High fidelity GPS satellite simulation

Abstract

Lockheed Martin Federal Systems is developing a high fidelity simulator for the Air Force's Global Positioning System (GPS) satellite command and control operations. This paper discusses the system architecture of the high fidelity GPS simulator, the handling of the state data for a simulation, and lastly, the space vehicle subsystem dynamic modeling algorithms. The system architecture consists primarily of a symmetric multiprocessor performing processor intensive functions of Space and Environment Simulation while a set of distributed workstation processors implement an assortment of user and communications interfaces. Simulation runs use a large set of state data pertaining to both the space vehicles and ground components. Users are able to manipulate a set of initial conditions (state data) before a run, and are able to save sets of state data at any point during a run. These sets can then be used as initial conditions for a subsequent run, in effect allowing a backingup capability for the simulations. In the area of dynamic subsystem modeling, this paper describes the algorithms that simulate each space vehicle subsystem as well as trades between model execution time and model fidelity. Subsystems discussed include orbit determination, thermal control, electrical power, telemetry, tracking, and commanding, and attitude determination.