Mathematics – Logic
Scientific paper
Sep 1972
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1972moon....4..307t&link_type=abstract
The Moon, Volume 4, Issue 3-4, pp. 307-307
Mathematics
Logic
Scientific paper
Purpose: The purpose of the Traverse Gravity Experiment is to measure the value of lunar gravity (relative to the value at the landing site) at selected points along the lunar surface traverse. A secondary purpose is to make an Earth-Moon gravity tie. Instrumental Accuracy and Elevation Corrections: The traverse gravimeter is capable of making measurements to an accuracy of about ±0.6 mgals. The free air correction on the Moon is about 0.2 mgals/m. The uncertainty of elevation accuracies at the gravity stations is expected to be between ±2 m and ±10 m with the smaller number considered more likely. Consequently, the error in the free air anomaly will lie between about ±0.6 mgals and ±2.1 mgals. Lateral Inhomogeneities Resolvable by the Traverse Gravimeter: The gravity difference associated with a layer 500 m thick, of density contrast 0.2 g per cubic centimeter, is 4mgals. Gravity stations 500 m apart will not resolve gravity signals with wavelengths under 1 k. Hence, the traverse gravimeter will only resolve density differences which extend at least a few hundred meters in vertical extent and have wavelengths of at leastl k. At the other extreme the gravimeter can record the effect of very deep and very large masses provided the gravity effect of these masses is at least a few milligals across the traverse. Usefulness of the Traverse Gravity Experiment: The gravity measurement will indicate the presence of lateral inhomogeneities at the kilometer or larger scale. In a general way, they will discriminate between the case where the subsurface contains a jumbled mass of rocks and different densities and the case where the subsurface layers have very small lateral inhomogeneities and, therefore, yield clues regarding the origin of the lunar surface. In a particular way, the lunar traverse gravity measurement will be able to establish the downward extension of rock outcrops on surface - central peaks in craters being an example of such outcrops. In this sense, the traverse gravity measurement provides a very useful extrapolation of surface geological observations. Time Required for Measurements: At the beginning and end of each traverse, the gravimeter will be removed from the LRV and a ‘normal’ and a ‘bias’ measurement taken with the gravimeter on the lunar surface. Each measurement takes about 2.5 min. During an LRV stop, it is necessary merely to start a ‘normal’ measurement by depressing a pushbutton. The gravity measurement still takes 2.5 min but the presence of the astronaut near the gravimeter is not required. After the measurement is taken, the value is stored in the logic circuitry; the astronaut can obtain the value at any later time by depressing a ‘read’ pushbutton. The gravity value is displayed and is read out by the astronaut. Number of Required Measurements: The number and location of gravity stations is site dependent, and cannot be firmly formulated until the landing site is chosen. As a guideline, one gravity measurement at every science stop would be extremely desirable.
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