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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 739 records · Page 41

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NASA NTRS1978

A high speed pointing system

A laser ranging system for use with the Space Shuttle, and applied to a precise determination of the distance between points arrayed on different tectonic plates, i.e., along the San Andreas fault, spaced at distances of 25, 50, and 100 km, is discussed with attention to the orbiting pointing system. The mount carrying the system contains a single elliptical mirror which directs ten laser firings per second (15-18 firings to each target), and receives the light reflected from the target. The mirror and all moving structural parts are constructed of Be. The axes are equipped with 19-bit shaft angle encoders and brushless torque motors. Care is taken to avoid structural resonances, and to ensure a minimum of servo settling time. A Kalman filter is used with the microprocessor system to interpolate low data rate commands to the higher data rates required by the pointing system.

Winston, G. C.↗

NASA NTRS1978

ISEE-C HKH high energy cosmic rays

The paper describes the ISEE-C multidetector cosmic ray telescope experiment. The HKH particle identifier sensor array is designed to identify the charge and mass of incident cosmic ray nuclei from H-1 to Ni-64 over the energy range of approximately 20 to 500 MeV/nucleon. Particle identification is based on the multiple energy loss technique. The scientific aspects of the experiment are briefly reviewed and consideration is given to the flight hardware, including sensors, event encoding, buffer memory, redundancy and commandability, and packaging.

Greiner, D. E.↗

NASA NTRS1978

Systematic errors in Hadamard transform optics

Error sources encountered in Hadamard transform optical instruments are discussed. Such errors are caused by factors including moving masks, incorrect mask alignment, defects in mask fabrication, missing data, drifts in background level, and diffraction. Techniques for error reduction and/or elimination are described for each of the cases considered. It is noted that the errors described occur in singly encoded spectrometers and imagers.

Sloane, N. J. A.↗

NASA NTRS1978

Astronomical monochromatic imaging as applied to the Io sodium cloud

Four types of instruments for recording monochromatic astronomical images are compared: filters; slitless spectrographs; multislit spectrographs; and interferometers. Each of these instruments has been used on the sodium emission cloud of Io, with varying degrees of success. Multislit spectrographs and interferometers encode the signal, and it can be extracted with a noise level close to that for photon statistics. This is not normally the case for filters and slitless spectrographs. On balance, it is found that a Mach-Zehnder interferometer provides the best system for imaging faint monochromatic signals on a brighter continuum background.

Murcray, F. J.↗

NASA NTRS1978

FM/CW radar system

An FM/CW radar system is presented with improved noise discrimination in which the received signal is multiplied by a sample of the transmitted signal, and the product signal is employed to deflect a laser beam as a function of frequency. The position of the beam is thus indicative of a discrete frequency, and it is detected by the frequency encoded positions of an array of photodiodes. The outputs of the photodiodes are scanned, then threshold detected, and used to obtain the range and velocity of a target.

Brey, H.↗

NASA NTRS1978

Indicated mean-effective pressure instrument

An apparatus for measuring indicated mean effective pressure (IMEP) of an internal combustion piston or rotary engine or of an external combustion engine such as a stirling engine is disclosed. An optical shaft encoder measures crankshaft angle of the engine. Changes in volume with respect to changes in crank angle of one or more cylinders (dV/d theta) is determined either empirically or algebraically from engine geometry and stored in a memory. As the crank angle changes, dV/d theta) is read from the memory and multiplied by chamber or cylinder pressure. The product (P dv/d theta) is then added to the total previously accumulated in the cycle. Each time theta changes by an amount equal to delta theta, the process is repeated. At the end of each engine cycle, the total is equal to the IMEP value for that cycle.

Rice, W. J.↗

NASA NTRS1979

Telephone multiline signaling using common signal pair

An operator can rapidly and automatically produce coded electrical signals by manipulating mechanical thumb wheel switches so as to instruct a service center to connect any number of telephone lines to the console thus enabling the operator to listen and/or talk over several lines simultaneously. The system includes an on-site console having several mechanically operated thumb wheel switches to which the desired lines to be connected can be dialed in. Electrical coded signals are fed to a number of banks of line AND gates representing units, tens and hundreds, a group of channel gates, and a command gate. These signals are gated out in a controlled manner to an encoder which generates tones that are transmitted over a single line to a communication service center.

Goodloe, R. R.↗

NASA NTRS1979

Feasibility of inertialess conscan utilizing modified DSN feedsystems

The closed-loop conical-scan (conscan) technique has proven to be a useful method for pointing the DSN antennas more accurately than is possible by open-loop methods. As presently implemented, the antenna beam is scanned about the received signal direction by physical movement of the antenna. While straightforward, this approach has at least two disadvantages. Firstly, because of structural distortions, finite angle encoder resolution, and drive servo response, the actual antenna beam direction only approximates the commanded beam direction. Secondly, because of the large mass moved during scan, the rate of scan is severely restricted. If there are significant gain or signal level variations during a scan period, the conscan system interprets these variations as antenna pointing error. Both of these disadvantages would be alleviated in an inertialess conscan system in which the beam scanning was performed electronically. Recently, standard JPL antenna feedhorn software was upgraded to calculate, among other things, asymmetric corrugated horn radiation patterns of the type that would be needed for electronic beam scan. The required horn excitation is discussed and the results were described.

Potter, P. D.↗

NASA NTRS1979

Application of remote sensing to state and regional problems

The author has identified the following significant results. The Lowndes County data base is essentially complete with 18 primary variables and 16 proximity variables encoded into the geo-information system. The single purpose, decision tree classifier is now operational. Signatures for the thematic extraction of strip mines from LANDSAT Digital data were obtained by employing both supervised and nonsupervised procedures. Dry, blowing sand areas of beach were also identified from the LANDSAT data. The primary procedure was the analysis of analog data on the I2S signal slicer.

Miller, W. F.↗

NASA NTRS1979

Spectral characteristics of convolutionally coded digital signals

The power spectral density of the output symbol sequence of a convolutional encoder is computed for two different input symbol stream source models, namely, an NRZ signaling format and a first order Markov source. In the former, the two signaling states of the binary waveform are not necessarily assumed to occur with equal probability. The effects of alternate symbol inversion on this spectrum are also considered. The mathematical results are illustrated with many examples corresponding to optimal performance codes.

Divsalar, D.↗

NASA NTRS1977

Non-parametric PCM to ADM conversion

An all-digital technique to convert pulse code modulated (PCM) signals into adaptive delta modulation (ADM) format is presented. The converter developed is shown to be independent of the statistical parameters of the encoded signal and can be constructed with only standard digital hardware. The structure of the converter is simple enough to be fabricated on a large scale integrated circuit where the advantages of reliability and cost can be optimized. A concise evaluation of this PCM to ADM translation technique is presented and several converters are simulated on a digital computer. A family of performance curves is given which displays the signal-to-noise ratio for sinusoidal test signals subjected to the conversion process, as a function of input signal power for several ratios of ADM rate to Nyquist rate.

Locicero, J. L.↗

NASA NTRS1978

Sensor data autonomy

'Smart' sensors onboard NASA space missions will require variable data output bandwidth as they respond to phenomena of interest. An Instrument Telemetry Packet (ITP) approach has been developed which encodes experimental instrument data into an autonomous data package, along with pertinent engineering parameters and ancillary data (time, position, attitude, etc.). New requirements for onboard concentration and buffering, as well as for end-to-end error control, arise from this approach. Emphasis is placed on packet protocols compatible with the data link standard ADCCP, to enable one set of ground support equipment to readily support instrument development, launch site checkout and mission operations phases.

Greene, E. P.↗

NASA NTRS1978

On-board data processing for the IRAS telescope system

Onboard data processing has been developed for the Infrared Astronomical Satellite (IRAS) telescope system to effectively utilize the RF bandwidth and minimize the ground-data processing costs. Use of filtering techniques, data deglitching circuits, and data encoding algorithms are combined with a microprocessor-controlled telescope system to achieve a system dynamic range of 100,000 with a noise equivalent flux density of no less than 10 to the minus 19th W/sq cm. Extraneous data, e.g., noise due to radiation hits, will be removed prior to transmission, thereby optimizing ground-data processing for the highest sensitivity and reliability. Simulation results are presented which demonstrate the advantages gained through the use of onboard data processing and illustrate the possible merging of these techniques with an array for the future evolution of 'smart' sensors.

Lum, H.↗

NASA NTRS1978

Large multi-lensed telescope - A receiver for point sources in the sky

A large 80-in. (2-meter) multilensed computer-controlled and encoder-pointed telescope is described. It is being used as the receiver in the high-performance lunar laser ranging station on Mt. Haleakala on the island of Maui, Hawaii; however, it could also be used for other astronomical applications when the moon is not up. This telescope, which was designed for applications requiring aperture but not field, could affect the design of future very large astronomical instruments intended mainly for point-source spectroscopy and similar applications. The telescope and its performance to date are discussed.

Faller, J. E.↗

NASA NTRS1978

Impact of advanced onboard processing concepts on end-to-end data system

An investigation is conducted of the impact of advanced onboard data handling concepts on the total system in general and on ground processing operations, such as those being performed in the central data processing facility of the NASA Goddard Space Flight Center. In one of these concepts, known as the instrument telemetry packet (ITP) system, telemetry data from a single instrument is encoded into a packet, along with other ancillary data, and transmitted in this form to the ground. Another concept deals with onboard temporal registration of image data from such sensors as the thematic mapper, to be carried onboard the Landsat-D spacecraft in 1981. It is found that the implementation of the considered concepts will result in substantial simplification of the ground processing element of the system. With the projected tenfold increase in the data volume expected in the next decade, the introduction of ITP should keep the cost of the ground data processing function within reasonable bounds and significantly contribute to a more timely delivery of data/information to the end user.

Sos, J. Y.↗

NASA NTRS1977

Coherent optical processing of synthetic aperture radar data

Consideration is given to the data processing algorithm used in synthetic aperture radar (SAR) systems. Examples are presented of radar imagery obtained with the ERIM X-band SAR system and processed with a precision optical processor. An optical recording of the data is the input to the coherent optical processing channel. The encoding technique, spatial format, and quality of the stored data are discussed. Several optical processor configurations are outlined, noting particularly the tilted-plane system. A scanning photodetector serves to convert the optical processor output image data into an electronic signal stream. Solid-state two-dimensional photodetector arrays may provide this function at increased speeds and with greater accuracy.

Cindrich, I.↗

NASA NTRS1978

Effects of data asymmetry on Shuttle Ku-band communications link performance

This paper systematically analyzes the signal-to-noise ratio degradations which can potentially occur due to data asymmetry in digital transmission systems. Suitable asymmetry models are developed and error probability performance for various types of data detectors (integrate-and-dump filter, filter-sample detector, and gated-integrate-and-dump filter) is derived. Although this work was done to resolve problems being encountered in the Shuttle Ku-band return link design, specifically for the 50 Mbit/s convolutionally encoded channel (NRZ format), generalizations are made which provide results for other cases of interest (other Ku-band return link channels, or other systems entirely). This paper therefore considers Manchester data formats (in addition to NRZ) and uncoded transmission (in addition to convolutionally coded transmission). The effects of bandlimiting are also considered.

Simon, M. K.↗

NASA NTRS1978

The Space Shuttle Ground Terminal Delta Modulation System

Shuttle voice processing uses a Variable Slope Delta Modulation scheme which is a variant of the ABATE algorithm. This paper summarizes the ground terminal subsystem which processes the multiplexed voice and telemetry data digital sequence in the downlink processing and digitizes the voice signal in the uplink processing. The Delta Modulation System (DMS) performance characteristics are given in terms of an intelligibility test score and in terms of time and frequency responses measured on a production system developed for NASA Goddard Space Flight Center. Implementation details of the encoder and decoder algorithms are given in terms of the circuit logic used to implement them.

Auger, R. L.↗