Design of Sun-Safe Controllers for Lunar Atmosphere and Dust Environment Explorer

This paper presents the development of sun-safe controllers, which are designed to keep the spacecraft power positive and thermally balanced in the event an anomaly is detected. Employed by NASA’s Lunar Atmosphere and Dust Environment Explorer, the controllers use the measured sun vector and the spacecraft body rates for feedback control. To improve the accuracy of sun vector estimation, the least-square minimization approach is applied to process the sensor data. A rotation with respect to the sun vector, which is proven to be effective in mitigating the momentum buildup due to the lunar gravity gradient, hence significantly extending the sun-safe duration, is commanded. To validate the controllers, the Lunar Atmosphere and Dust Environment Explorer spacecraft model engaging the sun-safe mode is first simulated and then compared with the actual Lunar Atmosphere and Dust Environment Explorer orbital flight data. The results demonstrate the applicability of the proposed sun-safe controllers.