Zhengshi Yu

Observability-Based Beacon Configuration Optimization for Mars Entry Navigation

In this paper, a novel observability analysis method of a nonlinear navigation system is proposed, and its application to the optimization of beacon configuration for Mars entry navigation is demonstrated. A Lie algebra-based approach to nonlinear observability is used to compute the observability matrix. The quadratic approximation to the Lie derivatives is then used to recursively calculate the observability matrix efficiently. Next, the inverse of the condition number of the observability matrix is chosen as a metric to evaluate the observability quality. To verify the accuracy and effectiveness of the proposed approach, Mars navigation scenarios with ranging measurements from multiple ground-based beacons are considered in simulation examples, and the optimal beacon configurations are obtained using a genetic algorithm. The extended Kalman filter is finally used to demonstrate the navigation performance. It is concluded that the proposed observability analysis method is able to optimize the beacon con...

Real-time Navigation for Mars Final Approach Using X-ray Pulsars

An accurate knowledge of Mars entry condition is the significant requirement for the successful aerocapture and pinpoint landing. In order to develop the real-time navigation scheme for Mars final approach, the feasibility of navigation embedded X-ray pulsar observations is verified, and the navigation performance is comparatively analyzed. In order to choose optimal navigation pulsars from pulsar candidates, the Fisher information matrix is utilized to evaluate the observability from the estimation theory point of view. The optimal navigation pulsars thus are selected such that the determinant of the Fisher information matrix is maximal. Two navigation scenarios based on the 2012 encounter at Mars of Curiosity spacecraft combining with X-ray pulsar based measurements are then considered to demonstrate the navigation performance. Furthermore, a series of research on the error ellipse in Mars B-plane and the distribution of estimated flight path angle indicate that Xray pulsar based navigation, which may provide more accurate knowledge of Mars entry condition, is a potential navigation scheme for Mars final approach in the future.

Sequence detection of planetary surface craters from DEM data

The research on identification and recognition of impact craters on planetary surface is focused on how to detect them from background. A novel sequence algorithm is proposed to crater detection that utilizes DEM data instead of images. By investigating the features of ideal craters, several constraints can be developed to extract candidate crater edges from other topographies. Based on the fact that the shape of most craters is approximate to an ellipse, the Least Median Square Ellipse Fitting Method can be used to exclude pseudo-edges, and to reserve the real edges which contain the feature of the crater. The location, orientation and other physical parameters of the crater can be determined by fitting real edges to an ellipse based on Robust Least Square Method. Mathematical simulations are performed with the moon DEM data. The results show that the topography-based crater detection algorithm offers an effective method for identification and characterization of ellipse-like impact craters, and the accuracy is high enough.

Trajectory curvature guidance for Mars landings in hazardous terrains

Focusing on the trajectory curvature, this paper presents an innovative and analytical guidance law for the construction of geometrically convex trajectories. Moving along such trajectories, the lander can increase the probability of a safe landing in hazardous terrains. Initially, the curvature theorems of the powered descent trajectories are developed. In these theorems, the inner relationship between trajectory curvature and lander states is revealed, and the state constraints for a geometrically convex trajectory are derived. Next, the trajectory curvature guidance is developed in an analytical formulation by satisfying the state constraints for a convex trajectory, and the selection of the key guidance parameters is investigated. Finally, the performance of the trajectory curvature guidance is analyzed in detail, illustrating its superior hazard avoidance and the camera’s field of view.