Abstract: A nonlinear processor for use as a signal limiter or predistortion equalizer includes a four-port, 3dB directional coupler. Signal to be distorted is applied to a first port of the coupler, and is coupled by second and third ports to a pair of nonlinear circuits. Each nonlinear circuit includes the source-to-drain transmission path of a FET. Each nonlinear circuit is grounded or short-circuited, to form a nonlinear reflective circuit which reflects the energy back to the associated port of the coupler. The nonlinearly reflected energy is received at the two coupler ports, and is combined and made available at the fourth coupler port. The input return loss of the processor is improved by matching the nonlinear circuits to each other.

Abstract: An attitude control system for a spacecraft includes sensors for generating attitude control signals and logic for producing torque demand signals in the form of a T.sub.d matrix. The thrusters are oriented in complementary pairs about the center of mass for, when energized, producing mutually opposite torques. Information about the location of thrusters and their thrusts may be represented by a pulse-width-to-torque transformation matrix C. A weighted pseudo inverse of C is precalculated asQ=WC'(CWC').sup.- (13)and is stored in memory associated with the flight computer, thereby avoiding the need for the flight computer to perform the intensive calculations of Q. Thruster pulsewidth for attitude control is easily calculated by the flight computer as.DELTA..sub.p =.tau..sub.p QT.sub.d (14)where .tau..sub.p is the control cycle time.

Abstract: In a system for locating one object relative to another where one object is referenced to an active beacon and the other object is referenced to a solid state imaging device, circuitry determines the centroid of the image of the beacon as imposed on the imager. In accordance with the invention, the beacon is operated successively at two different wavelengths and two different centroids are determined. Based on a priori knowledge of imager responses at the two different wavelengths, the location capabilities of the system are improved relative to that when only one wavelength is utilized.

Abstract: A multipurpose catheter apparatus for microwave aided balloon angioplasty includes a balloon capable of being filled with a lossy dielectric liquid, and bearing a metallization pattern. The catheter includes an electromagnetic transmission line. Radio frequency energy applied to the proximal end of the electromagnetic transmission line is radiated by an antenna within the balloon. The metallization pattern causes a portion of the energy applied to the proximal end of the transmission line to be reflected, which affects a characteristic such as impedance, return loss or time of reflection. A measurement apparatus measures the characteristic, and the distention of the balloon is determined from the measured characteristic. A guide filament may extend through the transmission line.

Abstract: A spacecraft attitude and/or velocity control system includes a controller which responds to at least attitude errors to produce command signals representing a force vector F and a torque vector T, each having three orthogonal components, which represent the forces and torques which are to be generated by the thrusters. The thrusters may include magnetic torquer or reaction wheels. Six difference equations are generated, three having the form ##EQU1## where a.sub.j is the maximum torque which the j.sup.th thruster can produce, b.sub.j is the maximum force which the j.sup.th thruster can produce, and .alpha..sub.j is a variable representing the throttling factor of the j.sup.th thruster, which may range from zero to unity. The six equations are summed to produce a single scalar equation relating variables .alpha..sub.j to a performance index Z: ##EQU2## Those values of .alpha. which maximize the value of Z are determined by a method for solving linear equations, such as a linear programming method.

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 restored range resolution, but the long pulse results in a large minimum range within which targets cannot be detected.

Abstract: A range tone system for determining the range between a satellite or spacecraft and a ground station FM modulates one of a 3968 Hz, 283 Hz or 35 Hz range tone onto a 27.77 Khz range tone. Modulation is accomplished by simultaneously addressing a plurality of PROMs by related clocks. The PROMs are preprogrammed with data representing the 27.77 KHz tone frequency-modulated by another range tone. Narrow-band filtering recovers the 27.77 KHz range tone from the received signal, and frequency demodulation coupled with narrowband filtering recovers the lower-frequency tone. The two recovered tones are processed simultaneously to provide both high resolution range information together with ambiguity resolution.

Abstract: A method for maintaining the attitude of a three-axis controlled satellite by use of magnetic torquers includes using magnetometers for measuring the direction of the ambient geomagnetic field. The direction of the net reaction wheel momentum is also determined. The angle between the direction of the geomagnetic field and the net reaction wheel momentum is determined. The angle is compared with a threshold value. Magnetic torquer power consumption is reduced by operating the magnetic torquers only when the angle exceeds the threshold value.

Abstract: A probe for use in a coax-to-waveguide transition is uniformly coated with a dielectric material by inserting the probe through an elastic membrane covering a container of uncured RTV elastomer to thereby dip the probe. The membrane wipes excess elastomer from the probe during withdrawal, and seals the RTV from ambient air to thereby prevent its premature curing in the container. If moved sideways before withdrawal, the coating thickness can be made to favor one side over another. A magnetic block is fitted into a waveguide. A slot in the magnetic block is also filled with uncured RTV elastomer. The probe is inserted into the slot, embedding it in the uncured RTV. Upon curing, the probe is protected from high voltage arcing to the waveguide. A cured RTV elastomer washer is preassembled to the probe before dipping, to precisely fill the void between the connector base and the magnetic block with a like material.

Abstract: A switched inerconnection system for interconnecting the data input and output ports of a plurality of individual data processors, terminals, sensors, robots or the like of a parallel data processing system includes a plurality of identical modules and custom interconnections. Each module includes on-board interconnections between input and output ports for providing interconnections among the processors coupled to that module, for thereby reducing the number of customized interconnections between modules.

Abstract: A perfusion balloon catheter, as for angioplasty, has the balloon formed so that, when inflated within a vas or coronary artery, one or more channels are provided for the flow of bodily fluids or blood past the inflated balloon. In one embodiment, the balloon has a toroidal shape which defines a central open channel. In another embodiment, the balloon defines a multiply-lobed form which allows flow between the lobes. Balloon catheters with open channels, when used for angioplasty, reduce the likelihood of early termination of the procedure due to chest pain.

Abstract: An optical beam scanner or spoiler includes an array of electrically controlled liquid crystal phase shifters. Each element of the phase shifter includes an active region where proper phase shift occurs, and also includes another region, generally near the edges of the element, in which light transmission does not occur or in which improper modulation results. The inefficient regions reduce the light transmission or modulation efficiency of the array. An aperture illuminator includes a Talbot plane phase plate (also known as a Fresnel image phase plate) interposed between the incident light beam and the liquid crystal array. The phase plate includes a transparent substrate with a binary pattern of regions of relatively higher and lower index of refraction in a repeating pattern with a period P. In a particular embodiment of the invention, the regions are physically raised and lowered portions of a surface.

Abstract: A hierarchical stack filter performs nonlinear filtering operations such as median filtering and other rank-order filtering. The stack filter has a number of stages in the stack which equals the number of bits in the words of the input word sequence, and each filter of the stack receives as a first input signal a window of the input sequence. Each filter stage has an expansion input port and an expansion output port. Each filter stage calculates a residue and couples the residue from its expansion output port to expansion input port of the filter stage of next lesser significance.

Abstract: The attitude of a space vehicle is controlled to direct an instrument in a particular direction. For certain maneuvers, the reorientation may temporarily result in an undesirable orientation of the spacecraft. For example, the instrument may be a telescope which, during slewing of the spacecaft from one direction in space to another, may pass through an attitude in which it is directed toward the Sun. A control system is provided which performs the attitude control with an avoidance constraint. The control system generates a first signal representative of the current and desired final orientations, and slews the attitude in response thereto. A second signal is also generated which represents the difference between the current orientation of a vector associated with the spacecraft and a vector in space which it is to avoid. A threshold signal is generated when the difference between the avoidance vectors is a particular value.

Abstract: A method for determining the attitude of a spacecraft without employing conventional attitude sensors, such as horizon sensors. A spin-stabilized spacecraft has an antenna mounted offset from the spin axis. The spacecraft is tracked over a substantial portion of its orbit from a ground (or tracking) station. A signal is transmitted from the spacecraft and received at the ground station. The spinning motion of the transmitting antenna causes the received frequency to oscillate sinusoidally due to Doppler shift acting on the transmitter-receiver range rate. The amplitude of the sinusoidal component of Doppler frequency shifts of the signals at several points along the orbit are used to determine the orientation of the spin axis. The attitude is adjusted as necessary, and thrusters are fired to move the spacecraft from the transfer orbit to the final orbit. The weight, cost and complexity of conventionl attitude sensors are eliminated from the spacecraft.

Abstract: An apparatus for singulating mailpieces such as envelopes spread out on a moving conveyor belt includes a robot for picking up the mailpiece associated with a leading edge. The conveyor belt has alternate black-and-white longitudinal stripes. A TV camera views the belt surface, and produces video representing the stripes and any mailpieces. The video is processed to produce signals representative of the locations of transitions in the video along the centers of the black and/or white stripes. The location representative signals are processed by calculating lines corresponding to one or more leading edges of the mailpiece, which may then be used for controlling the robot in known manner.

Abstract: The balance of a spin-balanced spacecraft may be dynamically adjusted by moving a liquid between or among containers spaced about the spin axis. The transfer of liquid is accomplished by controllable heaters associated with each container, for heating that container from which liquid is to be transferred to increase the pressure and drive out liquid. A spacecraft for accomplishing this method includes a balance sensing arrangements such as a gyroscope and logic for determining which container or containers are to be emptied and for controlling the heaters. Weight is minimized by accomplishing the transfer of liquid among fuel containers by way of manifolds which also supply fuel to thrusters.

Abstract: A spacecraft attitude control system uses at least four reaction wheels. In order to minimize reaction wheel speed and therefore power, a wheel speed management system is provided. The management system monitors the wheel speeds and generates a wheel speed error vector. The error vector is integrated, and the error vector and its integral are combined to form a correction vector. The correction vector is summed with the attitude control torque command signals for driving the reaction wheels.

Abstract: A beam steering arrangement for a plurality of beams of electromagnetic radiation from a like plurality of sources arrayed with a preselected source-to-source spacing includes a first lens array. The period of the lenses corresponds to that of the sources. The lenses of the first array may be converging or diverging lenses, but when illuminated by the sources, each produces a beam of light including at least a diverging portion. A second lens array is cascaded with the first lens array, with the lenses of the second array illuminated by the diverging beam portions. The second lens array collimates the diverging beam portions. The second lens array is translated in a direction approximately transverse to the undeflected beam direction in order to scan or deflect the collimated beams. This may result in overfilling of the input apertures of the lenses of the output lens array, with consequent reduction in the amplitude of the main beam, and with generation of beams of lower intensity in other directions.

Abstract: The magnitude and direction of the residual magnetic field or dipole of an orbiting spacecraft is estimated from the attitude-perturbing effects of its interaction with the magnetic field of the heavenly body about which it orbits. The measurements are performed over a significant portion of an orbit. The estimate uses h, the total spacecraft momentum in the body frame, and its body angular rate .omega.. The Earth's magnetic flux density B is determined either by magnetometer measurements, or by recourse to stored historical and ephemeris information.