Preliminary results of a sublimating propellant tank for dedicated micropropulsion system

Abstract

One of the micro-propulsion research activities currently conducted at Delft University of Technology is concerned
with the development of a low-pressure micro-resistojet based on a sublimating solid propellant. Specifically
the heater chip and expansion slots for this thruster have already undergone extensive research and testing and are at a very good level of maturity. In contrast, the propellant tank still requires some numerical and experimental analysis and is currently considered the main obstacle towards full implementation of this system in a spacecraft. The tank shall be designed to work with sublimating water ice, at temperature and pressure not exceeding 273 K and 611 Pa respectively, which are the triple-point conditions of water. A simple test vial, outfitted with a simple heater, as well as temperature and pressure sensors was filled with demineralized water. This was in turn frozen prior to placing the vial on a weighting scale in a vacuum chamber, which was used to measure the mass flow rate of sublimation. The experiments performed were adjusted gradually throughout the course of the project according to the data gathered up until a certain point. The final experiments clearly demonstrated the basic theory of sublimation and most importantly, how the mass flow rate due to sublimation can be manipulated by aid of the heater which accelerates the sublimation process up to a certain point. These first series of experiments will be followed by a second series, encompassing a more dedicated tank design in which pressure and the temperature at the crucial air/ice interface can be better controlled. These experiments form the basis for the design of an optimally controlled propellant tank, based on the concept of sublimation.