Anuscheh Nawaz

Investigation of the Magnetic Field in a Pulsed Plasma Thruster

The magnetic field between the electrodes of an 80 J ablative pulsed plasma thruster was both measured and determined analytically. This was done to better understand the acceleration process and assess the accuracy of the analytical method. The measurements at different positions in both breech-fed and side-fed propellant configurations were performed using a shielded induction probe of 1 mm in diameter. To calibrate the probe, a Helmholtz coil was built. The magnetic field was calculated using the law of Biot-Savart and assuming a current sheet thickness of 3 mm. The measured magnetic field showed an overall peak at 0.7 T. It was possible to confirm the induced current loop formed between the electrodes at the time when the overall current passes through zero. The comparison between the magnetic field model and the measurements at the propellant surface of a breech-fed thruster showed reasonably good accordance.

Surface Catalysis and Oxidation on Stagnation Point Heat Flux Measurements in High Enthalpy Arc Jets

Heat flux sensors are routinely used in arc jet facilities to determine heat transfer rates from plasma plume. The goal of this study is to assess the impact of surface composition changes on these heat flux sensors. Surface compositions can change due to oxidation and material deposition from the arc jet. Systematic surface analyses of the sensors were conducted before and after exposure to plasma. Currently copper is commonly used as surface material. Other surface materials were studied including nickel, constantan gold, platinum and silicon dioxide. The surfaces were exposed to plasma between 0.3 seconds and 3 seconds. Surface changes due to oxidation as well as copper deposition from the arc jets were observed. Results from changes in measured heat flux as a function of surface catalycity is given, along with a first assessment of enthalpy for these measurements. The use of cupric oxide is recommended for future heat flux measurements, due to its consistent surface composition arc jets.

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.

Comparison of Calorimetric Sensors - NASA Ames and IRS

A space act agreement between NASA Ames Research Center and the Institute of Space Systems at the University of Stuttgart was put in place in October 2011. The focus of this collaboration is the comparison and refinement of measurement techniques for plasma characterization. Within this paper, first test results from this collaboration will be presented, based on tests completed at NASA Ames arc jet facilities. A water-cooled energy balance calorimeter and a null-point calorimeter from the Institute of Space Systems were compared to a slug calorimeter and null-point calorimeter from NASA Ames. The results are expected to serve the plasma and entry community by providing comparative data between the two facilities and the three types of sensors.

Electrostatic Probe and Camera Measurements for Modeling the iMPD SIMP-LEX

In order to further investigate and characterize the instationary magnetoplasmadynamic thruster SIMP-LEX, measurement as well as modeling approaches were taken. Triple probe and time of ight probe measurements were conducted for a bank energy of 80J, varying the distance between the electrodes as well as the position of the probes along the axes. From these measurements, electron temperature, electron density and velocity of the plasma plume could be determined as a function of time. They showed to be in reasonably good agreement with data found in literature. Additionall, the position, form and velocity of the plasma plume was observed by means of a high speed camera in 100ns steps after thruster ignition. From these pictures it is possible to clearly discern three phases of one plasma pulse. It was also possible to determine a mean velocity of the rst plasma wave. To understand the thruster further and to be able to predict thruster characteristics, a model of the thruster was established bytaking a simple slug model approach. This model was extended to better represent the physical phenomena within the thruster. The data obtained from the measurements mentioned above were used to verify and correct this model.

Impact of plasma tube wall thickness on power coupling in ICP sources

The inductively heated plasma source at the Institute of Space Systems was investigated with respect to the wall thickness of the plasma tube using an air plasma. For this, the wall thickness of the quartz tube was reduced in steps from 2.5 to 1.25 mm. The significance of reducing the wall thickness was analyzed with respect to both the maximum allowable tube cooling power and the coupling efficiency. While the former results from thermal stresses in the tubes wall, the latter results from a minimization of magnetic field losses near the coil turns of the inductively coupled plasma (ICP) source. Analysis of the thermal stress could be validated by experimental data, i.e. the measurement of the tube cooling power when the respective tube structure failed. The coupling efficiency could be assessed qualitatively by simplified models, and the experimental data recorded show that coupling was improved far more than predicted.

Comparison of Heat Flux Gages for High Enthalpy Flows - NASA Ames and IRS

This article is a companion to a paper on heat flux measurements as initiated under a Space Act Agreement in 2011. The current focus of this collaboration between the Institute of Space Systems (IRS) of the University of Stuttgart and NASA Ames Research Center is the comparison and refinement of diagnostic measurements. A first experimental campaign to test different heat flux gages in the NASA Interaction Heating Facility (IHF) and the Plasmawindkanäle (PWK) at IRS was established. This paper focuses on the results of the measurements conducted at IRS. The tested gages included a flat face and hemispherical probe head, a 4” hemispherical slug calorimeter, a nullpoint calorimeter from Ames and a nullpoint calorimeter developed for this purpose at IRS. The Ames nullpoint calorimeter was unfortunately defective upon arrival. The measured heat fluxes agree fairly well with each other. The reason for discrepancies can be attributed to signal-to-noise levels and the probe geometry.

Monitoring Temperature in High Enthalpy Arc-heated Plasma Flows using Tunable Diode Laser Absorption Spectroscopy

A tunable diode laser sensor was designed for in situ monitoring of temperature in the arc heater of the NASA Ames IHF arcjet facility (60 MW). An external cavity diode laser was used to generate light at 777.2 nm and laser absorption used to monitor the population of electronically excited oxygen atoms in an air plasma flow. Under the assumption of thermochemical equilibrium, time-resolved temperature measurements were obtained on four lines-of-sight, which enabled evaluation of the temperature uniformity in the plasma column for different arcjet operating conditions.

Impulse Measurements and Thermal Investigation of SIMP-LEX

The pulsed instationary magnetoplasmadynamic thruster (I-MPD) SIMP-LEX (Stuttgart Instationary MPD Thruster for Lunar Exploration) is being developed at the Institut fur Raumfahrtsysteme (IRS) of the Universitat Stuttgart in order to serve as main propulsion system on board BW1 - the institutes small all electrical satellite bound to the moon by the end of this decade. This paper addresses two recent advances in the development of SIMP-LEX: Impulse measurements by means of a pendulum and thermal measurements and results for bank energies from 24 J to 80 J at various pulse rates. The impulse measure- ments were carried out on the laboratory model SIMP-0, using a reference unit including an impulse hammer for correlation between impulse and deflection of the pendulum. Ther- mal investigations include heating as well as cooling profiles. Analysis of this data leads to a mean emission coecient ¯ mean as well as the overall heat flux delivered to each electrode per pulse. Furthermore, the electron temperature was approximated from the heat flux onto the anode.

Development of electric propulsion systems at IRS

This paper presents recent developments in the field of electric propulsion for interplanetary missions such as the arcjet system TALOS and the magnetoplasmadynamic thrusters Van-Allen belt and SIMP-LEX. Investigations include measurement of mass bit, plasma current, plasma acceleration time, plasma thrust, and plasma dynamic properties. Thruster optimization includes ground testing, numerical simulations as well as thermal modelling.