We apply the end-to-end principle, which states that lower layers of systems should support the widest possible variety of services and functions, to ground station systems. We isolate core ground station services and discuss a mechanism for flexible application level support. Taking into account space system trends such as adoption of terrestrial Internet protocols, we develop a reference model that captures core ground services. In an effort to promote end user flexibility, we organize these services into hierarchical layers that allow low-level hardware commanding, automation of contact sessions, and peer-to-peer station cooperation across multiple space missions. Given this model, we describe our reference architecture and its implementation based on XML messaging and standard Internet software systems built with recovery-oriented design principles. We also discuss a testbed which consists of globally distributed, university ground station systems. 1.