This paper compares various architectural philosophies used in the design of GN&C systems for NASA human-rated and robotic spacecraft during the last four decades. This comparison gives insight into the options available for the GN&C systems of the new generation of space vehicles to be developed under NASA's Constellation Program (CxP). This study focuses on the component interconnectivity features behind cross-strapping and channelization, the two main architecting approaches for designing fault- tolerant GN&C systems. The features of theses two approaches, as well as hybrid versions of these approaches, are explained. The paper also discusses their advantages and disadvantages in terms of complexity, reliability, and fault-tolerance. Several systems developed by NASA for human-rated systems and robotic systems are analyzed and compared from this perspective. The final goal of this paper is to lay the foundations for a more in-depth study to assess commonality among different GN&C architectures for the CxP.