佐伯 孝尚

A new asteroid exploration spacecraft "Hayabusa2" as a follow on of "Hayabusa" was launched on 3rd of December 2014 from Tanegashima Space Center located in the south part of Japan. The planned missions of Hayabusa2 are round trip to the target asteroid "Ryugu", scientific observation of the asteroid, releasing small rover and lander to the surface of the asteroid for scientific and engineering purposes, releasing explosive called "Small Carry on Impactor" to the asteroid in order to make a crater on the surface of the asteroid and multiple times of touchdown including "pinpoint touchdown" toward the newly created crater in order to get "fresh" material underneath the surface of it. This paper show the recent result of operation in "cruising phase" such as Earth swing-by successfully conducted in December 2015. Then current status of detailed analysis for "Asteroid Proximity Phase" is provided such as the entire planning for proximity operation, global mapping and trajectory analysis for approach to the asteroid which could be essential for successful operations in this phase.

The first Epsilon rocket was launched successfully with a small payload 'HISAKI' on September 14th, 2013 in Japan. Epsilon has a new absorber structure in Payload Attach Fitting to reduce the vibration condition for payload. We designed the robust control logic to satisfy the compatibility of robust stability and response against various disturbances. The 3rd Stage under spinning has a Rhumb-line Control function which reduces the pointing error at separation and ignition of solid motor. We could insert the payload into the orbit precisely by 'LVIC' guidance, suitable for low thrust propulsion in Post Boost Stage. We will present the flight results of the Guidance & Control (G&C) system and dynamics of Epsilon rocket.

This paper describes a method of modeling general attitude dynamics of non-spinning momentum-biased spacecraft under strong influence of solar radiation pressure (SRP). This model, called "Generalized Sail Dynamics Model", can be applied to realistic sails with non-flat surfaces that have non-uniform optical properties. A coarse Sun-pointing, momentum-biased sail spacecraft is especially focused, for which an approximate solution for the equations of motion is analytically derived. Stability and some other fundamental characteristics of momentum-biased sail spacecraft dynamics, as well as theoretical connections with the past representative sail dynamical models are discussed in detail. Furthermore, the unique behaviors predicted by the model are verified using flight data of the Japanese interplanetary probe Hayabusa2.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. This paper describes modeling, dynamical characteristics and implementation of an attitude control method which actively utilizes solar radiation pressure (SRP). The theory behind this control method is called Generalized Sail Dynamics Model developed by the authors, and is successfully applied to Hayabusa2, a Japanese asteroid explorer launched in 2014. The quasi-stable property of the dynamics is proved, which enables to realize fuel-free Sun-tracking attitude using only one reaction wheel. As of August 2016, the attitude of Hayabusa2 is maintained within 10 deg offset from the Sun direction for 193 days in total without consuming any fuel. This was impossible with any other conventional control methods such as three-axis attitude stabilization. The theoretical background, pre-launch evaluation based on a finite element model analysis, and the identification process of the dynamics model carried out for the Hayabusa2 mission operation are presented in this paper.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. An asteroid explorer (Hayabusa, Hayabusa2, …) takes many images of the target asteroid, and the images are used for the navigation around the asteroid. Some of representative optical navigation methods detect feature points of the asteroid in the images such as rocks and craters. Hayabusa succeeded to touch down on the asteroid by use of the optical navigation method called GCP-NAV. However, these kinds of navigation methods need to construct the database of the feature points beforehand by the precise measurement of the asteroid ground. In this research, we constitute virtual feature points from the topographical information captured in the images, and propose an efficient, autonomous optical navigation method without large-scale measurement in advance.

Copyright © 2016 by the International Astronautical Federation (IAF). All rights reserved. The Japan Aerospace Exploration Agency launched an asteroid sample return spacecraft "Hayabusa2" on December 3, 2014 by the Japanese H2A launch vehicle. Following the successful return back of Hayabusa from the asteroid 25143 Itokawa, Hayabusa2 aims at the round trip mission to the asteroid 162173 Ryugu. Ryugu is a near-Earth C-type asteroid, which is believed to contain organic and hydrated minerals. Thus it is expected that its successful sample return may provide fundamental information regarding the origin and evolution of terrestrial planets as well as the origin of water and organics delivered to the Earth. The spacecraft is equipped with four 10mN-class ion engines that provide a total delta-V of approximately 2km/s, which enables to realize the round-trip journey between the asteroid and the Earth. Some enabling technologies include the sample collection mechanism, optical navigation cameras, reentry capsule, four asteroid surface rovers and the impactor. The impactor is a kinetic impact device to create a 2m-class crater on the surface of the asteroid, enabling us to observe/collect not only the surface but also the sub-surface of the asteroid. Hayabusa2 is heavier than former Hayabusa by 100kg and has increased reliability and drastically more science capability as a sample-return spacecraft. Hayabusa2 will reach Ryugu in the middle of 2018 and perform an asteroid proximity operation for 1.5 years. Three touch downs for sample collection and one crater generation by a high-speed kinetic impact are planned during the asteroid proximity operation. The sample is to be brought back to the Earth by a re-entry capsule in December 2020. Hayabusa2 successfully conducted the Earth gravity assist (EGA) operation on December 3, 2015, passing above Hawaii islands at the altitude of 3090km, and increasing the interplanetary flight velocity by 1.6km/s. After the EGA, the spacecraft is planned to actuate the ion engine in March 2016 for the powered-cruise operation toward Ryugu rendezvous in 2018. This paper shows a brief introduction to the mission objective and spacecraft design, and then describes the first two year operation including launch, Earth gravity assist and ion engine-powered cruise operation. Finally the paper also provides a future operation plan for the asteroid proximity operation.

Hayabusa2 is a current sample return mission of JAXA and it was launched on 3 December 2014. Hayabusa2 is the successor of Hayabusa, however, it is equipped with some new components. Small carry-on impactor (SCI) is one of the new components of Hayabusa2. SCI is a compact kinetic impactor and in the latter half of the proximity operation phase of Hayabusa2, the impact experiment will be performed. Because SCI has no attitude and orbit control functions, its impact accuracy depends on the separation accuracy. In this study, the results of the impact accuracy analysis are shown.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. This work discusses on designing fast and efficient Mars escape trajectory for Martian Moons eXplorer in the three-body system using chemical and electric propulsion. Chemical propulsion is used for fast low-energy escape from Mars and electric propulsion is used to increase v-infinity and to re-encounter with Mars for a gravity assist. We propose a method called “all-three-body method" and we compare the new method with the patched three-and-two-body method, and a parametric study is carried out. Using electric propulsion soon after Mars escape injection done by chemical propulsion, the all-three-body method would consume less fuel than patched three-and-two-body method. Limiting the use of chemical propulsion could also increase the final spacecraft mass when electric propulsion is used within 10 days after impulsive maneuver.

This study investigates the effective orbit maintenance maneuver for the periodic orbits around collinear equilibrium point (Lagrangian point) in Elliptic Restricted Three-Body Problem (ER3BP) using the Dynamical Systems Theory (DST). The assumed state displacement is stabilized by nullifying the unstable relative motion. The other displacement, which will not be deviated from the reference are permitted in this maneuver plan. The periodic orbits in the ER3BP are considered as multiple revolution orbit and, in total, by choosing the invariant unstable direction to calculate the stabilizing maneuver reduces control budget from choosing the unstable direction of each revolution obtained.

ソーラー電力セイルはソーラーセイルにより燃料を節約できるだけでなく,太陽から遠く離れた場所でも,大面積の薄膜太陽電池を利用して探査機に十分な電力を確保できる.ソーラー電力セイルで得た電力を用いて,高性能なイオンエンジンを駆動すれば,ソーラーセイルと合わせたハイブリッドな推進が可能となる.JAXA ではこのコンセプトを踏まえ,ソーラー電力セイルによる外惑星領域探査計画を提案している.本計画では,日本独自の外惑星領域探査技術を確立し,日本が太陽系探査を先導すること,および,新しい科学分野であるスペース天文学等を切り拓くことを目指している.本稿では,本計画について紹介し,初期検討結果を示す.

In this study, we show the multiple revolution orbits design in Elliptic Restricted 3-Body Problem (ER3BP) of Sun, Earth and a particle 3-body system. For the deep-space observation, the location around L2 point is suitable because of the wide field of view to the outer space. In near future, some missions are planned to be putted into the Sun-Earth L2 point orbits. Depending on the mission requirements, the periodic orbits may not be the necessary condition. Therefore, the multiple revolution orbit closed in configuration space under arbitrary conditions are considered. Additionally, a preliminary calculation of the orbit maintenance is provided. © 2013 2013 California Institute of Technology.