Colin Creager

Robotic Lunar Geotechnical Tool

Rover-mounted geotechnical systems are of paramount importance to lunar trafficability assessment, construction, and excavation/mining toward establishing permanent human presence on the Moon. These tools can also be used to determine density, when the regolith is used as radiation shield, for example. Two popular insitu devices for establishing geotechnical properties of soil are the Static Cone Penetrometer (SCP) and Dynamic Cone Penetrometer (DCP). However, both systems have shortcomings that may prevent them from being robotically-deployed in a low gravity environment. In this paper we describe an alternative system, called the Percussive Dynamic Cone Penetrometer (PDCP) that can be used to roboticallymeasure geotechnical soil properties in a low gravity environment. It is shown that PDCP data correlates well with the data obtained from both SCP and DCP testing, and by extension with California Bearing Ratio (CBR) and soil bearing strength. ACRONYMS

Inching locomotion for planetary rover mobility

New articulated planetary rovers offer alternative locomotion modalities beyond conventional rolling wheel mobility.12 These new modalities should be explored to overcome the limitations of traditional rolling mobility, and expand the areas of planetary surfaces amenable to exploration. The topic of this study is a hybrid push-roll locomotion mode called inching. Static (non-rolling) wheels are used in conjunction with the rolling wheels of a vehicle in order to increase net traction potential. Preliminary experiments have shown an approximate doubling in drawbar pull for the inching locomotion mode relative to pure rolling. This improvement is not accounted for by reductions to wheel motion resistance alone, and furthermore evidence is provided that static wheels are capable of reacting more ground thrust than rolling wheels. Further investigations using a transparent soil tank, and novel image processing techniques, reveal key differences in the soil shear failure interface under rolling and static wheels. For the cases studied, static wheels generated much deeper and more unified soil failure masses than rolling wheels. Further investigation is recommended to clarify the physics of these thrust development processes, and ultimately to populate the vehicle design space for inching locomotion.

Novel Experimental Technique for Visualizing and Analyzing Robot- Soil Interactions

A novel experimentation and analysis technique has been developed to enable detailed investigation of robot interactions with granular regolith. This technique, the Shear Interface Imaging Analysis Tool, provides visualization and analysis capability of soil shearing and flow as it is influenced by a wheel or excavation tool. The method places an implement (wheel, excavation bucket, etc.) in granular soil up against a transparent sidewall. During controlled motion of the implement, images are taken of the sub-surface soil, and are processed with optical flow software. Analysis of the resulting displacement field identifies clusters of soil motion and shear interfaces. The Shear Interface Imaging Analysis Tool enables analysis of robot-soil interactions in richer detail than possible before. Prior art relied on long-exposure images that provided only qualitative insight, while the new processing technique identifies sub-millimeter gradations in motion and can do so even for high frequency changes in motion (several Hz). Results are presented for various wheel types and locomotion modes: small/large diameter, rigid/compliant, with/without grousers, and rolling/inching. Results are also presented for an excavation bucket horizontally cutting granular soil.

Benefit of Push-Pull Locomotion for Planetary Rover Mobility

As NASAs exploration missions on planetary terrains become more aggressive, a focus on alternative modes of locomotion for rovers is necessary. In addition to climbing steep slopes, the terrain in these extreme environments is often unknown and can be extremely hard to traverse, increasing the likelihood of a vehicle or robot becoming damaged or immobilized. The conventional driving mode in which all wheels are either driven or free-rolling is very efficient on flat hard ground, but does not always provide enough traction to propel the vehicle through soft or steep terrain. This paper presents an alternative mode of travel and investigates the fundamental differences between these locomotion modes. The methods of push-pull locomotion discussed can be used with articulated wheeled vehicles and are identified as walking or inching/inch-worming. In both cases, the braked non-rolling wheels provide increased thrust. An in-depth study of how soil reacts under a rolling wheel vs. a braked wheel was performed by visually observing the motion of particles beneath the surface. This novel technique consists of driving or dragging a wheel in a soil bin against a transparent wall while high resolution, high-rate photographs are taken. Optical flow software was then used to determine shearing patterns in the soil. Different failure modes were observed for the rolling and braked wheel cases. A quantitative comparison of inching vs. conventional driving was also performed on a full-scale vehicle through a series of drawbar pull tests in the Lunar terrain strength simulant, GRC-1. The effect of tire stiffness was also compared; typically compliant tires provide better traction when driving in soft soil, however its been observed that rigid wheels may provide better thrust when non-rolling. Initial tests indicate up to a possible 40% increase in pull force capability at high slip when inching vs. rolling.

A Comparison Between the NORCAT Rover Test Results and the ISRU Excavation System Model Predictions Results

An Excavation System Model has been written to simulate the collection and transportation of regolith on the moon. The calculations in this model include an estimation of the forces on the digging tool as a result of excavation into the regolith. Verification testing has been performed and the forces recorded from this testing were compared to the calculated theoretical data. The Northern Centre for Advanced Technology Inc. rovers were tested at the NASA Glenn Research Center Simulated Lunar Operations facility. This testing was in support of the In-Situ Resource Utilization program Innovative Partnership Program. Testing occurred in soils developed at the Glenn Research Center which are a mixture of different types of sands and whose soil properties have been well characterized. This testing is part of an ongoing correlation of actual field test data to the blade forces calculated by the Excavation System Model. The results from this series of tests compared reasonably with the predicted values from the code.