664 IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY, VOL. 53, NO. 3, AUGUST 2011 Channel Characterization and EMC Assessment of a PLC System for Spacecraft DC Differential Power Buses Flavia Grassi, Member, IEEE, Sergio A. Pignari, Senior Member, IEEE, and Johannes Wolf Abstract—This paper investigates the possibility of using the powerline communications (PLC) technology to transmit data along differential dc power buses employed in spacecraft. To this end, a point-to-point interconnection between the power control and distribution unit (PCDU) and a dc/dc converter is consid- ered. The power bus is composed of a twisted-wire pair (TWP) above ground, and capacitive coupling and inductive decoupling networks are adopted. The analysis focuses on channel charac- terization and electromagnetic compatibility (EMC) assessment of a PLC link for low-speed interconnections with sensors. A trans- mission line model is adopted for the powerline (PL) involving measurement-based emission models for the power units connected to the line ends. Modal analysis is used to estimate the channel per- formance in terms of signal and noise transfer ratios. It is shown that use of a balanced transmission scheme assures higher perfor- mance both in terms of channel transfer function and immunity to the PL-conducted noise generated by dc/dc converters. A prototype of the PLC link, involving a specific implementation, is realized to prove feasibility and to analyze the system EMC behavior in terms of radiated emissions, conducted and radiated susceptibility. Index Terms—Differential dc power buses, modal analysis, pow- erline communications, spacecraft onboard communication. I. INTRODUCTION C URRENT research in the space sector is oriented to- ward distributed monitoring of the space environment via swarms of miniaturized satellites (e.g., nanosatellites). In line with this trend, saving mass and weight of onboard wiring har- ness is becoming an essential requirement for optimizing the spacecraft (S/C) architecture. In this scenario, application of the powerline communications (PLC) technology, with consequent elimination of lines dedicated to data transmission, appears to be particularly attractive. However, though application of the PLC technology to ac lines for power delivery is well-assessed [1], in- vestigation of the performance and the electromagnetic compat- Manuscript received October 15, 2010; revised January 26, 2011; accepted February 18, 2011. Date of publication April 7, 2011; date of current version August 18, 2011. This work was supported by the European Space Agency (ESA-ESTEC) under Contract 20913/07/NL/GLC. F. Grassi and S. A. Pignari are with the Department of Electrical Engineering, Politecnico di Milano, I-20133 Milano, Italy (e-mail: flavia.grassi@polimi.it; sergio.pignari@polimi.it). J. Wolf is with the Electromagnetics and Space Environment Division, European Space Research and Technology Centre (ESTEC), European Space Agency, 2200 AG Noordwijk ZH, The Netherlands (e-mail: Johannes. Wolf@esa.int). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TEMC.2011.2125967 ibility (EMC) properties of PLC systems for data-transmission along dc power buses [e.g., powerlines (PLs) used in the au- tomotive, avionic, and space sectors] is still the subject of on- going studies. As a matter of fact, dc PLs are usually affected by high levels of noise that may impair data transmission. As a consequence, ad hoc solutions in terms of couplers, modu- lation techniques, and communication protocols are needed for these applications, depending on the PL characteristics (e.g., PL topology, spectral properties, and levels of the expected noise, etc.). Also, recent research activities in this field are mainly ad- dressed to the automotive sector [2]–[5], where the PL consists of a single-ended interconnection above ground (i.e., the car chassis), whereas little has been done for dc differential power buses, widespread in the space sectors. Actually, the integration of power and data along such buses involves distinctive EMC features, strictly related to the transmission properties of dif- ferential lines, as well as to the emission characteristics of the power units (e.g., dc/dc converters) connected to the bus ter- minations. From the EMC standpoint, the two major issues are to verify that: 1) communication reliability and integrity is not jeopardized by electromagnetic (EM) disturbances generated by onboard power electronic equipment, and 2) radiation from the PL does not cause interference or noise in other electronic devices and sensitive payloads. In line with the aforementioned state-of-the-art, this article investigates the possibility to exploit PLC technology for S/C onboard communications by transmitting data along differential dc power buses. The investigation covers both theoretical and experimental aspects. In the first part of the paper, data trans- mission along a dc differential power bus (twisted-wire pair above ground) interconnecting two power units is investigated by resorting to numerical solution of the transmission line (TL) model in the modal domain. In the second part, performance and EMC tests carried out on a real prototype of the PLC link are used to supplement the theoretical work and to substantiate the original idea. The explored transmission scheme is targeted to low-speed point-to-point interconnections for communication with sen- sors. As a matter of fact, in typical satellite architectures, these data lines exhibit star topology as the power-supply lines, with the onboard computer (OBC) and the power control and distri- bution unit (PCDU) being the star-centers for data and power subsystems, respectively. As shown in [6], this specific archi- tecture offers a simple solution for the integration of the two subnetworks, based on star-points merging. Additionally, the star topology makes the resulting PLC network not affected 0018-9375/$26.00 © 2011 IEEE