Abstract: A method for East/West stationkeeping of a geostationary satellite maintains the osculating value of longitude from exceeding a specified deadband for a specified drift period between maneuvers. In the planning, the mean longitude, the mean drift rate and the mean eccentricity vector are calculated and then maneuvers are executed to maintain the values below a magnitude such that the osculating longitude will be within the specified deadband over a specified drift period. The target conditions are achieved through a plurality of maneuvers which initiate a period of free drift which lasts for a specified number of days. During the free-drift period, longitude remains within its deadband, and no additional maneuvers are needed or are performed. The method has the advantage that it can take into account limitations on thruster on-time by allowing for a generalized number of stationkeeping maneuvers.

Abstract: An encoder for selected linear error correcting codes, such as a BCH code, uses relatively low-speed circuitry to generate parities for correcting the code. A parity matrix derived from the BCH generator matrix is provided as data to a generator vector whereby the generator vector is used as a logical shift function generator. When the logical shift function is applied to the rows of the parity matrix, columns of parity are shifted into an EXCLUSIVE-OR tree to produce the parity bit of the column. The parity bit of the column is then injected into a data stream forming the encoded symbol for transmission, attaching the parity word following the data word. The apparatus may be constructed making maximum use of the standard, commerically available, relatively low-cost integrated circuits, but it is nevertheless capable of operating at speeds in excess 1 GBPS.

Abstract: Information-theoretic notions are employed to establish the predictability of a random number generated from a circuit exhibiting chaos in order to obtain a number from a sequence of numbers with a known level of randomness and security. The method provides a measure of information loss whereby one may select the number of iterations before or between bit sampling in order to extract a secure pseudo-random number. A chaotic output is obtained by use of a sample and hold circuit coupled in a feedback loop to a variable frequency oscillator, such as a voltage controlled oscillator circuit, and operated with a positive Lyapunov exponent. A source signal generator, such as a periodic wave generator, provides a driving signal to the sample and hold circuit.

Abstract: Apparatus and method are provided for causing different groups of particles from an accelerated electron or positron beam to interact exclusively in different sections of a free electron laser. The sections may be one or several amplifiers and an oscillator. The electron beam of a single accelerator used to excite a free electron laser is directed to traverse first an amplifier section or a sequence of amplifier sections and thereafter is directed into an oscillator section where the electron beam induces lasing. If the beam source is pulsed, this invention produces the proper time synchronization of electron and laser pulses. Specifically, delay times between optical pulses are employed among the oscillator and the amplifier or amplifiers to cause the laser to oscillate on the appropriate subharmonic or subharmonics of the accelerator repetition rate so that the intervening electron pulses are used only in the amplifier or amplifiers.

Abstract: One-dimensional sun sensing and angle measurement assemblies are deployed with substantially totally overlapping fields of view on a plane of a spacecraft body to protect sensors within a protected angular area of the plane, each of the analog sun sensors generating a signal indicative of incident sun along one axis and the presence of sunlight along an orthogonal axis thereto in the common plane. The sensors together generate an indication of the orientation of the sun relative to a target field of view which is a protected area. In an alternative embodiment, a digital sun sensor assembly is provided consisting of two or more independent digital channels and employing a slit aperture cooperating with a plurality of photocells laid out in a gray coded pattern. The digital device produces digital signals indicating relative position relative to axes in a plane.

Abstract: An efficient method for time-division multiplexing multiple digital signals into a single data stream for switching and/or transmission of information to a remote location. The apparatus according to the invention receives as input, to a multiplexer, a plurality of digital data streams of arbitrary word size and data rate, any one of the data rates being changeable with time such that the total data rate of all streams combined will, in general, greatly exceed the capacity of the multiplexer. Input digital signals are assumed to have an arbitrary word size and word rate subject to the constraint that the bit rate, that is, the word rate times the word size for each signal, is an integer multiple of a predetermined integer such that any time-varying mix of digital signals, regardless of word size, can be combined into a single time-division multiplexed bit stream in such a way that no individual signal, once placed in the format, will be moved to another place in the format.

Abstract: A method for controlling transition from thruster control to momentum wheel control to minimize nutation angle and transition time in a three-axis stabilized spacecraft employing an internal body fixed-momentum wheel as an attitude stabilizer. The method employs direct, substantially real-time measurement of momentum components and angular rates and generates paired roll thrust impluses and paired yaw thrust impulses in synchronization with the nutation period of the spacecraft to drive the spacecraft to a state of substantially zero nutation. The controller employs a deadbeat principle in a closed-loop real-time feedback system. In a preferred embodiment, the impulsive thruster firing commands in roll and yaw are simultaneous, spaced one-half nutation period apart in time with the effect that the target momentum is achieved in one to three pairs of impulse firings.

Abstract: A telescope body is disclosed. The telescope body generally includes a primary structure for holding a mirror, a secondary structure for holding a means for receiving a reflection from the mirror, and a mounting section connecting the primary and secondary structure. The primary and secondary structures include four-bar linkages which have linkage action planes intersecting at the focal point of the mirror. Apparatus for preventing the secondary structure from intruding in a raypath of light to the means for receiving a reflection is also disclosed.

Abstract: A method and apparatus for combining encoding and modulation creates signal sets from available amplitude and phase modulations by indexing ordered subspaces. The subspaces need not be limited to the class of subspaces known as binary subspaces. The resultant signal sets, for a preselected power and bandwidth, are widely separated and unlikely to be confused by the effects of channel noise. Such signals can be in either finite block or convolutional form, depending on the natural format of the desired transmission. Further according to the invention are basic apparatus for encoding and modulating as well as demodulating and decoding a signal in accordance with the invention. Specifically, a method is provided for decoding the incorporates a specific type of decoding/demodulation techniques which develops accurate estimates of the information from the received signal in a computationally efficient manner and which permits high speed operation using softdecision decoders.

Abstract: A microwave signal linearizer for a travelling wave tube amplifier (TWTA) provides for simple and flexible adjustment of a predistortion network suitable for independently compensating for a wide range of travelling wave tube amplifier-induced distortions. The linearizer or predistortion network is formed by three divided parallel passive microwave signal channels, the first channel having a coaxial microwave limiter diode network, the second channel having a variable attenuator for adjusting amplitude modulation (AM/AM) non-linearity, and a third channel for adjusting amplitude modulation to phase modulation (AM/PM) non-linearity. Signals directed to the first and second channels are combined in a 180.degree. hybrid network to produce a difference signal which is directed through a difference channel to a 90.degree. hybrid network. The signals through the third channel are directed to the 90.degree.

Abstract: A wideband, aperture-coupled microstrip antenna comprising a multilayer structure and including a feed layer, a ground plane including an aperture therethrough, a plurality of tuning layers formed of dielectric material, at least one of the tuning layers including therein a tuning element in the form of an electrically-conductive material, herein called a tuning patch, and final radiating layer including a radiating patch. The multiple tuning layers serve to extend the operational bandwidth of the antenna as compared to other microstrip antennas. Aperture coupling allows realization of the antenna using integrated circuit fabication techniques without the shortcoming of direct physical connections between the feedline and the radiator, and thus providing simple, yet reliable coupling between the feedline and the antenna.

Abstract: Mechanical oscillations of a mechanism containing a stepper motor, such as a solar-array powered spacecraft, are reduced and minimized by the execution of step movements in pairs of steps, the period between steps being equal to one-half of the period of torsional oscillation of the mechanism. Each pair of steps is repeated at needed intervals to maintain desired continuous movement of the portion of elements to be moved, such as the solar array of a spacecraft. In order to account for uncertainty as well as slow change in the period of torsional oscillation, a command unit may be provided for varying the interval between steps in a pair.

Abstract: Method and apparatus for providing selfadaptive feedback control loop bandwidth and phase margin regulation automatically, to rapidly and predictably closely compensate for externally-caused bandwidth and phase margin changes, such as caused by changing load inertia presented to an actuator. Regulation is effected by controlling a loop-bandwidth correcting compensation element whose change is rendered equal to that of the loop affecting external change, but opposite in phase and change in magnitude. In a preferred embodiment, a correcting apparatus is within an internal feedback control loop which, by automatically compensating against a stated allowable range of uncorrected bandwidth variation, provides uniform static and dynamic bandwidth regulation for both internal feedback control loop and, therefore, regulation of the feedback control loop bandwidth and phase margin.

Abstract: There is provided a digitally controlled first order hold circuit and waveform synthesizer for digitally controlling the representation of a function over an approximation interval. In accordance with the operation of the invention, the first order hold circuit and waveform generator receives a digital data input signal which contains initial condition data, up/down data, and slope data for the approximation interval. The initial condition data is loaded into an up/down counter which is incremented using counting data at a rate depending on the value of the slope data and in a direction depending on the value of the up-down data. In order to minimize delays arising from data acquistion, two frequency synthesizer circuits are provided such that one frequency synthesizer provides counting data while the other frequency synthesizer receives slope data. During alternating intervals, the other frequency synthesizer circuit provides counting data while the other circuit receives slope data.

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: An adapter which comprises a pre-manufactured assembly capable of infinite vertical adjustment and self-adjusting width capability. To this end, the adapter of the present invention comprises a two-part unit in which the two parts thereof are relatively shiftable widthwise of the rack, yet a first of the parts is telescoped within the second part and secured by screws to the adjacent side of the chassis unit to be mounted. The second part of the adapter can be snap-fitted into the central, hollow portion of a vertical rail of the rack and normally remains stationary with respect to such rail; whereas, the first part of the adapter can be inserted into the second part before the second part is inserted into the hollow center portion of the rail.

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 method and apparatus are provided for transmitting a microwave signal as a beam having a wavelength small as compared to the size of the reflecting surfaces, wherein a main reflector is stationary with respect to a sub-reflector and the main reflector is motional with respect to the feed. The invention comprises rotating the sub-reflector about a first rotational axis transverse and preferably orthogonal to the guide axis, the first rotational axis being on the vertex of a secondary reflector, thereby directing radiation from a fixed feed to the motional sub-reflector. The primary reflector and sub-reflector are disposed relative to one another to share a common focus or confocal point.

Abstract: An antenna reflector structure of the offset-fed type which is suitable for use on spacecraft. The reflector structure includes a central boom, a number of spaced ribs on the boom, an RF reflective mesh layer adjacent to the outer, transverse peripheral edges of the ribs, and contoured angle members for securing the mesh layer to the ribs to provide a specific contour for the reflector surface defined by the mesh layer. The boom can be of one-piece construction or formed from telescoped segments. The reflector structure is deployable and furlable. Several embodiments of the reflector structure are disclosed.

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.