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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 235 records · Page 13
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NASA NTRS1976

Wake vortex encounter hazards criteria for two aircraft classes

An investigation was conducted using a piloted, motion-base simulator to determine wake vortex hazard criteria for two classes of jet transport aircraft. A light business jet and a large multiengine jet transport were represented respectively. The hazard boundaries were determined in terms of the maximum bank angle due to the vortex encounter. Upsets as small as 7 deg in bank angle were considered to be hazardous at breakout altitude (200 ft (61.0 m)) for Instrument Flight Rule (IFR) and at 50 ft (15.2 m) for Visual Flight Rule (VFR) for both aircraft classes. Proximity to the ground was the primary reason for a hazardous rating. This was reflected in the reduction in the maximum bank angle at the hazard boundary and in more consistent ratings as altitude was decreased.

Sammonds, R. I.↗
NASA NTRS1975

Magnetospheric protons and electrons encountered by the moon in the plasma sheet

Results are summarized for a study of plasma-sheet particles (and their flow) encountered by the moon during its passage through the geomagnetic tail. The study is based on analysis of data obtained with a modulated Faraday cup on board the lunar-anchored spacecraft Explorer 35. It is shown that the electrons have a rapidly fluctuating non-Maxwellian energy distribution with a mean energy of several hundred electron volts and a density of approximately 0.2 per cu cm. Protons with energies of the order of 1 keV were usually detected above the instrument background when flowing towards earth at about 200 km/sec. It is suggested that strong terrestrial polar winds during the early history of the earth-moon system could have caused some erosion of the front side of the moon and that the relative smoothness of the same side could be explained in terms of gravitational shielding by the earth from the interplanetary rock flux.

Prakash, A.↗
NASA NTRS1976

A probability of encounter with interstellar comets and the likelihood of their existence

A theory of the probability of encounter of the sun with an interstellar comet at a distance comparable to the earth-sun distance is formulated, and a general expression is derived establishing the relationship among the influx rate of interstellar comets, the perihelion distance, the space density of the comets, the Maxwellian distribution of comet velocities in the interstellar cloud, and the cloud's systematic velocity relative to the sun. An upper limit of .0006 solar mass per cubic parsec is established for the space density of interstellar comets. The theoretical distribution of semimajor axes of interstellar comets shows that a strong hyperbolic excess must be present in the orbits of a majority of interstellar comets regardless of the dynamical characteristics of the comet cloud, except when the cloud is moving along with the sun and the distribution of individual velocities has a very low dispersion. This case, however, implies a possibility of capture by the sun and thus becomes a problem of an Oort-type cloud.

Sekanina, Z.↗
NASA NTRS1976

Flight-test experience of a helicopter encountering an airplane trailing vortex

This paper presents results of a flight-test experiment of a UH-1H helicopter encountering the vortex wake of a C-54 airplane. The helicopter was instrumented to record the pilot control inputs, determine the upset experience, and measure critical loads within the rotor system. During the flight-test program 132 penetrations of the vortex wake were made by the helicopter at separation distances from 3/8 to 6-1/2 nautical miles. Test results indicated that the helicopter upsets and the vortex induced blade loads experienced were minimal and well within safe limits. The upsets were very mild when compared to a typical response of a small airplane to the vortex wake of the C-54 airplane.

Dunham, R. E., Jr.↗
NASA NTRS1977

Mercury's helium exosphere after Mariner 10's third encounter

From Mariner 10 third encounter UV data, a value of .00045 was calculated as the fraction of the solar wind He++ flux intercepted and captured by Mercury's magnetosphere if the observed He atmosphere is maintained by the solar wind. If an internal source for He prevails, the corresponding upper bound for the global outgassing rate is estimated to be 4.5 x 10 to the 22nd power per sec. A surface temperature distribution was used which satisfies the heat equation over Mercury's entire surface using Mariner 10 determined mean surface thermal characteristics. The means stand off distance of Mercury's magnetopause averaged over Mercury's orbit was also used.

Curtis, S. A.↗
NASA NTRS1978

Consequences of a past encounter of the earth with an interstellar cloud

In its motion through the Galaxy the sun may have suffered a number of encounters with dense interstellar clouds for which the number density of molecular hydrogen is in excess of 1000 per cu cm. Several authors have shown that this is sufficient density to stop the solar wind inside earth's orbit. Earth's atmosphere would be subjected to an interstellar H2 flux of more than 7 billion per sq cm/sec for periods of the order of 100,000 years. Simple scaling arguments are used to examine several consequences for earth's atmosphere: (1) the ionospheric F region would largely disappear; (2) the water-vapor content of the middle atmosphere would be greatly enhanced, reducing the mesospheric ozone concentrations and thereby lowering the average temperature and altitude of the mesopause; (3) as a result of (2), widespread mesospheric ice clouds would occur, increasing the planetary albedo; and (4) the resultant radiative cooling at the surface may have been sufficient to 'trigger' an ice age.

Mckay, C. P.↗
NASA NTRS1978

Mercury's helium exosphere after Mariner 10's third encounter

From a comparison of the Mariner 10 third encounter UV spectrometer data with intensities generated from a newly constructed model exosphere, a new value of 4.5 x 10 to the -4th power for the fraction of the solar wind He(++) flux to be intercepted and captured by Mercury's magnetosphere, if the observed He atmosphere is maintained by the solar wind, has been derived. If an internal source for He prevails, the corresponding upper bound for the global outgassing rate is estimated to be 4.5 x 10 to the 22nd power/s. These values differ from those given earlier because of the present use of a surface temperature distribution satisfying the heat equation over Mercury's entire surface which employs Mariner-10-determined mean surface thermal characteristics. The mean standoff distance of Mercury's magnetopause averaged over Mercury's orbit is also used. Agreement between the observed and calculated intensities is found to be good. Minor discrepancies on the nightside of the terminator are explicable in terms of differences between actual and computed temperatures and scale height structure changes.

Curtis, S. A.↗
NASA NTRS1978

Flight tests of a simple airborne device for predicting clear air turbulence encounters

An airborne clear-air turbulence detector is being flight-tested on board NASA's C-141 and Learjet aircraft. The device is an infrared (IR) sensor in the water vapor band and is designed to detect changes in vapor concentrations associated with turbulence in shear conditions. Warnings of about 5 min have been demonstrated at flight altitudes from 9.1 to 13.7 km (30,000 to 45,000 ft). Encounter predictions were obtained 80% of the time, and false alarms were given about 6% of the time. Several simple algorithms were studied for use as signal output analyzers and for alert triggering.

Kurkowski, R. L.↗
NASA NTRS1978

Pioneer Venus encounter will occur in December

The encounter time line and mission profile are presented for the Pioneer Venus 1 Spacecraft and for the four probes and transponder bus that comprise Pioneer Venus 2. Known facts about Venus are reviewed and the history of discoveries about the planet is related. Operations of the orbiter and multiprobe are described as well as the 30 instruments being carried and provisions for data transmission.

Source record↗
NASA NTRS1979

Procedures for estimating the frequency of commercial airline flights encountering high cabin ozone levels

Three analytical problems in estimating the frequency at which commercial airline flights will encounter high cabin ozone levels are formulated and solved: namely, estimating flight-segment mean levels, estimating maximum-per-flight levels, and estimating the maximum average level over a specified flight interval. For each problem, solution procedures are given for different levels of input information - from complete cabin ozone data, which provides a direct solution, to limited ozone information, such as ambient ozone means and standard deviations, with which several assumptions are necessary to obtain the required estimates. Each procedure is illustrated by an example case calculation that uses simultaneous cabin and ambient ozone data obtained by the NASA Global Atmospheric Sampling Program. Critical assumptions are discussed and evaluated, and the several solutions for each problem are compared. Example calculations are also performed to illustrate how variations in lattitude, altitude, season, retention ratio, flight duration, and cabin ozone limits affect the estimated probabilities.

Holdeman, J. D.↗
NASA NTRS1979

A reexamination of plasma measurements from the Mariner 5 Venus encounter

Mariner 5 plasma data from the Venus encounter have been analyzed with twice the time resolution of the original analysis of Bridge et al. (1967). The velocity distribution function for each spectrum is used to determine more precisely the locations of boundaries and characteristic flow parameters in the interaction region around the planet. A new region is identified in the flow located between magnetosheathlike plasma inside the shock front and an interior low-flux region near the geometrical shadow of the planet. The region is characterized by a wide velocity distribution function and a decrease in ion flux. Using the highest time resolution magnetic field data, it is proposed that rapid magnetic field fluctuations in this region may result in an artificial broadening of the distribution function. It is concluded that very high time resolution is required in future experiments in order to determine the true nature of the plasma in this region.

Shefer, R. E.↗
NASA NTRS1979

Extreme ultraviolet observations from Voyager 1 encounter with Jupiter

Observations of the optical extreme ultraviolet spectrum of the Jupiter planetary system during the Voyager 1 encounter have revealed previously undetected physical processes of significant proportions. Bright emission lines of S(+2), S(+3), O(+2) indicating an electron temperature of 100,000 K have been identified in preliminary analyses of the Io plasma torus spectrum. Strong auroral atomic and molecular hydrogen emissions have been observed in the polar regions of Jupiter near magnetic field lines that map the torus into the atmosphere of Jupiter. The observed resonance scattering of solar hydrogen Lyman alpha by the atmosphere of Jupiter and the solar occultation experiment suggest a hot thermosphere (greater than or equal to 1000 K) with a large atomic hydrogen abundance. A stellar occultation by Ganymede indicates that its atmosphere is at most an exosphere.

Broadfoot, A. L.↗
NASA NTRS1979

Encounter with Venus - An update

This report deals with early results from the Pioneer Venus Orbiter and multiprobe missions, which encountered Venus on December 4 and December 9, 1978, respectively. Initial results for the multiprobe mission and for the first 30 days of the Orbiter mission have already been reported. Additional mission features and updated mission parameters based on refined tracking data and trajectory computations are presented here. Scientific results for both missions are discussed which cover the first 130 days (or orbits) of the nominal 243-day Orbiter mission.

Colin, L.↗
NASA NTRS1980

Voyager 1: Encounter with Saturn

The history of the Voyager Project is reviewed as well as known facts about Saturn and its satellites. Important results of encounters with Jupiter are summarized. Scientific objectives of the flyby of Saturn involve the planet's atmosphere, rings, and magnetic field interactions with the solar wind and satellites. The search for additional satellites, and various aspects of Titan, Rhea, Dione, Mimas, Iapetus, Hyperion, and Enceladas are also of interest. The instruments developed to obtain these goals are described.

Panagakos, N.↗
NASA NTRS1979

Jupiter's cloud distribution between the Voyager 1 and 2 encounters - Results from 5-micrometer imaging

As part of a continuing effort of ground-based support for Voyager target selection, infrared images in the 5-micrometer wavelength region were acquired in preparation for the Voyager 2 flyby of Jupiter. Observations were made during May 1979 from the Palomar 5-meter telescope and the new 3-meter NASA Infrared Telescope Facility at Mauna Kea and are compared to previous observations. Variations seen in the 5-micrometer flux distribution suggest global patterns of clouding over of some Jovian belts and clearing of others. These data were used to predict the Jovian cloud distribution at the time of the Voyager 2 encounter in order to target the imaging and infrared experiments to areas free of high obscuring clouds.

Terrile, R. J.↗
NASA NTRS1980

Scientific results from the Pioneer Saturn encounter - Summary

The scientific results of the Pioneer Saturn encounter with Saturn are summarized. The Pioneer mission was designed to image the planet, its satellites and rings, and measure its particulate environment and the magnetic field and photon and charged particle radiation by means of 11 operational scientific instruments and its 2.293-GHz telemetry carrier signal. Principle results of the mission include the discovery of an additional ring and a previously unidentified satellite, the further characterization of the physical properties of Saturn and its magnetic field, and the description of the planetary magnetosphere. The successful completion of the mission demonstrated the ability of spacecraft such as Voyager 1 and 2 to survive the particle environments of Saturn's rings and trapped radiation environments, and Pioneer Saturn is expected to continue transmitting information on the interplanetary medium and the solar wind interaction with the interstellar medium until the mid-1980's.

Opp, A. G.↗
NASA NTRS1980

Unified aerodynamic-acoustic theory for a thin rectangular wing encountering a gust

A linear aerodynamic-acoustic theory is developed for the prediction of the surface pressure distribution and three-dimensional acoustic far-field for a flat plate rectangular wing encountering a stationary short-wavelength oblique gust. It is suggested that for an infinite-span wing, leading- and trailing-edge responses to a short-wavelength gust are essentially independent. This idea is used to solve for the two-dimensional pressure field due to the passage of an infinite-span wing through an oblique gust. By allowing the field point to come down to the wing's surface, one finds an expression for the surface pressure distribution which agrees with that given in the two-dimensional aerodynamic theories of Amiet and Adamczyk. Spanwise Fourier superposition of two-dimensional solutions to the infinite-span wing problem is used to approximate the three-dimensional acoustic field due to the interaction of a stationary oblique gust with a flat-plate rectangular wing traveling at a subsonic speed.

Martinez, R.↗