Suboptimal lunar landing GNC using nongimbaled optic-flow sensors

Autonomous planetary landing is a critical phase in every exploratory space mission. Autopilots have to be safe, reliable, energy saving, and as light as possible. The 2-D guidance, navigation, and control strategy presented here makes use of biologically inspired landing processes. Based solely on the relative visual motion known as optic flow (OF), assessed with minimalistic 6-pixel 1-D OF sensors and inertial measurement unit measurements, an optimal reference trajectory in terms of the mass was defined for the approach phase. Linear and nonlinear control laws were then implemented to track the optimal trajectory. To deal with the demanding weight constraints, a new method of OF estimation was applied, based on a nongimbaled OF sensor configuration and a linear least-squares algorithm. The promising results obtained with software-in-the-loop simulations showed that the present full guidance, navigation, and control solution combined with our OF bio-inspired sensors is compatible with soft, fuel-efficient lunar spacecraft landing and might also be used as a backup solution in case of conventional-sensor failure.