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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

A TDM link with channel coding and digital voice.

The features of a TDM (time-division multiplexed) link model are described. A PCM telemetry sequence was coded for error correction and multiplexed with a digitized voice channel. An all-digital implementation of a variable-slope delta modulation algorithm was used to digitize the voice channel. The results of extensive testing are reported. The measured coding gain and the system performance over a Gaussian channel are compared with theoretical predictions and computer simulations. Word intelligibility scores are reported as a measure of voice channel performance.

Jones, M. W.↗
NASA NTRS1973

Microprogrammed digital filters for strapdown guidance application.

Discussion of an approach for implementing digital filters using microprogrammed control logic with read only memory (ROM) for strapdown guidance applications, and description of a second-order multiplexed system using multiprogrammed control instruction. The microprogramming technique for control using ROM is shown to enhance higher order digital filter realization. The high speed of digital circuits reduces propagation time and facilitates multiplexing. Programmed ROM's can be altered easily for different algorithms.

Kapadia, K.↗
NASA NTRS1975

Multipurpose panel, phase 1, study report

The feasibility of a multipurpose panel which provides a programmable electronic display for changeable panel nomenclature, multiplexes similar indicator display signals to the signal display, and demultiplexes command signals is examined. Topics discussed include: electronic display technology, miniaturized electronic and memory devices, and data management systems which employ digital address and multiplexing.

Parkin, W.↗
NASA NTRS1975

The revolution in data gathering systems

This paper gives a review of the data-acquisition systems used in NASA's wind tunnels from the 1950's to the present as a basis for assessing the impact of minicomputers and microcomputers on data acquisition and processing. The operation and disadvantages of wind-tunnel data systems are summarized for the period before 1950, the early 1950's, the early and late 1960's, and the early 1970's. Some significant advances discussed include the use or development of solid-state components, minicomputer systems, large central computers, on-line data processing, autoranging DC amplifiers, MOS-FET multiplexers, MSI and LSI logic, computer-controlled programmable amplifiers, solid-state remote multiplexing, integrated circuits, and microprocessors. The distributed system currently in use with the 40-ft by 80-ft wind tunnel at Ames Research Center is described in detail. The expected employment of distributed systems and microprocessors in the next decade is noted.

Cambra, J. M.↗
NASA NTRS1975

A dynamic packet-switching system for satellite broadcast channels

A new satellite multi-access scheme for packet-switching computer communications combines a dynamic allocation technique with conventional time-division multiplexing to minimize delays and maximize traffic thruput. The scheme is designed to give the shortest delays to short-duration interactive or priority traffic, at the expense of longer delays for large data transfers. Simulation results show markedly improved delay-thruput characteristics over conventional time-division multiplexing for a wide range of traffic mixes, with especially significant performance gains as the traffic imbalance among the nodes increases.

Binder, R.↗
NASA NTRS1975

Multimission spacecraft Dataplexer

The data multiplexing unit described is a low-power small-size building-block-type central data system designed for use on such spacecraft as the International Ultraviolet Explorer or the International Sun-Earth Explorer. Preprogrammed read-only memories are used to generate the telemetry format tailored to particular mission requirements. Low weight and low power dissipation are achieved with the aid of PMOS technology. The use of subcommutators in groups to meet particular spacecraft requirements allows low data rate experiments to be time-multiplexed into a single main input channel, to improve data collection and processing operations. The block diagram of the Dataplexer is discussed.

Cosme, R.↗
NASA NTRS1977

Monopulse receiver

A time division multiplexing and a quadraphase combining dual channel system were analyzed, designed, and tested. Analyses performed include the following: (1) boresight error as a function of the error channel bandwidth; (2) error channel interference with the sum channel functions; (3) threshold performance; and (4) error channel crosstalk, linearity, and drift as a function of signal level, Doppler, and environment. Test results indicate that the time division multiplexing system meets the design goals of the program. However, careful selection and alignment of all gain controlled amplifiers are required along with temperature compensation of the angle channel gain. The quadraphase system crosstalk performance is comparatively poor (-15 dB) with respect to the -30 dB requirements and this consequently affects gain tracking performance. Gain tracking was found to be + or - 20 percent rather than the + or - 5 percent specification. Data for the two systems is compared and recommendations are presented.

Source record↗
NASA NTRS1977

Cell-level battery charge/discharge protection system

The paper describes three design approaches to individual cell monitoring and control for sealed secondary battery cells. One technique involves a modular strap-on single cell protector which contains all the electronics required for monitoring cell voltage, responding to external commands, and forming a bypass circuit for the cell. A second technique, the multiplexed cell protector, uses common circuitry to monitor and control each cell in a battery pack. The third technique, the computerized cell protector, by replacing the hard-wired logic of the multiplexed cell protector with a microprocessor, achieves greatest control flexibility and inherent computational capability with a minimum parts count implementation.

Donovan, R. L.↗
NASA NTRS1976

Convolutional coding at 50 Mbps for the Shuttle Ku-band return link

Error correcting coding is required for 50 Mbps data link from the Shuttle Orbiter through the Tracking and Data Relay Satellite System (TDRSS) to the ground because of severe power limitations. Convolutional coding has been chosen because the decoding algorithms (sequential and Viterbi) provide significant coding gains at the required bit error probability of one in 10 to the sixth power and can be implemented at 50 Mbps with moderate hardware. While a 50 Mbps sequential decoder has been built, the highest data rate achieved for a Viterbi decoder is 10 Mbps. Thus, five multiplexed 10 Mbps Viterbi decoders must be used to provide a 50 Mbps data rate. This paper discusses the tradeoffs which were considered when selecting the multiplexed Viterbi decoder approach for this application.

Batson, B. H.↗
NASA NTRS1978

Microcomputerized electric field meter diagnostic and calibration system

A computerized field meter calibration system which includes an apparatus for testing the calibration of field meters normally utilized for measuring electromagnetic field potentials is described. A reference voltage is applied to the field meter for causing signals to be produced on the output terminals thereof. A bank of relays is provided for selectively connecting output terminals of the field meter to a multiplexer by means of a digital voltmeter and an oscilloscope. A frequency-shift-keyed receiver is also connected to one of the terminals of the field meter for transmitting and converting a frequency shift keyed signal to a digital signal which is, subsequently, applied to the multiplexer.

Holley, L. D.↗
NASA NTRS1980

Bubble-domain detector

Bubble domain detector employs transformer coupling for data retrieval. Method makes multidetection practical by time multiplexing. Multiplexer matrices can be scaled in 4 by 4, 4 by 8, 4 by 16, or larger combinations without diode steering.

Stermer, R. L.↗
NASA NTRS1979

A rocket-borne pulse-height analyzer for energetic particle measurements

The pulse-height analyzer basically resembles a time-sharing multiplexing data-acquisition system which acquires analog data (from energetic particle spectrometers) and converts them into digital code. The PHA simultaneously acquires pulse-height information from the analog signals of the four input channels and sequentially multiplexes the digitized data to a microprocessor. The PHA together with the microprocessor form an on-board real-time data-manipulation system. The system processes data obtained during the rocket flight and reduces the amount of data to be sent back to the ground station. Consequently the data-reduction process for the rocket experiments is speeded up. By using a time-sharing technique, the throughput rate of the microprocessor is increased. Moreover, data from several particle spectrometers are manipulated to share one information channel; consequently, the TM capacity is increased.

Leung, W.↗
NASA NTRS1978

Space Shuttle Orbiter audio subsystem

The selection of the audio multiplex control configuration for the Space Shuttle Orbiter audio subsystem is discussed and special attention is given to the evaluation criteria of cost, weight and complexity. The specifications and design of the subsystem are described and detail is given to configurations of the audio terminal and audio central control unit (ATU, ACCU). The audio input from the ACCU, at a signal level of -12.2 to 14.8 dBV, nominal range, at 1 kHz, was found to have balanced source impedance and a balanced local impedance of 6000 + or - 600 ohms at 1 kHz, dc isolated. The Lyndon B. Johnson Space Center (JSC) electroacoustic test laboratory, an audio engineering facility consisting of a collection of acoustic test chambers, analyzed problems of speaker and headset performance, multiplexed control data coupled with audio channels, and the Orbiter cabin acoustic effects on the operational performance of voice communications. This system allows technical management and project engineering to address key constraining issues, such as identifying design deficiencies of the headset interface unit and the assessment of the Orbiter cabin performance of voice communications, which affect the subsystem development.

Stewart, C. H.↗
NASA NTRS1978

A microprocessor based communications multiplexer/concentrator

In the past communications concentrators have been designed using mini-computers. In this work a design for a high speed concentrator (in the megabits range) is developed using the 3000 series bit slice microprocessor. The proposed concentrator realizes the functions of multiplexing of the data arriving on the low speed lines, demultiplexing of the data arriving on the high speed line, including canned responses and code conversion. The basic system hardware configuration and the principles of operation of the multiplexing and the demultiplexing subsystems are presented. The software for these two functions are also presented. Using queueing theory, an estimate of the required buffer size is provided. Possible areas of further improvement are also indicated.

Brown, D. W.↗
NASA NTRS1979

Multichannel temperature controller for hot air solar house

This paper describes an electronic controller that is optimized to operate a hot air solar system. Thermal information is obtained from copper constantan thermocouples and a wall-type thermostat. The signals from the thermocouples are processed through a single amplifier using a multiplexing scheme. The multiplexing reduces the component count and automatically calibrates the thermocouple amplifier. The processed signals connect to some simple logic that selects one of the four operating modes. This simple, inexpensive, and reliable scheme is well suited to control hot air solar systems.

Currie, J. R.↗
NASA NTRS1979

Multiwavelength monolithic integrated fiber-optic terminal

The paper presents the Multiwavelength Monolithic Integrated Fiber Optic Terminal (MMIFOT) developed under NASA sponsorship. The program aims to utilize the advantage of optical fiber and integrated optical device technology to achieve parallel transmission of many data channels over the same optical fiber link, and to develop an eight channel wavelength multiplexed fiber optic link that transmits eight bit words in a parallel format at a nominal rate of 20 Mw/s; in the second phase of the program a transmitter/multiplexer chip will be developed. The MMIFOT configuration, the receiver/demultiplexer development, and the waveguide detector development are discussed, concluding that the first phase of the MMIFOT program will culminate in the demonstration of an eight channel receiver/demultiplexer chip with a four channel breadboard multiplexer with the data rate of 20 Mbps per channel with a dynamic range of minimum 20 dB.

Rice, R. R.↗
NASA NTRS1979

Integrated infrared detector arrays for low-background astronomy

Existing integrated infrared detector array technology is being evaluated under low-background conditions to determine its applicability in orbiting astronomical applications where extended integration times and photometric accuracy are of interest. Preliminary performance results of a 1 x 20 elements InSb CCD array under simulated astronomical conditions are presented. Using the findings of these tests, improved linear- and area-array technology will be developed for use in NASA programs such as the Shuttle Infrared Telescope Facility. For wavelengths less than 30 microns, extrinsic silicon and intrinsic arrays with CCD readout will be evaluated and improved as required, while multiplexed arrays of Ge:Ga for wavelengths in the range 30 to 120 microns will be developed as fundamental understanding of this material improves. Future efforts will include development of improved drive and readout circuitry, and consideration of alternate multiplexing schemes.

Mccreight, C. R.↗
NASA NTRS1980

The 30/20 Gigahertz transponder study

Design features and performance parameters are described for three types of wideband multiple channel satellite transponders for use in a 30/20 GHz communications satellite, which provides high data rate trunking service to ten ground station terminals. The three types of transponder are frequency division multiplex (FDM), time division multiplex (TDM), and a hybrid transponder using a combination of FDM and TDM techniques. The wideband multiple beam trunking concept, the traffic distribution between the trunking terminals, and system design constraints are discussed. The receiver front end design, the frequency conversion scheme, and the local oscillator design are described including the thermal interface between the transponders and the satellite. The three designs are compared with regard to performance, weight, power, cost and initial technology. Simplified block diagrams of the baseline transponder designs are included.

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