Abstract: A multilayer semiconductor structure includes a germanium substrate having a first surface. The germanium substrate has two regions, a bulk p-type germanium region, and a phosphorus-doped n-type germanium region adjacent to the first surface. A layer of a phosphide material overlies and contacts the first surface of the germanium substrate. A layer of gallium arsenide overlies and contacts the layer of the phosphide material, and electrical contacts may be added to form a solar cell. Additional photovoltaic junctions may be added to form multijunction solar cells. The solar cells may be assembled together to form solar panels.

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: A power generator includes a current-generating cell having a layer of a fission source of heavy ions and alpha particles, and two semiconductor structures, one on each side of the layer of the fission source. The layer of the fission source is preferably Pu238 or Cf252. The semiconductor structure is preferably a silicon structure such as a silicon P-I-N diode. The cell includes two metal contact layers, each contacting a respective one of the semiconductor structures at a location remote from the layer of the fission source. A voltage source, such as a thermopile operating with heat produced from the current-generating cell, is in electrical communication with the two metal contact layers to apply a collection voltage across the current-generating cell. Two current collector leads are provided, with each current collector lead being in electrical communication with a respective one of the two metal contact layers.

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 optical fiber has a concentration of dopant ions residing within its core region. The dopant ions absorb optical energy at an excitation wavelength, converting that optical energy to heat and/or a change in the index of refraction and optical length of the optical fiber. Optical energy of the excitation wavelength is transmitted through the optical fiber simultaneously or sequentially with optical energy of a signal wavelength different from the excitation wavelength. The optical energy of the excitation wavelength controls the temperature of the optical fiber and/or its optical length as a result of (a) the temperature dependence of the refractive index and the physical length of the optical fiber, and (b) the change in polarizability of the optical fiber medium (and hence its refractive index) due to a change in the population distribution among the energy levels of the dopant ions.

Abstract: Methods are provided for dynamically processing successively-generated star tracker data frames and associated valid flags to generate processed star tracker signals that have reduced noise and a probability greater than a selected probability Pslctd of being valid. These methods maintain accurate spacecraft attitude control in the presence of spurious inputs (e.g., impinging protons) that corrupt collected charges in spacecraft star trackers. The methods of the invention enhance the probability of generating valid star tracker signals because they respond to a current frame probability Pfrm by dynamically selecting the largest valid frame combination whose combination probability Pcmb satisfies a selected probability Pslctd. Noise is thus reduced while the probability of finding a valid frame combination is enhanced. Spacecraft structures are also provided for practicing the methods of the invention.

Abstract: A satellite (30) programmed for sun-nadir steering and having a solar wing (36) mounted to the satellite body (35) and being selectively moveable about two mutually orthogonal axes (A, B). The solar wing (36) is mounted to the satellite body (35) by a pair of gimbals (43, 45) thus allowing two degrees of freedom and thereby permitting the solar wing (36) to be rotated about the two mutually orthogonal axes (A, B). A first motor (42) in operative engagement with the gimbal (43) selectively rotates the solar wing about the axis (A), while a second motor (46) in operative engagement with the gimbal (45) selectively rotates the solar wing about the second axis (B). A control circuit (40) is in operative engagement with the first and second motors and selectively causes the first motor to rotate the solar wing about the first axis to a predetermined position, and selectively causes the second motor to rotate the solar wing about the second axis to a predetermined position.

Abstract: For an antenna on a satellite in an inclined orbit about the Earth, cross-track motion resulting from the rotation of the Earth can be reduced in antenna coordinates by yawing and/or rolling the antenna (preferably by yawing and/or rolling the entire satellite, for example, by using a reaction wheel system) by an appropriate angle, which varies throughout the orbit.

Abstract: Control systems and methods are provided which enhance acquisition range, transient response and offset pointing accuracy in beacon-assisted orientation of a spacecraft to a desired spacecraft attitude Adsrd. The methods receive a beacon signal with antennas that are arranged in a fixed angular relationship to thereby form an attitude error signal Serr whose magnitude is a measure of the attitude difference between a current spacecraft attitude Acrnt and the desired spacecraft attitude Adsrd. A sum power P&Sgr; that is the sum of the signal powers from the antennas is sensed and a signal modifier Smod is generated that increases with decreases in the sum power P&Sgr;. The attitude error signal Serr is then modified with a term (1+Smod) to form an enhanced attitude error signal Serrenhd. In one embodiment, the signal modifier Smod is n|Pmax−P&Sgr;|m wherein n and m are positive numbers and Pmax is the sum power P&Sgr; when the attitude error is zero.

Abstract: An earth sensor for a communication satellite is provided which utilizes a camera for viewing the earth from the satellite and an optical correlator which optically processes the video data from the camera to provide attitude information to a satellite attitude control computer.

Abstract: For an antenna on a satellite in an inclined orbit about the Earth, cross-track motion resulting from the rotation of the Earth can be reduced in antenna coordinates by yawing the antenna (preferably by yawing the entire satellite, for example, by using a reaction wheel system) by an appropriate angle, which varies throughout the orbit.

Abstract: A battery system includes an electrical storage cell having a positive terminal and a negative terminal. The electrical storage cell is provided with a normally open bypass circuit path that is closed in the event of an open-circuit failure of the electrical storage cell. The bypass circuit path includes a first electrical conductor connected to the positive terminal of the electrical storage cell, a second electrical conductor connected to the negative terminal of the electrical storage cell, and a shorting gap between the first electrical conductor and the second electrical conductor. A mass of a fusible material is positioned at an initial mass location. A heat source is activatable upon the occurrence of an open-circuit condition of the electrical storage cell. The heat source is operable to melt at least a portion of the mass of the fusible material and thereby to close the shorting gap so that the first electrical conductor is in electrical communication with the second electrical conductor.

Abstract: A system and method of estimating the attitude of a spacecraft compares a three-axis inertial-based estimate of spacecraft attitude to a stellar-based estimate of the spacecraft attitude. A Kalman filter having some states associated with low spatial frequency errors compares the stellar-based attitude estimate to the inertial-based estimate of attitude and apportions total attitude error into two time varying matrices. A first time varying matrix is associated with star tracker low spatial frequency errors, a second time varying matrix is associated with gyro bias errors and attitude errors. The time varying matrices are used to apply corrective feedbacks to the stellar-based attitude estimate and the inertial-based estimate of spacecraft attitude, and are adaptively adjusted to minimize total estimated attitude error.

Abstract: A rocket engine includes a generally cylindrical annular combustion chamber, an injector attached to an injector end of the combustion chamber, a generally cylindrical annular step collar fitting within the combustion chamber at the injector end thereof, and an attachment of the combustion chamber, the injector, and the step collar. The maximum outer diameter of the step collar is from about 0.020 inches to about 0.024 inches smaller than the inner diameter of the combustion chamber, and has a length of from about 21 to about 31 percent of the length of the combustion chamber. The step collar is made of a material having a melting point greater than that of the combustion chamber. The attachment preferably includes a clip structure joining the combustion chamber and the step collar.

Abstract: A family of adhesives is provided for bonding cyanate ester composite articles together which is also plateable with metal once chemically etched. The adhesives comprise a polymeric matrix and a filler of metal powder or metal flakes. The polymeric matrix comprises at least one polyepoxide resin and at least one curing agent. In practice, the present adhesive is applied to the surface of cyanate ester composite articles to be bonded and is allowed to cure in air at a temperature less than 125° C. Thereafter, the surface of the assembly is chemically etched and then plated with metal. The present adhesives enable the complete coverage of the cyanate ester composite assembly with the plated metal, including the adhesive bondlines. A cyanate ester resin structure assembled with the present adhesive composition may, upon plating, replace certain metallic components in such applications as aircraft, spacecraft, and automobiles given its highly conductive and comprehensive metallic coating.

Abstract: A dynamic method for optimizing interference levels between multiple downlink beams transmitted from a satellite with a common frequency spectrum causes the power level of at least one of the interfering beams to be adjusted so as to produce desired interference levels within the beams' respective ground target areas. The beam power adjustments are preferably accomplished by varying the drive levels of the high power amplifiers on board the satellite, at least one of which is initially operated at less than its maximum rated power level. Single or multiple beam powers can be adjusted, either up, down or some up and some down. Power level adjustments are normally made in response to actual beam power profiles not matching design standards, to changing service priorities among the different beam target areas, and to changing signal power requirements for the different beams.

Abstract: An optical transition device provides a connection between two fiber structures. The device comprises a first transition body having a first transition body bore therethrough, a first fiber connector connected to the first transition body and having a first connector bore therethrough, a second transition body affixed to the first transition body and having a second transition body bore therethrough, and a second fiber connector connected to the second transition body and having a second connector bore therethrough. The first connector bore, the first transition body bore, the second transition body bore, and the second connector bore are coaxial along a transition axis. A graded-index lens is disposed within the transition body bores with an optical axis of the lens coincident with the transition axis. An axial positioning structure positions the graded-index lens axially along the transition axis.

Abstract: An antenna system having a rotatable and scannable reconfigurable shaped reflector with a movable feed system. The antenna system allows beam shapes to be rotated about an optimum axis and defocused while a spacecraft is in orbit in order to change a particular coverage pattern for the spacecraft.

Abstract: A coated electronic assembly comprises an electronic assembly, and a single-layer conformal coating overlying at least a portion of the electronic assembly. The conformal coating has a volume electrical resistivity of from about 108 to about 1014 ohm-centimeter. The conformal coating is formed of an organic polymeric binder, and a plurality of electrically semiconductive metal oxide filler particles dispersed in the binder. The binder and the filler particles have substantially the same visible-light refractive index. The binder may be a heat-curable or UV-curable urethane, and the particles may be doped (Al,Mg,Zn)3O4 or doped ZnO.

Abstract: The attitude of a spacecraft is controlled during an eclipse without the dependence on auxiliary power by configuring the spacecraft so that it will receive solar power after solar eclipse is passed. The spacecraft is then oriented with respect to a sun line. The spacecraft is then spun so that it maintains a desired angular momentum throughout the eclipse and provides passive stabilization of the attitude. After the eclipse has passed, the spacecraft power is restored and the spacecraft attitude is detected. All spacecraft units are then powered up and thereafter, normal on-station attitude is re-established and normal spacecraft operations are established.