OMOTENASHI trajectory analysis and design: Landing phase

OMOTENASHI is a JAXA 6U cubesat that aims to perform a semi-hard landing on the Moon's surface after being deployed into a lunar fly-by orbit by the American Space Launch System, Exploration Mission-1. OMOTENASHI is a challenging mission – performing a semi-hard landing with a cubesat. One of the main challenges comes from the trajectory, which is characterized by a single deceleration maneuver instead of multiple ones for orbit insertion, descent, hovering and landing. After the deceleration maneuver, there is no time to correct for navigation and execution errors so the robustness of the trajectory is key. This paper presents the analysis and design of the OMOTENASHI landing phase. It studies the performance of the subsystems involved in the landing and proposes a deceleration maneuver to set to zero the vertical velocity at burn-out with a specified height over the Moon's surface, followed by a free-fall. In order to assess the robustness of the trajectory, it considers uncertainties in the state vector and deceleration maneuver execution. The flight path angle at lunar arrival has a great impact on the landing success rate, which imposes a very strong constraint on the design of the transfer phase trajectory. Under the current subsystems design, the most critical factors in the landing success rate are the maneuver orientation and thrust duration. Results suggest accuracy requirements for the landing devices, solid rocket motor and attitude accuracy, as well as for the transfer phase trajectory design. Finally, the navigation and maneuver execution errors may cause OMOTENASHI to prematurely impact against the surface during the solid rocket motor burn. This calls for a trade-off between the targeted final height and the maximum landing velocity. •OMOTENASHI: a lunar semi-hard lander the size of a cubesat.•Earth-Moon transfer and landing trajectory design is highly coupled.•Error robust landing design is key.•Simplified model gives designer a first guess of sensitivities and critical errors.•High-fidelity model with real lunar local topography provides finer detail.