An electron cross-field transport model based on instantaneous simulated plasma properties is incorporated into a radial-axial hybrid simulation of a Hall plasma thruster. The model is used to capture the reduction of fluctuation-based anomalous transport that is seen experimentally in the region of high axial shear in the electron fluid. Similar transport barriers are observed by the magnetic confinement fusion community due to shear suppression of plasma turbulence through an increase in the decorrelation rate of plasma eddies. The model assumes that the effective Hall parameter can be computed as the sum of the classical term, a near-wall conductivity term, and a fluctuationbased term that includes the effect of shear. A comparison is made between shear-based, experimental, and Bohm-type models for cross-field transport. Although the shear-based model predicts a wider transport barrier than experimentally observed, overall, it better predicts measured plasma properties than the Bohm model, particularly in the case of electron temperature and electric potential. The shear-based transport model also better predicts the breathing-mode oscillations and time-averaged discharge current than both the Bohm and experimental mobility models. The plasma property that is most sensitive to adjustment of the fitting parameters used in the shear-based model is the plasma density. Applications of these fitting parameters in other operating conditions and thruster geometries are examined in order to determine the robustness and portability of the model. Without changing the fitting parameters, the simulation was able to reproduce macroscopic properties, such as thrust and efficiency, of an SPT-100-type thruster within 30% and match qualitative expectations for a bismuth-fueled Hall thruster.

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A bismuth-fed Hall thruster has recently been selected for further development as a potential solution for faster missions to the outer planets. With higher efficiency and higher power handling, this two-stage Thruster with Anode Layer (TAL) should meet the necessary requirements for such missions. As the thruster is developed, there will be a need for nonintrusive diagnostic methods to optimize the geometry and operating conditions. Such optical diagnostic methods for analyzing the velocity, energy, and number densities of BiI and BiII are developed and discussed here. Candidate transitions are selected and their lineshapes modeled with respect to hyperfine splitting and broadening mechanisms. Suitable transitions are selected on the basis of relative strength, hyperfine data, and accessibility to tunable diode lasers; candidate transitions include the 306.86, 784.25, and 854.7nm lines of BiI and the 143.68, 796.7, and 854.3nm lines of BiII. Preliminary spectrum measurements using a microwave discharge are presented and future work is discussed. Nomenclature A= magnetic moment hyperfine splitting parameter a = Voigt "a" parameter B = quadrupole moment hyperfine splitting parameter E = energy shift due to hyperfine splitting by nuclear spin = shift in wavelength/frequency from linecenter v = integrated range of wavelengths/frequencies v x = lineshape FWHM due to broadening mechanism, x E = energy between two electronic states F = total atomic angular momentum quantum number, including nuclear spin f 12 = oscillator strength x = lineshape function for broadening mechanism, x I = nuclear spin quantum number I v /I 0,v = ratio of transmitted to incident light intensity at a given wavelength/frequency, v In = relative intensity of hyperfine split transition J = total atomic angular momentum quantum number, excluding nuclear spin j = single electron angular momentum quantum number k v = spectral absorption coefficient L = total orbital angular momentum quantum number L a = absorption path length ,v = wavelength or frequency of light m = atomic mass n = number density S = total electron spin angular momentum quantum number S 12 = linestrength T = kinetic temperature u = bulk velocity v 0 = linecenter frequency w = parameter indicating distance from linecenter

Solar thermal propulsion offers a unique combination of high thrust and high specific impulse that can provide competitive advantages relative to traditional satellite propulsion systems. Enhancing the functionality of this technology will require a robust thermal energy storage method that can be combined with a means of thermal-to-electric conversion (i.e. thermophotovoltaic cells). This combination creates a high performance dual mode power and propulsion system that can eliminate the traditional photovoltaic-battery combination on existing satellites. A thermal energy storage system based on the phase change of molten elemental materials is proposed as the enabling technology. Molten boron is identified as the optimal phase change material (PCM), but presents significant engineering challenges. Thus, molten silicon is proposed as a near term, moderate performance storage option. A systems level comparison against existing technologies shows that both thermal storage materials present a performance benefit versus current technological benchmarks, and with optimistic future assumptions, it appears that a boron-based system can provide a ∆V improvement of more than 40% while maintaining rapid satellite maneuverability. An ongoing experimental effort is focused on producing a proof of concept thermal energy storage system. Materials testing has determined the stability of boron nitride in the presence of molten silicon in the short term, and solar furnace testing has resulted in silicon melting for the first time. Testing of the solar furnace using copper as a surrogate PCM has revealed experimental concerns with PCM heat transfer rates and has resulted in a design for a new full scale solar furnace. This furnace will operate at scales that are relevant to spacecraft development.