In the periodic orbit calculations in the CRTBP, a numerical method called the differential correction method is commonly used. However, the differential correction method could sometimes be unstable when the Newton method is used in its convergence process. To address this issue, this study proposes the bisection method in the convergence process. The obtained results show that the bisection method enables finding a greater number of periodic orbits in the CRTBP than the Newton method. Furthermore, a comprehensive search is possible to reveal numerous unstable periodic orbits, including those with long periods and complex structures, which are typically difficult to identify by conventional differential correction methods incorporated with the Newton method.

In planetary exploration missions, which require long-term operation, dinitrogen tetroxide containing 3wt% nitrogen monoxide (MON-3) is commonly used as the oxidizer in bipropellant propulsion systems. While MON-3 offers the advantage of being storable at ambient temperature, it has been reported to react with stainless steel used in piping materials, locally increasing the iron concentration and potentially causing malfunctions. Most previous studies have attributed such issues to flow path blockage caused by dissolved iron. However, in Mission “HAYABUSA2,” a phenomenon was observed that could not be sufficiently explained by this mechanism alone. In-flight data from Mission “HAYABUSA2” revealed impulse bit reduction, suggesting that the elevated iron concentration in MON-3 may have degraded its reactivity with hydrazine (N₂H₄). To investigate the mechanism, we conducted droplet tests using N₂H₄ droplets and a pool of MON-3, and measured the luminescence of OH* radicals in the combustion field. The results showed that although the peak combustion intensity remained unaffected by the increased iron concentration, the ignition delay time became longer, and the time to reach the peak intensity was extended. Based on these findings, we propose the mechanism underlying the observed impulse bit reduction.

Large space structures (LSS) should be treated as flexible bodies due to the significant impact of their elastic deformation on attitude maneuvers. However, accurately modeling the entire infinite-dimensional system during ground tests under gravity is inherently challenging. This paper presents a model-independent framework for LSS attitude control that tunes active disturbance rejection control (ADRC) via Bayesian optimization. The tuning parameters are selected automatically by minimizing a cost function that balances tracking error, control effort, and its derivative, thereby eliminating the need for manual trial and error. The proposed approach is validated in simulation on a flexible-structure satellite model with several vibration modes. The Bayesian optimization process converges quickly, yielding a controller that achieves rapid settling without overshoot, smooth slewing, and effective spillover suppression. In comparison, data-driven single- and two-degree-of-freedom PID controllers, obtained through virtual reference feedback tuning (VRFT), achieve nearly the same response but exhibit slight residual oscillations. These results demonstrate that Bayesian-optimized ADRC is a practical and high-performance alternative for the attitude control of LSS.