RF Cables: The Overlooked Satellite Component

In comparison to the difficult work of payload design and system integration, specifying the correct RF cables seems all-too simple. A passive microwave component, the purpose of an RF cable is simply to transport an analog signal from one physical location on the satellite to another. However, RF cabling design decisions can mean the difference between mission success and failure. RF cables can represent a potential weak link in overall system design because they are mechanically and electrically exposed. All too often, we find engineers have specified RF cables that either do not optimize for system performance or create mission risk. In this paper, we define three rules for small satellite designers to consider when specifying their RF interconnect. First, do no harm. We show why, for spaceflight applications, it is critical to specify cables that will not outgas, resist multipaction as appropriate, can withstand the radiation environment, and use materials that are not susceptible to whiskering. Second, understand how the tradeoffs among different RF cables affect overall system performance. RF cables most often influence system performance through three key RF cable performance parameters: attenuation, return loss, and phase stability. Those tasked with selecting cables must understand the contours of the cable’s electrical and mechanical performance trade spaces. Third, simplify your satellite assembly. Thoughtful cable assembly specification can reduce overall system mass, simplify cable management during the integration process, and reduce the risks of installation errors. Engineers should consider how to introduce requirements such as connector keying, cable marking, and appropriate minimum bend radii. Furthermore, new styles of connector interfaces such as TLMP address the electrical and mechanical weaknesses of traditional mil-spec interfaces such as SMP/SMPM for high frequency spaceflight applications. Often, cables are defined late in the overall satellite design process, with little time to consider the impacts of cable design choices. Applying these three rules will reduce risk and ensure that even the smallest of components support overall mission success.