Design of an Attitude Control System for a High-Altitude Balloon Payload

Physicists seek to uncover expansion history of the universe by examining polarization patterns in the cosmic microwave background (CMB). Observatories in the South Pole are used to examine these polarization patterns, but no sucient celestial source exists to properly calibrate these observatories. A method of calibrating these observatories would be to point a tuned microwave source to the ground-based observatory from a far distance. The purpose of this paper is to outline how the McGill High-Altitude Balloon (McHAB) team intends to use a high-altitude balloon with a reaction wheel actuator to slew and point the payload at altitudes of 15km to 20km to within an accuracy of 2 . A complementary lter with an inertial measurement unit (IMU) will be used to estimate the attitude of the payload. A proportional-derivative controller will be used to control the reaction wheel, and hence point the payload to a desired angle. The main processor will be a Raspberry Pi, a single-board computer using a single-core 700MHz ARMv6 CPU. The team has previously own a payload, McHAB-1, containing the Raspberry Pi and an IMU to test the attitude estimator and collect attitude data. The team has own a complete prototype of the system, McHAB-2, on April 28th, 2013. Data from this ight is presented showing that the reaction wheel can better point the system as the platform reaches higher altitudes.