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The familiarization course for the Apollo 17 ALSEP (ARRAY E) is presented. The subjects discussed are: (1) power and data subsystems, (2) lunar surface gravimeter, (3) lunar mass spectrometer, (4) lunar seismic profiling experiment, and (5) heat flow experiment.
Particular attention is given to aspects pertinent to teleoperation, remote control, onboard control, and man-machine relationships in carrying out scientific operations with such a vehicle. It is assumed that landed operations would comprise one Martian year and that the traverse would extend across an area approximately 500 km wide. The mission is assumed to be planned for the early 1980s. Its objective is to obtain data which will aid in answering a number of questions regarding the history of the solar system, the formation of Mars, and the evolution of life on Mars. A series of candidate rover payloads is proposed to meet the requirements. The smallest payload includes a TV camera, a general-purpose manipulator arm, a crusher and siever, an X-ray diffractometer-spectrometer, a gravimeter, a magnetometer, meteorological instruments, and a radio transponder.
The accomplishments of the Apollo 17 flight are summarized. The basic objective of the mission was to sample basin-rim highland material and adjacent mare material and to investigate the geological evolutionary relationship between these two major units. The lunar experiments which were conducted include: (1) lunar field geology, (2) surface electrical experiments, (3) lunar traverse gravimeter experiments, (4) lunar seismic profiling experiment, (5) lunar ejecta and meteorites experiment, (6) analysis of lunar atmosphere composition, and (7) heat flow experiments.
The major scientific contributions of Goddard Space Flight Center to the National Geodetic Satellite Program between 1965 and 1973 are presented and discussed. The primary results described are the determination of the earth's gravitational field from satellite tracking and surface gravimeter data to an accuracy of about 4 mGal for wavelengths of about 1000 km and larger; the construction of a detailed geoid suitable for geodetic, tectonic, and altimetry data analysis accurate to about 2 m over continents and to 2-5 m over the northeast Pacific and Atlantic oceans; and the positioning of globally distributed tracking stations to an accuracy of 5-10 m for the interconnecting of local geodetic datums. In addition, work on the observation of the earth and ocean tidal perturbations of satellites is discussed and reviewed.
Some gravitation theories, in contradiction to general relativity, allow the existence of a universal preferred reference frame. Also allowed in some theories can be a galaxy-induced anisotropy of the gravitation constant. The parametrized post-Newtonian theory predicts that in these cases, there will be anomalous earth-tide amplitudes at specific frequencies. An 18-month earth-tide record obtained with the superconducting gravimeter has been examined for such anomalies. The data allow for the existence of such effects but cannot prove it because of uncertainties concerning geophysical perturbations of the tides. However, an upper limit to the preferred frame parameter of the parametrized post-Newtonian formalism is established at 0.002. The results also set a less rigorous limit on the anisotropy parameter, of the order of 0.001.
The anisotropic generalization of the parameterized post-Newtonian (PPN) gravitational metric field is made for the case of theories with energy and momentum conservation laws. Such an anisotropic metric field will generally result in two-tensor or bimetric theories of gravity in an anisotropic universe. New anisotropic 3 x 3 spatial PPN matrices are introduced into the general metric expansion. Earth gravimeter measurements strongly restrict some anisotropies, while anisotropic inertial and gravitational mass for celestial bodies result from other combinations of the PPN matrices.
A seismic model of the moon, refined from previous models with the aid of new data and analyses for seismic events recorded by four Apollo lunar seismic stations and a gravimeter, is outlined. The current model has five zones. The crust is 55-60 km thick. The surface is covered by regolith of varying thicknesses and low seismic velocity. The seismic Q's are extremely high. The upper mantle, 250 km thick, is characterized by seismic velocities close to those of the earth's upper mantle, and shear wave Q of about 4000. Tidally controlled deep moonquakes are concentrated near the boundary of the middle mantle, 600-700 km thick. A lower mantle extending to an undetermined depth is characterized by high attenuation of shear waves. The existence of a low-velocity core is only tentatively proposed.
Two Apollo Soyuz experiments designed to detect gravity anomalies from spacecraft motion are described. The geodynamics experiment (MA-128) measured large-scale gravity anomalies by detecting small accelerations of Apollo in the 222 km orbit, using Doppler tracking from the ATS-6 satellite. Experiment MA-089 measured 300 km anomalies on the earth's surface by detecting minute changes in the separation between Apollo and the docking module. Topics discussed in relation to these experiments include the Doppler effect, gravimeters, and the discovery of mascons on the moon.
Results of gravity observations made in Canada from 1974 to 1978 reviewed, in order to estimate the true accuracy of present-day gravimetry and thereby assess the potential capability of the method for detecting crustal movements. The standard error of the mean of ties is 15-20 nm/s squared. Inter-instrument comparisons and other tests show, however, that a more realistic estimate of D meter accuracy is 30-40 nm/s squared. This accuracy can only be maintained over the long term where uncertainties in gravimeter calibration curves are minimized by resetting to the same dial reading on the resurveys. A further deterioration in accuracy to 40-50 nm/s squared occurs where reliance is placed on presently available D meter calibration curves. Despite the present accuracy limitations significant time variations in gravity of 100-150 nm/s squared are seen over spatial scales of 10-100 kilometers in Canada over a period of several months.
The technique of measuring gravity at sea was greatly improved by the development of spring-type surface-ship gravimeters which can be operated in a wide variety of sea conditions. A brief review of the most recent developments in marine gravity is presented. The extent of marine gravity data coverage is illustrated in a compilation map of the world's free-air gravity anomaly maps of the world's oceans. A brief discussion of some of the main results in the interpretation of marine gravity is given. Some comments made on recent determinations of the gravity field in oceanic regions using satellite radar altimeters are also presented.
Diurnal and long period earth tides were measured to high accuracy and precision with the superconducting gravimeter. The results provide new evidence on the geophysical questions which have been attacked through earth tide measurements in the past. In addition, they raise new questions of potential interest. Slow fluctuations in gravity of order 10 micron gal over periods of 3 to 5 months were observed and are discussed.
Superconducting instruments for gravitational studies and their state of development are discussed. Consideration is given to accelerometers, gravimeters, superconducting gyroscopes, and inertial guidance and navigation systems. This is followed by discussion of applications to tests of gravitational theories, determination of elastic properties of planets, and navigation.
Seismological objectives and equipment used in the passive seismic, active seismic, lunar seismic profiling, and the lunar gravimeter experiments conducted during Apollo 11, 12, 14, 15, 16, and 17 missions are described. The various formats in which the data form these investigations can be obtained are listed an an index showing the NSSDC identification number is provided. Tables show manned lunar landing missions, lunar seismic network statistics, lunar impact coordinate statistics, detonation masses and times of EP's, the ALSEP (Apollo 14) operational history; compressed scale playout tape availability, LSPE coverage for one lunation, and experimenter interpreted events types.
Research on the seismotectonics of plate boundaries is summarized. Instrumental development and an observational program designed to study various aspects of the seismotectonics of southern California and the northern Gulf of California are described. A unique superconducting gravimeter was further developed and supported under this program for deployment and operation at several sites. Work on Earth tides is also discussed.
Records from seven superconducting gravimeters operated at five different locations in California and one in Boulder, CO, are examined after removal of tides and the gravitational attraction of the atmosphere. Fluctuations over periods between a few days and several months were observed at all sites with peak amplitudes of order 10 microgal. By contrast, a 640-day record obtained with one of the instruments in Germany showed peak fluctuations of only 2 microgal. In most of the records the causes of these aperiodic variations were not determined so that they serve to set limits on the vertical motion or displacement of mass at the respective locations. However, at The Geysers geothermal field, much of the gravity variation is correlated with seismic activity, reinjection rate, and rainfall. Measurements of this type were not possible prior to the development of the superconducting device. Consequently, these results provide the first evidence for the existence of gravity variations on the time scale and of the magnitude described here. Vertical crustal motion, motion related to seismic events, and hydrological phenomena can lead to variations on this scale. Unambiguous identification of causal relationships will require either special circumstances such as found at The Geysers or operation of the instruments in pairs.
A balloon-borne experiment, flown at 30 km altitude over New Mexico, was used to test dynamic differential Global Positioning System (GPS) tracking in support of gravimetry at high-altitudes. The experiment package contained a gravimeter (Vibrating String Accelerometer), a full complement of inertial instruments, a TI-4100 GPS receiver and a radar transponder. The flight was supported by two GPS receivers on the ground near the flight path. From the 8 hour flight, about a forty minute period was selected for analysis. Differential GPS phase measurements were used to estimate changes in position over the sample time interval, or average velocity. In addition to average velocity, differential positions and numerical averages of acceleration were obtained in three components. Gravitational acceleration was estimated by correcting for accelerations due to translational motion, ignoring all rotational effects.
Growing interest in high precision studies of the Earth's gravitational field warrant a critical review of precision requirements to yield useful results. Several problems are now under consideration. All of these problems involve, more or less, the precise value of the vertical gradients of gravity. The principle conclusion from this review is that the essential absence of Free Air Vertical Gravity Gradient control and actual values of gravimeter calibrations require serious attention. Large errors in high topography on official published gravity maps also cannot be ignored.
Results of previous JPL developments are summarized and the current work related to lunar roving missions is discussed. Objectives of a long lunar transverse are reviewed and include lunar resource prospecting and base site surveys. Rover design criteria are presented, noting that payload instrumentation would include both television cameras for driving and cameras producing panoramic facsimile for high-fidelity scientific imaging and landmark navigation, as well as a multipurpose imaging system with multispectral, close-up, and microscopic capabilities. Instrumentation providing for chemical and mineral analysis, a gravimeter, and a magnetometer are also important. Rover performance requirements include a capability to support a 50 kg payload mass with a rover mass of 500 to 600 kg, powering and supporting the payload, managing the on-board resources available to each instrument, and handling all of the mission data. Desert tests of lunar roving navigation and field geology are discussed.