Venus Strategy for Exploration (1970) / Chapter Skim
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5 PLANETOLOGY
5 PLANETOLOGY
Pages 50-65
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From page 50... ...
Ideally, these would include such things as the chemical composition and mineralogy of the surface'materials, the heat flux coming from the interior, the presence or absence of an iron core, and the variation of elastic-wave velocity with depth and density. The difficulties of making many of these necessary measurements under the conditions prevailing on Venus are severe; nevertheless, a program of measurements on the scale proposed for the Planetary Explorers will permit some highly significant measurements to be made.
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From page 51... ...
These include passive and a<;:tiveseismic measurements and measurements of elemental composition using natural and induced gamma radiation. These are suggested for one or more lander missions following the early probe missions which should, in addition to their intrinsic importance, serve to define the problems of making scientific measurements in the deep atmosphere of Venus.
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From page 52... ...
However, it does se.em likely that a device based on the much more penetrating nuclear gamma radiation could provide the data desired. A simple sodium iodide gamma-ray spectrome ter placed on the surface would permit measurement of thena tural radioactivity of potassium, uranium, and thorium.
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From page 53... ...
It seems possible that the weight of the entire instrument, including these materials, could be held down to approximately 15 lb, although a much more detailed design study would be necessary to determine a reliable value for the weight. Inclusion of the neutron source would probably preclude the simultaneous measurement of U and Th, because of inter ferences of the induced gamma radiation with the natural radia tion, although measurement of K might still.
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From page 54... ...
The question of whether this surface analysis could be carried on the same lander as a seismic experiment must await a more detailed design study. It does not seem out of the question that this may be possible, provided that the weight of explosive used for an active seismic experiment is appro priately limited.
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From page 55... ...
An active source -- from a bomb probe -- is necessary to provide any sensing of the interior, if the seismicity is too low. In any event, such a controlled source would be highly desirable as a means of calibrating the signals from natural sources.
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From page 56... ...
In particular, we foresee that, in the best of circumstances, future passive systems should have surface lifetimes of several months. Referring to Table 1, we emphasize our feeling that a fair strategy requires the seismic program to be given reduced priority if unfavorable conditions are found.
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From page 57... ...
RADAR AND THERMAL MAPPING OF THE SURFACE OF VENUS Radar experiments are capable of precise measurements of range and velocity between an orbiting vehicle and a remote, passive planetary surface. Determination is also possible of surface scattering from which bulk electrical properties, surface structures at wavelength and larger size, and mean surface slopes may be inferred.
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From page 58... ...
Perhaps a dozen permanent scattering anomalies have been shown to exist, although the precise nature of these anomalies has not been established. That they arise from lo cal variations in surface roughness at a scale of the observing wavelength is clear, but whether they represent young moun tainous regions, flows of lava, large meteoritic impact cra ters, dune fields, or simply debris is not known.
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From page 59... ...
Bistatic Radar Measurements from an Orbiter Bistatic radar measurements provide a direct measurement of large-scale surface slopes and the bulk electrical properties.
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From page 60... ...
observations strictly constrain the range of possible surface models. Planetologi cally, such observations provide unique data on both large- and small-scale surface structures and bulk electrical properties.
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From page 61... ...
Radiometric measurements do not give actual surface temperatures unless the emissivity is known. This quantity can be inferred from the radar measurements, which therefore give valuable support to the radiometer.
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From page 62... ...
In addition, local perturbations in orbiter ac celeration may be determined directly from residuals in the Doppler tracking data. From this method comes a series of profiles of local variations in gravity.
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From page 63... ...
3. The local variations in gravity as determined by acceleration residuals in the tracking may be modeled in terms of near-surface masses and are of intrinsic interest along with other planetological imaging.
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From page 64... ...
Thus the very low rotation rate of Venus may be un favorable to dynamo action, but any quantitative statement is lacking. The discovery at Venus of a small magnetic field of internal dynamo origin would, therefore, be of fundamental interest, both from the viewpoint of its physical constitution and also for the theory of planetary magnetic fields.
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From page 65... ...
Magnetometers should also be given very serious consideration for the balloon missions because these will give both the simultaneous ~easurements at widely spaced positions and the observations of temporal variations needed to determine the conductivities of the ionosphere and surface layers as well as the extent to which the anemopause (ionopause) and ionosphere screen out the effects of changes in the interplanetary magnetic field and in solar-wind pressure.
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