EPS Sensitivity Studies Using the PTS Simulation Code for Specific Satellite Applications

Abstract

The Lockheed Martin Power Tools Suite (PTS) code has been developed and updated to provide detailed simulation of the entire Electric Power System (EPS) for general satellite missions. The code is able to model various EPS architectures, including the standard A2100 and A2100M busses. The code contains a large library of EPS component models to simulate the operation of each EPS component, including non-linear operational models for various solar array cells, batteries, and diodes. The solar array modules include models for cells, strings, string diodes, groups, group diodes, wire harnesses, slip rings, cabling, wings, sunlight variation, and aging effects. The battery modules include models for cells, diodes, one battery, the total battery, charging and discharging efficiency models, battery heaters, battery heating, changing temperature, harness, cabling, and aging effects. The bus modules include models for diodes, cabling, and current distribution to the loads. Various load modules are included to simulate the given constant power or constant current load profiles which vary with time during the mission. A major concern in the operation of such satellite systems is the prediction of the maximum state-of-discharge (SOD) of the batteries during the most challenging mission phases. Missions designed for low Earth orbit, for medium Earth orbit, and for geosynchronous Earth orbit each have an expected limit of the maximum SOD at mission stages and at end-of-life. The effect of each of the mission input parameters on the SOD at such stages is examined for specific satellite missions. The parameters that contribute the most affect to the SOD are identified and discussed. These results are also directly applicable to the Hubble Space Telescope battery depletion problem. The use of these PTS code models enables much more accurate simulations of EPS behavior, battery degradation, and lifetime estimates that are needed in the Aerospace Industry today.