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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Radar systems for the water resources mission. Volume 4: Appendices E-I

The use of a scanning antenna beam for a synthetic aperture system was examined. When the resolution required was modest, the radar did not use all the time the beam was passing a given point on the ground to build a synthetic aperture, so time was available to scan the beam to other positions and build several images at different ranges. The scanning synthetic-aperture radar (SCANSAR) could achieve swathwidths of well over 100 km with modest antenna size. Design considerations for a SCANSAR for hydrologic parameter observation are presented. Because of the high sensitivity to soil moisture at angles of incidence near vertical, a 7 to 22 deg swath was considered for that application. For snow and ice monitoring, a 22 to 37 deg scan was used. Frequencies from X-band to L-band were used in the design studies, but the proposed system operated in C-band at 4.75 GHz. It achieved an azimuth resolution of about 50 meters at all angles, with a range resolution varying from 150 meters at 7 deg to 31 meters at 37 deg. The antenna required an aperture of 3 x 4.16 meters, and the average transmitter power was under 2 watts.

Moore, R. K.↗
NASA NTRS1977

National geodetic satellite program, part 1

The major accomplishments of the GEOS-B, C-band systems project is assessed. The project objectives are given, namely: (1) primary objectives that must be met for project success; (2) secondary objectives that were sufficiently important to warrant serious consideration; and (3) other objectives that were important to the project and for which additional effort would be desirable. The primary objectives are presented and discussed in detail.

Belgin, J.↗
NASA NTRS1978

Design of microstrip disk antenna arrays

The radio frequency characteristics and design parameters for microstrip disk antenna elements and planar arrays are presented. Two C-band model arrays (an 8 element linear and an 8 by 8 planar) were designed, fabricated, and tested to demonstrate the technique of using microstrip elements for array applications. These arrays were designed with a cosine amplitude distribution.

Bailey, M. C.↗
NASA NTRS1978

Design and fabrication of microstrip antenna arrays

A microstrip array project was conducted to demonstrate the feasibility of designing and fabricating simple, low cost, low sidelobe phased arrays with circular disk microstrip radiating elements. Design data were presented for microstrip elements and arrays including the effects of the protective covers, the mutual interaction between elements, and stripline feed network design. Low cost multilayer laminate fabrication techniques were also investigated. Utilizing this design data two C-band low sidelobe arrays were fabricated and tested: an eight-element linear and a sixty-four element planar array. These arrays incorporated stripline Butler matrix feed networks to produce a low sidelobe broadside beam.

Source record↗
NASA NTRS1978

Switchboard in the sky

Geostationary parking orbits for the present generation of communications satellites, e.g., Intelsat, Westar, Molniya, Navsat, etc., are becoming crowded. It is noted that the C-band over North America will in future be subject to still less attenuation with the introduction of smaller (4.5 m) antennas for earth-bound receive-only applications. It is suggested, at least for the present, that more bands be added, e.g., K-, Ku-, and S-bands. To handle the potential market for communications satellite services during the years after 1985, much larger facilities will be needed. The fabrication of large platforms using the STS is discussed as the most practical solution, stressing that virtually every geosynchronous communications antenna for U.S. domestic use can be assembled on one platform positioned at an especially favorable location.

Fordyce, S. W.↗
NASA NTRS1978

Radar cross section measurements of a scale model of the space shuttle orbiter vehicle

A series of microwave measurements was conducted to determine the radar cross section of the Space Shuttle Orbiter vehicle at a frequency and at aspect angles applicable to re-entry radar acquisition and tracking. The measurements were performed in a microwave anechoic chamber using a 1/15th scale model and a frequency applicable to C-band tracking radars. The data were digitally recorded and processed to yield statistical descriptions useful for prediction of orbiter re-entry detection and tracking ranges.

Yates, W. T.↗
NASA NTRS1979

Radar error statistics for the space shuttle

Radar error statistics of C-band and S-band that are recommended for use with the groundtracking programs to process space shuttle tracking data are presented. The statistics are divided into two parts: bias error statistics, using the subscript B, and high frequency error statistics, using the subscript q. Bias errors may be slowly varying to constant. High frequency random errors (noise) are rapidly varying and may or may not be correlated from sample to sample. Bias errors were mainly due to hardware defects and to errors in correction for atmospheric refraction effects. High frequency noise was mainly due to hardware and due to atmospheric scintillation. Three types of atmospheric scintillation were identified: horizontal, vertical, and line of sight. This was the first time that horizontal and line of sight scintillations were identified.

Lear, W. M.↗
NASA NTRS1979

Results of GEOS 3/ATS 6 satellite-to-satellite tracking orbit determination experiment

The purpose of the Geos 3/ATS 6 satellite-to-satellite tracking experiment was to develop, test, and evaluate methods of deriving orbit estimates from satellite-to-satellite tracking data. The results of the form of conventional orbit overlap tests, and a comparison of a Geos 3 orbit estimate obtained from satellite-to-satellite (SST) tracking data with an orbit estimate derived form C-band data. The method recommeded for estimating orbits from SST data is a Bayesian least squares procedure utilizing independent ranging to the relay satellite.

Argentiero, P.↗
NASA NTRS1980

A new phase for NASA's communications satellite program

NASA's research in communications satellite technology is discussed, including orbit-efficient techniques and applications by the commercial sector. Attention is given to expanding the capacities of the C-band (6-4 GHz) and the Ku-band (14-11 GHz), opening the Ka-band (30/20 GHz), broadly applied 're-use' of the spectrum, and developing multibeam spacecraft antennas with on-board switching. Increasing wideband services in video, high-speed data, and voice trunking is considered, as are narrow-band systems that may be used for data collection or public safety, with possible expansion to a thin-route satellite system. In particular, communication for medical, disaster, or search-and-rescue emergencies may be met by the integration of a satellite service with land mobile communications via terrestrial radio links. Also considered is a large geostationary platform providing electrical power, thermal rejection, and orbital station-keeping for many communications payloads.

Dement, D. K.↗
NASA NTRS1980

Airborne microwave radiometer remote sensing of lake ice

The NASA Langley C-Band Stepped Frequency Microwave Radiometer was used to conduct airborne remote sensing measurements of the Great Lakes ice cover during the winters of 1978 and 1979. In order to evaluate the use of microwave radiometry for remote sensing of fresh water ice, an initial experiment was conducted in February 1978. After the results were analyzed an algorithm was developed, and a more comprehensive mission was completed in March 1979, which related the thermal emission from lake ice to meaningful geophysical quantities. A clear discrimination of pressure ridges and rubble from base ice was observed, and evidence was found which showed gradual changes in the thickness of the base itself. Results indicate that passive microwave sensors can provide a measure of lake ice within uncertainties presented by the attenuation coefficient, and the changes in surface reflectivity imposed by surface roughness.

Swift, C. T.↗
NASA NTRS1981

Some analysis on the diurnal variation of rainfall over the Atlantic Ocean

Data collected from the GARP Atlantic Tropical Experiment (GATE) was examined. The data were collected from 10,000 grid points arranged as a 100 x 100 array; each grid covered a 4 square km area. The amount of rainfall was measured every 15 minutes during the experiment periods using c-band radars. Two types of analyses were performed on the data: analysis of diurnal variation was done on each of grid points based on the rainfall averages at noon and at midnight, and time series analysis on selected grid points based on the hourly averages of rainfall. Since there are no known distribution model which best describes the rainfall amount, nonparametric methods were used to examine the diurnal variation. Kolmogorov-Smirnov test was used to test if the rainfalls at noon and at midnight have the same statistical distribution. Wilcoxon signed-rank test was used to test if the noon rainfall is heavier than, equal to, or lighter than the midnight rainfall. These tests were done on each of the 10,000 grid points at which the data are available.

Gill, T.↗
NASA NTRS1982

FIREX mission requirements document for nonrenewable resources

The proposed mission requirements and a proposed experimental program for satellite synthetic aperture radar (SAR) system named FIREX (Free-Flying Imaging Radar Experiment) for nonrenewable resources is described. The recommended spacecraft minimum SAR system is a C-band imager operating in four modes: (1) low look angle HH-polarized; (2) intermediate look angle, HH-polarized; (3) intermediate look angle, IIV-polarized; and (4) high look angle HH-polarized. This SAR system is complementary to other future spaceborne imagers such as the Thematic Mapper on LANDSAT-D. A near term aircraft SAR based research program is outlined which addresses specific mission design issues such as preferred incidence angles or polarizations for geologic targets of interest.

Dixon, T.↗
NASA NTRS1981

Shuttle STS-2 mission communication systems RF coverage and performance predictions. Volume 1: Ascent

The RF communications capabilities and nominally expected performance for the ascent phase of the second orbital flight of the shuttle are provided. Predicted performance is given mainly in the form of plots of signal strength versus elapsed mission time for the STDN (downlink) and shuttle orbiter (uplink) receivers for the S-band PM and FM, and UHF systems. Performance of the NAV and landing RF systems is treated for RTLS abort, since in this case the spacecraft will loop around and return to the launch site. NAV and landing RF systems include TACAN, MSBLS, and C-band altimeter. Signal strength plots were produced by a computer program which combines the spacecraft trajectory, antenna patterns, transmit and receive performance characteristics, and system mathematical models. When available, measured spacecraft parameters were used in the predictions; otherwise, specified values were used. Specified ground station parameter values were also used. Thresholds and other criteria on the graphs are explained.

Porter, J. A.↗
NASA NTRS1981

Advanced 30/20 GHz communication satellites

Increasing demands for satellite communications channels have filled the C-band, have begun to fill the Ku-band, and have resulted in a developmental effort to utilize 2.5 GHz of the 30/20 GHz Ka band. Problems of rain attenuation in the Ku and Ka bands are explored, and solutions are indicated in the use of antenna gain coupled with ground terminal site diversity, and higher satellite power capabilities. Tradeoffs in satellite design are focused on the number of reflectors, increased f/d, gain and sidelobe performance, and total satellite capacity. The NASA 20/30 GHz program is described, including design features of two test systems to be launched in the 1980's to examine the functioning limits of two baseline systems.

Sivo, J. N.↗
NASA NTRS1981

Shuttle /STS-1/ entry trajectory reconstruction

The methods and data used to reconstruct the Shuttle entry trajectory aerodynamics from 180 km to landing are reviewed. Onboard accelerometer and gyro measurements are used with a weighted least squares filter along with ground tracking data to provide the evolving spacecraft state. The software development is described, noting that computations include linear acceleration and angular rate data, aerodynamic coefficient, and inertial measurement units, sampled at 170 Hz. Ground tracking data was gathered on S- and C-bands; Guam data is considered critical as it was taken during the blackout at the beginning of entry. The generation of a best estimate trajectory, combining flight and ground data, yields inplane parameters of altitude, flight path angle, and velocity for comparison with navigational instrumentation. Predicted lift/drag ratios were found to be accurate from Mach 1-25, and up to 23% low below Mach 1.

Compton, H. R.↗
NASA NTRS1981

Chasing the Space Shuttle

The use and modifications of the T-38 aircraft as chase planes for the STS-1 landing are discussed. Two planes tracked the approach at Edwards AFB, with the lead plane responsible for airspeed and altimetry calibration, technical photography, landing gear status, and height-above-touchdown calls; the second T-38 provided live TV and back-up. Modifications included extension of the landing gear extension speed, increasing the area of the speedbrakes, and installation of a TV system; the goal was to stay with the Shuttle below 40,000 ft while it descended at 15,000 ft/min. Ten T-38's were modified and the deployment of lead and back-up crews during the first Shuttle flight is outlined. Western Test Range C-band radar data of the Orbiter position were transformed into intercept coordinates and VHF relayed to the chase craft. Photographs were taken of the right and left sides and underside of the Shuttle while flying with the speedbrake up to match the Shuttle speed.

Mcbride, J. A.↗
NASA NTRS1981

Aircraft radar response to soil moisture

An analysis is presented of aircraft response to soil moisture in the upper surface layer of agricultural fields. Measurements (taken at 1.6 GHz and 4.75 GHz using HH and HV polarizations, and at 13.3 GHz using VV polarization from an experiment conducted in 1978 at Colby, Kansas) are used to derive the radar soil moisture sensitivities and correlations. It is shown that the aircraft response to soil moisture is optimum at C-band frequencies and incidence angles of 10-20 deg. confirming previous truck-radar results. Like-polarization radar response is unaffected by vegetation but is dependent on row-tillage patterns; cross-polarization response also is unaffected by vegetation but is approximately independent of tillage patterns. These results show that remote sensing radars can be used effectively for the detection and estimation of near-surface soil moisture in agricultural fields.

Bradley, G. A.↗
NASA NTRS1980

30/20 GHz demonstration system for improving orbit utilization

To guard against severe rain losses at 30 and 20 GHz, techniques are being developed which provide the high antenna gain needed to increase communications margins and frequency reuse capability through beam isolation, while providing complete coverage of the U.S. Effective bandwidths from a single satellite location may then reach tens of gigahertz, with capacity tailored to match nonuniform geographic demand patterns. Satellite onboard processing which includes forward-error-correction and the routing of channels to terminals will reduce scanning antenna requirements and increase rain margins, through the adaptive use of system margins to support those terminals experiencing rain. These antenna and onboard processing techniques are adaptable to C-band and Ku-band, in addition to Ka-band.

Holmes, W. M., Jr.↗