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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Very Long Baseline Interferometry observations of 257 extragalactic radio sources in the ecliptic region

Very Long Baseline Interferometry observations of 257 extragalactic radio sources with 10 deg of the ecliptic have been conducted at a frequency of 2.29 GHz. Compact components with flux densities greater than 0.1 Jy and angular sizes smaller than the fringe spacings of 2.5 and 3.2 milliarsec were detected in 144 radio sources. This survey was conducted to find compact radio sources to form a high accuracy reference frame for planetary spacecraft navigation. This stable reference frame may also be useful for long-term studies of planetary dynamics.

Wehrle, A. E.↗
NASA NTRS1984

Radio interferometric determination of intercontinental baselines and earth orientation utilizing deep space network antennas - 1971 to 1980

Progress has been made toward the realization of the potential of radio interferometry for measuring crustal motions and global rotations of the earth with accuracies at the centimeter level. In this connection, a series of experiments, primarily with NASA's Deep Space Network (DSN) antennas, has been conducted to develop two generations of very long baseline interferometric (VLBI) systems. A description is presented of the employed techniques, an analysis of the experiments, and the results of geophysical significance. Attention is given to the interferometry technique, the geometric delay model, propagation media calibrations, and the observing strategy.

Sovers, O. J.↗
NASA NTRS1985

Hardware test program for evaluation of baseline range-range rate sensor concept

The baseline range/range rate sensor concept was evaluated. The Interrupted CW (ICW) mode of operation continued with emphasis on establishing the sensitivity of the video portion of the receiver was 7 dB less than the theoretical value. This departs from test results of previous implementations in which achieved sensitivity was within 1.5 to 2 dB of the theoretical value. Several potential causes of this discrepancy in performance were identified and are scheduled for further investigation. Results indicate that a cost savings in both per unit and program costs are realizable by eliminating one of the modes of operation. An acquisition (total program) cost savings of approximately 10% is projected by eliminating the CW mode of operation. The modified R/R sensor would operate in the ICW mode only and would provide coverage from initial acquisition at 12 nmi to within a few hundred feet of the OMV. If the ICW mode only were selected, then an accompanying sensor would be required to provide coverage from a few hundred feet to docking.

Source record↗
NASA NTRS1985

Advanced Moisture and Temperature Sounder (AMTS) baseline 5 study report

An Advanced Moisture and Temperature Sounder (AMTS) passive infrared atmospheric sounding system is described. Instrument requirements are developed. Parametric and scaling equations for a grating spectrometer instrument approach are developed which define detector noise limited performance in terms of instrument, orbit, and spatial coverage parameters. Instrument design criteria are developed and a baseline instrument design is presented. Error sources are identified and corresponding system error component values are estimated. Within narrow limits, the highest level of performance achievable with a stand alone infrared sounder using current state of the art technology is established. Additional trade offs necessary to establish a reasonably optimal system design in terms of performance, cost, and risk are identified.

Evans, N. L., Jr.↗
NASA NTRS1986

Differential Very Long Baseline Interferometry for 50 nanoradian deep space navigation - Results from quasar pair experiments

Deep space tracking experiments completed at JPL have demonstrated a 50-nanoradian angular positioning accuracy with wideband differential Very Long Baseline Interferometry (delta VLBI). This meets the stringent navigation requirements of NASA's Galileo mission, scheduled for launch in May 1986 and for encounter with Jupiter in December 1988. Pairs of extragalactic radio sources (quasars) with well-known coordinates were used to simulate deep space navigation passes in which quasar-spacecraft pairs are observed. This paper discusses the accuracy of the delta VLBI technique and how it is affected by source separations, source elevations, source strengths, solar plasma and ionosphere. Several observation strategies are discussed and one is shown to be especially effective in minimizing these major error sources.

Trinkle, B. K.↗
NASA NTRS1987

Geotaxis baseline data for Drosophila

Geotaxis profiles for 20 Drosophila species and semispecies at different ages have been examined using a calibrated, adjustable slant board device. Measurements were taken at 5 deg intervals ranging from 0 deg to 85 deg. Clear strain and species differences are observed, with some groups tending to move upward (- geotaxis) with increasing angles, while others move downward (+ geotaxis). Geotactic responses change with age in some, but not all experimental groups. Sample geotaxis profiles are presented and their application to ecological and aging studies are discussed. Data provide a baseline for future evaluations of the biological effects of microgravity.

Schnebel, E. M.↗
NASA NTRS1987

Baseline tensile tests of composite materials for LDEF (Long Duration Exposure Facility) exposure

Tensile specimens of five graphite fiber reinforced composite materials were tested at room temperature to provide baseline data for similar specimens exposed to the space environment in low-Earth orbit on the NASA Long Duration Exposure Facility. All specimens were 4-ply (+ or - 45 deg)s layups; at least five replicate specimens were tested for each parameter evaluated. Three epoxy-matrix materials and two polysulfone-matrix materials, several fiber volume fractions, and two sizes of specimen were evaluated. Stress-strain and Poisson's ratio-stress curves, ultimate stress, strain at failure, secant modulus at 0.004 strain, inplane shear stress-strain curves, and unidirectional shear modulus at .004 shear strain are presented.

Witte, William G.↗
NASA NTRS1986

Communications considerations of the very long baseline interferometry demonstration using the tracking and data relay satellite system

A desire for increased angular resolution at microwave frequencies has led to the development of radio telescopes with very lage effective apertures. Very long baseline interferometry (VLBI) has made it possible to synthesize telescopes with effective dimensions of a large fraction of an earth diameter. By using a satellite-borne radio telescope as part of a VLBI array, the dimensions of the earth cease to be a limitation. A demonstration was performed to show that the orbiting VLBI (OVLBI) concept is feasible. The Tracking and Data Relay Satellite System (TDRSS) was used as the orbiting element of the VLBI demonstration. Stability tests were made before the observations to determine the suitability of the TDRSS for OVLBI use. The first successful OVLBI observations were performed using the 64-m antenna observatories of NASA's Deep Space Network in Tidbinbilla, Australia, and of the Institute for Space and Astronautical Science in Usuda, Japan in conjunction with the TDRSS.

Levy, G. S.↗
NASA NTRS1986

Precision of vertical position estimates from very long baseline interferometry

It is found that the precision of VLBI measurements of vertical crustal motions is limited by errors in the modeling of the propagation delay through the earth's neutral atmosphere, and by errors in finding the orientation of a fixed crust coordinate system in the VLBI reference frame. The repeatability of baseline length measurements study indicates a vertical position precision of about 8 cm, averaged over 13 sites and 4.5 years of data, while the repeatability of vertical position estimates for a Richmond, FL site is found to yield a precision of about 7 cm for 42 observations made over an 11-month period. An overall precision of 8 cm for a 24-hour VLBI observing session is obtained, and the effects of earth orientation parameter errors is contingent on the distances between the VLBI sites.

Herring, T. A.↗
NASA NTRS1987

Displacements of the earth's surface due to atmospheric loading - Effects of gravity and baseline measurements

Atmospheric mass loads and deforms the earth's crust. By performing a convolution sum between daily, global barometric pressure data and mass loading Green's functions, the time dependent effects of atmospheric loading, including those associated with short-term synoptic storms, on surface point positioning measurements and surface gravity observations are estimated. The response for both an oceanless earth and an earth with an inverted barometer ocean is calculated. Load responses for near-coastal stations are significantly affected by the inclusion of an inverted barometer ocean. Peak-to-peak vertical displacements are frequently 15-20 mm with accompanying gravity perturbations of 3-6 micro Gal. Baseline changes can be as large as 20 mm or more. The perturbations are largest at higher latitudes and during winter months. These amplitudes are consistent with the results of Rabbel and Zschau (1985), who modeled synoptic pressure disturbances as Gaussian functions of radius around a central point. Deformation can be adequately computed using real pressure data from points within about 1000 km of the station. Knowledge of local pressure, alone, is not sufficient. Rabbel and Zschau's hypothesized corrections for these displacements, which use local pressure and the regionally averaged pressure, prove accurate at points well inland but are, in general, inadequate within a few hundred kilometers of the coast.

Van Dam, T. M.↗
NASA NTRS1987

Studies of multi-baseline spaceborne interferometric synthetic aperture radars

A set of Seasat SAR data that were obtained in nearly repeat ground track orbits is utilized to simulate the performance of spaceborne interferometric synthetic aperture radar (ISAR) systems. A qualitative assessment of the topography measurement capability is presented. A phase measurement error model is described and compared with the data obtained at various baseline separations and signal-to-noise ratios. Finally, the implications of these results on the future spaceborne ISAR design are discussed.

Li, F.↗
NASA NTRS1988

Loran-C monitor correlation over a 92-mile baseline in Ohio

Two Loran C monitors, at Galion and Athens, Ohio, were operated over a one-year period, measuring chain 9960 Time Delay (TD) and Signal to Noise Ratio (SNR). Analysis of data concentrated on correlation of short term TD variations during the winter months of 1985 to 86, over the 92 nm baseline. Excellent correlation was found, with slight additional improvement possible if local temperature is also included in the analysis. Although SNR and TD effects were suspected during the presence of thunderstorms near the monitors, the scope of the study did not permit storm by storm analysis. A computer tape data base of all measurements was produced, with measurements at both sites included. Data recording and analysis concentrated on the fall and winter months of September 1985 to February 1986.

Lilley, Robert W.↗
NASA NTRS1987

Monitoring biological impacts of space shuttle launches from Vandenberg Air Force Base: Establishment of baseline conditions

Space shuttle launches produce environmental impacts resulting from the formation of an exhaust cloud containing hydrogen chloride aerosols and aluminum oxide particulates. Studies have shown that most impacts occur near-field (within 1.5 km) of the launch site while deposition from launches occurs far-field (as distant as 22 km). In order to establish baseline conditions of vegetation and soils in the areas likely to be impacted by shuttle launches from Vandenberg Air Force Base (VAFB), vegetation and soils in the vicinity of Space Launch Complex-6 (SLC-6) were sampled and a vegetation map prepared. The areas likely to be impacted by launches were determined considering the structure of the launch complex, the prevailing winds, the terrain, and predictions of the Rocket Exhaust Effluent Diffusion Model (REEDM). Fifty vegetation transects were established and sampled in March 1986 and resampled in September 1986. A vegetation map was prepared for six Master Planning maps surrounding SLC-6 using LANDSAT Thematic Mapper imagery as well as color and color infrared aerial photography. Soil samples were collected form the 0 to 7.5 cm layer at all transects in the wet season and at a subsample of the transects in the dry season and analyzed for pH, organic matter, conductivity, cation exchange capacity, exchangeable Ca, Mg, Na, K, and Al, available NH3-N, PO4-P, Cu, Fe, Mn, Zn, and TKN.

Schmaizer, Paul A.↗
NASA NTRS1986

Hover performance tests of baseline metal and Advanced Technology Blade (ATB) rotor systems for the XV-15 tilt rotor aircraft

Rotor hover performance data were obtained for two full-scale rotor systems designed for the XV-15 Tilt Rotor Research Aircraft. One rotor employed the rectangular planform metal blades (rotor solidity = 0.089) which were used on the initial flight configuration of the XV-15. The second rotor configuration examined the nonlinear taper, composite-construction, Advanced Technology Blade (ATB), (rotor solidity = 0.10) designed to replace the metal blades on the XV-15. Variations of the baseline ATB tip and cuff shapes were also tested. A new six-component rotor force and moment balance designed to obtain highly accurate data over a broad range of thrust and torque conditions is described. The test data are presented in nondimensional coefficient form for the performance results, and in dimensional form for the steady and alternating loads. Some wake and acoustic data are also shown.

Bartie, K.↗
NASA NTRS1988

A few parts in 10 to the 8th geodetic baseline repeatablity in the Gulf of California using the Global Positioning System

GPS geodetic measurements of 350-650 km baselines across the Pacific-North America plate boundary in the Gulf of California are presented. The analysis employs a four-station U.S. fiducial network and combined carrier phase and pseudorange data. Water vapor radiometer data at the Gulf sites are used to calibrate the GPS signal for wet tropospheric path delays. Residual tropospheric delays are modeled as first-order exponentially correlated stochastic processes. The measurement precision for horizontal components is a few parts in 10 to the 8th or better.

Tralli, David M.↗
NASA NTRS1989

Very-Long-Baseline Interferometry Using Cheap Satellites

Celestial radiation below 25 MHz, heretofore inaccessible, yields new insights. Report discusses feasibility of array of small satellites deployed in high orbit around Earth to monitor celestial radio sources at frequencies less than 25 MHz. Objective to make high-angular-resolution map of such sources over entire sky by use of very-long-baseline interferometry (VLBI).

Mahoney, M. J.↗
NASA NTRS1988

MERI: An ultra-long-baseline Moon-Earth radio interferometer

An extension of the very long baseline technique currently used with ground based telescopes which will produce a resolution of 0.4 micro-arcsec at 300 GHz is described. The MERI array will open an entirely new regime of wavelengths, resolutions, and sensitivities for radio astronomy. As with any such leap in astronomical instrumentation, this advancement will result in the observation of a variety of known radio sources and the exploration of their structures in unprecedented detail. Even so, it may be the serendipitous discoveries, which are by definition impossible to predict, that ultimately justify the construction of MERI.

Burns, Jack O.↗