SEARCH · Engineering Papers

Results for “SWiFT”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 829 records · Page 46

All sources NASA NTRS DOE OSTI

NASA NTRS1988

Interferometric synthetic aperture microwave radiometry for the remote sensing of the earth

Interferometric aperture synthesis is presented as an alternative to real aperture measurements of the earth's brightness temperature from low earth orbit. The signal-to-noise performance of a single interferometric measurement is considered, and the noise characteristics of the brightness temperature image produced from the interferometer measurements are discussed. The sampling requirements of the measurements and the resulting effects of the noise in the measurements on the image are described. The specific case of the electronically steered thinned array radiometer (ESTAR) currently under construction is examined. The ESTAR prototype is described in detail sufficient to permit a performance evaluation of its spatial and temperature resolution. Critical aspects of an extension of the ESTAR sensor to a larger spaceborne system are considered. Of particular importance are the number and placement of antenna elements in the imaging array. A comparison of the implementation methodologies of radio astronomy and earth remote sensing is presented along with the effects of the source brightness distribution, the antenna array configuration and the method used for array scanning.

Ruf, Christopher S.↗

NASA NTRS1988

Multifrequency passive microwave observation of saline ice grown in a tank

Microwave radiometers observed artificial sea ice formation. During initial ice growth, interference fringe effects can occur both from changing ice thickness and snow or frost which may prove useful in interpreting layer thicknesses. A simulation of multiyear ice was attempted by allowing the ice to desalinate, but the resulting emissivity spectrum was more characteristic of lake ice. A multiyearlike spectrum was obtained when rubble was deposited on the ice surface.

Grenfell, T. C.↗

NASA NTRS1988

Atmospheric profiling of water vapour with a 20.5-23.5 GHz autocorrelation radiometer

A tropospheric water vapor profiling system is presented. The hardware consists of an upward looking radiometer (CORRAD) deployed at ground level. The CORRAD measures the autocorrelation of the downwelling thermal emission from the atmosphere over a passband of 20.5 to 23.5 GHz out to a maximum time delay of 6.1 ns. This produces 100 MHz resolution imaging of the complete emission spectrum about the 22.235 GHz water vapor resonance line. The 31 equivalent frequency channels produced by Fourier transformation of the data provide additional constraints on the inversion process required to estimate the water vapor profile, as compared to standard 2 to 5 frequency channel profiling systems. The CORRAD hardware is described, and radiometer and radiosonde profiles are compared.

Ruff, C. S.↗

NASA NTRS1989

Local stiffener and skin pocket buckling prediction by special PASCO modeling technique: Correlation to test data

Waffle panels are often used on fuselage structures such as that of the Space Shuttle. The waffle panel design is an efficient design for carrying biaxial, in-plane, and shear loads. The WAFFLE program was designed for application on waffle panels. The Panel Analysis and Sizing Code (PASCO) program was designed for analyzing and sizing uniaxially stiffened panels. The application of the PASCO program in conjunction with the WAFFLE program is discussed to account for both the fillet radius and the presence of stiffness in both directions. The results of the tests are used to verify that these adjustments are valid and necessary if accurate analysis of the waffle panel is to be achieved.

Yin, Dah N.↗

NASA NTRS1987

Passive microwave remote sensing of salinity in coastal zones

The theory of measuring coastal-zone salinity from airborne microwave radiometers is developed. The theory, as presented, shows that precision measurements of salinity favor the lower microwave frequencies. To this end, L- and S-Band systems were built, and the flight results have shown that accuracies of at least one part per thousand were achieved.The aircraft results focus on flights conducted over the Chesapeake Bay and the mouth of the Savanna River off the Georgia Coast. This paper presents no new work, but rather summarizes the capabilities of the remote sensing technique.

Swift, Calvin T.↗

NASA NTRS1989

Near-field acoustic characteristics of a single-rotor propfan

The near-field noise characteristics of the SR-7L, an eight-blade, single-rotor, wing-mounted, tractor propfan have been determined. It is found that the noise is dominated by discrete tones, usually at the first order (and occasionally at the second or third order) of the blade-passage frequency. The highest noise levels were noted at conditions of high tip helical speeds and high dynamic pressures.

Bartel, H. W.↗

NASA NTRS1989

Fluctuating pressures on wing surfaces in the slipstream of a single-rotor propfan

Measurements of the fluctuating pressure levels (FPLs) induced on a Propfan Test Assessment wing by the SR-7L propfan slipstream within the airplane flight envelope were obtained as a function of propfan operating conditions. It is shown that FPLS were high over most of the flight envelope, and that the spectra were dominated by the propfan first-order blade passage frequency tone. The highest FPLs were found at the lowest aircraft test altitudes and Mach numbers and for propfan conditions of lowest rotational tip speed and highest power.

Swift, G.↗

NASA NTRS1988

Mechanical pumps for superfluid helium transfer in space

Two alternate mechanical pump concepts have been identified for the transfer of superfluid helium in space. Both pumps provide flow at sufficient head and have operating characteristics suitable for the Space Infrared Telescope Facility (SIRTF) refill mission. One pump operates at a relatively low speed and utilizes mechanical roller bearings, while the other operates at a higher rotational speed using either electromagnetic or tilting pad gas-dynamic bearings. The use of gas bearings requires transfer of normal helium so that the gas pressure within the pump casing is high enough to operate the bearings. The operating characteristics of both pumps are predicted, the dimensions are estimated and major technology issues are identified. The major issues for each pump design are cavitation performance and bearing development. Roller bearings require quantified reliability for operation in space while electromagnetic bearings require basic development as well as a complex control system. The low speed pump has significantly poorer hydraulic efficiency than the high speed pump.

Izenson, M. G.↗

NASA NTRS1988

Surface contour radar observations of the directional wave spectrum during Fasinex

The surface control radar (SCR), a 36-GHz computer-controlled airborne radar which generates a false-color coded elevation map of the sea surface below the aircraft in real time, is described. The SCR turned out to be ideal for documenting the wave spectra during Fasinex (the Frontal Air-Sea Interaction Experiment) due to its high spatial resolution and rapid mapping capability over extensive areas. Synoptic weather maps for February 15-18, 1986 are presented.

Walsh, E. J.↗

NASA NTRS1989

Propfan Test Assessment (PTA): Flight test report

The Propfan Test Assessment (PTA) aircraft was flown to obtain glade stress and noise data for a 2.74m (9 ft.) diameter single rotation propfan. Tests were performed at Mach numbers to 0.85 and altitudes to 12,192m (40,000 ft.). The propfan was well-behaved structurally over the entire flight envelope, demonstrating that the blade design technology was completely adequate. Noise data were characterized by strong signals at blade passage frequency and up to 10 harmonics. Cabin noise was not so high as to preclude attainment of comfortable levels with suitable wall treatment. Community noise was not excessive.

Little, B. H.↗

NASA NTRS1990

SR90, strontium shaped-charge critical ionization velocity experiment

In May 1986 an experiment was performed to test Alfven's critical ionization velocity (CIV) effect in free space, using the first high explosive shaped charge with a conical liner of strontium metal. The release, made at 540 km altitude at dawn twilight, was aimed at 48 deg to B. The background electron density was 1.5 x 10(exp 4) cu cm. A faint field-aligned Sr(+) ion streak with tip velocity of 2.6 km/s was observed from two optical sites. Using two calibration methods, it was calculated that between 4.5 x 10(exp 20) and 2 x 10(exp 21) ions were visible. An ionization time constant of 1920 s was calculated for Sr from the solar UV spectrum and ionization cross section which combined with a computer simulation of the injection predicts 1.7 x 10(exp 21) solar UV ions in the low-velocity part of the ion streak. Thus all the observed ions are from solar UV ionization of the slow (less than critical) velocity portion of the neutral jet. The observed neutral Sr velocity distribution and computer simulations indicate that 2 x 10(exp 21) solar UV ions would have been created from the fast (greater than critical) part of the jet. They would have been more diffuse, and were not observed. Using this fact it was estimated that any CIV ions created were less than 10(exp 21). It was concluded that future Sr CIV free space experiments should be conducted below the UV shadow height and in much larger background plasma density.

Wescott, Eugene M.↗

NASA NTRS1989

Observations on electromagnetic bias in radar altimeter sea surface measurements

Because the relative radar cross section of the sea surface increases below mean sea level and decreases above it, the range measurements of satellite radar altimeters are biased toward the wave troughs. Published and unpublished direct measurements of this electromagnetic (EM) bias are examined as well as the predictions of theoretical developments. The EM bias is predominantly a function of the radar frequency used, averaging 1.2 percent of the wave height of Ka band and 3.3 percent of the wave height at X band. The airborne measurements present a consistent picture of the variation of the relative radar cross section as a function of deviation from mean sea level. A technique to measure EM bias at the Ku and C band operating frequencies of the Topex satellite altimeter is described.

Walsh, Edward J.↗

NASA NTRS1990

Ca(+) emission in the sunlit ionosphere

In the course of a program of twilight airglow observations, the resonance fluorescence emissions from calcium ions were measured. In particular, twilight sequences were obtained during the period of December 19-22, 1987, which coincided with the Ursids meteorite shower. During this meteorite event the intensities of the Ca(+) emission lines at 3934A increased to the point that the surface brightness profiles could be inverted to volume emission rate profiles. These profiles show evidence for strong spatial redistribution of the Ca(+) over the course of three days. Observations of these emissions during meteor shower periods could provide a valuable tracer for the processes responsible for the transport of ions in the D, E, and F region, allowing the full altitude and latitude extent of the distribution to be determined.

Torr, Marsha R.↗

NASA NTRS1989

Determinations of cloud liquid water in the tropics from the SSM/I

Upward-looking microwave radiometric observations were used to validate the SSM/I determinations, and also as a basis for the determination of new coefficients. Due to insufficiency of the initial four channel algorithm for cloud liquid water, the improved algorithm was derived from the CORRAD (the University of Massachusetts autocorrelation radiometer) measurements of cloud liquid water and the matching SSM/I brightness temperatures using the standard linear regression. The correlation coefficients for the possible four channel combinations, and subsequently the best and the worst combinations were determined.

Alishouse, John C.↗

NASA NTRS1989

Airborne discrimination between ice and water - Application to the laser measurement of chlorophyll-in-water in a marginal ice zone

The concurrent active-passive measurement capabilities of the NASA Airborne Oceanographic Lidar have been used to (1) discriminate between ice and water in a large ice field within the Greenland Sea and (2) achieve the detection and measurement of chlorophyll-in-water by laser-induced and water-Raman-normalized pigment fluorescence. Passive upwelled radiances from sea ice are significantly stronger than those from the neighboring water, even when the optical receiver field-of-view is only partially filled with ice. Thus, weaker passive upwelled radiances, together with concurrently acquired laser-induced spectra, can rather confidently be assigned to the intervening water column. The laser-induced spectrum can then be processed using previously established methods to measure the chlorophyll-in-water concentration. Significant phytoplankton patchiness and elevated chlorophyll concentrations were found within the waters of the melting ice compared to ice-free regions just outside the ice field.

Hoge, Frank E.↗

NASA NTRS1989

Applying kinematic GPS to airborne laser remote sensing

Results from the application of differential carrier phase tracking of the Global Positioning System (GPS) constellation of satellites to precise positioning (sub-10 cm) of an aircraft are presented. These aircraft positions are utilized in the process of providing geodetic quality position information for airborne laser 'footprint' locations on the surface of the earth. The combination of these techniques provides a rapid, cost effective means for collecting geodetic and topographic data, including sea surface topography. Operational techniques and constraints, along with results from recently collected data, are presented.

Krabill, William B.↗

NASA NTRS1990

Simulation of the ejection of plasma from the polar ionosphere

In the present numerical model for calculating H(+) and O(+) ion densities, fluxes, and temperatures, as well as the temperature of electrons, on a convecting magnetic field line, the one-dimensional fluid equations are solved along a field line path extending from 100-km altitude into the magnetotail. The evolution of O(+) and H(+) densities is calculated on field lines convecting over the polar cap. The results obtained indicate that centrifugal force is effective in accelerating ionospheric H(+) plasma outward into the magnetotail, while the 'smothering' effect of the H(+) plasma, on top of the O(+) plasma, prevents any ejection of the latter as long as its scale height is smaller than that of the H(+) plasma.

Swift, Daniel W.↗

NASA NTRS1990

Initial results in the development of a synthetic aperture microwave radiometer

A radiometer that measures the complex correlation of the voltage from pairs of antennas at many different baselines is being developed. Each baseline produces a sample point in the Fourier transform of the scene, and a map of the scene is obtained after all measurements have been made by inverting the transform. A substantial reduction in the antenna collecting area required compared to a conventional imaging radiometer can be obtained in this manner. An aircraft prototype being developed is a hybrid which uses real aperture antennas to obtain resolution along-track (stick antennas) and uses aperture synthesis to obtain resolution across-track. The prototype was flight-tested aboard the NASA P-3 in June 1988. During this flight a map was made of the Delmarva Peninsula south of NASA's Wallops Flight Facility. This initial map shows the major land/water features and compares very favorably with a Landsat image of the area, suggesting a bright outlook for the development of this technique in the future.

Le Vine, David M.↗