Automation of Operations for a Spacecraft in Geo Transfer Orbit

Operating a spacecraft in an elliptical geo transfer orbit throughout the mission life presents multiple constraints and unique operational challenges. The long-term operation at lower perigee altitudes in the presence of atmospheric drag compounds momentum build-up and necessitates optimized momentum desaturation cycles. When perigee height is not maintained, atmospheric drag affects the apogee height. Reaction wheel speeds vary drastically with each perigee passage and due to external disturbances, requiring periodic thruster operations to maintain wheel speeds within limits and ensure stable attitude. To address these complexities, operational strategies have evolved from initial manual ground commands to automation with effective utilization of onboard features, notably leveraging the On-Board Timer (OBT) system for all key tasks such as solar array positioning at perigee, eclipse operations, auto momentum dumping during non-visibility periods, perigee raising maneuvers and payload operations. Attitude control switches efficiently between inertial (sun-safe) and payload (earth-oriented) modes to achieve operational requirements amidst time-varying visibility windows and frequent eclipses. Comprehensive automation was progressively implemented to manage constraints like overhead pass, varying signal and power levels, and limited station visibility without using external station support, ultimately allowing the spacecraft to maintain service and optimize payload usage in an elliptical orbit. This progression streamlined ground resource usage and provided valuable lessons for future satellite missions operating under non-ideal conditions and prolonged orbit raising, such as electric propulsion system-based orbit raising.