International space station electrical power system performance and operational lessons learned

The electrical power system of the International Space Station (ISS) represents the largest space-based power system ever designed. After more than a year of real-time operations of the ISS EPS, numerous power system operations and resource management lessons have been learned. This work first provides details of the electrical power system architecture and electrical system hardware used on the ISS, along with comparisons between the specified performance and the actual performance of the system and its components. Nominal operations as well as some of the anomalies seen in the first year of operations are then described, and lessons learned from these experiences are discussed. Attention is also given to the operational flexibility designed into the system. The ability to modify operational setpoints and update onboard software and firmware have provided the operations team with the tools necessary to work around many system anomalies. This work describes these design features, provides examples of how they have been used, and provides operational flexibility recommendations for future vehicle designs. This work further describes the telemetry used to monitor the health and performance of the electrical power system. Examples of data that has been useful in monitoring the system as well as in troubleshooting anomalies are provided. Recommendations are provided for modifications to the telemetry stream that would make operations more effective. Numerous lessons learned relative to power resource management are given. Vehicle design robustness and sizing of the power system have had a direct and ongoing impact on the amount and complexity of the operations resources required for ISS power and energy management. During the build up of the space station, very tight power margins often exist. This factor, coupled with the desire to optimize power availability to the payloads, has resulted in an operator-intensive power resource management challenge. This work describes the complexity of these operations and includes recommendations for reducing this complexity.