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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

A study of radar cross section measurement techniques

Past, present, and proposed future technologies for the measurement of radar cross section were studied. The purpose was to determine which method(s) could most advantageously be implemented in the large microwave anechoic chamber facility which is operated at the antenna test range site. The progression toward performing radar cross section measurements of space vehicles with which the Orbital Maneuvering Vehicle will be called upon to rendezvous and dock is a natural outgrowth of previous work conducted in recent years of developing a high accuracy range and velocity sensing radar system. The radar system was designed to support the rendezvous and docking of the Orbital Maneuvering Vehicle with various other space vehicles. The measurement of radar cross sections of space vehicles will be necessary in order to plan properly for Orbital Maneuvering Vehicle rendezvous and docking assignments. The methods which were studied include: standard far-field measurements; reflector-type compact range measurements; lens-type compact range measurement; near field/far field transformations; and computer predictive modeling. The feasibility of each approach is examined.

Mcdonald, Malcolm W.↗
NASA NTRS1987

Color postprocessing for 3-dimensional finite element mesh quality evaluation and evolving graphical workstation

Three general tasks on general-purpose, interactive color graphics postprocessing for three-dimensional computational mechanics were accomplished. First, the existing program (POSTPRO3D) is ported to a high-resolution device. In the course of this transfer, numerous enhancements are implemented in the program. The performance of the hardware was evaluated from the point of view of engineering postprocessing, and the characteristics of future hardware were discussed. Second, interactive graphical tools implemented to facilitate qualitative mesh evaluation from a single analysis. The literature was surveyed and a bibliography compiled. Qualitative mesh sensors were examined, and the use of two-dimensional plots of unaveraged responses on the surface of three-dimensional continua was emphasized in an interactive color raster graphics environment. Finally, a postprocessing environment was designed for state-of-the-art workstation technology. Modularity, personalization of the environment, integration of the engineering design processes, and the development and use of high-level graphics tools are some of the features of the intended environment.

Panthaki, Malcolm J.↗
NASA NTRS1986

Self indexing latch system

A self-latching jaw assembly is described which includes a pair of jaws for latching a fitting of an associated structure such as the keel fitting of a space telescope. The jaw assembly automatically locates the fitting received on a positioning pedestal and latches it in its original location on the pedestal without need of precision alignment. The first jaw is actuated and moved to the right whereupon a reciprocating plunger, extended from the nose of the jaw senses the hub of the spool. A jaw position responsive switch is then actuated to terminate the drive motor of the jaw. The astronaut will then actuate the drive motor of the jaw and the jaw will move to the left, whereupon the standoff will engage the face of the jaw in a latching position. In the latching position, the noses of the jaws will be under the flanges of the spool.

John C Gibson↗
NASA NTRS1987

High pressure cosmochemistry of major planetary interiors: Laboratory studies of the water-rich region of the system ammonia-water

Several studies relative to high pressure cosmochemistry of major planetary interiors are summarized. The behavior of gas-ice mixtures at very high pressures, studies of the phase diagram of (NH3) sub x (H2O) sub 1-x at pressures to 5GPa and temperatures from 240 to 370 K, single crystal growth of ammonia dihydrate at room temperature in order to determine their structures by x-ray diffraction, spectroscopy of chemical reactions during shock compression in order to evaluate how the reactions affect the interpretation of equation of state data obtained by shock methods, and temperature and x-ray diffraction measurements made on resistively heated wire in diamond anvil cells in order to obtain phase and structural data relevant to the interiors of terrestrial planets are among the studies discussed.

Nicol, Malcolm↗
NASA NTRS1986

Plasma structures in Comet Halley

Large-scale plasma phenomena based on results of spacecraft probing of comets Halley and Giacobini-Zinner and on International Halley Watch are discussed. The data show that: the basic mechanism for the comets' interaction with the solar wind (Alfven, 1957) is correct; that the turn-on and turn-off of plasma activity follows the description of Mendis and Flammer (1984); and that disconnection events are associated with sector boundary crossings and an essential element in the morphology of developed plasma tails (Niedner and Brandt, 1978).

Brandt, John C.↗
NASA NTRS1986

Plasma-tail activity at the time of the Vega encounters

Physical associations are sought between Halley's plasma tail activity seen in ground-based imagery and near-comet, solar wind/IMF measurements obtained by the Vega spacecraft. Disconnection Events (DE's) and the sector boundary/frontside magnetic reconnection model (Niedner and Brandt, 1978) of their origin are discussed. Strong support for the model comes from 2 DE's: a major event whose onset, on March 7 to 8, is strongly correlated with a reversal of the comet's magnetic barrier observed by Vega-1 and Vega-2 and with an IMF sector boundary observed by Vega-1; and a minor event on March 7 which may be associated with the two-polarity (possibly reconnecting) magnetic barrier seen by Vega-1 on March 6, when the solar-wind density was low.

Niedner, Malcolm B., Jr.↗
NASA NTRS1987

Comet-solar wind interaction as viewed from the International Cometary Explorer Mission (ICE) and from the earth

An overview of large-scale plasma phenomena is presented based on results of the ICE spacecraft probing of comet Giacobini-Zinner and on worldwide submissions to the Large-Scale Phenomena Discipline Specialist Team of the International Halley Watch. Results indicate that the magnetic field capture and draping model, originated by Alfven, is correct. Examples of tail 'turn on' and evolution are presented with emphasis on the observed Disconnection Events (DEs). The sector boundary model of DEs is consistent with the data and a dramatic example of synergism between in situ data from the VEGAs and ground-based imagery for the DE originating March 8.6, 1986 is presented.

Brandt, John C.↗
NASA NTRS1986

Dynamics of cometary plasma tails

Cometary plasma tail data obtained before and after the current appearance of Halley's Comet are reviewed. The relation between the formation of plasma tails and comet/solar-wind interactions is discussed. The ion rays and helical waves of the plasma tail are described. The disconnection events and interaction of bright comets with the IMF, associated with the current appearance of Comet Halley, are examined. Consideration is given to the cometary magnetic barriers observed by the Vega-1 and Vega-2 spacecraft.

Niedner, Malcolm B., Jr.↗
NASA NTRS1986

Chlorine chemistry in the Antarctic stratosphere - Impact of OClO and Cl2O2 and implications for observations

Theories have been proposed to relate the reduction of O3 during Antarctic spring to catalytic cycles involving chlorine and bromine species. A necessary condition for any chlorine-catalyzed scheme is that a large fraction of the chlorine must be in the form of ClO in the lower stratosphere. It has been suggested that these high levels of ClO could be maintained by fast heterogeneous reactions, whose rates are not known at present. Model calculations based on the above mechanisms predict considerable amounts of OClO and Cl2O2, particularly during the night. Results of calculations of the diurnal variations of ClO, OClO, and Cl2O2 during Antarctic spring are presented for different cases. Results from the calculations suggest that coincident measurements of the total column abundance and diurnal variation of ClO and OClO may help constrain key aspects of the proposed chemical mechanisms. Removal of O3 by the catalytic cycle involving Cl2O2 could be as important as that involving BrO for present levels of chlorine, provided that Cl2O2 photolyzes rapidly to yield Cl and ClO2. It is shown that there is no synergy between these two cycles, since they both compete for the available ClO.

Rodriguez, Jose M.↗
NASA NTRS1986

A study of the damping capacity of graphite epoxy composites in a vacuum

The damping properties of a graphite epoxy composite material (used in the construction of the Hubble Space Telescope) are measured under a variety of conditions in a vacuum chamber to simulate conditions in space. An improved method is proposed which utilizes several points of the response curve near a resonance to estimate the damping ratio and the undamped resonance frequency. The damping of a graphite epoxy tube is monitored for four weeks to study moisture desorption and temperature effects. A significant variation is observed in the damping ratio with temperature.

Rao, Mohan D.↗
NASA NTRS1986

Prediction of light aircraft interior sound pressure level from the measured sound power flowing in to the cabin

The validity of the room equation of Crocker and Price (1982) for predicting the cabin interior sound pressure level was experimentally tested using a specially constructed setup for simultaneous measurements of transmitted sound intensity and interior sound pressure levels. Using measured values of the reverberation time and transmitted intensities, the equation was used to predict the space-averaged interior sound pressure level for three different fuselage conditions. The general agreement between the room equation and experimental test data is considered good enough for this equation to be used for preliminary design studies.

Atwal, Mahabir S.↗
NASA NTRS1987

The IHW island network

Early astronomical photography of comets at perihelion encouraged the establishment of an International Halley Watch (IHW) Team for regularly photographing the Comet. The February 1986 period was particularly troublesome due to the limitations of cometary visibility in the Southern Hemisphere. Schmidt cameras were placed on Tahiti, Easter Island, Faraday Station on the Antarctic Peninsula, Reunion Island and in South Africa. Blue- and red-filter B/W images were obtained every night and color prints were occasionally shot. Each night's images were examined before the next night's photography. Several interesting anecdotes are recounted from shipping, manning and operation of the telescopes.

Niedner, Malcolm B., Jr.↗
NASA NTRS1987

Ultraviolet spectrophotometry of Comet Giacobini-Zinner during the ICE encounter

The IUE's UV spectrophotometer was used to monitor Comet Giacobini-Zinner's H2O production rate from June to October, 1985, in support of the International Cometary Explorer (ICE) mission. Observation results for the spatial and temporal variation and the abundance or upper limits of C, CO, CO(+), CO2(+), CS, H, Mg(+), O, OH, and S, between September 9 and 12, included the time of the ICE encounter: at this time, the H2O production rate obtained was consistent with a number of gas production rates derived indirectly from the ICE experiments. A comparison of the CO2(+) ion abundance with the total electron density measured by the plasma electron and radio science experiments on ICE implies an ion deficiency relative to electrons, so that the satisfaction of charge balance criteria requires the presence of a major ion population not detected by remote sensing.

Mcfadden, Lucy A.↗
NASA NTRS1987

The ammonia-water phase diagram and its implications for icy satellites

A Holzapfel-type diamond anvil cell is used to determine the NH3 - H2O phase diagram in the region from 0 to 33 mole percent NH3, 240 to 370 K, and 0 to 5 GPa. The following phases were identified: liquid; water ices Ih, III, V, VI, VII, and VIII; ammonia monohydrate, NH3.H2O; and ammonia dihydrate NH3.2H2O. Ammonia dihydrate becomes prominent at moderate pressures (less than 1 GPa), with planetologically significant implications, including the possibility of layering in Titan's magma ocean.

Johnson, Mary L.↗
NASA NTRS1987

Dual laser gyro test program

This paper addresses the results of a comparative test evaluation of two similar-sized but otherwise dissimilar ring laser gyroscopes (RLG's). Both units were tested side by side, with the input axes (IA's) parallel, on the same test table. This report describes the rationale and design factors considered important to the test objectives. Emphasis was placed upon the evaluation of the scale factor (SF) linearity, drift rate stability (short term and long term), and derived rate. Conclusions drawn were (1) that dual operation had an observable but insignificant effect on the test results, (2) that the benefits of dual operation outweighed the additional design and analysis efforts required at the outset of the program, and (3) that the performance characteristics of the two test articles were significantly different. The differences between the two test articles (1) led to suggestions which could direct one vendor toward obtaining improved performance and (2) resulted in the creation of a conceptually new method (DELTA TIME-COUNT histogram) for quickly assessing the quality of laser gyros (or any digital sensor device for that matter).

Jones, Malcolm E.↗
NASA NTRS1987

Large-scale interaction of the solar wind with comets Halley and Giacobini-Zinner

In-situ measurements of comets Halley and Giacobini-Zinner have confirmed the accepted basic physics of comet/solar wind interaction. The solar wind magnetic field is captured by the comet through the mechanism of field-line loading by cometary ions and the field lines drape around the cometary ionosphere. With this basic model in hand, the large-scale structure of the plasma tail as revealed by submissions to the Large Scale Phenomena Network of the International Halley Watch is reviewed. The turn-on and turn-off of plasma activity seem consistent with theory. Some 16 obvious disconnection events (DEs) have been recorded. Preliminary results showed agreement with the sector-boundary model; a detailed analysis of all DEs will be required in order to make a definitive statement. A study of plasma activity around the time of the VEGA encounters provides strong support for the sector-boundary model and illustrates once again the power of simultaneous remote and in-situ measurements.

Brandt, John C.↗
NASA NTRS1987

Plasma-tail activity and the interplanetary medium at Halley's Comet during Armada Week: 6-14 March 1986

The encounters of five spacecraft with Halley's Comet during 6-14 March 1986 offered a unique opportunity to calibrate the solar-wind interaction with cometary plasmas as recorded by remote wide-field and narrow-field/narrowband imaging. Perhaps not generally recognized in the comet community is the additional opportunity offered by the Halley Armada to study the structure of the solar-wind and interplanetary magnetic field (IMF) in three dimensions using five sets of data obtained over similar time intervals and heliocentric distances, but at somewhat different heliolatitudes. In fact, the two problems, i.e., comet physics and the structure of the interplanetary medium, are coupled if one wants to understand what conditions pertained at the comet between the encounters. This relationship is discussed.

Niedner, Malcolm B., Jr.↗
NASA NTRS1986

An experimental investigation of the aerodynamics of a NACA 64A010 airfoil-flap combination with and without flap oscillations. Part 1: Steady-state characteristics

A NACA 64A010 airfoil with a sealed-gap 1/4-chord flap was tested between splitter plates in the NASA Ames 11- by 11-Foot Transonic Wind Tunnel at Mach numbers from 0.50 to 0.85, and Reynolds numbers based on chord from 3 to 13 million. Although the main purpose of the test was to obtain unsteady pressure data with the flap oscillating, no unsteady data are presented in this paper. The steady-state data are presented and compared with other test data to provide a basis for evaluating the results. Pressure data at two span stations are used to deduce early boundary-layer transitions at the midspan at higher Mach numbers, angles of attack, and flap angles. The effects of flap angle on pressures, normal force, pitching moment, and hinge moment are also presented in the report. Mach number errors caused by the splitter-plate configuration and the angle of attack are evaluated using pressure measurements near the floor and ceiling of the wind tunnel.

Buell, Donald A.↗