In-flight pointing calibration model of large aperture antennas for deep space missions

Large aperture antennas and operations at Ka-band frequencies enable higher data rates for deep space missions but require accurate pointing to realize the desired performance gains due to their inherently narrow beamwidth. We describe an in-flight pointing calibration model to aid the design and analysis of large aperture spacecraft telecommunications systems and to inform requirements on the spacecraft attitude control system (ACS) and ground support equipment. Understanding the expected residual in-flight antenna pointing calibration error allows the determination of the potential need for alternative methods to aid spacecraft high gain antenna pointing. The physically based time domain model incorporates both ground station and spacecraft contributions to the residual in-flight pointing calibration error. Spacecraft contributions are dominated by antenna pointing deviations from the commanded pointing positions due to spacecraft ACS performance limitations. The treatment of residual calibration error within a spacecraft's high gain antenna pointing budget is analyzed. The interpretation of in-flight calibration results is discussed. NASA's Europa mission is used as an example to evaluate the utility of this model for future large aperture deep space missions. The mission proposes to fly a 3-m Ka-band high gain antenna for science data return to Earth. Using typical assumptions for ground and spacecraft performance a 3-σ residual pointing calibration error of 0.20 mrad is obtained.