Timing analysis of the X-38 space station crew return vehicle avionics

We analyze the timing properties of the X38, an autonomous spacecraft currently being designed and built by NASA as a prototype of the International Space Station (ISS) Crew Return Vehicle (CRV). The CRV will be permanently attached to the ISS, and has the capability to automatically and safely bring to Earth a crew of seven (7) passengers in the event of an emergency ISS evacuation. The avionics hareware and software design phase for this spacecraft is currently underway and tools for representing, analyzing and verifying the hard real time timing aspects of the system are required. As a tool to verify planned performance of the safety critical system functions, an initially high level specification of the X-38 multiprocessor system task structure is modeled in Real-Time Logic (RTL) and Presburger Arithmetic representations, and the associated constraint graph and safety analysis is provided. In addition to the graph-theoretic approach to timing analysis, we also need a tool for representing the scheduling aspects of the system. Several commercially available real time scheduling analysis tools were subjectively evaluated against the requirements of this project, and a brief evaluation summary is presented.