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  • 61.40  (3)
  • STRUCTURAL MECHANICS  (3)
  • 61.80  (2)
  • Spacecraft Design, Testing and Performance  (2)
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  • 1
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    In:  CASI
    Publication Date: 2016-06-07
    Description: Apollo project - progress and national benefits
    Keywords: STRUCTURAL MECHANICS
    Type: Proceedings of the Fourth National Conference on the Peaceful Uses of Space; NASA-SP-51
    Format: application/pdf
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  • 2
    Publication Date: 2019-06-27
    Description: Structural mechanics of deformation and fracture - responses of model viscoelastic materials to impact
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-80918
    Format: application/pdf
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  • 3
    Publication Date: 2019-07-12
    Description: The Laser Interferometer Space Antenna (LISA) is a mission designed to detect low frequency gravitational-waves. In order for LISA to succeed in its goal of direct measurement of gravitational waves, many subsystems must work together to measure the distance between proof masses on adjacent spacecraft. One such subsystem, the telescope, plays a critical role as it is the laser transmission and reception link between spacecraft. Not only must the material that makes up the telescope support structure be strong, stiff and light, but it must have a dimensional stability of better than 1 pm Hz(exp -1/2) at 3 mHz and the distance between the primary and the secondary mirrors must change by less than 2.5 micron over the mission lifetime. CFRP is the current baseline materiaL however, it has not been tested to the pico-meter level as required by the LISA mission. In this paper we present dimensional stability results, outgassing effects occurring in the cavity and discuss its feasibility for use as the telescope spacer for the LISA spacecraft.
    Keywords: Spacecraft Design, Testing and Performance
    Type: GSFC.JA.5667.2011
    Format: application/pdf
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  • 4
    Publication Date: 2019-06-27
    Description: Mechanical behavior of materials with temperature dependent viscosity, using electric analogy on nonlinear Maxwell model
    Keywords: STRUCTURAL MECHANICS
    Type: ; ACE(
    Format: text
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  • 5
    Publication Date: 2019-07-13
    Description: The LISA mission observes gravitational waves by measuring the separations between freely floating proof masses located 5 million kilometers apart with an accuracy of - 10 picometers. The separations are measured interferometrically. The telescope is an afocal Cassegrain style design with a magnification of 80x. The entrance pupil has a 40 cm diameter and will either be centered on-axis or de-centered off-axis to avoid obscurations. Its two main purposes are to transform the small diameter beam used on the optical bench to a diffraction limited collimated beam to efficiently transfer the metrology laser between spacecraft, and to receive the incoming light from the far spacecraft. It transmits and receives simultaneously. The basic optical design and requirements are well understood for a conventional telescope design for imaging applications, but the LISA design is complicated by the additional requirement that the total optical path through the telescope must remain stable at the picometer level over the measurement band during the mission to meet the measurement accuracy. We describe the mechanical requirements for the telescope and the preliminary work that has been done to understand the materials and mechanical issues associated with the design of a passive metering structure to support the telescope and to maintain the spacing between the primary and secondary mirrors in the LISA on-orbit environment. This includes the requirements flowdown from the science goals, thermal modeling of the spacecraft and telescope to determine the expected temperature distribution, layout options for the telescope including an on- and off-axis design. Plans for fabrication and testing will be outlined.
    Keywords: Spacecraft Design, Testing and Performance
    Type: 8th International LISA Symposium; Jun 28, 2010 - Jul 02, 2010; Stanford, CA; United States
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 52 (1991), S. 335-338 
    ISSN: 1432-0630
    Keywords: 61.40 ; 61.80 ; 72.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract n-type a-Si:H films have been irradiated with light, electrons, protons and heavy ion beams. It is shown that the non-thermal creation of dangling-bond defects activates significant densities of previously inactive phosphorus dopants. The relevance of these results is discussed with respect to equilibration phenomena in doped material and with respect to degradation phenomena in a-Si:H solar cells.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 53 (1991), S. 235-240 
    ISSN: 1432-0630
    Keywords: 61.40 ; 61.80 ; 72.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Hydrogenated amorphous silicon (a-Si:H) films have been irradiated with H+, B+, P+, and Ar+ ion beams. The accumulation and the annealing of irradiation-induced defects has been investigated through a series of electronic transport and PDS measurements. We find that for all projectiles damage accumulation is dominated by atomic displacement collisions with the damage saturating for energy transfers in excess of about 10 eV/target atom. Annealing at elevated temperatures causes the conductivity of doped and irradiated a-Si:H films to increase according to stretched exponential decay curves. All annealing parameters derivable from such fits scale with the energy originally dissipated into atomic displacement collisions. For energy transfers up to 10 eV/target atom the activation energy for annealing increases up to a saturation value and, at the same time, an increasing fraction of the irradiation-induced defects becomes stable against annealing at moderate temperatures (T a〈250° C). We discuss these results with respect to damage accumulation data in crystalline silicon (c-Si) and with regard to the annealing of metastable defects in a-Si:H.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 54 (1992), S. 40-46 
    ISSN: 1432-0630
    Keywords: 61.40 ; 71.55 ; 82.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Amorphous (a-) semiconductors like a-Si:H and the chalcogenide glasses possess a general tendency to establish an overall equilibrium between the electronic system and the lattice with its dopant and defect sites. In the present paper the chemical interactions which establish these equilibria within the bulk of the a-semiconductor lattices are compared to chemical interactions in liquid electrolytes, particularly to those in H2O. These considerations reveal close similarities between autocompensation doping in a-semiconductors and acid/base reactions in H2O. The effects of light and field-effect induced defect formation, on the other hand, are shown to be related to the phenomenon of electrolysis in H2O. The consideration of these analogies further emphasizes the roles of charge-carrier localization and that of H-diffusion in promoting dopant and defect equilibration reactions in a-semiconductors.
    Type of Medium: Electronic Resource
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