Reaction Wheel Performance Characterization Using the Kepler Spacecraft as a Case Study

摘要

The Kepler spacecraft had lost two of its four reaction wheels by 2012, and the Kepler attitude engineers were forced to create a novel concept of operations to continue the mission. Monitoring the health and performance of the surviving wheels became a critical task, as loss of another wheel would be mission-ending. To support these efforts, a group of students at the Laboratory for Atmospheric and Space Physics developed, verified, and refined an analysis tool to identify changes in reaction wheel behavior. The tool compares the data we are interested in analyzing to a verified set of baseline data, then filters the comparison to further highlight trending. The baseline data is created for each wheel independently, and it associates commanded torque to reaction wheel speed. The tool compares the measured data from the spacecraft with the baseline, producing a set of residuals that we call delta torque. These values are passed through a Kalman filter and the resulting trend line is studied to find changes in behavior. We have identified torque changes that occurred in the two failed wheels before they were lost completely. Since the start of K2, our tool has also identified friction events in the remaining two reaction wheels. This tool was developed specifically for the Kepler mission, but the method could be easily applied to any mission that uses reaction wheels.