Scarab is a prototype rover for Lunar missions to survey resources in polar craters. It is designed as a prospector that would use a deep coring drill and apply soil analysis instruments to measure the abundance of elements of hydrogen and oxygen and other volatiles including water. Scarab's chassis can adjust the wheelbase and height to stabilize its drill in contact with the ground and can also adjust posture to better ascend and descend steep slopes. This enables unique control of posture when moving and introduces new planning issues. Scarab has undergone field testing at Lunar-analog sites in Washington and Hawaii in an effort to quantify and validate its mobility and navigation capabilities. We report on results of the experiments in slope ascent and descent and in autonomous kilometer-distance navigation in darkness. Keywords Space and planetary robotics, rough-terrain mobility, autonomous navigation, Hawaii field experiment 2. Rover Configuration Scarab was conceived as a work machine with a serialized mission: drive, charge batteries, drill, charge again, analyze soil samples, charge and repeat. The number of repetitions might be 25, leading to 25 kilometers of traverse, 25 cores,

Curiosity landed on plains to the north of Mount Sharp in August 2012. By June 2016 the rover had traversed 12.9 km to the southwest, encountering extensive strata that were deposited in a fluvial-deltaic-lacustrine system. Initial drives across sharp sandstone outcrops initiated an unacceptably high rate of punctures and cracks in the thin aluminum wheel skin structures. Initial damage was found to be related to the drive control mode of the six wheel drive actuators and the kinematics of the rocker-bogie suspension. Wheels leading a suspension pivot were forced onto sharp, immobile surfaces by the other wheels as they maintained their commanded angular velocities. Wheel damage mechanisms such as geometry-induced stress concentration cracking and low-cycle fatigue were then exacerbated. A geomorphic map was generated to assist in planning traverses that would minimize further wheel damage. A steady increase in punctures and cracks between landing and June 2016 was due in part because of drives across the sharp sandstone outcrops that could not be avoided. Wheel lifetime estimates show that with careful path planning the wheels will be operational for an additional ten kilometers or more, allowing the rover to reach key strata exposed on the slopes of Mount Sharp.

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This work presents an experimental method for visualizing and analyzing machine‐soil interactions, namely the soil optical flow technique (SOFT). SOFT uses optical flow and clustering techniques to process images of soil interacting with a wheel or tool from photos taken through a glass wall of a soil bin. It produces results that are far richer than past approaches that utilized long‐exposure photography. It achieves a performance comparable to particle image velocimetry or particle tracking velocimetry, but without the need for specialized measurement equipment or specially marked soil particles. The processing technique demonstrates robustness to different soil types. Ground‐truth and cross‐validation experiments exhibit subpixel accuracy in estimating soil motions. An example of an application of this technique for field robotics research is the detailed study of push‐rolling for slope climbing and soft soil traverse. Push‐rolling advances a vehicle by rolling a subset of its wheels while changing its wheelbase to keep the other wheels static and pushing against the ground. Experiments show that push‐rolling achieves higher net traction than conventional rolling. Observing the two aspects of push‐rolling (rolling and horizontal pushing) using SOFT shows that they result in entirely different forms of soil shearing (“grip failure” and “ground failure,” respectively). SOFT also demonstrates how the direction of soil motion is more efficiently utilized for horizontal thrust by pushing than conventional rolling. Ongoing work utilizing SOFT has also demonstrated its potential use in studying excavation tool interactions, the effects of grousers on wheel efficiency, as well as a variety of other wheel‐soil interactions.

Alpha spectrometry is a commonly used technique for the measurement of uranium isotopes in environmental samples because it is widely available at a relatively low cost. For natural uranium the (234)U to (238)U activity ratio should be 1 and the (238)U to (235)U activity ratio should be 21.7. However, a lower (238)U to (235)U ratio is usually observed in alpha spectrometric analysis of environmental soil samples. This observation has led to the conclusion that soils from nuclear weapons facilities were contaminated with highly enriched uranium. This study was undertaken to test the reliability of using activity ratios from alpha spectrometry to infer the presence of highly enriched uranium in soil samples. The results of these experiments indicate that the (238)U to (235)U activity ratio is not a reliable indicator, but that the (234)U to (238)U activity ratio can be used to qualitatively indicate the presence of highly enriched uranium at concentrations near 10 ng g(-1) and above.