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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 1,153 records · Page 64

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NASA NTRS1973

Technology requirements for post-1985 communications satellites

The technical and functional requirements for commercial communication satellites are discussed. The need for providing quality service at an acceptable cost is emphasized. Specialized services are postulated in a needs model which forecasts future demands. This needs model is based upon 322 separately identified needs for long distance communication. It is shown that the 1985 demand for satellite communication service for a domestic region such as the United States, and surrounding sea and air lanes, may require on the order of 100,000 MHz of bandwith. This level of demand can be met by means of the presently allocated bandwidths and developing some key technologies. Suggested improvements include: (1) improving antennas so that high speed switching will be possible; (2) development of solid state transponders for 12 GHz and possibly higher frequencies; (3) development of switched or steered beam antennas with 10 db or higher gain for aircraft; and (4) continued development of improved video channel compression techniques and hardware.

Burtt, J. E.↗

NASA NTRS1974

Feasibility study in the application of optical signal analysis to non-destructive testing of complex structures

Advantages of the large time bandwidth product of optical processing are presented. Experiments were performed to study the feasibility of the use of optical spectral analysis for detection of flaws in structural elements excited by random noise. Photographic and electronic methods of comparison of complex spectra were developed. Limitations were explored, and suggestions for further work are offered.

Baker, B.↗

NASA NTRS1973

Water quality determination by photographic analysis

Aerial reconnaissance techniques to extract water quality parameters from aerial photos are reported. The turbidity can be correlated with total suspended solids if the constituent parts of the effluent remain the same and the volumetric flow remains relatively constant. A monochromator is used for the selection of the bandwidths containing the most information. White reflectance panels are used to locate sampling points and eliminate inherent energy changes from lens flare, radial lens fall-off, and changing subject illumination. Misleading information resulting from bottom effects is avoided by the use of Secchi disc readings and proper choice of wavelength for analyzing the photos.

Klooster, S. A.↗

NASA NTRS1973

Capabilities of electrodynamic shakers when used for mechanical shock testing

The results of a research task to investigate the capabilities of electrodynamic vibrators (shakers) to perform mechanical shock tests are presented. The simulation method employed was that of developing a transient whose shock response spectrum matched the desired shock response spectrum. Areas investigated included the maximum amplitude capabilities of the shaker systems, the ability to control the shape of the resultant shock response spectrum, the response levels induced at frequencies outside the controlled bandwidth, and the nonlinearities in structural response induced by a change in test level.

Keegan, W. B.↗

NASA NTRS1973

Task six report: Spacecraft communication terminal evaluation

An analytical comparison is made of space communication accomplished at six different wavelengths. In the radio band, 2.25, 7.5, and 14.5 GHz systems are analyzed, while at optical wavelengths, 0.53, 1.06 and 10.6 micron systems are examined. The purpose of the comparison is to determine which of these systems will require the least hardware weight to perform a given communication task. The problem is solved by requiring each communication system to meet a given performance while selecting combinations of transmitted power and antenna diameter to obtain the least overall system weight. This performance is provided while maintaining practical values for parameters other than antenna diameter and power, which also affect system performance. The results of the analysis indicate that for future data links over ranges of 42,000 to 84,000 km and with data bandwidths of 100 to 1000 MHz, the CO2 laser system will provide the required performance with the least total system weight impact on a spacecraft.

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NASA NTRS1974

SAO/NASA joint investigation of astronomical viewing quality at Mount Hopkins Observatory: 1969-1971

Quantitative measurements of the astronomical seeing conditions have been made with a stellar-image monitor system at the Mt. Hopkins Observatory in Arizona. The results of this joint SAO-NASA experiment indicate that for a 15-cm-diameter telescope, image motion is typically 1 arcsec or less and that intensity fluctuations due to scintillation have a coefficient of irradiance variance of less than 0.12 on the average. Correlations between seeing quality and local meteorological conditions were investigated. Local temperature fluctuations and temperature gradients were found to be indicators of image-motion conditions, while high-altitude-wind conditions were shown to be somewhat correlated with scintillation-spectrum bandwidth. The theoretical basis for the relationship of atmospheric turbulence to optical effects is discussed in some detail, along with a description of the equipment used in the experiment. General site-testing comments and applications of the seeing-test results are also included.

Pearlman, M. R.↗

NASA NTRS1974

Task 60 test report, evaluation of IRIG-A 21 channel constant bandwith FM multiplexer for shuttle development flight instrumentation

A frequency modulated (FM) multiplexer, consisting of 21 IRIG-A constant bandwidth (CBW) voltage-controlled oscillators (VCO's) was tested to determine its suitability for use in multiplexing 21 data signals which have frequency ranges of dc to 2 kHz. Tests were preformed with the composite signal, consisting of the mixed outputs of the 21 VCO's connected directly to a set of subcarrier discriminators, with the signal recorded on magnetic tape and played back through the discriminators and with the signal transmitted by a frequency-modulated FM S-band radio frequency RF transmitter to a FM receiver and through the subcarrier discriminators. Tape speed flutter was induced to determine the reduction in flutter noise which can be obtained by the tape speed compensation equipment. The RF transmission test included transmitting the composite signal at a nominal RF received signal of -73 dbm and at RF levels of -83 and -86 dbm.

Haddick, C. M.↗

NASA NTRS1973

Narrow-band photography of Jupiter and Saturn

Jupiter and Saturn were photographed with narrow-bandwidth interference filters from 3000 to 9200A and in the 1-2 micron region with an infrared-sensitive vidicon. Changes with wavelength are noted in the limb darkening and surface detail.

Fountain, J. W.↗

NASA NTRS1972

Handbook for the calculation of approximate data for spaceborne sensors

In allocating the RF spectrum for the transmission of sensed data from space to earth, the characteristics of the data produced by each sensor are discussed. For example, data may be in the form of a continually varying voltage (analog) or may be a series of discrete pulses (digital). For the analog signal, its important characteristics to the spectrum allocator are its highest frequency component (bandwidth) and its range from minimum values (dynamic range or signal-to-noise ratio). For the digital signal, the characteristic of interest is the bit rate.

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NASA NTRS1973

The use of correlation receiving systems for detection of noise sources at short distances

The use of a directional receiving system to detect noise sources masked by isotropic noise field interference at distances comparable with the distance between the two receivers, was discussed. Wide band noise was also examined. Results indicate the following limitations must be considered when using the method: (1) the system is directional only in the plane of the base, (2) directional power of the system is impaired with a decrease in the bandwidth of the noise source spectrum, (3) the system does not permit unambiguous determination of the direction to noise sources, located on both sides of the base line, and (4) the system has a comparatively low output signal-to-noise ratio.

Tarabarin, V. V.↗

NASA NTRS1973

Engineering studies related to geodetic and oceanographic remote sensing using short pulse techniques

For the Skylab S-193 radar altimeter, data processing flow charts and identification of calibration requirements and problem areas for defined S-193 altimeter experiments are presented. An analysis and simulation of the relationship between one particular S-193 measurement and the parameter of interest for determining the sea surface scattering cross-section are considered. For the GEOS-C radar altimeter, results are presented for system analyses pertaining to signal-to-noise ratio, pulse compression threshold behavior, altimeter measurement variance characteristics, desirability of onboard averaging, tracker bandwidth considerations, and statistical character of the altimeter data in relation to harmonic analysis properties of the geodetic signal.

Miller, L. S.↗

NASA NTRS1974

Program on application of communications satellites to educational development: Design of a 12 channel FM microwave receiver

The design, fabrication, and performance of elements of a low cost FM microwave satellite ground station receiver is described. It is capable of accepting 12 contiguous color television equivalent bandwidth channels in the 11.72 to 12.2 GHz band. Each channel is 40 MHz wide and incorporates a 4 MHz guard band. The modulation format is wideband FM and the channels are frequency division multiplexed. Twelve independent CATV compatible baseband outputs are provided. The overall system specifications are first discussed, then consideration is given to the receiver subsystems and the signal branching network.

Risch, C. O.↗

NASA NTRS1974

Design of a 12 channel fm microwave receiver

Risch, C. O.↗

NASA NTRS1974

Infrared heterodyne spectroscopy of astronomical and laboratory sources at 8.5 micron

The first infrared heterodyne spectrometer using tuneable semiconductor (PbSe) diode lasers has been constructed and was used near 8.5 micron to measure absorption line profiles of N2O in the laboratory and black body emission from the Moon and from Mars. Spectral information was recorded over a 200 MHz bandwidth using an 8-channel filter bank. The resolution was 25 MHz and the minimum detectable (black body) power was 1 x 10 to the minus 16th power watts for 8 minutes of integration. The results demonstrate the usefulness of heterodyne spectroscopy for the study of remote and local sources in the infrared.

Mumma, M.↗

NASA NTRS1973

Hexagonal multiple phase-and-amplitude-shift-keyed signal sets

Selection of a particular signal set array for a bandwidth-constrained multiple phase-and-amplitude-shift-keyed (MPASK) communication system for a linear additive Gaussian noise channel requires consideration of factors such as average and/or peak power vs symbol error probability, signal amplitude dynamic range, simplicity of generation and detection, and number of bit errors per symbol error (Gray code properties). A simple technique is presented for generating and optimally detecting the honeycomb (hexagonal) signal set, i.e., the signal set that has the tightest sphere-packing properties. The symbol and bit error probability performance of this set is compared to other two-dimensional signal sets that have been investigated in the literature, and is shown to be slightly superior from an average power standpoint. The paper concludes with a comparison of all of these signal sets from the standpoint of the factors listed above.

Simon, M. K.↗

NASA NTRS1973

Distortion generated in angle-modulation systems by phased arrays

The magnitude and characteristics of distortion produced in demodulated signals by corporate-fed phased arrays are reviewed. Graphs depicting distortion, plotted as a function of signal characteristics and array geometry, display the effects of large arrays on broadband signals. These curves show that distortion in angle-modulation systems is more a function of modulation index than of bandwidth. The data presented provide a basis for predicting distortion levels in practical array systems and for extending analyses to other signal-array configurations.

Rogers, J. D.↗

NASA NTRS1973

Radar satellite altimetry and ocean wave height estimation

The design of a radar satellite altimeter having a plus or minus 10 cm topographic resolution at 20 meter (peak-to-trough) ocean wave heights is described. In addition to altimetry, the resulting design also provides a measurement of significant wave height over the range of 1.0 to 20 meters to within plus or minus 10%. A full deramp pulse compression technique followed by an analog filter bank to separate individual range returns is used in the radar transmitter/receiver design to reduce the A/D converter bandwidth from a rather impractical 330 MHz to less than 1 MHz. The altimeter design utilizes an onboard maximum likelihood estimate (MLE) processor to achieve the plus or minus 10 cm topographic resolution. It is shown that an MLE processor provides simultaneous optimum (minimum variance) estimates of satellite altitude, ocean wave height and electromagnetic ocean surface reflectivity.

Dooley, R. P.↗

NASA NTRS1973

Optical instrumentation engineering in science, technology and society; Proceedings of the Sixteenth Annual Technical Meeting, San Mateo, Calif., October 16-18, 1972

Visual tracking performance in instrumentation is discussed together with photographic pyrometry in an aeroballistic range, optical characteristics of spherical vapor bubbles in liquids, and the automatic detection and control of surface roughness by coherent diffraction patterns. Other subjects explored are related to instruments, sensors, systems, holography, and pattern recognition. Questions of data handling are also investigated, taking into account minicomputer image storage for holographic interferometry analysis, the design of a video amplifier for a 90 MHz bandwidth, and autostereoscopic screens. Individual items are announced in this issue.

Katz, Y. H.↗