Attitude control of the LUNAR-A penetrator system and its flight test

The paper reveals the essential feature of the attitude control of the lunar penetrator system and evaluates its fundamental performance. The spinning LUNAR-A mother spacecraft, orbiting a low lunar elliptic orbit, is to release penetrator modules one by one, which penetrate into the moon's surface carrying scientific instruments. This final phase of the journey is featured by a rhumb line controlled attitude maneuver followed by an active nutation control, to ensure the proper impact point attitude. The accuracy of the control will play a key role in the mission as it directly affects the level of the impact load. Although the maneuvering strategy itself cannot be considered special, a relatively high spinning rate of the module makes the problem absolutely different. The level of fluctuation in response time delay of the actuating system has significant influence on the control accuracy: as small as 1 msec of error leads to approximately 0.7 degree of directional dispersion, almost half the required accuracy. Thus a special autonomous delay compensating algorithm has been developed while the active nutation control is also expected to enhance the control capability of the system. The performance of the entire attitude control system has been finally established through a flight test via an ISAS' sounding rocket in January 1997.