Design of bolted preload electromechanical impedance monitoring device for CubeSat

With the rapid development of long-term orbiting spacecraft, deep space exploration and reusable carriers, spacecraft structures increasingly require safety and reliability. During the long-term service of the spacecraft structure, the bolts are prone to loosening. Electromechanical impedance (EMI) method is sensitive to bolt loosening. This paper developed a small integrated, low-power EMI monitoring device for CubeSat to detect bolt loosening, since CubeSat is low cost and has a long-time service in the orbit. The monitoring device is a two-layer structure of 0.6U. The upper layer is the experimental specimen layer. The other layer is the impedance measurement layer which can measure and transfer the impedance and temperature information. This layer consists of impedance measurement module, channel selection module, microprocessor module, communication module and power management module. The impedance results obtained by the monitoring device matched well with these by impedance analyzer. Besides, the influence of temperature on impedance measurement was studied, and two methods of compensating impedance curves were compared. Finally, the bolt loosening experiment was performed on one bolted beam of the specimen at different temperatures. The results show that, combined with the temperature compensation of the real part curve of the impedance, the bolt loosening can be clearly distinguished from the healthy condition. This monitoring device and temperature compensation method are expected to be applied on the CubeSat.