Space-based solar power via LEO satellite networks: Synchronization efficiency analysis

Abstract

A novel solar power harvesting technique that uses a network of low earth orbit (LEO) spacecraft formation has been discussed in the literature [1]. Here, all spacecraft within a formation harvest solar energy and simultaneously transmit the power to the ground station. LEO spacecraft within formation travels at a very high speed with respect to each other. Thus, a significant Doppler across satellites within formation is experienced. In addition, the distance of each satellite in the formation to the ground receiver is different. These two effects (Doppler and distance) respectively lead to the reception of unequal frequency and phase angles from different spacecraft at the ground receiver, and accordingly destructive addition of the signals is possible. This reduces the overall accumulated power at the ground receiver and decreases power transfer efficiency of the proposed LEO formation. In this paper, a frequency and phase angle synchronization method to cope with the associated problem is presented. Here, each spacecraft transmits the wireless power at its own carrier frequency, such that the frequency of the transmitted wireless power matches the designated frequency upon arrival at the ground station. In addition, each spacecraft transmits the wireless power at its own initial phase angle with respect to a reference spacecraft. The proposed frequency and phase angle synchronization ensures no frequency and phase angle difference between each wireless power upon arrival the ground station. A ring formation, in which all spacecraft are flying in one circular orbit is considered. Two scenarios are discussed, and the corresponding transmission efficiency analysis are presented: (1) All spacecraft simultaneously transmit their signal to the ground receiver using the presented synchronization method; and, (2) A reference spacecraft collects power from neighboring spacecraft and transmits the wireless power to the ground receiver. The impact of synchronization on the transmission efficiency with respect to the transmission frequency, altitude, the number of spacecraft and resynchronization rate is studied.