H. Bruce Land

Instrumentation Development for Micro Pulsed Plasma Thruster Experiments

Miniaturized pulsed plasma thrus ters (PPTs) are poised to fulfill a variety of propulsion tasks on future spacecraft ranging from microsats to expansive space structures. Several varieties of micro -PPTs have been successfully designed and fabricated. Evaluation of these devices require s the development of sensitive techniques for measuring thrust and exhaust characteristics. This paper discusses the development of a miniature thrust stand with a resonant frequency around 300 Hz that can capture the shot -by -shot behavior of the micro PP T device. The steps taken to experimentally calibrate the stand and resolve initial discrepancies with analytic models are discussed. Data recorded to date indicate that impulse bit detections as small as 1 ∝N-sec are possible. This paper also briefly discusses some simple time -of -flight techniques used for measuring plume velocity in these devices.

Micro Pulsed Plasma Thruster Technology Development

Miniaturized pulsed plasma thrusters (PPTs) are poised to fulfill a variety of propulsion tasks on the forthcoming generation of microsats. Indeed the fabrication and operation of micro-PPTs that use an ablating solid propellant have already been proven to be viable. This paper discusses the results of some experiments using 2-D ablative micro-PPTs. These tests were intended to illustrate the effects of thruster miniaturization upon fundamental performance characteristics. Issues that arise when pursuing reliable long-term operation of these devices are also discussed. In an effort to address and circumvent these issues, an alternative micro-PPT concept that uses a vaporizing liquid propellant is presented. The design, fabrication, and preliminary testing of a prototype based upon this concept are discussed.

Experimental Evaluation of a Micro Liquid Pulsed Plasma Thruster Concept

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.

Addressing arc flash problems in low voltage switchboards: A case study in arc fault protection

Marine switchboards are manufactured to specifications similar to industrial switchboards but sustain arcing faults more frequently. Thus, the marine environment can serve to accelerate aging, showing what industrial switchboards will experience over time. U.S. Navy data are used to show that faulty connections are the primary cause of arcing faults in marine switchboards. Various approaches to arc detection and to the prevention of arcing failures will be examined. The approaches which were integrated into an automatic arc fault protection system for the Navy will be discussed. The historical effectiveness of arc fault protection systems on Navy ships will be discussed. The authors believe that the success achieved in this harsh marine environment is statistically significant and holds lessons for the deployment of arc fault protective systems in critical land-based power distribution systems.