Photovoltaic electrolysis propulsion system for interplanetary CubeSats

CubeSats are a new and emerging low-cost, rapid development platform for space exploration research. Currently, CubeSats have been flown only in Low Earth Orbit (LEO). Advancements in propulsion can enable these spacecraft to achieve capture orbits around the Moon, Mars and beyond. Such enabling technology can make science-focused planetary CubeSat missions possible for low cost. However, Cubesats, because of their low mass, volume and launch constraints, are severely limited by propulsion. Here we present an innovative concept that utilizes water as the propellant for a 6U, 12 kg, Interplanetary CubeSat. The water is electrolyzed into hydrogen and oxygen on demand using onboard photovoltaic panels, which would, in turn, be combusted to produce thrust. However, important challenges exist with this technology including how to design and operate high efficiency Polymer Electrolyte Membrane electrolyzers at cold temperatures, how to efficiently separate the water from the hydrogen and oxygen produced in a microgravity environment and how to utilize the thrust generated to produce efficient trajectories. Our proposed solution utilizes a centrifuge that separates water from the reactants. The system uses salts, such as lithium chloride, to reduce the freezing point of water. Our techniques identify a method to operate the propulsion system up to -80 °C. Analysis of the combustion and flow through the nozzle using both theoretical equations and finite-volume CFD modeling shows that the specific impulse of the system is in the 360 s to 420 s range. At this efficiency, and from preliminary results a 12 kg CubeSat with 7.8 kg of propellant provides a Δν of 4,400 m/s. In theory, this is sufficient for Lunar or Mars capture orbits once deployed from LEO. These feasibility studies point to a promising pathway to further test the proposed concept.