Automated Test and Acceptance System for Battery Cells and Battery Packs for the Development of Highly-Efficient Battery Packs for Small Spacecraft

Abstract

CubeSat missions are flying a variety of battery technologies and range of battery capacities. As the CubeSat form factors continue to grow in size, the battery capacities will need to grow too. Thus maximizing battery capacity and the efficiency of battery packs are increasingly more important. To address this need for our university-built CubeSats, a new automated system used for flight testing battery cells was developed to optimize the capacity and long-term performance of a battery pack. The important steps of creating a low-cost, highly-efficient battery pack are described in detail, along with an overview of the safety acceptance testing for CubeSats deployed from the International Space Station (ISS), a location with some of the most demanding acceptance criteria, and often used as a launch platform for CubeSats. These steps include selecting the battery pack materials, developing the testing hardware and related automation software, and selecting matched battery cells for the flight battery packs. Our automation software is publicly available. The task of matching the maximum voltages and capacities of individual battery cells is an important but often time consuming process if not automated. Our battery test system autonomously charges and discharges multiple Lithium Polymer cells independently and at the same time tracks the current, voltage, and elapsed time of each cycle for capacity calculations. From these results we can combine cells to maximize the capacity for a flight battery pack. This battery test system also provides automated battery pack charge / discharge cycling to identify the battery packs with the higher efficiencies to be selected for flight. The measured state of charge curves for a battery pack, and the trending of those curves, is important for mission planning and operations. Our battery test system is low cost, and the build and test processes are easy to replicate, making it highly desirable for small spacecraft.