# Slip Estimation for Mars Rover Zhurong Based on Data Drive
###### Abstract  
China's Mars rover Zhurong successfully landed on Mars on 15 May 2021, and it is currently conducting an exploration mission on the Red Planet. This paper develops slip estimation models for the Mars rover Zhurong based on the data drive approach. Data were obtained by Zhurong's validator ground indoor tests, and the test site was equipped with a low-gravity simulation device and simulated Mars soil to simulate the Mars conditions as much as possible. The obtained slip models trained by BP and GA-BP algorithms were applied to estimate Zhurong's longitudinal (slip_x) and lateral slip (slip_y) on Mars, and the slip estimation values were used to display Zhurong's actual driving path. The analyzed results prove that the GA-BP slip models perform better than the BP models, and can both be applied for correcting [PERSON]'s path. The proposed models have high potential in guiding the path planning and monitoring of the slip for the Mars rover Zhurong. M 1 2022 2  
Zhurong is a six-wheel rover, which can be seen as a special kind of wheeled robot working on Mars. For a wheeled robot, slip means the actual velocity of the wheel different from the command velocity, which can be regarded as a measure of the lack of traction [2]. Slip directly leads to deviation from the scheduled path and the inability to reach targeted goals. A high slip means a severe lack of traction, which can cause wheel sinkage and even permanent immobility [3; 4; 5]. Most Mars and Lunar rovers had suffered slip-related hazards of varying degrees. For example, the rovers [PERSON] and Curiosity fortunately escaped from the high slips, and the rover Opportunity resumed movement after being entrapped for five weeks; in the worst case, the rover [PERSON] experienced significant slips and became stuck with permanent immobility at a stationary science platform. Therefore, it is essential to focus on slip for [PERSON]'s safety. 1. Model-based approach. Slip is caused by the complex interaction between the wheel and soil, which allows the estimation of the wheel-level slip by utilizing accurate kinematic and dynamical equations with a slip variable [6; 7]. Some research has also focused on the enhancement of 3D kinematic models to predict the body-level slip for articulated, wheeled mobile robots [8; 9; 10; 11]. The model-based approach explains slip from the perspective of motion and force mechanisms, but the estimation accuracy is dependent on the knowledge of soil parameters and the accuracy of the model, which is not the best choice for a planetary exploration. 2. Visual-based approach. Visual odometry is a reliable source of information, which is widely used in planetary explorations. Its main working principle is that in the process of movement, image data are collected from the surrounding environment through the camera, a continuous image sequence is used as the input signal, and its motion estimation is obtained by calculating its own pose change [12; 13]. However, it has some limitations for planetary rovers, such as the sequence image matching calculation cost being high [14], the feature point matching on the surface features being sparse or the shadow area being limited, and it is not suitable for high-speed operation environments (>0.8 m/s), as the image would appear blurry in a high-speed motion environment [15]. 3. Data-based approach. Based on the data mining algorithm, the collected historical data are used as the input, and the corresponding slip observations are used as the output, so as to train to obtain the corresponding slip estimation value. [PERSON] et al. [16; 17] established a nonlinear regression mapping relationship between terrain geometry and slip by using a locally weighted projection regression (LWPR) and neural network, and the obtained models had a good slip prediction performance. The dataset used to train and validate the models was all obtained on completely natural, off-road terrains. [PERSON] et al.