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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Extinction of the Stagnation Point Diffusion Flame: Effect of Conductive Heat Loss into Solid Interior

The flammability boundary of a solid is U-shaped with the ordinate as ambient oxygen percentage (or total pressure) and the abscissa represents flow velocity, gravity level, stretch rate, etc. The left side of the flammability boundary is the quenching branch, and the right side is the blow-off branch. Quenching is due to a weak flame whose heat release from combustion cannot overcome the excessive heat losses from, for example, radiation. Blow-off is due to a short gas residence time that is smaller than the chemical reaction time (traditionally referred to as the small Damköhler number effect). For thick solids, the heat conduction into the solid interior has a long transient after ignition before the solid temperature reaches the steady state. During this slow transient, there is excessive (i.e. more than that at the steady state) gas phase heat conduction into the solid interior. From the viewpoint of the quasi-static gaseous flame, this is an additional heat loss that will affect the gas flame's flammability. In this work, a previously developed one-dimensional axisymmetric stagnation-point diffusion flame model is extended to account for the excessive heat loss into the solid beyond the steady burning state. A non-dimensional excessive conductive heat loss parameter Ψ is defined in the paper to account for the transient solid effect. For each Ψ, the gas phase is considered reaching a quasi-steady state. Extensive numerical computations have been performed to determine the extinction boundary and the characteristics of near-limit flames. The U-shaped flammability boundary is now a series of boundaries with Ψ as a parameter. Flame structures under the same environment condition but with different Ψ are compared. For a given oxygen ambient, the extinction boundary Ψ vs stretch rate is an inverted U-shape. The boundary consists of a blowoff branch and a radiative quenching branch. Extensive computed data including flame and pyrolysis temperatures, burning rate, flame standoff distance, species concentration, and reaction rate are presented along the extinction boundaries. Heat balance analysis is performed for both the gas phase and the gas-solid interface. Along the extinction boundary, the relative importance of conduction, convection, radiation, and chemical reaction are analyzed in detail.

Stagnation point diffusion flame↗
NASA NTRSDate not supplied

Aerial Vehicle Routing and Scheduling for UAS Traffic Management: A Hybrid Monte Carlo Tree Search Approach

We present the Multi-Route Weighted Package Delivery Problem (MRWPDP) and a scalable solution methodology as a major step towards enabling an airspace deconfliction service for drone delivery operations. The problem is motivated by Strategic deconfliction under the FAA’s “Unmanned Aircraft Systems Traffic Management” Concept of Operations. MRWPDP falls under a class of vehicle routing and scheduling problems, and as such is NP-Hard. In MRWPDP, a graph network is given which consists of depots, drop-off sites, and multiple routes connecting the two. In addition, routes are weighted by the associated ground risk and total travel distance for package delivery. The goal is to optimally schedule the departure time and assign routes to a known set of vehicles at the depot. We propose a heuristic solution to the problem by borrowing techniques from Mixed Integer Linear Programming (MILP), Constraint Programming, and Monte Carlo Tree Search (MCTS). The resulting hybrid framework is MCTS with Bound-and-Prune (BP) and rapid simulated updates (U), or MCTS-BP-U. This approach is able to quickly provide a feasible solution for MRWPDP, even for large problem instances up to 1000 vehicles. We provide a MILP formulation of MRWPDP and compare its performance against MCTS-BP-U in terms of solution quality. An agent-based model simulation is conducted as a final step to validate the efficacy of our approach.

air traffic scheduling↗
NASA NTRSDate not supplied

Aerial Vehicle Routing and Scheduling for UAS Traffic Management: A Hybrid Monte Carlo Tree Search Approach

We present the Multi-Route Weighted Package Delivery Problem (MRWPDP) and a scalable solution methodology as a major step towards enabling an airspace deconfliction service for drone delivery operations. The problem is motivated by Strategic deconfliction under the FAA’s “Unmanned Aircraft Systems Traffic Management” Concept of Operations. MRWPDP falls under a class of vehicle routing and scheduling problems, and as such is NP-Hard. In MRWPDP, a graph network is given which consists of depots, drop-off sites, and multiple routes connecting the two. In addition, routes are weighted by the associated ground risk and total travel distance for package delivery. The goal is to optimally schedule the departure time and assign routes to a known set of vehicles at the depot. We propose a heuristic solution to the problem by borrowing techniques from Mixed Integer Linear Programming (MILP), Constraint Programming, and Monte Carlo Tree Search (MCTS). The resulting hybrid framework is MCTS with Bound-and-Prune (BP) and rapid simulated updates (U), or MCTS-BP-U. This approach is able to quickly provide a feasible solution for MRWPDP, even for large problem instances up to 1000 vehicles. We provide a MILP formulation of MRWPDP and compare its performance against MCTS-BP-U in terms of solution quality. An agent-based model simulation is conducted as a final step to validate the efficacy of our approach.

air traffic scheduling↗
NASA NTRSDate not supplied

High-Altitude ADS-B/GPS LPV Flight Tests on a NASA ER-2 Research Airplane

The research presented in this paper describes the conceptual design of a system architecture that integrates Automatic Dependent Surveillance-Broadcast (ADS-B) and Global Positioning System (GPS) Localizer Performance Vertical (LPV) guidance technology onto a unique high-altitude research airplane: a United States Air Force (USAF) / Lockheed Martin (Bethesda, Maryland) Aeronautics U-2S airplane. The design features modern display capabilities to provide air-to-air surveillance and precision navigation, to adhere to Federal Aviation Administration (FAA) certification standards for operations in upper Class E airspace. The National Aeronautics and Space Administration (NASA) variant of the U-2S, now called the Earth Resources (ER-2) airplane, remains unrivaled in the art of sustained high-altitude flight for scientific expeditions. Capable of routinely cruising above flight level (FL) 650 that had been considered, at inception, the domain of only the most elite experimental research aircraft types. Nicknamed the Dragon Lady, this U-2S research testbed is still one of the most advanced aircraft in the world. The exceptional military design of the vehicle, security guidelines, and the performance envelope of the ER-2 posed unique challenges to the integration of modern civilian avionics. ADS-B epitomizes the next generation of surveillance technology, incorporating both air and ground aspects. ADS-B provides air traffic control (ATC) with a more accurate picture of the three-dimensional positioning of aircraft in various phases of flight, including en route, terminal, approach, and ground operations. The airborne surveillance system broadcasts its identification, position, altitude, velocity, and other information. GPS LPV represents a significant advancement in aviation technology, emphasizing the pivotal role that GPS and Performance-Based Navigation concepts will play in the foreseeable future. This technology represents a shift from sensor-based navigation to performance-based navigation, allowing for more flexible and efficient use of airspace. This research described herein is structured as follows: Section II, “Systems Background,” provides a systems background and description of an ADS-B and GPS LPV system equipped on the high-altitude ER-2 research airplane to satisfy the FAA airworthiness requirements for high-altitude flight operations. Section III, “Flight Test System,” describes the flight-test airplane systems. Section IV, “Analysis of GPS SBAS, Safety, and Ground Tests,” provides an overview of the GPS Satellite-Based Augmentation System (SBAS) and an analysis of the GPS LPV metrics, safety, and ground tests. Section V, “High-Altitude Flight Tests,” describes the high-altitude flight tests, including 3 flight-test results, analysis, human factors, and lessons learned. Section VI, the conclusion, draws insights from the lessons learned, discusses the design challenges associated with ADS-B and GPS LPV, and showcases the paramount significance of these pivotal technologies in aircraft surveillance and navigation.

Ricardo A. Arteaga↗
NASA NTRSDate not supplied

207Pb-206Pb Geochronology and Microstructures of Phosphates From Apollo 14 and 15 Soils

Phosphates (apatite and merrillite) are common accessory minerals in many Apollo basalt and regolith samples. Phosphates typically have lower closure temperatures than their companion accessory phase zircon for their U-Pb and (U-Th)/He geochronologic systems [e.g., 1, 2]. As such, the ages of phosphates in impact melt-bearing breccias have typically been used to constrain the ages of impact events [3]. Phosphates have also served as anchors for 207Pb-206Pb isochrons allowing for precise ages of basaltic samples to be determined [4]. Apatite is also a reservoir for volatile species (e.g., F, Cl, OH, S) [e.g., 5, 6] which are important for investigating the formation and evolution of the lunar interior [7-11]. Recent work by [11] and [12] has shown that deformation and exposure to high temperatures, especially those in impact environments, can influence both apatite chronology and chemistry. Here we present the first chronology and microstructure results of a large consortium study aimed at unraveling the impact and endogenous volatile record of phosphates extracted from lunar soils. These soils potentially sample a larger range of lithologies than the rocks returned by Apollo astronauts, and should, therefore, represent a more global phosphate record. For more information on low temperature (U-Th)/He thermochronology, please see the companion abstract [13].

C A Crow↗
NASA NTRS1985

Applications of variational principles in computing rotational flows

Ecer and Akay (1983) have developed a variational formulation of rotational flow for Euler equations. The present paper provides a summary of these developments. The considered variational formulation provides a transformation of a type considered by Clebsch (1859). In this transformation, a new set of variables replaces the more commonly used primitive variables u(i), rho and p. Here, u(i) denotes the velocity components, while rho is the density, and p the pressure. The employed transformation produces a natural uncoupling of the equations when written in a quasi-linear form. After obtaining the governing equations in terms of the 'Clebsch variables', a solution scheme developed for calculating steady flows is discussed. Attention is given to numerical solutions of Euler equations based on the derived variational principles, and a study of inviscid, separated flows is conducted.

Ecer, A.↗
NASA NTRS2001

High- and low-LET induced chromosome damage in human lymphocytes: a time-course of aberrations in metaphase and interphase

PURPOSE: To investigate how cell-cycle delays in human peripheral lymphocytes affect the expression of complex chromosome damage in metaphase following high- and low-LET radiation exposure. MATERIALS AND METHODS: Whole blood was irradiated in vitro with a low and a high dose of 1 GeV u(-1) iron particles, 400MeV u(-1) neon particles or y-rays. Lymphocytes were cultured and metaphase cells were collected at different time points after 48-84h in culture. Interphase chromosomes were prematurely condensed using calyculin-A, either 48 or 72 h after exposure to iron particles or gamma-rays. Cells in first division were analysed using a combination of FISH whole-chromosome painting and DAPI/ Hoechst 33258 harlequin staining. RESULTS: There was a delay in expression of chromosome damage in metaphase that was LET- and dose-dependant. This delay was mostly related to the late emergence of complex-type damage into metaphase. Yields of damage in PCC collected 48 h after irradiation with iron particles were similar to values obtained from cells undergoing mitosis after prolonged incubation. CONCLUSION: The yield of high-LET radiation-induced complex chromosome damage could be underestimated when analysing metaphase cells collected at one time point after irradiation. Chemically induced PCC is a more accurate technique since problems with complicated cell-cycle delays are avoided.

Non-NASA Center↗
NASA NTRS1962

BUCKLING AND POST-BUCKLING OF ELASTIC SHELLS

Some theoretical investigations of buckling of elastic shells are surveyed in this report. Only geometrically perfect shells are considered; initial dents and out-of-roundness are not taken into account. Several questions raised by the studies are: (a) Under what conditions is the infinitesimal theory of buckling of shells adequate? (b) How does the energy theory of buckling of shells correlate with the method based on equilibrium equations for bending moments, tensions, and shears in a buckled configuration? (c) How important are nonlinear terms in the tangential displacements u, v in the strain-displacement relations for buckling and post-buckling studies? (d) How important are the boundary conditions for u, v in affecting stability? (e) If a condition of snap-through is approached, how much external work is required to push the shell "over the hump" into the buckled configuration? (f) How reliable are mathematical approximations used previously in the infinitesimal theory of buckling of shells? Tentative and incomplete answers to some of these questions are suggested.

ELASTIC BUCKLING↗
NASA NTRS1963

AN AEROTHERMOCHENMCAL ANALYSIS OF EROSIVE BURNING OF SOLID PROPELLANT

In a solid propellant rocket of a side burning type, the flow rate of the hot combustion gases parallel to the burning surface is approximately proportional to the distance from the leading edge of the propellant. In the present paper, therefore, the erosive burning of the solid propellant is analyzed by tile boundary-layer approximation in aerothermochemistry for the case where the velocity, u ∞ , of the hot combustion gas stream outside the boundary layer increases linearly with the distance, x, from the leading edge of the propellant, i.e., u ∞ = Gx, and the effects of the hot gas stream on the burning rate of the propellant are examined.

GAS STREAM↗
NASA NTRS1960

Tracking and Orbit-Determination Program of the Jet Propulsion Laboratory

The lunar-probe tracking program at the Jet Propulsion Laboratory has two prime objectives: (1) provide real-time predictions of the direction of the probe from various observation stations; (2) establish a reliable trajectory corresponding to the actual flight path of the probe. The tracking program, although developed for use with lunar probes, can be used for interplanetary probes if certain modifications are made. The program, as developed for the IBM 704 digital computer, has two distinct phases. First, the equations of motion and the variational equations are integrated to each observation time where the elements of the equation A (sub u) equals b [linearization of the maximum likelihood equations] are computed. The second phase is concerned with the solution of a specified subset of A (sub u) equals b. Flexibility and ease of operation have been major objectives in writing the 704 program. The number of data points and tracking stations that may be used is limited only by computing time and core storage. Input formats and operating instructions are presented for utilizing the various computational options available in the program.

Carr, Russell E.↗
NASA NTRS1960

Aerospace medicine and biology. an annotated bibliography, 1954 literature, volume iii

While this third volume of the bibliography was in preparation, a number of changes and new developments took place which, it is hoped, will be instrumental in furthering the bibliography's main objective: to provide as rapidly as possible comprehensive coverage of the aerospace-medical and bio-astronautical literature. To begin with, it will be noted that the title of the compilation has been changed from Aviation Medicine to Aerospace Medicine and Biology. This will bring into relief the fact that the general subject scope of the bibliography has been expanded to include new areas of interest in space-medical and space-biological research. Thus, to the subject fields heretofore covered by the bibliography (a full listing of which may be found in the Preface to Volume 2) new ones have been added, such as Biological Rhythms, Biological Orientation, Closed Ecological Systems, Physiological and Psychological Effects of Heat, Cold, Isolation, Restraint, and many others. Another important change was administrative in nature. Sponsorship of the bibliography for the fiscal year 1959/60 was taken over by the U. S. Advanced Research Project Agency (ARPA), the U. S. Aeronautics and Space Administration (NASA), and the Defense Research Board of Canada. Under a substantially increased budget, the Library of Congress was enabled to produce two volumes during the fiscal year. The Library also agreed to prepare selected abstracts from the current aerospace and bio-astronautic literature, which are published monthly in Aerospace Medicine, the official organ of the Aerospace Medical Association.*) If the present rate of production can be maintained, it will be possible to bring the bibliography up to date within about three years. In format, style, and arrangement, this volume follows closely the preceding ones. References are arranged alphabetically by author; abstracts are informative; and full bibliographic information is provided, including foreign and translated titles, volume and issue numbers, place of publication (if foreign), inclusive paging, full dates, and library call numbers or other location symbols. While the bulk of the publication is devoted to journal articles, reports, and monographs published during the year 1954, items published in 1952 or 1953 not included in the preceding volumes have been incorporated in this volume. For quick identification, the publication years of these off-year references have been printed next to the first author's name. As before, cumulated corporate and secondary author and subject indexes are included, the latter being revised and enlarged considerably, in keeping with the over-all expansion of subject scope.

Aerospace medicine↗
NASA NTRS1968

Distillation device supplies cesium vapor at constant pressure

Distillation apparatus in the form of a U tube supplies small amounts of pure cesium vapor at constant pressure to a thermionic converter. The upstream leg of the U tube is connected to a vacuum pump to withdraw noncondensable impurities, the bottom portion serves as a reservoir for the liquid cesium.

Basiulis, A.↗
NASA NTRS1951

Wind-tunnel investigation of the descent characteristics of bodies of revolution simulating anti-personnel bombs

An investigation has been conducted in the Langley 20-foot free spinning tunnel to study the relative behavior in descent of a number of homogeneous balsa bodies of revolution simulating anti-personnel bombs with a small cylindrical exploding device suspended approximately 10 feet below the bomb. The bodies of revolution included hemispherical, near-hemispherical, and near-paraboloid shapes. The ordinates of one near-paraboloid shape were specified by the Office of the Chief of Ordnance, U. S. Army. The behavior of the various bodies without the cylinder was also investigated. The results of the investigation indicated that several of the bodies descended vertically with their longitudinal axis, suspension line, and small cylinder in a vertical attitude,. However, the body, the ordinates of which had been specified by the Office of the Chief of Ordnance, U. S. Army, oscillated considerably from a vertical attitude while descending and therefore appeared unsuitable for its intended use. The behavior of this body became satisfactory when its center of gravity was moved well forward from its original position. In general, the results indicated that the descent characteristics of the bodies of revolution become more favorable as their shapes approached that of a hemisphere.

Sher, S. H.↗
NASA NTRS1971

Dynamics of heat-pipe reactors

A split-core heat pipe reactor, fueled with either U(233)C or U(235)C in a tungsten cermet and cooled by 7-Li-W heat pipes, was examined for the effects of the heat pipes on reactor while trying to safely absorb large reactivity inputs through inherent shutdown mechanisms. Limits on ramp reactivity inputs due to fuel melting temperature and heat pipe wall heat flux were mapped for the reactor in both startup and at-power operating modes.

Niederauer, G. F.↗
NASA NTRS1971

Mini gas-core propulsion concept

A propulsion concept is presented that can achieve specific impulses of 1000 to 2000 seconds for thrust levels on the order of 100 pounds (445 N) and maintain a small (1.22 m) reactor diameter for a total power-plant weight of approximately 10,000 kg. The concept combines a small (0.61 m) diameter spherical gas core centrally located, followed by a moderator (BeO-15 cm), surrounded by a driver fuel region and contained in a pressure vessel (ID of 1.22 m). Best results (i.e., highest ratio of cavity power to total power) occur with U-233 isotope as the fuel in both the cavity and the driver, although U-235 can also be used. Concept may also have application in the testing of a gas-core reactor and MHD devices and in high temperature-pressure materials research.

Hyland, R. E.↗
NASA NTRS1972

Excitation of the Werner bands of H2 by electron impact

Absolute cross sections for the excitation of the H2 Werner band system were measured from energy threshold to 300 eV for electron impact on H2. The bands were observed in emission in the wavelength region 1100A to 1250A. The measured cross sections were compared with published transition probabilities, leading to the conclusion that the Werner bands are suitable as the basis for a relative spectral response calibration only when the bands are observed under sufficiently high resolution. The effect of the perturbation between the C 1Pi u and B 1 Sigma-u states of the hydrogen molecule was clearly observed in anomalies in the rotational intensity distribution in bands of the (3 v '') progression.

Stone, E. J.↗