Attitude Optimization to Increase Scientific Data Returned from the EXACT and IMPRESS CubeSats

This paper presents a method to improve mission performance for Cube Satellites (CubeSats) with scientific missions. The proposed approach proactively plans slew maneuvers which trade mission objectives against power constraints. There are many scientific CubeSat missions which require pointing a sensor payload at a target in space. During the design phase of these missions there exists a trade-off between ambitious missions with many pointing targets, and hardware cost. In the past, many CubeSats have used naive event-triggered mode switching-e.g. slewing towards a ground station for downlinking only when it becomes visible rather than in advance-which serves to reduce the total amount of scientific data transmitted to the ground over the mission lifetime. In this work, we develop a mission planning method that maximizes data volume downlinked over attitude history. We formulate the optimization problem as an integer program over the space of attitude histories and subject to battery level constraints. The optimal solution is an attitude sequence that can be used as a reference for a low-level controller to track. We demonstrate the approach using simulated data for the upcoming CubeSat EXACT, which has a celestial scientific target in addition to requiring ground-pointing for data transmission and Sun-pointing for power. Extensions of the work to benefit the related CubeSat IMPRESS are also discussed. Using the quality metric of total data volume received on the ground, we demonstrate the effectiveness of this approach in maximizing downloaded science data while maintaining the battery within operating limits.