As the NEXT ion thruster progresses towards higher technology readiness, it is necessary to develop the tools that will support its implementation into flight programs. An ion thruster thermal model has been developed for the latest prototype model design to aid in predicting thruster temperatures for various missions. This model is comprised of two parts. The first part predicts the heating from the discharge plasma for various throttling points based on a discharge chamber plasma model. This model shows, as expected, that the internal heating is strongly correlated with the discharge power. Typically, the internal plasma heating increases with beam current and decreases slightly with beam voltage. The second is a model based on a finite difference thermal code used to predict the thruster temperatures. Both parts of the model will be described in this paper. This model has been correlated with a thermal development test on the NEXT Prototype Model 1 thruster with most predicted component temperatures within 5-10 °C of test temperatures. The model indicates that heating, and hence current collection, is not based purely on the footprint of the magnet rings, but follows a 0.1:1:2:1 ratio for the cathode-to-conical-to-cylindrical-tofront magnet rings. This thermal model has also been used to predict the temperatures during the worst case mission profile that is anticipated for the thruster. The model predicts ample thermal margin for all of its components except the external cable harness under the hottest anticipated mission scenario. The external cable harness will be re-rated or replaced to meet the predicted environment. AIAA 2007-5218This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

This publication discusses the concept, projected capabilities, technology development plan, and preliminary performance data obtained for an Annular-Geometry Ion Engine (AGI-Engine). The AGI-Engine is the basis for a new class of Next-Generation Electric Propulsion Thrusters under investigation at NASA Glenn Research Center. The AGI-Engine holds the promise of achieving substantial increases in input power (>10X) and power density (2-3X) relative to conventional ion thrusters at specific impulse values of interest for near-term mission applications. Nomenclature

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A thermal computer model of the 30-cm NASA solar electric propulsion technology application readiness (NSTAR) xenon ion thruster has been produced using a lumped-parameter thermal nodal-network scheme. This model contains 104 nodes on the thruster and was implemented using SINDA and TRASYS on various UNIX workstations. The model includes the radiation and conduction heat transfer, the effect of plasma interaction on the thruster, and an account for nely perforated surfaces. The model was developed in conjunction with an NSTAR thruster out tted with approximately 20 thermocouples for thermal testing at the John H. Glenn Research Center. The results of these experiments were used to calibrate and con rm the computer model rst without and then with the plasma interaction. The calibrated model was able to predict discharge chamber temperatures to within 10 ± C of measured temperatures. To demonstrate the ability of the model under various circumstances, the heat ux was examined for a thruster operating in a deep-space environment. NomenclatureA I = area of I th element, m 2 A J = area of J th element, m 2 C i = thermal capacitance at node i , cal/g¢ K F i j = form (view) factor G j i = linear conductor attaching node j to node i , W/K H j i = radiation conductor attaching node j to node i , W/K 4 J A = ion current hitting grid, A J B = ion beam current, A N = number of nodes Q i = heat source or sink for node i , W r i j = distance between the i th and j th element, m T k + 1 i = temperature of node i for the k + 1 iteration, K T n + 1 i = temperature of node i at time t + D t , K T k j = temperature of node j for the kth iteration, K T n j = temperature of node j at time t, K U + = ionization energy, eV V P = discharge chamber plasma potential with respect to ambient space plasma potential, V h i = angle between normal of i th element and the line connecting the i th and j th element, rad h j = angle between normal of j th element and the line connecting the i th and j th element, rad U N = neutralizer power, W U sh = self-heating power deposited in the discharge chamber in the form of heat, W U T = total thruster power, W

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