Tetsuo YOSHIMITSU

© 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.

© 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.

Soft soils cover on planetary surfaces, so the wheels for exploration rovers easily slip. Understanding an interaction between a wheel and soft soils is important for a traction control to improve rover traversability. The interaction between the wheel and soft soils has been studied in a field of terramechanics. Since the classical terramechanics-based wheel model considers only a static state of a wheel sinkage, the wheel model is not applicable to the wheel sinkage and slip. Thus the dynamic normal stress model and shear deformation model were proposed to deal with the problems of the wheel sinkage and the slip. The dynamic normal stress model was proposed by considering the wheel sinking velocity and a variation of soil state for solving the problem of wheel sinkage. And the shear deformation model was proposed by considering the shear characteristics for solving the problem of wheel slip. The shear deformation model was formulated by the shear test. The simulation verified the validity of the dynamic normal stress model and the shear deformation model in the transient state. In this paper, a single wheel experiments was performed to evaluate the shear deformation model by comparing the simulation results and the experimental results. Then the characteristics of the wheel sinkage and slip and the effectiveness of the model were confirmed.

A microgravity experiment system using a high altitude balloon has been developed. In order to accommodate payloads larger than previous system which employed three- dimensional drag-free control, one-dimensional drag-free control has been applied. The first test flight was conducted in Aug. 2014. A gravity level below 10(-3) G was obtained for more than 30 seconds during the free-fall of the capsule. A combustion experiment was conducted during the low gravity condition.

© 2014 SPIE. Recent progress in wide field of view or all-sky observations such as Swift/BAT hard X-ray monitor and Fermi GeV gamma-ray observatory has opened up a new era of time-domain high energy astro-physics addressing new insight in, e.g., particle acceleration in the universe. MeV coverage with comparable sensitivity, i.e. 1 ∼ 10 mCrab is missing and a new MeV all-sky observatory is needed. These new MeV mission tend to be large, power- consuming and hence expensive, and its realization is yet to come. A compact sub-MeV (0.2-2 MeV) all-sky mission is proposed as a path finder for such mission. It is based on a Si/CdTe semiconductor Compton telescope technology employed in the soft gamma-ray detector onboard ASTRO-H, to be launched in to orbit on late 2015. The mission is kept as small as 0:5 X 0:5 X 0:4 m3, 150 kg in weight and 200 W in power in place of the band coverage above a few MeV, in favor of early realization as a sub-payload to other large platforms, such as the international space station.

In recent years, small body exploration missions have received a lot of attention. JAXA completed Hayabusa mission in 2010 and succeeded in getting samples from the asteroid. JAXA is also developing the Hayabusa2 spacecraft, the post sample return mission to a near-earth asteroid. A novel and tiny hopping rover called MINERVA was installed into Hayabusa spacecraft. Then, with these experiences, some rover packages are under development for Hayabusa2 spacecraft. The mission concept is the same as MINERVA, but multiple rover system is introduced. Because the target asteroid parameters may be different from the previous target in Hayabusa mission, the rover system is newly designed in Hayabusa2 mission. This paper describes the challenge of mobilizing a robotic probe for small body surface exploration. This paper proposes a hopping mechanism and shows the effectiveness of the proposed hopping robot by micro gravity experiments. This paper also discusses the required intelligence for small body exploration robot.

Planetary surfaces are covered with soft soil. So the wheels for exploration rovers easily slip and lose the traction force. Understanding the interaction between wheel and soft soil is important for traction control to make rovers travel long distances efficiently. The interaction between wheel and soft soil has been studied in the field of terramechanics. Since terramechanics-based wheel model considers only the static state of wheel sinkage, the wheel model is not applicable to the dynamic sinkage. Therefore the authors deal with the problems of wheel sinkage and slip. The traction mechanics in the dynamic sinkage is important in order to predict the wheel motion when the sinkage becomes to be the static state. This paper presents a terramechanics-based wheel dynamics model with consideration of the dynamic sinkage. This paper also proposes dynamic wheel models for solving the problem of wheel sinkage and a shear deformation model for solving the problem of wheel slip. This paper evaluates the proposed models by simulation study. The simulation results show that the proposed models are able to solve these problems and they are applicable to the dynamic wheel sinkage.

MeV and sub-MeV energy band from ̃ 200 keV to ̃ 2 MeV contains rich information of high-energy phenomena in the universe. The CAST (Compton Telescope for Astro and Solar Terrestrial) mission is planned to be launched at the end of 2010s, and aims at providing all-sky map in this energy-band for the first time. It is made of a semiconductor Compton telescope utilizing Si as a scatterer and CdTe as an absorber. CAST provides allsky sub-MeV polarization map for the first time, as well. The Compton telescope technology is based on the design used in the Soft Gamma-ray Detector (SGD) onboard ASTRO-H, characterized by its tightly stacked semiconductor layers to obtain high Compton reconstruction efficiency. The CAST mission is currently planned as a candidate for the small scientific satellite series in ISAS/JAXA, weighting about 500 kg in total. Scalable detector design enables us to consider other options as well. Scientific outcome of CAST is wide. It will provide new information from high-energy sources, such as AGN and/or its jets, supernova remnants, magnetors, blackhole and neutron-star binaries and others. Polarization map will tell us about activities of jets and reflections in these sources, as well. In addition, CAST will simultaneously observe the Sun, and depending on its attitude, the Earth. © 2012 SPIE.

Visual odometry refers to the use of images to estimate the motion of a mobile robot. Real-time systems have already been demonstrated for terrestrial robotic vehicles, while a near real-time system has been successfully used on the Mars Exploration Rovers for planetary exploration. In this paper, we adapt this method to estimate the motion of a hopping rover on an asteroid surface. Due to the limited stereo depth resolution and the continuous rotational motion on a hopping rover, we propose to use a system of multiple monocular cameras. We describe how the scale of the scene observed by different cameras without overlapping views can be transferred between the cameras, allowing us to reconstruct a single continuous trajectory from multiple image sequences. We describe the implementation of our algorithm and its performance under simulation using rendered images. (C) Koninklijke Brill NV, Leiden and The Robotics Society of Japan, 2011

Precise localization is important for a rover on small planetary bodies including asteroids and comets. Conventional localization methods are not adequate on small body surface because of the small body's irregular shape and small mass. Localization by camera images obtained on-board will not match the resolution of the map made by the spacecraft. Celestial navigation has little accuracy because the gravity direction on the small planetary body can not be used as a standard direction. It is not realistic to arrange multiple navigation spacecraft near the small planetary body like GPS. In this paper, we propose a reasonable localization method of a rover for a small planetary body. It uses two-way range measurement between a rover and a mother spacecraft. The measurements are conducted repeatedly. This method is available to the whole surface of the planetary body while it needs only one spacecraft. Numerical simulations evaluated the localization accuracy on ITOKAWA-size-body whose radius is less than 1[km]. We also analyzed the influence of uncertainties in rotation parameters of a small body and position of a spacecraft on localization accuracy.

In November 2005, Hayabusa performed descent flights to the Itokawa surface five times. The Itokawa surface is full of boulders against expectation and there are few flat areas where the spacecraft can touchdown safely. With the reaction wheels lost prior to the events, it was very difficult to control translation motion accurately, since the guidance accuracy of several millimeters per second was requested. The guidance and navigation before launch assumed the autonomous guidance by identifying the illumination center aboard. However, it was not successful due to the highly irregular shape of the asteroid. On the other hand, the scenario based on the terrain recognition in quasi real time well worked. It was anticipated not useful before launch, since Such process was conceived to take a lot of time and not effectively useful in real time operation. The Hayabusa project team devised and built the special tool on the ground and had tuned it before the successful three touchdowns and one long landing on the surface. (C) 2009 Elsevier Lid. All rights reserved.

After the success of remotely-sensed global observation by SELENE orbiter, Japan has been focusing on the in-situ exploration of the Moon. To know more about the Moon, numerous missions have to be launched to the Moon for surveying different interesting places. Naturally the cost of single mission must be reduced. Japan has been considering a landing mission for about ten years as a next mission to the Moon. This has a few tons of weight and costs a few million euros including the launch vehicle because it also features the future manned mission. Obviously it is not suitable for scientific in-situ exploration, which must be conducted repeatedly. The authors have been studying a small lander on the Moon or the planets in order to enable the multiple in-situ explorations cheaply. With the technologies developed in our studies, the mission named SLIM (Smart Lander for Investigating Moon) has been proposed to demonstrate an autonomous, accurate and soft landing on the specified place of the Moon. SLIM is also helpful to increase the success probability of the nation-led flagship landing mission when it is conducted as a precursor. This paper describes the proposed SLIM mission.

We present a two-step iterative algorithm to estimate the trajectory of a hopping rover. In the first step, a monocular scheme of visual odometry is adapted to estimate an initial portion the hopping trajectory. From this, the parameters for the ballistic motion are recovered, and the trajectory is extrapolated to predict the positions of the rover for the remainder of the hop. In the second step, we devise a scheme called "selective vision", combining the ideas of active vision and guided search. An envelope lying between the start and end of a hop is defined, within which features most likely to be re-observed across a hop are detected and matched. Performing pose estimation on the these matched features allow the relative motion between a camera frame within the visual odometry step and a camera frame within the extrapolated trajectory to be estimated. The newly determined camera frame in the extrapolated trajectory can then be used to refine the Parameters of the ballistic motion, and the trajectory can be re-extrapolated to predict future positions of the hopping rover. Following this scheme, it is possible to estimate the trajectory of a hopping rover undergoing continuous rotational motion with only one set of cameras without continuous tracking of terrain features.

In recent years, such small body exploration missions as asteroids or comets have received remarkable attention in the world. In small body explorations, especially, detailed in-situ surface exploration by tiny rover is one of effective and fruitful means and is expected to make strong contributions towards scientific studies. Performance of mobility on surface explorer is highly dependent on the gravitational environment. Some researchers have proposed novel locomotion mechanisms for extremely small terrestrial bodies like asteroids. Hopping is a possible method under micro-gravity. It is not proved, however, that the proposed method of locomotion is optimum for a given level of gravity. The purpose of this paper is to analyze which level of gravity is optimum for each mechanism, and which mechanism or parameter is optimum for each level of gravity. This paper discusses classification of locomotion mechanism. This paper compares the speed of hopping and wheeled robots and some simulation studies are performed to analyze the detailed mobility of wheeled robots.

To provide long duration and good quality of micro-gravity environment with moderate cost, we proposed and have been developed an experiment system that is released from a high altitude balloon. The experiment system has a double-shell drag-free structure and it is controlled not to collide with the inner shell to realize good quality of micro-gravity environment. This paper shows the configuration of the experiment system and summarizes its five-year development including three flight test results. The fist stage of the development was successfully completed this year. The next step is micro-gravity fall with engine for longer duration of experiment. Another direction of the development is real operation of the system for micro-gravity scientists. Those future plans are also described.

Rocket-shaped vehicle is developed to conduct microgravity experiment by dropping from the high-altitude balloon. Its design strategy and development status is introduced. Also, the result of its 2nd flight test is summarized to show the feasibility of the balloon-based microgravity experiment.

The first microgravity experiment using a new free-fall capsule released from 40km altitude was performed on May, 2006 based on a drag-free technique. The fundamental data for analyzing the drag-free control,the flight sequence, and the wireless communication between the capsule and a control room were successfully obtained in the first test flight.

This, paper describes a path planning method for a planetary microrover to make a path oil planetary surface, A planetary rover is required to travel safely over a long distance For many days in unfamiliar terrain, Hence it is very important how a planetary rover processes sensory information to understand the environment and to make decisions, The authors have developed a newly small rover for future lunar or planetary exploration. As a new data structure for a map information. an extended elevation map has been introduced, which includes the effect of the size of the rover. The proposed path planning call be conducted in such a way as if the rover were a point while the size of the rover is automatically taken into account. A map obtained by sensors includes uncertainty. So a path planning scheme based oil traversability probability is also proposed. The validity of the proposed method is verified by computer simulations.