Modeling relationships using graph state variables

The Mission Data System is a unified flight, ground, simulation, and test software system for space missions. Currently, its first application will be the Mars Smart Lander mission, where common MDS software frameworks will be adapted for use in interplanetary cruise, entry-descent-landing, and rover operations. A key architectural theme of MDS is explicit modeling of states. This provides a sound foundation for estimation, control, and data analysis. Certain essential states are relative rather than absolute. Relative states are defined in graph state variables (GSVs) as relationships between nodes in a graph. GSVs are a general graph-based state representation that (1) derives a state´s value by combining relationships, (2) produces different results for different derivation paths, (3) handles changes to topology and relationships between nodes, and (4), represents dependencies between relationships (e.g. correlations). This paper shows example GSV representations for spacecraft orientation, location, trajectories, dynamics, and kinematics.