . . . . 107DETERMINATION O F THE LUNAR RADIUS . . . . . . . . . . . . . . . . . . . 108REFERENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

    METEOROID MEASUREMENT EXPERIMENT . . . . . . . . . . . . . . . . . . . 111

    PRELIMINARY RESULTS O F GRAVITATIONAL-FIELD ANALYSIS . . . . . . .

    RESULTS FROM LUNAR ORBITER I RANGING DATA . . . . . . . . . . . . . .

    LUNAR RADIUS DETERMINED FROM THE V/H SENSOR EXPERIMENT . . . . .

    By Charles A.GurtlerREFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

    RADIATION MEASUREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . 115By Trutz FoelschePRELIMINARY RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116RADIATION-DOSAGE MEASUREMENT SYSTEM . . . . . . . . . . . . . . . . 115

    A PPE N D IX - PHOTOGRAPH INDEXES, GEOLOGIC TERRAlN MAPS.AND EXPLANATION OF GEOLOGIC FEATURES . . . . . . . . . . . . . . . . . . 119vi

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    SUMMARYThe primary objective of the Lunar Orbiter Program is to secur e, by high-resolution

    photography, topographic and geologic dat a of the lunar sur fac e. Such information, whichis necessar y fo r the selection and confirmation of landing sites fo r Pr oje ct Apollo, willal so extend man's scienti fic knowledge of the moon. Secondary objectives of the programare an improvement in the definition of the luna r gravitational field and the dete rminationof meteoroid and radiation flux in the lunar environment.

    It is the purpose of th is r epo rt to prese nt the preliminary res ult s of the flight ofLunar Orb iter I, the first of f ive flight spacecraf t, which w a s launched from Cape Kennedy,Florida, August 10, 1966, and which subsequently became the first U.S. satellite to orbitthe moon. The spacecr aft remained in orbi t until October 29, 1966, at which time, t oavoid inte rference with Lunar O rbit er II, it was deliberately destroyed by slowing itsvelocity and allowing it to cr as h into the moon.

    Due to a problem with the operation of the came ra sh utte r mechanism, the high-resolution exposures (l -me ter resolution at 46-km altitude) showed a varying de gree ofsm ea r and thus did not meet mission requiremen ts. The medium-resolution exposures(8-meter resolution at 46-km altitude) showed sufficient new te rr ai n features of engi-neering and scientific inte rest to warra nt inclusion in this report.

    Analysis of the re assembled photographs shows a lunar c ru st that is fractured andfaulted. Mass-wasting is seen where lar ge boulders and debri s have tumbled into cra te rs .The moon appears to have been highly dynamic and affected by volcanic activity. However,despite the ove rall roughness char acte rist ics of the lunar sur face , some photographs showlocal regions of r elat ive smoothness, particu larly in the darker mare . Photographs of thefar side of the moon show a surface that, i n general, is much rougher than the nea r sideas a res ult of a higher terr a-to- mare ratio on the far side.

    The resul ts of the secondary experiments were also valuable. Having regi ster ed noimpacts throughout the mission, the meteoroid se ns or s helped to re fine the es timat es ofthe meteor activity in the vicinity of the moon by sev er al orde rs of magnitude and thus toindicate that it w a s no worse than that found in the ea rth environment. The radiation doserate (0.5 to 1 mrad /hr) during trans it to the moon corresponded to that produced by galac-tic cosmic ray s; but during the so lar flares of August 28 and September 2, 1966, doserates as high as 70 mrad/hr and 7 rad/hr, respectively, were experienced. The initia lobjective of the selenodesy experiment is to determine the coefficients in the expansion ofthe lunar gravitational field equation in sp heri cal harmonics and to establish the numberof coefficients required i n the solution. Much has been learned in this respect. Althoughinsuff icient tracking dat a have been received and analyzed fo r long-term predict ion of the

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    behavior of a sat ell ite in orbit about the moon, shor t-t erm prediction (the duration of thephotographic mission) can be made with a high degr ee of confidence.

    INTRODUCTIONA major goal of s ev er al unmanned space pro gra ms of the National Aeronautics and

    Space Administration has been to obtain detailed information of the lunar s urf ace as wellas othe r lunar environmental information to support the planning and operations of futureApollo manned lunar landings. This report presen ts the preliminary re sul ts of photogra-phy of the lunar te rr ain from an orbiting spacecraft (Lunar Orbiter I) and of some experi-ments conducted during the period of photography as well as an additional 2 months offlight. A t the end of th is period the spa cecraft w a s delibera tely destroyed by lunar impact.

    Pr io r to the time of lunar probes, landers, and orb it ers , the study of the lunar ter -rain w a s made fro m many telescop ic observat ions fro m ear th. The best photographicresolut ion that has been achieved is of the order of 250 meters. Two NASA flight pro-gr am s have contributed to the ove ra ll knowledge of the moon and to the needs of theApollo manned lunar-landing program. Each Ranger space cra ft obtained photographs ofloca l reg ions of the moon which were progressively mor e detailed as the spacecraftclosed upon its impact point. Its final photograph of se ve ra l hundred squa re fee t of arearesolved local ter rai n features to le ss than a mete r in dimension. The Surveyor I soft-landing spacec raft successful ly photographed te rr ai n detai ls in June 1966 to a few centi-me te rs locally nea r the landing point. On its flight in August 1966, the Lunar Orbiter,designed fo r photography of la rge areas of the moon with two cam er as having 1- and8-me ter resolut ion capability, achieved extensive coverage with the wide-angle c ame ra(8-mete r resolution). In fact , the wide-angle ca me ra photographed about 41 500 km2 ofselected areas for Apollo landing-site study, 360 000 km2 of other areas on the front sideof the moon, and 5 200 000 km2 of the far side of the moon fr om al ti tudes of about 1500 km(250-meter resolution). In addition, Lunar Orb iter I obtained information of scienti ficint ere st regarding the lunar environment and physical propert ies of t he moon.

    The Lunar Orbiter Project is managed by the Langley Research Center under theovera ll direct ion of the Office of Space Sciences and Application. The Lunar Orbi termission includes a plan for five flights of a Lunar Orbite r space vehicle which consi stsof the Atlas-Agena launch vehicle and the spacecraft. The Lewis Research Center hassystems-management responsibility for the launch-vehicle syst em and integration of thespacecra ft with the launch vehicle as w e l l as flight-operation functions up to Agena-spacecraft separation. The Jet Propulsion Laboratory has the systems-managementresponsibility for the DSIF (Deep Space Instrumentation Facility) and SFOF (Space FlightOperations Facility ) operations in support of space flight. Responsibility for design andproduction of the spacecra ft and mission support during flight opera tions rests with the2

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    prime contrac tor, The Boeing Company. Major subcontracto rs are Eastman Kodak Com-pany fo r the photographic subsystem and Radio Corporation of America fo r electricalpower and communications equipment.

    This rep ort includes a preliminary assessm ent of the lunar terr the selectedpotential Apollo sites photographed as well as the prelimiradiation, lunar radius, and selenodesy experiments. The matecollected from the scientis ts and specia list s of the Langley Res ear clogical Survey, Aeronautical Chart and Information Service, and the Army Map Service .The contributors are acknowledged in the appropriate sections.

    MISS ION OBJECTIVESPRIMARY OBJECTIVES

    (1 ) To place the three-axis stabilized Lunar Orbiter spacecraft into lunar orbit.(2 ) To obtain, by high-resolution photography, detailed lunar topographic and geo-

    logical information about various t er ra in types to as se ss th eir suitability for use aslanding sites by Apollo and Surveyor spacecra ft and to improve man's knowledge of themoon.

    SECONDARY OBJECTIVES(1) To photograph the Surveyor I landing site to perm it the extrapolation of the

    Surveyor I data to other photographed areas .(2 ) To provide precision traj ecto ry information fo r use in improving the definitionof the lunar gravi tational field.(3) To provide measuremen ts of micrometeoroid and radiation f l ux in the lunar

    environment, primar ily f or spacecraft performance analysis.

    M I S S I O N DESIGNThe following terr ain- sampling ground rul es were established:(1)To obtain seve ral s amples of each of the significant te rr ai n types.(2 ) To insure that si milar t err ain types be reasonably dist ribu ted because of Apollolaunch-window considerations.(3) To concentrate on the most promising areas within the Apollo zone of k450 longi-

    tude and ~t50atitude.

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    OTHER MISSION CONSTRAINTSAlthough the object ive w a s to photograph nine select ed equatorial s ite s, obtaining

    maximum coverage with only one pa ss p er site (except fo r the Surveyor site where twopasses were to be made), an additional requirement w a s to be able to cover any point inthe Apollo zone. Thi s objective fixed the orb it inclination to approximately 1 2 O . Anotherlimitation w a s that lighting conditions and altitude be adequate for the detect ion of coneswith a base d iamete r of 2 mete rs and a height of 1/2 meter, and the detection of areas7 me ter s squ are and with slopes not g rea ter than 7O.

    ORBIT DESIGNThe earth-moon tra nsi t time for Lunar Orbiter is approximately 90 hours. Upon

    reach ing the moon, a first deboost maneuver places the spacecraft into an elliptical orbitwhose perilune altitude is about 200 km. The spacecra ft remains in this orbit for sever aldays during which tim e the orbit is more closely defined, a fte r which a second deboostreduces the perilune to 46 km nominal, It is from th is orb it that the primar y photographic

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    55

    50

    45EFFECTS

    I I I-45 WEST 0 EA ST 45DESCEND I NG NODE LONGITUDE, deg

    15EY

    g- 10

    5

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    0 0 5 10 15TRUE ANOM AL Y, d e g

    Figu re 2- Photog raph ic a l t i tude const ra in ts .

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    . -?a

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    A -5 A -4 A -3 A-2 A - 1

    A -6\A -7\ \ \A - 9 . 1 A - 8 . 1Figure 4.- Sites selected for Lunar Orbiter I .

    LUNAR ORBITER SPACECRAFTThe Lunar Orbiter spacecraft is launched and inserted into translunar flight by a

    two-stage launch vehicle consisting of the A t l a s SLV-3/Agena D. Two isometric viewsof the spacecraf t with components identified are given in figure 5. The spacecraft weighs386 kg, is 1.67 meter s high, and 1.52 met er s in diame ter with antennas and sol ar panelsfolded. With antennas and so la r panels deployed, the span is increased to 5.64 me te rsalong the antenna booms and 3.7 met er s acros s the sol ar panels. The spacecraft incor-pora tes seven major subsystems, but only the photographic subsystem is described inthis repor t. Apparatus used in the meteoroid and radiation measurements is covered inthe sect ions describing these experiments.

    The major e lements of the photographic subsystem (fig. 6 ) a r e a dual-lens camera,a film processor, and a readout sys tem. From the nominal altitude of 46 km a lens witha foca l length of 610 mm allows high-resolution exposu res of an a rea on the lunar su rfaceof 16.6 by 4.2 km, whereas an 80-mm wide-angle lens provides medium-resolution cover-age of 37.4 by 31.6 km. The lenses a r e oriented so that the high-resolution (1 meter)photograph records the same area as found in the center of the companion medium-resolut ion (8 me ter ) photograph. The photographs, taken simultaneously, are interlacedon a single s t r ip of Kodak high definition film SO-243, 70 mm wide and 80 met er s long, asshown in figure 7. The photographic modes are illustra ted in figure 8. The SO-243 film .was sele cted because it is relatively insensitive to radiation, and although its aerial expo-sure index of 1.6 is slow compared to m ore common emulsions, it has an extremely finegrain and thus an exceptionally high resolving power of 250 lines/mm. Pr ior to use , theedges of the film a r e preexposed with framelet numbers , 9-level gray sca le, and resolvingpower charts.

    Both lenses open simultaneously at a fixed ape rture of f/5.6. A between-the-lensshutter is used with the 80-mm lens , a double-curtain focal-plane shu tter with the8

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    I /&HEATSHIELDCOARSESUN SENSOR

    CAMERA THERMAL DOORSOLAPANE

    MICROMETEOROID

    LOW-GAI NANTENNA

    EQUIPMENT MOUNTING DECKJ

    R A D IA T IO N

    VELOClTYCONTROL ENGINECOARSE SUN

    OXIDIZER TANKMICROMETEOROID

    ANTENNANOTE: SHOWN WITH THERMAL BARRIER REMOVED

    Figure 5.- Lunar Orbiter Spacecraft.

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    TAKEUP ANDSTORAGETAKEUPLOOPERCOMPOSITE /%FILM

    SUBSYSTEMPROCESSORAND DRYER

    V/HOUTPUTS f ! \

    SCANNERy EADOUTLOOPER

    LOCITYCTOR

    Figure 6.- Photographic-subsystem functional diagram.

    610-mm lens. Shutter speeds of 1/25, 1/50,o r 1/100 sec are selectable by transmittedcommands. The number of fra me s persequence (1,4, 8, or 16) and time intervalbetween exposures are also selectable.

    The film is held in the focal plane byplatens which clamp it under vacuum andhold it flat during exposure. Thes e platensmove during exposure to reduce imagesme ar caused by the rapid movement of thespacecraf t over the lunar surface. Thisplaten movement is referred to as image-motion compensation (IMC) and is providedthrough a mechanical linkage by an ele ctro -mechanical device called a velocity overheight (V/H) sensor. The V/H sensordete rmines the rat io of spacecra ft velocityV to spacec raft altitude H by opticallylocking onto the image of the luna r su rfacein the high-resolution camera and causingthe platens of each cam er a to move at thevelocity of its image. The sens or also pro-vides a measurement of yaw of the space-craft (crab angle) which can be employed tocor rec t spacecraf t attitude.

    In a norm al photographic sequence, the spacecraft is oriented for photography, thelenses are uncovered by the opening of a thermal door in the space craft, the V/H sensoris activated, and the camera is turned on. After the "camera on" command, the camerasoperate in an automatic sequence to (1)clamp film to the platen and draw it flat by differ-ential pressure , (2) tart moving the platens in synchronism with the image motion,(3) open the s hutt ers fo r simultaneous exposures, (4) etur n the platens to the rest posi-tion, and (5) advance film for the next exposure. This sequence is repeated until all pho-tographs commanded are taken.

    After exposure, the film is stored in the camera storage looper. The came ra stor-age looper consists of a se ri es of fixed roll ers in a stationary car riag e and a series ofrollers in a movable ca rr ia ge which rides on a track. As film ent ers the looper, a springcauses the movable c ar ri age to move away fro m the fixed ca rri age and thus to provide astorage capacity for up to 6 meters (20 f t ) of film. Thi s came ra storage looper st or esthe film until it can be processed.10

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    (A) GROUND FORMAT

    Figure 7.- Film-format diagram.

    HIGH RESOLUTION-MEDIUM RESOLUTION-

    ORBITAL PERIOD3. 5 HOURSPERILUNE ALTITUDE46 KILOMETERS

    .- . -. .a. SINGLE EXPOSUREAT THE ~6 KILOMETERALTITUDE.HIGH RESOLUTION COVERAGE S 16.6 KM X 4.15 kMMEDIUM RESOLUTION COVERAGE S 37.4 KM X 31.6 kMb. DESIGN MISSION TARGET STE COVERAGE 16CONSECUTIVEEXPOSURES DUKING ONE ORBITAL PASSObER THE TARGETS I TE . THE INTERVAL BETWEEN EXPOSURES (APPROXIMATELY2.2 SECONDS) IS TIMED TO PROVIDE OVERLAP OF THE HIGHRESOLUTfON FRAMES.

    C. EIGHT TYPICAL FRAMES FROM A SITE EXAMINATION TYPEMISSION- CONTIGUOUS HIGH RESOLUTION COVERAGEISPROVIDED BY RAP10 EXPOSURE RATE AS IN (b) TO GIVE HIGHRESOLUTION FORWARD OVERLAP AND BY PHOTOGRAPHINGO N CONSECUTIVE ORBITS (9 8 O) TO GIVE HIGH RESOLUTIONSIDE OVERLAP.d. EIGHT TYPICAL EXPOSURESFROM STE SEARCHTYPE MISSION -STEREO MEDIUM RfSOLUTION COVERAGE IS PROVIDED 8Y IN-CREASING THE TIME INTERVAL BETWEEN EXPOSURES (APPROX-IMATELY8 .8 SECONDS) TO OBTAIN 50%MEDIUM RESOLUJIONFORWARD OVERLAP AND BY PHOTOGRAPHING O N ALTERNATEORBITS (7 8 ) TO OBTAIN MEDIUM RESOLUTION SIDE OVERLAP.

    Figure 8.- Photographic modes.

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    After a photographic sequence, the photographic-subsystem pro ces sor -dr yer , oncommand, process es film from the cam era storage looper at a rate of 6.09 m/min(2.4 in./min). The fi lm is pressed into contact with Kodak bimat film, type SO-111,which accompli shes the processing . Kodak bimat film is a product consisting of a nor-mal fi lm base coated with a gelatin laye r. This gelatin layer is presoaked with a specialmonobath pro cessing solution. The solution both develops and fixes the photographicimage during the 3.4 min the bimat and film are in contact on the processing drum . Pro-cessing temperatur e is closely controlled to 29.5O C.

    After processing, the bimat and film are separated . The bimat moves to a takeupspool and the film passe s onto a dryer drum. The film is in contact for a period of11.5 min with the dr yer drum which is controlled to a te mp er atur e of 35O C. Moisturedriven from the film by the heat of the dry er drum is absorbed by sp ecia l chemical saltsin pads around the dr yer , and thus a control led humidity environment is maintained withinthe photographic subsystem.

    A f t e r leaving the drye r drum, the film is transport ed through the readout st oragelooper and readout mechanism and is stored on a takeup spool. The film is now readyfor readout.

    At the completion of all photography, the procedure is to cut the bimat and read outthe pi ctur es by running the film in rev erse and taking it up on the film supply reel.Because of limitations on the number of fr ames that can be scanned per orbit , this pro-cedure tak es about 2 weeks. However, throughout the miss ion, the readout looper pro-vides the capability of reading out up to four fra me s at a time for priority re turn ofimportant data and to provide monitoring of syst em performance.

    The readout section (fig. 9) consists of a line-scan tube, a photomultiplier tube, andassociated optics and electronics. In the line-scan tube, a spot of light (112 microns in

    LINE-SC AN TUBE

    SCANNER LEN

    LIGHFCOLLECTOR

    VIDEO AMPLIFIER

    Figure 9.- Film-scanning functional diagram.

    diam eter ) from the electron gun moveslinearly ac ro ss the face of a revolvingphosphor drum. Although the drumrotates so that on subsequent scan s adifferent area is bombarded, the lineproduced rema ins fixed in space. Thespot is focused by the scanner lensand projected as a reduced image(6.5 microns) onto the film. The lensis moved at right angles to the filmafter each scan. The result is a frame-let consist ing of 18 000 scan lines, each2.67 mm long, a cro ss the width of the

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    70-mm film. At the completion of a framelet the film is advanced 2 .54 mm prior to thenext scan which is in the reve rse direction across the film. A complete dual-exposureframe, 29 8 mm long, r equir es about 117 framelets.i

    The light passing through the film is modulated by image density and sensed by thephotomultiplier tube through the assoc iated light-collector optics. An elec tri ca l signa lproportional to the intensity of th e transmit ted light is genera ted and amplified. Timingand synchronizing pulses are added. The video data, occupying a frequency spectru mfrom 0 to 230 kHz is then sent to the spac ecra ft communications equipment where it ismodulated on a 310-kHz sub carr ier (single-sideband, suppres sed-carr ier). The 310-kHzsub carr ier oscillator also provides a 38.75-kHz pilot tone for transmission and subsequentsu bc arr ier re insertio n by the ground equipment demodulator. The 50-bits-per-secondpulse-code-modulation (PCM) tele met ry da ta a r e diphased modulated (Oo or 180) onto a30-kHz su bc arr ier . The video, pilot tone, and telemetry signals are summed, and theresulting composite signal phase modulates the S-band ca rr ie r.

    The transmitted signals are received at one of the Deep Space Stat ions (DSS) locatedat Goldstone, California; Madrid, Spain; or Woomera, Austra lia. The 10-MHz intermedi-ate frequency of the DSS receiver, containing the composite signal, is recorded on

    (A) SPACECRAFT FILM FCRMAT

    2.67 mm X 57.15 mm

    (B) GROUND FILM FORMAT

    16.875

    (D) COMPOSITE OF ONE HIGH RESOLUTION FRAMEC) REASSEMBLED PHOTO

    G:;;*Figure 10.- Photograph reassembly.

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    magnetic tape for permanent storage . At the same time, it is passe d to the ground com-munications equipment which r ecovers the telemet ry and videground reconstruction elec tronics where it is converted to a line sca n on a cathode-raytube. The variations in light intensity on this cathode-ray tube correspond to the va ria-tions i n image density on the spacec raft film.

    The line on the cathode-ray tube is recorded on a moving ro ll of 35-mm te levisionrecord ing film SO-349. The image on the 35-mm film is more than seven times the sizeof the image on the spacecra ft film. After processing, the film is reasse mbled by a reas-sembly pri nte r. Th is equipment prin ts, on Kodak 24.2-cm aerogra phic duplicating film(type 5427), 14 tri mmed 35-mm f ra me le ts , side by side, to make up a subframe. At leasttwo subfram es are required to constitute a medium-resolution photograph, and at leastseven subframes for a high-resolution photograph. Photographic reassembly is illustratedinfig ure 10.

    A summary of the photographic-subsystem component specifications is as follows :Photographic package:

    Dimensions, cm . . . . . . . . . . . . . . . . . . . . . . . 66 by 58.8 by 81.3Weight,kg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65.8Temperature, OC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 to 2 1Pressuriz ation, kg/m2 abs . . . . . . . . . . . . . . . . . . . 703.1 to 1336Relative humidity, per ce nt. . . . . . . . . . . . . . . . . . . . . . . 50 f 20

    Lenses:Type. . . . . . . . . . . . . . . . . . .Elements . . . . . . . . . . . . . . . .Focal length, mm. . . . . . . . . . . .Diameter, cm. . . . . . . . . . . . . .Length, cm . . . . . . . . . . . . . . .Maximum re lative a pert ure . . . . . .Shutter . . . . . . . . . . . . . . . . .Exposure, sec. . . . . . . . . . . . . .Film image, cm . . . . . . . . . . . .Half-field angle, deg . . . . . . . . . .Resolution (on axis), lines/mm . . . .

    High resolu tionPaxoramic

    6610

    13.8323.132

    f15.6focal plane

    1/25, 1/50, 1/10010.5

    5.51 by 22.29115

    Medium resolutionXenotar

    580

    3.6273.772f/2.8

    (stopped at f/5.6)between lens

    1/25, 1/50, 1/10028.0

    5.51 by 6.5115

    Film (EK-SO-243):W i d t h , m m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70Length,m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

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    Thickness, mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.473W e i g h t , k g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Exposure index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 .6Resolution, lines /mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250Processing speed, cm/min . . . . . . . . . . . . . . . . . . . . . . . . . 6 . 1Process ing time, min/frame . . . . . . . . . . . . . . . . . . . . . . . . 3 .2 2Proces sing temperature, OC . . . . . . . . . . . . . . . . . . . . . . 2 9 f 0 .5Drying speed, cm/min . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 .1Drying time, min/frame . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 .7Drying temperatu re, O C . . . . . . . . . . . . . . . . . . . . . . . . 35 f 1.0

    Proc ess ing (lamination with EK-SO- 111):

    Readout:Line-scan tube:

    Drum speed, rp m. . . . . . . . . . . . . . . . . . . . . . . . . . . . .lo00Line length, c m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 . 0 3Spot diamet er, mi crons . . . . . . . . . . . . . . . . . . . . . . . . . 112Focal length, mm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 .3Aperture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . f /2 .4Half-field angle, deg . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 .7Scan line interv al, lines /mm. . . . . . . . . . . . . . . . . . . . . . .Scan line length, mm . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 ,67Spot dia met er, micron s . . . . . . . . . . . . . . . . . . . . . . . . . 6 .5

    Readout rate, sec/framelet. . . . . . . . . . . . . . . . . . . . . . . . . 22Framelet size, mm . . . . . . . . . . . . . . . . . . . . . . . . 2 .67 by 57.58

    Scanner lens:

    Film scan:286

    PHOTOGRAPHIC COVERAGEDuring the period of photography, 211 exposures were made, each exposure con-

    sis ting of a high-resolution fra me and a medium-resolution fr am e. Because of difficul-ties with the high-resolution shutter, only 1 3 of the high-resolution frames were of goodquality. The distribution of the photographs taken w a s as follows:

    Site A-0 (high orbit)Prime sites (A-1 to A-9.2)Film set frames:

    Alternate sites (B sites)Far sideNear sideEarthThermal door closed

    20136151122

    2

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    1 1 1 2 1 3 1 40

    I A-2 I- 16o I

    5 1 6 1 7 1 8 1 9 1 0A-0

    I

    70 A-280 A-2 B-4 A-3-

    210 A-9.2b1 1 2 1 3 1 4 1 5 6 1 7 1 8 1 9 1 0 1

    A Sites ide nt i f iedB Alternate si tesE Earth

    F I it e A-0 and pr im e s i tesUI]ilm-set framerlear sideFar sidel>a Thermal door closed

    F i g u r e 11.- D is t r i b u t i o n of L u n a r Or b i t e r I photographs.

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    This distribution is illustrated i n figure 11,which shows the sequential order of allphotographs taken of pr ime and other sites. The location of each of the photographs withrespect to the lunar surface is shown in the appendix in maps 1 and 2 which were pr e-pared by the Aeronautical Chart and Information Center (ACIC).

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    SC IENTlF I C RESULTS

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    LUNAR SURFACE CHARACTERISTICSTERRAIN ASSESSMENT APPROACH

    Selection of T er ra in U n i t sIn view of the methods employed by the group analyzing the Lunar O rbi ter I photog-raphy for rapid data sc reen ing fo r potential Apollo sites, much of the information gathered

    for th is secti on of the re port is keyed directly to the specific targ et sites photographedand treate d as individual study areas. Major ter rai n units were selected on the basis ofearth-based observations at an aver age reso lution of about 1 km, and geologic te rr ai nmapping w a s employed as the basic means of evaluating and comparing the roughness ofthe sites. This type of mapping delineates units with different morphologic charact eri s-tic s. These units are listed as follows in orde r of incr easing rela tive roughness as deter-mined from earth-based observations:

    Dark mar eAverage regional m areMare ridgesUpland plainsRay-covered m areFloor of deformed cratersSubdued uplandsCrater r imSculptured uplands

    Once delineated, the te rr ai n units were described and characteri zed by c ra te r size -frequency and slope-measuremen t data. The derivation of these data and their implica-tions as to relative roughness are briefly discussed for p art s of all the sites except two(A-2 and A-6) where resolution w a s reduced because of lighting and exposure conditions.Brief explanations are presented in the appendix with the map for each sit e. The mappingwas done on preliminary photographs prepared at an approximate scale of 1:90,000. Somestereoscopic examination w a s made, but monoscopic examination w a s more usual.

    Crater-density data have been used as an index of the compara tive roughness of thesmoothest ter rai n units. Crat er counts were made i n sample areas of 50 km2 with cra te r-diameter intervals of 50 meters. Crat er density is not, however, a precise index of totalroughness. Variations in crater morphology are al so important but have not been con-sidered here.

    Some slope and topographic-profile information has been obtained fo r specific a re asby photogrammetric and photoclinometric techniques. Thes e data are included herein.

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    least effective resolution (larges t minimum-size crate r). Photogeologic interpre tationand mapping for comparative purposes is not feasible or , at least, is made difficult inareas where the photographic quality is degraded. Lunar Orbi ter I sites A-2 and A-6are, therefore , not considered in detail in this preliminary analysis and only par ts ofsites A-1, A-8.1, and A-4 have been evaluated. Site A-7 has been evaluated, however,in sp ite of the overexposure of the film caused by high sun angle and high reflectance,because of its importance to Apollo site-selection analysis.

    2

    10015 0 -

    to:5-

    I

    Photographic ProcessingA number of ste ps in photographic processing affect the overal l quality of negatives

    and contact prints. The most serious of these is in the initial production of 35-mm film(by the Ground Reconstruction Equipment (GRE) fro m the magnetic-tape recordings of thetelemetered video signal). Constant sett ings of the cont rast rat io on the GRE yield photo-graphs which incorporate the effects of the previously mentioned variables. Some areaswere , therefore, "overexposed" on both negatives and prin ts. By increasing the contras tcontrol on the GRE, the average resolution was considerably increased in these areaswhen new negatives were produced fro m the original magnetic-tape data. Counts of total

    cra ter s in the same are a of site A-7 on a"low gain" and on a "high gainf' print of a1

    the high-gain photograph as on the low-gainphotograph. The significance of this differ-ence is apparent when the A-7 curves arecompared with the cumulative size-frequencydistribution function representing theSurveyor I area in site A-9.2. The low-gainprint gives a false impression that the areais relatively smooth. Cr ate r size-frequencydata have also been plotted from high-gainphotographs for sites A-1, A-4, A-8.1, aswell as A-7. Although these data do not

    : \

    I ' " I

    1000 SS-I>\ M-162a"1 M-16? ...\high ga in(u lo w gain .\EY

    medium-resolution f ram e illu strate the effec-tive enhancement of this originally over-exposed area (fig. 12). Approximately twiceas many small cr ate rs were measured on

    estimates are generally suitable for pro-viding some quantitative confirmation of thevisual classification shown on the geologic

    Figure 12.- Cumulative crater size-frequency distribu-tions for an area in site A- 7 as measured on iow-and high-gain reconstructed prints and forSurveyor I area of site A-9.2 [SS-I).

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    terra in maps. It should be noted, however, that such gain adjustment to favor overexposedareas w i l l reduce the detectability of f eature s in areas origina lly i n shadow and now sub-merged in increased effective shadow.

    Photographic Supporting DataSpacecraft altitude for photographic sc al e calculations and sol ar incidence angle for

    determining cra te r depth by shadow-measurement methods were necessary inputs forApollo landing analysis screen ing procedur es. Unfortunately, the only dat a availab leduring sc reening operations were the computer-predicted data calculations rather thanactual tracking data. Photographic scale er ro rs of 5 to 10 percent are possible fro m thepredicted data.

    Crater-Diameter DeterminationOne of the techniques used in the study of the lunar t e rr ai n is the determination of

    the cr ate r di ameters and depths. For rapid screening of th e large number of LunarOrbi ter photographs for Apollo landing-site selection, a nominal diameter-to-depth ratiow a s established for a particula r fram e. The purpose of this particular approach w a s toobtain and define a cr at er diameter crit ical to the Apollo landing. The cra te r depth w a sestablished either by parallaxbar measurements or by a shadow-measurement method.If the sun elevation angle w a s not too large, the shadow method w a s preferred.

    Delineation of Rough Ter ra inMany areas, such as hilly regions with steep slopes with a high density of craters,

    large cr ate rs, closely spaced craters, crater chains, high escar pmen ts, and single hil ls,which are obviously unsuitable for Apollo landings but neverthele ss of scientif ic in ter est ,are delineated on the available photography fo r each si te. Stereoscopic evaluation w a smade to aid this interpretation where stereoscop ic photographic coverage was available.If ster eoscopic coverage was not available, thi s delineation w a s made monoscopically.

    Crater CountsFor the crater-count survey at each sit e, the nominal crater size w a s determined

    according to the following measurement cri ter ia:

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    Diameter class ,mm Mean value, Nominal crater size,mm m0.0 to 0.5 0.3 270.5 to 1.0 .75 701.0 to 1.5 1.25 1101.5 to 2.0 1.75 160

    Measure all cr at er s Measured valuegrea ter than 2.0

    In general, the crater-count survey included the range of diam eter s from about 30 me te rsto 1000 met ers .

    ProfilesProf iles we re derived photogrammetrically on a stereocom parator over som e of t he

    areas. The purpose of the profi les , in addition to the evaluation of c rat er geometry, w a sto determine the slopes in certain area s caused by features other than crat ers . Also,regional slopes acr oss the a re as may be determined from these profiles.

    The slope values presented in this r eport include inherent er r o r s due to frame letdistort ions and inac curacies of the stereoscopic measurements. Ther efore, they a r e onlyapproximate values.

    NomenclatureInasmuch as the materi al presented in this report w a s obtained from varied sources

    without a standard set of definitions o r nomenclature, the following explanations arepresented.

    The nomenclature f or Apollo s it es photographed by Lunar Orbite r I w a s establishedas A-1, A-2, to A-9.2. The letter A has no part icul ar significance other than being indic-ative of th e first flight or Mission I. The decimal identification of a site such as 8 .1 or9.2 merely indicates a change (either prior to or during flight) in the final site selectionfrom that originally planned.

    Geologic fea tur es of the lunar ter ra in are identified as follows. The four bas ic ter-rain units are represen ted by Roman numerals : Mare (I), Upland (11),Craters (III),andStructu ral Featu res (IV), as defined by Halm. Subunits of classif ica tion in each basicterr ain unit are groups repr esen ted by capital letters and subdivis ions of these groupsrepresent ed by Arabic numerals. In a few instances it w a s necessary to represent a fur-th er breakdown of spec ial te rr ai n units by lowercase letters. Fo r example, a crater r imwith bright halos and rays, so defined, is III-A-3c.

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    ANALYSISThe following materi al is a brief description of each of the prime sites photographed

    by Lunar Orbiter I and, in most cases, some preliminary te rra in assessment observations.The geologic interpretation of each site is accompanied by a tabulation of the te rr ai n typesidentified on the site photographs. The te rr ai n maps have some specific differences inthe notations for t er ra in types due to the partic ular method used by the different membe rsof the scr eening group. Although deta ils varied, the definitions of basic ter ra in typesnoted in the section of t hi s r epo rt entitled "Selection of t er ra in units" were used by allanalysts. Most of the overall te rr ai n asse ssme nt w a s conducted by study of the fram elet sreassemb led into site or area geologic te rr ai n maps. Each site is located, for referencepurposes, on the ACIC lunar char ts prep ared from earth observations.

    Site A-1Location.- Site A-1 lies within the lowlands of the weste rn extremity of Mare

    Fecunditatis and a portion of the ea stern extremity of the continental cent ra l highland. Itis covered by Lunar Orbit er I medium-resolution frames 52 to 67. The selenographiccoordinates for the c or ne rs of the site are:

    Longitude Latitude40.3O E 0.2O N40.0 E 1.20 s43.8O E 0.5O S43.5O E 1.9O s

    as illustra ted in figure 1 3 , the index map for the site.Preliminary ter rai n assessment.- Site A -1 includes both m ar e and upland t er ra in .

    The geologic fea tur es, shown in map 3, and the detailed map explanation are presented inthe appendix. The geologic te rr ai n analysis w a s made by Terry W. Offield of the U.S.Geological Survey.

    Mare (I).- The mare surface in this site is apparently homogenous, moderatelycra ter ed, and only slightly lineated. The cumulative cr at er size-f requency distributionin figure 14 indicates a moderately cratered surface.

    Upland (II).- Upland topography bord ers the m ar e on the west (map 3). Small -scaleroughness and a high density of sm al l cra te rs can be dis cerned on slopes with low effec-tiv e sun angles. Horizontal to subhorizontal layering or fracturing can also be detected.This upland a re a has high relief relative to the mare .

    Terraces (II-B1) commonly occur at the base of ste ep upland slopes. Thi s unit isprobably formed by mass-wasting of mat eri al fro m the st eep slopes.

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    -10001500 -

    (uE0Ys 100:cW 50 -Ew-W>DS.-.I--

    IO:5-

    5V

    I

    Crater (m).-Cra ter s vary from well-formed (III-A) to shallow subdued craters (III-B)(map 3). Cr at er s with bright rim s and ray s(III-A-3c) appear to be randomly distr ibuted onthe ma re and characteri stically have rough ter-raced, rubbly walls (III-A-la). The mar e has amottled appearance , which possibly suggests ahigh density of craters sma lle r than the limit ofresolution (20 meter s).

    Blocks elevated above the general maresurface appear to be remnants of a large, pre-mare crater. This conclusion is based primar-ily on studies made at earth-based resolutions(Terry W . Offield, U.S . Geological Survey, 1966).Layering and frac turing is observed in a fewplaces on these exposures.

    Structural features (IV).- The mare sur -face is complicated by s tru ctu ral and volcaqicfeatures such as rills (IV-C-1), chain craters(IV-H), domes (IV-B), low ridges (IV-A), faults,lineaments, and irregular depressions (IV-G).Thes e units are described in the geologic-terrainmap explanation and shown in map 3.

    I I I I t I , , I , 1 I I I I I I

    The only infrared anomaly (J . M. Saa ri and R. S. Shorthill, Res. Note 66-4, BoeingSci. Res. Lab., Nov. 1966) is centrally located within the sit e. Two named fea tur es ar eincluded within the l imit s of the site photographed: Secchi X and Lubbock P.

    The high sun elevation (29O) at the time of the si te A -1 photography reduced theshadow lengths and in many c as es may have resul ted in no shadows being cast by cratersor protuberances. Thus, many small objects in the mar e area s, or even relatively larg eobjects in hummocky areas, where slopes may tend to in cre ase the rel ative sun elevation,may be unidentifiable.

    Site A-2Location.- Lunar Orbit er site A-2 is a highland site bordering the southeast part ofMare Tranquillitatis. It is covered by medium-resolution f rame s 68 to 83. The seleno-

    graphic coordinates fo r the co rner s of the site are:

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    Longitude Latitude34.0 E 1.1' N33.7O E 0.20 s37.7O E 0.4O N37.0 E 0.90 s

    as illustra ted in figu re 15, the index map for the site. A subframe fr om high-resolutionfr am e H-70 was a lso studied in the evaluation of si te A-2.

    Preliminary terrain assessment .-The quality of photography did not permit ter rai nass ess men t to the desi red degree. However, the general nature of the te rr ai n of theregion is shown in the appendix in map 4 . A better analysis will be poss ible by use ofenhanced photographs.

    Thre e named features within the boundaries of t his sit e ar e cr at er Censorinus V,hill Maskelyne Zeta, and crater Maskelyne TA.

    It is of i nte res t to note that in the area of thi s part icular site available lunar ch art sshow ar ea s of smooth te rr ai n in cer tai n regions with occasional grouping of craters 2 to3 km in diam eter . However, these medium-resolution photographs from Lunar Orbiter Ireveal as many as 20 craters 1/2 to 3/4 km in diameter in a local region bounded by an 8 -by 5-km ellipse and numerous sma ller cr at er s of all si zes down to the resolution limit ofthe medium-resolution photography. Cr at er s less than 23 mete rs in diameter were tooindistinct to be measurab le. An analysis of one nearby, simi la r area covered by bothmedium- and high-resolution photography indicates approximately 2 1 imes as many cra -t e r s visible in the high-resolution photograph as th er e were in the medium-resolutionphotograph. This fr am e of high-resolution photography was smeared , but craters assmall as 13 me te rs in diamete r could be measured. The sun elevation angle at the cam-e r a in te rsec t point was 23.7O, which should not cause an appreciable lo ss of detail. How-ever, a close inspection of the photography indica tes that within thi s area there is a highpercentage with a los s of detail. In fact, an earl y photograph of p ar t of th is region takena few orbit s prio r to passing over thi s site shows numerous slope reve rsa ls present inar ea s indicated "relatively smooth," a res ult which fur the r emphasizes th e significanceof lighting angle on the reflectance level and its influence on the amount of de tailed inter -pretation of lunar te rr ai n that can be made with confidence.

    2

    Site A-3Location.- Site A-3 lies in southwestern Mare Tranquillitatis. It is covered by

    Lunar Orbiter I medium-resolution fra mes 85 to 100. The selenographic coordinates fo rthe corners of the site are:

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    Figure 15.- Index ma p for site A-2.

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    Figure 16.- Index ma p for site A-3.

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    Longitude Latitude24.6O E 1.6O N24.30 E 0.2' N28.00 E 0.9O N27.70 E 0.5O S

    as illustrated in figure 16, the index map for the site.Preliminary ter rai n assessment.- The terr ain map for site A-3 is given in the

    appendix as map 5 and is accompanied by the explanation of geologic features . The geo-logic terrain analysis was made by Maurice J. Grolier of the U.S. Geological Survey.The nominal site is divisible into two regions of approximately equal area: a westernpart , which appea rs dark er and smoother in earth-based photographs, and an easternregion interrupted by subparallel ridges trending northwestward (Maurice J. Grolier,U.S. Geological Survey, 1966). A lo hift eastward in the location of t he center f romthe nominal site occurred during the mission, so that only a small, but still representa-tive, sam ple of the western region was photographed.

    M a r e (1-A).- The average regional mare is a plain of r elatively low relief, varyingin crater density and size. The mar e surface is interrup ted by northwestward-trendingridges and a small segment of a rill, Rima Maskelyne I, in the extrem e northeast corn erof the site. Depressions, crater fields, isolated boulders, and a few domelike hill s arepresent. At smal l scale, all these featur es contribute to the surficial roughness of themare.

    The mare surface is cratered at varying densities and is divided accordingly intothr ee subunits: a rougher mare (1-A-1), a smoother mare (I-A-2), and a rayed mare(I-A-R).Areal statistical samples are outlined in map 5. The rougher m are becomes moreareally extensive, eastward acro ss the site. Its cra ter density is 670 craters (34 met ersin diameter) per 50 km2. Unit I-A-1 in th is site is apparently smoother than the maresurface at the Surveyor I landing site in Oceanus Procellar um (Lunar Orbiter site A-9.2)for craters less than 200 met ers in diameter . For larg er cr ate rs, the Surveyor I landingsite is smoother (fig. 17).

    The smoother m are unit, I -A-2 , has a crater density ranging from 600 to 740 cra-ters (34 meter s in diameter) per 50 km2. The unit is generally less densely cra tere dthan the Surveyor I landing site, except fo r craters that are more than 200 mete rs i ndiameter (fig. 17).

    Mare unit I-A-2 is smoothest in the southwestern corner of the site. The cumula-tive size-frequency curve shows a crater density of 230 craters (32 meters in diameter)per 50 km2 (not shown in fig. 17). Even in th is sampled area, unit I-A-2 has a higher

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    I -A-RII-A-R2 ,

    crater density than the Surveyor I landingsite for craters more than 235 meters indiameter.ss-I

    - I - A - I500 y I - A - 2 1The rayed mare, I-A-R, has a slightlyo o 0 _ I-A-Z2

    higher reflectivity than the surrounding mare,and locally may even display a specu lar qual-ity as noted near the c ente r of m ap 5. Therayed mar e, especially in the west ern half ofthe site, is rougher than the Surveyor landing

    01 - I-A-R3Y5:ca,S-2 100:

    .A 50: site for craters smaller than 45 meters in

    .-, diameter. It may even be very densely-f 101 about 5 me te rs deep..I- pitted, with pits about 25 me te rs wide and0

    5- The three ma re subunits are compara-ble in cra ter density for craters ranging from60 to 130 mete rs in diameter. The eastern-most ray i n the ea ste rn quar ter of the site

    IO 50 100 500 1000 (map 5) has the lowest cra te r density in theentire site. This ray has about 325 craters(34 meters in diameter) per 50 km2 andappea rs relatively smooth. The reflectivityof this ray is diffuse and intermediate betweenthe reflectivity of other rayed mare areas

    I I t l " I I I S I ' I I

    Crater diameter, metersF i g u r e 17.- Cumula t ive cra te r s ize - f requency d is t r ibu -t i o n s f o r sa m p l e s o f va r i o u s m a r e u n i t s in si te A- 3compared w i t h tha t fo r rep resen ta t i ve da rk maresamp le (SS-1) in Su r ve yo r I area of si te A-9.2.

    (0.096 to 0.102) and that of r idges within the site (0.109 to 0.114). The diffuse reflectivityof t his ray appear s rel ated to $he thinness of the deposit and its lateral gradation onto non-rayed mare . Cra ter s older than the ray are not completely obliterated; they appe ar sub-dued under or through the ray. Some cra te rs , mostly in the diamete r range between 33and 70 me te rs , appear to be contemporaneous with, or more recent than, the ray. Thesecr at er s a r e sh arp, well-formed, and commonly exhibit a light halo around them. Theiroccurrence is in a ratio of 1 to 2.5 with that of the craters older than the r ay.

    The rela tive smoothness of the rayed ma re ca n be visually appraised in LunarOrbiter medium-resolution photographs. It is confirmed by s tati sti cal analysis, at leastwithin a broad range of crater diameters in the thre e areas sampled.

    Apparently, the raye d ma re i n the e as te rn region of the photographed area does notstand in positive relief above the surrounding mare ; it even appears slightly lower. Thehypothesis is that the surfi cia l roughness of a ray might be related to the distance to thecrater fro m which it origina tes. At long distances fro m the crater of origin, deposition

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    ra th er than pitting may occur and slight compressing or reworking of the lunar surf icia llayer at the time of ra y deposition may have a smoothing effect on m ar e topography.

    Cr at er s (III-A).- Cr at er s are divided into well-formed and subdued cr at er s. Onlythe larg est of the well-formed craters, about 1km in diameter or more, have been dif-ferentiated . Most of these craters have raised rims that exhibit rather high reflectivitytoward the sun. (A s used in this report, "raised rim tfapplies to e ither bedrock rai sedabove the level of surrounding ma re by mechanical deformation or to a ri ng of ejecta. )Lunar slo pes and, to a less er extent, crate r ri ms are commonly lined with slumpterracettes.

    The largest crate r is Sabine E, a well-formed, almost rim le ss cra te r of high reflec-tivity in the northwest corn er of the site. Sabine E is about 5 km wide and 0.790 km deep(AIC chart 60C). A peculiar matted s tru cture , not unlike burlap weave, is displayed alongthe inner s lopes of Sabine E. This st ructure, made up of both radial and concentricffthreads,lfmay or may not reflect the bedrock that underlies the lunar surface. "Burlapweave" structure is prominently and repeatedly displayed in the w a l l s of cr at er fields,depression s, escarpments, and fault sca rps . It is distinct from slump terr acett es, andappears to be a bedrock characteristic at or near the lunar surface at the resolution ofLunar Orbite r medium-resolution fram es. The threads i n the weave observed in escarp -ments a r e nearly at right angles to each other and trend northwest or northeastward.

    Well-formed cr at er s of many kinds, in the 50- to 100-meter-diameter range, dotthe mar e surface. They include craters with a raised rim, or even a lip, c ra te rs with alight halo around a ri m with or without ray s, and cra te rs with very rugged, nearly vert i-cal interior w a l l s , and a circular shelf down the wall. The shelf is suggestive of the exis-tence of a lunar surficial laye r. Subdued cr at er s, mostly less than 0.5 km in diameter,r imless or with low rim , dot the mar e surface . They are, for the most part , feat ures ofnegative relief and of vary ing depth.

    Crat er fields (III-C).- Most crater fields are elongated clu st er s of ghostlike, over-lapping cr at er s, with angular outlines. Commonly, the cluste r exhibits a raised rim,which, in distinction with the rai sed r im of most well-formed cr at er s, appear s to involvebedrock deformation around the c ra te r field. Large cr at er fields include from two tose ve ra l dozens of individual craters, commonly arranged linearly.

    Another type of crater field involves very closely spaced, sepa rate subdued cr at er s,generally less than 0.5 km in diam eter . Th is type of cr at er field, although not differen-tiated from the first type, is little more than a very rough, densely cra ter ed mare .

    Crater fields have a low crater density with a cer ta in range of crater diameter andmay be smoother than the mare itsel f. They appear to sha re this ch arac teri stic withpar ts of m are rid ges and mar e depressions. This rath er su rpri sing and unexpected

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    finding may be due to the oblit eration of many cr a te rs by slumping along stee p slopes , orby smoothing pro ces ses associated with uplift, collapse, and subsidence.

    Mare ridg es (IV-A).- Mare ridges are prominently asym metr ic with a stee p south-w e s t slope and a gentle southeast slope. They occur in discontinuous, linear to curvil inearsegments, 0.5 km wide and many kilometers long, somewhat en echelon, and trendingnorthwestward. Some segments, bounded by linea r escarpm ents , are suggestive of ter-restrial fault blocks. The intermontane plain between blocks as shown in map 5 is moreheavily cr at er ed than the ridges and apparently less than the surrounding mare.

    Mare r idges appear to be the loci of low domical hil ls of two types, undifferentiatedin map 5 .

    Domes (IV-B).- The first type of domelike hi lls occu rs on ridges, as in the south-cen tra l par t of the s ite , where two such hills r is e 130 and 60 met ers above the generallevel of the ridge. An elongated dome, possibly made up of two coalesc ing hi lls, al soocc urs on the ridge in the southw estern part of the ridge . The top of th is dome appearsrelatively smooth and flat. High reflectivity is char acte rist ic of thes e hills; slump te r-racettes, referred to as tttree-b ark" texture, commonly occur on thei r slopes. The sec-ond type of hills mapped as domes occurs on the ma re, along the si des or ridges or nearthei r tapering end (map 5 ) .

    Mare depressions (IV-G).- Mare depressions ar e irreg ula r areas below the regionalma re level with rounded, ghostlike crat er s. The sur fac e of the depressions is relativelydark and smooth. It is generally le ss c rate red than the sorrounding mare.

    Summary.- Site A-3 is one of the smoothes t sites photographed during Mission I,when its roughness is evaluated in ter ms of cr at er density and size. The least crateredar ea s occur in the southwesternmost part of the si te, in terra in unit I -A-2 , and also onthe easternm ost ray I-A-R. Photographs of the nonridged mare , west of the site, anddetailed analysis of rays with high-resolution photographs were requ ired for fu rther eval-uation of thes e two most promising terrain units.

    Two named fea tu res within the boundaries of the site A-3 are cr at er Sabine E andRima Maskelyne.

    Site A-4Location.- Site A-4 is in the cent ral highlands area between Mare Tranquill itatis and

    Sinus Medii. It is covered by Lunar Orbite r I medium-resolution fra mes 105 to 112. Theselenographic coordinates for the cor ne rs of the site are:

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    Figure 18.- Index ma p for site A-4.

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    fills a str uct ura l trough lying between -.strongly sculptured uplands with moderateto steep slopes. The surf ace of the plains- IOOOy

    cra ter s ranging in size from a few kilome-t e r s to about 20 meters (the limit of photo-graphic average identification resolution). gand distribution throughout the unit, andinclude both bright halo cr at er s and well-formed craters with moderate albedos.Many of the cr at er s with moderate albedocontain conical or domical mounds on theirfloo rs. Crat er counts (fig. 19) fro m one of 0the smoothest appearing areas in the unitindicate a high crater density, appreciablyhigher than that in smooth ma re units. Con-sis ten t with the preflight evaluation of theupland-plains units based on telescopic pho-

    500 -orming material is densely populated by(uEY\The cra te rs vary appreciably in size , shape, 0" iooT

    L1Q)So- 50-2.cP)>Q_-t-

    IO:5 -

    S

    I

    36

    ss- i.

    iI , I I I I I , , I I I 1 , I I I lIO 50 100 500 1000

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    The cr at er s Theon Senior B and Theon Senior A and Theon Senior are the prominentfeatures located within this site as shown in map 7.

    Site A-5Location.- Si te A-5 is located near the approximate center of the vis ible face of the

    moon, and l ie s in the southwes tern portion of Sinus Medii. It is covered by Lunar OrbiterMission I medium-resolution fram es 118 to 133. The selenographic coordinates for theco rn er s of the site are:

    Longitude Latitude3.0 W 1.0' N0.2' E 0.3' N0.l0 w 0.9O s3.2' W 0.3O S

    as illustr ated in figure 20, the index map for the site. The cr at er Oppolzer A is the onlynamed featu re within the area photographed.

    Prelimi nary terr ain asse ssment.- The site A-5 ter rai n map (map 8 ) and the accom-panying explanation of geologic features ar e presented in the appendix. The geologic ter-rain analysis w a s made by Lawrence C. Rowan of the U.S. Geological Survey. Th is siteprovides an average sample of regional ma re . Uplands border the site on the southeastand west and an isolated block of upland trends northwest ac ro ss the m ar e in the westernpart of the site. The mare surface is rela tive ly rough and complicated by the presence ofcra ter fields, irregul ar depressions, mare ridges, troughs, well-formed cra ter s, andmodified, subdued craters. A zone of apparent st ruc tur al weakness extends northeast-ward across the site, merging into a larg e ma re ridge. Te rr ai n units of minor extentinclude linear rills, lineaments, and faults, and a smal l dome.

    Mare (I).- Average regional mare covers about 65 percent of the are a. The di st ri -bution of c ra ters with differ ing morphology is variable, so that terrain subdivisions aredifficult to delineate. Only one subdivision, unit I-A-2, is presently recognized.

    A wide range of roughness is indicated by the cumulative size-frequency distribu-tions (fig. 21) of sample areas 1 and 3 as located in map 8 . The most pronounced differ-ences are for crate rs less than 100 met ers in diameter and gre ate r than 200 mete rs indiameter. Sample 1 has about twice as many craters 50 mete rs in diameter as sample 3.Samples 2 and 4 are not shown in map 8, but ar e of intermediate density. Samples 1 and3 appear, then, to re pres ent end-members of the crater-d ensity spectrum on the regionalmare surface at thes e identification resolutions.

    Mare subunit I-A-2 is the smoothest ar ea found in the site. The cra ter density(fig. 21) is markedly lower than for any other unit. The area of thi s unit is , unfortunately,

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    Figure 20.- Index ma p for site A-5.

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    5000 3\

    1000:N 500-E0Y

    -?u" 100:cW 501zw-W>0.-+3 IO70 5 -,

    relatively sma ll (22 km2) and elongated in thenorth-south direction.

    7 +;\ ',Figure 21.- Cum ulative crater-size frequencydistributions for samples 1 an d 3 an dunit I -A -2 in regional mare ( I -A) , foruplands ( I l-C), and for crater f ields ( I I I-C)in s it e A- 5 compared with that for repre-sentative dark mare sample (SS-1) i nSurveyor I area of site A-9.2.

    The relat ive roughness of s amples 1 and 3appears to be confirmed by slope-component sam-ples of these areas. Statistical rel ative rough-ness parameter s for sample 3 are: absolutearithmet ic mean ZAb = 1.00 and the algeb raicstan dard deviation O A ~ 1 . 2 O . In contrast, val-ues for sample 1 are the XAb = 2.5O and theO A ~ 2.6'. Values for unit I-A-2 have not yetbeen obtained.

    Upland (II).- Two main upland te rr ai n unitsa r e apparent:

    (1)Upland, hummocky and cratered . Hum-mocky, cratered upland, mapped as II-B, ccursin the west and southwest of the site. One sub-division, II-3-1(map 8), is apparently a transi-tional unit between the isolated upland block (II-C)and the surrounding regional ma re . This unit issomewhat more subdued than unit II-B.

    (2 ) Upland, sculptu red, moderate relief.Te rr ai n mapped as II-C (map 8) is principally anisolated north-northwest-trending block of upland

    in the west ern pa rt of the site. It has moderate relief (75 to 150 me ter s) relative to thenorthwest-trending faults and lineaments. Regional slopes, measured in an approximateeast-west dire ction by photogrammetric and photoclinometric techniques, range f rom 4Oto 8O. The topographic prof ile S-14 shown in figu re 22 and located in map 8 was measuredphotoclinometrically. For 8-meter slope lengths, flAb = 5.0' and = 6.0' in thi ssample. Thes e values suggest that the sma ll-s cale roughness of th is upland unit is signif-icantly gre at er than that of the regional ma re .

    ' surrounding regional mar e. The block is sculptured by prominent northeast - and

    The cumulative size-frequency distribu tion function for craters in unit II-C is shownin figure 21. Although the density of craters less than 75 meter s in diameter is similarto that of th e regional mar e, t her e is a marked deficiency of 75- to 500-meter-diametercraters. This featu re has been noted in other upland areas and may be due to destructionof craters by mass-wasting.

    Crater (XII).- Craters are subdivided into two groups, well-formed craters (III-A)and modified, subdued craters (III-B). The chara cte r of t hes e two types, as well as

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    descriptions of their component subunits,is given in the geologic t er ra in map expla-nation with map 8.

    Army Map Service photogramme-trists have compiled numerous topo-graphic profiles acro ss various crater(figs. 23 and 24) o demons trate funda-mental features. Profile s 15 and 17repr esen t III-A craters with characteris-tic moderately ste ep slopes and rais edrims; the latter profile is modified slightlyby a slump block on the w e s t side. Cra-ters 111-B (profile 10)generally have mor e

    2000 subdued rim s and les s stee p w a l l s . W e l l -formed cr at er s with bright r im s appearto be randomly distributed ac ros s thesite. The w a l l s of thes e cr at er s arecharacteri stically rubbly, te rra ced , andsteep, with blocks and aggregates in the

    50-

    0 I I 1600 20bo types. Several of these ar e shown he re0 500 1000(a) Profile S-14; upland ( I l l - C ) .' - 1 1

    00 500 1000 I500

    (b) Profile 5-18: egional mare (I-A).Figure 22.- Topographic profiles of area s in site A-5.Measurements in meters; vertical exaggeration approxi-mately X6. Derived by photoclinometric technique.

    floors. Profiles 3 and 13 repr esen t these features. The photoclinometrically derivedprofile S-18 n figure 22 shows a low, broad 111-B c rater with a slightly raised e aste rnrim . Topographic profile data are especially important for interpre ting the engineeringproperties of the lunar surface material as w e l l as te rr ai n roughness and w i l l be usedextensively in future analyses of the prime s ite s.

    -.

    Cra ter fields a re widely distributed and contribute greatly to the roughness. Thecomponent craters are usually somewhat subdued. They vary in si ze from field to field,but generally have constant dia met ers within a field. The cumulative size-frequency di s-tribution rep resen ting unit IH-C (fig. 21) shows that the individual c ra te rs are generallylarge (> 100 mete rs in diameter). This unit is commonly transit ional into i rreg ulardepressions and troughs.

    Structural features (IV) .-Most prominent among the linear or curvilinear structuralfeatures is the lar ge ma re ridge extending acr oss the north-central part of th e site. Itappears to be highly fr acture d and faulted and, to the southwest, me rge s with a fracturedzone. This s ame zone may displace the upland block in the wes t .

    Faults, lineaments, and rills trend predominately northeas t and north, coincidingwith the fundamental "lunar grid" tre nds . Chain craters a r e commonly alined north-southor for m loops.40

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    Figure 23.- Location of site A- 5 profiles shown in figure 24.

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    I S L3 0 0 400

    5013 0

    0 500

    I5010050

    IO 00

    10050

    15 0500 1000 1500

    1005017 0

    0 500

    Figure 24.- Concluded.

    Telescopic observations indicate that t his site cons ists , for the most part , of lowridges and hi lls (Dahlem, 1966). Open areas between ri dges appear as broad plains con-taining a few scattered crater lets ; and, there is little observational evidence of extensivecratering , whereas the Lunar Orbiter I photography reveals many additional terrain fea-tu re s including numerous cr at er s much sma ll er than the 1/2-km-diameter limit imposedby earth-based observation.

    Site A-6Location.- Site A-6 lies within the nor thern sec tor of the cent ral continental high-

    lands and includes portions of the Flammarion and Spa re r highland bas ins . It is coveredby Lunar Orbiter E medium-resolution fra me s 141 to 148. The selenographic coordinatesfo r the cor ner s of the site are:

    Longitude Latitude4.50 w 2.8O S4.70 w 4.0 S0.5O E 3.70 s0.3O E 5.1's

    as illustra ted in figure 25, the'index map for the site.43

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    Figure 25.- Index ma p for site A-6.

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    Preliminary terr ain assessment.-The quality of photography did not per mit te r ra inassessment to the degree desired for site A -6 . The high sun elevation degraded the detai lof lunar te rr ai n fea tur es as shown in map 9 , which can only be used as a qualitative guidefo r overall assessment. Enhanced photographs will make a better analysis possible.

    Included within site A -6 are the crater Spbrer A at upper center, a major portion ofthe F lammarion basin in the northwest, and Rgaumur A in the east. The nor the rn half ofSporer and a sm al l portion of F lamm ario n B also lie within the site.

    Earth-based observers have described a portion of the Fl ammarion floor as con-taining a low ridge, dropping into a shallow basin, with numerous shallow depressionsalined with the ridge. Thes e earth-based observations generally describ e the ar ea assee n in the Lunar Orbi ter photography. The Lunar Orb iter medium-resolution photogra-phy reveals more depressio ns and c ra te rs , ranging downward in s ize fro m those depictedin the charts to featur es at the limit of the resolution of the photography. These depres-sion s join and overlap to give the surfa ce a hummocky texture. This texture is moreextr eme and noticeable to the east of the ridge descr ibed but still exists to a lesser degreein the a rea evaluated fo r possible landings. However, the high sun elevation at the t ime ofthe si te photography (35O) makes it difficult to estimate rela tive smoothness. Manydepressio ns and craters throughout this area ar e barely discernible.

    Site A -7Location.- Site A -7 is located in the lowland-mare area between Lansbfr g and Fra

    Mauro cra ter s. It is covered by Lunar Or bite r I medium-resolution fram es 57 to 172.The selenographic coordinates for the co rner s of the site are: f

    Longitude Latitude23.6O W 2.4's23.9O W 3.8' S20.4O W 3.0 S20.6' W 4.5O s

    as illustrated in figure 26, the index map for the site.Preliminary terrain assessment.- The site A -7 ter rai n map (map 10) and the expla-

    nation of the geologic features are given in the appendix. The geologic te rr ai n analysi sw a s made by Richard E. Eggleton of th e U.S. Geological Survey. The area shown conta insabout 92 percent regional mar e and 5 percent terra. The largest well-formed cra ter i nthe site, Fra Mauro B, mapped as unit III-A, occupies about 3 percent of the total area.The mare surface is abundantly cratered, and the craters a r e 1 .7 km o r less in

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    Figure 26.- Index ma p for site A-7.

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    cres t-to -cre st diameter. Several rays , which in full-moon photographs appear as broad,light-colored streaks, cro ss the site. Some ridg es rise above the su rfa ce of the mar e inthe eas tern third of the site. The sun elevation above the horizon at this site exceeded30 and r esulted in the inability to detect craters less than 26 to 30 km in diameter. Thedensity extr eme s indicating excessive light intensity are shown graphically in the uppercurve of figu re 27 , wherein nearly all the photometric density trace is above the range ofthe preexposed gra y s cal e on the film-edge data. For the purpose of analys is of photog-raphy of this site, the cr at er counts were made on prin ts of medium-resolution fra me swhich had been assembled f rom f ilm made at a high-gain se tti ng on the GRE as notedpreviously.

    The geology of the s it e and an extensive surrounding area has been mapped previ-ously by R icha rd E. Eggleton, U.S . Geological Survey, 1965. A preflight site-evaluationreport by W e s t (1966) includes significant quantitative tre atm ent of rel ati ve full-moonalbedo and of ter rai n roughness parameters.

    1.551.401.25

    3hu)a,-0wu)3-

    c_-= 1.10-

    .95cn

    .80

    .65

    50

    .35

    ---

    -----

    Frame 157 Framelet 591Lunar scene density trace

    Figure 27.- Photometric density trace for site A-7.

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    Mare, undifferentiated (I-A).- Topographically, the surface of the reg ional ma re ischaracte rized by variations in both density and si ze of c ra te rs . Earth-based and Rangerphotographs have shown that i solated c irc ular craters larger than about 0.75 km in diame-ter are randomly distributed over the mar e surface. Isolated craters of approximatelythis diameter and crater fields are excluded from the m are te rr ai n units.

    The regional ma re in this site is subdivided into four main units: I-A, I-A-4,I-A-6, and I-A-7. Terr ain units I-A-2, I-A-3, and I-A-5 are transitional. Terrainroughness in t he seven units is expressed in te rm s of cr at er density per unit area,decreasing fr om unit I-A-1 to unit I-A-7.

    Cr at er counts shown in the cumulative frequency curve of figu re 28 show thatunit I-A-4 in th is site ha s a crater density of about 500 craters (with a diam eter of60 me te rs ) per 50 km2.

    Te rr ain unit I-A-1 is cha rac ter ize d by an abundance of cr a te rs, from 0.25 to 0.5 kmin diam eter . Te rr ai n units I-A-2 and I-A-3 are generally less cra ter ed and they lackcr at er s in the diameter range of the la rge r cr at er s of unit I-A-1. The fourth mare t er -

    1000:500-

    EY5: 100:u30-5 50-2LcW>u.-+7 107" 5 -5

    ra in unit, I-A-4, is markedly less crateredthan the first thre e mare units, as is unitI-A-5. Te rr ai n unit I-A-6 is essentiallycoextensive with light-colored s tr ea ksobserved in earth-based lunar photographsat 1-km resolution. Mare surface thatappears thickly mantled with ray materi alis labeled 111-E. Te rr ai n unit I-A-7 is asmall, nearly c rater less a rea, measuringabout 2 by 4 km, about 17 km west of thenortheast corne r of the si te; associate dwith it are low, dome-shaped hills.

    Upland (II).- The upland is restrictedto the eas tern quart er of th is site. It iscovered by cr at er s 0.25 to 1.5 km in diame-ter. The upland is subdivided into threeunits of incr easing local relief: 11-B, 11-C,and II-Ci, as shown in t he explanation withmap 10.Craters (HI).- Individual c ra te r s andcrater components have been mapped onlywhere they might constitute a terra in hazardto lunar landing and surface operations.48

    ss-l %I - A - 4I-A-6rn -C- l?

    I t I l ~ l 1 l l 1 I I I I I I I I 1

    F ig u r e 28.- Cumu lative crater size-frequency distribu-t ions for areas in site A-7 compared with that forrepresentative dark mare sample (SS-1) inSurveyor 1 area of site A-9.2.

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    Craters fall within two broad categories: well-formed craters and modified craters,generally of subdued form . Cr at er s with convex-upward int eri or walls, or dimple cra-ters, are a spec ial kind of well-formed c ra te rs .

    (1) Well-formed craters (III-A). The components of well-formed craters are theinte rior wall, the floor, the sma ll mounds at the bottoms of craters, and the rim .

    The int eri or wall, which may include par t of the floor , is commonly smooth, but maybe rough locally. In Fra Mauro B the int erio r wall is mapped as III-A-lb; it is moderatelysmooth, but it has lltree-ba rkl* exture, and a low ridge, probably a debris s tre am trendingdownslope. The to e of the slope at the bottom of unit III-A-lb in Fra Mauro B is mappedas unit III-A-lbl. It may be analogous to II-C-1.less than 200 me te rs in dia met er. They typically have rai se d rim s with concave-upwardprofile s. Because of the sm al l si ze of these craters, the unit includes crater w a l l andfloor also. The ri m material of these cra ter s is likely to be blocky.

    Te rr ai n unit III-A-3c includes craters with bright halos and ray s. Such cr at er s are

    Another type of well-formed cr at er , the dimple cr at e r (III-D), is most common intwo cl uster s in the terra in the southeas t qua rte r of the site. Dimple craters have convex-upward int erio r slopes, suggesting that particulate sur fici al materi al may have draineddown a hole in the center .

    (2 ) Modified cra ters (III-B). The components of subdued craters include the inte riorw a l l , smooth or rough, a mound at the bottom, and a rim . Commonly, the ri m grades intothe in teri or slope in subdued craters.

    (3 ) Crater fields (III-C). The cra te r fields ar e subdivided into the two te rr ai nunits III-6-1 and III-C-2. Cr at er s that touch or partly overlap each other are referredto as composite craters. As observed on earth-based lunar photographs, composite cra-ters are abundant in the fi elds of satellitic cra ter s that surround many large lunar craters.Commonly, they lack crater wall and rim i n the a rea of over lap and they occur in groupsof 5 to 20 individual craters. This unit exhibits the whole range of crater si ze s and depth-to-diameter ratios.

    Some craters in the diamete r range f rom 0.15 to 0.4 km have a te rr ac e completelyringing the upper part of the int eri or wall. Thes e craters occur with an areal density ofabout 0.6 to 0.7 per km2 and nearly all of them are st eep walled above and below the bench.The bench commonly is a well-developed shelf, 5 to 10 me te rs below the level of the m ar eimmediately surrounding the crater. Such crater walls are mapped as unit I I I -A-lc .Where the c ir cul ar shelf is ill defined, the crater wall is mapped as III-A-lcl ; where thelevel of th e shelf var ie s from a few mete rs to a few tens of me te rs below the surroundingmare, the crater wall is mapped as III-A-lc2. These terraces may be at the b ase of aweak surface l ayer.

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    The rim of well-formed c ra te rs constitutes unit III-A-3. Commonly, the rim s ofcr at er s lar ger than 15 km ac ros s ar e hummocky near the r im crestand troughs furt her out. Unit III-A-3a, the hummocky te rr ain, is mMauro B. Another r im unit, III-A-3a1, is located in the upper par t of the interi or wallof Fra Mauro B. It may rep res ent the outcrop of crater rim material in the crater walland show the thickness of thi s unit. The crater lip with ste ep slope and tree -bark textureis classified as unit III-A-3d.

    The ou ter pro file of craters with rais ed ri ms var ies between two extremes. One isconcave upward, with slope of lo o to 15' nea r the rim crest; the slope along the in