Yasuhiro Kawakatsu's research while affiliated with Japan Aerospace Exploration Agency and other places

This work deals with the modeling and analysis of different disturbing forces acting over the trajectory of a spacecraft with a low-thrust acceleration model using Fourier Series expansion and differential equations of motion with singularities removed by adoption of equinoctial orbital variables. The focus of the analysis is to present a discussing where singularities are removed and with the addition of the forces due to the Earth's flattening at the poles and the third-body perturbation due to the moon in the dynamical system. The outcomes are important for the understanding and design of the dynamics adopted in projects such as transportation of cargo to cislunar region (intended for continuous lunar exploration) and the JAXA's DESTINY+ mission, a initiative planned to escape the Earth in a spiral trajectory, swingby with the Moon and potentially have a flyby with two asteroids. The planned launch date currently is mid of 2024.

The present work intends to analyze the type of dynamics under which the spiral trajectory phase of the DESTINY+ mission will evolve considering gravitational perturbations from Earth. The type of motion involved in this phase of the mission deal the continuous raising altitude low-thrust trajectory which will depart from the Earth towards the Moon. After a lunar swing-by, the trajectory will be redirected by a gravity assist towards a flyby with the asteroid 3200 Phaeton. Due to the characteristics of this mission, where low-thrust will be used to change the trajectory, some disturbing forces need to be accounted. Thus, as the focus of the present work, the flattening at Earth's poles is investigated considering its effect over the low-thrust phase. Additionally, the use of equinoctial elements for the modeling of the dynamics is adopted in order to avoid zero-eccentricity and zero-inclination singularities. The models are validated using results available in literature and high precision orbit propagators.

During interplanetary flight, several sources of stochastic disturbances and dynamical uncertainties may deviate a spacecraft from its nominal trajectory. This manuscript proposes a systematic robust trajectory design method, where quantitative information concerning uncertainty on the system dynamics and stochastic navigation errors are directly accounted for in the mission-planning process. A linear feedback control law is designed to steer the probability distribution of the spacecraft state towards a target distribution at an assigned final time, minimizing the propellant consumption while guaranteeing robustness to disturbance and uncertainties. A hybrid multiple-shooting approach is adopted, where the mean trajectory and the open-loop controls are optimized according to a multiple-shooting scheme, while a single-shooting scheme is adopted for propagating higher-order statistical moments of the spacecraft state distribution. The proposed approach is applied to the analysis of the extended mission phase of the future JAXA mission DESTINY+. The final dispersion on the state is expected to be reduced by a few orders of magnitude, with a small increase in fuel consumption.

This paper is devoted to an interdisciplinary method modelling the internal structure of differentiated asteroids via a data-driven approach called invertible neural networks (INNs). The model estimation of the internal structure can be generalized as an inverse problem of estimating internal parameters from a set of observations. Previous works (e.g. Park et al. 2014, Takahashi and Scheeres 2014) used the full gravity field data measured to derive the heterogeneous mass distribution. However, in our method, only the flight state of the spacecraft is adopted as the observation data. Since the internal parameters may not be uniquely determined, typical feedforward neural networks cannot simply be applied to such an inverse problem. The invertible neural networks (INNs) adopted in this paper can ‘read’ the interior information from a flight trajectory of the spacecraft directly. The INNs are employed to establish the two-directional mapping between the group of physical parameters and the set of flight state observations of position and velocity. The INNs are trained in a bi-directional way using four losses. Finally, the performances of the trained networks are shown in both overfit and underfit situations where the internal structure of asteroids can be estimated by this INNs-based method accurately and effectively. The results also show that even when the degeneracy occurs, the true solution still falls inside the estimation distribution.

Martian Moons eXploration (MMX) is a mission under development in JAXA in cooperation with NASA, CNES, ESA, DLR to be launched in 2024. This paper introduces the result of its preliminary design and the latest status of the MMX program, putting more weight on the novel part of the mission. The goal of MMX is to reveal the origin of the Martian moons and then to make progress in our understanding of planetary system formation and of primordial material transport around the border between the inner- and the outer part of the early solar system. Additionally, the mission is to survey two Martian moons and return samples from Phobos. Add to those MMX's contribution to the planetary science field, on the growing discussion on the International Space Exploration activities, MMX's contribution to future human Mars exploration is also considered as an essential aspect of the program. Following the system definition study results presented in the previous conference, the following items will be reported in this paper. First, as a result of the comprehensive completion of the Phase-B activities, the preliminary design is completed in coordination with the design of the spacecraft system, mission instruments, and operation plans. This paper describes the proximity and surface operations around Phobos in detail. Second, Phase-C activities have started, incorporating engineering models manufacturing and tests. Those of critical technologies for surface exploration are described in detail. Moreover third, the programmatic aspects, including international cooperation frameworks and the program schedule, are presented.

Geostationary transfer orbits (GTOs) are geocentric orbits widely considered for kick-stage operations of satellites for deep space missions. A piggyback spacecraft departing from GTOs requires a low transfer cost. The type of GTO and launch timings of piggyback missions, on the other hand, are typically determined by the primary mission that carried the piggyback spacecraft. This research introduces a new transfer strategy that coordinates piggyback spacecraft’s departure timing from Earth to deep space via an Earth synchronous orbit (ESO) after departure from a GTO. It also enables the spacecraft to change its velocity direction by introducing Earth gravity assists. Connecting several GTOs and interplanetary trajectories via ESOs reduces the ΔV required for the transfers. It leads to using transfer opportunities previously considered unsuitable for missions or miniaturizing the kick motor. As a result, ESOs allow for a broader launch opportunity for deep space piggyback probes. In addition, the feasibility of ESOs is shown numerically by comparing direct and ESO-assisted transfers from GTOs to Mars with the required ΔV.