Detailed Characterization of Magnetic Fields Surrounding the Whorl Ii Spacecraft Simulator and Application to Attitude Determination

The research presented in this report focuses on the Whorl II spacecraft simulator in Virginia Tech’s Space Systems Simulation Laboratory (SSSL). The goal of this research is to improve the reliability and accuracy of the magnetometer aboard Whorl II that is used for attitude determination. Magnetic interference surrounding the simulator causes unacceptable margins of error its perceived attitude. The first step in solving this problem was to characterize the magnetic fields surrounding the simulator. With this information, it was determined that the primary cause of magnetic interference is the ferrous, steel pedestal that supports the simulator. The behavior of the magnetic interference and the role of the magnetometer in attitude determination led to the final solution: to redesign the method of magnetometer calibration. This new method calibrates the raw magnetometer data dynamically, meaning that the calibration method changes in response to the position of the simulator. This significantly improves the accuracy of the magnetometer in attitude determination. 1. Spacecraft Simulators The Space Systems Simulation Laboratory (SSSL) at Virginia Tech houses the Distributed Spacecraft Attitude Control Systems Simulator, or DSACSS. The primary purpose of the DSACSS is to provide a test bed to aid in the development of distributed control laws for the pointing and spacing of a formation of satellites. DSACSS is actually composed of two separate spacecraft simulators, Whorl I and Whorl II. These simulators are mounted on spherical air bearings to simulate floating in a space environment. Whorl I (Figure 1) is in a tabletop configuration that enables full freedom in yaw and ±5° of tilt in pitch and roll. Whorl II (Figure 2) is in a dumbbell configuration that enables full freedom in yaw and roll with ±30° of freedom in pitch. 2 These simulators employ most of the same components for sensing and controlling their motion and orientation. For control, the simulators use momentum wheels and cold gas thrusters in each axis. For sensing, they use 3-axis accelerometers and magnetometers. The accuracy of these sensors is key to the work being done by researchers in the lab. Figure 1: Whorl I spacecraft simulator with its magnetometer circled at the end of its boom. 7 Figure 2: Whorl II spacecraft simulator with its magnetometer circled at the end of its boom. 7 Yaw, pitch, and roll axes are labeled. Yaw Axis Roll Axis Pitch Axis