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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 1,333 records · Page 74

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NASA NTRS1981

V/STOL propulsion control analysis: Phase 2, task 5-9

Typical V/STOL propulsion control requirements were derived for transition between vertical and horizontal flight using the General Electric RALS (Remote Augmented Lift System) concept. Steady-state operating requirements were defined for a typical Vertical-to-Horizontal transition and for a typical Horizontal-to-Vertical transition. Control mode requirements were established and multi-variable regulators developed for individual operating conditions. Proportional/Integral gain schedules were developed and were incorporated into a transition controller with capabilities for mode switching and manipulated variable reassignment. A non-linear component-level transient model of the engine was developed and utilized to provide a preliminary check-out of the controller logic. An inlet and nozzle effects model was developed for subsequent incorporation into the engine model and an aircraft model was developed for preliminary flight transition simulations. A condition monitoring development plan was developed and preliminary design requirements established. The Phase 1 long-range technology plan was refined and restructured toward the development of a real-time high fidelity transient model of a supersonic V/STOL propulsion system and controller for use in a piloted simulation program at NASA-Ames.

Source record↗

NASA NTRS1983

Evidence for helical kink instability in the Venus magnetic flux ropes

Empirical models of the magnetic field structure of flux ropes found in the Venus ionosphere are seen as suggesting that the ropes are unstable to long-wavelength (more than 100 km) helical-kink perturbations. The onset of such an instability can explain the apparent volume distribution of flux ropes with altitude, as well as their orientation as a function of altitude. In the subsolar region, the fraction of volume occupied by flux ropes increases from approximately 20 percent at high altitudes to more than 50 percent at low altitudes; this is a greater increase than would be expected if ropes convect downward as simple straight horizontal cylinders. The helical kink instability raises the fractional volume occupied by ropes by turning the originally straight, horizontal flux tubes into corkscrew-shaped structures as they convect to lower altitudes. It is noted that this instability also explains why high altitude ropes tend to be horizontal and low altitude ropes appear to have almost any orientation.

Elphic, R. C.↗

NASA NTRS1984

Small gravitationally elicited voltage transients in pea stems

Decapitated veritcal stem segments were observed for 45 min, noting the number of transients mu V for each 5-min interval. Results for two sets of stem segments are plotted. The average frequencies were 0.72 + or -0.05 and 0.66 + or - 0.04 per 5 min. One set of segments was swiveled gently to the horizontal position; then, recording continued for another 90 min. Transients continued in the vertical controls at a closely similar average rate 0.78 + or - 0.04 per 5 min. However, after the first 5-min interval the horizontally placed plants exhibited transients at an increased average rate of 1.08 + or - 0.04 per 5 min. The frequency of transients also increased following horizontal placement of intact shoots. However, it appears that this increase had two components: one due to gravity reception, and one due to the redistribution of indolacetic acid (IAA) believed to mediate gravitropic curvature (or, more specifically, to the increase of IAA in the lower tissue.

Pickard, B. G.↗

NASA NTRS1984

Interactions of light and gravity on growth, orientation, and lignin biosynthesis in mung beans

Mung beans (Vigna radiata L.) seedlings grown on the third Space Transport Mission (STS-3) showed marked orientation problems (some of the stems elongated horizontally and many of the roots were growing upward) and had a lower lignin content than the ground based controls. This research was initiated to determine if the atypical growth characteristics of mung beans grown in microgravity could be simulated using horizontal clinostats. Most of the effort focused on the design, construction and testing of the clinostats. In order to closely approximate the growth conditions of the plants grown in the plant growth unit on STS-3, cylindrical lexan minichambers were constructed. Results showed that plants grown using these clinostats in the horizontal position exhibit similar growth characteristics to the plants grown on STS-3 (disorientation of both stems and roots), while the vertical stationary and vertical rotating controls exhibit normal growth.

Jahns, G. C.↗

NASA NTRS1983

A comment on some drawbacks of monostatic radars

All Mesosphere, Stratosphere, Troposphere (MST) radars now in operation or under construction use the monostatic mode, that is to say, the same antenna for both transmitting and receiving. Consequently, it is never possible to determine more than one component of the atmospheric velocity at one point in space. Two important properties of gravity waves which are difficult if not impossible to determine by the monostatic method are discussed. The first of these is the polarization of the gravity waves; that is, the complex ratio of the wave functions of vertical and horizontal motion. A second quantity of importance is the horizontal wavelength of gravity waves. Both of these problems could be overcome by use of a bistatic system. Such a system has the additional advantage of making it possible to measure at very low altitudes, and to look away from the transmitter (for example to make a horizontal section through a thunderstorm). However, bistatic operation, in the practical sense, requires not only an additional highly directive antenna, but also that both the transmitting and receiving antennas should be fully steerable.

Bowhill, S. A.↗

NASA NTRS1984

Laboratory studies of baroclinic instability at small Richardson number

As part of the support program for the Atmospheric General Circulation Experiment, laboratory studies of baroclinic and other convective instabilities were performed for a thin layer of fluid between thermally conducting horizontal discs. There were three types of modes identified. The first has a spiral-arm appearance, and exists for large enough horizontal thermal forcing, weak enough static stability, and large enough rotation. The source of this wave is shown to be the Eady mode of instability. The second mode is due to convective instability in the thermal boundary layers which exist due to the thermally conducting horizontal boundaries. Finally, for strong enough negative static stability, thermal convection of the Benard type appears. The most significant result is that the symmetric (Solberg) mode was not found, even though the infinite-plane theory predicts this mode under certain experimental conditions.

Miller, T. L.↗

NASA NTRS1982

Crop identification with multifrequency, multipolarization, and multiangle radars

In a corn and soybeans test site in Webster County, Iowa, airborne radar scatterometers were used on August 19 and September 10, 1980, to investigate the backscattering properties of these crops at wavelengths of 2.3, 6.3, and 19 cm (Ku-, C-, and L-band, respectively). Both horizontal transmit-horizontal receiver (HH) polarization and horizontal transmit-vertical receive (HV) polarization combinations were used at L- and C-band. Only the VV polarization combination was available at Ku-band. Measurements were obtained at 10 angles of observation from 5 to 50 deg in steps of 5 deg (referenced to the nadir). Excellent separation between corn and soybeans was achieved when either C-band HV at 50 deg or when a defined depolarization factor was used at C-band. Good separation existed at L-band also using either L-band HH at 50 deg or an L-band polarization factor. Significant row direction effects were observed for all HH data near 10 deg. Significant effects of surface soil moisture were observed for all configurations at L-band and C-band.

Paris, J. F.↗

NASA NTRS1983

Seismic coupling and uncoupling at subduction zones

Some of the correlations concerning the properties of subduction zones are reviewed. A quantitative global comparison of many subduction zones reveals that the largest earthquakes occur in zones with young lithosphere and fast convergence rates. Maximum earthquake size is directly related to the asperity distribution on the fault plane. This observation can be translated into a simple model of seismic coupling where the horizontal compressive stress between two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface. Plate age and rate can control asperity distribution directly through the horizontal compressive stress associated with the vertical and horizontal velocities of subducting slabs. The basalt to eclogite phase change in the down-going oceanic crust may be largely responsible for the uncoupling of subduction zones below a depth of about 40 km.

Ruff, L.↗

NASA NTRS1984

A numerical study of the vertical transport of momentum in a tropical rainband

The vertical transport of horizontal momentum in a convective tropical rainband is studied using a two-dimensional cloud ensemble model. Twelve simulations are made under the same large-scale conditions. The vertical transports of v momentum (parallel to the rainband) are essentially the same in all of the simulations, even though the structure of the clouds is different in each of the runs. The magnitude of the v-momentum transport by clouds is fairly large. It takes only half of a day to smooth out the tropical low-level easterly jet parallel to the rainband if no other processes are operating. The vertical transports of u momentum (perpendicular to the rainband) are quite different in all of the simulations. This difference can be explained by the dissimilarities in the distributions of horizontal momentum associated with various cloud configurations. The simulated vertical transports of horizontal momentum are compared with those computed with the Schneider and Lindzen scheme. The results suggest that their scheme is basically correct and usable if some improvements are made.

Soong, S.-T.↗

NASA NTRS1985

Payload transportation at KSC

Cargo ground processing at John F. Kennedy Space Center (KSC) involves either a horizointal or vertical mode of assembly and processing of the STS payloads. Consequently, cargos are commonly referred to as horizontal or vertical payloads. The process flow for each mode requires different facilities and transportation requirements. Occasionally, a mixed mission cargo containing both horizontal and vertical payload elements will require a combination of horizontal and vertical transportation between facilities. Some of the engineering challenges and innovative solutions to satisy the unique on-site payload transportation requirements at KSC. In particular, some of the more demanding design requirements of the multiuse mission support equipment are presented, and the resulting engineering designs and unique solutions are outlined.

Donahue, M. E.↗

NASA NTRS1985

Transduction of the Root Gravitropic Stimulus: Can Apical Calcium Regulate Auxin Distribution?

The hypothesis was tested that calcium, asymmetrically distributes in the root cap upon reorientation to gravity, affects auxin transport and thereby auxin distribution at the elongation zone. It is assumed that calcium exists in the root cap and is asymmetrically transported in root caps altered from a vertical to a horizontal position and that the meristem, the tissue immediately adjacent to the root cap and lying between the site of gravity perception and the site of gravity response, is essential for mediation of gravitropism. Tip calcium in root gravicurvature was implicated. The capstone evidence is that the root cap has the capacity to polarly translocate exogenous calcium downward when tissue is oriented horizontally, and that exogenous calcium, when supplied asymmetrically at the root tip, induces curvature and dictates the direction of curvature in both vertical and horizontal corn roots.

Edwards, K. L.↗

NASA NTRS1985

Participation of Ethylene in Two Modes of Gravistimulation of Shoots

In order to elucidate the role of ehtylene in gravitropism, detailed time courses for ethylene production in horizontal and upright plants were measured. Tomato and pea were chosen as examples of plants which exhibit different patterns of gravitropic curvature. Tomato seedlings were placed in gas-tight lucite boxes from which air was sampled and analyzed for ethylene. During the first 2 min interval after one set of plants was turned horizontal ethylene production was double the baseline. Similarly, plants rotated 3 rpm about a vertical axis transiently doubled ethylene production when the axis was shifted 90 deg. In order to clarify the role of this 2-min burst, the effect of exogenous ethylene was studied. In peas, epicotyls were excised, equilibrated until wound ethylene had subsided to a low stable level, and ethylene production was measured in vertical and horizontal segments. As for tomatoes, excised pea epicotyls increased their rate of ethylene production during the first 2 min of gravistimulation. Also, very low concentrations of exogenous ethylene slightly enhance curvature. On the other hand, higher levels of ethylene and 1-aminocyclopropane-1-carboxylic acid (ACC) inhibit overall curvature.

Harrison, M.↗

NASA NTRS1984

Effects of line-of-sight velocity on spaced-antenna measurements, part 3.5A

Horizontal wind velocities in the upper atmosphere, particularly the mesosphere, have been measured using a multitude of different techniques. Most techniques are based on stated or unstated assumptions about the wind field that may or may not be true. Some problems with the spaced antenna drifts (SAD) technique that usually appear to be overlooked are investigated. These problems are not unique to the SAD technique; very similar considerations apply to measurement of horizontal wind using multiple-beam Doppler radars as well. Simply stated, the SAD technique relies on scattering from multiple scatterers within an antenna beam of fairly large beam width. The combination of signals with random phase gives rise to an interference pattern on the ground. This pattern will drift across the ground with a velocity twice that of the ionospheric irregularities from which the radar signals are scattered. By using spaced receivers and measuring time delays of the signal fading in different antennas, it is possible to estimate the horizontal drift velocities.

Royrvik, O.↗

NASA NTRS1983

Analysis of Synthetic Aperture Radar data acquired over a variety of land cover

An analysis has been conducted of two-look-angle, multipolarization X-band SAR results. On the basis of the variety of land covers studied, the vertical-vertical polarization (VV) data is judged to contain the highest degree of contrast, while the horizontal-vertical (HV) polarization contained the least. VV polarization data is accordingly recommended for forest vegetation classification in those cases where only one data channel is available. The inclusion of horizontal-horizontal polarization data, however, is noted to be capable of delineating special surface features.

Wu, S. T.↗

NASA NTRS1985

The structure of the convective atmospheric boundary layer as revealed by lidar and Doppler radars

Results on the structure of the convective atmospheric boundary layer based on the analyses of data from the instrumented NSSL-KTVY tower, airborne Doppler lidar, and ground-based Doppler radars are presented. The vertically averaged wind over the boundary layer was found to be insensitive to baroclinicity, supporting the hypothesis of Arya and Wyngaard (1975). The computed momentum flux profiles were affected by baroclinicity. Horizontal wind spectra from lidar, radar, and tower data compared well with each other both in shape and magnitude. A consistent peak found near 4 km in all the computed spectra might have been caused by horizontally symmetric cells with horizontal wavelength 4 times the boundary-layer height as shown in Kuettner (1971) for the case of weak wind shear.

Eilts, M. D.↗

NASA NTRS1985

On the source region of flux transfer events

An examination has been conducted of the region of occurrence of flux transfer events for three distinct orientations of the interplanetary magnetic field: nearly horizontal in the solar magnetospheric equator, diagonally southward at 45 deg to the magnetospheric equator and nearly due south. For horizontal IMF conditions the FTE's occur in a horizontal band about + or - 6 earth radii wide. For diagonally southward IMF conditions, the FTE's occur in a diagonal swath about + or - 6 earth radii wide passing through the subsolar point. For duskward but nearly due southward IMF conditions, the observations reveal FTE's throughout the northern morning quadrant. These observations are consistent with a near equatorial source for flux transfer events and hence with component merging and not anti-parallel merging. These observations also help understand the energetic ion anisotropies seen in these events.

Russell, C. T.↗

NASA NTRS1985

Temperature profile retrieval by two-dimensional filtering

A two-dimensional spatial filter, optimum in the minimum-mean-square error sense, has been used to retrieve atmospheric temperature profiles from TIROS-N and NOAA-6 Microwave Sounding Unit measurements. This approach considers correlations both in the vertical and horizontal (along the orbital track) directions. It is found that lower retrieval errors result from the 2-D technique, compared with the 1-D technique, especially in the troposphere. The additional horizontal information used in the 2-D formulation substantially improves temperature retrievals over a severe cold front where vertical correlations are lessened. The improved results of the 2-D filter in the upper troposphere point to the presence of profile components in the null space of the weighting functions that are horizontally correlated with the observed data.

Nathan, K. S.↗

NASA NTRS1986

Simulations of gravity waves in frontal zones

Recent observations of frontal systems passing over the PROFS network in Colorado by Shapiro (1984) indicate the horizontal scale of some fronts can be on the order of a few kilometers or less. Motivated by Shapiros results, esearchers re-ran an earlier numerical simulation of frontogenesis by Williams (1972) (where a very simple stretching deformation forcing of a front is considered) using as high a resolution in both the vertical and horizontal as was possible. Highest resolution that we considered consisted of a grid with a vertical spacing of 32 meters and a horizontal spacing of 260 meters in the immediate vicinity of the surface front. The purpose was to examine development of the frontal structures as the scale of the front became very small. Two sources for banded structures in clouds were found: (1) in the stationary waves above the front and (2) in waves propagating upward from breaking waves under the front.

Gall, R.↗