Experimental evaluation of cone index gradient as a metric for the prediction of wheel performance in reduced gravity

摘要

Traversing granular regolith in reduced gravity remains a challenge for wheeled rovers. Earth-based testing cannot fully predict rover mobility as it precludes gravity's effects on the soil. The simulant GRC-1 was designed to account for this by matching cone penetrometer readings from Apollo; the assumption is that replicating the cone penetrometer response of lunar soil will also replicate its response to vehicle loading. Cone penetrations were performed in GRC-1 at three densities in 1-g and 1/6-g aboard parabolic flights producing effective lunar-g. A fourfold decrease in cone index gradient (G) was seen in 1/6-g, indicating significantly reduced shear strength. Wheel experiments in GRC-1 in 1/6-g at one density and two slip values were compared to 1-g experiments at a lower density producing the same G value. In 1-g, drawbar pull was 44% higher and sinkage was 13.5% lower, indicating that the assumption made during the creation of GRC-1 was not quite correct, and that caution should be exercised when interpreting results obtained with this simulant. At the loosest possible density in 1-g, drawbar pull was still 24% higher than in lunar-g; sinkage was 76% higher. Future experiments utilizing a stronger simulant in lunar-g are outlined to elaborate upon these findings. (c) 2021 ISTVS. Published by Elsevier Ltd. All rights reserved.