David Krejci

Development of a µPPT for CubeSat Applications

An analytical model based on an oscillatory circuit equation and dynamic equation for a uniform plasma slug has been developed in order to provide a design tool which is able to predict the dependence of µPPT performance on electrode configuration and circuit paramters. The results of the model show good aggrement with experimental results and have been implemented to improve µPPT performance. Thruster performance has been experimentally characterised for a capacitance range of 2 to 31 µF and propellant surface areas of 0.25 to 1.5 cm2 for low energy operation. Results indicate that the impulse bits required for picosatellite missions are achievable with the application of miniaturised thruster heads and energy densities of approximatley 5 to 10 Jcm2.

Assessment of Catalysts for Hydrogen-Peroxide-Based Thrusters in a Flow Reactor

Hydrogen peroxide is a candidate propellant for rocket-propulsion applications with the potential to replace highly toxic propellants currently used. Decomposition of hydrogen peroxide yields a high-temperature oxygen-steam mixture, which can be used as monopropellant or as oxidizer in a bipropellant configuration. This work examines different types of cellular ceramic-based catalysts for hydrogen-peroxide decomposition at miniature scale of nominal mass flows of 0.3  g s−1. An exhaustive investigation of different catalysts in a flow reactor configuration similar to a propulsion application is conducted. The test matrix includes honeycomb monoliths with different channel geometries, densities, lengths, different carrier materials, and wash-coating procedures, as well as different types of catalysts such as pellets and foams. Thirty nine catalyst configurations with a total of 121 catalysts have been experimentally investigated based on their transient and stationary performance at design mass-flow levels...

Hydrogen Peroxide Decomposition for Micro Propulsion: Simulation and Experimental Verification

Hydrogen peroxide is under investigation with regard to its potential to replace the presently used highly toxic oxidizers such as NTO or MON-3. Catalytically decomposed hydrogen peroxide results in a steam-oxygen mixture at elevated temperature and can be used either as a monopropellant or as an oxidizer in a bipropellant system. In order to achieve high decomposition efficiencies it is essential to understand and to be able to control the decomposition processes in detail. In particular, the choice of catalyst is one of the most essential issue in designing a propulsion system based on hydrogen peroxide. However a catalyst is defined by a multidimensional parameter matrix including the catalyst nature, diameter, length, inner and outer shape, heat capacity and conductivity of the carrier material, and, manufacturing method and many others. Reliable experimental investigation of a catalyst is a time consuming effort. To guide the experimental assessment, Fotec (formerly Austrian Institute of Technology – AIT) has developed an analytical model of the decomposition implemented into a numerical thermal model. The one dimensional decomposition model coupled to a finite element structural domain of the decomposition chamber is used to investigate the impact of the catalyst and, in addition, of the chamber structure on the decomposition behavior. Special focus is laid on the transitional behavior of hydrogen peroxide conversion to facilitate immediate start-up of the thruster system. The numerical results have been validated with experimental values. The comparison shows high accuracy of the predictions not only in the general decomposition behavior but also in intrinsic details such as the transitional behavior. Major findings of the model such as the existence of a radial temperature gradient across the catalyst have been experimentally validated. These findings point to an overestimation of experimentally determined decomposition performances, in the case of temperature measurements just downstream of the catalysts cental line. Another major finding is the identification of an mass flow overload threshold by the simulation, yielding a sudden decrease in decomposition performance after surpassing the threshold. This sudden decrease in decomposition performance has been experimentally verified.

Analytic model for the Assessment of the Electrode Configuration of a µPPT

The analytic model presented is aimed at understanding the dependency of Micro Pulsed Plasma Thruster performance on electrode geometry parameters. An advanced, one dimensional electromechanical model, based on accurate inductance calculation and a detailed description of the inhomogeneous magnetic field distribution accelerating the plasma, will be introduced. Including effects of inhomogeneity in an analytical model of a µPPT not only enables an accurate description of the plasma acceleration process for configurations with large propellant height compared to width, but can also be a valuable design tool regarding thruster geometry and its impact on performance. The effect of electrode separation and thickness on plasma acceleration and performance will be discussed, as well as the influence of changing electrical parameters. The impact of flared electrodes is investigated and found as a possible way to increase energy transfer into the plasma and therefore thruster performance. The model is validated by comparison to data from experimental investigation on a miniaturized Pulsed Plasma Thruster.