Results for “Probability of Collision” — Page 20

NASA NTRS1973

Condensation in CO2 free jet expansions. II - Growth of small clusters.

An investigation into the kinetics of molecular clustering processes which occur in the highly supersaturated vapor of a CO2 free jet is described. Terminal cluster concentrations in expansions from room temperature and reservoir pressures in the range from 400 to 900 torr were determined for trimeric CO2 for nozzle diameters of .0076 cm, .015 cm, and .023 cm and in the case of CO2 tetramer and pentamer for .015 cm nozzle diameter. The measurements were made mass spectrometrically in a supersonic molecular beam apparatus. A kinetic analysis was developed from an extension of the critical nucleus concept of nucleation theory and rate equations based on intermolecular collisions. The observed cluster populations could be accounted for by the theory by adopting sticking probabilities of approximately .03 for monomer impinging on dimer, trimer, and tetramer.

Dorfeld, W. G.↗

NASA NTRS1980

Physical loss of long-period comets

Loss of long-period comets from the solar system through a variety of physical processes is investigated. It is shown that planetary collision, defined as a comet passing within the Roche radius of any planet, has a probability of 1.35 x 10 to the -7th per perihelion passage for a long-period comet on a randomly oriented orbit. Sublimation of all volatiles for a one-kilometer radius hydrate ice nucleus would require on the order of 600 to 27,600 perihelion passages, depending on the surface albedo and assuming a perihelion distance of one astronomical unit. Analysis of observational records indicates that for dynamically 'new' comets in the Oort-Schmidt sense there is about a 10% probability of the comet randomly disrupting on its first perihelion passage. This probability drops to 4% per perihelion passage for older long-period comets, and less than 1% for short-period comets. The consequences of these loss mechanisms when incorporated into Monte-Carlo studies of long-period comet evolution are also discussed.

Weissman, P. R.↗

NASA NTRS1984

Theory and modeling of atmospheric turbulence, part 1

The cascade transfer which is the only function to describe the mode coupling as the result of the nonlinear hydrodynamic state of turbulence is discussed. A kinetic theory combined with a scaling procedure was developed. The transfer function governs the non-linear mode coupling in strong turbulence. The master equation is consistent with the hydrodynamical system that describes the microdynamic state of turbulence and has the advantages to be homogeneous and have fewer nonlinear terms. The modes are scaled into groups to decipher the governing transport processes and statistical characteristics. An equation of vorticity transport describes the microdynamic state of two dimensional, isotropic and homogeneous, geostrophic turbulence. The equation of evolution of the macrovorticity is derived from group scaling in the form of the Fokker-Planck equation with memory. The microdynamic state of turbulence is transformed into the Liouville equation to derive the kinetic equation of the singlet distribution in turbulence. The collision integral contains a memory, which is analyzed with pair collision and the multiple collision. Two other kinetic equations are developed in parallel for the propagator and the transition probability for the interaction among the groups.

Source record↗

NASA NTRSDate not supplied

Sensitivity Study of Dust-Laden Flows in the DLR GBK Facility using the DUST-US3D Framework

The current work is aimed at performing a detailed numerical sensitivity study of dust-laden flow through the DLR GBK facility using the DUST-US3D frame-work. A three-dimensional volumetric grid of the GBK facility with emphasis on a precise reproduction of the dust particle injection process and the transit of particles through the facility has been developed for this work. The sensitivity study on this grid involves varying particle injection parameters such as the diameter distribution probability function, input velocity magnitude, and input velocity direction and accounting for particle-particle collisions. The resulting impact on particle-related statistics such as the dust mass flow rate is studied, and comparisons made to experimental data.

Dusty Flows↗

NASA NTRS1999

Predicting Close Approaches and Estimating Impact Probabilities for Near Earth Objects

Recent popular movies have raised public consciousness of the very real possibility of a comet or asteroid collision with the Earth.

Near↗

NASA NTRS2016

Architecture for Mitigating Short-Term Warning Cosmic Threats: READI Project

Earth is being constantly bombarded by a large variety of celestial bodies and has been since its formation 4.5 billion years ago. Among those bodies, mainly asteroids and comets, there are those that have the potential to create large scale destruction upon impact. The only extinction-level impact recorded to date was 65 million years ago, during the era of dinosaurs. The probability of another extinction-level, or even city-killer, impact may be negligible, but the consequences can be severe for the biosphere and for our species. Therefore it is highly imperative for us to be prepared for such a devastating impact in the near future, especially since humanity is at the threshold of wielding technologies that allow us to do so. Majority of scientists, engineers, and policymakers have focused on long-term strategies and warning periods for Earth orbit crossing Near-Earth Objects (NEOs), and have suggested methods and policies to tackle such problems. However, less attention has been paid to short warning period NEO threats. Such NEOs test current technological and international cooperation capabilities in protecting ourselves, and can create unpredictable devastation ranging from local to global scale. The most recent example is the Chelyabinsk incident in Russia. This event has provided a wakeup call for space agencies and governments around the world towards establishing a Planetary Defense Program. The Roadmap for EArth Defense Initiative (READI) is a project by a team of international, intercultural, and interdisciplinary participants of the International Space University's Space Studies Program 2015 hosted by Ohio University, Athens, OH proposing a roadmap for space agencies, governments, and the general public to tackle NEOs with a short warning before impact. Taking READI as a baseline, this paper presents a technical description of methodologies proposed for detection and impact mitigation of a medium-sized comet (up to 800m across) with a short-warning period of two years on a collision course with Earth. The hypothetical comet is on a highly-inclined orbit having a high probability for Earth impact after its perihelion. For detection, we propose a space-based infrared detection system consisting of two satellites located at the Earth-Moon Lagrange points L1 and L2 coupled with space observatories, like the James Webb telescope and the Centennial telescope. These telescopes are supported by ground-based telescopes, like the Arecibo and Green Bank telescope, in the search for NEOs. Upon detection, the comet is tracked constantly using space- and ground-based telescopes. The deflection system is two-pronged, firstly involving the use of a high energy Directed Energy Laser Terminals (DELT) placed at Sun-Earth Lagrange points L4 and L5 so as to initiate and increase the ablation rate of the comet and deviate it from its collision trajectory, and secondly by the Hypervelocity Comet Intercept Vehicle (HCIV), a space-borne system combining a kinetic impactor with a thermonuclear device. The policy and international collaboration aspects to implement these methods are also outlined in the paper. The techniques mentioned could also be applied to mitigate medium-to-large sized asteroids (up to 2km across).

Laser Applications↗

NASA NTRS2016

Planetary Defense Architecture for Mitigating Short-Term Warning Cosmic Threats: READI Project

Earth is being constantly bombarded by a large variety of celestial bodies and has been since its formation 4.5 billion years ago. Among those bodies, mainly asteroids and comets, there are those that have the potential to create large scale destruction upon impact. The only extinction-level impact recorded to date was 65 million years ago, during the era of dinosaurs. The probability of another extinction-level, or even city-killer, impact may be negligible, but the consequences can be severe for the biosphere and for our species. Therefore it is highly imperative for us to be prepared for such a devastating impact in the near future, especially since humanity is at the threshold of wielding technologies that allow us to do so. Majority of scientists, engineers, and policymakers have focused on long-term strategies and warning periods for Earth orbit crossing Near-Earth Objects (NEOs), and have suggested methods and policies to tackle such problems. However, less attention has been paid to short warning period NEO threats. Such NEOs test current technological and international cooperation capabilities in protecting ourselves, and can create unpredictable devastation ranging from local to global scale. The most recent example is the Chelyabinsk incident in Russia. This event has provided a wakeup call for space agencies and governments around the world towards establishing a Planetary Defense Program. The Roadmap for EArth Defense Initiative (READI) is a project by a team of international, intercultural, and interdisciplinary participants of the International Space University's Space Studies Program 2015 hosted by Ohio University, Athens, OH proposing a roadmap for space agencies, governments, and the general public to tackle NEOs with a short warning before impact. Taking READI as a baseline, this paper presents a technical description of methodologies proposed for detection and impact mitigation of a medium-sized comet (up to 800m across) with a short-warning period of two years on a collision course with Earth. The hypothetical comet is on a highly-inclined orbit having a high probability for Earth impact after its perihelion. For detection, we propose a space-based infrared detection system consisting of two satellites located at the Earth-Moon Lagrange points L1 and L2 coupled with space observatories, like the James Webb telescope and the Centennial telescope. These telescopes are supported by ground-based telescopes, like the Arecibo and Green Bank telescope, in the search for NEOs. Upon detection, the comet is tracked constantly using space- and ground-based telescopes. The deflection system is two-pronged, firstly involving the use of a high energy Directed Energy Laser Terminals (DELT) placed at Sun-Earth Lagrange points L4 and L5 so as to initiate and increase the ablation rate of the comet and deviate it from its collision trajectory, and secondly by the Hypervelocity Comet Intercept Vehicle (HCIV), a space-borne system combining a kinetic impactor with a thermonuclear device. The policy and international collaboration aspects to implement these methods are also outlined in the paper. The techniques mentioned could also be applied to mitigate medium-to-large sized asteroids (up to 2km across).

Laser Applications↗

NASA NTRS1973

Dissociation rate of bromine diatomics in an argon heat bath

The evolution of a collection of 300 K bromine diatomics embedded in a heat bath of argon atoms at 1800 K was studied by computer, and a dissociation-rate constant for the reaction Br2 + BR + Ar yields Br + Ar was determined. Previously published probability distributions for energy and angular momentum transfers in classical three-dimensional Br2-Ar collisions were used in conjunction with a newly developed Monte Carlo scheme for this purpose. Results are compared with experimental shock-tube data and the predictions of several other theoretical models. A departure from equilibrium is obtained which is significantly greater than that predicted by any of these other theories.

Razner, R.↗

NASA NTRS1990

NGC 1614 - An IR-luminous merger but not (yet?) an active galaxy

New observations of the merging galaxy NGC 1614 are described. The system has a nuclear region of QSO-like luminosity, but shows no direct evidence for an active nucleus. It is heavily and unevenly reddened across its nucleus, while infrared imaging also shows a 'ridge' of dust. The inner spiral structure of the galaxy has normal rotation for an inclined disk, as indicated by the H-alpha emission. A linear 'tail' to the S and extended arms to the E have more positive velocities, and probably are the remains of an interacting companion and the tidal plume(s) caused by the collision. The only H I seen in emission appears to coincide with bright knots of H-alpha and forbidden O III emission of the base of the tail. The lack of direct evidence for an active nucleus indicates that if NGC 1614 is a precursor to a Seyfert-like system the AGN has not yet turned on.

Neff, S. G.↗

NASA NTRS1989

Grains charges in interstellar clouds

The charge of cosmic grains could play an important role in many astrophysical phenomena. It probably has an influence on the coagulation of grains and more generally on grain-grain collisions, and on interaction between charged particles and grains which could lead to the formation of large grains or large molecules. The electrostatic charge of grains depends mainly on the nature of constitutive material of the grain and on the physical properties of its environment: it results from a delicate balance between the plasma particle collection and the photoelectron emission, both of them depending on each other. The charge of the grain is obtained in two steps: (1) using the numerical model the characteristics of the environment of the grain are computed; (2) the charge of a grain which is embedded in this environment is determined. The profile of the equilibrium charge of some typical grains through different types of interstellar clouds is obtained as a function of the depth of the cloud. It is shown that the grain charge can reach high values not only in hot diffuse clouds, but also in clouds with higher densities. The results are very sensitive to the mean UV interstellar radiation field. Three parameters appear to be essential but with different levels of sensitivity of the charge: the gas density, the temperature, and the total thickness of the cloud.

Bel, N.↗

NASA NTRS1994

Results of critical velocity experiments with barium, strontium, and calcium releases from CRRES satellite

As part of the NASA Combined Release and Radiation Effects Satellite (CRRES) chemical release program in September 1990, two Ba and also one each Sr and Ca canisters of a boron-titanium thermite mixture, which vaporizes the element on ignition, were released near perigee after dusk in the South Pacific to study the critical velocity effect proposed by Alfven. The critical velocities of these three elements are 2.7, 3.5, and 5.4 km/s respectively, all well below the orbital velocity of 9.4 km/s. On September 10, 1990, a Sr and Ba pair (G-13, or critical ionization velocity (CIV) I) was released near Rarotonga at approximately 515 km altitude in a background electron density of 3.4 x 10(exp 6)/cu cm. On September 14, 1990, G-14 or CIV II released a Ca and Ba pair west of New Caledonia near 595 km at an electron density of 1.5 x 10(exp 6)/cu cm. Ions of all three elements were observed with low-light level imagers from two aircraft after they had transited up the magnetic field lines into the sunlight. Emissions from the spherically expanding neutral gas shells below the solar terminator, observed with cameras filtered for the Ba(+) ion line at 4554 A and also in unfiltered imagers for approximately 15 s after release, are probably due to excitation by hot electrons created in the CIV process. The ions created clearly lost much of their energy, which we now show can be explained by elastic collisions: Ba(+) + O. Inventories of the observed ions indicate yields of 0.15% and 1.84% for Ba in the first and second experiments, 0.02% for Sr and 0.27% for Ca. Ionization from all the releases continued along the satellite trajectory much longer (greater than 45 s) than expected for a CIV process. The ion production along the satellite track versus time typically shows a rapid rise to a peak in a few seconds followed by an exponential decrease to a level essentially constant rate. The characteristic distances for CIV I and II are 47 and 62 km, respectively. We interpret the early time rise and exponential fall to be due to CIV ionization, of 0.014% (CIV I) and 0.40% (CIV II) for the Ba releases. The later ions produced at a constant rate probably have origins from other such processes as stripping and associative ionization collisions with atmospheric constituents primarily O, and charge exchange with O(+), He(+), and H(+). We suggest that the much larger Ba ionization rate in CIV II than CIV I is due to the fact that the release occurred in the peak Ca density where hot electrons were already present.

Wescott, E. M.↗

NASA NTRS2016

Safeguarding a Lunar Rover with Wald's Sequential Probability Ratio Test

The virtual bumper is a safeguarding mechanism for autonomous and remotely operated robots. In this paper we take a new approach to the virtual bumper system by using an old statistical test. By using a modified version of Wald's sequential probability ratio test we demonstrate that we can reduce the number of false positive reported by the virtual bumper, thereby saving valuable mission time. We use the concept of sequential probability ratio to control vehicle speed in the presence of possible obstacles in order to increase certainty about whether or not obstacles are present. Our new algorithm reduces the chances of collision by approximately 98 relative to traditional virtual bumper safeguarding without speed control.

safeguarding↗

NASA NTRS1984

Coarse-grained chondrule rims in type 3 chondrites

Coarse-grained rims composed of olivine, with or without low-Ca pyroxene, occur around all types of chondrules and compound chondrules in type 3 carbonaceous chondrites and around ordinary chondrites. The dark zoned chondrules and coarse grained rims were formed by the heating of clumps of opaque matrix material to subsolidus-subliquidus temperatures in the solar nebula. The most likely source of the heat that formed the coarse grained rims is the mechanism responsible for chondrule formation. CV chondrites may have formed in a region where the chondrule formation mechanism was less efficient, probably at greater solar distances than the ordinary chondrites. Alternatively, CV chondrules may have suffered fewer particle collisions prior to agglomeration.

Rubin, A. E.↗

NASA NTRS1989

Do asteroids have satellites?

A substantial body of indirect evidence suggests that some asteroids have satellites, although none has been detected unambiguously. Collisions between asteroids provide physically plausible mechanisms for the production of binaries, but these operate with low probability; only a small minority of asteroids are likely to have satellites. The abundance of binary asteorids can constrain the collisional history of the entire belt population. The allowed angular momentum of binaries and their rate of tidal evolution limit separations to no more than a few tens of the primary's radii. Their expected properties are consistent with failure to detect them by current imaging techniques.

Weidenschilling, Stuart J.↗

NASA NTRS1985

Search for anomalous fragments produced in collisions with heavy target nuclei and in delta Z = 1 peripheral interactions

We exposed a stack of CR39 track detectors containing Ag foils to a 1.7-GeV/nucleon 56Fe beam and investigated the anomalous mean-free-path effect. Neither the whole set of 7517 nor a subset of 2542 interacting fragments produced probably in the Ag target show an effect. By combining the data of this and an earlier experiment we can also exclude an effect for 3219 interacting fragments produced in delta Z = 1 collisions.

Polyethylene Glycols↗

NASA NTRS2017

Constraints on Mechanisms of Chondrule Formation from Chondrule Precursors and Chronology of Transient Heating Events in the Protoplanetary Disk

The mineralogy, petrography, and oxygen-isotope compositions of porphyritic chondrules—dominant chondrule type in most chondrite groups—suggest formation by incomplete melting of isotopically diverse precursors during localized transient heating events in dust-rich regions of the protoplanetary disk characterized by 16O-poor compositions (D17Odust+gas~ –7‰ to +4‰) relative to the inferred Sun’s value (D17O ~ –28 ± 2‰). The chondrule precursors included Ca,Al-rich inclusions (CAIs), amoeboid olivine aggregates (AOAs), chondrules of earlier generations, fine-grained matrix-like material, and possibly fragments of pre-existing planetesimals. Like porphyritic chondrules, igneous CAIs formed by melting of isotopically diverse precursors during transient heating events, but in an isotopically distinct, solar-like reservoir of the protoplanetary disk (D17O dust + gas ~ –24‰), probably near the proto Sun. Based on a narrow range of the initial 26Al/27Alratios inferred from the internal Al-Mg isochrons in igneous CAIs, their melting started at the very beginning of Solar System formation (t0), defined by the CV CAIs with U-corrected Pb-Pb age of 4567.3 ± 0.16 Ma and the canonical 26Al/27Al ratio of (5.25 ± 0.02) ¥ 10–5, and lasted at least 0.3 Ma. The U-corrected Pb-Pb absolute and 26Al-26Mg relative ages of porphyritic chondrules from type 3 ordinary, CO, CV, and CR carbonaceous chondrites (assuming uniform distribution of 26Al in the disk at the canonical level) suggest chondrule formation started at t0 and lasted for about 4 Ma. These observations may preclude formation of the majority of porphyritic chondrules by splashing of differentiated planetesimals and by collisions between planetesimals; instead, they are consistent with melting of dust balls by bow shocks or magnetized turbulence in the disk. Some porphyritic chondrules in equilibrated (petrologic type 4–6) ordinary chondrites contain relict fragments of coarse-grained chromite, ilmenite, phosphates, and albitic plagioclase. The similar mineral assemblage is commonly observed in type 4–6 ordinary chondrites, but is absent in type 3 chondrites, suggesting these chondrules formed by incomplete melting of thermally metamorphosed ordinary chondrite material, possibly by impacts. The CB metal-rich carbonaceous chondrites contain exclusively magnesian non-porphyritic chondrules crystallized from complete melts. These chondrules formed in a gas-melt plume generated by a hypervelocity (≥20 km/s) collision between planetesimals ~4.8 Ma after t0 in a transition or a debris disk. One of the colliding bodies was probably differentiated. The CH metal-rich carbonaceous chondrites contain chondrules formed by different mechanisms. The magnesian non-porphyritic chondrules formed in the CB impact plume ~4.8 Ma after t0. The chemically diverse (magnesian, ferroan, and Al-rich) porphyritic chondrules formed by incomplete melting of isotopically diverse precursors in the protoplanetary disk, most likely prior the CB impact plume event. We conclude that there are multiple mechanisms of chondrule formation that operated over the entire life-time of the disk.

Chondrules↗

NASA NTRS1970

Dispersion discontinuities of strong collisionless shocks

Linear fluid equations are used to estimate wave train properties of strong collisionless shocks. Fast shocks exhibit several dispersion changes with increasing Mach number. For perpendicular propagation into a finite-beta plasma, an ion cyclotron radius trailing wave train exists only for (M sub F)2 is smaller than 2. Oblique fast shocks have a leading ion inertia wave train if M sub A is smaller than root of M(+)/M(-) cos theta/2 and a trailing electron inertia train if M sub A is greater than root of M(+)/M(-) cos theta/2. If the downstream sound speed exceeds the flow speed, linear wave theory predicts a trailing ion acoustic structure which probably resides within the magnetic shock. For a turbulent shock model in which an effective electron-ion collision frequency exceeds the lower hybrid frequency, ions decouple from the magnetic field; the shock wave train now trails with electron inertia and electron gyroradius lengths. Comparisons of this turbulent model and observations on the earth's bow shock are made.

Coroniti, F. V.↗

NASA NTRS1972

Comments on lunar origin.

Consideration of the tidal evolution of the earth-moon system in the light of recent published studies of lunar origin. The subjects include the factors of orbital evolution, the auxiliary Model Zero, orbital evolution along the outgoing branch, capture models, capture probability, capture with break-up, the tidal evolution of circular and elliptical fragmented rings, and precession and collisions in a ring of fragments. A numerical integration of precessions is performed for the actual nonzero mass of the moon and for a lunar distance of about 22 earth radii. A simplified Model Zero is found to compare well with Goldreich's solution (1968). It is concluded that the moon must have become freely yielding to tidal deformation at distances less than about 8 earth radii. Arguments are given in favor of the capture theory as a basis for the genesis of the moon.

Opik, E. J.↗