福田 盛介

In this paper, a signal-processing method for a lunar lander using deep learning is proposed. The ability for pinpoint soft landing on a lunar/planetary surface broadens the range of scientific and exploration missions. To perform pinpoint landing, measurement of the relative velocity with respect to the surface is essential. Landing radar is a sensor that measures the relative velocity. To measure the velocity, the landing radar irradiates the surface with a pulse wave and observes the Doppler shift. High-precision measurement on complex terrains, a crater, or a slope has always been the problem of landing radar because the irradiated terrains strongly affect the accuracy. We propose a measurement system that performs with high accuracy on complex terrains using convolutional neural networks. Moreover, we confirm that the proposed method could improve the measurement accuracy compared with the existing method.

© The Authors, published by EDP Sciences, 2017. The lithium-ion secondary batteries have been widely used for the space programs, today. Among them, REIMEI was one of the first satellites using lithium-ion secondary battery. In 2005, the satellite was launched, and injected into the low earth polar orbit. Eleven years has passed since the launch and over 60,000 cycles of charge and discharge was experienced in space. The lithium-ion secondary cell of the REIMEI battery was designed using spinel manganese oxide type material for the positive electrode, and the graphitized type carbon for the negative electrode. The cell case was made of aluminium laminated film and the structure was reinforced by the epoxy resin and aluminium housing. After the operation of eleven years, the cells still maintain the appropriate uniform balance and operative. In order to identify the internal condition of the battery/cell, we calculated the ac impedance by the pulse duration to the on-board battery.

© The Authors, published by EDP Sciences, 2017. Understanding the behavior of Li-ion cells during thermal runaway is critical to evaluate the safety of these energy storage devices under outstanding conditions. Li-ion cells possess a high energy density and are used to store and supply energy to many aerospace applications. Incidents related to the overheating or thermal runaway of these cells can cause catastrophic damages that could end up costly space missions; therefore, thermal studies of Li-ion cells are very important for ensuring safety and reliability of space missions. This work evaluates the thermal behavior of Li-ion cells before and after storage degradation at high temperature using accelerating rate calorimeter (ARC) equipment to analyze the thermal behavior of Li-ion cells under adiabatic conditions. Onset temperature points of self-heating and thermal runaway reactions are obtained. The onset points are used to identify non-self-heating, self-heating and thermal runaway regions as a function of state of charge. The results obtained can be useful to develop accurate thermo-electrochemical models of Li-ion cells.

© 2017 International Astronautical Federation IAF. All rights reserved. This paper proposes a guidance law that is suitable for the terminal phase of a precise lunar landing. During this phase, as a spacecraft continues its vertical descent for a few minutes until touchdown, such preparatory actions for landing as vertical braking, terrain relative navigation, position correction maneuver, and obstacle detection and avoidance must be taken continuously or simultaneously. The developed guidance law can produce a vertical descent trajectory with low calculation resources, where the fuel consumption and maneuver time for horizontal position correction are minimized. Moreover, the developed law is designed to output two indexes ( and ) that indicate the feasibility of vertical braking and horizontal position correction prior to trajectory computation, in order to prevent any divergence. The simulation results verify that the proposed law performs effectively in evaluating the feasibility of a trajectory based on the discriminants and , in addition to computing trajectories for minimizing fuel consumption and maneuver time when both discriminants are greater than or equal to zero.

The lithium-ion secondary batteries have been widely used for the space programs, today. Among them, REIMEI was one of the first satellites using lithium-ion secondary battery. In 2005, the satellite was launched, and injected into the low earth polar orbit. Eleven years has passed since the launch and over 60,000 cycles of charge and discharge was experienced in space.The lithium-ion secondary cell of the REIMEI battery was designed using spinel manganese oxide type material for the positive electrode, and the graphitized type carbon for the negative electrode. The cell case was made of aluminium laminated film and the structure was reinforced by the epoxy resin and aluminium housing. After the operation of eleven years, the cells still maintain the appropriate uniform balance and operative. In order to identify the internal condition of the battery/cell, we calculated the ac impedance by the pulse duration to the on-board battery.

The satellite borne batteries should be composed by safe materials if we don't want to have a risk of explosion caused by batteries. Therefore, we focused on two safe batteries. One is a lithium-ion battery with an ionic liquid electrolyte, and the other is a LiFePO4/C type lithium-ion battery. To check whether the batteries are suit for space applications or not, we demonstrate the ionic liquid type batteries and LiFePO4/C type battery in orbit by mounting on "Hodoyoshi-3" microsatellite, and test LiFePO4/C type cell on the ground at various conditions for a better understanding.On the ground tests, AC impedance and capacity of the cells were initially measured, and charge/discharge cycling was constantly repeated at 10, 23 and 45 degrees C. The cells were discharged by constant current (CC) protocol to DOD 50% with 1.0 C for 30 minutes. They were then charged by a constant-current/constant voltage (CC-CV) protocol to 3.6 V for 65 minutes with 0.5 C. For capacity check, the cells were charged at 1.0 C in CC-CV mode until their charge current becomes 60 mA, and discharged at 1.0 C in CC mode to 2.0 V at 23 degrees C. The AC impedance was measured by applying 100 mA of AC oscillation over the frequency range from 0.01 Hz to 10 kHz at SOC 50%.As a result, the decrease in the impedance for the charge transfer through the cycles was observed at each test condition. Furthermore, especially in over recommended charge condition at 10 degrees C, cells that were charged and discharged at 1.1 A/1.1 A were led to internal short circuit. The results suggested that the negative electrode performed as a "lithium-ion excess" by cycles. We define "lithium-ion excess" that lithium-ion happens to stay inside the negative electrode without desorption after cells discharge.

Copyright © 2016 by the International Astronautical Federation (IAF). All rights reserved. Energy storage devices are very important for space missions, Li-ion cells are used to supply energy to spacecrafts or satellites during the eclipse/night time. These cells possess a high energy density but can cause catastrophic incidents that could end up costly space missions, those incidents are manly related to the overheating or thermal runaway of Li-ion cells, leading to possible fire and explosion as observed by incidents in the electronics and aerospace industries. The thermal analysis of Li-ion secondary cells is very important for ensuring safety and reliability of space missions. The thermal behavior of a Li-ion cell is dominated by the exothermic reactions between its electrolyte and electroactive materials. Thermal runaway occurs when the exothermic reactions go out of control, thus the self-heating rate of the cell increases to the point that it begins to generate more heat than what can be dissipated. Understanding the behavior of Li-ion cells during thermal runaway is critical to evaluate the safety of these energy storage devices under outstanding conditions. In this work we analyze the thermal runaway behavior of 18650 Li-ion cells before and after storage and cycling degradation at high temperatures. The thermal behavior of the cells is analyzed using accelerating rate calorimetry. Non-self-heating, self-heating and thermal runaway regions of the cells as a function of state of charge and temperature are identified and compared among the cells. Li-ion cells were tested inside an accelerating rate calorimeter (ARC) 2000™ to record their thermal behavior under adiabatic conditions. Onset temperatures of self-heating and thermal runaway reactions are identified, and by using these onset points thermal mapping plots are made. We are able to identify non-self-heating, self-heating and thermal runaway regions of degraded and non-degraded Li-ion cells as a function of state of charge. The results shows that degraded Li-ion cells tend to be thermally unstable at low state of charges.