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  • 61.40  (3)
  • 72.80N  (2)
  • Spacecraft Design, Testing and Performance  (2)
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  • 1
    Publikationsdatum: 2019-07-12
    Beschreibung: 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.
    Schlagwort(e): Spacecraft Design, Testing and Performance
    Materialart: GSFC.JA.5667.2011
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2019-07-13
    Beschreibung: 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.
    Schlagwort(e): Spacecraft Design, Testing and Performance
    Materialart: 8th International LISA Symposium; Jun 28, 2010 - Jul 02, 2010; Stanford, CA; United States
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 54 (1992), S. 40-46 
    ISSN: 1432-0630
    Schlagwort(e): 61.40 ; 71.55 ; 82.60
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 41 (1986), S. 253-258 
    ISSN: 1432-0630
    Schlagwort(e): 72.80N
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract We compare the electronic properties of gas-phase and implantation doped a-Si:H films and analyze their properties within the framework of Street's auto-compensation model [1]. We find that this model can consistently explain the varying degrees of sensitivity with respect to doping for differently prepared a-Si:H materials. In agreement with sub-band-gap absorption data our analysis indicates that the density of native dangling bond defects is increased when the film thickness is decreased and when thin films are further subjected to ion bombardment. Considering the temperature dependence of conductivity, we find that the auto-compensation model can provide an explanation for the high-temperature kink in the conductivity of doped a-Si:H films but that it fails to account for the experimentally observed universality of the “Meyer-Neldel-rule” behaviour of the conductivity prefactor in differently prepared and doped a-Si:H films.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 45 (1988), S. 41-51 
    ISSN: 1432-0630
    Schlagwort(e): 66.3L ; 68.60 ; 72.80N
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract We show that, through the diffusive re-arrangement of Si-H bonds, the a-Si∶H lattice is able to establish thermal equilibrium between the densities of band tail trapped charge carriers and dangling bond defects. When this equilibrium is disturbed by changes in temperature, carrier injection or illumination, dangling bond defects have to be generated or annealed out via H-diffusion processes. Based on the concept of charge-induced bond breaking, we develop a mathematical formalism for the diffusive re-arrangement of Si-H bonds and show that our formalism can account for a variety of observations that have been made in the context of defect-generation and annealing experiments.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 52 (1991), S. 335-338 
    ISSN: 1432-0630
    Schlagwort(e): 61.40 ; 61.80 ; 72.20
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 53 (1991), S. 235-240 
    ISSN: 1432-0630
    Schlagwort(e): 61.40 ; 61.80 ; 72.20
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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