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  • MECHANICAL ENGINEERING  (3)
  • Astrophysics  (2)
  • Metallic Materials  (2)
  • 1
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    Mass drivers. 3: Engineering (1979)
    In:  CASI
    Details
    Publication Date: 2006-01-12
    Description: The last of a series of three papers by the Mass-Driver Group of the 1977 Ames Summer Study is presented. It develops the engineering principles required to implement the basic mass-driver. Optimum component mass trade-offs are derived from a set of four input parameters, and the program used to design a lunar launcher. The mass optimization procedures is then incorporated into a more comprehensive mission optimization program called OPT-4, which evaluates an optimized mass-driver reaction engine and its performance in a range of specified missions. Finally, this paper discusses, to the extent that time permitted, certain peripheral problems: heating effects in buckets due to magnetic field ripple; an approximate derivation of guide force profiles; the mechanics of inserting and releasing payloads; the reaction mass orbits; and a proposed research and development plan for implementing mass drivers.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Ames Res. Center Space Resources and Space Settlements; p 119-157
    Format: text
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  • 2
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    Mass drivers. 1: Electrical design (1979)
    In:  CASI
    Details
    Publication Date: 2006-01-12
    Description: A mass driver is an electrical device used to accelerate payloads of any material to a high velocity. Small vehicles (called buckets) containing superconducting coils carry the payloads. These buckets are accelerated by pulsed magnetic fields, timed by information on their position, and are guided by induced magnetic fields set up in a surrounding guideway. Upon reaching the correct velocity, the buckets release their payloads, then they are slowed for recirculation to be reused. A rationale is presented that leads to a relatively simple and near-optimum design, as well as basic programs for calculating acceleration. The transverse oscillation frequencies are found to be invariant to guideway transverse dimensions.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Ames Res. Center Space Resources and Space Settlements; p 87-100
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  • 3
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    Mass drivers. 2: Structural dynamics (1979)
    In:  CASI
    Details
    Publication Date: 2006-01-12
    Description: Various structural and dynamical problems related to both small-scale forces between the drive coils and within the bucket structure as well as the overall combined large-scale dynamical interaction of the bucket stream and MDRE (Mass Drive Reaction Engine) structure are examined. The large-scale dynamics appear weakly stable. Finally, MDRE operation in an inverse-square-law gravitational field is discussed and the required curved shape of the guideway is computed.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Ames Res. Center Space Resources and Space Settlements; p 101-118
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  • 4
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    A Cepheid Distance to NGC 4603 in the Centaurus Cluster (1999)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: In an attempt to use Cepheid variables to determine the distance to the Centaurus cluster, we have obtained images of NGC 4603 with the Hubble Space Telescope for 9 epochs (totalling 24 orbits) over 14 months in the F555W filter and 2 epochs (totalling 6 orbits) in the F814W filter.
    Keywords: Astrophysics
    Type: The Astrophysical Journal
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  • 5
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    Extreme Emission Line Galaxies in CANDELS: Broad-Band Selected, Star-Bursting Dwarf Galaxies at Z greater than 1 (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: We identify an abundant population of extreme emission line galaxies (EELGs) at redshift z approx. 1.7 in the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) imaging from Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3). 69 EELG candidates are selected by the large contribution of exceptionally bright emission lines to their near-infrared broad-band magnitudes. Supported by spectroscopic confirmation of strong [OIII] emission lines . with rest-frame equivalent widths approx. 1000A in the four candidates that have HST/WFC3 grism observations, we conclude that these objects are galaxies with approx.10(exp 8) Solar Mass in stellar mass, undergoing an enormous starburst phase with M*/M* of only approx. 15 Myr. These bursts may cause outflows that are strong enough to produce cored dark matter profiles in low-mass galaxies. The individual star formation rates and the co-moving number density (3.7x10(exp -4) Mpc(sup -3) can produce in approx.4 Gyr much of the stellar mass density that is presently contained in 10(exp 8) - 10(exp 9) Solar Mass dwarf galaxies. Therefore, our observations provide a strong indication that many or even most of the stars in present-day dwarf galaxies formed in strong, short-lived bursts, mostly at z 〉 1.
    Keywords: Astrophysics
    Type: GSFC.JA.6335.2012
    Format: application/pdf
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  • 6
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    A Review Of Modelling Small-Crack Behavior And Fatigue-Life Predictions For Aluminum Alloys (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The small-crack effect, where small fatigue cracks grow faster and at lower stress-intensity factors than large cracks, has been found to be significant for many materials and loading conditions. In this paper, plasticity effects and crack-closure modelling of small fatigue cracks are reviewed. A crack-closure model with a cyclic-plastic zone-corrected effective stress-intensity factor range (related to the cyclic J-integral) and microstructural data on crack-initiation sites were used to calculate small-crack growth rates and fatigue lives for unnotched and notched specimens made of two aluminum alloys. The crack-closure transient from the plastic wake was shown to be the dominant cause of the small-crack effect and plasticity effects on the cyclic-plastic zone-corrected stress-intensity factor range were negligible except at extremely high stress levels. Small-crack growth rates and fatigue lives under both constant-amplitude and spectrum loading from tests and analyses agreed well.
    Keywords: Metallic Materials
    Type: NASA-TM-111551 , NAS 1.15:111551 , (ISSN 8756-758X)
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  • 7
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    Fatigue Analyses Under Constant- and Variable-Amplitude Loading Using Small-Crack Theory (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: Studies on the growth of small cracks have led to the observation that fatigue life of many engineering materials is primarily "crack growth" from micro-structural features, such as inclusion particles, voids, slip-bands or from manufacturing defects. This paper reviews the capabilities of a plasticity-induced crack-closure model to predict fatigue lives of metallic materials using "small-crack theory" under various loading conditions. Constraint factors, to account for three-dimensional effects, were selected to correlate large-crack growth rate data as a function of the effective stress-intensity factor range (delta-Keff) under constant-amplitude loading. Modifications to the delta-Keff-rate relations in the near-threshold regime were needed to fit measured small-crack growth rate behavior. The model was then used to calculate small-and large-crack growth rates, and to predict total fatigue lives, for notched and un-notched specimens under constant-amplitude and spectrum loading. Fatigue lives were predicted using crack-growth relations and micro-structural features like those that initiated cracks in the fatigue specimens for most of the materials analyzed. Results from the tests and analyses agreed well.
    Keywords: Metallic Materials
    Type: NASA/TM-1999-209329 , L-17862 , ARL-TR-2001 , NAS 1.15:209329
    Format: application/pdf
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