佐伯 孝尚

© 2020, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Hayabusa2 is an asteroid sample return mission by JAXA. The spacecraft was launched in 2014 and arrived at the target asteroid Ryugu on 27 June 2018. During 1.5-year proximity phase, several critical operations including two landing/sampling operations were successfully performed. They were based on autonomous image-based descent and landing techniques. This paper describes an image-based autonomous navigation of the Hayabusa2 mission using artificial landmarks named target markers (TMs). Its basic algorithm, and in-flight results in the 1st touchdown and its rehearsal are shown.

© 2020, Univelt Inc. All rights reserved. The Hayabusa2 spacecraft successfully landed on the asteroid Ryugu on February 22nd, 2019. Because of the abundance of boulders, the touchdown operation required high accuracy for spacecraft safety. This research, therefore, investigates a precision landing sequence using retroreflective marker tracking. The trajectory for the touchdown operation is computed based on a high-fidelity gravity model to minimize the landing error. This paper provides trajectory reconstruction results based on actual flight data. Consequently, it is demonstrated that a landing accuracy of 3 m can be achieved, resulting in the successful touchdown.

© 2020, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Asteroid Explorer Hayabusa2 arrived at asteroid Ryugu in June of 2018. During its stay around Ryugu, Hayabusa2 undertook several challenging missions such as collecting a soil sample and deploying rovers, a lander, and an impactor. The design and success of the final descent from an 8.5-m height above the surface, with subsequent sample collection upon spacecraft touchdown is one of the most important operations in the sampling mission campaign. The spacecraft dynamics estimation is selected for its approach. This estimation is based on dynamics analysis using a precise spacecraft model and an onboard experiment. This paper describes an overview of the sampling mission operation, focusing on the final descent and touchdown, the operational design thereof that includes the spacecraft dynamics analysis and onboard experiment, and the actual results of our first sampling operation.

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. On October 3rd, 2018, the MASCOT lander has been deployed successfully by the Hayabusa2 spacecraft from an altitude of 41m onto the C-type near-Earth asteroid (162173) Ryugu. After a free-fall of approx. 6 minutes MASCOT has experienced its first contact with the asteroid. The lander underwent a bouncing phase of ~ 11 minutes before it finally came to rest at its first settlement point where it entered into its on-surface operational mode. The lander was able to perform science measurements with its payload suite at 3 locations on Ruygu. After about 17 hrs of operations, the MASCOT mission terminated with the last communication contact. The lander was jointly developed by the German Aerospace Centre (DLR) and the Centre National d'Etudes Spatiales (CNES). The payload suite of four scientific instruments is provided by DLR Berlin (MASCam wide-angle camera with colour illumination and MARA thermal IR radiometer), IAS Paris (MicrOmega hyperspectral IR soil microscope) and TU Braunschweig (MASMag magnetometer). The paper will outline the path of the lander on the asteroid and present a summary of the scientific observations. These first results are related to the progress of the Hayabusa2 mission and its MINERVA-II rovers on the background of a recap of the landing site selection process.

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. One of the primary operations in the Hayabusa2 mission is touchdown on the asteroid Ryugu, which was successfully performed on February 21st, 2019. Because of the abundance of boulders on the asteroid surface, it was challenging to guarantee a safe and secure landing. To identify a promising landing site and design a feasible landing trajectory even under such a situation, this research develops detailed site selection and dispersion analysis strategies. The dispersion of the landing points is computed by a Monte Carlo simulation. Moreover, the distributions of landing conditions, such as a surface contact angle and a clearance distance, are analyzed, validating the feasibility of the touchdown operation. Consequently, a circular area with a radius of 3 m was selected as a safe landing site, leading to the successful landing.

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. The asteroid explorer Hayabusa2 was launched by Japan Aerospace Exploration Agency (JAXA) on December 3rd, 2014. The main mission of the probe is to sample pieces of asteroid and bring it back to the Earth in order to do more advanced scientific analysis on the ground. After three years' cruising phase, Hayabusa2 finally arrived at the asteroid Ryugu on June 28th, 2018, and a mission operation has been started. Hayabusa2 carries several rovers and separates them to land on the asteroid surface. One of these rovers is called MASCOT which was developed under the collaboration between Deutsches Zentrum für Luft- und Raumfahrt (DLR) and Centre national d'études spatiales (CNES). This rover was planned to be separated to the asteroid surface and executes several missions on the asteroid surface. In order to support this mission, the mother ship Hayabusa2 is requested to separate this rover at very low altitude around 50m and after separation to hover around 3 km altitude for realizing the assured communication link with MASCOT. On October 2nd - 5th, 2018, we performed the operation for MASCOT release. In the decent operation, Hayabusa2 was successfully guided to the target point which is specified by the MASCOT team, and the MASCOT was released at 51m altitude which satisfies the altitude criteria defined between MASCOT team and Harabusa2 operation team. After ascent to altitude 3km, Hayabusa2 started the hovering operation in order to ensure the communication between Hayabusa2 and MASCOT. The spacecraft position was adequately controlled to hover around the target position, and the MASCOT operation after landing was successfully executed. In this paper, we introduce the GNC operation scheme and show the flight results of entire operation for MASCOT release.

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. Hayabusa2 is a Japanese sample return mission from the asteroid Ryugu. The Hayabusa2 spacecraft was launched on 3 December 2014 and arrived at Ryugu on 27 June 2018. It will stay there until December 2019 for in situ science observation and surface sample collection and will return to the Earth with the collected sample in December 2020. During the stay, the spacecraft is planned to carry out several numbers of descent operation to deploy and land rovers, and to touchdown and collect surface sample. On 22nd February 2019, the spacecraft successfully touched down on Ryugu. Since the surface of Ryugu is extremely rough and full of boulders, and the number of areas with small-enough and low-enough boulders is limited. The target point named “L08-B” has “safety area” with radius of only 3m and the accuracy required to the GNC (Guidance, Navigation and Control) of the spacecraft was challenging. For the “pinpoint touchdown” it was necessary to follow step-by-step approach including touchdown rehearsal descent operations in order to check GNC sequence, performance of laser sensors such as LIDAR (long range laser altimeter) and LRF (short range four beam laser distance sensor), to collect closer images of the surface of Ryugu and to drop TM (Target Maker) that is retro-reflected ball used for image-based navigation reference. There are three key GNC features for “pinpoint touchdown”, that is (1) position control of the spacecraft from the altitude of 20km to 45m toward the area that TM is in the field of view of navigation camera, (2) feed-forward attitude control of the spacecraft in order to align to the unlevel touch down area using noisy LRF output, (3) high precision six-degrees-of-freedom feed-back control using TM as a lateral position navigation reference in order to descend and touch down to the small safety area. This paper introduces strategy, sequence and algorithms for the last two GNC features for touch down of Hayabusa2 stated above with numerical simulation results and actual flight data.

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. A Japanese interplanetary prove “Hayabusa2" was launched on December 3rd, 2014. After long transfer period including the ion engine powered cruising, the prove arrived at the vicinity of C-type asteroid 162173 Ryugu on June 27th, 2018 and started its 1.5 years asteroid proximity phase aiming "touchdown" for surface sample collection to carry back to the Earth by end of 2020. Overcoming the asteroid's unexpected exceptionally rough surface covered by substantial numbers of harmful boulders, first touchdown was accomplished on February 21st, 2019 to confirm nominal progress of entire touchdown sequence which is expected to have secured surface sample. This paper focuses on planning methodology and operation of entire touchdown sequence. First, boundaries and restriction for operation planning including representative features of landing target are described. Then, operation sequence introducing “pinpoint touchdown method” newly developed for Hayabusa2 together with schematics of onboard function as well as circumstances and results of rehearsals. Finally, achievements of Hayabusa2's first touchdown operation targeting L08-E1 area are reported based on actual event timeline and flight data.

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. Hayabusa2 is a Japanese interplanetary probe launched on December 3, 2014. It arrived at asteroid Ryugu on June 27, 2018. During stay around Ryugu, it has succeeded in several challenging operations, including two rovers/a lander landings, two sample collections, and a kinetic impact. The kinetic impact is one of the biggest challenges of the Hayabusa2 mission. Investigating the physical and chemical properties of the internal materials and structures is an important scientific objective. Small Carry-on Impactor (SCI) was developed to achieve the aim. The SCI is a compact kinetic impactor designed to remove the asteroid surface regolith locally and create an artificial crater. The spacecraft deployed the SCI on April 5, 2019, and the SCI successfully created an artificial crater with a diameter of 10 m. This paper describes the operation planning of the kinetic impact and summarizes the operation results.

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. Hayabusa2 is a Japanese interplanetary spacecraft to explore the near-Earth asteroid Ryugu. The spacecraft touched down to Ryugu for soil sample collection on 21 February 2019 for the first time. This paper presents an overview and flight results of a guidance, navigation and control method used in the touchdown operation. The method consists of on-board and on-ground guidance systems including an image-based navigation technique using a shape model and ground control points of the asteroid. The flight results show that the performance of the systems satisfied accuracy requirements and contributed to the success of the operation.

© 2019, Univelt Inc. All rights reserved. This research investigates retrograde teardrop orbits (RTOs) about asteroids subject to strong solar radiation pressure. RTOs are closed orbits that are made periodic by introducing a deterministic impulsive delta-V within each period. This type of artificial periodic orbit provides high flexibility in orbit design compared with natural periodic orbits. RTOs are promising options for asteroid missions because of their stability and small delta-V values (on the order of 10 cm/s or less). This paper presents the dynamical theories of RTOs and possible applications for the Hayabusa2 mission.

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. Japan Aerospace Exploration Agency (JAXA) launched the 1st C-type asteroid exploration and sample return probe "Hayabusa2" in December 3rd, 2014, and it arrived at C-type asteroid \Ryugu (1999ju3)" in the end of June, 2018. Hayabusa2 conduced science observation and several rehearsals of touch-down (TD) operation. Then, Hayabus2 has succeeded 1st TD and sampling operation on the surface of Ryugu on February 22nd, 2019. TD operation for sampling is conducted at the surface area “L08-E1” where is without 50-cm sized or larger boulders and with the local surface angle of <30 deg for safety. Hayabusa2 controls 6-DOF (position, velocity) by autonomous on-board function and attitude / angular rate by feed-forward command at the altitude of 8.5 m before the final descent phase. Then, Hayabusa2 descents by a free fall in initial velocity -7.4cm/s from 8.5m altitude. After approximately 100 seconds, Hayabusa2 touches the surface of Ryugu and collects sample using the sampling system that applies the same projectile method as that of 1st Hayabusa. The projectile is shot for sampling, which is triggered by the detection of the bending of the sampler horn by a short-range laser range finder (LRF-S2). For planning the TD operation, the important thing is to set sequence of event from final descent phase and detection parameters. We simulated applying dynamics model of Hayabusa2 including a sampler horn model and a surface reaction model to verify the sequence, detection method and parameters. Multibody dynamics and ground contact model are implemented in this simulator. Hayabusa2 has several detection methods to detect the touch-down and trigger shot of projectile for sampling, that is, fluctuation of signal of distance and intensity measured by LRF-S2, attitude /angular rate fluctuation measured by the inertia reference unit of AOCS subsystem, acceleration integral value. We discussed appropriate threshold values for each detection method based on the result of the dynamics simulation. The dynamics simulation is also used to study spacecraft dynamics and safety of both spacecraft and the sampler horn during spacecraft contacts on the asteroid which surface properties are unknown. In this paper, the design and parameter decision process which includes TD simulation results will be described. In addition, we will report the result of actual 1st TD dynamics and sampling operation, which is the world's first achievement in the deep space exploration.

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. Hayabusa2 arrived at the C-type asteroid Ryugu in June 2018. During one and a half year of the Ryugu-proximity operation, we succeeded in two rovers landing, one lander landing, two spacecraft touchdown/sample collection, one kinetic impact operation and two tiny reflective balls and one rover orbiting. Among the two successful touchdowns, the second one succeeded in collecting subsurface material exposed by the kinetic impact operation. This paper describes the asteroid proximity operation activity of the Hayabuas2 mission, and gives an overview of the achievements done so far. Some important engineering and scientific activities, which have been done in synchronous with the spacecraft operations to tackle with unexpected Ryugu environment, are also described.

© 2019, Univelt Inc. All rights reserved. An optical navigation method for autonomous landing on asteroids using asteroid shape model is presented. Vertices of the shape model are tracked in the sequential images obtained by a monocular camera. The proposed method does not need the process of landmark detection or mapping. The pose of the spacecraft is estimated using particle filter, considering the dynamics around the asteroid. The performance of the developed navigation method is evaluated via numerical simulation; it is based on the touchdown rehearsal operation in Hayabusa2 Mission to show the effectiveness of the proposed method against actual asteroid exploration missions.

© 2018 Univelt Inc. All rights reserved. The Epsilon launch vehicle, the newest version of Japan’s solid propulsion rocket, made its maiden flight in September of 2013. The purpose of the Epsilon launch vehicle is to provide small satellites with responsive launching with low-cost, user-friendly and efficient launch system. The first flight was successfully finished, JAXA has been conducting intensive researches on a more powerful and lower cost version of Epsilon. In order to minimize technical risks and to keep up with demand of future payloads, JAXA plans to take a step-by-step approach toward Future Launch System. As the first upgrade toward Future Launch System, JAXA has started the development of the Enhanced Epsilon. This development is mainly the renewal of the second stage, and also includes each subsystem’s improvement. This paper describes the development and flight result of the Enhanced Epsilon’s Guidance and Control System.

© 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. In the case of initial guess in the trajectory design to use the swing-by, Zero Patched Conics Method is often used. In this method, the sphere of influence of the swing-by target body is treated as a point. It can be that the trajectory is calculated by the two body problem with the central body and connected analytically. However, the trajectory obtained by this method often cannot be connected due to multi body problem. Therefore, in this study, we propose a method called “Improved Zero Patched Conics Method” to make a connectable pair of the trajectories before and after swing-by that conforms to multi-body problem. This method can improve the connection the trajectories before and after the swing-by in multi body problem.

<p>1．はじめに</p><p>小惑星探査機「はやぶさ2」はC型小惑星Ryuguの探査およびサンプルリターンを行うミッションである。電気推進（イオンエンジン）による小惑星往復航行を行い，リモートセンシング観測を行った後に小惑星表面にタッチダウンして物質を採取する。また，人工クレータをつくり小</p>

© 2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. This paper describes the modeling, dynamical characteristics, and implementation of an attitude control method that actively uses solar radiation pressure. The theory behind this control method is called the generalized sail dynamics model, which was developed by the authors and successfully applied to Hayabusa2, which is a Japanese asteroid explorer launched in 2014. The quasi-stable property of the dynamics is proved, which enables the implementation of a fuel-free sun- Tracking attitude using only one reaction wheel. As of August 2016, the attitude of Hayabusa2 was maintained within 10 deg offset from the sun direction for 193 days in total without consuming any fuel. The auto-sun tracking, single-wheel, and fuel-free features were distinctive as compared to any other conventional control methods, such as three- Axis stabilization, and brought many merits to practical spacecraft operations. The theoretical background, the prelaunch evaluation based on a finite element model analysis, the identification process of the dynamics model carried out for the Hayabusa2 mission operation, and their effectiveness are presented in this paper.

© Copyright 2017 by the International Astronautical Federation (IAF). All rights reserved. Launched in December 2014 the Japanese spacecraft Hayabusa2 (HY2) and its small passenger MASCOT (Mobile Asteroid surface SCOuT) have meanwhile successfully performed more than half of their 4-year-long voyage to reach their target body, asteroid (162173) Ryugu, formerly referred to as 1999 JU3. While Hayabusa2 is aiming to characterize Ryugu on a global scale and to return samples to Earth, MASCOT's mission is to land on the surface, perform in-situ investigations and thus provide ground truth and context information for the overall Hayabusa2 science activities. The lander was jointly developed by the German Aerospace Centre (DLR) and the Centre National d'Etudes Spatiales (CNES). It is equipped with a sensor suite of four scientific instruments: a hyperspectral IR spectrometer (MicrOmega, IAS Paris), a camera (MasCam, DLR Berlin), a radiometer (MARA, DLR Berlin) and a magnetometer (MasMag, TU Braunschweig) to investigate Ryugu's surface structure, composition and physical properties including its thermal behaviour and magnetization. The planned on surface sequence of measurements will be repeated in a different site after MASCOT's relocation on the asteroid surface. Therefore a mobility subsystem was developed to make MASCOT jump due to applied angular momentum of an eccentric rotating mass inside the system. Since the characteristics of Ryugu such as the exact orientation of the rotation axis, the thermal conditions, shape and surface structure will be known only after arrival of Hayabusa2 in July 2018 there will be only a few weeks available to select a landing site and refine the specific MASCOT mission parameters according to the conditions found, before the landing can take place, in October 2018. MASCOT's on-asteroid lifetime is limited by the capacity of its primary battery which is the main driver to make maximum use of the given time. In order to prepare MASCOT's operation within these constraints, both, space and ground systems have to be well prepared and descent and on-asteroid phases need to be rigorously planned and tested. This paper will summarize the already performed and planned in-flight activities such as health checks, calibration activities, data transfer tests, and will report on MASCOTs overall health state. Beyond that, all on-ground activities such as the landing site selection process, the verification of operational timelines, planning and training aspects will be outlined.

© Copyright 2017 by the International Astronautical Federation (IAF). All rights reserved. Hayabusa-2 is an asteroid sample return mission operated by the Japanese space agency, JAXA. It was launched in December 2014. The spacecraft has already performed half of its 4-year-long cruise to reach the mission target, a kilometer-sized C-type asteroid, one of the most pristine class of objects in our Solar System, called Ryugu. Its analysis, with a special emphasis on organics and hydrated minerals, will give essential clues for the understanding of the Solar System formation and evolution. The small lander MASCOT (Mobile Asteroid surface SCOuT) carried aboard Hayabusa-2 is intended to land on the surface for in-situ investigations while the probe is aiming to study Ryugu on a global scale and to return samples to Earth. MASCOT was jointly developed by the German Aerospace Centre (DLR) and the Centre National d'Etudes Spatiales (CNES). It is equipped with a sensor suite consisting of four fully-fledged instruments. DLR was responsible for developing the MASCOT lander and its ground segment, and is in charge of planning and conducting lander operations. CNES supplied the near-IR hyperspectral microscope MicrOmega developed at IAS, the antennas and the electrical power system that would be essential contributors to the on-asteroid operation success. Some of these subsystems are partly inherited from the Philae lander aboard the Rosetta mission. CNES is responsible for the MASCOT flight dynamics and is also providing a support for RF link, based on the expertise gained on the past science missions. The characteristics of Ryugu including the shape will be known only after arrival of Hayabusa-2 in July 2018. Moreover, the MASCOT's primary battery is expected to supply power to the lander only for 2 asteroid days to perform science activities on the surface. Thus, the time available will be very short for either task and the different processes and teams involved have to be well prepared and trained. This paper is a complement to the project status presented in the "MASCOT - Preparations for its landing in 2018: a status update from ground and space one year ahead of the landing on Ryugu" [1]. It will summarize the already performed and planned activities to prepare the French expertise center at CNES while focusing on the improvements/adaptations made on the subsystems inherited from Philae.