Bipropellant Enabled Solid Oxide Fuel Cell Stack Power Supply: Energy Agility for Space Vehicles

Abstract

Spacecraft often have instances where they are required to operate for long periods of time with significant power requirements and no access to solar power. While a battery system could be designed to meet these occasional, and possibly unexpected requirements, creating a power supply to meet these infrequent demands results in having a battery system that is excessively large, massive, and inefficient. A Solid Oxide Fuel Cell (SOFC) system capable of running on the same fuel and oxidizer as the onboard thruster of a bipropellant thruster equipped spacecraft can eliminate much of the added mass and volume needed to enable batteries to meet extreme power demands and create more operational flexibility on how the chemical energy in stowed bipropellants are used. If the spacecraft needs thrust, the bipropellant can be ignited to provide thrust. If the spacecraft needs electric power, the spacecraft can consume bipropellant to generate auxiliary power. In this work, the proven bipropellant pair ammonia (NH3) and nitrous oxide (N2O) are shown to be a viable fuel and oxidant for hydrogen (H2) consuming air breathing SOFCs, as spontaneous NH3 decomposition will generate H2 and spontaneous N2O decomposition will generate O2. A scale up to a 5-cell SOFC stack fed NH3 and N2O produced power up to ~89W. Higher power can be achieved by scaling up the number of cells in a stack to achieve required power demands. The results of this study demonstrate the potential and feasibility of integrating SOFCs with a bipropellant thruster to creating a dual functioning spacecraft system that can satisfy operational power requirements and on-orbit maneuverability.This material is based on research sponsored by Air Force Research Laboratory under agreement number FA9453-21-C-0060. The views expressed are those of the authors and do not reflect the official guidance or position of the United States Government, the Department of Defense or of the United States Air Force. Approved for public release; distribution is unlimited. Public Affairs release approval #AFRL20230023. Figure 1