Abstract: A filter which uses both an analog portion and a digital portion to optimize the filter performance. A simple analog filter provides a rough filtering of the input signal. The output of the analog filter is converted into digital form and supplied to a digital filter. The coefficients of the digital filter are changed by a digital computer in order to correct for the errors in the filtered signal produced by the analog filter. The coefficients necessary for the digital filter to provide an error offset are determined by comparing the filtered value of a test signal through the analog filter to an ideal filtered value of such test signal.

Abstract: Method and apparatus are disclosed for inducing dimensional stability in cured composite structures using acoustic emission analysis to identify the appropriate level and extent of coincident thermal conditioning. Temperature of the composite structure is lowered at a bounded rate to a minimum temperature typical of the intended operating environment. Passive stress wave acoustic emissions of the composite are analyzed to generate a signature of stress relaxation events over time. When the rate of stress relaxation events decreases below a predetermined percentage of the maximum rate, and remains below that level for a period of time sufficient to predict operational stability, thermal conditioning is terminated.

Abstract: A frequency discriminator (1) stabilizes a voltage controlled oscillator (5), particularly one operating at microwave frequencies. A single dielectric resonator (2), typically positioned within a housing (8), is excited by an r.f. input (30). The dielectric resonator (2) generates in response to the excitation first and second orthogonal modes of r.f. electromagnetic energy at slightly different frequencies. The two orthogonal modes are converted to d.c. output signals (39, 40) of opposite polarity and substantially the same magnitude, e.g., by diodes (35, 36). Frequency offsets are obtained by tuning screws (43, 44) and/or by changing the amount of dielectric (2) in the path of the characterizing vector corresponding to the mode being frequency-offset.

Abstract: Apparatus for autonomously performing stationkeeping maneuvers for three-axis stabilized spacecraft (1) such as geosynchronous satellites. For each of one or more spacecraft axes (y, z) the invention autonomously performs desaturation of a momentum/reaction wheel (31-32, 41, respectively) associated with that axis, while simultaneously accomplishing the preselected compensation of the spacecraft's east-west position. Thrusters (35-38, 45-48) having a polarity corresponding to the desired desaturation polarity are fired in a particular sequence: when a preselected east-west firing bias is present, the thrusters fired are solely from that face of the spacecraft (1) needed to counteract the east-west deviation. After the bias has been worked down, thrusters are fired from alternating spacecraft faces.

Abstract: Apparatus for improving the resolution and/or field of view of an optical system without degrading the signal-to-noise ratio. An optical image of the object (1) in an image plane (8) is divided into n subimages, where n is any positive integer. Each of the n subimages is separately refocused (by 10, 20, 30) and detected (by 11, 21, 31). The optical system can be a staring or a scanning system, and can operate at any wavelength. When the number of subimages is two, an image bisector (7) is used. The bisector (7) comprises first and second highly reflective planar surfaces (12, 22). A knife edge (2), formed by the intersection of the reflective surfaces (12, 22), lies in the image plane (8). In the more general case, n-1 reflective surfaces are used, each having a knife edge lying in the image plane (8).

Abstract: A frequency independent beam waveguide comprises a row of equispaced identical axisymmetric phase setting means (1), which may be lenses or reflectors, or a combination of both, spaced a distance D apart from each other. The focal length of each phase setting means (1) is D/2. A launcher (2) spaced a distance D away from the first phase setting means (1A) in the row emits a beam of electromagnetic energy in the direction of said row. The phase and amplitude distribution in the cross-section (A) of the beam at the mouth of the launcher (2) is duplicated every other phase setting means (1) along the row (at locations B), independent of the frequency of the launched beam. As a result, the beam propagates along the row.

Abstract: Stars are sensed by one or more instruments (1, 2) on board a three-axis stabilized satellite, for purposes of assisting in image navigation. A star acquistion computer (64), which may be located on the earth, commands the instrument mirror (33, 32) to slew just outside the limb of the earth or other celestial body around which the satellite is orbiting, to look for stars that have been cataloged in a star map stored within the computer (64). The instrument (1, 2) is commanded to dwell for a period of time equal to a star search window time, plus the maximum time the instrument (1, 2) takes to complete a current scan, plus the maximum time it takes for the mirror (33, 32) to slew to the star. When the satellite is first placed in orbit, and following first stationkeeping and eclipse, a special operation is performed in which the star-seeking instrument (1, 2) FOV is broadened.

Abstract: A passive propellant management system for a spacecraft liquid propellant tank (1) comprises several preferably V-shaped channels (2) which communicate liquid propellant from regions within the tank (1) to an outlet port (8), which expels liquid propellant but not pressurant gas. A liquid/bubble chamber assembly (9) couples the channels (2) with the outlet port (8). The channels (2) comprise relatively open portions (11) and relatively closed portions (10). In the relatively open portions (11), liquid is retained in a gap (12) between open ends of the V channels (2) and the inner wall of the tank (1). In the relatively closed portions (10), a screen, mesh or perforated plate (14) covers the open end of the V channels (2), intermediate the V channels (2) and the inner wall of the tank (1). The placement of the relatively open and closed portions (11, 10, respectively) is intentionally preselected based upon mission requirements. Where pressurant gas ullage is expected to be present, e.g.

Abstract: A layer of HgCdTe (15) is epitaxially grown on a crystalline support (10). A single crystal CdTe substrate (5) is first epitaxially grown to a thickness of between 1 micron and 5 microns onto the support (10). Then a HgTe source (3) is spaced from the CdTe substrate (5) a distance of between 0.1 mm and 10 mm. The substrate (5) and source (3) are heated together in a thermally insulating, reusable ampoule (17) within a growth temperature range of between 500.degree. C. and 625.degree. C. for a growth time of between 5 minutes and 13 hours. In a first growth step embodiment, the source (3) and substrate (5) are non-isothermal. In a second growth step embodiment, the source (3) and substrate (5) are isothermal. Then an optional interdiffusion step is performed, in which the source (3) and substrate (5) are cooled within a temperature range of between 400.degree. C. and 500.degree. C. for a time of between 1 hour and 16 hours.

Abstract: A threadless linear actuator apparatus comprising a sealed actuator unit with a sealed housing for a set of spool-shaped roller bearings. The roller bearing set includes at least one variable pitch loading roller and two fixed pitch rollers arranged in a skewed relationship about a cylindrical drive shaft. A variable moment is applied to the apparatus through a moment applied about an axis which is perpendicular to and intersects the drive shaft axis which, when applied, varies the pitch of the pivotable loading roller.

Abstract: A three-axis controlled spacecraft (1), typically a satellite, is spun up about its roll axis (20) prior to firing a motor (2), i.e., a perigee kick motor, to achieve the requisite degree of angular momentum stiffness. Thrusters (21) for imparting rotation about the roll axis (20) are activated in open-loop fashion, typically at less than full duty cycle. Cross-axis torques induced by this rotational motion are compensated for by means of closed control loops for each of the pitch and yaw axes (30, 40, respectively). Each closed control loop combines a prebias torque (72) with torques (75, 74) representative of position and rate feedback information, respectively. A deadband (52) within each closed control loop can be widened during the spinup, to conserve fuel. Position feedback information (75) in each of the control loops is disabled upon saturation of the gyroscope associated with the roll axis (20).

Abstract: An r.f. phase modulator operable at up to extremely high frequencies. A circulator (1) having input, output, and isolated ports (2, 3, 4, respectively), channels an r.f. carrier (15) in a prescribed direction. Fitting into an open end of the output port (3) is a moving reflective surface (6) coupled via a moving plunger (7) fixedly mounted at one end thereof to a housing (5) fixedly mounted with respect to the circulator (1). A modulating signal (9) is applied to the plunger (7), causing the reflective surface (6) to move linearly within the output port (3). This change in path length of the carrier (15) produces linear phase modulation thereon. The plunger (7) can comprise a magnetostrictive material (7A), a piezoelectric material (7B), a thermally expansive material (7C), or a combination thereof. The invention can be used for temperature compensation and phase stabilization as well as phase modulation.

Abstract: A circuit for extending the frequency range of a digitally generated FM signal (f). A digital frequency generator (1) generates a precise FM waveform at a frequency up to about 50 MHz. Coupled to the FM signal (f) is a phase lock loop (53, 55, 57) comprising a voltage controlled oscillator (VCO) (57) whose output frequency can be much higher than the frequency of the FM signal (f). In a first embodiment, a crystal oscillator (61), mixer (59), and low pass filter (63) are used to bring the output (f') of the VCO (57) down into the range of the digital frequency generator (1). In a second embodiment, an analog frequency divider (73) is used to bring the output (f') of the VCO (57) into the range of the digital frequency generator (1). In a third embodiment, the single sideband (SSB) generator (37) from the digital frequency generator (1) and a counter (66) are used in a partly analog, partly digital, negative feedback loop.

Abstract: a ratating sensor responsive to infrared or electro-optic radiation has a nearly hemispherical field of view. The sensor comprises a rotating platform (3) supporting a planar multidetector focal plane array (1). The array (1) has three or four sides. Two of the sides are straight lines. One or two sides are portions of conic sections. Individual detectors (2) within the array (1) can be continuous or discrete, and are organized into rows generally following the shape of the conic section(s). In either embodiment, time delay integration is performed row by row within the array (1) so as to equalize the sensitivity and resolution for each portion of the viewed scene. Several arrays (1) can be mounted within the carrier vehicle (8), mounted at different field angles. In this embodiment, the shape of the arrays (1) vary from a sector of a circle to rectangular.

Abstract: A systolic array (1) for reducing the time required to solve an algorithm having cyclic loop dependency, i.e., nested loops in which values calculated by inner loops depend upon indices of said inner loops and upon indices of outer loops. The array (1) comprises a chain of several identical serially connected and sequentially accessed cells. In the preferred embodiment, each cell, except for first and last cells in the chain, is connected to its two adjacent cells only. Multiprocessing is employed: at certain times during the algorithm solving, more than one cell is simultaneously activated to perform portions of the solving, so that the total time required to solve the algorithms is shortened to be a linear function of n.times.m. The algorithm can represent measurement of the distance between two symbolic strings, or other problems in artificial intelligence or logic.

Abstract: An optical projection system, e.g., an imaging infrared system, is compensated for errors caused by scan-to-scan jitter, framing jitter, vibrational effects, and scan nonlinearities. One or two closed control loops compensate for errors associated with mirrors (32, 52) of the optical projection system. In the scan control loop, a set of scan reference marks (75) in a reference plane (7) is superimposed onto a scan position detector (59) lying in a plane (10) containing a detector array (9), producing a scan error compensation signal (56). For wide scan fields of view (72), the scan position detector (59) comprises two pairs (94, 95) of triangular detectors, and means (86) for periodically switching therebetween.

Abstract: An extremely narrow-band bandpass electromagnetic filter comprises a waveguide (1) dimensioned below cutoff and having two or more active sections (30) each containing a dielectric resonator (6). The number of resonators (6) corresponds to the number of poles of filtering. The physical dimensions of the waveguide (1) can advantageously be further reduced by means of passive coupling means (40), where the waveguide (1) cross-section is smaller than in the active sections (30). Each passive coupling means (40) inductively couples adjacent active sections (30). Mode suppression rods (10) electrically connect opposing waveguide walls (2, 3) midway between each pair of adjacent dielectric resonators (6). Preferred embodiments are illustrated, in which the resonators (6) are tranversely oriented within the waveguide (1). Electromagnetic energy travels within the waveguide (1) in a single TE.sub.10 evanescent mode (TE.sub.01.delta. within the resonators (6)).

Abstract: Apparatus for producing a projected real-time visible display (9). A light source (2) and associated collimator (3,4) produces a collimated light beam (18) which is modulated by a linear array (6) of electronically controlled optical elements (16) with input data (30) that is formatted in a line-by-line fashion. A nutating mirror (8) sweeps the resulting modulated light beam (19) in synchronism with the input image line-segmented data (30), thereby producing the projected display (9). Elements comprising an electronic control circuit (11), which couples the input signal (30) to the modulator (6) and controls the nutation of the mirror (8), are presented, along with a timing diagram (FIG. 3) showing the functioning of the elements comprising said control circuit (11).

Abstract: The operating speed and dynamic input range of a digital FIR filter are markedly improved by encoding the signal by powers of two and using the thus encoded signal to shift (rather than multiply) the coefficient at each tap of the filter. A multiplexed shifter for simultaneously shifting all digits of the coefficient is also disclosed.

Abstract: Pixels within a satellite camera (1, 2) image are precisely located in terms of latitude and longitude on a celestial body, such as the earth, being imaged. A computer (60) on the earth generates models (40, 50) of the satellite's orbit and attitude, respectively. The orbit model (40) is generated from measurements of stars and landmarks taken by the camera (1, 2), and by range data. The orbit model (40) is an expression of the satellite's latitude and longitude at the subsatellite point, and of the altitude of the satellite, as a function of time, using as coefficients (K) the six Keplerian elements at epoch. The attitude model (50) is based upon star measurements taken by each camera (1, 2). The attitude model (50) is a set of expressions for the deviations in a set of mutually orthogonal reference optical axes (x, y, z) as a function of time, for each camera (1, 2). Measured data is fit into the models (40, 50) using a walking least squares fit algorithm.