Crewed space vehicle training has always required highfidelity models of vehicle systems. Many of these systems, particularly of the “flow” variety, benefit from modeling the system as a whole, rather than relying only on the interactions between individual components. In general, system properties (temperatures, voltages, flow rates, etc.) are modeled both internal to and between physical components (valves, batteries, etc.). Lacking knowledge of the system atlarge, integration of flows between individual components is extremely difficult without incurring model instability and errors. The same analogous problem applies among fluid, thermal, and electrical systems. Nodal analysis is a method commonly used in industry to avoid this problem by representing these systems as a simultaneous system of equations.

The goal is to have a single, consistent software tool for modeling electrical, heat, and fluid states of space vehicle systems with sufficient fidelity and efficiency to support real-time, fulltask and part-task training of vehicle crew and flight controllers. The tool takes advantage of analogous concepts among all three disciplines to improve code reuse and maintainability. The tool uses nodal analysis to solve large systems (networks), and is flexible and extendable enough to be applied to future hydraulic and propulsion systems as needed.

GUNNS is a flow system modeling software package that combines nodal analysis and the hydraulic-electric analogy to simulate fluid, electrical, and thermal systems. It has sufficient compactness and fidelity to model these aspects of space vehicles in real time for vehicle crew and flight controller training. It has a reusable component and system design that allows integration with a graphical user interface (GUI), providing capability for rapid GUI-based simulator development, ease of maintenance, and associated cost savings. GUNNS is compatible with and optimized for NASA’s Trick simulation environment, but can be run independently of Trick.

Potential applications include realtime simulation of flow systems (fluid, thermal, electrical), particularly in space vehicles. Applicable uses include fluid simulation of life-support systems and cabin atmosphere, coolant loops, and propulsion and hydraulic systems. Thermal applications include passive and active thermal control systems. Electrical applications include DC circuit and electrical power systems.

This work was done by Jason L. Harvey, Teems Lovett, and Kevin Supak of L-3 Communications Corporation for Johnson Space Center. MSC-25468-1