STAR TRACKER REAL-TIME HARDWARE IN THE LOOP TESTING USING OPTICAL STAR SIMULATOR

Abstract

The demand for highly accurate attitude determination sensors has increased in the last few decades. One of the best and more accurate attitude determination sensors for spacecraft is the star tracker, which determines 3-axis attitude with an accuracy of a few arc-secs. In order to achieve this high accuracy, the star tracker hardware and software can be tested on-ground with an accurate optical simulator. This work presents an open-loop and closed-loop hardware test bench to demonstrate a star tracker’s functionality. The test bench consists of an optical star field simulator, a real-time simulation computer and the star tracker to be tested. A dSPACE real-time simulator is used to simulate vehicle attitude and the associated sky image is provided as input to the star tracker camera using the optical simulator. To close the simulation loop, the dSPACE simulator can respond to the star tracker measurements by changing the vehicle dynamics and thus the simulated star field image. The hardware-in-the-loop test bench was used to test the star tracker for the Hybrid Navigation Experiment for the SHEFEX-2 sounding rocket mission, which will be launched in late 2011. The test bench was first calibrated and aligned to remove errors in the simulation. End-to-end results using both the open- and the closed-loop test benches are then analyzed and discussed, which include measuring the total turn-around time and maximum vehicle rotation rate for the star tracker.