PRESSURE LOSSES IN A NOVEL, VISCOUS SPACECRAFT PROPELLANT AND IMPACTS ON COMPATIBILITY WITH TRADITIONAL MONOPROPELLANT ARCHITECTURES

Abstract

Hydrazine offers a unique list of benefits as a spacecraft propellant that have made it the most selected fuel for chemical in-space propulsion, either in its pure form or as one of its derivatives. This is true for both monopropellant and bipropellant applications, as one of pure hydrazine’s many benefits is the ability to simultaneously operate in both modes. However, hydrazine is also very hazardous and requires significant logistics to work with on the ground. As a result, there has been an industry-wide search for high-performance replacements that mitigate the hazards and associated logistics. These have been collectively termed ‘green propellants’. Two of the most well-known green propellants, ASCENT and LMP-103S, are ionic liquids that propose to completely replace hydrazine. The focus of this thesis is a third green propellant known as Green Hydrazine Propellant Blend (GHPB). GHPB retains hydrazine as a base constituent, but as a hybrid between the conventional and ionic classes of propellants, it is considered less hazardous. Unlike the previous green propellants, GHPB is designed to be used as a ‘drop-in’ replacement with existing hydrazine architectures. However, it is much more viscous than hydrazine leading to uncertainties about pressure losses and cavitation. The objective of this thesis is to relieve some of this uncertainty by measuring pressure loss and flow rate in four common propulsion system components (a latch valve, a filter, and two venturis) over a range of flow rates that are representative of those encountered in an operational spacecraft. The data are used to infer the minor loss coefficient (for non-cavitating flows) and the discharge coefficient (for cavitating flows) as functions of flow rate for each component. Knowing the values of these coefficients is crucial for predicting thruster injection pressures and hence for designing a propellant delivery system. The values of these coefficients as well as the true pressure losses are plotted as functions of flow rate. Pressure losses are found to be approximately 5 times higher than those associated with hydrazine for a given flow rate. These results are put into context by using them to calculate the pressure distribution in the propulsion system of the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) spacecraft if hydrazine were replaced with GHPB. The results show that total pressure losses would be 3-14 times greater with GHPB than with hydrazine over the course of the PACE mission. However, GHPB’s higher viscosity also reduces the amplitude of pressure transients associated with startup by about a factor of 3. This means that the venturis needed to protect valves from startup transients in hydrazine-based systems are not needed with GHPB. Eliminating the venturis reduces the total pressure losses associated with GHPB to 1.7 – 8.5 times those associated with hydrazine.