Micro- and Nanosatellite Sensorless Electromagnetic Docking Control Based on the High-Frequency Injection Method

This paper proposes a sensorless electromagnetic docking method suitable for micro- and nanosatellites. Based on the circuit model of the electromagnetic docking device, an algorithm for calculating the distance between two satellites on the basis of the high-frequency injection (HFI) method has been developed. In the specific implementation, first, a high-frequency (HF) voltage is injected into one of the two electromagnets; second, the HF currents induced by both electromagnets are measured and their respective root-mean-squares (RMSs) are calculated; third, two RMSs are substituted into a specific formula to obtain a variable carrying distance information; finally, the variable is utilized to calculate the distance estimation using the look-up table interpolation method. This paper presents a closed-loop electromagnetic docking controller which includes an outer distance loop and an inner speed loop and adopts the distance estimation as the feedback. The proposed sensorless electromagnetic docking method is verified by the distance estimation tracking response test and the ground-based docking test. The results indicate that low-impact docking can be achieved under the initial condition that the two satellites have a certain degree of misalignment. The proposed method can be adopted as a primary or as a redundant electromagnetic docking solution for resource-critical micro- and nanosatellites.