Double Fail-Safe Attitude Control System for Artificial Meteor Microsatellite ALE-1

In this paper, we propose the design of a double fail-safe attitude control system (ACS) architecture for safe artificial meteor release and show evaluation results verified by a hardware-in-the-loop-simulator (HILS). ALE Co., Ltd. and the Space Robotics Laboratory of Tohoku University developed a 60-kg-class microsatellite ALE-1. ALE-1 can create on-demand artificial meteors using a gas-pressurized mass driver to release small balls, which are the source pellets of artificial meteors, for commercial entertainment events and scientific experiments in the upper atmosphere. Released pellets re-enter the upper atmosphere around an altitude of 60 km and burn up after approximately 1/5 of the orbit travel. Since the mass driver is fixed to the satellite body, ACS is responsible for the control of the pellet release direction and satellite position at the time of release. To avoid the insertion of pellets into an unintended orbit at the pellet release, we designed a double fail-safe ACS which consists of three independent CPUs and attitude sensors dedicated to each CPU. The final releasing decision is made by a mechanical unanimity system using solenoid valves which have to be opened in the proper order. Therefore, if any combination of two or fewer breakdowns occur simultaneously, the ACS can immediately abort releasing pellets. We could confirm the correct operation of the pellet release control using our HILS evaluation environment.