DESTINATION MOON: A History of the Lunar Orbiter Program
- The investigators conducted laboratory experiments using soils with grain sizes ranging from 0 to 125 microns and gravels ranging from 2 to 4 millimeters with gradations and layering. Tests were run under air and vacuum conditions to determine behavior of water at various flow rates and temperature levels on test soils. Results showed that, in the presence of air; water formed terrestrial-like stream channels. In a vacuum at freezing temperatures water formed dendritic ice memo and continued to flow under the ice, frequently penetrating to the surface and freezing. Water then sublimated, leaving a hummocky surface. Some soil downalope movement occurred., but no stream channels developed. Results show that ice will readily form in a vacuum to a thickness which allows liquid water to exist under it. Model streams produced in a vacuum did not erode rille-like channels. Results support, Lingenfelter's predictions (Science, Vol. 161, p. 266).
- There in a major implication in the mathematical calculations of the Moon's orbit as rechecked and improved by H. Gerstenkorn. About one billion years ago the Moon, a separate planet orbiting the Sun, passed very close to Earth. Both bodies continued to attract each other until the Moon assumed a retrograde orbit about the rapidly spinning Earth. The Moon moved within the Roche limit in a polar orbit around Earth, causing part or the lunar surface to break away bombard Earth. Following this the Moon began to recede from Earth until it came to occupy its present orbit. Loosened materials fel1 back on the Moon as meteors, making major craters. Geological investigations might substantiate Gerstenkorn's theory.
- Infrared observations or the Moon in the 8- to 14-micron atmospheric window have delineated macroscopic lunar surface thermal behavior. Shorthill has discovered further lunar thermal anomalies. The craters Aristarchus, Copernicus, and Tycho cool much less rapidly than surrounding areas during eclipse. The observations made by the authors have not determined the geometric scale of the structure of hot and cold regions. Surface rocks in these areas my be responsible for the less rapid cooling rates because they are probably thermally connected to a subsurface temperature of 200 degrees Kelvin.
- This report describes the use of Lunar Orbiter II photographs in conducting a test in which the subjects were required to fix the location of a Lunar Module in a simulated crater field near U. S. route 89, northeast of Flagstaff, Arizona.
- The author questions the survivability of an impacting body. He postulates that 1) craters formed by impacting events are dry, not lava-filled, 2) isostatic distortions occurred, but before this was complete, lava appeared from the body of the Moon and selectively fil1ed the lower areas. This lava was denser than surrounding rock; which presumably could have been more acidic, and 3) tension cracks (rilles) and compression fractures (wrinkle ridges) show that later subsidence and compression has occurred. Thus far only the dense material centered in craters and capable of yielding gravitational effects has been measured.
- This report outlines the necessary requirements and constraints which would have to be met in order to put a Lunar Orbiter in an Earth-return trajectory around the far side of the Moon. This constitutes the basis of a contingency plan, should the Orbiter have failed to go into orbit around the Moon. During the fly-by the Orbiter could have taken useful Photographs of the far side of the Moon. Upon return to the Earth the spacecraft would burn its remaining propellant to deboost into Earth orbit for readout of the data.
- In studying existing spherical harmonic expansions of the Moon's gravitational potential and the difference among the lunar principal moments of inertia, the authors found two large gravitational anomalies not associated with those of Miller and Sjogren. One on the east limb of the Moon near Mare Marginis appears to be associated with a large circular basin, 900 kilometers in diameter, centered at 91 degrees east, 25 degrees north, with Mare Marginis filling in the southwest corner.
- On the far side, Lunar Orbiter photos disclose that the authors feel is an enormous circular basin now very heavily eroded. The basin is l,000 kilometers in diameter, centered at 173 degrees east, 11 degrees north. They propose that this be called Occultum (Hidden Basin).
- Various theories exist about the origin of lunar sinuous rilles such as Schroter's Valley. The mechanism producing them can be categorized under aqueous erosion, faulting, and subsidence. Each of these does not stand the intensive investigations of the rilles' topography. Aqueous erosion is the least tenable of all the mechanisms because it necessitates the presence of very high vapor pressures for any liquid at 1unar surface temperatures. Observable evidence speaks against faulting as the major mechanism causing rilles. Igneous processes suggest another mechanism, but, outflow of lava creates a raised feature, not a depression. Yet one process could explain their formation: nuses ardentes, or fluidized outflows of gas-dust mixtures. The presence of sinuous rilles in the vicinity of craters whose formation seems to be volcanic strongly suggests a relationship supporting this mechanism as the process by which these surface features have been formed.
- Lunar Orbiter I photographs reveal portions of the Flamsteed Ring near the Surveyor I site. The convex body resembling a flow of viscous lava located Apollo landing site A 9.2 at 2 degrees south latitude, 43 degrees west longitude has partially invaded nine craters in the area. This suggests that the flow material is younger than the maze material. The investigators conclude that these topographic features indicate the presence of extruded intermediate lavas of acidic composition. Such lavas are more viscous than basic lavas. The investigators further conclude that the Flamsteed Ring in not the result of basaltic flows despite lover gravity on the Moon. These conclusions are preliminary.
- The work of these two men shows that near-surface slab-like models produce anomalies of the magnitude, observed from tracking data of the Lunar Orbiters. The authors assume that maria fill can be represented by a thin circular disk of dense rock at the lunar surface, imbedded in less dense material. Submare and adjacent rim material has either lower density because this has been breciated, and pulverized by impact, or is a high-density material if brought to the impact site by an impacting body.
- This report concerns geological characteristics of the Moon, general composition, lunar geological processes, and cratering by possible cometary materials. Lunar Orbiter V photographs are used in the analysis of craters Messier and Messier A.
- Lunar Orbiter V photographs H-216 and H-217 of the Marius Hills constitute the basis for a geological survey which a manned roving vehicle could conduct during a five-day period on the lunar surface. Included in this report are two large geological maps with scales of 1:200,000 and 1:25,000 respectively.
- A new interpretation of lunar ring structures is the result of analysis of data from Lunar Orbiter and Surveyor. Instead of accepting the hypothesis that "elementary" rings represent old, partially filled craters, the authors posit the hypothesis that they are recent volcanic structures. Elementary ring structures occur mostly on flat, smooth floors of maria. They consist of lunaritic materials in hills or wrinkle ridges of both. The rings approximate circles or polygons and parts of them coincide in direction with local tectonic patterns. The rings are generally incomplete. The authors do not claim that all incomplete rings on the Moon have the me origins or are of the me type.
- A Lunar Orbiter II photograph of an area in western Mare Tranquillitatis shows a boulder track down the wall of the crater Sabine D. Assuming a spherical boulder of r= 6.5 meters and a density of 3.0 grams/centimeter3, then the surface bearing strength in equal to 4 times 106 dyne/centimeter2 at a depth of 75 centimeters. This preliminary measurement is significant because it can be used as a lower limit of bearing strength over a length of 650 meters versus the footpad-sized measurement of a landed spacecraft. The area of this measurement is also significant because it in a potential landing site for Apollo.
- Firsoff discusses the implications of Lunar Orbiter photography in relation to two main theories about the formation of lunar surface features: water and volcanic/meteoric. The existence of sinuous rilles, of long valleys and evidences of "aprons" to the west and southwest of Tsiolkovsky suggest water action in various forms from high-pressure sublimation to ash-covered glaciers. Many formations could not have resulted from lava flows as understood by known behavioral characteristics of such flows on Earth. Under conditions on the Moon lava cannot travel far. Water, however when escaping to the surface under extreme pressure from within, could cause explosions and craters to form. Moreover, if one assumes that Orientale, was formed in an astroidal impact event, then this would have released sufficient gases and meter trapped within to have formed a temporary lunar atmosphere. The impact mould have triggered far-reaching processes and initiated prolonged volcanic activity whose effects would have affected the entire lunar surface.
- Lunar Orbiter photography reveals closely spaced parallel lineament sets in such areas as the craters Gambart, Maskelyne F, Gambart C, Kepler, and Copernicus, and also in Oceanus Procellarum and in Martus. These may be surface expressions of underlying faults or fractures. It in not certain if these lineament sets more restricted in formation to a single time span. Lineament sets parallel to polygonal sides or rayed and unrayed craters suggest the presence of a precrater parallel joint system. These surface lineaments may have been produced by Earth tidal forces. This would indicate that the Moon's surface in and has been a working unit through much of lunar history.
- This report describes tests conducted to determine the usefulness of Lunar Orbiter photographic negatives in determining slopes on the Moon's surface. Random tests were conducted to define the reliability of film density measured against the gray scale. Results show that negatives with density readings higher than step nine of the gray scale give erroneous slope measurements.
- Gilvarry posits the theory that positive and negative mascons have been caused by a series of events after the initial formation of the Moon: The lunar seas constitute the oldest exposed areas of the surface. Their presence and the existence of positive and negative gravitational anomalies in irregular maria rule out the lava mechanism formation theory and support the theory of a lunar hydrosphere at some time after the Moon's formation. Experiments with various soil types under conditions involving simulated lunar hydrosphere, atmosphere, and vacuum conditions offer explanations for the nature of maria materials, the former existence of surface water acting as a transport mechanism for these materials, and the differing iostatic conditions between maria and highland areas. Negative muscons would have resulted when overlying water flowed to lower areas or escaped into space. The geographical location of negative mascons supports this supposition. Water, in turn, carried deposits down to the great circular maria whose depths, produced by meteoric impacts, accepted greater sedimentation and, therefore, increased mass concentrations.
- The authors discuss the formation of the Tsiolkovsky crater on the farside of the Moon. They base their observations on data from Lunar Orbiter III; high- and medium-resolution frame No. 121. Tsiolkovsky is a landmark on the far side, a young, distinct and very large crater in an area saturated with craters. The authors discuss the probable origins of Tsiolkovsky in relation to: 1) the distribution of craters around it, 2) the nature and shape of its rim, 3) radial gouges and crater chains, and 4) the presence of an apparent ejecta blanket. They conclude that Tsiolkovsky formed as a result of an impacting astroidal body or a giant volcanic explosion, and they prefer the former hypothesis to the latter.
- All five Lunar Orbiters flew micrometeoroid flux experiments to test the frequency of micrometeoroid hits in the lunar environment. The only other spacecraft which had attempt to do this was the Soviet Luna 10. This spacecraft had registered particle impacts exceeding by two orders of magnitude the average of interplanetary space. The Lunar Orbiter experiments had a configuration which detracted from maximum exposure to the lunar environment. Test material on board each spacecraft consisted of pressurized beryllium copper detectors covering an area of 0.282 square meters, of which only 0.186 square meters was effectively exposed. Over a one year period five Orbiters recorded a total of 22 hits or one-half the record registered in Earth orbit by Explorers 16 and 23, using the same kind of detectors. The investigators caution that these data are too tentative to form a general theory about micrometeoroid flux near the Moon.
- Hartmann has examined rectified pictures from the Russian Zond III of portions of the Moon's far side and of Orientale Basin. He discusses the significance of the pictures in theories concerning the formation of lunar basins and the maria. Of special interest is Orientale which involves a whole system of craters, crater chains, concentric mountain rings and scarps including the Rook and Cordillera mountains. Photographic data is still too scarce to determine what role, if any, volcanism, tectonic activity, and ejected rubble played in modifying ancient continental uplands.
- This brief article describes a flow-like surface feature in a farside crater some 70 kilometers south of Tsiolkovsky. Initial analysis of Lunar Orbiter photography indicates that the flow has a thickness of at least 20 meters at a point about 4 kilometers east of G in the superimposed schematic on the photograph. The author rules out the possibilities of it being a mudflow or an air-cushioned landslide because of vacuum conditions. He suggests that it is considerably more like an ashflow tuff.
- A selection of photographs giving complete coverage of the Moon, front and back, and referenced o the surface by index map.
- The Authors conducted infrared studies of the Moon in eclipse on April 13, 1968, and their observations were the first to confirm the thermal anomalies observed by Saari and Shorthill in December 1964. They conclude that because, hundreds of anomalies have remained unchanged in 3.5 years, they are not the result of ephemeral activity on the lunar surface. They detected a linear thermal anomaly at the western edge of More Humorun which unlike prominent crater anomalies, is warmer than its surroundings before sunset. It remains warmer after sunset. Lunar Orbiter IV photography of Mare Humorum, at a ground resolution of 54 meters, shows no unusual surface structures which would support the belief that the anomaly is caused by low-thermal-inertia material. The more probable cause is an internal heat source because 1) beat flow to the surface would make an area warmer than its surroundings during lunar afternoon, and 2) the geological position of the anomaly supports this.
- The scientific objectives, operational guidelines and surface exploration constraints of a five-day mission of the Marius Hills constitute the subject of this report. Lunar Orbiter V photographs of this region have been used in constructing preliminary geological maps and descriptions of the traverses which astronauts could perform in a lunar roving vehicle.
- The author discusses in detail the Lunar Orbiter photographic mission. Among its major tasks the Orbiter spacecraft is designed to obtain useful topographical data of the lunar surface for the Apollo Program. Special methods of photometric data reduction not be applied to Lunar Orbiter photography because of the peculiar characteristics of reflectivity of the lunar surface. Preflight calibrations will be necessary to compensate for any distortions in high-resolution photography due to the Moon's surface characteristics and the fact that the film will not be returned to Earth.
- A selected compilation of photographs that illustrate the heterogeneous nature of the lunar surface, including four stereographic views in color and accompanied by index maps. Many features are similar to features or Earth; others have no Earth counterpart. Also included are photographic guideposts for planning manned exploration of the surface.
- The authors offer a summary of the various theories on the origins of the Moon and its shape and internal composition. They point out that no theory has explained the nature of the Moon's core nor the distribution of the density of subsurface material. They do not suggest the presence of mass concentrations (Mascons) on the Moon.
- The report points out that there is a difference between the Moon's center of figure or volume and the center of its mass. There appears to be a systematic excess of elevation of continental areas over maria, relative to the Moon's center of mass. A comparison of the mascons with the lunar map indicates excess masses are concentrated within the inner rings of the Imbrium and Nectare Basins. If mascons are assumed to be masses, of nickel-iron, then they correspond to a layer about 12 kilometers thick. Isostatic models of the Moon also fit the date, but Lunar Orbiter data does not sufficiently resolve which model.
- Ranger and Mariner software program were found to be in adequate for Lunar Orbiter. Thus the Lunar Orbiter Program developed new concepts for flight control and the necessary software to implement them. Among other things the optimization of the midcourse aim point and the orbit injection point became a necessary and practical procedure. A man element trajectory program was developed to facilitate orbital transfers by greatly reducing computation times to a few minutes rather than hours as was necessary under the special perturbation analysis approach.
- The authors present a defense of the theory of water on the Moon as the major cause of sinuous rilles. Their analysis is based upon data from Lunar Orbiter IV photography and upon Urey's hypothesis of a lunar atmosphere existing at one time in the past. They point out that volcanic ashflows, as suggested by Gold, cannot explain the length and meandering or many rilles. Nor can faulting. However, waterflow under a layer of surface ice offers a viable explanation. Moreover, certain events could. have caused outgassing of major volatiles H20 and CO2. Major meteor impacts would have released trapped volatiles and could have led to a temporary atmosphere. They conclude that the distribution of sinuous rilles is the only available, unambiguous indicator of location of subsurface volatiles.
- Lunar Orbiter photographs show sinuous rilles resembling meandrous channels of terrestrial streams. Thirty of these are visible from Earth. Lunar Orbiter revealed significant new features in the smaller meandrous channels inside the larger rilles. The authors by hypothesize that the rilles are features caused by water erosion in the form of ice-covered rivers whose source is subsurface water released through the impacts of meteors.
- The author describes the achievements of Luna III in 1959 and compares them with those of the Zond III mission in 1965 The latter confirms the data of the former concerning the lunar far side: it is more heavily cratered than the front side. On the whole the craters exhibit similar features to those on the front side. Crater chains also exist on the far side but are much longer, in some cases 1,500 kilometers. Numerous ring-shaped concavities called thalassoids also can be seen in Zond III pictures. In size and shape they com pare to maria. No such thalassoids are present on the front side. Lipskii concludes that available data show the Moon's surface to be continental with maria resulting from endogenic depressions being filled with lava.
- MacDonald discusses the several modern theories concerning the nature and composition of the Moon's interior. He states that even a chemically homogeneous Moon would undergo discontinuities in the structure of subsurface material. Surface features and the lack of evidence of major faulting imply a constant volume of the Moon. Little conclusive evidence exists to prove or disprove current hypotheses. The author suggested a lunar orbiter spacecraft circling the Moon could be tracked and that this would provide data on the Moon's gravitational field its mean moment of inertia, and other fundamental data which would reveal more about the nature of the Earth's natural satellite.
- This report covers the results of orbit determination programs in the first four Orbiter missions. Orbit determination proved to be very accurate and precise with tolerable deviations from planned parameters. Some deviations between planned and executed midcourse, deboost, and orbit maneuvers resulted from oscillation in Doppler residuals, especially in low photographic orbits. Uncertainty of lunar gravitational constraints orbital statistics not entirely valid. One accomplishment of the program was the improvement of orbit determination as a result of predicted photo-location by real-time and postflight orbit determination. On the Lunar Orbiter III mission the difference between the two factors was about 5 kilometers and considerably worse for certain sites in the first two missions.
- The author points out that the Lunar Orbiter Program was by far the most productive of the precursor probes in terms of total amount of information received and the nature of that information in certain areas vital to further exploration. The author discusses several of the most significant topographical features which Lunar Orbiter photographed and concludes that the photographic data greatly help in identifying morphological classes of these features.
- The authors summarize the mission of Lunar Orbiter and concentrate upon its usefulness in the more refined determination of the lunar gravitational field and the Moon's shape and mass. They briefly review the existing knowledge on these subjects and then describe in detail various technical approaches to the problem of determining spacecraft orbital parameters and what they will show about the Moon.
- The authors have drawn preliminary conclusions about the significance of the orbital behavior of Lunar Orbiter I based upon early tracking data. Their primary task was the establishment of a rough estimate about the Moon's gravitational field from more extensive date from the other four Lunar Orbiter missions. Preliminary results of their investigation show that orbital variations during periods of photography did not degrade the quality of photographs. Tracking data used in this analysis were two-way Doppler data providing a measure of relative velocity of the spacecraft and the NASA. Deep Space Network stations in California, Spain, and Australia.
- The investigators have used ranging residuals data from the first two Orbiter missions to test corrections in the lunar ephemeris. Most residuals were reduced to lose than 100 meters. Preliminary ephemeris tapes at the Jet Propulsion Laboratory were used to analyze raw data. Tracking data from the Deep Space Network stations enabled the investigators to refine the mathematical calculations. Variations in ranging residuals from the three stations verify unusual Doppler residuals obtained near pericenter passage of Lunar Orbiter I. These were not attributed to onboard, system anomalies and appeared to be real and to show that the spacecraft had an anomalous motion of 60 meters near pericenter.
- The authors have analyzed the results of Earth-based coherent two-way radio Doppler data from the Lunar Orbiters. They found the residuals consistency to be too high. This could be caused by: 1) forces such as gravity, solar pressure, gas jets; 2) errors in tracking data; and 3) software problems in the computer. They then utilized higher harmonics models of the Moon, and the residuals reduced, reaching agreement between separated flight an the saw trajectory.
- The authors have constructed a gravipotential map of the near side of the Moon based upon orbital accelerations of the Lunar Orbiter spacecraft. These show gravitational anomalies termed "mascons" beneath the lunar surface in all five of the ringed maria. This suggests a correlation between mass anomalies and the ringed maria. Conclusions are tentative.
- A brief description of the Lunar Orbiter Program's history, this report describes the spacecraft, its mission, and what the first Lunar Orbiter accomplished.
- Norman discusses the Apollo requirements for cartographic and topographic data on the lunar surface., the landing sites, and their approaches. Photogrammetry plays a mandatory role in determining accurate coordinates for landing sites and reference marks called landing-site landmarks. Lunar Orbiter photographic data has provided the only applicable source for making large-scale maps of the Apollo landing zone. How this is done constitutes the subject of the article. The author concludes that Lunar Orbiter successfully demonstrated the potential of surveying and mapping the Moon or a planet from space.
- Analyses of Lunar Orbiter I photographs of Oceanus Procellarum showing craters of morphology indicate a correlation between crater size and crater shape as a result of meteorite impact against a surface consisting of fragmental material of varying thicknesses overlying cohesive substrata. The analysis of these data indicate that 85% of the area considered has surface thickness between 5 and 15 meters. Photographs from Luna 9 and Surveyor I support this indication. Moreover, formation of new rock surfaces appears to have occurred intermittently, leading to a complex stratigraphic sequence of alternating hard and fragmented rock. The existence of concentric craters substantiates this sequence.
- The distribution of the 1unar regolith thickness for twelve areas on the Moon has been determined using high-resolution photographs from Lunar Orbiter II, III, and V. All but one area lie within ten degrees of the equator. The exception is in Mare Imbrium. The article compares lunar crater geometry with laboratory craters. Results show that the regolith thickness varied from 3.3 meters in the southern portion of Oceanus Procellarum to 16 meters in the crater Hipparchua. The report also discusses the delineation of flow fronts and the discovery of many linear markings on the presumed flows. These lineaments my be crater chains of a collapsed or drainage origin. Still other lineaments may be lava channels. The authors conclude that the thickness of the regolith is a function of crater density. Over time impacting bodies break down the lunar surface and create the regolith which is the result of impact fragmentation.
- This report describes a system for determining the relative age of craters on the lunar surface by using as a basis their major topographical components. From this the authors have constructed a preliminary morphological continuum which they use to classify craters over the entire surface of the Moon. Lunar Orbiter photography was instrumental in providing them with reliable data.
- The photometric method for deriving surface elevations from a single picture of the lunar surface in the absence of stereoscopic pictures is described. The author uses ganger photographs as subjects and concludes that a derivation of quantitative topographic information about an object scene is possible. At best the resulting data are indirect. and estimation of errors seems unrealistic by-analytical. means. Moreover, calculations show that it is wrong to assume uniform albedo, for large areas.
- Photography from Lunar Orbiter III, a topographic map of the, Surveyor III landing site, and photographs from Ranger VIII, and IX are utilized in applications of the power spectral density (PSD) function to determine relative roughness of different types of lunar terrain. Such information would be valuable in the construction and operation of a lunar roving vehicle.
- Scherer describes the Lunar Orbiter spacecraft as a platform designed to carry a camera system which can take high- and medium-resolution photographs of the Moon's surface. The spacecraft has four objectives: 1) obtain photography of wide areas of the Moon to certify Apollo and Surveyor landing sites, 2) define gravitational field of the Moon through refined tracking of the spacecraft, 3) measure micrometeoroid and radiation flux during extended lifetime of spacecraft, and 4) provide a spacecraft for equipment checkout and personnel training of the Apollo tracking network.
- The author bases his interpretation on studies of impacts of steel projectiles into concrete and soils and then makes large extrapolations upward in size. On the Moon an impacting body must penetrate below the surface to a depth of 290 kilometers before pressure can be released sufficient to melt material. His results suggest that lava-filled maria formed when large iron objects struck the lunar surface at a velocity so low that there was no immediate fracture of the object. The impact produced a large crater and material flowed to the surface to fill the crater. Each mare was formed by one large iron object impacting, and the remnants of this dense object under the mare are the mascon.
- Swann describes how investigation of the Moon's surface can test the hypotheses based upon terrestrial observations of the geological history of the Earth in an effort to determine the origins of both bodies. The Apollo system constitutes the basic capability with which such extended lunar exploration can be carried out.
- The first three Lunar Orbiter spacecraft photographed 8% (600,000 square kilometers) of the near side of the Moon. High-resolution photographs show that the surface is dotted with a great number of small, perfectly circular craters from 50 meters diameter down to the limit of resolution. The majority of these are cup-shaped with distinctly sharp rims. But many also have shallow interiors and indistinct rims. The authors conclude that these craters were formed by primary and secondary impacts. Fresh craters my those which have material on the exterior slopes which is distinctly different from adjacent material of the inter-crater areas. These young craters also tend to have a profusion of angular blocks on the floors and exterior slopes. The albedo of these blocks and other ejecta material is relatively high. The number of fresh craters is much lose than the number of craters not exhibiting these features.
- Lunar Orbiter I bounced continuous-wave signals off of the Moon's surface, and these were received on Earth. Using the frequency spectrum and studying Doppler shifts, the investigators located discrete, heterogeneous scattering centers on the lunar surface. Shadowing, especially within five degrees of the terminator would effectively "hide" some scattering centers. On the other hand variations in surface reflectivity provide a model which will explain the observations. This could mean that material in scattering areas is considerably more compact or different from material, in surrounding areas. The use of continuous-wave bistatic radar appears to offer a new, method for mapping and study of lunar and planetary surfaces.
- This two-part report discusses saw of the problems inherent in an extended lunar surface mission in the Orientale region and the scientific points of interest which such a mission might best help to explore. Lunar Orbiter photography played a significant role in the preparation of this report. The authors discuss various arguments about the origins of Orientale and the geological features which would be most significant in a surface investigation.
- The Moon as a viscosity higher than that of Earth by a factor of 104. Mascons represent a non-isostatic condition in the surface of the Moon. Apparently an object collided with the Moon's surface flattened out and left high-density material that has remained since the maria were formed. Lava flows cannot account for what in observed on the Moon. Maria areas on the Moon are not lava flows, and no liquid masses exist below the Moon. Thus large objects collided with the Moon in its early history. These objects should be similar to meteorites in composition and density. Finally, the Moon has sufficient rigidity to support these masses.
- Urey summarizes several arguments against the presence of water on the Moon, and then he presents his own detailed argument, based upon his knowledge and new data from Lunar Orbiter photographs, in support of the presence of water on the Moon. The existence of rilles and of such landmarks as Schroter's Valley, the irregularities of the crater Krieger north of Aristarchus, and the knowledge of terrestrial geological processes causing pingos in areas of permafrost strongly support the theory that water has existed on the Moon and has caused various lunar surface formations. Urey defends the view that water, not lava or dust-gas mixtures, formed the maria and that these may yet be frozen seas. However, he concludes that this in no way defines the composition of the solid materials in the maria.
- This report, done under contract to NASA, explains the usefulness of stereoscopic photography transmitted to Earth by Lunar Orbiters II, III, and V in mapping the Moon. High-resolution stereo photographs include coverage otherwise unobtainable from a vertical mode. Moreover, the exaggerated height effects in convergent stereo photography should increase the accuracy in the determination of ground point elevations. The report discusses the problems of using existing computer programs and available photographic data for convergent photo triangulation. It also outlines the best methods for accomplishing triangulation. Tests with Lunar Orbiter data proved that accuracy of triangulation is increased by using high-resolution stereo photographs.
