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Actuator is portable and can be used in high-temperature (over 500 C) environments by incorporating tungsten metal film and quartz window. Actuator can be triggered when it is not directly in laser beam path by utilizing fiber optics. It is advantageous for remotely switching ultra-high voltage systems.
The development and characteristics of a lidar system for atmospheric measurements are discussed. The lidar system employs a Q-switched ruby laser that radiates an intense pulse of light into the atmosphere to illuminate aerosol particles in the laser beam. Light backscattered from the particles is received by a Cassegrain telescope equipped with a sensitive photomultiplier tube. The output signal of the photomultiplier tube is displayed on an oscilloscope and recorded on polaroid film.
There are a number of applications in which linear noise models are inappropriate. In the paper, the use of bilinear noise models in circuits and devices is considered. Several physical problems are studied in this framework. These include circuits involving varying parameters (such as variable resistance circuits constructed using field-effect transistors), the effect of switching jitter on sampled data system performance and communication systems involving voltage-controlled oscillators and phase-lock loops. In addition, several types of analytical techniques for stochastic bilinear systems are considered. Specifically, the moment equations of Brockett for bilinear systems driven by white noise are discussed, and closed-form expressions for certain bilinear systems (those that evolve an Abelian or solvable Lie groups) driven by white or colored noise are derived. In addition, an approximate statistical technique involving the use of harmonic expansions is described.
Design considerations applicable to a space-borne single microprocessor based packet switch are identified. These include system architecture decisions and microprocessor selection. The division of tasks among different subroutines is discussed. The primary design criterion is to maximize throughput. The extension to a multi-satellite network is discussed. The maximum throughput attainable is derived. A queue theoretic model has been developed and expressions for average response times and average queue sizes are obtained. A number of graphs showing the effect of various design parameters on the average response time and the average queue sizes are presented.
The satellite switched frequency division multiple access system provided a detailed system architecture that supports a point to point communication system for long haul voice, video and data traffic between small Earth terminals at Ka band frequencies at 30/20 GHz. A detailed system design is presented for the space segment, small terminal/trunking segment at network control segment for domestic traffic model A or B, each totaling 3.8 Gb/s of small terminal traffic and 6.2 Gb/s trunk traffic. The small terminal traffic (3.8 Gb/s) is emphasized, for the satellite router portion of the system design, which is a composite of thousands of Earth stations with digital traffic ranging from a single 32 Kb/s CVSD voice channel to thousands of channels containing voice, video and data with a data rate as high as 33 Mb/s. The system design concept presented, effectively optimizes a unique frequency and channelization plan for both traffic models A and B with minimum reorganization of the satellite payload transponder subsystem hardware design. The unique zoning concept allows multiple beam antennas while maximizing multiple carrier frequency reuse. Detailed hardware design estimates for an FDMA router (part of the satellite transponder subsystem) indicate a weight and dc power budget of 353 lbs, 195 watts for traffic model A and 498 lbs, 244 watts for traffic model B.
Leakage suppressed despite O-ring wear. New design eliminates leakage in vacuum selector valve on Space Shuttle waste-control subsystem. Applied to improve sealing in laboratory and industrial vacuum systems and other plumbing involving switching among lines with pressure differentials of order of 1 atmosphere (0.1 MPa).
The International Solar Polar Mission (ISPM) onboard instrumentation for the magnetic field experiment to establish, on the basis of in-situ observations, the heliolatitude dependence of the interplanetary magnetic field, is described. The prime output consists of vector measurements, made by two triaxial magnetometers, of the ambient magnetic field along the orbit of the spacecraft. The onboard data processor generates two data streams to be transmitted through the spacecraft telemetry. The low speed, analog data stream consists of averaged and despun vector measurements, digitized in the spacecraft analog to digital converter (ADC). The despinning algorithm used in the analog processor is described. The high speed, digital data stream consists of vector measurements digitized in the instrument ADCs, generating up to two vector samples per sec. Multiple data-path switching is used to increase system reliability and to allow cross calibration of the ADCs. On board facilities for inflight calibration are described.
A microprocessor system is provided with added memories to expand its address spaces beyond its address word length capacity by using indirect addressing instructions of a type having a detectable operations code and dedicating designated address spaces of memory to each of the added memories, one space to a memory. By decoding each operations code of instructions read from main memory into a decoder to identify indirect addressing instructions of the specified type, and then decoding the address that follows in a decoder to determine which added memory is associated therewith, the associated added memory is selectively enabled through a unit while the main memory is disabled to permit the instruction to be executed on the location to which the effective address of the indirect address instruction points, either before the indirect address is read from main memory or afterwards, depending on how the system is arranged by a switch.
Prototype exhibited efficiency of 93.9 percent. 25-kW resonant dc/dc power converter designed, developed, fabricated, and tested, using Westinghouse D7ST transistors as high-power switches. D7ST transistor characterized for use as switch in series-resonant converters, and refined base-drive circuit developed. Technical base includes advanced switching magnetic, and filter components, mathematical circuit models, control philosophies, and switch-drive strategies. Power-system benefits such as lower losses when used for high-voltage distribution, and reduced magnetics and filter mass realized.
Simulation circuit operates under remote, automatic, or manual control to produce electrical outputs similar to pressure transducer. Specific circuit designed for simulations of Space Shuttle main engine. General circuit concept adaptable to other simulation and control systems involving several operating modes. Switches and amplifiers respond to external control signals and panel control settings to vary differential excitation of resistive bridge. Output voltage or passive terminal resistance made to equal pressure transducer in any of four operating modes.
Speed and torque ranges in generator mode extended. System of shunt resistors, electronic switches, and pulse-width modulation controls torque exerted by large, three-phase, electronically commutated dc motor. Particularly useful for motor operating in generator mode because it extends operating range to low torque and high speed.
The use of robotic manipulators for the mating and demating of umbilical fuel lines to the Space Shuttle Vehicle prior to launch is investigated. Force feedback control is necessary to minimize the contact forces which develop during mating. The objective is to develop and demonstrate a working robotic force control system. Initial experimental force control tests with an ASEA IRB-90 industrial robot using the system's Adaptive Control capabilities indicated that control stability would by a primary problem. An investigation of the ASEA system showed a 0.280 second software delay between force input commands and the output of command voltages to the servo system. This computational delay was identified as the primary cause of the instability. Tests on a second path into the ASEA's control computer using the MicroVax II supervisory computer show that time delay would be comparable, offering no stability improvement. An alternative approach was developed where the digital control system of the robot was disconnected and an analog electronic force controller was used to control the robot's servosystem directly, allowing the robot to use force feedback control while in rigid contact with a moving three-degree-of-freedom target. An alternative approach was developed where the digital control system of the robot was disconnected and an analog electronic force controller was used to control the robot's servo system directly. This method allowed the robot to use force feedback control while in rigid contact with moving three degree-of-freedom target. Tests on this approach indicated adequate force feedback control even under worst case conditions. A strategy to digitally-controlled vision system was developed. This requires switching between the digital controller when using vision control and the analog controller when using force control, depending on whether or not the mating plates are in contact.
The effects of age and sex on the human-body responses to -50 torr LBNP were investigated in subjects who have undergone LBNP tests at the Kennedy Space Center. The comparison of results obtained on women and age-matched men indicated that men had larger relative increases in calf circumference and greater increases in peripheral resistance during the exposure to LBNP than the women; on the other hand, women displayed greater increases in thoracic impedance and heart rate. The comparison of the results on men of different ages (between 29 and 56 y) indicated that older subjects had greater increases in peripheral resistance and less heart rate elevation in response to LBNP. It is suggested that the age-related circulatory differences were due to a reduction in vagal response and a switch to predominant sympathetic nervous system influence in older men.
Proposed integrated in-line array of semiconductor lasers intended to provide high reliability and/or long operating lifetime. Multiple integrated collinear semiconductor lasers share common optical waveguide but individually electrically excited. When one device fails, another switched on. Important advantage in systems in which both reliability of diode lasers and alignment of those lasers with other optical components critical.
A detailed computer simulation was used to illustrate the steady-state and dynamic operating characteristics of a 20-kHz resonant spacecraft power system. The simulated system consists of a parallel-connected set of DC-inductor resonant inverters (drivers), a 440-V cable, a node transformer, a 220-V cable, and a transformer-rectifier-filter (TRF) AC-to-DC receiver load. Also included in the system are a 1-kW 0.8-pf RL load and a double-LC filter connected at the receiving end of the 20-kHz AC system. The detailed computer simulation was used to illustrate the normal steady-state operating characteristics and the dynamic system performance following, for example, TRF startup. It is shown that without any filtering the given system exhibits harmonic resonances due to an interaction between the switching of the source and/or load converters and the AC system. However, the double-LC filter at the receiving-end of the AC system and harmonic traps connected in series with each of the drivers significantly reduce the harmonic distortion of the 20-kHz bus voltage. Significant additional improvement in the waveform quality can be achieved by including a double-LC filter with each driver.
Australia will be introducing a dedicated Mobile Satellite Communications System following the launch of the AUSSAT-B satellites late in 1991. The Mobile Satellite System, MOBILESAT, will provide circuit switched voice/data services and packet-switched data services for land, aeronautical and maritime users. Here, an overview is given of the development program being undertaken within Australia to enable a fully commercial service to be introduced in 1992.
The research performed by GTE Government Systems and the University of Colorado in support of the NASA Satellite Communications Applications Research (SCAR) Program is summarized. Two levels of research were undertaken. The first dealt with providing interim services Integrated Services Digital Network (ISDN) satellite (ISIS) capabilities that accented basic rate ISDN with a ground control similar to that of the Advanced Communications Technology Satellite (ACTS). The ISIS Network Model development represents satellite systems like the ACTS orbiting switch. The ultimate aim is to move these ACTS ground control functions on-board the next generation of ISDN communications satellite to provide full-service ISDN satellite (FSIS) capabilities. The technical and operational parameters for the advanced ISDN communications satellite design are obtainable from the simulation of ISIS and FSIS engineering software models of the major subsystems of the ISDN communications satellite architecture. Discrete event simulation experiments would generate data for analysis against NASA SCAR performance measure and the data obtained from the ISDN satellite terminal adapter hardware (ISTA) experiments, also developed in the program. The Basic and Option 1 phases of the program are also described and include the following: literature search, traffic mode, network model, scenario specifications, performance measures definitions, hardware experiment design, hardware experiment development, simulator design, and simulator development.
The unequal error protection capabilities of convolutional and trellis codes are studied. In certain environments, a discrepancy in the amount of error protection placed on different information bits is desirable. Examples of environments which have data of varying importance are a number of speech coding algorithms, packet switched networks, multi-user systems, embedded coding systems, and high definition television. Encoders which provide more than one level of error protection to information bits are called unequal error protection (UEP) codes. In this work, the effective free distance vector, d, is defined as an alternative to the free distance as a primary performance parameter for UEP convolutional and trellis encoders. For a given (n, k), convolutional encoder, G, the effective free distance vector is defined as the k-dimensional vector d = (d(sub 0), d(sub 1), ..., d(sub k-1)), where d(sub j), the j(exp th) effective free distance, is the lowest Hamming weight among all code sequences that are generated by input sequences with at least one '1' in the j(exp th) position. It is shown that, although the free distance for a code is unique to the code and independent of the encoder realization, the effective distance vector is dependent on the encoder realization.