Abstract: A compact, stable, and optically efficient two dimensional spatial light modulator-based electro-optical control system for large (>1000 elements) phase-based phased array antennas uses two externally phase-locked lasers to generate respective pluralities of first and second light beams that are respectively mutually orthogonally polarized. Respective ones of the first and second light beams are combined to pass along collinear and coincident paths to form a plurality of combined light beams. The frequency difference between the first and second light beams which form the constituent beams in each combined beam cause an interference pattern that, upon heterodyne detection of the optical signal and conversion to an electrical antenna drive signal, provides control of the carrier frequency for driving the antenna.

Abstract: A nonrectangular antenna aperture is provided comprising four quadrants for receiving electromagnetic signals. The aperture has the capability to form a predetermined sum beam, a predetermined first difference beam, a predetermined second difference beam, and a predetermined double difference beam so that the product of the first and second difference beams is substantially equal to the product of the sum and the double difference beams.

Abstract: Two variable frequency, fixed bandwidth bandpass 10, 410 are cascaded to form a bandpass filter with variable center frequency and variable bandpass. Each filter 10, 410 includes first (16, 416) and second (24, 424) mixers separated by a fixed bandpass filter (20, 420). Each mixer includes a control input terminal 30, 32: 430, 432 which receives a control signal (f.sub.LO, f.sub.OFF). The center frequency of the filter arrangement is controlled by the frequency of control signal f.sub.LO, and the bandwidth is controlled by the difference frequency between f.sub.LO and f.sub.OFF. A tracking arrangement 456 allows direct control of the bandpass by control of the frequency of an offset oscillator 458.

Abstract: A multichannel communication system carries signals having a different frequency range in each channel. In order to achieve a particular output power level from each channel, an amplifier is associated with each channel to boost the signal level. For reliability, a switching arrangement switches amplifiers among the channels in accordance with a priority, or substitutes a redundant amplifier for a degraded or failed unit in a channel. The amplifier is subject to distortion at the desired output level, and is cascaded with a distortion equalizer or linearizer for reducing the total distortion. In accordance with the invention, each distortion equalizer is fixedly connected in one channel, and is optimized for the relatively narrow frequency range of that channel, rather than being switched together with the amplifier and being optimized over the total or cumulative bandwidth of all the channels.

Abstract: An RF-transparent sunshield membrane covers an antenna reflector such as a parabolic dish. The blanket includes a single dielectric sheet of polyimide film 1/2-mil thick. The surface of the film facing away from the reflector is coated with a transparent electrically conductive coating such as vapor-deposited indium-tin oxide. The surface of the film facing the reflector is reinforced by an adhesively attached polyester or glass mesh, which in turn is coated with a white paint. In a particular embodiment of the invention, polyurethane paint is used. In another embodiment of the invention, a layer of paint primer is applied to the mesh under a silicone paint, and the silicone paint is cured after application for several days at room temperature to enhance adhesion to the primer.

Abstract: An antenna suited for a communications satellite includes two separately located, mutually orthogonally polarized feed antennas such as vertically and horizontally polarized linear horns. The horns feed an active reflector antenna array. The array includes a plurality of mutually orthogonally polarized antenna elements such as crossed dipoles or square patch antenna with cross feeds for two independent orthogonal polarizations. The feeds of the antenna elements are coupled to amplifier modules. Each module includes a circulator for each polarization, coupled to a processor including a low noise amplifier, controlled phase shifter, variable gain amplifier and power amplifier. The output of the power amplifier feeds the antenna element through the circulator. The large number of radiating elements allows high power using power amplifier with relatively modest capabilities.

Abstract: A zero-dB hybrid or directional coupler includes a first through waveguide extending between first and third ports and a second through waveguide, parallel to the first waveguide, and extending between second and fourth ports. A plurality of branch waveguides extend between the first and second through waveguides, and are adjusted to couple signal from the first port only to the fourth port, and from the second port only to the third port (within in limits of systems isolation). Particular normalized branch line impedances provide best operation. A communication system especially adapted for use as a spacecraft uses a zero-dB coupler in a "planar" waveguide system to transpose or "crossover" the positions of two system ports, whereby the physical positions of the various ports are arranged in the same relation as their phase progression.

Abstract: An antenna beamformer is provided for coupling to a circular antenna aperture comprising a plurality of vertical beamformers and four horizontal beamformers coupled to the vertical beamformers so that each horizontal beamformer has the capability to form a different predetermined electromagnetic field radiation pattern.

Abstract: A spacecraft includes bipropellant and monopropellant engines or thrusters. The oxidizer-fuel mixture ratio of the bipropellant engine is not known exactly. The spacecraft is loaded with only sufficient oxidizer to achieve the velocity for transfer from an intermediate orbit to geosynchronous orbit if the mixture ratio is nominal. Therefore, more fuel can be loaded. If the bipropellant engine burn is nominal, there is no excess oxidizer when on-orbit and more fuel is available for stationkeeping. If the burn is oxidizer-rich, there is a velocity shortfall, which is made up by firing monopropellant engines. If the burn is oxidizer-lean, the geosynchronous orbit is achieved with a load of excess oxidizer, which must be moved during each stationkeeping maneuver. A net gain of stationkeeping time results in any of the three mixture ratio cases by comparison with loading of sufficient oxidizer for a full bipropellant burn under worst-case mixture conditions.

Abstract: A small target phased array Doppler detection system receives signals from remote moving targets and determines Doppler frequency shift and the respective powers of coherent electromagnetic signals for the purpose of detection and identification of relatively small, slow moving targets in the presence of scattering echoes due to clutter. The system employs covariance analysis of the received signals followed by eigenanalysis to produce eigenvectors and eigenvalues. A superresolution algorithm creates dwell manifold vectors which indicate velocities of targets from the eigenvectors. The relative power of radar echoes contribute information relevant to the identification of real moving targets as opposed to false alarms.

Abstract: Arrays of helical antennas are desired for operation at spaced-apart frequencies, such as 1.5 and 2.5 GHz. In order to reduce mutual coupling between the antenna elements of the lower-frequency array, they are spaced apart by more than .lambda.. Grating lobes occur due to the spacing. The lengths of the lower-frequency helices are adjusted to move the nulls in their radiation patterns into congruence with the unwanted peaks of the array pattern, thereby suppressing the grating lobes. In order to reduce the total area of the combined arrays, the higher-frequency antennas of the second array are interleaved with the elements of the first array. At the higher frequency, the antenna elements of the second array are spaced apart even further, in terms of wavelength, than the elements of the first array, so mutual coupling of the antennas of the second array is reduced even more than in the first array.

Abstract: A spacecraft includes a pair of pressurized propellant tanks. The pressure may be provided from a common pressurant tank. Each propellant tank has a propellant output port. A manifold includes a first branch coupled between a common juncture and the output port of the first tank, and a second branch between the juncture and the output port of the second tank. At least the second tank is associated with a heater. A controllable valve, such as a normally open pyrovalve, is coupled in the second branch. In order to fully utilize the propellant in the tanks, the second tank is differentially heated relative to the first when the tanks are nearly empty, to create a tendency toward a pressure difference, which drives propellant from the second tank to the first. When all or most of the propellant is transferred, the valve is operated to close off the second branch of the manifold, to isolate the now-empty tank.

Abstract: A spacecraft includes an attitude control system using one or more reaction wheels, the speed of which from time to time lie near and pass through zero angular velocity. When operated for extended periods of time at low speeds, the lubrication films are not distributed uniformly on the wheel bearings, leading to reduced lifetime. Reliability is maintained by a threshold comparator coupled to compare wheel speed with a lower limit value, for operating a torquer associated with the spacecraft body when the wheel speed drops below the lower limit, in a manner which tends to raise the wheel speed. In a particular embodiment of the invention, the lower limit is integrated with a wheel overspeed unloading.

Abstract: A robot is controlled to move from a predetermined rest point to contact a moving target. The control parameters of the robot are not known. Control is effectuated by predetermining the time required for the robot to move from a rest position to each of a plurality of points within the region in which the target is expected to be found. When the target is identified, its location near the predetermined points at a future time is computed. The known time required from motion of the robot from the rest position to predetermined points adjacent the future location of the target is determined by reference to stored information. The exact time required for the motion may be interpolated between the predetermined points. The time for robot motion is subtracted from the future time to determine the time at which robot motion begins. In a particular embodiment of the invention, a robot coacts with a circular conveyor belt to retrieve objects from the conveyor and transport them to a dump point.

Abstract: A stowable and self-deployable array antenna includes flat, rectangular antenna panels hinged side-by-side so that when deployed they are coplanar, and they fold like an accordion for stowing. The deployed array antenna is stiffened by lateral stiffening panels hingedly attached to every other hinge between antenna panels, and to the unhinged ends of the antenna panels. Foldable longitudinal stiffening panels hinged between adjacent lateral stiffening panels. Each hinged connection includes a pair of thin spring elements, corresponding to a portion of a cylinder. The two spring elements of each hinge are spaced apart with their concave sides facing, and with the axes of the defining cylinder parallel. The hinge pivots, when the spring elements buckle, about a line orthogonal to a line extending between the cylinder axes. The hinges are used as the structural elements of self-deployable masts. The mast may have a polygonal cross-section.

Abstract: A ranging system such as a radar system transmits signal pulses toward a diffuse target, such as an atmospheric disturbance. The echoes are processed by quantizing and by doppler filtering to produce a plurality of frequency components representing the radial velocities of various parts of the disturbance, which components are expected to be contaminated by an unknown amount of noise. The noise value is established by squaring the echo signals to produce power-representative signals. The signal samples are ranked according to amplitude, and one or more of the largest-value samples are discarded to reduce the order of the sample set. A Kolmogorov-Smirnov test statistic is generated and compared with a threshold established by the desired confidence level. If the test statistic exceeds the threshold, the order of the sample set is again reduced, and the test statistic again compared with the threshold.

Abstract: A multipurpose system provides radar surveillance for air traffic control purposes. The system includes four separate active phased-array antennas, each with .+-.45.degree. coverage in azimuth, from 0.degree. to 60.degree. in elevation. Each antenna element of each phased-array antenna is coupled by a low-loss path to the solid-state amplifier associated with a transmit-receive (TR) module. Each antenna produces a sequence of pencil beams, which requires less transmitted power from the TR modules than a fan beam, but requires more time because the pencil beam must be sequenced to cover the same volume as the fan beam. In order to scan the volume in a short time, the PRF is responsive to the elevation angle of the beam, so higher elevation angles use a higher PRF. Low elevation angle beams receive long transmitter pulses for high power, and pulse compression is used to restore range resolution, but the long pulse results in a large minimum range within which targets cannot be detected.

Abstract: A multipurpose system provides radar surveillance for air traffic control purposes. The system includes four separate active phased-array antennas, each with .+-.45.degree. coverage in azimuth, from 0.degree. to 60.degree. in elevation. Each antenna element of each phased-array antenna is coupled by a low-loss path to the solid-state amplifier associated with a transmit-receive (TR) module. Each antenna produces a sequence of pencil beams, which requires less transmitted power from the TR modules than a fan beam, but requires more time because the pencil beam must be sequenced to cover the same volume as the fan beam. In order to scan the volume in a short time, the PRF is responsive to the elevation angle of the beam, so higher elevation angles use a higher PRF. Low elevation angle beams receive long transmitter pulses for high power, and pulse compression is used to restore range resolution, but the long pulse results in a large minimum range within which targets cannot be detected.

Abstract: A three-axis attitude control system for a spacecraft in an equatorial orbit includes at least a horizon sensor for producing pitch-representative signals. A star sensor has a boresight parallel to the spacecraft pitch axis, and produces signals representative of the two-axis location of a selected pole star relative to the boresight. The star sensor signals are processed in conjunction with the pitch-representative signals and with orbit-location information, to produce roll and yaw information. The pitch, roll and yaw information controls spacecraft torquing. In a particular embodiment of the invention, the horizon sensor arrangement also produces roll signals, which are processed with the roll signals from the star sensor.

Abstract: A multipurpose system provides radar surveillance for air traffic control purposes. The system includes four separate active phased-array antennas, each with .+-.45.degree. coverage in azimuth, from 0.degree. to 60.degree. in elevation. Each antenna element of each phased-array antenna is coupled by a low-loss path to the solid-state amplifier associated with a transmit-receive (TR) module. Each antenna produces a sequence of pencil beams, which requires less transmitted power from the TR modules than a fan beam, but requires more time because the pencil beam must be sequenced to cover the same volume as the fan beam. In order to scan the volume in a short time, the PRF is responsive to the elevation angle of the beam, so higher elevation angles use a higher PRF. Low elevation angle beams receive long transmitter pulses for high power, and pulse compression is used to restore range resolution, but the long pulse results in a large minimum range within which targets cannot be detected.