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At least 955 records · Page 53
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NASA NTRS1984

The ionization structure of planetary nebulae. IV - NGC 6853

Upgraded UV and IR data were taken of the planetary nebula NGC 6853 in the same region as previous optical data to improve the data base on various ionized species in the nebula. The spectral range 1400-9600 A was scanned, and good agreement was obtained between UV and optical ionization abundance data, although the 4267 A C II line yielded a C(2+) abundance larger than indicated by the UV data. The discrepancy concentrated around the central star. Ionization abundances were determined for He, O, N, NC, C, Ar, and S relative to H, and the causes of discrepancies in the abundances compared to those of previous investigators are discussed. It is noted that, as in the planetary nebula NGC 6720, lighter element abundances are higher than solar values, which suggests mixing of processed materials in the envelope of the two nebulae.

Barker, T.↗
NASA NTRS1985

Orbit determination singularities in the Doppler tracking of a planetary orbiter

On a number of occasions, spacecraft launched by the U.S. have been placed into orbit about the moon, Venus, or Mars. It is pointed out that, in particular, in planetary orbiter missions two-way coherent Doppler data have provided the principal data type for orbit determination applications. The present investigation is concerned with the problem of orbit determination on the basis of Doppler tracking data in the case of a spacecraft in orbit about a natural body other than the earth or the sun. Attention is given to Doppler shift associated with a planetary orbiter, orbit determination using a zeroth-order model for the Doppler shift, and orbit determination using a first-order model for the Doppler shift.

Wood, L. J.↗
NASA NTRS1985

An assessment of thermal, wind, and planetary wave changes in the middle and lower atmosphere due to 11-year UV flux variations

Hines (1974) speculated that solar-induced modifications of the middle and upper atmosphere may alter the transmissivity of the stratosphere to upwardly propagating atmospheric waves. It was suggested that subsequent constructive or destructive interference may result in a change of phase or amplitude of these waves in the troposphere leading to weather or climate changes. The present investigation has the objective to bring together both radiative transfer and planetary wave studies in an effort to assess specifically whether Hines mechanism can be initiated by the solar ultraviolet flux variability assumed to be associated with the 11-year solar cycle. The obtained results suggest that the presently studied mechanism, which links solar-induced zonal wind changes in the stratosphere and mesosphere to planetary wave changes in the troposphere, is not strong enough to cause substantive changes in the troposphere.

Callis, L. B.↗
NASA NTRS1985

A model of the planetary nebula NGC 2392 determined from velocity observations

High-resolution slit spectra are combined with published photometric and velocity data to develop a model of the double-ring planetary nebula NGC 2392. The inner ring is due to an incomplete, prolate spheroid shell with most of the material concentrated near the minor axis circumference. The spheroid is seen almost pole-on, open at the sharp ends, and the formal velocity of expansion (93 km/s) at the ends is a record high for planetary nebulae. The outer ring is a nearly round spheroid of approximately 16 km/s expansion velocity and a different tilt angle than the inner shell. It is surrounded by rapidly expanding material with velocities of at least 75 km/s. A high-velocity stream of material is formed at the open ends of the inner shell and is accelerated by the central star's stellar wind to velocities of at least + or - 190 km/s, providing the first direct evidence for the kinematic role of a strong stellar wind. The inner shell age is approximately 800 yr, arguing that the shell material was preferentially ejected from the equator of the parent star, in contradiction with the usual predictions of theory.

Odell, C. R.↗
NASA NTRS1984

The generation of mesospheric planetary waves by zonally asymmetric gravity wave breaking

A semispectral numerical model is used to study the influence of a longitudinally varying gravity wave source on the general circulation of the winter mesosphere. The gravity wave source consists of stationary (topographic) waves with a longitudinally varying amplitude distribution that is approximated by the first two terms in a zonal harmonic expansion (i.e., the zonal mean plus planetary wavenumber 1). The computed zonal mean circulation in the mesosphere is nearly the same as that computed for a zonally symmetric gravity wave source of equal amplitude. However, the asymmetric source excites a strong stationary wavenumber 1 disturbance near the level of gravity wave breaking (equal to about 71 km). This disturbance has a zonal wind maximum about 1/4-cycle upstream from the gravity wave drag maximum. It is concluded that vertically propagating gravity waves produced in the troposphere are a possible source for mesospheric planetary waves.

Holton, J. R.↗
NASA NTRS1984

Measuring planetary neutron albedo fluxes by remote gamma-ray sensing

In order to measure the planetary neutron albedo fluxes, a neutron-absorbing shield which emits gamma rays of characteristic energy and serves as a neutron detector, is added to a gamma-ray spectrometer (GRS). The gamma rays representing the neutron flux are observed against interference consisting of cosmic gamma rays, planetary continuum and line emission, and gamma rays arising from the interaction of cosmic rays with the GRS and the spacecraft. The uncertainty and minimum detection limits in neutron albedo fluxes are calculated for two missions, a lunar orbiter and a comet nucleus rendezvous. A GRS on a lunar orbiter at 100 km altitude detects a thermal neutron albedo flux as low as 0.002/sq cm/s and an expected flux of about 0.6/sq cm/s is measured with an uncertainty of 0.001/sq cm/s, for a 100 h observation period. For the comet nucleus, again in a 100 h observing period, a thermal neutron albedo flux is detected at a level of 0.006/sq cm/s and an expected flux of about 0.4/sq cm/s is measured with an uncertainty of 0.004/sq cm/s. The expanded geological capabilities made possible by this technique include improvements in H sensitivity, spatial resolution, and measurement depth; and an improved model of induced gamma-ray emission.

Haines, E. L.↗
NASA NTRS1985

Transport of ozone in the middle stratosphere - Evidence for planetary wave breaking

Data from the Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) for the period October 25, 1978-May 28, 1979 are used in a descriptive study of ozone variations in the middle stratosphere. It is shown that the ozone distribution is strongly influenced by irreversible deformation associated with large amplitude planetary-scale waves. This process, which has been described by McIntyre and Palmer as planetary wave breaking, takes place throughout the 3-30 mb layer, and poleward transport of ozone within this layer occurs in narrow tongues drawn on the tropics and subtropics in association with major and minor warming events. These events complement the zonal mean diabatic circulation in producing significant changes in the total column amount of ozone.

Leovy, C. B.↗
NASA NTRS1984

Future studies of planetary rings by space probes

Recent space probe observations of the rings of Jupiter and Saturn have furnished a substantial enhancement of the current understanding of the outer planets' rings. Voyager 2 offers further opportunities for the study of the Neptune and Uranus ring systems. The Galileo mission to Jupiter furnishes the first opportunity for long term space probe studies of a planetary ring system. It is suggested that an appropriately instrumented Saturn orbiter would not only provide a similar opportunity for the study of the Saturn rings, but may also be the only means by which to adequately address the nature of the diverse phenomena displayed by this prototypical planetary ring system.

Stone, E. C.↗
NASA NTRS1985

The causation and sensitivity of the northern winter planetary waves

High-resolution calculations of the wintertime stationary atmospheric response to planetary scale topographic and thermal forcings have been made using a numerical model that solves the spherical primitive equations linearized about observed zonal wind and temperature fields. The model equations are presented and their numerical implementation is discussed. The model inputs and parameters are presented and the model's response to relativistic forcing is analyzed. In middle latitudes the response to topographic forcing strongly dominates the response to thermal forcing. In the midlatitude troposphere, the topographic response is insensitive to changes in the zonal wind. In the stratosphere, both the variance and mean are dominated by the topographic response. In general, the sensitivity of the planetary waves to changes in the zonal wind is found to be much smaller than other recent calculations have indicated.

Jacqmin, D.↗
NASA NTRS1985

Discovery of oxygen in the PG 1159 degenerate stars - A direct evolutionary link to O VI planetary nebula nuclei and confirmation of pulsation theory

The discovery of strong O VI absorption/emission lines in five members of the PG 1159 degenerate stars is reported. It is shown that the optical spectra are dominated by C IV, O VI, and He II, with no detectable N lines. It is confirmed that the planetary nebula-central star, K1-16, which is found to be a pulsating star by Grauer and Bond (1984), is a member of the spectroscopic group. The detection of strong oxygen features in the photospheres of the objects provides support of the prediction of Starrfield et al. (1984). The properties of the PG 1159 stars are compared with the so-called O VI central stars of planetary nebulae and both groups of stars are found to have similar spectral features, temperatures, and luminosities. The implications of the O VI/PG 1159 evolutionary link are assessed.

Sion, E. M.↗
NASA NTRS1985

Laboratory evaluation and application of microwave absorption properties under simulated conditions for planetary atmospheres

Radio absorptivity data for planetary atmospheres obtained from spacecraft radio occultation experiments and Earth-based radio astronomical observations can be used to infer abundances of microwave absorbing atmospheric constituents in those atmospheres, as long as reliable information regarding the microwave absorbing properties of potential constituents is available. The use of theoretically-derived microwave absorption properties for such atmospheric constituents, or laboratory measurements of such properties under environmental conditions which are significantly different than those of the planetary atmosphere being studied, often lead to significant misinterpretation of available opacity data. Steffes and Eshleman showed that under environmental conditions corresponding to the middle atmosphere of Venus, the microwave absorption due to atmospheric SO2 was 50 percent greater than that calculated from Van Vleck-Weiskopff theory. Similarly, the opacity from gaseous H2SO4 was found to be a factor of 7 greater than theoretically predicted for conditions of the Venus middle atmosphere. The recognition of the need to make such measurements over a range of temperatures and pressures which correspond to the periapsis altitudes of radio occultation experiments, and over a range of frequencies which correspond to both radio occultation experiments and radio astronomical observations, has led to the development of a facility at Georgia Tech which is capable of making such measurements.

Steffes, P. G.↗
NASA NTRS1985

Planetary image conversion task

The Planetary Image Conversion Task group processed 12,500 magnetic tapes containing raw imaging data from JPL planetary missions and produced an image data base in consistent format on 1200 fully packed 6250-bpi tapes. The output tapes will remain at JPL. A copy of the entire tape set was delivered to US Geological Survey, Flagstaff, Ariz. A secondary task converted computer datalogs, which had been stored in project specific MARK IV File Management System data types and structures, to flat-file, text format that is processable on any modern computer system. The conversion processing took place at JPL's Image Processing Laboratory on an IBM 370-158 with existing software modified slightly to meet the needs of the conversion task. More than 99% of the original digital image data was successfully recovered by the conversion task. However, processing data tapes recorded before 1975 was destructive. This discovery is of critical importance to facilities responsible for maintaining digital archives since normal periodic random sampling techniques would be unlikely to detect this phenomenon, and entire data sets could be wiped out in the act of generating seemingly positive sampling results. Reccomended follow-on activities are also included.

Martin, M. D.↗
NASA NTRS1985

The role of FGGE data in the understanding and prediction of atmospheric planetary waves

The augmented observational data base provided by FGGE offers a unique opportunity to improve the understanding and prediction of atmospheric planetary waves. Substantial progress was made, but a number of problems remain. The research on planetary waves conducted thus far with FGGE data is reviewed. Areas of progress are summarized, and some remaining problems are discussed.

Baker, W. E.↗
NASA NTRS1986

Laboratory evaluation and application of microwave absorption properties under simulated conditions for planetary atmospheres

The recognition of the need to make laboratory measurements of simulated planetary atmospheres over a range of temperatures and pressure which correspond to the altitudes probed by radio occultation experiments, and over a range of frequencies which correspond to both radio occultation experiments and radio astronomical observations, has led to the development of a facility at Georgia Tech which is capable of making such measurements. Construction was completed of the outer planets simulator and measurements were conducted of the microwave absorption and refraction from nitrogen under simulated Titan conditions. The results of these and previous laboratory measurements were applied to a wide range of microwave opacity measurements, in order to derive constituent densities and distributions in planetary atmospheres such as Venus.

Steffes, P. G.↗
NASA NTRS1986

Preliminary development of a global 3-D magnetohydrodynamic computational model for solar wind-cometary and planetary interactions

This is the final summary report by Resource Management Associates, Inc., of the first year's work under Contract No. NASW-4011 to the National Aeronautics and Space Administration. The work under this initial phase of the contract relates to the preliminary development of a global, 3-D magnetohydrodynamic computational model to quantitatively describe the detailed continuum field and plasma interaction process of the solar wind with cometary and planetary bodies throughout the solar system. The work extends a highly-successful, observationally-verified computational model previously developed by the author, and is appropriate for the global determination of supersonic, super-Alfvenic solar wind flows past planetary obstacles. This report provides a concise description of the problems studied, a summary of all the important research results, and copies of the publications.

Stahara, S. S.↗
NASA NTRS1985

He2-36 - A planetary nebula with a high velocity jet?

The ultraviolet spectrum of the planetary nebula He2-36 was observed in the low-dispersion mode of the IUE. Strong emission lines of semiforbidden C III, He II, and C IV are observed, as well as some weak line and a moderately strong stellar continuum, suggesting a hot companion to the visual A2 III central star. The extinction to He2-36 was determined from the He II I (1640)/I (4686) ratio. The C IV line has an unusual split structure. If the 1545 component is due to a blueshifted component from the 'jet' emanating from the nebula, its velocity would be -600 km/s, which is unique for a planetary nebula.

Feibelman, W. A.↗
NASA NTRS1985

Planetary mission operations - An overview

An overview of the missions operations systems (MOS) used to support NASA planetary missions is given. The principal factors governing the design characteristics of MOS are discussed, including: the communications requirements of spacecraft over long distance from the earth, the fragility of the scientific payloads, and the inability to carry out planetary missions more than a few times a decade. The uplink and downlink parts of the MOS of Galileo and Voyager spacecraft are illustrated as examples of successful MOS design. A black and white photograph of the operations control center of JPL is provided.

Haynes, N. R.↗
NASA NTRS1985

Planetary programs

The goals of the NASA planetary exploration program are to understand the origin and evolution of the solar system and the earth, and the extent and nature of near-earth space resources. To accomplish this, a number of missions have been flown to the planets, and more are in active preparation or in the planning stage. This paper describes the current and planned planetary exploration program starting with the spacecraft now in flight (Pioneers and Voyagers), those in preparation for launch this decade (Galileo, Magellan, and Mars Observer), and those recommended by the Solar System Exploration Committee for the future. The latter include a series of modest objective Observer missions, a more ambitious set of Mariner Mark IIs, and the very challenging but scientifically rewarding sample returns.

Mills, R. A.↗