Distributed Space-Segment Control Using SCL

Distributed, autonomous space-segment command and control is one of the main objectives of present-day spacevehicle design. This objective is oftentimes difficult to achieve, however, since the spacecraft bus and the payload are usually manufactured by two different organizations and have correspondingly different designs and architectures. As a result, bus-to-payload communication is usually restricted to payload command sequences; payload science and housekeeping data are often the only products that flow back to the spacecraft bus. SCL, a modular and distributed fifth-generation command-andcontrol environment, may be used to bridge the buspayload interface, coordinating autonomous temporal and event-driven control between both environments. Although using the SCL run-time engine on both the payload and the bus represents the most straightforward and effective method for implementing this coordinated space-segment control, similar results may be achieved even if SCL is only used in one of the two environments. In this paper we will examine some of the operational efficiencies that are gained by developing and implementing distributed command-and-control flightsystem architectures using SCL. Specific case studies were chosen representing the recent evolution of event-driven flight systems. Each successive system introduced improved event-monitoring techniques, yielding thirdand forth-generation systems encompassing a solid foundation for autonomous operations.