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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 55 records · Page 3
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NASA NTRS1975

The GSFC 20 and 30 GHz millimeter wave propagation experiment

The Goddard Space Flight Center Millimeter Wave Experiment (MWE) aboard ATS-6, designed to evaluate the propagation characteristics of earth-space communications links at 20 and 30 GHz, is outlined, and the major results to date are presented. The 20 and 30 GHz transmitters operate through spot beam or continental coverage antenna systems. The transmitted signals consist of 9 tones spaced out to 1440 MHz. A communications link 6 GHz up and 20 or 30 GHz down is provided. Attenuation ratio measurements between the 20 and 30 GHz links indicate values higher than those predicted. Clear sky scintillations have been observed with spectral components up to about 50 Hz. Observations of rain depolarization indicate that attenuation effects predominate over depolarization effects in frequency re-use communications systems in the 20 GHz region. Various methods of predicting path attenuation are under investigation.

Ippolito, L. J.↗
NASA NTRS1976

An empirical relationship for path diversity gain

Existing 15.3 and 16 GHz path diversity gain data for earth-space propagation paths are used to generate an empirical relationship for diversity gain as a function of terminal separation distance and single terminal fade depth. The agreement between the resulting closed form expression and the data is within 0.75 dB in all cases.

Hodge, D. B.↗
NASA NTRS1975

The GSFC 20 and 30 GHz millimeter wave propagation experiment

The preliminary results of the Goddard Space Flight Center Millimeter Wave Experiment, flown aboard ATS-6 to investigate the propagation characteristics of earth-space communications links at 20 and 30 GHz, are discussed. The spacecraft transmitters operate through spot beam (2 deg) or continental coverage (6 by 9 deg) antenna systems. The transmitted signals consist of a set of nine tones spaced out to 1440 MHz to allow measurement of wideband attenuation and coherence through precipitation. Initial data on precipitation depolarization and attenuation effects indicate that attenuation effects will exert the stronger influence on the design of frequency re-use communications systems in the 20 GHz region. The use of four ground terminals separated by 30 to 78 km to reduce the effects of rain attenuation has been successful, with improvement approaching the theoretical maximum demonstrated for five events. Preliminary results on the use of on-beam radar measurements for predicting rain attenuation are encouraging.

Ippolito, L. J.↗
NASA NTRS1976

The OSU self-phased array for propagation measurements using the 11.7 GHz CTS beacon

A self phased array was developed for propagation measurements on an earth-space path. The 11.7 GHz CTS beacon was used as the signal source. The self phased array was used to measure angle of arrival as well as attenuation and scintillation statistics. The performance of the array is described, and sample data are presented. The tracking capability of the self phased array was also studied. This technique permits fully electronic, nonmechanical satellite tracking, thus simplifying unmanned operation and eliminating severe weather tracking constraints.

Theobold, D. M.↗
NASA NTRS1977

Amplitude scintillation at 2 and 30 GHz on earth space paths

Extensive amplitude scintillation measurements were made simultaneously at 2.075 and 30 GHz on earth-space propagation paths. These measurements were performed as the Applications Technology Satellite (ATS-6) was moved slowly from a synchronous position over India to a new synchronous position over the United States. The variance, path loss, covariance, and spectra are discussed as functions of the path elevation angle. These results are also compared with earlier simultaneous scintillation measurements at 20 and 30 GHz during the movement of ATS-6 to its position over India.

Hodge, D. B.↗
NASA NTRS1977

Amplitude scintillation at 2 and 30 GHz on earth space paths

Extensive amplitude scintillation measurements have been made simultaneously at 2.075 and 30 GHz on earth-space propagation paths. These measurements were performed as the Applications Technology Satellite (ATS-6) was moved slowly from a synchronous position over India to a new synchronous position over the United States. The variance, path loss, covariance, and spectra are discussed as functions of the path elevation angle. These results are also compared with earlier simultaneous scintillation measurements at 20 and 30 GHz during the movement of ATS-6 to its position over India.

Hodge, D. B.↗
NASA NTRS1978

A global model for rain attenuation prediction

A model was developed for the prediction of rain attenuation statistics for 8 rain rate climate regions spanning all land regions from the equator to the poles. The model uses empirically determined rain rate distributions for each climate region and an empirical model to estimate path averaged rain rate for given values of point rain rate. Attenuation distribution observations were compared with model predictions. Good agreement was obtained for earth-space paths at 0.1 percent of the year. At the extremes, 0.01 and 1 percent of the year the observations were generally within the model estimate bounds but the agreement is not as good as at 0.1 percent of the year. The discrepancies are attributed to the limited duration of the attenuation observations and to the limited number of rain rate distribution observations.

Crane, R. K.↗
NASA NTRS1979

Transionospheric propagation predictions

The current status and future prospects of the capability to make transionospheric propagation predictions are addressed, highlighting the effects of the ionized media, which dominate for frequencies below 1 to 3 GHz, depending upon the state of the ionosphere and the elevation angle through the Earth-space path. The primary concerns are the predictions of time delay of signal modulation (group path delay) and of radio wave scintillation. Progress in these areas is strongly tied to knowledge of variable structures in the ionosphere ranging from the large scale (thousands of kilometers in horizontal extent) to the fine scale (kilometer size). Ionospheric variability and the relative importance of various mechanisms responsible for the time histories observed in total electron content (TEC), proportional to signal group delay, and in irregularity formation are discussed in terms of capability to make both short and long term predictions. The data base upon which predictions are made is examined for its adequacy, and the prospects for prediction improvements by more theoretical studies as well as by increasing the available statistical data base are examined.

Klobucher, J. A.↗
NASA NTRS1980

Millimeter wave attenuation prediction using a piecewise uniform rain rate model

A piecewise uniform rain rate distribution model is introduced as a quasi-physical model of real rain along earth-space millimeter wave propagation paths. It permits calculation of the total attenuation from specific attenuation in a simple fashion. The model predications are verified by comparison with direct attenuation measurements for several frequencies, elevation angles, and locations. Also, coupled with the Rice-Holmberg rain rate model, attenuation statistics are predicated from rainfall accumulation data.

Persinger, R. R.↗
NASA NTRS1981

The CTS 11.7 GHz angle of arrival experiment

The objective of the experiment was to determine the statistical behavior of attenuation and angle of arrival on an Earth-space propagation path using the CTS 11.7 GHz beacon. Measurements performed from 1976 to 1978 form the data base for analysis. The statistics of the signal attenuation and phase variations due to atmospheric disturbances are presented. Rainfall rate distributions are also included to provide a link between the above effects on wave propagation and meteorological conditions.

Kwan, B. W.↗
NASA NTRS1981

Radio propagation for space communications systems

This paper presents a review of the most recent information on the effects of the earth's atmosphere on space communications systems. Models and techniques used in the prediction of atmospheric effects as influenced by frequency, geography, elevation angle, and type of transmission are discussed. Recent data on performance characteristics obtained from direct measurements on satellite links operating to above 30 GHz are reviewed. Particular emphasis is placed on the effects of precipitation on the earth-space path, including rain attenuation, and rain and ice-particle depolarization. Sky noise, antenna gain degradation, scintillations, and bandwidth coherence are also discussed. The impact of the various propagation factors on communications system design criteria is presented. These criteria include link reliability, power margins, noise contributions, modulation and polarization factors, channel crosstalk, error-rate, and bandwidth limitations.

Ippolito, L. J.↗
NASA NTRS1981

Propagation data bases

Existing data bases accumulated as the result of experiments to gather propagation data on millimeter wave Earth-space links are described. The satellites used are described and results of the significant experiments conducted in the United States are summarized. The data bases consist primarily of cumulative attenuation statistics, though some depolarization measurements are included. Additional summaries of propagation data are cited.

Source record↗
NASA NTRS1981

Prediction techniques

Prediction methods and related propagation results for the evaluation of Earth-space communication paths operating above 10 GHz are presented. Gaseous attenuation, rain, cloud, fog, sand, and dust attenuation, path diversity, signal fluctuations and low angle fading, depolarization effects, bandwidth coherence, and sky noise are considered.

Source record↗
NASA NTRS1985

Fundamental remote sensing science research program: The Scene Radiation and Atmospheric Effects Characterization Project

The Scene Radiation and Atmospheric Effects Characterization (SRAEC) Project was established within the NASA Fundamental Remote Sensing Science Research Program to improve our understanding of the fundamental relationships of energy interactions between the sensor and the surface target, including the effect of the atmosphere. The current studies are generalized into the following five subject areas: optical scene modeling, Earth-space radiative transfer, electromagnetic properties of surface materials, microwave scene modeling, and scatterometry studies. This report has been prepared to provide a brief overview of the SRAEC Project history and objectives and to report on the scientific findings and project accomplishments made by the nineteen principal investigators since the project's initiation just over three years ago. This annual summary report derives from the most recent annual principal investigators meeting held January 29 to 31, 1985.

Deering, D. W.↗
NASA NTRS1986

The combined release and radiation effects satellite, a joint NASA/DOD program

The Combined Release and Radiation Effects Satellite (CRRES) program is a two-phase joint USAF/NASA program consisting of a low Earth orbit (LEO) phase and a geosynchronous transfer orbit (GTO) phase. The mission has been carefully planned to help clarify the geospace environment picture and its effects on space hardware, communications, and man. CRRES instruments were selected for synergism, accuracy, and applicability, and will be cross-calibrated for consistency. They will provide data to fill the gaps in geospace modeling data already obtained, and will update and correct existing models. The chemical release experiments and low altitude instruments will clarify the character of the ionosphere in low Earth orbit and the high altitude chemical release experiments will improve knowledge of how trapped particle populations behave out as far as synchronous altitudes. The ionospheric studies will lead to significantly improved Earth-space intercommunications.

Berrier, D. J.↗
NASA NTRS1989

Atmospheric transmission calculations for optical frequencies

A quantitative study of the transmission loss through the entire atmosphere for optical frequencies likely to be used for an earth-space communication link using existing data bases on scattering and absorption characteristics of the atmospheric constituents is presented.

Shaik, Kamran↗
NASA NTRS1989

An intercomparison of longwave measurements by ERBE radiometers on the NOAA-9 and ERBS satellites

Two instrument modules of each satellite on which the Earth Radiation Budget Experiment (ERBE) is orbiting observe components of the earth radiation budget with three different scales of earth view. An intercomparison of longwave measurements by these instruments provides relative information concerning radiometric performance at satellite altitude, techniques of estimating upwelling exitances, and an end-to-end evaluation of the data processing system. Results indicate that the ERBE radiometers are mildly sensitive to varying thermal loads from the spacecraft and/or the earth-space environment. Radiometric variations at the satellite and methods of data interpretation contribute about equally to the uncertainty of radiant exitances from the earth.

House, Frederick B.↗