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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 217 records · Page 12
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NASA NTRS1974

Analysis of vortex wake encounter upsets

The problem of an airplane being upset by encountering the vortex wake of a large transport on takeoff or landing is currently receiving considerable attention. This report describes the technique and results of a study to assess the effectiveness of automatic control systems in alleviating vortex wake upsets. A six-degree-of-freedom nonlinear digital simulation was used for this purpose. The analysis included establishing the disturbance input due to penetrating a vortex wake from an arbitrary position and angle. Simulations were computed for both a general aviation airplane and a commercial jet transport. Dynamic responses were obtained for the penetrating aircraft with no augmentation, and with various command augmentation systems, as well as with human pilot control. The results of this preliminary study indicate that attitude command augmentation systems can provide significant alleviation of vortex wake upsets; and can do it better than a human pilot.

Johnson, W. A.↗
NASA NTRS1974

Pioneer 10 mission - Summary of scientific results from the encounter with Jupiter

Data on the Jovian atmosphere and radiation environment transmitted by Pioneer 10 as it passed by Jupiter are discussed. The presence of a strong magnetic field, of energetic electron precursers, and of flat disk-shaped particle distribution is noted at a distance of 360 Jovian radii from the planet. Previously available data on Jovian satellites are augmented from Pioneer 10 data. The normal operation of the data collecting and transmitting systems of the mission after encounter with Jupiter is noted.

Opp, A. G.↗
NASA NTRS1974

Preliminary Pioneer 10 encounter results from the Ames Research Center plasma analyzer experiment

Preliminary results from the Ames Research Center plasma analyzer experiment for the Pioneer 10 Jupiter encounter indicate that Jupiter has a detached bow shock and magnetopause similar to the case at Earth but much larger in spatial extent. In contrast to Earth, Jupiter's outer magnetosphere appears to be highly inflated by thermal plasma and therefore highly responsive in size to changes in solar wind dynamic pressure.

Wolfe, J. H.↗
NASA NTRS1974

Observations at Venus encounter by the plasma science experiment on Mariner 10

Preliminary results from the rearward-looking electrostatic analyzer of the plasma science experiment during the Mariner 10 encounter with Venus are described. They show that the solar-wind interaction with the planet probably involves a bow shock rather than an extended exosphere, but that this is not a thin boundary at the point where it was crossed by Mariner 10. An observed reduction in the flux of electrons with energies greater than 100 electron volts is interpreted as evidence for some direct interaction with the exosphere. Unusual intermittent features observed downstream of the planet indicate the presence of a comet-like tail hundreds of scale lengths in length.

Bridge, H. S.↗
NASA NTRS1974

Observations at Mercury encounter by the plasma science experiment on Mariner 10

A fully developed bow shock and magnetosheath were observed near Mercury, providing unambiguous evidence for a strong interaction between Mercury and the solar wind. Inside the sheath there is a distinct region analogous to the magnetosphere or magnetotail of earth, populated by electrons with lower density and higher temperature than the electrons observed in the solar wind or magnetosheath. At the time of encounter, conditions were such that a perpendicular shock was observed on the inbound leg and a parallel shock was observed on the outbound leg of the trajectory, and energetic plasma electron events were detected upstream from the outbound shock crossing. The interaction is most likely not atmospheric, but the data clearly indicate that the obstacle to solar wind flow is magnetic, either intrinsic or induced.

Ogilvie, K. W.↗
NASA NTRS1974

Magnetic coordinates for the Pioneer 10 Jupiter encounter

The magnetic coordinates of the Pioneer 10 spacecraft and the five innermost satellites are given around the time of Jupiter encounter, Dec. 1-8, 1973. The D sub 2 offset dipole model of Smith et al. (1974) is used to make the calculations. Magnetic coordinates are needed for the interpretation of the trapped particle measurements, including the absorption effects of the satellites. Contours of constant field magnitude and magnetic latitude are given at the surface of Jupiter for the D sub 2 model. The system III longitude of a spacecraft at Jupiter is derived, and formulas are given for the relationships between system I, II, and III longitudes. The longitude of the magnetic dipole increases by about 3 deg/yr, owing to the inaccurate rotation rate used to define system III longitude.

Mead, G. D.↗
NASA NTRS1975

Preliminary interpretation of plasma electron observations at the third encounter of Mariner 10 with Mercury

Plasma electron count observations made during the first and third encounters of Mariner 10 with Mercury (i.e., during Mercury I and III) are reported. They provide detailed information on the magnetosphere of Mercury, especially those from Mercury III. A low-flux region was observed about closest approach (CA) of Mercury III, whereas no such region was detected by the lower-latitude Mercury I; a hot plasma sheet was measured on the outgoing (and near-equator) trajectory of Mercury I, while only cool plasma sheets were observed in the magnetosphere by Mercury III. Findings are similar, on a reduced scale, to models of the earth's magnetosphere and magnetosheath.

Hartle, R. E.↗
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.↗