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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Four years of dust particle measurements in cislunar and selenocentric space from Lunar Explorer 35 and OGO 3.

Since July 1967, knowledge concerning the distributions of picogram size particulate matter in selenocentric space has been obtained from the Lunar Explorer 35 dust particle experiment. For almost 40% of the time, the mean sporadic cumulative flux is quite similar to the flux in interplanetary space. However, there are fluctuations of an order of magnitude during major meteor showers. The coincident increase of the flux in selenocentric space during the shower periods has been observed for the fourth year. The 100-picogram sensor does not show an increase during shower times, indicating a mass threshold of less than 100 picograms for particles with velocities equal to or greater than lunar escape velocity. The flux values from Lunar Explorer 35 are compared to other long-lifetime measurements in selenocentric, cislunar and interplanetary space with excellent agreement for masses less than one nanogram.

Alexander, W. M.↗
NASA NTRS1972

Evidence from Stream Meteoroids

The physical behavior and composition of shower meteors were examined in an effort to establish the structure of its parent comet. Properties considered include degree of fragmentation and density.

Mccrosky, R. E.↗
NASA NTRS1972

Comet Encke: Meteor metallic ion identification by mass spectrometer

Metal ions including Na-40(+), Mg-24(+), Si-28(+), K-39(+), Ca-40(+), Sc-45(+), Cr-52(+), Fe-56(+), and Ni-58(+) were detected in the upper atmosphere during the beta Taurids meteor shower. Abundances of these ions relative to Si(+) show agreement in most instances with chondrites. A notable exception is 45(+), which is Sc(+), is 100 times more abundant than neutral scandium found in chondrites.

Goldberg, R. A.↗
NASA NTRS1972

Reality of comet nucleus.

The prime problem of a comet mission must be to settle whether the cometary nucleus has an actual tangible material existence, or whether it arises from some optical effect present only at times within comets. The absence of any large particles in a comet seems to be demonstrated by certain meteor showers. A feature that would seem to indicate that a comet consists primarily of a swarm of particles is that the coma in general contracts as the comet approaches the sun, roughly in proportion within the distance, and then expands again as it recedes.

Lyttleton, R. A.↗
NASA NTRS1974

Silicon ions below 100 km: A case for SiO2(+)

Silicon ions are normally detected at altitudes above 100 km and within sporadic E layers. Traces have rarely been observed within the more permanent metallic layer near 93 km. This is surprising since silicon is an important constituent of chondritic meteorites, which ablate material in this region to provide a primary source of the metallic species observed there. Evidence is presented that Si(+)ions form SiO2(+) at the lower altitudes, and exist in this ionic state prior to recombination. A rocket launched from El Arenosillo, Spain on 3 July 1972, at 0743 LMT, during the predicted period of the Beta Taurids meteor shower, passed through a continuous belt of metallic ions that began near 85 km, ended near 115 km, and exhibited an order of magnitude increase in the form of a layer near 114 km. Si(+)was measured in and below the ledge down to 103 km. It showed a rapid decrease below this height. Radiative association is offered as a primary mechanism for SiO2(+) production.

Goldberg, R. A.↗
NASA NTRS1974

Optical studies of meteors at Mount Hopkins Observatory

The 10-m optical reflector and an array of phototubes are used to extend the optical measurements beyond the present limit achieved by the Vidicon system. The first detection of optical meteors with M sub v = + 12 is reported. It is hoped that this system can be used to determine intermediate points in the meteor frequency mass curve for sporadic meteors and to study in detail the faint components of meteor showers. Preliminary observations made on three nights in September 1974 are presented.

Weekes, T. C.↗
NASA NTRS1975

Silicon ions below 100 km - A case for SiO2/+/

An investigation regarding the occurrence of Si ions is conducted, taking into account an unusual metal ion structure observed during a meteor shower event. Loss processes involving silicon oxides are considered in connection with a study of the reasons for the unique Si(+) distribution found. It is suggested that below 100 km Si(+) is rapidly depleted by two- and three-body reactions with molecular oxygen, forming SiO2(+) which then recombines.

Goldberg, R. A.↗
NASA NTRS1977

Comet Halley - The orbital motion

The orbital motion of Comet Halley is investigated over the interval from A.D. 837 to 2061. Using the observations from 1607 through 1911, least-squares differential orbit corrections were successfully computed using the existing model for the nongravitational forces. The nongravitational-force model was found to be consistent with the outgassing-rocket effect of a water-ice cometary nucleus and, prior to the 1910 return, these forces are time-independent for nearly a millennium. For the 1986 return, viewing conditions are outlined for the comet and the related Orionid and Eta Aquarid meteor showers.

Yeomans, D. K.↗
NASA NTRS1979

Sulfur chemistry in the E-region

Sulphur chemistry of meteoric species in the E-region is examined. Reactions and their rate coefficients of sulphur above 90 km are discussed, together with the gross chemistry of meteoric species. It was found that the sulphur deposited by ablating meteroids in the E-region is rapidly converted to SO above 90 km, with SO(+) the principal ionic species in concentrations of few ions per cu cm or less. By 80 km, other sulfur compounds may become significant, sulphur chemistry becoming quite complex in the stratosphere. It is possible that this chemistry plays a role in the formation of aerosols near the main meteroid ablation altitude of 92 km. Ions of mass 48 amu observed at the 94 to 107 km altitude in the 1976 Perseid meteor shower are interpreted as SO(+) ions.

Swider, W.↗
NASA NTRS1982

Halley's Comet

Since 240 B.C., Chinese observers have documented a nearly unbroken record of scientifically useful observations of Periodic Comet Halley (P/Halley). Investigations of the comet's motion by Western astronomers are discussed, taking into account the first successful prediction of a cometary return by Halley (1705), computations conducted by Rosenberger (1830), and studies performed by Cowell and Crommelin (1910). Comet Halley's motion and nongravitational forces are considered along with meteor showers associated with P/Halley. The physical properties of P/Halley are examined, giving attention to the visual observations, the light curve of P/Halley, the coma, the tails, direct photographs, spectrograms, and the emission spectrum of P/Halley. Other subjects explored are related to the cometary nucleus, the mass of P/Halley, the rotation period and axial inclination, the composition, a nominal model of P/Halley's coma, and plans for investigations in connection with the coming apparition of Comet Halley.

Newburn, R. L., Jr.↗
NASA NTRS1986

Interplanetary dust: The interstellar connection

Although not proven, there is the widespread belief that comets consist, at least in part, of interstellar material that was originally present in the solar nebula. Furthermore, there are strong arguments in favor of the view that much of the interplanetary dust complex is derived from comets. The main arguments supporting this view are based on mass balance, analysis of the orbital parameters of meteors, and the long known association between meteor showers and specific comets. Laboratory measurements on interplanetary dust particles (IDPs) collected in the stratosphere have confirmed the view that many of the dust particles are primitive in the sense that they show striking enrichments of D/H relative to average solar system materials. It has also been demonstrated that the mid-infrared absorption spectra of one infrared red class of particles show strong similarities to IR sources such as the protostar W-33A. However, the laboratory studies of IDPs have shown that they represent a diverse set of objects and the measurement of the orbital parameters of specific dust particles is essential to answering the question of sources. The observation of the IRAS dust bands reopens the question of the role of asteroids in supplying a significant fraction of the dust and part of the diversity observed may be due to the fact that some of the dust is asteroidal and some cometary. In addition, some fraction of interplanetary dust must consist of an interstellar component intercepted by the solar system in its motion through the local interstellar medium. It has been shown that dust derived from nearby stars will have 75% of their orbits with eccentricities or equal to 1.1 and might be difficult to distinguish from interplanetary dust based on orbital measurements alone.

Carey, W. C.↗
NASA NTRS1987

Comment on the paper 'On the influx of small comets into the earth's upper atmosphere'

The possibility that comets containing up to 100 tons of ice encounter the earth's atmosphere at a rate of one every 20 min is discussed. Cometary 'hail storms' were proposed to explain observed regular transient decreases in the atmospheric UV dayglow intensity. The decreases take the form of dark 'holes' up to 50 km across. The probability that clouds of objects assumed to be as dark as the nucleus of Comet Halley between the earth and moon would be detectable by ground-based electrooptical deep space telescopes is considered. Conflicting projections of the number of objects which would be detected per hour are examined. High correlations are noted between cometary passages (Comets Encke, Tuttle, Tempel) and intervals of meteor showers (Taurids, Leonids, Geminis, etc.). The holes, however, are not correlated or coincident with the showers. It is suggested that dedicated searches for the unclassified dark objects be carried out in November, when cometary fluxes are high.

Soter, Steven↗
NASA NTRS1989

Atomic emission in the ultraviolet nightglow

An observation of the ultraviolet nightglow between 2670 A and 3040 A was conducted over White Sands Missile Range on October 22, 1984, at 0020 hours LST during the Orionids meteor shower. A 1/4-meter UV spectrometer operating at 3.5 A resolution viewed the earth's limb at tangent heights between 90 km and 110 km for 120 seconds. By inverting the observed limb intensities, a total zenith intensity of 1.4 kR is inferred for the Herzberg I system. Excess emission above the Herzberg I (7,3) band at 2852 A is identified as the Mg I resonance line. The intensity ratio of the Herzberg I band system to the 2972 A line from O(1S) was less than that predicted from the accepted O(1S) branching ratio and acceptable ratios of Herzberg I to 5577 A emissions. Arguments supporting the identification of the Herzberg III band system are also advanced.

Sharp, W. E.↗