(Distributed Integrated Environment for CFA Analysis, Simulation, and Testing)
Recognizing a need for multi-spacecraft mission (MSM) technology development, Emergent implemented a spacecraft simulation environment for testing distributed spacecraft flight software (FSW) for clusters, constellations, and formations of spacecraft called the Distributed Integrated Environment for CFA Analysis, Simulation, and Testing (DIECAST), it was originally used to test an autonomous orbit maintenance application for MSMs, the Cluster Flight Application (CFA), which was previously developed by Emergent in support of the Defense Advanced Research Projects Agency (DARPA) System F6 Program.
DIECAST has since been enhanced and expanded and can now be used to rapidly test FSW in a range of on-orbit scenarios with a variable number of spacecraft, spacecraft properties, orbit elements, and relative cluster geometries. Emergent has developed spacecraft sensor and actuator models that enable emulation of cooperative flight scenarios and inter-module communication within a spacecraft cluster. Sensor data and control commands are exchanged between the MSM simulation and the FSW. The resulting navigation and trajectory performance data is logged by the DIECAST simulation and used for performance assessment throughout the FSW development lifecycle.
DIECAST continues to be valuable in the development process for the FSW. It enables developers to run the FSW in a desktop environment for a high-fidelity simulated flight environment that runs faster than real-time. DIECAST is built on the NASA Trick Simulation Environment (Trick), which provides a framework for building model-based simulations for spacecraft in a variety of orbits, including the Shuttle and the Orion Crew Vehicle.
DIECAST simplifies the problem of FSW verification by providing a common FSW interface for embedded and processor-in-the-loop (PIL) testing and allows all scenarios to be evaluated with run-time inputs to a single build of the simulation. Figure 1 shows the FSW embedded within the DIECAST simulation. The FSW applications are compiled into libraries and wrapped with a Trick adaptor that enables the services to be run and scheduled by the Trick simulation executive. Embedding the FSW in the simulation allows the FSW functionality to be exercised in a controlled and repeatable fashion.
A key benefit of this approach is that it enables incremental progression from prototype FSW development to PIL-based FSW testing with a real-time operating system (RTOS). Figure 2 shows how the same simulation architecture, models, and interfaces are used when testing with the FSW running on a RTOS. Custom adaptors were developed for each environment allowing the same core FSW to be exercised in DIECAST and the flight runtime environment.