Katsuhiko Yamada

We propose a mission concept, called the space interferometer laboratory voyaging towards innovative applications (SILVIA), designed to demonstrate ultra-precision formation flying between three spacecraft separated by 100 m. SILVIA aims to achieve submicrometer precision in relative distance control by integrating spacecraft sensors, laser interferometry, low-thrust, and low-noise micro-propulsion for real-time measurement and control of distances and relative orientations between spacecraft. A 100 m scale mission in a near-circular low Earth orbit has been identified as an ideal, cost-effective setting for demonstrating SILVIA, as this configuration maintains a good balance between small relative perturbations and low risk of collision. This mission will fill the current technology gap towards future missions, including gravitational wave observatories such as the decihertz interferometer gravitational wave observatory (DECIGO), designed to detect the primordial gravitational-wave background, and high-contrast nulling infrared interferometers such as the large interferometer for exoplanets (LIFE), designed for direct imaging of thermal emissions from nearby terrestrial planet candidates. The mission concept and its key technologies are outlined, paving the way for the next generation of high-precision space-based observatories.

In this study, we propose a landing guidance control method for the Moon using two control methods. The landing of a spacecraft on the Moon is divided into two phases: the powered descending phase and the vertical descending phase. The powered descending phase aims to optimize the entire trajectory to satisfy the termination constraint, instead of allowing for a relatively long control period. This phase performs feedback control using trajectory updates via nonlinear optimization. The vertical-descending phase aims to achieve accurate control over a short control period. This phase applies nonlinear model predictive control for fast optimization on finite time intervals. First, the landing of a spacecraft on the Moon is modeled as a two-body problem of the Moon and spacecraft, and equations of motion are derived. Subsequently, we formulated an optimization problem for each phase and developed the proposed landing guidance method by combining the two control methods. Furthermore, numerical simulations based on the derived equations of motion were performed to confirm the effectiveness of the proposed method and to compare its performance with another optimization method, the successive convexification (SCvx) algorithm.

This paper considers the position and attitude control of a quadcopter in the presence of stochastic disturbances. Basic quadcopter dynamics is modeled as a nonlinear stochastic system described by a stochastic differential equation. Subsequently, the position and attitude control is formulated as a nonlinear stochastic optimal control problem with input saturation constraints. To solve this problem, a continuous-time stochastic differential dynamic programming (DDP) method with input saturation constraints is newly proposed. Finally, numerical simulations demonstrate the effectiveness of the proposed method by comparing it with the linear quadratic Gaussian and the deterministic DDP with input saturation constraints.

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This study discusses a pseudo periodic orbit that is a nearly periodic orbit around a small asteroid such as the Martian moon Deimos. By taking differences of orbital elements between the spacecraft and the asteroid as state variables, basic equations of the relative motion are derived based on Gauss' variational equations. From the basic equations, the initial state of the spacecraft to fly on the pseudo periodic orbit and its period are approximately derived. Furthermore, the stability of the pseudo periodic orbit is analytically examined from the state transition matrix of the linearized equation around the nominal orbit. Numerical studies are executed to verify the analytical results of the conditions and stability of the pseudo periodic orbit.