浅村 和史

The lithium-ion secondary cells/batteries are commonly used for the spacecraft, today. 'REIMEI' satellite is also an example using lithium-ion secondary battery. It used 3 Ah-class off-the-shelf lithium-ion secondary cells, which used the spinel LiMnO4 for the positive and graphite for the negative electrode. Seven cells were connected in series, and two series strings were connected in parallel. The satellite was launched in August, 2005, and injected into the low earth polar orbit. Initially, the battery performance was simulated based on the dependency of the cell performance on temperature. Considering the impedance and discharge performance depending on temperature, the end-of-discharge-voltage during the operation had been precisely controlled. Seven years operation of the lithium-ion secondary battery under the micro-gravity conditions have been demonstrated through the REIMEI operation in space.

We are in progress to develop a system for automatic operation of a satellite in order to reduce human load at satellite steady operation phase. The ground station for small satellite REIMEI (INDEX : INnovative-technology Demonstration EXperiment) is used as a test bench for verification of the proposed method. In our new automatic operation system, a scheduler software as a substitutive operator manages all the operations through a unified procedure, including sending command, receiving telemetry, and driving antenna in accordance with an operation time line which is prepared before the operation pass. The scheduler also performs diagnostics of satellite anomaly based upon the received telemetry data and status of the ground station. In case that some anomaly of the satellite is detected, the scheduler initiates an emergency schedule that was prepared depending on the emergency level. The automatic operation system is nearly completed for downlink operations of the data recorder that account for 75% of REIMEI steady operation. This approach is very effective to reduce psychological and physical load of operators.

ジオスペースERG探査計画の紹介