Simulation of LEO Missions with NiH or LiIon Batteries Including Dead Bus Recovery Using the Power Tools Suite EPS Simulation Codes

Abstract

*The Power Tools Suite (PTS) has been under development at Lockheed Martin for many years and is being used in the simulation of several satellite programs. PTS includes a large library of models for the simulation of Electric Power System (EPS) components. These include various solar array (SA) cells, various battery cells (e.g. Nickel Cadmium, Nickel Hydrogen, Lithium Ion), different types of battery charging units and techniques, different harness, bus bar, and cable losses, and different load requirements (e.g. constant power or constant current). These models include the effects of light intensity (for SA), voltage, current, temperature, DOD (for battery cells), and aging. The simulation codes also include a sizing code and a dynamic simulation code. The sizing code determines the sizes of the battery and the solar array in order to satisfy the mission or sizing requirements. The dynamic code simulates the time-dependent behavior of the EPS over any given mission duration, such as either during a worst case scenario, or from pre-launch to final ascent. The time steps are user defined, and the user provides all of the time-dependent input variables and the required EPS loads as input. This paper discusses the application of the PTS Tools and Codes to a typical Low Earth Orbit (LEO) unmanned spacecraft using either Nickel-Hydrogen (NiH) or Lithium Ion (LiIon) batteries in the EPS. The use of a LiIon battery may require significant changes in the design of the EPS bus to satisfy the mission requirements for a particular LEO mission. Such changes are discussed as far as proprietary restrictions will allow. The impact of a possible new requirement “Dead Bus Recovery” on the EPS design is also addressed.