Kurt A. Polzin

Thrust stand for electric propulsion performance evaluation

An electric propulsion thrust stand capable of supporting testing of thrusters having a total mass of up to 125kg and producing thrust levels between 100μN to 1N has been developed and tested. The design features a conventional hanging pendulum arm attached to a balance mechanism that converts horizontal deflections produced by the operating thruster into amplified vertical motion of a secondary arm. The level of amplification is changed through adjustment of the location of one of the pivot points linking the system. Response of the system depends on the relative magnitudes of the restoring moments applied by the displaced thruster mass and the twisting torsional pivots connecting the members of the balance mechanism. Displacement is measured using a noncontact, optical linear gap displacement transducer, and balance oscillatory motion is attenuated using a passive, eddy-current damper. The thrust stand employs an automated leveling and thermal control system. Pools of liquid gallium are used to deliver ...

Faraday Acceleration with Radio-Frequency Assisted Discharge

A new electrodeless accelerator concept that relies on an rf-assisted discharge, an applied magnetic field, and electromagnetic acceleration using an inductive coil is presented. The presence of a preionized plasma allows for current sheet formation at lower discharge voltages and energies than those found in other pulsed inductive accelerator concepts. A proof-of-concept experiment, supported by optical and probe diagnostics, has been constructed and used to demonstrate low-voltage, low-energy current sheet formation and acceleration. Magnetic field data indicate that the peak sheet velocity in this unoptimized configuration operating at a pulse energy of 78.5 J is 12 km/s. Visual observations indicate that plasma follows the applied magnetic field from the rf discharge to the face of the planar acceleration coil, while magnetic field probing and visualization using a fast-framing camera show the formation and acceleration of the current sheet.

Comprehensive Review of Planar Pulsed Inductive Plasma Thruster Research and Technology

Nomenclature B, B = magnetic induction, T C = capacitance, F E = electric field, V=m E0 = initial energy, J e0 = specific energy, J=kg I = current, A Ibit = impulse bit, N s Isp = specific impulse, s j = current density, A=m _ L = dynamic impedance, H=s LC = coil inductance, H L0 = initial inductance, H L0 = inductance per unit length, H=m L = inductance ratio M = mutual inductance, H; molecular mass, kg mbit = mass bit, kg=pulse mc = critical mass, kg Q1 = first ionization potential, J r = radial coordinate, m Re = external resistance, Rp = plasma resistance, t = time, s ue = exhaust velocity, m=s v = velocity, m=s Vp = plasma voltage, V V0 = initial charge voltage, V z = axial coordinate, m z0 = electromagnetic stroke length, m = dynamic impedance parameter L = inductance change, H = resistivity, m; efficiency, % = nonpropulsive energy fraction A = linear mass density, kg=m = magnetic flux, W 1, 2 = critical resistance ratios

Performance optimization criteria for pulsed inductive plasma acceleration

A model of pulsed inductive plasma thrusters consisting of a set of coupled circuit equations and a one-dimensional momentum equation has been nondimensionalized leading to the identification of several scaling parameters. Contour plots representing thruster performance (exhaust velocity and efficiency) were generated numerically as a function of the scaling parameters. The analysis revealed the benefits of underdamped current waveforms and led to an efficiency maximization criterion that requires the circuits natural period to be matched to the acceleration timescale. It is also shown that the performance increases as a greater fraction of the propellant is loaded nearer to the inductive acceleration coil

Scaling and Systems Considerations in Pulsed Inductive Plasma Thrusters

Performance scaling in pulsed inductive thrusters is discussed in the context of previous experimental studies and modeling results. Two processes, propellant ionization and acceleration, are interconnected, where overall thruster performance and operation are concerned, but they are separated here to gain physical insight into each process and arrive at quantitative criteria that should be met to address or mitigate inherent inductive thruster difficulties. The use of preionization to lower the discharge energy relative to the case where no preionization is employed, and to influence the location of the initial current sheet, is described. The relevant performance scaling parameters for the acceleration stage are reviewed, emphasizing their physical importance and the numerical values required for efficient acceleration. The scaling parameters are then related to the design of the acceleration coil and the pulsed power train that provides current to the acceleration stage. An accurate numerical technique that allows computation of the inductance of a planar acceleration coil using an axisymmetric magnetostatic solver is described and validated against measured coil inductance values. Requirements for the pulsed power train are reviewed. Several power train and circuit topologies are described, highlighting the impact that each can have on inductive thruster performance and on systems issues associated with high-current switching, lifetime, and power consumption.

Performance of a low-power cylindrical hall thruster

Recent mission studies have shown that a Hall thruster which operates at relatively constant thrust efficiency (45-55%) over a broad power range (300W - 3kW) is enabling for deep space science missions when compared with slate-of-the-art ion thrusters. While conventional (annular) Hall thrusters can operate at high thrust efficiency at kW power levels, it is difficult to construct one that operates over a broad power envelope down to 0 (100 W) while maintaining relatively high efficiency. In this note we report the measured performance (I(sub sp), thrust and efficiency) of a cylindrical Hall thruster operating at 0 (100 W) input power.

Ablative Z-Pinch Pulsed Plasma Thruster

The design, performance, and basic features of ablative pulsed plasma thrusters based on the z-pinch configuration are discussed through a series of experiments and numerical simulations. The motivation stems from the promise of the z-pinch configuration for increasing the thrust-to-power ratio and mass utilization efficiency above those of ablative thrusters with a conventional rectangular geometry. The performance of a series of ablative z-pinch pulsed plasma thrusters is characterized using a swinging-gate thrust stand and mass ablation measurements. The performance measurements are complemented by additional experimental diagnostics (current monitoring and high-speed photography) and numerical modeling in order to gain an understanding of the acceleration mechanism and provide direction for future design iterations. Three iterations in the design of the thruster result in thrust-topower ratios ranging from 12‐45 µN/W, with specific impulse and thrust efficiency values spanning 240‐760 s and 2‐9%, respectively. Numerical simulations show reasonable quantitative agreement with the experimental data and predict the existence of an optimal thrust chamber aspect ratio, which maximizes the thrust-to-power ratio.

Plasma Propulsion Options for Multiple Terrestrial Planet Finder Architectures

A systems-level trade study is presented comparing the propulsion requirements and associated final masses for different architectural implementations of the Terrestrial Planet Finder mission. The study focuses on the millinewton-level propulsion chores associated with rotation and repointing an array. Three interferometer configurations, free-flying, monolithic and tethered, lead to estimates of thrust and power requirements and spacecraft masses associated with the different plasma propulsion systems required to perform maneuvers throughout a mission. The parametric study includes the following plasma propulsion options: Hall thruster, field emission electric propulsion, ablative pulsed plasma thruster, ablative Z-pinch pulsed plasma thruster and gas-fed pulsed plasma thruster. Not all of the thrusters considered can perform the necessary propulsive chores for each architecture, but for the most promising thruster and architecture combinations, it is found that the initial mass for a system falls between 3050 and 4060 kg. The tether, in general, possesses the lowest initial mass of the three architectures followed by the free flyer and the monolith. Finally, the thrust-to-power ratio, maximum deliverable thrust or impulse bit, and capability of a propulsion system to process enough power to produce a required thrust level are shown to be more important factors than the specific impulse in determining the proper thruster choice for moderate to high thrust maneuvers.

Faraday Accelerator with Radio-frequency Assisted Discharge (FARAD)

Abstract : A new electrodeless accelerator concept that relies on an RF-assisted discharge, an applied magnetic field, and electromagnetic acceleration using an inductive coil is presented. The primary advantage of this concept is that a preionized plasma is employed to lower the initial voltage threshold which applies to the formation of an inductive current sheet in other pulsed inductive accelerator concepts.

A similarity parameter for capillary flows

A similarity parameter for quasi-steady fluid flows advancing into horizontal capillary channels is presented. This parameter can be interpreted as the ratio of the average fluid velocity in the capillary channel to a characteristic velocity of quasi-steady capillary flows. It allows collapsing a large data set of previously published and recent measurements spanning five orders of magnitude in the fluid velocity, 14 different fluids, and four different geometries onto a single curve and indicates the existence of a universal prescription for such flows. On timescales longer than the characteristic time it takes for the flow to become quasi-steady, the one-dimensional momentum equation leads to a non-dimensional relationship between the similarity parameter and the penetration depth that agrees well with most measurements. Departures from that prescription can be attributed to effects that are not accounted for in the one-dimensional theory.