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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
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.↗
NASA NTRS1974

Fluxgate magnetometers for outer planets exploration

The exploration of the interplanetary medium and the magnetospheres of the outer planets requires the implementation of magnetic field measuring instrumentation with wide dynamic range, high stability, and reliability. The fluxgate magnetometers developed for the Pioneer 11 and Mariner-Jupiter-Saturn missions are presented. These instruments cover the range of .01 nT to 2 million nT with optimum performance characteristics and low power consumption.

Acuna, M. H.↗
NASA NTRS1975

New broadband square-law detector

Compact device has wide dynamic range, accurate square-law response, good thermal stability, high-level dc output with immunity to ground-loop problems, ability to insert known time constants for radiometric applications, and fast response times compatible with computer systems.

Reid, M. S.↗
NASA NTRS1972

Feasibility of using Eastman Kodak type 3400 film for high altitude multispectral photography

A photographic test flight of the NASA RB-57F was conducted on March 25, 1972, over Houston and West Texas, to determine the suitability of Eastman Kodak type 3400 film as a replacement for type 2402 film in the Hasselblad cameras. An additional purpose was to test GAF film type 2914, a new black and white film similar to 2402, but with higher maximum gamma and greater dynamic range.

Perry, L.↗
NASA NTRS1974

Analysis of data from satellite experiments

Identical ultraviolet photometer experiments were carried on the eccentric orbiting OGO-5 spacecraft and on the polar orbiting OGO-6 spacecraft. The experiments operated flawlessly and, due to sophisticated electronic design, allowed signals to be processed accurately over a large dynamic range. Scientific results gained from the post-mission data analysis efforts are summarized.

Thomas, G. E.↗
NASA NTRS1974

Feasibility of hydromagnetic wave measurements on space shuttle

The feasibility of using a hydromagnetic wave sensor on the space shuttles was investigated. It was found that although existing sensors are inadequate in terms of resolution, dynamic range, and frequency range, they can be modified to make the necessary measurements. It is shown that since the sensor cannot be mounted on the shuttle itself because of high levels of magnetic noise, a free subsatellite that can be positioned and stabilized may be used for locating the hydromagnetic wave sensor. Other results show that studies of long period waves would require either an array of sensors in shuttle orbit or a long-term mapping of the crustal anomalies, and that effective wave studies would require at least two variably spaced sensors in shuttle orbit and one ground station.

Mcpherron, R. L.↗
NASA NTRS1975

Skylab program earth resouces experiment package. Volume 4: Sensor performance evaluation (S193 R/S)

The results of the sensor performance evaluation of the 13.9 GHz radiometer/scatterometer, which was part of the earth resources experiment package on Skylab. Findings are presented in the areas of housekeeping parameters, antenna gain and scanning performance, dynamic range, linearity, precision, resolution, stability, integration time, and transmitter output. Supplementary analyses covering performance anomalies, data stream peculiarities, aircraft sensor data comparisons, scatterometer saturation characteristics, and RF heating effects are reported. Results of the evaluation show that instrument performance was generally as expected, but capability degradations were observed to result from three major anomalies. Conclusions are drawn from the evaluation results, and recommendations for improving the effectiveness of a future program are offered. An addendum describes the special evaluation techniques developed and applied in the sensor performance evaluation tasks.

Kenney, G. P.↗
NASA NTRS1974

A mass spectrometer concept for identifying planetary atmosphere composition

The design and use of mass spectrometers to measure and identify atmospheric gas compositions of planets are discussed. Special emphasis during the design phase was given to dynamic range that the instrument must have, mass range the instrument must cover, and precision of the measurements that are necessary, for example to confirm isotope ratios. Some problems encountered in the use of the instrument are illustrated using data from the Pioneer-Venus program.

Spencer, N. W.↗
NASA NTRS1974

Mass spectrometric measurements of atmospheric composition

The development of a magnetic sector field analyzer for continuous sampling and measurement of outer planetary atmospheres is discussed. Special features of the analyzer include a dynamic range of 10 to the minus 7th power, a mass range from 1 to 48 AMU, two ion sensitivities, a special scan time of 35 sec at 14 BPS, and the use of ion counting techniques for analysis.

Hoffman, J. H.↗
NASA NTRS1975

Skylab program: Earth resources experiment package. Sensor performance evaluation. Volume 6: (S194) L-band radiometer

Analysis of the Skylab S194 L-band radiometer experiment data provided significant results pertaining to the actual realized performance during flight. Analysis of preflight test data provided a baseline from which to compare the experiment flight performance, although many radiometric data performance capabilities could only be demonstrated in the flight environment. The final results establish the overall hardware performance of the S194 system from which prospective users of the flight data can refer for various scientific applications. Instrument performance is presented in the areas of housekeeping and internal calibration parameters, antenna system integrity, dynamic range, linearity, precision, resolution, and absolute accuracy. Supplementary evaluations were included for an error analysis of system calibration stability. Results of the evaluation show that the instrument performance was generally as expected. Conclusions are drawn from the final evaluation results, and recommendations for improving the effectiveness of a future program are offered.

Kenney, G. P.↗
NASA NTRS1975

Multi-mode optical sensor (B) evaluation test report

An evaluation test series was performed on the unit to develop realistic specifications for a similar device for use on the orbiter vehicle. Tests included sensitivity, target dynamic range, tracking angular rate, external magnetic field effects, and photocathode uniformity. Several demonstrations of operation under automatic control were also prepared, using a desk calculator for numerical control and for subsequent reduction of data derived from the test.

Smith, R. A.↗
NASA NTRS1975

An optical radar for airborne use over natural waters

An optical radar for detecting targets in natural waters was built and tested in the Gulf of Mexico. The transmitter consists of a Q switched neodymium glass laser, with output amplified and doubled in KDP to 0.53 micrometer wavelength. The receiver incorporates a noval optical spatial filter to reduce the dynamic range required of the photodetector to a reasonable value. Detection of targets to a depth of 26 meters (84 feet) was achieved with a considerable sensitivity margin. The sensitivity of the radar is highly dependent on the optical attenuation coefficient. In general, measured returns fell between the values predicted on the basis of monopath and multipath attenuation. By means of simple physical arguments, a radar equation for the system was derived. To validate this theoretical model, measurements of optical attenuation and of water surface behavior were also instrumented, and some of these results are given.

Levis, C. A.↗
NASA NTRS1975

A new broadband square law detector

A broadband constant law detector was developed for precision power measurements, radio metric measurements, and other applications. It has a wide dynamic range and an accurate square law response. Other desirable characteristics, which are all included in a single compact unit, are: (1) high-level dc output with immunity to ground loop problems; (2) fast response times; (3) ability to insert known time constants; and (4) good thermal stability. The detector and its performance are described in detail. The detector can be operated in a programmable system with a ten-fold increase in accuracy. The use and performance of the detector in a noise-adding radiometer system is also discussed.

Reid, M. S.↗
NASA NTRS1974

Odd-bit symmetric QASK

Multiple-amplitude and phase-shift-keyed (MAPSK) signal set selection is influenced by factors such as average and/or peak signal-to-noise ratio for a given error probability, dynamic range of signal amplitudes, simplicity of generation and detection, and number of bit errors per adjacent symbol error. This paper compares two possible quadrature-amplitude-shift-keyed (QASK) signal sets for the case where the number of bits per symbol is odd (for the even-bit case, the square array is the only viable QASK choice). The symmetric QASK version out-performs the rectangular QASK set at a very modest implementation penalty. This permits symmetric QASK to be considered in future odd-bit system studies.

Smith, J. G.↗