Abstract: A spacecraft equipment panel including heat pipes operable in a zero-gravity environment for cooling the equipment mounted to the panel is not operable in an Earth-gravity environment because the two-phase working fluid in the heat pipes tends to pool at the bottom of the heat pipe when the heat pipe is vertical. An apparatus and method for overcoming this condition employs infrared lamps positioned on a mounting frame to heat the bottoms of the heat pipes to vaporize the working fluid therein, whereby the heat pipes become operable for transporting heat while in a vertical orientation and under the influence of gravity.

Abstract: A release device is actuated to release a workpiece by operation of either of two elongated shape memory metal alloy (SMMA) members. Each SMMA member has on one end a feature that engages a fitting on the workpiece, while its other end is mounted to a housing. A heater on each SMMA member raises its temperature to a transition temperature at which it returns to an unstressed (e.g. shorter) length, thereby releasing the workpiece. The two SMMA elements may be disposed in opposite directions from the housing or may be coaxial or offset and disposed in the same direction.

Abstract: A thermally-actuated switch includes a pair of switch contacts openable or closeable in response to a change in the length of a shape memory metal (SMM) rod. The SMM rod is caused to change its length by having its temperature increased by heat produced when electrical power dissipated in a heating element that is coupled in electrical circuit with the switch contacts. To this end, the heating element is thermally coupled to the SMM rod, such as by a common heatsink. Where the switch is to be openable, the heating element is preferably in series circuit with the contacts, and where the contacts are closeable, the heating element is preferably in parallel therewith.

Abstract: A structural panel has thin inner and outer facesheets bonded to a lightweight structural interior core of a honeycomb material. The inner facesheet is for receiving equipment that generates heat to be dissipated and the outer facesheet is adapted to dissipate such heat, such as by radiation. A plurality of closely-spaced heat pipes interior to the panel are thermally coupled to each other and to the inner facesheet for receiving heat from the equipment mounted thereon. A plurality of spaced-apart heat pipes interior to the panel are at about right angles to the closely-spaced heat pipes and are thermally coupled to the outer facesheet and to the closely-spaced heat pipes proximate their intersections therewith. Heat to be dissipated flows along short, direct and efficient paths from the equipment to the inner facesheet, to the closely-spaced heat pipes, to the spaced-apart heat pipes and to the outer facesheet from whence it is dissipated.

Abstract: An RF-transparent sunshield membrane covers an antenna reflector such as a parabolic dish. The membrane includes at least two dielectric sheets of polyimide film 1 mil thick. The surface of the outer film facing away from the reflector is coated with an electrically semiconductive coating such as vapor-deposited germanium having a thickness in the range of 200 .ANG. to 600 .ANG.. A member, such as a glass fiber mat, may be located in the space between the two dielectric sheets for maintaining the sheets in spaced-apart relationship. In another embodiment of the invention, the surface of the film facing the reflector may be reinforced by an adhesively attached polyester or glass fiber mesh.

Abstract: An RF-transparent sunshield membrane covers an antenna reflector such as a parabolic dish. The membrane includes a single dielectric sheet of polyimide film 1 mil thick. The surface of the film facing away from the reflector is coated with a layer of semiconductor material such as vapor-deposited germanium having a thickness in the range of 200 .ANG. to 600 .ANG.. In another embodiment of the invention, the surface of the film facing the reflector may be reinforced by an adhesively attached polyester or glass fiber mesh.

Abstract: A spacecraft adapted for operation in a low inclination angle earth orbit comprises north, south, east and west panels defining a spacecraft interior volume. The north and south panels are oppositely disposed with respect to each other and the east and west panels are oppositely disposed with respect to each other. The spacecraft interior volume generally and preferably lacks structural elements that substantially restrict thermal radiation among the panels. The north and south panels, to which spacecraft equipment is usually mounted, each include conductive heat pipes for reducing the temperature differences across each panel. The exterior surfaces of the north, south, east and west panels have a covering, preferably of optical solar reflectors (OSRs), for radiating thermal energy therefrom, wherein the OSRs have a solar absorptivity that is substantially less than their thermal emissivity.

Abstract: A process and apparatus for making high purity aluminum nitride from organometallic aluminum, such as an alkylaluminum compound. A gaseous alkylaluminum compound and gaseous ammonia are introduced into a heated reaction zone where the gases are mixed and high purity aluminum nitride is produced. The high purity aluminum nitride is collected in the form of a powder or deposited as a thick, dense layer on an appropriate substrate mounted in the reaction chamber. A carrier gas such as hydrogen gas, may be used to conduct the alkylaluminum compound from a suitable reservoir containing liquid alkylaluminum compound to the reaction chamber. A preferred alkylaluminum compound is triethylaluminum.

Abstract: A resistance strip heater includes a pair of elongated, mutually parallel electrical conductors or buses lying on a dielectric substrate. Each bus includes a conductive region extending toward the other conductor, and the locations of the conductive regions of the two buses alternate along the lengths thereof. An elongated resistance arrangement has its axis of elongation parallel to the buses, is physically supported between the buses, and is electrically connected to mutually adjacent ones of the conductive regions, so that the resistance arrangement is electrically connected across the buses. In a particular embodiment of the invention, the resistance arrangement is a plurality of elongated chip resistors arranged in an array. The substrate may be a polyimide sheet, and a corresponding cover sheet may be used. The strip heater can be cut virtually anywhere along its length without affecting its operability.

Abstract: A shape memory alloy (SMA) actuator predeformed in compression actuates a cable cutter mechanism. A cable or other item to be cut is placed between an anvil and a movable blade affixed to the SMA element. The SMA element is heated by an electrical resistance heater to cause it to return to its undeformed elongated state, thereby moving the blade against the anvil to compress and sever the cable or other item. Ones of the shape memory alloy actuator have a plurality of parallelly arranged SMA elements, every other one of which is predeformed in compression and intermediate ones of which are predeformed in tension. The elements are coupled end-to-end so that, when they are heated to cause them to return to their undeformed states, their respective elongations and shrinkages combine at the output to produce an actuation that is the cumulation in the same direction of the changes of all the elements. The plurality of elements may be in a side-by-side or concentric arrangement.

Abstract: A shape memory alloy (SMA) actuator predeformed in tension actuates a separation device mechanism. A segmented nut, which engages a threaded bolt to be held and released, is held together by a nut retainer that is movable with respect to the nut and is affixed to the SMA element. The SMA element is heated by an electrical resistance heater to cause it to return to its undeformed state, thereby moving the retainer relative to the nut segments. When the retainer disengages from the segments, the segments are free to move outwardly thereby releasing the bolt or other item. Ones of the shape memory alloy actuator have a plurality of parallelly arranged SMA elements, every other one of which is predeformed in compression and intermediate ones of which are predeformed in tension.

Abstract: A solar cell voltage regulating arrangement which is particularly advantageous for use in spacecraft includes a light valve such as a liquid crystal cell disposed before the solar cell, to thereby controllably vary the light transmission to the solar cell. A control arrangement varies the transmission of the liquid crystal to control the output voltage.

Abstract: A rectangular waveguide series junction has a layer of photoconductive material in one branch near the junction. The photoconductive material, when dark, is essentially a dielectric, which effectively increases the dimension of the waveguide branch over what it would be if not modified, thereby increasing its impedance at the series junction and causing power division preferentially into the branch. When illuminated, as by a laser or LED, the photoconductive layer becomes a conductor instead of a dielectric, and the dieletric "increase" in the dimension is eliminated. Instead, the conductive material actually decreases the cross-section, to thereby reduce the actual impedance of the branch at the junction point. This reduces the amount of coupling below that for an unmodified waveguide branch. Thus, the amount of coupling into the branch at the junction is increased by the dielectric constant when the photoconductor is dark, and decreased by the conductivity when illuminated.

Abstract: For use in a spacecraft for correcting amplifier distortion, a wideband distortion corrector avoids the need for directional couplers. The corrector includes a FET mounted in a miniature microwave-type housing. Signal flows through the source-to-drain channel. A gate impedance selected to be inductive at the operating frequency is coupled from the FET gate to the platform of the package, and may be simply a loop of bond wire. The channel connects by a strip transmission line to an amplifier, the distortion of which is to be corrected. For enhanced bandwidth, an inductor is coupled between the FET source and drain electrodes within the miniature housing. The platform of the package is coupled to the reference conductor of the transmission line. In one embodiment, direct bias voltage is applied by way of a bias tee across a strip transmission line and ground, and galvanic connections cause the bias to appear between the FET gate electrode and the channel.

Abstract: A power amplifier arrangement includes a power divider for dividing the signal to be amplified into equal-amplitude components. Each component is amplified by a signal amplifying path. The amplified signals are applied to a phase-sensitive power combiner. The combined signal appears at the sum port and a phase-related difference signal appears at a difference port of the combiner. The difference signal is processed to produce a control signal for controlling the relative phases of the signals passing through the signal amplifying paths.

Abstract: A printed circuit radiating element comprises a geometrically symmetric planar area of a conducting material separated from a ground plane by a dielectric medium. The driving point of the radiating element is at the base of a notch in one side thereof so that the driving impedance is reduced from that obtained when the element is driven at its edge. Symmetrically disposed on opposite sides of an axis of symmetry of the element along which the driving point lies are two notches which restore the electrical symmetry of the radiating element thereby to suppress higher order modes. The suppression of these higher order modes results in a radiation pattern with minimal cross-polarized energy in the principal planes and high port-to-port isolation which could not be achieved with an asymmetrical element. Two driving points may be employed with the radiating element to produce a dual linearly polarized antenna and a reactive combiner or hybrid may be employed to obtain circularly-polarized radiations.

Abstract: An RF-transparent blanket provides thermal protection against solar and laser radiation. The blanket includes an outer layer of a transparent Kapton dielectric sheet with an outer surface coated with electrically conductive transparent indium-tin oxide to aid in suppressing electrostatic discharge. A second layer includes a transparent Kapton dielectric sheet with a coating of white silicone paint on the surface facing the first sheet. The outermost Kapton sheet protects the paint from long-term damage due to charged particle fluence and ultraviolet radiation. Further sheets of uncoated transparent Kapton, which may be embossed, are interposed between the second layer and a surface upon which an antenna is mounted to provide thermal insulation.

Abstract: A deployable crossed log-periodic dipole array antenna includes a plurality of bays, each associated with four elongated, flexible antenna elements, each element having an S-shaped cross-section for stiffness. Each bay also includes a spool. The spools have a "squared circle" shape adapted to the natural curvature of the antenna elements. A drum surrounds and is coaxial with all the spools, and the antenna elements extend through apertures in the drum. Rotation of the drum winds and unwinds the flexible antenna elements from their spools simultaneously. When the drum begins to wind for retraction of the elements toward a stowed condition, some bays are arranged so that the elements begin to wind about the spools immediately, whereas other bays are arranged so that the antenna elements rotate about hinges over an angle such as 90.degree. or 180.degree. before beginning to wind onto their spools.

Abstract: First and second sandwich panels each have first and second face sheets, held in a mutually parallel, spaced-apart relationship by a low-density core. The panels are joined along an edge, which may be curved. The joinder is made by a plurality of thin, flat "L"-shaped joining pieces, each having first and second legs, which may be at skew angles if the panels are joined at skew angles. The first leg of the first joining piece is affixed, as by adhesive, to the first face sheet of the first panel and to the exposed core of the second panel, and the second leg of the first joining piece is affixed to the second face sheet of the second panel. The second joining piece, adjacent the first, has its first leg affixed to the first face sheet of the second panel and to the exposed core of the first panel, and its second leg affixed to the second face sheet of the first panel. Other additional fasteners may alternate along the length of the edge to be joined.

Abstract: A satellite attitude control system is usable in the absence of any inertial yaw attitude reference, such as a gyroscope, and in the absence of a pitch bias momentum. Both the roll-yaw rigid body dynamics and the roll-yaw orbit kinematics are modelled. Pitch and roll attitude control are conventional. The model receives inputs from a roll sensor, and roll and yaw torques from reaction wheel monitors. The model produces estimated yaw which controls the spacecraft yaw attitude.