Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Comet”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

H2O(+) ions in comets: Comet Kohoutek (1973f) and comet Bradfield (1974b)

The image tube Cassegrain slit spectra of comet Kohoutek and Bradfield calibrated and reduced to relative intensities are discussed. Monochromatic changes in the surface brightness for various neutral and ionized molecules are determined. The intensities of C2 and CN decreased approximately four times faster than the intensity change for the H2O(+) features. It is shown that the excitation mechanism for the observed H2O(+) bands is by fluorescent scattering of the incident solar radiation. The effects of solar activity on the photoionization rate of H2O in a comet are discussed. Observations of another bright comet at the time of maximum solar activity are needed to determine changes in band intensities of comet tail ions due to solar activity.

Wehinger, P.↗
NASA NTRS1981

Comet Bradfield 1979 X - The gassiest comet

The Comet Bradfield 1979 X provided the most recent opportunity to obtain quantitative photometric data on a comet. Although the comet was not unusually luminous, its very close approach to earth made it possible to observe it from the time of discovery at a heliocentric distance of just over 0.5 AU until it was beyond 1.5 AU from the Sun. The observations conducted are discussed along with aspects of data reduction. It was found that the OH production of comets can be experimentally studied on the basis of a routine procedure. The Comet Bradfield 1979 X was one of the gassiest comets ever observed, comparable to Comet P/Encke. The production rates of all molecular species were found to decline sharply with heliocentric distance.

Ahearn, M. F.↗
NASA NTRS1972

Comets: Scientific data and missions; Proceedings of the Tucson Comet Conference, University of Arizona, Tucson, Ariz., April 8, 9, 1970.

Current knowledge of comets is surveyed, and comet-rendezvous mission constraints, opportunities, modes, and spacecraft capabilities are discussed. Attention is given to cometary nuclei, infrared measurements of comets, the nature and origin of the cometary head, L-alpha photometry of Comet Bennett, Types I and II tails, comet spectra and orbits, and evidence from stream meteoroids. Some scientific criteria for a cometary mission are considered. Individual items are announced in this issue.

Kuiper, G. P.↗
NASA NTRS1981

Comet showers and the steady-state infall of comets from the Oort cloud

The theoretically-determined location of the boundary between semimajor axes of those comets entering the planetary system only in bursts or showers, and those which arrive in a steady stream, is abrupt and falls at the observed inner edge of the Oort cloud. It is proposed that the comets were formed in the outer parts of the collapsing protosun, which had a radius of less than 5000 AU. If so, then: (1) a first-generation comet cloud may have been produced, with a radius of more than 1000 AU, and the coupled dynamical perturbations of passing stars and Jupiter would lead to the formation of a comet cloud similar to the Oort; while (2) if the Oort cloud comets originated in this inner cloud, and were later ejected into their present orbits by the perturbations of passing stars and Jupiter, the total inner cloud mass is two orders of magnitude greater than that of the Oort cloud.

Hills, J. G.↗
NASA NTRS1979

Relative motions of fragments of the split comets. III - A test of splitting and comets with suspected multiple nuclei

A quantitative test of splitting for comets with suspected multiple nuclei has been formulated using a model which assumes the motions of cometary fragments to be due primarily to outgassing. The model expresses the relative motion of the cometary fragments in terms of the time of splitting and the differential force, which are determined by measurements of the position angle and the separation distance between fragments. The test is applied to 18 comets suspected of having multiple nuclei, of which the comets Sawerthal 1888 I, Campbell 1914 IV, Whipple-Fedtke-Tevzadze 1943 I, Honda 1955 V, Wild 1968 III and Tago-Sato-Kosaka 1969 IX were found to be clear cases of split comets and Davidson 1889 IV and Periodic Giacobini 1896 V were judged to be likely candidates. At least three of the secondary nuclei confirmed can be classified as short-lived companions, while only two appear to be persistent.

Sekanina, Z.↗
NASA NTRS1973

Orientation-dependent effects in Oort's theory of comet origin. II - Anisotropies in the distribution of long-period comet orbits.

The statistical significance of anisotropies in the distribution of orbital orientations among the long-period and nearly parabolic comets is evaluated. It is suggested that these anisotropies are not the result of observational selection effects. A numerical model for the distribution of orbital orientations is constructed, based on Oort's theory of comet origin and the assumption that the observed anisotropies are caused by multiple planetary perturbations over the course of many perihelion passages. The model, which is restricted to comets with perihelion distances less than 0.3 AU, does not predict any significant anisotropies.

Joss, P. C.↗
NASA NTRS1977

Scientific rationale and strategies for a first comet mission: Report of the Comet Halley science working group

The science objectives of a first comet mission are reviewed and related to what is known or can be expected to be learned in the near future from ground-based and near earth observations. A set of instruments and their science objectives are defined for a mission to Comet Halley during its 1985/86 apparition. The benefits from a fast flyby, a slow flyby, or a rendezvous mission and the relative impact of each on the instrument payload were assessed. The relative scientific value of encounters with the comet at distances from the sun ranging from 1 AU to 2.5 AU, including possible tradeoffs between flyby velocity and distance was considered. Pre- and post-perihelion encounters were likewise evaluated.

Source record↗
NASA NTRS1973

Comet exploration - Scientific objectives and mission strategy for a rendezvous with comet Encke.

A rendezvous mission which includes an extended stay of 80 days or longer in the vicinity of the comet is considered. Such a mission with exploration maneuvers through the coma and tail and circumnavigation of the nucleus is made feasible by the use of solar-electric propulsion. The physical characteristics of comet Encke are examined, giving attention to the icy conglomerate model of the nucleus, solar wind interaction, and chemical composition. Scientific objections are discussed together with mission profile options.

Meissinger, H. F.↗
NASA NTRS1977

Scientific rationale and strategies for a first comet mission. Report of the Comet Halley science working group. An executive summary

The justification, scientific objectives, instrumentation, and strategy for a first comet mission are discussed. Topics include: mission target; rendezous, propulsion system requirements, measurement objectives, instrument capabilities for rendezvous and the tail probe payload, and backup missions if rendezvous with Halley's comet is not possible to achieve. Support research to be done by NASA is recommended.

Source record↗
NASA NTRS1979

An analysis of the infrared continuum of comets. II - Comet Kohoutek

An analysis of the infrared observations of comet Kohoutek has been carried out on the basis of silicate grain models. The 'observed' grain temperature has been obtained as a function of the heliocentric distance, and it is compared with the expected distribution. In the visible region, one requires for the refractive index, (m = n-ik), n of about 1.6 and k less than 0.05. The total number of grains varies essentially as the inverse square of radial distance; the size of the particles in the antitail of the comet Kohoutek is greater than 5 microns. The ratio of infrared flux from grains to the incident solar flux at wavelengths of a few microns is calculated.

Swamy, K. S. K.↗
NASA NTRS1980

Sodium D-line emission in Comet West /1975n/ and the sodium source in comets

A spectrum of the sodium D-line emission from Comet West (1975n) taken at heliocentric distance 1.4 AU is analyzed by comparing the D-line brightness to that in the underlying continuum. Using the observations of this comet by Ney and Merrill, it is found that the dust grains which dominate the visible and infrared continua are too cool to provide the observed sodium atoms through evaporation of sodium metal or a sodium compound from grain surfaces. Though sodium metal may evaporate from a small-grain component, it is suggested that molecules embedded in the volatile nuclear matrix are a more plausible source of sodium. The relationship between this source and the interstellar sodium abundance is discussed.

Oppenheimer, M.↗
NASA NTRS1981

Dust emission from comets at large heliocentric distances. I - The case of comet Bowell /1980b/

Alternative processes of dust emission from comets at large heliocentric distances are considered, in order to explain the dust coma observed in comet Bowell (1980b) at a heliocentric distance as large as 7.17 AU. It is shown that the electrostatic blow-off of dust from a charged, H2O-dominated nucleus having a layer of loose, fine dust may be the formation process of the dust coma, with the coma size expected from the process being comparable to the observed value and the dust grain size being equal to or less than 0.4 microns in size. The upper limit for the total mass in the coma is 3.9 x 10 to the 8th g, and the spatial extension less than 10,000 km. The observed activity may alternatively be due to dust entrainment by the sublimating gas from a CO2-dominated nucleus.

Houpis, H. L. F.↗
NASA NTRS1982

Vaporization in Comets; outbursts from Comet Schwassmann-Wachmann 1

Revised estimates are presented which show that the total mass and kinetic energy in a typical Comet P/Schassmann-Wachmann 1 outburst are lower than previously estimated, and that this mass is comparable to the mass of gas vaporized, as inferred from recent observations of CO(+) in this comet. The storage of energy suggested by many authors is therefore not neccessary. A simple equilibrium vaporization of CO2 or CO which is suddenly exposed, on a nucleus that is otherwise primarily composed of H2O, is proposed. Under these conditions, calculations of the variation of vaporization with rotational phase indicate that the mechanism can quantitatively produce outbursts of the size observed.

Cowan, J. J.↗
NASA NTRS1973

Identification of comet nucleus from comet coma.

The study of comets is of important scientific value as part of the exploration of the solar system. This paper proposes a method, called 'stationary target identification,' to detect the nucleus within the coma. The method makes use of the fact that the coma is ever expanding about the nucleus. Therefore, when a radar beam is used for detection, the coma particles will produce a return signal that is Doppler shifted. The effects of the spatial extent of the coma and Doppler bandwidth of the coma returns upon the required data processing are considered. Also different methods of implementation are considered.-

Brock, H. I.↗
NASA NTRS1978

New osculating orbits for 110 comets and analysis of original orbits for 200 comets

Osculating orbits are presented for 110 nearly parabolic comets. Combining these with selected orbit determinations from other sources, a total of 200 orbits are considered where the available observations yield a result of very good (first-class) or good (second-class) quality. For each of these, the original and future orbits (referred to the barycenter of the solar system) are calculated. The Oort effect (a tendency for original reciprocal semimajor axis values to range from zero to +100 millionths per AU) is clearly seen among the first-class orbits but not among the second-class orbits. Modifications in original reciprocal semimajor axis values due to the effects of nongravitational forces are considered.

Marsden, B. G.↗