Localization method of space robot with two-way range under uncertainties in rotational parameters

Our previous work has presented a method of localization based on radio waves, useful for a rover on a small planetary body, whose diameter is less than 1 [km]. The important advantage of this method is that it can apply to a rover on small body, while conventional methods of localization cannot apply to. This work assumed that parameters of rotational motion of investigating body are exactly known, however, it is difficult to determine these parameters on remote planetary body in advance. In order to cope with uncertainties in rotational motion, a recursive method of localization has been introduced a recursive method of localization has been introduced by inflating the variance matrix of estimation error. However, improvement in localization accuracy achieved by this method was limited. It is necessary to estimate rotation parameters to localize a rover with sufficiently-high accuracy. This presentation provides an estimation strategy to localize a rover under some uncertainties in rotation parameters. A smoother-based method of estimation is proposed here for a rover on small planetary body. The idea is to collect long-time observation data and use smoother-based approach. Estimation method has been derived into optimization problem with constraints and variation method has been applied to solve it. Simulation results are shown to demonstrate localization accuracy of a rover and estimation accuracy of rotational parameters.