Hiroki Kato

Rocket-propelled exploration robot: Shooting scouter, concept and evaluation of flight dynamics

This paper presents the concept and evaluation of flight dynamics for the small sized rocket-propelled exploration robot, “Shooting Scouter”. Most of the planetary rovers are actuated by the wheels, causing their velocity limited by the electrical power restriction and the heat exhausting efficiency of the motors. Also the locomotion distance is strongly influenced by features of the terrain of the planetary surfaces. To realize the system capable of improving those problems, we focused on the rocket propellant and proposed the robot named Shooting Scouter. Due to the rocket propellant, Shooting Scouters locomotion is not influenced by features of the terrain. In addition, according to the launching payload capacity of the launching rocket, small-sized lightweight actuators have the advantage of a low launching cost. However, a small-sized lightweight airframe causes a higher sensitivity for the deviation of the center of gravity, resulting in loss of control and missing the target site. This paper presents the evaluation of flight dynamics of Shooting Scouter and presents technologies to land Shooting Scouter on the target site, that can be used in space environment. One of the technologies is to stabilize the attitude during the flight. We focused on the technology to stabilize the attitude of the spinning satellite. The function to spin the reaction wheel inside the airframe is integrated on the design of Shooting Scouter, while the reaction force of the wheel is employed for the post-landing locomotion. The other technology is to improve accuracy of flying direction and distance by managing the center of gravity. A simplified center of gravity measuring device is developed to calibrate the deviation. Our experimental results show these technologies achieved stabilizing attitude during the flight and reduced the landing point error of Shooting Scouter.

Real-time spacecraft actuator fault diagnosis with state-segmented particle filtering

Fault diagnosis permits computational redundancy, which renders a system sustainable and eventually leads to hardware cost reduction. To achieve the posterior distribution computation needed for fault diagnosis along with motion estimation, we suggest a particle filtering (PF)-based state-segmentation approach. Here, both a continuous state vector and fault states are segmented accordingly to allow flexible reasoning for fault diagnosis and motion estimation. For each segmented space, an attempt is made to construct a corresponding posterior distribution independently, resulting in a reduction of the number of particles. Our experimental simulation demonstrates fault diagnosis among billions of fault states. Our state-segmentation approach reduced 98% of particles compared with the ordinal PF approach. Graphical Abstract

Development of simulation system for multi-pair crawlered and transforming explorer

This paper describes a development of simulation system to verify performance of our proposing multi-crawlered and transforming lunar and planetary explorers. Firstly, we propose a new type of explorer capable of transforming its configuration and with a multiple pair of crawler mechanisms to improve mobility in extra-rough terrain. Secondly, modeling equations for a multiple pair of crawlers connected to transformable legs are formulated. The application of the model to a conceptual examination and transforming pattern to facilitate mobility over extra-rough terrain is discussed, whereupon physical parameters for a conceptual design model are identified through experiment using developed conceptual model. Finally, the hill-climbing performance was evaluated to assess the effectivity of the proposed explorer and validate the proposed simulation method.

Caging-based grasp with flexible manipulation for robust capture of a free-floating target

This paper discusses robust capture of a free-floating target using a robotic arm. The position error resulting from sensor errors and time delay can cause undesired contact and unstable control. In this paper, we propose a caging-based rigid gripper and impedance control, which enables the robot to capture the target robustly without precise motion tracking and large force interaction. The performance of the proposed method is verified experimentally using an air-floating system that emulates planar microgravity motion.

Distance control of rocket-propelled miniature exploration robot

A rocket-propelled miniature robot is capable to explore sites that planetary rovers cannot reach with efficiency in locomotion distance per mass. The technical difficulty is the significant variance in its flight distance because of two factors: sensitivity of error in the center of gravity with respect to the thrust axis, and solid rocket engines deviance in thrusting force. To overcome the issue, our flight distance control strategy includes flight trajectory forming, and the flight trajectory prediction including the opposing shot. With our method, we experimentally showed the flight distance to the forward direction improved by a factor of four in variance reduction.

Real-time robust motion tracking using 3D point cloud for space debris removal

This paper discusses a motion tracking system for space debris removal using 3D point cloud data. Real-time robust motion tracking is essential for successful rendezvous and docking with a tumbling space debris target. Although various motion tracking methods have been developed for such a mission, the robustness is not guaranteed when a complete target image cannot be obtained within a sensors limited field of view. We propose a real-time robust motion tracking method that focuses on a payload adapter ring, which is an attachment interface between a satellite and rocket. This method can provide a target pose even when sensor data of the tracking feature is limited as in the above-mentioned case. Moreover, this method is simply designed to enable real-time calculations using limited computational resources. The practical capability of the proposed method was experimentally verified using a small satellite mock-up and compared with the conventional Iterative Closest Point (ICP) algorithm. The experimental results proved that the proposed method can perform real-time motion tracking with high accuracy even when an obtained image is partially missing information. In this experiment, when using the proposed method, the useful field of view for motion tracking was increased by 66 % when compared with the ICP algorithm.

Modeling and analysis of tether-based mobile robot based on flight experiments

This paper discusses the dynamics of a tether-based mobile robot in space. The tether-based mobile robot is constrained geometrically using several tethers and can move within an area bounded by the tethers anchors by changing the tethers lengths. This robot is equipped with an extendable and retractable arm that approaches the tethers anchor and reposition it to another point for changing the accessible area and covering a wider area. The Japan Aerospace Exploration Agency conducted an experiment called Robot Experiment on Japanese Experimental Module (REX-J) on the International Space Station for demonstrating such a systems fundamental capabilities. In this paper, the flexibilities of the extendable arm and tethers used in the REX-J are evaluated through image analysis of flight data. This analysis provides the robots dynamics in three dimensions, which can not be verified experimentally on the ground. In addition, we propose dynamic models for the extendable arm and the tethers. The proposed models are validated by comparing the flight data and the simulation results obtained using the proposed model.