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At least 811 records · Page 45

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NASA NTRS1983

Fiberoptics technology and its application to propulsion control systems

Current work on optical sensors and optically controlled actuators for use in air-breathing engine control systems is reviewed with particular reference to the design and operation of several new fiber-optic devices. These include a tachometer, a rotary position encoder, a Fabry-Perot interferometer and a rare-earth sensor for measuring engine gas temperatures, a high-temperature photoswitch designed for the range -55 to 260 C, and optical cables and connectors. The advantages of optics over conventional wire systems used for sensing and actuator control are briefly discussed.

Baumbick, R. J.↗

NASA NTRS1981

Tri-state delta modulation system for Space Shuttle digital TV downlink

Future requirements for Shuttle Orbiter downlink communication may include transmission of digital video which, in addition to black and white, may also be either field-sequential or NTSC color format. The use of digitized video could provide for picture privacy at the expense of additional onboard hardware, together with an increased bandwidth due to the digitization process. A general objective for the Space Shuttle application is to develop a digitization technique that is compatible with data rates in the 20-30 Mbps range but still provides good quality pictures. This paper describes a tri-state delta modulation/demodulation (TSDM) technique which is a good compromise between implementation complexity and performance. The unique feature of TSDM is that it provides for efficient run-length encoding of constant-intensity segments of a TV picture. Axiomatix has developed a hardware implementation of a high-speed TSDM transmitter and receiver for black-and-white TV and field-sequential color. The hardware complexity of this TSDM implementation is summarized in the paper.

Udalov, S.↗

NASA NTRS1983

Two-dimensional photometry of planetary nebulae

In connection with the study of planetary nebulae, problems still exist in understanding such basic properties as three-dimensional structure, optical opacity to the central star's ionizing flux, and electron temperature and electron density variations within the nebular gas. To study these properties, two-dimensional images taken in many spectral lines are required. However, such a study presents a formidable problem in data analysis. In the present investigation, an attempt has been made to overcome the difficulties by using an imaging system which encodes the data digitally. Calibrated intensity maps could be constructed to test models of ionization structure and to produce two-dimensional maps of electron temperature and density. Both the results of a uniform-shell test and the nature of the solutions for the volume emissivity were found to support a nebular model in which the bright ring is part of a closed shell of variable density that resembles the torus proposed by Minkowski and Osterbrock (1960).

Kupferman, P. N.↗

NASA NTRS1982

Developing lake sampling strategies with existing Landsat data

On the basis of the assumptions that Landsat image densities relate to water quality, that lake densities can be modeled, and that homogeneous water quality areas can therefore be predicted, a method is developed for the selection of optimum water quality sampling locations on Oneida Lake in central New York. Patterns of Oneida Lake density on 24 Landsat band 5 images were traced from the screen of a density slicer, and the lake was gridded into 161 1.25 X 1.25-km cells, with image density levels encoded for each cell. Cell density levels were then employed as the dependent variable in correlations and multiple regression equations with degree days, resultant wind speed, and resultant direction. Cell density levels were averaged over two-week periods, and the averages were correlated with water quality measurements.

Philipson, W. R.↗

NASA NTRS1982

Onboard processing for a 30/20 GHz communications satellite

A systems configuration for the baseband processor for a TDMA communications satellite utilizing the 30 GHz uplink and 20 GHz downlink bands will be discussed. The baseband processor functions include QPSK burst demodulation, convolutional decoding, data routing, encoding, QPSK modulation, and antenna steering. The performance of the burst demodulator will be examined. Power and weight estimates for the baseband processor will be presented.

Reisenfeld, S.↗

NASA NTRS1982

Imaging spectrometer - An advanced multispectral imaging concept

The concept of an imaging spectrometer, which is being studied as a potential Space Shuttle experiment, is evaluated as a 'push-broom' imager that includes a spectrometer to disperse each line of imaging information into its spectral components. Using this instrument, the dispersed energy falls upon a two-dimensional focal plane array that detects both spatial and spectral information. As the line field of view is advanced over the earth by the motion of the spacecraft, the focal plane is read out constantly, which produces 'push-broom' images at multiple wavelengths. Ground instantaneous fields of view of 10 m in the visual and 20 m in the infrared are provided by the system, at a spectral resolution of 20 nm over the range from 0.4-2.5 microns. The system utilizes a triple-pass Schmidt optical system with a mosaic focal plane. A subset of the data stream is selected and encoded for transmission by the use of onboard processing.

Wellman, J. B.↗

NASA NTRS1984

Modeling concepts for communication of geometric shape data

ANSI5, an abbreviation for Section 5 of the American National Standard under Engineering Drawing and Related Documentation Practices (Committee Y14) on Digital Representation for Communication of Product Definition Data (ANSI Y14.26M-1981), allows encoding of a broad range of geometric shapes to be communicated through digital channels. A brief review of its underlying concepts is presented. The intent of ANSI5 is to devise a unified set of concise language formats for transmission of data pertaining to five types of geometric entities in Euclidean 3 space (E(3)). These are regarded as point like, curve like, surface like, solid like, and a combination of these types. For the first four types, ANSI5 makes a distinction between the geometry and topology. Geometry is a description of the spatial occupancy of the entity, and topology discusses the interconnectedness of the entity's boundary components.

Collins, M. F.↗

NASA NTRS1984

Optical systolic solutions of linear algebraic equations

The philosophy and data encoding possible in systolic array optical processor (SAOP) were reviewed. The multitude of linear algebraic operations achievable on this architecture is examined. These operations include such linear algebraic algorithms as: matrix-decomposition, direct and indirect solutions, implicit and explicit methods for partial differential equations, eigenvalue and eigenvector calculations, and singular value decomposition. This architecture can be utilized to realize general techniques for solving matrix linear and nonlinear algebraic equations, least mean square error solutions, FIR filters, and nested-loop algorithms for control engineering applications. The data flow and pipelining of operations, design of parallel algorithms and flexible architectures, application of these architectures to computationally intensive physical problems, error source modeling of optical processors, and matching of the computational needs of practical engineering problems to the capabilities of optical processors are emphasized.

Neuman, C. P.↗

NASA NTRS1984

Real time pressure signal system for a rotary engine

A real-time IMEP signal which is a composite of those produced in any one chamber of a three-lobed rotary engine is developed by processing the signals of four transducers positioned in a Wankel engine housing such that the rotor overlaps two of the transducers for a brief period during each cycle. During the overlap period of any two transducers, their output is compared and sampled for 10 microseconds per 0.18 degree of rotation by a sampling switch and capacitive circuit. When the switch is closed, the instantaneous difference between the value of the transducer signals is provided while with the switch open the average difference is produced. This combined signal, along with the original signal of the second transducer, is fed through a multiplexer to a pressure output terminal. Timing circuits, controlled by a crank angle encoder on the engine, determine which compared transducer signals are applied to the output terminal and when, as well as the open and closed periods of the switches.

Rice, W. J.↗

NASA NTRS1984

Effects of NRZ-M Modulation on Convolutional Codes Performance

Non-return-to-zero mark (NRZ-M) modulation is often used to resolve data sense in suppressed carrier telemetry systems because such systems are subject to half cycle slips that result in complementing the encoded data stream. The performance of coded telemetry systems with NRZ-M is sensitive to the order in which the various operations are done. A system that demodulates the NRZ-M waveform and then decodes performs differently from a system that does the decoding first. The performance of the NASA standard (7, 1/2) convolutional codes is determined for several systems using NRZ-M. Several different demodulation schemes for NRZ-M are considered. It is shown that, even for the best soft-decision method examined, there is a 2.7 dB loss at a decoded bit error rate of 0.005 if the NRZ-M demodulation occurs before rather than after Viterbi decoding.

Deutsch, L. J.↗

NASA NTRS1984

Cut-off rate calculations for the outer channel in a concatenated cooling system

Concatenated codes were long used as a practical means of achieving long block or constraint lengths for combating errors on very noisy channels. The inner and outer encoders are normally separated by an interleaver, so that decoded error bursts coming from the inner decoder are randomized before entering the outer decoder. The effectiveness of this interleaver is examined by calculating the cut-off rate of the outer channel seen by the outer decoder with and without interleaving. Interleaving never hurts the performance of a concatenated code, and when the inner code rate is near the cut-off rate of the inner channel, interleaving significantly improves code performance.

Herro, M. A.↗

NASA NTRS1983

An extended d(min) = 4 RS code

A minimum distance d sub m - 4 extended Reed - Solomon (RS) code over GF (2 to the b power) was constructed. This code is used to correct any single byte error and simultaneously detect any double byte error. Features of the code; including fast encoding and decoding, are presented.

Deng, H.↗

NASA NTRS1983

BCH codes for large IC random-access memory systems

In this report some shortened BCH codes for possible applications to large IC random-access memory systems are presented. These codes are given by their parity-check matrices. Encoding and decoding of these codes are discussed.

Lin, S.↗

NASA NTRS1984

Analysis of space telescope data collection systems

The Multiple Access (MA) communication link of the Space Telescope (ST) is described. An expected performance bit error rate is presented. The historical perspective and rationale behind the ESTL space shuttle end-to-end tests are given. The concatenated coding scheme using a convolutional encoder for the outer coder is developed. The ESTL end-to-end tests on the space shuttle communication link are described. Most important is how a concatenated coding system will perform. This is a go-no-go system with respect to received signal-to-noise ratio. A discussion of the verification requirements and Specification document is presented, and those sections that apply to Space Telescope data and communications system are discussed. The Space Telescope System consists of the Space Telescope Orbiting Observatory (ST), the Space Telescope Science Institute, and the Space Telescope Operation Control Center. The MA system consists of the ST, the return link from the ST via the Tracking and Delay Relay Satellite system to White Sands, and from White Sands via the Domestic Communications Satellite to the STOCC.

Ingels, F. M.↗

NASA NTRS1984

A Strategy for Successful Deep Space Information Transmission in Bad Weather

To retrieve data during bad weather, most missions slow the data rate to accommodate a certain amount of attenuation, or to allow for all but a very small percentage of all-weather conditions. This system has two well-known and balancing disadvantages: no data is received reliably during very bad weather, and the data rate is slowed during good weather. A system of processing is described that encodes the most critical data more heavily, allowing it to be retrieved under bad conditions, while at the same time allowing most of the data to be sent at a higher data rate.

Swanson, L.↗

NASA NTRS1982

Galileo probe relay receiver

For the Jovian mission, the data link from the Galileo probe to the orbiter uses suppressed-carrier Manchester encoded BPSK modulation and is protected with R = 1/2, K = 7 convolutional coding. The receiver closes the link by acquiring, tracking, and demodulating the data. It has to operate in a highly stressed environment with severe frequency offset, frequency rate, wind gust, and antenna spin conditions. Salient features are described and breadboard test data presented.

Prouty, D. A.↗

NASA NTRS1982

Digital TV tri-state delta modulation system for Space Shuttle ku-band downlink

A tri-state delta modulation/demodulation (TSDM) technique which provides for efficient run-length coding of constant-intensity segments of a TV picture is described. Aspects of the hardware implementation of a high-speed TSDM transmitter and receiver for black-and-white TV or field-sequential color or NTSC format color are reviewed. Run-length encoding of the TSDM output can consistently reduce the required channel data rate well below one bit per sample. As compared with a bistate delta modulation system, the present technique eliminates granularity in the reconstructed video without degrading rise or fall times. About 40 chips are used by TSDM when used to handle the luminance information in a color link. A possible overall space and ground functional configuration to accommodate Shuttle digital TV with scrambling for privacy is presented.

Udalov, S.↗

NASA NTRS1983

Galileo probe relay receiver - Acquisition and tracking

The probe-to-orbiter data link for the Jovian mission uses a Manchester encoded BPSK waveform which is demodulated by the Galileo probe relay receiver. Signal acquisition and tracking consists of a sequential probability ratio signal search, frequency acquisition with a least-squares estimator, wide-band phase lock acquisition, and a self-regulating mode control. A discrete Fourier transform serves as the basic mechanism to generate the algorithms that provide this orderly transition to phase tracking. Acquisition and tracking is addressed in this paper with emphasis on key algorithms, rationale, and theoretical/measured performance.

Von Der Embse, U. A.↗