NASA is planning a series of small-payload Venus missions, with launches beginning in 1976, some of which may be suited to small active and passive seismic experiments. Because the Earth and Venus are nearly the same size, one may theorize many parallels in seismic and tectonic activity, and any differences will provide information about the development of the Earth, as well as of Venus. A combined passive and active experiment with two separated short-period, three-component seismometers and one explosive charge may be carried as 3 entry vehicles on one spacecraft. The weight of explosive, however, is limited to about 20 kg. This limits the charge-seismometer separation to 1 or 2 km. Acoustic and radio ranging devices measure the positions of the 3 probes on the surface. Seismic velocities would be obtained for any layering down to about 500-m depth. A velocity transducer peaked at 20 Hz is desired for the active experiment, and would give some indication of the presence of microquakes on Venus, although a 1-sec period would be better for a passive experiment. An average science data rate of 30 bps would be adequate if the record from the active experiment is recorded for slower playback. A lifetime of 24 hr appears feasible. A dual launch of identical payloads landed in widely-separated areas would give a vastly greater return for the passive experiment. Although not unambiguous, the data should provide some information on seismic velocities, density, and anelasticity. Science and engineering data returned would determine desirability and feasibility of subsequent long-lived passive experiments with long-period, high-temperature instruments.

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