Penetration forces for subsurface regolith probes.

摘要

Investigating planetary bodies using penetrometers can provide detailed information about its history and evolution. An estimation of subsurface density and porosity can be made from the shape of the penetration curve. Using penetrometers mounted on planetary platforms could be challenging due to the uncertainty of the subsurface composition and since the maximum allowed force for penetration is the weight of the lander or rover on the surface. Estimation of penetration forces can provide a reliable constraint on the maximum reachable depth without endangering the whole mission. Therefore, knowledge of the required penetration force to specific depths can be helpful in designing the length and shape of the probe. Test probes covering the anticipated diameter (2.5, 1.9, 1.2 and 0.9 cm diameter) and tip angle (30°, 60°, 90°and 120°) were inserted mechanically into regolith analogs. The results showed that tip angle does not have a major effect, while probe diameter and density of the regolith are the most important parameters. Increasing probe diameter from 0.9 to 1.9 cm (i.e. a factor of 2) leads to an increase in penetration force from 200 to 1000 N (i.e. a factor of 5) at 20 cm depth. An increase in bulk density from 1550 to 1700 kg/m3 leads to an increase in penetration force from 10 to 200 N at 20 cm depth. Square probes required less force than circular ones which can allow for easier design of lateral windows.