The observer presented in this paper, which was based on the use of three minimalistic bio-inspired Visual Motion Sensors (VMS) detecting Optic Flow (OF) cues, states was intended as a backup solution in the case of Inertial Measurement Unit (IMU) failure. Contrary to most previous Guidance Navigation and Control (GNC) solutions for planetary landing, which have involved a sensor suite including an IMU, an innovative strategy is presented here for estimating states without any need for inertial measurements, based solely on information about the relative velocity of the images of the surrounding environment. A Linear Parameter Varying (LPV) observer designed on a LPV system linearized around a reference trajectory, estimates: the ventral OF, the expansion OF and the local pitch angle. A previously developed observer was applied here to a larger class of nonlinear systems by making an ingenious change of variable. Simulations performed on a lunar landing scenario yielded satisfactory performance and showed the robustness of the OF based observer to initial uncertainties and measurement noise.

This paper proposes a key feature for vision based automatic landing of a UAV: the addition to a given control law of the constraint that a given ground point be maintained in the camera field of view (FoV). This feature is an application case of an output constraint method recently developed and available for any nonlinear system. This method is based on an observation made for relative degree one systems, and extended iteratively to any nonlinear system. The landing aircraft application case considered in this article consists of the design of a control law for an aircraft to maintain a given ground point in the camera field of view for visual servoing purpose. Simulation results confirm the effectiveness of the approach.