Tony Schönherr

Characteristics of plasma properties in an ablative pulsed plasma thruster

Pulsed plasma thrusters are electric space propulsion devices which create a highly transient plasma bulk in a short-time arc discharge that is expelled to create thrust. The transitional character and the dependency on the discharge properties are yet to be elucidated. In this study, optical emission spectroscopy and Mach-Zehnder interferometry are applied to investigate the plasma properties in variation of time, space, and discharge energy. Electron temperature, electron density, and Knudsen numbers are derived for the plasma bulk and discussed. Temperatures were found to be in the order of 1.7 to 3.1 eV, whereas electron densities showed maximum values of more than 1017 cm−3. Both values showed strong dependency on the discharge voltage and were typically higher closer to the electrodes. Capacitance and time showed less influence. Knudsen numbers were derived to be in the order of 10−3−10−2, thus, indicating a continuum flow behavior in the main plasma bulk.

Propellant Utilization Efficiency in a Pulsed Plasma Thruster

In a pulsed plasma thruster discharge, the propellant utilization efficiency is commonly seen as the weak point for its thrust performance, and for its low thrust efficiency respectively. However, the value depends strongly on operational settings and the design of the pulsed plasma thruster itself. To access this efficiency to understand further the influence of parameters, a method combining experimental and modeling efforts is proposed within this paper. By using various optical methods, including high-speed camera imaging, emission spectroscopy, and Mach–Zehnder interferometry, the plasma bulk velocity for different energy configurations of the SPPT-68 ADD SIMP-LEX is derived. Together with the total ablated mass and an improved slug model, the ratio of mass accelerated in the discharge process is computed and, thus, the propellant utilization efficiency is derived. Velocities in the range of 25 to 55  km/s were measured, leading to propellant utilization efficiencies of about 40 to 60% depending on t...

Influence of Electrode Shape on Performance of Pulsed Magnetoplasmadynamic Thruster SIMP-LEX

The pulsed magnetoplasmadynamic thruster SIMP-LEX (Stuttgart impulsing magnetoplasmadynamic thruster for lunar exploration) is developed to serve as a main propulsion system for the lunar mission BW1. Optimizing the thrusters performance is necessary to increase the efficiency and the mean exhaust velocity without increasing the systems mass and energy requirements. Results of experiments varying the flare angle and the gap between the electrodes, the applied voltage, as well as using tongue-shaped or rectangular electrodes are shown and evaluated by means of a statistical approach using Taguchi matrices. Furthermore, an analytical approach toward the influence on the change in inductance along the x axis for these parameters was taken and the resulting performance characteristics are presented. Both tongue shape and flare angle, show a positive effect on the performance, that is, impulse bit, mean exhaust velocity, and thrust efficiency. A maximal I bit is given for a flare angle of ≈20 deg.

A hyperbolic-equation system approach for magnetized electron fluids in quasi-neutral plasmas

A new approach using a hyperbolic-equation system (HES) is proposed to solve for the electron fluids in quasi-neutral plasmas. The HES approach avoids treatments of cross-diffusion terms which cause numerical instabilities in conventional approaches using an elliptic equation (EE). A test calculation reveals that the HES approach can robustly solve problems of strong magnetic confinement by using an upwind method. The computation time of the HES approach is compared with that of the EE approach in terms of the size of the problem and the strength of magnetic confinement. The results indicate that the HES approach can be used to solve problems in a simple structured mesh without increasing computational time compared to the EE approach and that it features fast convergence in conditions of strong magnetic confinement.

Analysis of effective parameters on ablative PPT performance

Purpose – The purpose of this paper is to comprehensively review most of the significant works ever done worldwide to study the effects of essential parameters on pulsed plasma thruster (PPT) performance and to analyze the effects of each parameter on PPT performance.Design/methodology/approach – All the important works studying PPT performance are categorized by the parameter they have studied and its effect on the thruster performance, and their works have been reviewed to analyze the influence of each parameter.Findings – The analysis leads to elucidation of the effects of different geometrical parameters including aspect ratio, electrode width, electrode spacing, electrode shape, electrode length, and flare angle, in addition to the effects of other parameters such as electrode material, propellant type, propellant temperature, spark distance from propellant, pulse repetition frequency, discharge energy, capacitance, and hood angle on PPT performance.Research limitations/implications – The analysis is...

Analysis of Atmosphere-Breathing Electric Propulsion

To extend the lifetime of commercial and scientific satellites in low Earth orbit (LEO) and below (100-250 km of altitude) recent years showed an increased activity in the field of air-breathing electric propulsion as well as beamed-energy propulsion systems. However, preliminary studies showed that the propellant flow necessary for electrostatic propulsion at these altitudes exceeds the mass intake possible within reasonable limits, and that electrode erosion due to oxygen flow might limit the lifetime of eventual thruster systems. The pulsed plasma thruster (PPT), however, can be successfully operated with smaller mass intake and at relatively low power. This makes it an interesting candidate for air-breathing application in LEO and its feasibility is investigated within this paper. An analysis of such an air-breathing PPT system shows that for altitudes between 150 and 250 km, drag compensation is at least partially feasible assuming a thrust-to-power ratio of 30 mN/kW and a specific impulse of 5000 s. Further, to avoid electrode erosion, inductively heated electrothermal plasma generator technology is discussed to derive a possible propulsion system that can handle gaseous propellant without unfavorable side effects. Current technology can be used to create an estimated 4.4 mN of thrust per 1 mg/s of mass flow rate, which is sufficient to compensate the drag for small satellites in altitudes between 150 and 250 km.

A flux-splitting method for hyperbolic-equation system of magnetized electron fluids in quasi-neutral plasmas

A flux-splitting method is proposed for the hyperbolic-equation system (HES) of magnetized electron fluids in quasi-neutral plasmas. The numerical fluxes are split into four categories, which are computed by using an upwind method which incorporates a flux-vector splitting (FVS) and advection upstream splitting method (AUSM). The method is applied to a test calculation condition of uniformly distributed and angled magnetic lines of force. All of the pseudo-time advancement terms converge monotonically and the conservation laws are strictly satisfied in the steady state. The calculation results are compared with those computed by using the elliptic-parabolic-equation system (EPES) approach using a magnetic-field-aligned mesh (MFAM). Both qualitative and quantitative comparisons yield good agreements of results, indicating that the HES approach with the flux-splitting method attains a high computational accuracy.

Characteristics of a non-volatile liquid propellant in liquid-fed ablative pulsed plasma thrusters

In the past several decades, the use of electric propulsion in spacecraft has experienced tremendous growth. With the increasing adoption of small satellites in the kilogram range, suitable propulsion systems will be necessary in the near future. Pulsed plasma thrusters (PPTs) were the first form of electric propulsion to be deployed in orbit, and are highly suitable for small satellites due to their inherent simplicity. However, their lifetime is limited by disadvantages such as carbon deposition leading to thruster failure, and complicated feeding systems required due to the conventional use of solid propellants (usually polytetrafluoroethylene (PTFE)). A promising alternative to solid propellants has recently emerged in the form of non-volatile liquids that are stable in vacuum. This study presents a broad comparison of the non-volatile liquid perfluoropolyether (PFPE) and solid PTFE as propellants on a PPT with a common design base. We show that liquid PFPE can be successfully used as a propellant, an...

Evaluation of discharge behavior of the pulsed plasma thruster SIMP-LEX

The pulsed plasma thruster Add Simp-lex, developed at the IRS, was investigated at the University of Tokyo to further characterize the thruster’s performance and discharge behavior. This was done by experimental investigation of configurations with a different amount of capacitors and discrete applied voltages. To do so, a measurement system for the discharge current and the optical properties was built up and successfully applied. Further, the numerical model for the prediction of the current-normalized magnetic flux density was improved and the convergence properties of the integration towards the change in inductance studied. From the discharge current waveforms and the pictures taken from the propagating plasma, information about the amount of plasma creations, their propagation velocity and the oscillation behavior was deducted. For further characterization, the energy transfer efficiency and the electrical efficiency was derived from these data, leading to a tool to compare different configurations. It was found, that a middle voltage yields higher electrical efficiencies of about 40% whereas the energy transfer efficiency is higher the lower the applied voltage.

Magnetized Electron Flow Calculation Using a Hyperbolic System

The hyperbolic-equation-system (HES) approach has been developed for the calculation of magnetized electron fluids in quasi-neutral plasmas. The HES approach has been applied to a particle-fluid hybrid modeling of a Hall thruster, to evaluate the applicability of the approach to practical simulations. The validity of the use of the HES approach is confirmed based on three aspects. First, the calculated thruster performance is in good agreement with the experimental results. Also, it is proven that the two-dimensional conservation law of the electron flow is strictly computed with the HES approach. Lastly, the Boltzmann relation along magnetic lines of force is confirmed, which indicates the effect of magnetic confinement is accurately calculated.