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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Observations and impressions from lunar orbit

On Apollo 16, the command module pilot made observations of particular surface features and processes to complement photographic and other remotely sensed data. Emphasis was placed on geological problems that required the extreme dynamic range and color sensitivities of the human eye; repetitive observations of varying sun angles and viewing directions; and, in some cases, on-the-scene interpretations. Visual observations and impressions recorded during the mission verified the effectiveness of the hardware and techniques used. The orbiting observer functioned both as a sensor, in otherwise inaccessible areas such as earthshine and shadows, and as a designator of potentially significant data that were acquired on the photographic record.

Mattingly, T. K.↗
NASA NTRS1972

A slope reversal video processor having amplitude and pulse width discrimination.

A timing discriminator whose output is relatively insensitive to input pulse width and amplitude is described. The video-handling technique is known as slope reversal processing and is based on tapped delay line estimation methods. The concept, design, breadboard construction, and preliminary laboratory test results are reviewed. The processor system features (1) a peak input voltage dynamic range of 80x starting at 100 microvolts; (2) a four stage preamplifier/line-driver having a voltage gain of 2400x; (3) a tapped delay-line estimator implemented for slope reversal triggering by differential comparison; (4) a nominal plus or minus 2.5 nsec shift of the output trigger leading edge over the entire input voltage range, (5) up to 7 dB discrimination against pulse widths less than 35 nsec; and (6) up to one order of magnitude reduction in the false alarm rate compared to a constant fraction system.

Hoge, F. E.↗
NASA NTRS1973

Scaling aircraft noise perception.

Following a brief review of the background to the study, an extensive experiment is described which was undertaken to assess the practical differences between numerous alternative methods for calculating the perceived levels of individual aircraft flyover wounds. One hundred and twenty recorded sounds, including jets, turboprops, piston aircraft and helicopters were rated by a panel of subjects in a pair comparison test. The results were analyzed to evaluate a number of noise rating procedures, in terms of their ability to accurately estimate both relative and absolute perceived noise levels over a wider dynamic range (84-115 dB SPL) than had generally been used in previous experiments. Performances of the different scales were examined in detail for different aircraft categories, and the merits of different band level summation procedures, frequency weighting functions, duration and tone corrections were investigated.

Ollerhead, J. B.↗
NASA NTRS1973

Statistics for ionospherically diffracted VHF/UHF signals.

In this paper, a general characterization of the statistics for an ionospherically diffracted, monochromatic plane wave is presented. The main results are restricted to weak scatter, although two possible extensions that accommodate large phase perturbations and multiple scatter are discussed. A detailed discussion of the first-order statistics of amplitude is given. The general Gaussian distribution is discussed together with its Nakagami-distribution approximation and the log-normal distribution. By using a segment of ATS-3 satellite data recorded at Lima, Peru, we show equally good fits to Gaussian and log-normal distributions at least for the limited dynamic range available. The Nakagami distribution provides only a poor approximation.

Rino, C. L.↗
NASA NTRS1973

Digital hardware and computer system for a digital image recorder.

Description of the digital memory and related computer system used at the Palomar Mountain Observatory. The memory was designed to have a large number of pixels, a high capacity for each pixel, and fast access for use with a variety of image sensors. As an image integration and storage device, this memory is shown to possess ideal properties, namely, it is strictly linear, has a wide dynamic range, and the image does not deteriorate with time. The observer has a visual display which enables him to monitor the image as it is being integrated.-

Dennison, E. W.↗
NASA NTRS1973

Space application of SEC vidicons - The OSO 7 coronagraph.

An externally occulted Lyot coronagraph employing a digitized SEC vidicon detection system is a prime experiment aboard the NASA Orbiting Solar Observatory 7 (OSO 7). Continuing daily operation since the 29 September 1971 launch has produced more than 2200 pictures of the solar white light corona covering the region between 3 R and 10 R. Important advantages of the SEC vidicon in this application are its ability to integrate an electron image and store it for long periods prior to readout. Special applications of digital techniques are employed in stepping and pulsing the readout electron beam, thereby realizing the detector's inherent qualities of high resolution and large dynamic range.

Brueckner, G.↗
NASA NTRS1973

Design and performance characteristics of the Vertical Temperature Profile Radiometer /VTPR/ for atmospheric temperature soundings.

Description of the design and operation of a radiometer which derives atmospheric temperature profiles on the basis of spectral measurements in eight optical filter channels. The radiometer achieves its eight-channel capability by sequentially viewing the eight optical filters mounted in a rotating filter wheel, with a single IR detector and electronic amplification channel processing the signal for all the filters. The advantages and disadvantages of this sequential approach as compared to eight 'parallel' radiometric channels are discussed. The proposed radiometer provides a relative calibration accuracy between seven out of the eight channels of better than 0.1% rms of the full dynamic range. The absolute accuracy achievable between in-flight calibrations of six minutes, or between two-hour calibrations using optical temperature correction factors, is better than an rms value of 0.15% of full scale. The radiometric correlation between the in-flight calibration source of the instrument and a reference standard blackbody is better than an rms value of 0.5% of full scale.

Falbel, G.↗
NASA NTRS1973

Reliability of cosmic dust data from Pioneers 8 and 9.

A comprehensive study of the characteristics and capabilities of the Pioneer cosmic dust mission is presented to facilitate accurate astronomical adaptations of the data by independent researchers. The characteristics of the sensor and associated electronics as they relate to dynamic range, field of view, and penetration effects in the film are discussed, comparisons are made between flight and simulation data, and statistical analyses are made of the reliability of the flight data. It is shown that the measurements from the Pioneer experiment are highly reliable and provide a valuable contribution to man's knowledge of the meteoroid environment of the solar system.

Gruen, E.↗
NASA NTRS1973

Investigation of techniques for correction ERTS data for solar and atmospheric effects

Significant findings during this report period are: (1) The feasibility of using techniques for obtaining and using atmospheric parameter to transform ERTS data into absolute target reflectance was demonstrated. (2) Ground-truth instrumentation must have a dynamic range of 100,000 for obtaining the full set of atmospheric parameters encountered in the field. (3) Atmospheric transmittance for January through May 1973 varied from 13 to 18 percent in the ERTS bands. (4) Energy scattered to the spacecraft from the atmosphere for the March overflight was equivalent to that produced by a target having a reflectance of 11% in band 4, 5% in band 5, 3% in band 6, and 1% in band 7. (5) This atmospheric radiance varies as a function of sun zenith angle (scatter angle) and is predicted to change by 30% for sun angles at the latitude of the Michigan test site. (6) If not removed from spacecraft measurements before computing reflectance of surface targets, this radiance is a major source of error.

Rogers, R. H.↗
NASA NTRS1973

Experiments for the study of cosmic gamma-ray bursts

Several experiments are outlined which are designed for investigating cosmic gamma ray bursts; they form a research program that includes balloon experiments currently under development and satellite experiments proposed for future missions. The satellite proposals, in most cases, are either suggested for payloads that are presently defined as to experimental complement, or are for hypothetical spacecraft. Thus, these proposals at present serve to indicate, at least, the possible usefulness of various space missions for cosmic gamma-ray burst studies. Taken as a whole, this program of gamma ray burst experiments should improve on the present observations of the temporal variations, size spectrum, energy spectra, polarizations, directional locations and distribution of source directions, each by several orders of magnitude of improved resolution or of dynamic range.

Cline, T. L.↗
NASA NTRS1973

Magnetospheric modulation effects on solar cosmic rays from simultaneous OGO 1 and 3 ion chamber data in 1968 and 1969

Simultaneous observations by identical ionization chambers aboard the satellites OGO-1 and OGO-3 are utilized to investigate spatial variations in particle intensity near and inside the magnetosphere during the solar cosmic ray events of September 1966. Cross-correlation of the absolute proton flux computed from the chamber rate during three solar particle events shows good agreement with the measurements by the IMP-F Solar Proton Monitor during the same events. The chamber has a dynamic range of over six orders of magnitude. Before launch it was calibrated in the laboratory with radiation dosages in the range 1 R/hr-6000 R/hr. The OGO-1 and OGO-3 chambers, which were normalized in the laboratory prior to the launch, are found to maintain their normalization within approximately equal to 1 per cent during their flight. The high sensitivity and absolute inter-comparability of the instruments allow small intensity differences to be detected and it is established that the observed differences can be explained by a magnetospheric screening effect when an anisotropic beam of particles is present in space. Evidence is presented to show that the screening is at times complete for a duration of as much as 110 min in the tail of the magnetosphere so that during this period the solar cosmic rays (E approximately equal to 15 MeV) have virtually no access to that region of the magnetosphere. Small intensity fluctuations of a temporal nature observed and found to be subjected to a damping effect inside the magnetosphere.

Hofmann, D. J.↗
NASA NTRS1974

Development and evaluation of television tubes for space astronomy

An improved vidicon image sensor for space astronomy applications is developed that features reliably sealed ultraviolet transmitting windows and achieves acceptable photocathode quantum efficiency on these MgF2 windows. New preamplifier designs improve the dynamic range by reduction of the readout noise.

Spitzer, L.↗
NASA NTRS1973

Discrete regulation of transfer function of a circuit in experimental data automatic collection and processing systems

A device for discrete control of the circuit transfer function in automatic analog data processing systems is reported that coordinates the dynamic range of the vibration level change with the signal range of the processing device output. Experimental verification of the device demonstrates that its maximum control speed does not exceed 0.5 sec for a frequency nonuniformity of about 10%.

Lyubashevskiy, G. S.↗
NASA NTRS1974

Variable CO2 laser attenuator

An infrared wavelength variable attenuator based on contra-rotating germanium wedges is examined theoretically. The device redirects the paths of internal reflections associated with an optical flat to avoid closely spaced parallel beams at the output. Complementary wedges separated by an air gap compose an optical flat which, when combined with a masking arrangement, restricts unwanted reflections. A model of the device was built and experimentally evaluated. The results compare favorably with the dynamic range of attenuation of 2 to 50 db from theoretical calculations, and show a substantial reduction in the etalon effect associated with pairs of optical flats.

Klein, B. J.↗
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

Design and performance characteristics of the vertical temperature profile radiometer /VTPR/ for atmospheric temperature soundings

Various design characteristics and performance achievements of the vertical temperature profile radiometer (VTPR) are discussed. It is shown that the VTPR provides a relative calibration accuracy of better than 0.1% rms of the full dynamic range and has been operating successfully in space on the ITOS spacecraft for more than eleven months. The absolute accuracy achievable between in-flight calibrations of 6 minutes, or between 2-hour calibrations using optical temperature correction factors, is better than an rms value of 0.15% of full scale. The radiometric correlation between the VTPR in-flight calibration source and a reference standard blackbody is better than an rms value of 0.5% of full scale.

Falbel, G.↗
NASA NTRS1974

Search for celestial X-ray bursts

Progress in two experimental programs is reported. One program involves the search through satellite data for existing evidence for fast photon intensity bursts with energies exceeding 80 keV. The second program is concerned with the development of very sensitive instrumentation to make possible studies of X-ray and gamma ray bursts in the region from 0.1 to 15 MeV with angular resolution, energy resolution, and time resolution, taking into account the complete dynamic range from several nanoseconds to several hours.

Cline, T. L.↗