For the design of lunar missions that require precise, soft landing, efficient methods for the computation ofoptimal Decent & Landing (DL) trajectories and re-targeting capabilities are needed. In the system and mission design, the first step is to analyze different optimal DL strategies and assess the impact of the relevant design parameters. In addition, different optimal strategies must be analyzed considering constraints from the navigation and hazard avoidance systems. Afterwards, an autonomous guidance scheme must be defined ableto reach the desired landing site in the presence of navigation and execution errors and able to reach adifferent landing site (re-targeting). A hybrid direct/indirect optimization method is presented that is very fastand robust allowing the analysis of the different DL strategies. It provides optimal DL trajectories that aredefined by a reduced number of parameters and are easily flyable. The guidance algorithm is based on ananalytical approach for initial guess computation and is used to analyze the re-targeting capability and todefine the operational conditions to be stored on-board. In the unconstrained problem, the guidance strategymerely solves a non-linear system of equations.
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