Abstract: A system and method for acquiring the Earth by a three-axis stabilized spacecraft in the presence of a significantly time-varying Sun-Earth angle including obtaining an Earth cone described by rotating the nadir vector about the Sun vector, slewing the spacecraft about an axis until the Earth sensor boresight touches an edge of the Earth cone, updating the Earth cone due to the changing Sun-Earth separation angle, performing a spiral coning maneuver about the updated Earth cone until the Earth sensor detects the Earth, and locking onto the Earth so as to hold the Earth sensor boresight coincident with the nadir vector. Additionally, the spacecraft may be rotated about the nadir vector so as to bring the spacecraft into a desired final attitude.

Abstract: A modular payload support for placement in an enclosure defined by the sidewalls of a launch vehicle includes a central hub, a plurality of trusses, and a plurality of modular outer panels. Each of the trusses includes an inner edge secured to the hub and extends radially outward from the hub. Each of the trusses further includes an outer edge, and a modular outer panel is secured to each of the truss outer edges. Each modular outer panel is adapted for attachment to the vehicle sidewall, with each modular outer panel being sized to span the available distance between the truss outer edge and the vehicle sidewall. Each of the trusses is constructed of a number of layers or plies, so that the trusses may be tailored to meet strength and stiffness requirements of a contemplated application.

Abstract: A friction retaining device for holding and releasing reflector panels of a satellite. The retaining devices having a friction bushing mounted thereon to prevent the reflectors from becoming disengaged from the clamp. The retaining device has a pair of opposing arms having upper ends that communicate with bumpers on the reflectors and lower portions that communicate with a release mechanism. Upon actuation of a pyrotechnic device, the reflectors are deployed. At the same time, the release mechanism disengages the lower portions of the opposing arms allowing them to remove the bumpers from the reflectors.

Abstract: A system for simultaneously measuring strains in a test member includes spatial-position members which are coupled to different portions of the test member and first and second displacement sensors which are spaced apart by a sensor space and coupled to the spatial-position members. Linear and bending deformations of the test member are calculated as functions of the responses of the displacement sensors and of the sensor space.

Abstract: A simple joining process for members of passive microwave structures is described which reduces passive intermodulation. The process forms an aperture in a first member and forms a second member to have dimension which exceeds the aperture dimension by a dimension differential. The members are joined by initially causing them to have a temperature differential that is sufficient to permit the second member to be positioned across the aperture. The dimension differential is selected to generate mutually-induced radial stresses in the members, after the temperature differential is removed, which enhance the metal-to-metal contact between the members and, thereby, improve passive intermodulation (PIM) performance. Preferably, the dimension differential is selected to cause the second member to elastically buckle and exert a buckling stress against the first member. Additional interface structures are provided to resist operational axial forces, e.g., vibration, that tend to dislodge the members.

Abstract: A power system includes at least two battery cell modules. Each battery cell module has a lithium-ion battery cell, and a battery cell controller operably connected to the lithium-ion battery to control the charging and discharging of the lithium-ion battery cell. A central charge/discharge controller is operably connected to each of the battery cell controllers, allowing the charging and discharging of each lithium-ion battery cell to be individually controlled.

Abstract: A solar power source has a solar power converter, and a solar concentrator positioned to reflect incident light toward the solar power converter. The solar concentrator includes a support having a texture pattern formed thereon, and a reflector surface on the support. The support includes a layer of plastic, and the reflector surface is a layer of a metal, such as aluminum, deposited on the layer of plastic. The texture is formed in the layer of plastic, and is visible on a free surface of the reflector. The texture pattern may be a set of parallel linear recesses.

Abstract: A method and system for detecting collision of transmitted signals in a random-access, multiple-path communication system utilizes a packet coding arrangement where a transmitting transceiver terminal assembles a plurality of packets into a coded transmit block. Each transmit block is coded with an error detection code, or assigned time slots, so that a routing controller will discard an entire transmit block if any of the packets are not properly decoded. Each transmit block further includes a self-addressed packet, wherein receipt of the self-addressed packet by the transmitting terminal indicates that no collision has occurred. Thus, the present invention does not require any additional circuitry or control of the routing controller, nor transmission of an acknowledgement signal in order to detect collision of transmitted signals.

Abstract: A control circuit for a power supply for at least one Traveling Wave Tube (TWT) that uses the cathode voltage as a reference point allowing independent, variable control of each TWT. The cathode current is varied by varying the anode voltage. Therefore, it is not necessary to operate the TWT below maximum power at full cathode current. The result is improved operating efficiency for the TWT. A single power supply is capable of powering several TWT's resulting in a significant weight and cost savings for space applications.

Abstract: A method and system for providing global variable data rate connectivity in a satellite-based communications network includes a plurality of communications satellites for transmitting and receiving signals in a plurality of coverage areas. User terminals transmit and receive signals to and from the satellites. A set of the user terminals located in one of the coverage areas and associated with one of the communications satellites has a variable bandwidth associated therewith. The variable bandwidth is determined based on the collective bandwidth requirements of each of the user terminals in the set. Each of the user terminals may request a change in their bandwidth requirement independent of the variable bandwidth associated with the collective set of the user terminals.

Abstract: A microelectromechanical (MEM) device includes a substrate and a flexible cantilever beam. The substrate has positioned thereon a first interconnection line separated by a first gap and a second interconnection line separated by a second gap parallel to the first interconnection line. The substrate also has positioned thereon a first and second primary control electrode wherein one of the first and second primary control electrodes is positioned on one side of one of the first and second interconnection lines and the other one is positioned on the other side of the other first and second interconnection lines. The flexible cantilever beam has a top surface and a bottom surface and a beam width slightly larger than the gap widths at the gaps. A flexible anchor is secured to the bottom surface of the beam at a center of the beam and attached to a center of the substrate so as to position the beam orthogonally to the first and second interconnection lines.

Abstract: A phased array (20) and method for constructing the same are disclosed. The phased array (20) includes a superstructure (22) with cavities (40) therein. A cover plate (28) is mounted to the superstructure (22) and cooperates with the cavities (40) to form cavity style filters therebetween and to form a box-beam type superstructure. Ideally, the superstructure (22) is self supporting. Electronic modules (32) and amplifiers (33) are mounted to the superstructure (22). The method includes machining a block of material to form a webbed superstructure with cavities (40) therein. A cover plate (28) is mounted to the superstructure (22) over the cavities (40) to form cavity style filters. Amplifiers (32) and antenna elements (30) are then affixed to the superstructure (22) and cover plate (28). Ideally, the cover plate (28) is affixed to the superstructure (22) using an electrically conductive adhesive.

Abstract: The method and apparatus for determining group delay of a satellite communications channel includes a low frequency vector network analyzer and microwave swept synthesizer which together generate modulated signals. A sample of the signals transmitted to a satellite and the signals retransmitted from the satellite are compared in the network analyzer to obtain the phase of the signals. The phase of a reference signal is measured prior to and after each test frequency of the communications channel. A quasi-real time phase reference can be obtained by interpolation. Thus, the reference phase due to movement of the satellite with respect to the earth station during group delay measurement may be removed.

Abstract: Structures and methods are provided to effect satellite maneuvers in the presence of disturbance torques with enhanced fuel efficiency. A thruster control loop is combined with a wheel control loop in which the wheels respond to an estimate of the disturbance torques (e.g., an angular acceleration estimate, a thruster torque command or a filtered thruster torque command) to create a counteracting gyroscopic torque. Simulations of the invention's methods have shown they have the authority of all-thruster control systems and fuel efficiency that rivals that that of all-wheel control systems.

Abstract: A system and method for changing the radiation pattern of an antenna assembly of a satellite in orbit is provided. The antenna assembly includes a reflector antenna fed by a feed assembly. The reflector antenna transmits and receives signals within a radiation pattern. The reflector antenna and the feed assembly are movably mounted to a sliding mechanism so that they can be displaced with respect to one another. The displacement causes defocusing as the reflector antenna is displaced from the focus point. The defocusing causes the radiation pattern to become more compact or broadened. Thus, the radiation pattern of the satellite provided with a single reflector antenna and a single feed element may be changed while the satellite is in orbit. The system and method include gimballing the reflector antenna to steer the radiation pattern.

Abstract: A method for shaping reflected radio frequency signals includes geometrically shaping a reflector surface of an antenna to focus the beam, and reflectively shaping the reflector surface with phasing elements that emulate geometric shaping to configure the beam to a predetermined shape. In the preferred embodiment, the antenna comprises a geosynchronous satellite antenna conveying signals from a wave guide horn to or from a predetermined geographic area on earth. The use of a parabolic-approaching surface of reflectarray phasing elements for shaping the beam substantially improves the beam pattern bandwidth over the performance of previously known shaped beam reflectarrays.

Abstract: A method of fastening a line to an object to form a continually adjustable nonreturn knot to adjust the length and tension of the line. The line is passed from one side of an object to another through one or more holes in the object and one portion is tucked under another portion of itself, creating a nip, to pinch the one portion against a surface of the object. The friction added by the nip is sufficient to prevent the line from being pulled through the knot in one direction but is insufficient to prevent it from being pulled through in the opposite direction. In variations of the embodiments of the knot, a release line is also attached to the line proximate the nip to relieve the friction added by the nip sufficiently to allow the line to be pulled through the knot in either direction.

Abstract: An apparatus for deploying an umbrella-type structure such as an antenna reflector is provided. The umbrella-type structure includes a plurality of rib members movable from a stowed configuration to a deployed configuration. The deployment apparatus comprises a movable deployment tube and a hub pivotally attached to the plurality of rib members and slidably attached to the deployment tube. The hub is adapted to move along the deployment tube. The deployment apparatus further includes a plurality of rib deployment straps connecting the deployment tube to the rib members and a mechanism for moving the deployment tube in order to tension the rib deployment straps which in turn pull the rib members into the deployed configuration. The apparatus includes structural members made of composite materials, having a low (near zero) coefficient of thermal expansion, low density, and high strength.

Abstract: A sun-referenced safe-hold control system for momentum-biased satellites employs a safe-hold processor responsive to a set of sun sensors to detect attitude errors of the solar wings. Safe-hold processor provides independent control logic which rotates the solar wings to ensure that sunlight is maintained incident on the solar wings to maintain solar power in the safe-hold mode. In addition, the safe-hold processor provides independent control of the momentum wheel to place the spacecraft body in a passively stable nutational state. Passive nutational stability inherent in a momentum-biased satellite about two axes of the spacecraft enables the safe-hold processor to actively control the spacecraft about only one of its axes. The spacecraft safe-hold control system increases the period in which spacecraft health is guaranteed by adding active, closed-loop control of the solar wings.

Abstract: Flexible, lightweight reflective sheets are positioned to concentrate solar radiation upon spacecraft solar panels. The sheets are held with inner and outer spring members which urge each sheet from a gathered edge-stowed configuration towards a deployed, planar configuration. The outer spring members further urge each fully extended sheet to rotate about an axis along the panel's edge in a direction away from the solar panel's face. Restraint members in the form of tethers limit this rotation to place the sheet in a stable deployed position and orientation chosen by design to reflect solar radiation onto the panel face. The increased incident radiation permits a reduction of the number of solar cells needed to satisfy a power requirement, and allows consequent savings in spacecraft cost and weight.