Experimental evaluation of cone index gradient as a metric for the prediction of wheel performance in reduced gravity. (February 2022)

• Record Type: Journal Article
• Authors: Daca, Adriana; Tremblay, Dominique; Skonieczny, Krzysztof
• Is Part Of: Journal of terramechanics. Volume 99(2022)
• Page Start: 1
• Page End: 16
• Publication Date: 2022-02
• Subjects: planetary rovers -- reduced gravity -- cone index gradient -- wheel-soil interactions -- parabolic flights -- GRC-1 -- soil simulants -- mobility; Trafficability -- Periodicals; Praticabilité (Routes) -- Périodiques; Trafficability; Periodicals; 629.222
• DOI: 10.1016/j.jterra.2021.09.003
• Languages: English
• ISSNs: 0022-4898

Abstract

Highlights: Cone penetrations were performed in GRC-1 in 1-g & 1/6-g (in parabolic flights). Cone index gradients (G) were 4× lower in 1/6-g, indicating reduced shear strength. Wheel tests were done in GRC-1 in 1-g & 1/6-g at densities producing equal G values. 1-g tests over-predict mobility with 44% higher drawbar pull and 14% lower sinkage. Caution should be exercised when using 1-g tests in GRC-1 to predict lunar mobility. Abstract: 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.