Researchers at The Johns Hopkins University Applied Physics Laboratory (APL) have developed a novel miniaturized pulsed plasma thruster (PPT) concept that utilizes a liquid propellant. Such devices could theoretically provide ultra-low dry mass, high specific impulse (Isp), flexible propellant options, and long-term reliability in a single package. Experimental devices have been designed and fabricated to help evaluate the concept. Typically, these devices have been powered by 0.5 1.0 μF capacitors at 200 700 V. Electrical discharge characteristics have been measured and peak currents have been estimated to be about 1.9 kA for a device powered by a 0.937 μF capacitor at 600 V. Impulse bit measurements have been facilitated by a custom-built thrust stand. The thrust stand was calibrated by dropping small nylon balls on the thruster and measuring the momentum transfer with a high speed camera. Impulse bits from a thruster powered by a 0.937 μF capacitor over a 200 700 V range were found to vary from 0.4 – 0.6 μN-s. Additional testing and analysis techniques are planned to quantify the propellant mass consumed per impulse bit. These and further experiments can be used to evaluate and improve microliquid PPT (MILIPULT) devices.

We address the burning of propellants with randomly distributed pores by making simplifying assumptions and developing two simulation methods based on those assumptions. One method represents the propellant and pores as a 3-dimensional matrix of cubic cells, and the other method represents pores as perfect spheres that expand after ignition. Convergence studies performed for both methods determine the appropriate running conditions. We compare the two methods as well as theoretical lattice results, and show that, for porosities between 0.02 and 0.1, the random pore distributions have higher burn speeds than any of the lattices, while for porosities between 0.001 and 0.02 some lattices have higher burning rates than a random distribution of pores. The matrix method also has higher burn rates than the spherical expansion method due to the inherent inaccuracy in the use of cubic cells to approximate the domain. We use a time delay for pore ignition in the expansion method in order to match results from the literature. The required delay results in burning through 40% of the pore radius before the rest of the pore ignites.

We have developed a micro-scale pulsed plasma thruster (PPT) that uses water vapor as propellant and produces impulse bits on the order of 1 µN-s. Thrusters on this scale are valuable for use on small satellites, to provide attitude control or stationkeeping with a small mass and low power. Measuring the performance of such a small thruster can be very challenging, so novel methods are required. In this paper, we will present progress on the development of a vibration-based thrust stand for use with very light, low thrust devices. We attach a thruster to a metal flexure that vibrates when the thruster fires, while an interferometer measures the vibrational displacement. To calibrate the response, we drop small balls onto the thrust stand while recording with a high-speed camera to determine the impulse bit. We present three dierent methods for correlating the impulse bit to the vibration pulse wave. Impulse bit measurements are given for various thruster configurations as a function of the voltage of the main thruster discharge. The impulse bit curves do not change by a large amount between the thrusters, indicating that the thrust stand provides consistent results.