Microgravity Performance Evaluation for Zero Gravity Robot in China's Space Station

A zero gravity robot (ZGR) is a two-body standalone system to isolate ambient disturbances to provide a high-level microgravity environment. ZGR demonstrates a new means to realize long-term and high-level microgravity in space station. In this article, the microgravity performance of this system is evaluated via conducting researches on design and simulation of the control system. The configuration of the ZGR system and its working modes are first presented. Subsequently, the design methodology of the control system is described, including dynamic modeling and control law design for implementing active vibration isolation and drag-free flying. Active vibration isolation technology can attenuate vibration in the high-frequency bands for a long time. The key problem is to determine the controller parameters to achieve a high-level vibration attenuation performance. Drag-free control technology can provide a high-level microgravity environment for a limited time under the spatial constraints, when the payloads follow a purely gravitational orbit. The key problem is to extend the drag-free flying time under the spatial constraints. The microgravity performance is finally evaluated by numerical simulations. The simulation results show that vibration attenuation in the range of [0 dB, −160 dB] at [0.008 Hz, 100 Hz] can be achieved, microgravity level of 10−7 g can be expected, and the drag-free flying with the optimized initial states can lead to 557 s under the spatial constraints of ±500 mm and ±10°. Besides, the tradeoff among vibration attenuation, microgravity level, and microgravity duration is finally discussed.