Abstract: A voltage tracking system for an ion thruster includes a discharge chamber, a screen grid, an accelerator grid, and an accelerator grid voltage controller. The discharge chamber contains plasma at a given potential. The screen grid is adjacent to the discharge chamber and is voltage biased relative to the plasma to form a plasma sheath that repels electrons and attracts ions from the discharge chamber plasma. The accelerator grid is adjacent to the screen grid and has a voltage for accelerating the ions to create thrust and prevent any electrons from backstreaming into the ion thruster from the beam plasma. The accelerator grid voltage controller supplies voltage to the accelerator grid. The accelerator grid voltage controller adjusts the magnitude of the accelerator grid voltage to minimize the amount of voltage required to prevent electron backstreaming into the ion thruster.

Abstract: An electric thruster has at least a portion of a surface of at least one of the component elements of its housing surface treated to increase the thermal transmission at the surface. The surface treatment is selected to increase the thermal absorption and thence the absorption of heat at the interiorly facing surfaces of the treated component, and/or to increase the thermal emissivity and thence radiation heat loss at the exteriorly facing surfaces of the treated component, and/or to increase the effective surface area through which heat is absorbed or emitted. The surface-treated housing components are assembled together with a cathode assembly, an ionization chamber, a propellant gas source, and a magnetic structure to form an electric thruster.

Abstract: An electric thruster has at least a portion of a surface of at least one of the component elements of its housing surface treated to increase the thermal transmission at the surface. The surface treatment is selected to increase the thermal absorption and thence the absorption of heat at the interiorly facing surfaces of the treated component, and/or to increase the thermal emissivity and thence radiation heat loss at the exteriorly facing surfaces of the treated component, and/or to increase the effective surface area through which heat is absorbed or emitted. The surface-treated housing components are assembled together with a cathode assembly, an ionization chamber, a propellant gas source, and a magnetic structure to form an electric thruster.

Abstract: A voltage tracking system for an ion thruster includes a discharge chamber, a screen grid, an accelerator grid, and an accelerator grid voltage controller. The discharge chamber contains plasma at a given potential. The screen grid is adjacent to the discharge chamber and is voltage biased relative to the plasma to form a plasma sheath that repels electrons and attracts ions from the discharge chamber plasma. The accelerator grid is adjacent to the screen grid and has a voltage for accelerating the ions to create thrust and prevent any electrons from backstreaming into the ion thruster from the beam plasma. The accelerator grid voltage controller supplies voltage to the accelerator grid. The accelerator grid voltage controller adjusts the magnitude of the accelerator grid voltage to minimize the amount of voltage required to prevent electron backstreaming into the ion thruster.

Abstract: An ion thruster has a hollow cathode assembly including a heater with an inner ceramic sleeve and an outer ceramic sleeve. The outer ceramic sleeve overlies the inner ceramic sleeve with a filament volume between the two sleeves. A wound filament has windings disposed within the filament volume, and a mass of ceramic powder fills the remaining portion of the filament volume between the windings of the filament. A cathode is disposed within the inner ceramic sleeve of the heater. The heater is assembled by preparing the filament and forming it into a wound cylinder, and then encapsulating it and the powder between the inner and the outer ceramic sleeves. The hollow cathode assembly may serve as a portion of a plasma source or as a portion of a charge neutralizer.

Abstract: An ion thruster includes a source of a plasma of ions and electrons, and an ion-optics system located in sufficient proximity to the source of the plasma to extract ions therefrom. The ion-optics system has at least two domed grids arranged in a facing-but-spaced-apart relationship to each other. Each grid has a local reference vector that is perpendicular to the surface of the grid and a reference plane perpendicular to the reference vector. Each of the grids is formed of anisotropic pyrolytic graphite having an “ab” crystallographic plane that lies substantially in the reference plane. In one form, the “ab” crystallographic plane lies coplanar with the reference plane at all locations on each domed grid made of pyrolytic graphite. In another form, the “ab” crystallographic plane has a constant orientation at all locations on the domed grid.

Abstract: An ion thruster has a source of a plasma, and an ion-optics system located in sufficient proximity to the source of the plasma to extract ions therefrom. The ion-optics system includes at least two grids arranged in a facing-but-spaced-apart relationship to each other, with each grid being axisymmetric about a grid axis. Each grid includes a peripheral region defining a grid plane perpendicular to the grid axis, a first region of curvature adjacent to the peripheral region, and a second region of curvature along the grid axis such that the first region of curvature lies between the second region of curvature and the peripheral region. The first region of curvature is a convexly curved segment of a first sphere relative to the grid plane, and the second region of curvature is a concavely curved segment of a second sphere relative to the grid plane.

Abstract: Electrostatic propulsion systems for spacecraft include a plurality of electrostatic thrusters that are continuously coupled to power forms of a power supply system. Ionizable gas is fed to a selected one of the thrusters to selectively initiate the thrust of that electrostatic thruster. In other embodiments, heater power forms are coupled only to the selected thruster to reduce power consumption and increase cathode lifetime. The propulsion system has a reduced complexity and is especially suited for spacecraft in which only one thruster is ever fired at a given time.

Abstract: Positional accuracy of apertures in nonplanar electrodes is improved with a new fabrication method. This method precedes process steps which establish a photoresist pattern that defines apertures with deformation steps which produce a nonplanar electrode. Thus, the deformation steps do not have an opportunity to spatially alter the photoresist pattern. The improved positional accuracy enhances the performance and lifetime of ion thrusters which include nonplanar electrodes that are fabricated with this process.

Abstract: Ion erosion of grids is reduced in an ion thruster with a multiple-grid ion-optics system. The thruster has an array of aperture sets in which aperture areas change in a perimeter region of the array. In one ion-optics system embodiment, a screen aperture area is reduced and a decelerator aperture area is increased in aperture sets that are proximate to the perimeter of the array. Prototype tests of this embodiment have illustrated significant reduction of ion erosion.

Abstract: A molecular beam epitaxy (MBE) growth method and apparatus is disclosed which achieves a significantly improved sticking coefficient for materials like Hg upon a substrate, and thus a higher efficiency. A highly ionized, low pressure plasma is formed consisting of a mixture of ions of one substance of a compound to be epitaxially grown, neutral particles of the substance and electrons, and also preferably both ionization and excitation radiation. The plasma is directed onto a substrate together with a flux of the other substance in the compound; the flux can be in the form of either a vapor, or a second plasma. Radiation assisted epitaxial growth for Hg compounds in which ionization and excitation radiation are formed from Hg vapor and used to assist epitaxial growth with neutral Hg particles is also described. The plasma is formed in a special discharge chamber having a hollow cathode with an emissive-mix-free cathode insert.

Abstract: A molecular beam epitaxy (MBE) growth method and apparatus is disclosed which achieves a significantly improved sticking coefficient for materials like Hg upon a substrate, and thus a higher efficiency. A highly ionized, low pressure plasma is formed consisting of a mixture of ions of one substance of a compound to be epitaxially grown, neutral particles of the substance and electrons, and also preferably both ionization and excitation radiation. The plasma is directed onto a substrate together with a flux of the other substance in the compound; the flux can be in the form of either a vapor, or a second plasma. Radiation assisted epitaxial growth for Hg compounds in which ionization and excitation radiation are formed from Hg vapor and used to assist epitaxial growth with neutral Hg particles is also described. The plasma is formed in a special discharge chamber having a hollow cathode with an emissive-mix-free cathode insert.

Abstract: An ion propulsion system is disclosed. The invention includes a ionizing system for ionizing a gaseous propellant within a chamber to produce a plasma. The ionizing system includes a cathode 14 to provide a source of electrons and anodes 11 and 13 to accelerate the electrons to velocitites sufficient to ionize the gaseous propellant. The invention further includes an ion extraction system 20 for expelling an ion beam from the plasma. A particularly novel aspect of the invention is the provision of a control system 45 and 46 for modulating the current of the ion beam by modulating the current through the anode 11 and 13.

Abstract: An emission current control system for balancing the individual emission currents from an array of hollow cathodes has current sensors for determining the current drawn by each cathode from a power supply. Each current sensor has an output signal which has a magnitude proportional to the current. The current sensor output signals are averaged, the average value so obtained being applied to a respective controller for controlling the flow of an ion source material through each cathode. Also applied to each controller are the respective sensor output signals for each cathode and a common reference signal. The flow of source material through each hollow cathode is thereby made proportional to the current drawn by that cathode, the average current drawn by all of the cathodes, and the reference signal. Thus, the emission current of each cathode is controlled such that each is made substantially equal to the emission current of each of the other cathodes.