Jim Van Gaasbeck, Allan Posner and Brian Buckley, Interface & Control Systems, Inc.
Distributed, autonomous space-segment command and control is one of the main objectives of present-day space-vehicle 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-and-control environment, may be used to bridge the bus-payload 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 flight-system 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 third- and forth-generation systems encompassing a solid foundation for autonomous operations.