Dynamic Anchoring in Soft Regolith for Celestial Exploration
Recent exploration missions to celestial bodies have shown an increasing demand for surface based landers and rovers designed to perform experiments on the ground, rather than relying purely on traditional orbiting observatories. Many of the scientifically interesting locations have proven hazardous and difficult to reach and traverse, driving the need for different methods of locomotion. Some of these locations lie in deep, permanently shadowed craters or in rocky, highly uneven landscapes. Various wheeled, flying, jumping and legged rovers have been proposed, some of which have been implemented with success and problems alike. Even though the Curiosity rover has the largest wheels of any unmanned rover ever sent to another celestial body, it still has very limited slopes it can ascend and must avoid soft soil conditions. The Philae lander that attempted to perform a controlled descent onto a comet surface bounced multiple times due to the ineffectiveness of its two on-board anchoring mechanisms. The presented work focuses on a category of legged rovers intended to climb up steep slopes covered in soft soil or regolith, such as those found on crater walls on the moon and Mars. The envisioned rover would utilized dynamic anchors on the feet of its legs to claw into the surface, engaging and disengaging with each step. Physical testing is performed by using a robotic arm to engage a series of anchors with a lunar regolith simulant, while measuring the associated anchoring forces. In total, 20 anchor configurations are tested and evaluated to determine the geometries with the most beneficial characteristics for dynamic anchoring. Additionally, two methods for predicting the anchoring forces are presented and compared to the physical test data. One method uses the Discrete Element Method to model and simulated the actual anchor and regolith interactions. The other methods is a mathematical regression to curve fit the physical data for interpolation between the tested anchors. Both methods show reasonable accuracy in the predicted forces, and with peak forces predicted well within an order of magnitude. Several anchor geometries show sufficient holding forces for use on future legged exploration rovers. A case study is performed using the test data that shows the slope ascend capability of an assumed rover on the surface of the moon to evaluate the physical capability of this new type of rover.