摘要 :
Results from a long duration test of a cusped-field plasma thruster operating at an anode power of 165 W are presented and discussed. Profile measurements of the boron nitride insulator were performed before and after the 204 h te...
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Results from a long duration test of a cusped-field plasma thruster operating at an anode power of 165 W are presented and discussed. Profile measurements of the boron nitride insulator were performed before and after the 204 h test, enabling the quantification of average erosion rates over a large portion of the interior. Unlike most Hall thrusters, the lifetime is not limited by erosion near the exit plane, due to the positioning of magnetic circuit elements. Additionally, the maximum erosion rate is found to be lower than rates measured in low-power Hall thrusters by at least 50%. The lifetime of this laboratory prototype is estimated at 1220 h based on the time needed to erode through the insulator in one of the ring-cusps. Therefore, fortifying cusps with additional or a more durable material would increase the lifetime of future designs. A summary of long duration tests and erosion measurements in Hall thrusters is also provided. A concurrent analysis of deposition within the thruster shows the accumulation of a conductive and ferromagnetic material between cusps. Finally, estimates of electron temperature and ion loss widths near the wall are obtained based on measured distributions of erosion in each cusp. During the tests discussed here, the thruster operated in the 'high- current' mode, characterized by strongly oscillatory anode currents. Erosion rates upstream of the exit cusp may be lower in the 'low-current' mode, where anode current oscillation amplitudes are smaller by two orders of magnitude.
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An innovative approach of connecting multiple arcjet thrusters to a single arcjet power conditioning unit (PCU) is presented. The approach uses fuses and a coordinated electronic controller to perform the functions of operating mu...
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An innovative approach of connecting multiple arcjet thrusters to a single arcjet power conditioning unit (PCU) is presented. The approach uses fuses and a coordinated electronic controller to perform the functions of operating multiple thrusters with one PCU, therefore eliminating the need for high current, high voltage arcjet selector switches. Phase I effort will design the controller and identify the proper fuse as well as conduct liaison with other high power arcjet experimenters to verify this innovative approach. (Author)
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This report describes progress, in experimental development, plasma diagnostics, and modeling, in advanced pulsed plasma thrusters (PPT) for application to formation-flying satellite constellations such as TechSat21. The research ...
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This report describes progress, in experimental development, plasma diagnostics, and modeling, in advanced pulsed plasma thrusters (PPT) for application to formation-flying satellite constellations such as TechSat21. The research concentrated on coaxial Teflon PPTs, predominantly of the electrothermal (high thrust) type, with an average power of 100 watts. During this effort, performance advances were made both in the thruster design and in the pulsed circuitry driving the discharge, aided by increased understanding derived from a two-fluid model. The results of this research led to the development, under separate contract to CU Aerospace, of a PPT flight test model (PPT-8) which was tested at the AFRL Electric Propulsion Laboratory.
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The importance of a uniform current density profile in the exhaust beam of an electrostatic ion thruster is discussed in terms of thrust level and accelerator system lifetime. A residence time approach is used to explain the nonun...
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The importance of a uniform current density profile in the exhaust beam of an electrostatic ion thruster is discussed in terms of thrust level and accelerator system lifetime. A residence time approach is used to explain the nonuniform beam current density profile of the SERT II divergent magnetic field thruster and to propose a magnetic field modification (the cusped magnetic field geometry) which should produce a highly uniform beam profile. A discharge chamber model is proposed and mathematical expressions are derived which relate the thruster discharge power loss, propellant utilization, and double-to-single ion density ratio to the geometry and plasma properties of the dis¬charge chamber. These relationships are applied to a cylindrical discharge chamber model of the SERT II thruster and suggest that, in addition to the magnetic field modification, the discharge chamber length of this thruster should be reduced. These modifications should result in a thruster having a highly uniform beam profile, good performance, and a low double ion population.
Experimental results are presented for a wide range of the discharge chamber length. The thruster designed for this investigation was operated with a cusped magnetic field as well as a divergent field geometry, and the cusped field geometry is shown to be superior from the standpoint of beam profile uniformity, performance, and double ion population. Beam profile measurements 6 mm downstream of the accelerator grid indicate the beam profile flatness parameter (which quantitatively describes the uniformity of the profile) is 0.7, and throttled thruster operation results in a beam flatness parameter of 0.82. At about the same thrust and performance levels, the beam flatness parameter of the cusped field thruster is 40 percent higher than the SERT II thruster value. This implies a 40 percent increase in the accelerator system lifetime due to a reduction in localized erosion of the accelerator grid caused by the impingement of charge-exchange ions.
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This research focuses on experimentally characterizing the performance parameters of a colloid thruster with porous emitters through optical techniques. Porous emitters are different than traditional needle emitters in how they al...
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This research focuses on experimentally characterizing the performance parameters of a colloid thruster with porous emitters through optical techniques. Porous emitters are different than traditional needle emitters in how they allow a variation in the number and size of Taylor Cones throughout a range of propellant volumetric flow rate conditions. An algorithm is created to calculate the estimated minimum and maximum number of emitter sites based on magnified images of the porous emitter heads. Theoretical thruster performance parameters are then established from the estimated number of emitter sites. Experimental techniques for measuring the thrust and exhaust exit velocity are proposed. They are then analyzed for their compatibility and limitations with colloid thruster testing based on the theoretical performance parameters. The research and analysis lays the foundation for future colloid thruster testing and characterization. This baseline model and analysis can be refined through laboratory testing in order to be used for future mission analysis determining the viability of the new porous emitter as an enhanced colloid thruster feature over traditional needles.
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Impulse bits produced by conical theta-pinch inductive pulsed plasma thrusters possessing cone angles of 20deg, 38deg, and 60deg, were quantified for 500J/pulse operation by direct measurement using a hanging-pendulum thrust stand...
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Impulse bits produced by conical theta-pinch inductive pulsed plasma thrusters possessing cone angles of 20deg, 38deg, and 60deg, were quantified for 500J/pulse operation by direct measurement using a hanging-pendulum thrust stand. All three cone angles were tested in single-pulse mode, with the 38deg model producing the highest impulse bits at roughly 1 mN-s operating on both argon and xenon propellants. A capacitor charging system, assembled to support repetitively-pulsed thruster operation, permitted testing of the 38deg thruster at a repetition-rate of 5 Hz at power levels of 0.9, 1.6, and 2.5 kW. The average thrust measured during multiple-pulse operation exceeded the value obtained when the single-pulse impulse bit is multiplied by the repetition rate.
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High-power electromagnetic thrusters have been proposed as primary in-space propulsion options for several bold new interplanetary and deep-space missions. As the lead center for electric propulsion, the NASA Glenn Research Center...
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High-power electromagnetic thrusters have been proposed as primary in-space propulsion options for several bold new interplanetary and deep-space missions. As the lead center for electric propulsion, the NASA Glenn Research Center designs, develops, and tests high-power electromagnetic technologies to meet these demanding mission requirements. Two high-power thruster concepts currently under investigation by Glenn are the magnetoplasmadynamic (MPD) thruster and the Pulsed Inductive Thruster (PIT).
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The focus of the PPT basic research program at AFRL has now shifted to understanding the sources of the low energy efficiency. Based on previous research modifications such as changing the electrode geometry, discharge frequency, ...
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The focus of the PPT basic research program at AFRL has now shifted to understanding the sources of the low energy efficiency. Based on previous research modifications such as changing the electrode geometry, discharge frequency, and discharge energy may all result in moderate increases to the energy efficiency. What is required from a basic research standpoint is a diagnostic capability that can acquire information with sufficient accuracy to enable PPT designers to understand why certain influences increase performance - and then design PPTs which maximize these effects. To model a fluid description of the PPT plasma, the critical measurements are magnetic field and density. Temperature, composition and charge state also become critical as the models become more detailed. This paper describes a magnetic field probe array used at AFRL to map the magnetic fields in a laboratory model PPT. The paper focuses on determining to what extent the probe perturbs the plasma, the measurement limitations. Also discussed are options towards making this critical measurement with increased accuracy.
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