Using xPC Target to test the control system of a nano satellite

This paper demonstrates the use of xPC Target system to simulate the space environment for testing and verifying the control system algorithms of a nano satellite. Setup includes a Host and a Target system connected via an appropriately selected communication link. Target system is connected to a data acquisition card through PCI bus. In this paper, a satellite system with magnetic actuation using magnetorquers is considered. In the proposed setup, Simulink environment is used in the Host system to model three sensors - GPS, sun sensor and magnetometer. The designed Simulink model predicts the real time space environment values for the spacecraft. These predicted values are compiled in the Host system, and output is transferred to the Target system. The Target system is configured to run Simulink at a kernel level to provide real time simulations. Data acquired at I/O ports of Target system is provided to the controller running attitude determination and control systems algorithm. The attitude values predicted by the controller are compared with the simulated sensor values, and the error rate is calculated. This error rate determines the current measure to be passed through the magnetorquer. In addition, current measure at the output is given as a feedback to the Simulink model for the prediction of the next set of sensor values. A Matlab based data acquisition tool is used to provide initial sensor readings and to monitor all the input and output parameters in real time. An analysis of complete hardware in loop simulation is described, and simulation results are provided in this paper.