Abstract: A digital system for controlling the attitude of a spacecraft (14), e.g., a satellite, with respect to three orthogonal axes. The system can control satellites (14) in parking orbit, transfer orbit, or final operational orbit, whether or not the satellite (14) employs one or more momentum wheels. A processor (2) converts weighted data from spacecraft sensors (12), representing angular orientation and angular velocities about each of the three axes, into thruster pulsetrain signatures to command the firing of each of six thrusters positioned about spacecraft (14), a positive and a negative thruster being positioned to impart both directions of angular momentum about each of the three axes. Each thruster pulsetrain signature is created once every processed error cycle period T1, and contains a varying number of pulses of varying widths. A negative feedback PWPF loop (2, 16, 20, 22, 24) is actuated for each of the three axes, preferably several times each T1 in order to achieve better thruster on/off resolution.

Abstract: A vacuum dewar for infrared detectors is disclosed, in which unitary Kovar leads are used to reduce heat load and improve reliability and ruggedness. The Kovar leads are encapsulated in the glass walls of the hollow stem which carries the sensor array and supplies cryogenic fluid for cooling the array. The Kovar leads extend throughout the entire length of the stem to form both the electrical feed-through and the contact points at each end of the stem for the attachment of wire leads or cables, and to form a reinforcing structure for the stem. A fabrication method is also disclosed, in which a unitary Kovar leadframe is held under tension while two concentric glass tubes, between which the leadframe is vacuum-sandwiched, are fused together to form a stem encapsulating continuous Kovar leads throughout its length, while preventing excessive oxidation of the Kovar leads.

Abstract: Apparatus for enhancing the stability of a spacecraft (2) about a sensing axis (4). The spacecraft (2) may be of the three axis stabilized or spin stabilized variety. An attitude sensor (3) determines the offset angle (A) formed between a face (8) of the spacecraft (2) and an astronomical body (6), such as the earth. The sensor (3) produces an attitude signal (14) which is processed by compensation electronics (21) and fed to a torquing means (25) to close the angle (A) to within a desired preselected deadband (24).

Abstract: A current balanced linear amplifier which does not contain a transformer. A differential transistor pair (22, 32) forms the amplifying element, with at least one transistor (22 or 32) having an input signal (71, 72) applied to its base. A current sink (52) sinking a fixed value of current (I) is coupled to the commonly-coupled emitters of the transistor pair (22, 32). Coupled to the collector of each amplifying transistor (22, 32) is a self-biasing constant current source (2, 12) which produces a fixed amount of current (I/2) equal to one half the current (I) sunk by the current sink (52). Each self-biasing constant current source (2, 12) comprises a field effect transistor (2, 12) having a capacitor (6, 16) connected between the gate G and source S of the FET (2, 12) in a positive feedback arrangement. The balanced current output (61, 62) is taken from the collectors of each of the two amplifying transistors (22, 32).

Abstract: A method and apparatus for demodulating quadrature phase shift keyed (QPSK) signals in a manner which reduces crosstalk between channels. The in phase (I) data is recovered first by recovering the carrier frequency and then multiplying the carrier frequency by the QPSK signal. The I channel is contemplated to require higher power and thus the crosstalk error in the recovered I channel data is relatively small. The QPSK signal is then modulated with the recovered I channel data. The resulting signal is multiplied by a carrier in quadrature to the recovered carrier to produce a second signal in which the crosstalk component has been eliminated and which contains the quadrature (Q) channel data with the I channel modulation. The I channel modulation is removed by modulating the signal again by the I channel data to produce a signal containing only the Q channel data.

Abstract: An active cooling system (40, 41) for cooling electrochemical cells (11) that are arranged in a stack (9) in a fuel cell or battery (3). The cooling system (40, 41) comprises cooling panels (15, 16) carrying a cooling fluid that flows adjacent to, and parallel to the plane of, each cell (11). The rate of cooling fluid flow past each cell (11) is made to be substantially equal, so that each cell (11) experiences substantially the same cooling environment, adding to the longevity of the fuel cell or battery (3). This can be accomplished by equalizing the resistance to cooling fluid flow for each cooling path (12), e.g., by using pressure equalizing, monotonically increasingly sized orifices (28) in an input manifold (25). Dual cooling panels (15, 16) are preferably employed, in a counterflow mode. The panels (15, 16) may be divided into parallel channels (33). Heat pipe panels (35) containing a two-phase fluid may be used in lieu of panels (15, 16) that contain cooling fluid in a single state.

Abstract: A structure (47) is rotatable 360.degree. about a vertical azimuth axis and 90.degree. or more about an orthogonal elevation axis. The structure (47) is mounted upon a rotating turret (6) in the general shape of an inverted pyramid, with a vertical generally cylindrical torque tube (11) protruding from the bottom of the turret (6). A drive wheel (12) is attached to the bottom of the tube (11) and provides a mechanical advantage for azimuthal rotation because it is larger than the wheel (25, 26, 30) connecting the top of the tube (11) with the bottom of the turret (6). The turret (6) rotatably turns about tripod base (46) by means of wheels (29) mounted beneath the rim (30) of said upper wheel (25, 26, 30). Elevational motion is provided by means of a lead screw (16) connecting rotating turret (6) with structure (47), which can be a modular mass-producible solar radiation reflector consisting of many identical reflective panels (1), each having the shape of a portion of the surface of a sphere.

Abstract: An improved detector array for scan receiver applications whereby each contiguous element of the array is connected to a summing port with its adjacent element.

Abstract: A microwave coupler for coupling microwave energy from a first waveguide to a second waveguide disposed side by side along a propagation length includes a common coupling means, and specifically, orifices along the propagation length wherein the coupling orifices are sized to promote coupling of a favored field mode of electromagnetic energy according to a Bessel function distribution of energy along the length of the waveguide. The Bessel function distribution provides for wideband, low-loss coupling of the favored field mode and maximal isolation from non-favored field modes. The invention is particularly useful for extracting a type TE.sub.21 circular mode signal from a signal containing TE.sub.11 and TE.sub.21 circular modes wherein the TE.sub.21 mode signals are used for generating elevational and azimuthal tracking signals.

Abstract: A vacuum dewar for infrared detectors is disclosed, in which unitary Kovar leads are used to reduce heat load and improve reliability and ruggedness. The Kovar leads are encapsulated in the glass walls of the hollow stem which carries the sensor array and supplies cryogenic fluid for cooling the array. The Kovar leads extend throughout the entire length of the stem to form both the electrical feed-through and the contact points at each end of the stem for the attachment of wire leads or cables, and to form a reinforcing structure for the stem. A fabrication method is also disclosed, in which a unitary Kovar leadframe is held under tension while two concentric glass tubes, between which the leadframe is vacuum-sandwiched, are fused together to form a stem encapsulating continuous Kovar leads throughout its length, while preventing excessive oxidation of the Kovar leads.

Abstract: A double dielectric resonator (1) having lower and upper preferably cylindrical dielectric elements (3, 5, respectively) is used to stabilize an oscillator operating at microwave frequencies. The dielectric elements (3, 5) are separated by a distance (d) which is greater than zero but less than an amount that will eliminate magnetic coupling between the dielectric elements (3, 5), and preferably less than an amount that will push the oscillator into a nonlinear region of the frequency versus separation (d) curve. The major axes (43, 45, respectively) of the dielectric elements (3, 5) are aligned, or else parallel but offset slightly. The invention may be used with reflection type, parallel feedback, and series feedback oscillators.

Abstract: A guidance system for small spinning projectiles which is mechanically simple, has low power requirements, uses relatively unsophisticated electronics, and is capable of withstanding large gas pressures and accelerations. The system uses a one-piece fin assembly which is de-spun so that its guidance fins maintain a constant attitude with respect to the ground. The guidance fins and their hub can be nutated simultaneously and independently in two orthogonal planes by pivoting and translating a single control rod. The hub cooperates with the projectile body to reduce its base drag and thereby extend its range.

Abstract: A bipolar metal-gas battery cell stack (1) eliminates the heavy bipolar plates (11) of the prior art by means of locating the series electrical connections (25, 27) between oppositely polarized electrodes (5, 7) of adjacent cells (3) external to the cells (3) in a dielectric frame (21, 23). As a result, the reliability of said electrical connections (25, 27) is improved, weight is saved, and reactant gas screens (15) and electrolyte reservoirs (13) can beneficially be made of compressible lightweight materials. Electrolyte is beneficially confined within each cell (3), and secondary (overcharge) gasses are beneficially confined within each cell (3) in a region (17) proximate the positive electrode (7). A hydrophobic barrier (29) and the frame segments (21, 23) prevent intercell migration of electrolyte and secondary gasses.

Abstract: An imaging radar seeker (8) for producing two-dimensional images of a target (2) is mounted on a missile (6) or other moving body, such as an automobile. A computer (40) directs the seeker (8) to operate sequentially in searching, tracking, and imaging modes. In the searching mode, a combination of circumferential rotation of antenna (12) of seeker (8) and frequency scanning of electromagnetic energy fed to antenna (12) enables seeker (8) to search for its target (2) over a conical field-of-view (16) or a wider, peripheral belt field-of-view (16). In the imaging mode, circumferential rotation of antenna (12) is stopped, and the tilt angle (A) of the linear array (32) of antenna (12) is stepped or continuously moved to compensate for radial movement of the radiated beam (14) caused by frequency stepping imparted by a frequency synthesizer (20). This keeps the beam (14) fixed in space and centered on target (2).

Abstract: A compact, low-profile broad-banded log-periodic antenna comprises a planar conductor (3) partially sandwiched by but electrically insulated from two substantially parallel spaced-apart ground planes (4, 8). The sandwich extends as far as an imaginary plane (15) that is orthogonal to conductor (3) and to the ground planes (4, 8). Conductor (3) comprises an alternating series of radiating loops (L(n)) and non-radiating transmission-line loops (L(j)). The non-radiating loops (L(j)'s) lie on the ground plane (4, 8) side of plane (15). The radiating loops (L(n)'s) lie on the other side of plane (15). Optional additional ground planes (6, 10) may be employed, in which case they lie in plane (15) and meet one of the primary ground planes (4 or 8, respectively) along a common edge. The length (d) of the loops (radiating or non-radiating), the spacing (D) between loops, and the height (h) and width (w) of the radiating loops (L(n)) are all scaled by a factor (S) which is less than 1 but greater than 0.

Abstract: Heat exchangers (2) with particular use as solar receivers are mass-produced by weaving on a textile loom a yarn of high modulus fibers (18, 20) into a repeating series of substantially flat preforms (4), forming a set of interconnected passageways (26, 30, 32) connecting one side of each preforms (4) with an opposite side thereof. The separated preform (4) are each wrapped around a mandrel to give each the shape of a cylindrical sleeve (2). The sleeve (2) is impregnated in a low modulus matrix, dried, and sintered for rigidization. In a first sealing embodiment, the outer sleeve surface (24) is sealed or weatherproofed, and the surfaces of the internal passageways (26, 30, 32) are sealed, but the radiation absorbing inner sleeve surface (22) is not sealed. In a second sealing embodiment, the outer surface (24), the radiation absorbing inner surface (22), and the exchanger ends (14, 34) are sealed, but the surfaces of inner passageways (26, 30, 32) are not sealed.

Abstract: A stable electromagnetic oscillator (30) comprises an amplifying element (3) in feedback association with a dual mode resonant cavity (12) that provides a double pole bandpass filter function. Two orthogonal modes (1 and 2) of electromagnetic energy resonate within the cavity (12). An output from the amplifying element (3) excitationally couples into the first mode (1), while the second mode (2) couples into the input of the amplifying element (3). The output (8) of the oscillator (30) is obtained from the first mode (1). Optional injection lock can be used for greater stability by means of coupling a stable a.c. reference (9) into the cavity (12) in alignment with the second mode (2). Optional electronic frequency tuning comprises a phase or frequency comparator (11) and a reference a.c. source (13), producing a d.c. feedback signal fed to varactor diodes (10). Coupling ports (4, 5, 6, 7) of the cavity (12) can be, e.g., irises, capacitive probes, coaxial probes, or any combination thereof.

Abstract: A moving target detector for spinning bodies such as projectiles or missiles uses a linear detector array so mounted on the body as to periodically scan an arcuate target area during the spin of the body. Compensation for the resulting optical growth of the target area image as the body approaches the target is accomplished by serially reading the image information from the detector elements (in a direction radial of the target area) into a delay element chain at a variable rate, and dumping the delay chain contents in parallel into the image memory at a fixed rate. The readout rate variation is pre-programmed prior to launch, and feed-back loop may be provided to adjust the rate if the image evaluation circuits detect apparent radial movement of evidently stationary objects near the target.

Abstract: Transients and steady state error induced in maneuvering a satellite due to a disturbance torque caused by thrust mismatch or differential in the alignment of thrusters with respect to the center of mass are minimized by introducing a torque balancing bias at the input of a thrust modulator of the thrusters prior to sensing position or attitude error. The bias may instantly off-modulate the thruster control signal to cancel the effects of attitude transients before errors develop. Other axes thrusters may be on-modulated instantaneously to compensate for cross-axis torque. The bias may be introduced into the satellite control scheme by manual ground control or in automatic on-board compensation based on stored parameters obtained for example from calibration measurements. Specifically, the torque balancing bias may be developed by reference to thrust mismatch detected and stored during previous maneuvers, thus anticipating expected attitude error without actual detection thereof.

Abstract: A structure (47) is rotatable 360.degree. about a vertical azimuth axis and 90.degree. or more about an orthogonal elevation axis. The structure (47) is mounted upon a rotating turret (6) in the general shape of an inverted pyramid, with a vertical generally cylindrical torque tube (11) protruding from the bottom of the turret (6). A drive wheel (12) is attached to the bottom of the tube (11) and provides a mechanical advantage for azimuthal rotation because it is larger than the wheel (25, 26, 30) connecting the top of the tube (11) with the bottom of the turret (6). The turret (6) rotatably turns about tripod base (46) by means of wheels (29) mounted beneath the rim (30) of said upper wheel (25, 26, 30). Elevational motion is provided by means of a lead screw (16) connecting rotating turret (6) with structure (47) which can be a modular mass-producible solar radiation reflector consisting of many identical reflective panels (1), each having the shape of a portion of the surface of a sphere.