# Slip Estimation for Mars Rover Zhurong Based on Data Drive
## 4 Results and Discussion
### On-Orbit Validation  
The BP models and GA-BP models which learned from the ground tests data were validated using [PERSON]'s on-orbit data. The real-time actual coordinates during [PERSON]'s walking process could not be obtained, so it was impossible to directly verify the accuracy of the predicted slip values during the walking process. We could convert the predicted slip_x and slip_y into a longitudinal offset \(\Delta x\) and lateral offset \(\Delta y\), respectively. Therefore, we could obtain the slip prediction corrected path points. When we compared the end point of the predicted path with the actual points, the predictive effect of the models could be seen. The specific implementation steps were as follows:  
1. The planning path could be drawn from the planning curvature, planning distance, and planning target point. Positive curvatures represented right turns, negative curvatures represented left turns, and a larger planning curvature value meant a smaller steering radius. According to the introduction in Section 2.2, [PERSON] travelled according to the planning path during the blind walking stage. Figure 13 shows the coordinates of the planning path. Each starting point was regarded as (0,0), with +\(Y\) facing east and +\(X\) facing north. We could draw the planning path based on the planning curvature, planning target point, and planning distance.
2. Visual positioning was performed when [PERSON] completed a blind walk to obtain the real positioning of the actual point.
3. The offsets \(\Delta x\) and \(\Delta y\) of path points were calculate from the predicted slip, and so we could obtain a serial of predicted path points with slip correction. These predicted path points formed a predicted path. It should be noted that the \(\Delta x\) and \(\Delta y\) of slip prediction were based on the rover's body coordinate system, and need to be transformed into \(\Delta X\) and \(\Delta Y\) through a coordinate transformation.
4. We compared the coordinates of the end point of the BP and GA-BP predicted path with the actual point.  
In this paper, an on-orbit validation was conducted based on data obtained from mid-June 2021 (sol.27-sol.36) with five movements. Table 4 shows the planning path information and actual end points of arrival. We could see that there was always a deviation \(\Delta L\) between the actual path end point and the planning point, The maximum \(\Delta L\) could be obtained as 0.6784 m. Table 5 displays the information of the BP and GA-BP predicted end points of the path. In each set of data, the \(\Delta L\)_BP and \(\Delta L\)_GABP were always smaller than \(\Delta L\); combined with the predicted path and planning path shown in Figure 14, we could see that the predicted end points were closer to the actual points. From the relative positional relationship between the actual end point and the planned path, it could be seen that the rover deviated to the right during the driving process. Both BP and GA-BP predicted paths simulated this movement trend, but the BP model predicted the path to a greater degree of deviation compared to the GA-BP model, which led to the BP predicting end points relatively far from the actual end point, especially in Figure 14d. The GA-BP model had  
Figure 13: Path planning coordinates.