Spacecraft Wireless System Performance Degradation due to Impedance Mismatch in Cables and Connectors

Abstract

Existing cables and connectors between external antennas and internal radios need to be used when retrofitting a deployed space habitat with new wireless communication standards. Electrical performance specifications for these may not have anticipated modern frequencies and data rates, and selection can have been driven by other factors such as vacuum performance of penetrations, and ease of connection and disconnection by a suited astronaut in vacuum. Older cables and connectors could crack and fray with time or degrade due to environmental extremes. Then the radio signals may encounter multiple reflections due to the impedance mismatches within the degraded cables and connectors. This may cause signal distortion and thus degrade the wireless system performance. Performance of the assembled cables cannot be tested on the ground because some segments are already installed in the habitat and a hardware emulator likely would not have identical reflection coefficients. And performance of degraded cables is speculative. Then stochastic investigation becomes necessary, to characterize the probability that a combination of reflections will occur that would so distort the signal as to degrade performance. The purpose of this study is to analyze the mismatch effects of the cables and connectors numerically by using electromagnetic modeling techniques. A computational modeling method used to analyze the impedance mismatch effects for a wireless communication system is presented in this paper. Hardware in the loop is then used to evaluate a pair of actual proprietary receiver implementations against a large sample of possible cable distortions and so quantify technical risk.