Tetsuo Yoshimitsu

Micro-hopping robot for asteroid exploration

Abstract Exploration missions for small planetary bodies such as asteroids and comets have received significant attentions in recent years. In upcoming missions, it is very important for planetary science to make science-equipped robots hang around the surface of small bodies. In order to provide an exploration robot on the surface of small bodies whose gravity is very small, the authors have researched the mobility under the micro-gravity and have developed a small robot which is specialized in the micro-gravity environment. This paper describes the mobility and the system design of the developed robot and is accompanied with explanation of the strategy how to explore and navigate along the small body surface.

Path planning for newly developed microrover

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

Intelligent rover with hopping mechanism for asteroid exploration

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.

Relative localization of a hopping rover on an asteroid surface using optical flow

Exploration in the low-gravity environment on an asteroid surface is best achieved by using a hopping rover. Robust and effective control of such a rover will require autonomous navigation, for which accurate localization is an important element. The combination of a hopping platform on an extraterrestrial, low-gravity environment presents unique challenges for the task of localization. In this paper, the authors will evaluate the use of optical flow as a relative localization technique.

Visual Odometry for a Hopping Rover on an Asteroid Surface using Multiple Monocular Cameras

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.

Intelligent micro probe robot for small body exploration

Recently small body exploration missions have received a lot of attention in the world. In small body explorations, especially, detailed in-situ surface exploration by tiny probe is one of effective and fruitful means and is expected to make strong contributions towards scientific studies. JAXA/ISAS is promoting MUSES-C mission, which is the worldpsilas first sample and return attempt to/from the near earth asteroid. Hayabusa spacecraft in MUSES-C mission took the tiny probe, which was expected to perform the in-situ surface exploration by hopping. This paper describes the system design, mobility and intelligence of the developed unmanned explorer. This paper also presents the ground experimental results and the flight results.

Concept of a small satellite for sub-MeV and MeV all sky survey: the CAST mission

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.

Hopping Odometry: Motion Estimation with Selective Vision

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.

Locomotion Mechanism of Intelligent Unmanned Explorer for Deep Space Exploration

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.

Sensitivity analysis and influence discussion of estimation errors in rotation parameters in localization of rovers on small planetary bodies with single source of radio waves

Direct investigations are required for future missions to small planetary bodies, in addition to obtain terrain maps and collecting samples from the surface. Rovers, mobile robots on surface of a planetary body, are effective in investigating into several specific points. We proposed a method of localization for navigating rovers to specific features. The proposed method measures two-way range between the rover and the mother spacecraft orbiting around the investigating planetary body using radio waves. The proposed method can be applied with reasonable accuracy on large and small planetary bodies and it can particularly be used with sub-hundred-meter-sized bodies, which conventional methods cannot be applied to. Sensitivity analysis of the proposed method is summarized in this paper, according with estimation errors in rotation parameters of the planetary body. A method of estimation is described here, which takes into account errors of rotational parameters.