Novel propellant settling strategies for liquid rocket engine restart in microgravity

The active deorbiting and passivation of launch vehicles has become key for the implementation of modern space debris mitigation guidelines. Appropriate engine restart conditions must be provided as part of this process. Ullage motors have been traditionally employed to induce active settling and ensure a gas-free propellant supply to the engines. Although robust and reliable, ullage motors are also heavy, which motivates the study of alternative approaches to the problem. Classic propellant management devices could potentially be employed in this context, but they are hardly applicable to high flow rate cryogenic liquid systems. This paper explores several novel propellant settling strategies that are particularly well suited for cryogenic propellants. In particular, three distinct Magnetic Positive Positioning concepts, a hydrogen-peroxide-based Propellant Gasification System, and a hybrid device that combines both approaches are introduced. The preliminary technical analysis indicates that the successful development of these technologies could lead to mass savings of hundreds of kilograms and economic gains of several hundred thousand dollars per launch.