Improvement of an iodine compatible fluidic subsystem at TRL 6
Improvement of an iodine compatible fluidic subsystem at TRL 6
The fluidic sub-system is responsible for delivering a certain mass flow rate of gaseous propellant depending on the mission needs. To obtain the desired thruster performance and efficiency throughout the thruster’s life, the mass flow should be constant within a certain degree of error. SO-3 is dedicated to the improvement of the iodine fluidic line developed by T4I for the Regulus-50 propulsion unit4, currently at TRL 8. The main components of the fluidic line are a flow regulator, an injector, and a tank interface. The flow regulator is the technologic core of this sub-system, it has the delicate duty of maintaining the mass flow rate constant by means of a pair of actuators and pressure and temperature transducers. The present capability of the fluidic line is to provide a 0.1 mg/s mass flow rate with a stability of ±5%. Due to the reactivity of iodine, all the components wetted by the propellant are made of materials that present extremely high chemical compatibility with this compound. The improvements that are targeted for this project can be summarized in the following four points:
1) Employment of custom-made actuators specifically designed to be used with gaseous iodine.
2) Improvement of printability, repeatability, and cost effectiveness of Additive Manufacturing (AM) processes by means of an iterative design & manufacture process.
3) Reduction of fluidic system mass by using advanced materials and surface treatments.
4) Optimization of the thermal paths towards the mechanical interfaces.
The first point is of the outermost importance given the absence of Commercial Of-The-Shelf (COTS) micro-fluidic actuators that can work at the operative conditions imposed by the presence of iodine, i.e., temperatures higher than 100 °C, very low pressure in the order of tenths of millibar, extremely corrosive environment. T4I, and its historical providers, has been iterating the development of new actuators whose design is tailored on iodine compatibility, since the early development of Regulus-50.
The second point stems from the fact the current fluidic sub-system is 100% 3D-printed with metal AM technologies. The need of miniaturizing the system called for an extremely focused optimization of the volume budget. Specifically, design-manufacturing iterations between T4I and AM providers proved to be essential. The challenge here is to improve the repeatability of the AM process in the perspective of the industrialization and a possible mass production of this sub-system.
The third point concerns the fact that most of the materials that exhibit a good or excellent compatibility with iodine, present a high density resulting in relatively heavy components. The use of state-of-the-art surface treatments could reduce the subsystem mass to one third of the current design.
Last but not least, since the fluidic subsystem must be kept at the same temperature of the sublimated iodine (e.g., > 100 °C) it is very important to minimize the thermal losses toward the interfaces to (i) reduce the pre-firing operations (pre-heating of the system) and (ii) to increase the overall system efficiency since the power lost in thermal dispersion is directly related to a decrease of the electric power available to the thruster.
As a result, SO-3 is a propaedeutic activity to improve and standardize the propellant management technology in order to develop a building block that can be suitable for many types of electric propulsion systems.