Observability-based visual navigation using landmarks measuring angle for pinpoint landing

Abstract Visual navigation by landmarks on the surface of the planet and small body is a potential main navigation method for pinpoint landing, which is a very challenging and necessary task in future Mars and asteroid exploration missions. In this paper, a method to reduce the complexity caused by nonlinear characteristic of six-degree-of-freedom (6-DOF) state estimation using pixel values of navigation landmark is proposed. Based on the invariance of angles in optical image, the position and attitude in pixel observation equations are decoupled by choosing angles between the line-of-sight (LoS) vectors of landmarks as observations, hence the solution can be obtained with high accuracy and low complexity. Then, the influence of landmark distribution on navigation accuracy can be analyzed, through evaluating the observable degree of landmark by LoS angle observation matrix. Based on the analysis, an optimal navigation landmarks selection method and the corresponding navigation algorithm are given. Finally, Monte Carlo simulations are used to verify the effectiveness of the proposed navigation algorithm, and evaluate the influence of related factors on navigation accuracy.