Abstract: A zero-momentum spacecraft's attitude is controlled by determining the torque required about a control axis to maintain the desired attitude, and, during each of recurrent control cycles, enabling a magnetic torquer if the torque demand exceeds a threshold. During each of the control cycles, thruster(s) are enabled to make up the difference between the torque demand and the estimated torque produced by the magnetic torquer. In determining the torque demand, the attitude rate signal is low-pass filtered to reduce noise, and the control loop bandwidth is maintained by totalling the estimated torque applied by the magnetic torquer and thrusters, integrating and high-pass filtering the estimated torque signals, and adding the filtered estimated torque with the filtered attitude rate signals to generate low-noise attitude rate signals. A three-axis system is described.

Abstract: Two opaque sheets made from the same electrically conductive polymer material have adjoining edges. Each sheet is carbon loaded, electrically conductive, opaque black polymer on a first broad side thereof. The sheets are joined along a seam region by means of an opaque, electrically conductive adhesive tape. The electrically conductive adhesive tape includes an elongated opaque sheet of electrically conductive polymer material of the same kind as that of the two opaque sheets which the tape joins. The opaque, electrically conductive adhesive tape also includes a layer of electrically conductive adhesive, which is connected to the electrically conductive polymer material. In a particular embodiment of the invention, the polymer material is polyimide. In a preferred embodiment, the two opaque sheets are thermal coverings for a spacecraft, and each includes a sheet of opaque polyimide, carbon loaded which is electrically conductive, on the exterior of the thermal coverings.

Abstract: An antenna array for use in space includes an optical solar reflector (OSR)-like structure (310, 510), with sheet of transparent dielectric material (320, 520) and a metallic mirror (322, 522) formed on the sheet. In order to allow the individual antenna elements to radiate electromagnetic energy, the metallic mirror contains apertures (330, 530) which, in one embodiment, define the antenna elements, and which, in another embodiment, are registered with the antenna elements of the array. Where the mirror exists, insolation is reflected, and the heat gain from insolation is minimized. At the locations of the apertures in the mirror, insolation passes through the OSR-like structure, which may tend to increase the temperature of the structure. According to the invention, the apertures are covered with a thin layer (370, 570) of semiconductor material such as germanium or silicon, which does not affect the electromagnetic energy flow.

Abstract: A sigma-delta analog-to-digital converter (10) provides high loop gain for suppression of noise components by use of a regenerative feedback loop or resonator (50), which produces a comb resonance response 212), embedded in the main degenerative feedback loop (48). The main loop includes an ADC (32) which samples at a clock frequency, which in turn defines a Nyquist frequency. The main loop also includes a DAC (38) which has a transfer function (42), which is equalized by a filter (44). The resonator (50) includes a low-pass filter (52) which matches the equalized main loop transfer function, a DC block (56), and a null filter (54) which nulls the resonator gain at the comb peak which lies above the Nyquist frequency. The open-loop transfer function of the regenerative loop (50) is set to unity gain and 0.degree..+-.N 360.degree. phase at the frequency of the analog input signal. A multipole embodiment (510) has multiple regenerative loops (55o) which produce multipole noise rejection (642).

Abstract: A spacecraft is controlled by a composite attitude signal including two components with different passbands. In one embodiment, a spacecraft attitude control system includes an attitude sensor and a controller which provides a time derivative function. High frequency noise components of the sensed attitude signal are enhanced by the derivative, and tend to cause attitude jitter or excess power consumption. The jitter is reduced by low pass filtration of the sensor signal, but this undesirably reduces the high frequency response of the attitude sensor. The high frequency response is restored by high pass filter coupled to a reaction or momentum wheel tachometer, which produces a signal representative of the high frequency components of the body rate. A summing circuit couples together the filtered attitude sensor signals with the high frequency components of the wheel speed signal to produce a relatively noise free broadband body rate signal.

Abstract: A radar system which uses an active phased-array antenna achieves improved clutter improvement factor (CIF) by powering the various transmit-receive (TR) modules of the antenna with direct voltage (DC) derived from a plurality of phases of the power-line alternating current (AC). Each TR module receives power which originates with one phase of the source AC. The phases are selected so that the modulation of the radio-frequency (RF) signals by each TR module tends to cancel in the summed signal from the array antenna.

Abstract: A bidirectional power converter array has overall voltage feedback, an error signal generator, and plural bidirectional power converter modules. Each module of the array includes a series inductor and local feedback based upon the inductor current. Each module also has a resistive current sensor, providing wideband local feedback. A low-pass filter is coupled to the current sensing resistor to reduce switching noise. The low-pass filter also reduces the bandwidth of the local feedback signal, so interactions with the overall feedback occur, which may result in instability. A winding transformer-coupled to the series inductor generates AC signal representing high-frequency components of the inductor current, relatively free of switching noise. The AC current sample is added to the low-frequency components derived from the resistor and low-pass filter, to form a low-noise local feedback signal, with sufficient bandwidth to reduce unwanted interactions with the overall system feedback.

Abstract: Monopulse radar operation is improved by nulling a single mainlobe jammer and multiple sidelobe jammers while maintaining the angle measurement accuracy of the monopulse ratio. A sidelobe jammer cancelling adaptive array is cascaded with a mainlobe jammer canceller, imposing a mainlobe maintenance technique or constrained adaptation during the sidelobe jammer cancellation process so that results of the sidelobe jammer cancellation process do not distort the subsequent mainlobe jammer cancellation process. The sidelobe jammers and the mainlobe jammer are thus cancelled sequentially in separate processes.

Abstract: A transducer array according to the invention includes forty-two acoustic transducers for use in a fluid medium, with each of the transducers having maximum lateral dimensions of less than one acoustic wavelength in the medium, whereby the transducers themselves tend to radiate isotropically. The elements of the array are located at the vertices of an regular geodesic two-frequency icosahedron. The transducer array also includes a driver or a receiver, or both, and arrangements for coupling them to the array elements. A switching circuit can couple the array elements alternately to the driver or receiver, depending upon the operating mode. A conventional delay controller is coupled to the acoustic transducers, for controlling an acoustic beam formed by the array. In a particular embodiment of the invention, the array is operated at frequencies selected so that the inter-transducer spacing of any two mutually adjacent transducers does not exceed 2.lambda./3, and is not less than .lambda./3.

Abstract: A spacecraft (10) includes and attitude sensor (16) for generating sensed attitude signals. A controllable drive arrangement (238) is coupled to a reaction wheel (46), for driving it in response to speed error signals. The drive results in changes in reaction wheel speed. The spacecraft has a digital speed sensor (248) coupled to the reaction wheel, for generating quantized speed signals. A reaction wheel speed error signal generator (234) produces speed error signals in response to the difference between the attitude command and the sensed attitude signals, corrected by signals responsive to the speed of the reaction wheel, whereby at low reaction wheel speeds, the quantization causes attitude errors.

Abstract: A monopulse signal processor provides target monopulse ratios and thus target angles having an improved accuracy in those situations where a low signal-to-noise ratio subsists and the monopulse ratio is derived from a sequence of pulses. The monopulse ratio value is determined by: ##EQU1## and .SIGMA..sub.Ii is the in-phase component of the sum signal for the i.sup.th pulse, .SIGMA..sub.Qi is the quadrature component of the sum signal for the i.sup.th pulse, .DELTA..sub.Ii is the in-phase component of the difference signal for the i.sup.th pulse, and .DELTA..sub..OMEGA.i is the quadrature component of the difference signal for the i.sup.th pulse.

Abstract: A process and apparatus for making high purity aluminum nitride from organometallic aluminum, such as an alkylaluminum compound. A gaseous alkylaluminum compound and gaseous ammonia are introduced into a heated reaction zone where the gases are mixed and high purity aluminum nitride is produced. The high purity aluminum nitride is collected in the form of a powder or deposited as a thick, dense layer on an appropriate substrate mounted in the reaction chamber. A carrier gas such as hydrogen gas, may be used to conduct the alkylaluminum compound from a suitable reservoir containing liquid alkylaluminum compound to the reaction chamber. A preferred alkylaluminum compound is triethylaluminum.

Abstract: A multitrack optical disk has two or more circular or spiral tracks, which are recorded or played back in simultaneous sets for high data rates. Tracking is accomplished by sets of first and second tracking pads, which lie partially on and partially off the track paths. The amount of inter-track space required to accommodate the track pads is reduced by placing the overlap of the tracking pads in the same inter-track space, and by tracking any additional simultaneous tracks in excess of two by mechanical coupling with the first two.

Abstract: A three-dimensional array (10) of semiconductor chips (24, 124) includes stacked 2D high density interconnect (HDI) modules (12, 14) held by adhesive (16). Each HDI module has a ceramic substrate (20, 120) with a cavity (22, 122) dimensioned to accommodate a chip. An interconnect sheet (28, 128) has a conductor pattern (30, 130) and vias (32, 132) which interconnect the chips of each HDI module. Thermal conduction from the upper module (12) to the lower module (14) is inhibited by the low thermal conduction of the lower interconnect sheet (128), tending to raise the chip temperature. Thermal conduction is improved by thermally conductive posts (44) extending between upper (20) and lower (120) substrates through apertures (140) in the interconnect sheet (128). If the posts (44) are electrically conductive, they may be used for electrical interconnections among modules of the 3D array.

Abstract: A communications station (10) couples a bidirectional input-output signal path (16') to two unidirectional signal paths; a transmit signal path (12') and a receive signal path (14'), using a controllable hybrid (20). A feedback control system in the station minimizes the amount of transmit signal appearing at the receive output port (24) of the hybrid (20). The control system spreads the spectrum of a pilot signal (40) by means of a biphase modulator (46) and a pseudorandom generator (42) to produce a spread-spectrum pilot, which is added, in a summer 30, to the transmit signal. The spread-spectrum pilot signal covers the bandwidth of the information signal, and is reflected in an amount and with a phase which depends upon the relative impedance presented to the hybrid (20) by the bidirectional signal path (16').

Abstract: A dual-polarized antenna includes a planar line or surface array of reradiating elements of two different polarizations. Each reradiating element in one embodiment is a short-circuited vertical or horizontal dipole. The vertical and horizontal dipoles may be collocated on the array to form crossed short-circuited dipoles. The elements of each polarization form an array separate from the elements of the other polarization. Within each of the two separate arrays, the 1/.lambda. of each reradiator is adjusted to provide a phase shift which causes a collimated beam incident on the array to result in reradiation or "reflection" of energy in the form of a beam converging at a focal point. Therefore, each planar reradiator array acts as a parabolic reflector with a particular focal point. The focal points for the vertical and horizontal arrays are different, and a feed of the appropriate polarization is located at each of the two focal points.

Abstract: A color television camera includes a panchromatic light sensor such as a CCD imager. Light from a scene to be imaged is filtered by an electronically controlled light filter such as an etalon, which is scanned from color to color at the field rate, so that the image for each field is generated by a different color. The periodic spectral line or spectral band response of a single etalon is improved by a cascade of two etalons with different periodicity, which pass only a single spectral line or band. When an RGB color sequence is used, a complete color signal frame is generated in three fields. The imager may be operated at a field rate higher than the standard field rate, such as 90 Hz. for use with conventional 30 Hz. color frame rate, and a memory may be coupled to the output of the imager to store the three-field sequence of signals which occurs during each standard color frame, so that a complete color signal is available during each standard color frame.

Abstract: A notch filter includes a directional coupler (16) with an input port (17a), coupled output port (17b), coupled 0.degree. (17d) and direct 90.degree. (17c) ports. A cylindrical dielectric resonator (40) is supported by a spacer (58) above a ground plane (14) and dielectric substrate (12). A first microstrip transmission line includes a strip conductor (22) coupled at one end to the coupled 0.degree. port, and extending parallel to a tangent to the edge of the resonator at a central plane (44), terminating in an open-circuit (226). A second transmission line includes a strip conductor (24) coupled to the direct 90.degree. port (17c) and extending parallel to the first transmission line, on the other side of the resonator. The first and second transmission lines each have an electrical length .lambda./4 between the central plane (44) and their open-circuit terminations, to reflect a high current to the plane.

Abstract: A spacecraft (8) includes a movable appendage such as solar panels (12) operated by a stepping motor (28) driven by pulses (311). In order to reduce vibration andor attitude error, the drive pulses are generated by a clock down-counter (312) with variable count ratio. Predetermined desired clock ratios are stored in selectable memories (314a-d), and the selected ratio (R) is coupled to a comparator (330) together with the current ratio (C). An up-down counter (340) establishes the current count-down ratio by counting toward the desired ratio under the control of the comparator; thus, a step change of solar panel speed never occurs. When a direction change is commanded, a flag signal generator (350) disables the selectable memories, and enables a further store (360), which generates a count ratio representing a very slow solar panel rotational rate, so that the rotational rate always slows to a low value before direction is changed. The principles of the invention are applicable to any movable appendage.

Abstract: A travelling-wave tube (TWT) for a satellite communication system includes a cathode current regulator which compares a sensed I.sub.K signal with a cathode current reference to form an cathode current error signal, and controls the cathode current in response to the cathode current error signal. Helix arc protection is provided by a helix current shut-down, which compares the helix current with a particular reference, and shuts the TWT supply down when helix current flows. Desirable high efficiency TWTs have a small input drive range between maximum TWT output and a defocussed condition, in which beam current flows in the helix. Sudden changes in path attenuation may result in an RF overdrive condition, and cause helix current flow, and undesirably shut down the TWT. A helix current limiter senses the helix current, and compares it with a reference which represents less helix current than that which causes shutdown, to produce a helix current error signal.