ATTITUDE DETERMINATION AND CONTROL APPROACH TO ACHIEVE CO-LOCATED MICROWAVE RADIOMETER AND GPS RADIO OCCULTATION MEASUREMENTS ON A NANOSATELLITE

The Microwave Radiometer Technology Acceleration (MiRaTA) mission is a 3U CubeSat that was selected by the NASA Earth Science Technology Office to demonstrate a new tri-band passive microwave radiometer for sensing temperature, water vapor, and cloud ice and the use of a GPS radio occultation (GPSRO) experiment for temperature calibration, as well as supporting subsystem technologies such as the attitude determination and control system (ADCS). These new sensing modalities can dramatically enhance the capabilities of future weather and climate sensing architectures. The MiRaTA mission will demonstrate high fidelity, well-calibrated radiometric sensing from a nanosatellite platform. The radiometer and GPSRO technology elements are currently at TRL5 but will be advanced to TRL7 at mission conclusion. This demonstration mission, nominally to be launched and deployed into a 600 km sun-synchronous orbit in 2016, will mark the first implementation of temperature and humidity radiometric sounding and GPSRO atmospheric sounding on a single 3U CubeSat. The attitude determination and control performance of the MiRaTA nanosatellite is critical to mission success. A deliberate slow pitch-up maneuver from radiometer nadir pointing to 90-105 degrees and back will be periodically executed to permit the radiometer and GPSRO observations to sound overlapping volumes of atmosphere where sensitivity, calibration, and dynamic range are optimal. Enabling this agility with a nanosatellite platform requires an ADCS capable of performing, among other tasks, successful detumble after deployment and maintaining three-axis stable pointing to a goal of +/-1 degrees of accuracy during science operations throughout the mission. We describe the sensor and actuator selection, flight software development, end-to-end modeling techniques, and hardware-in-the-loop testing planned for MiRaTA.