Thrust Stand for Electric Propulsion Performance Evaluation

An electric propulsion thrust stand capable of supporting thrusters with total mass of up to 125 kg and 1 mN to 1 N thrust levels has been developed and tested. The mechanical design features a conventional hanging pendulum arm attached to a balance mechanism that transforms horizontal motion into amplified vertical motion, with accommodation for variable displacement sensitivity. Unlike conventional hanging pendulum thrust stands, the deflection is independent of the length of the pendulum arm, and no reference structure is required at the end of the pendulum. Displacement is measured using a non-contact, optical linear gap displacement transducer. Mechanical oscillations are attenuated using a passive, eddy current damper. An on-board microprocessor-based level control system, which includes a two axis accelerometer and two linear-displacement stepper motors, continuously maintains the level of the balance mechanism - counteracting mechanical %era drift during thruster testing. A thermal control system, which includes heat exchange panels, thermocouples, and a programmable recirculating water chiller, continuously adjusts to varying thermal loads to maintain the balance mechanism temperature, to counteract thermal drifts. An in-situ calibration rig allows for steady state calibration both prior to and during thruster testing. Thrust measurements were carried out on a well-characterized 1 kW Hall thruster; the thrust stand was shown to produce repeatable results consistent with previously published performance data

Photographic, magnetic, and interferometric measurements of current sheet canting in a pulsed electromagnetic accelerator

The propagation speed and canting angle of current sheets in a pulsed electromagnetic accelerator were measured using three different techniques: high-speed photography, magnetic field probes, and laser interferometry. Current sheet canting may have ad-verse effects on accelerator performance. The goal of the present work is to provide a database of cant-ing angles under a variety of experimental condi-tions. Eight different propellants (hydrogen, deu-terium, helium, neon, argon, krypton, xenon, and methane) were tested in a rectangular-geometry ac-celerator, at pressures ranging from 50-400 mTorr. The photographic, magnetic, and interferometric di-agnostics were used to infer the spatial configura-tion of the current sheet by measuring the its opti-cal emission, current density, and electron density, respectively. The three techniques gave qualitative agreement; the magnetic and interferometric mea-surements gave general quantitative agreement as well. The canting angle was found to depend o