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  • ACOUSTICS  (2)
  • Lunar and Planetary Science and Exploration  (2)
  • 2005-2009  (2)
  • 1990-1994  (2)
  • 1965-1969
  • 1940-1944
  • 1
    Publication Date: 2019-07-13
    Description: This paper presents a new method for computing acoustic signals from helicopter rotors in forward flight. The aerodynamic and acoustic solutions in the near field are computed with a finite-difference solver for the Euler equations. A nonrotating cylindrical Kirchhoff surface is then placed around the entire rotor system. This Kirchhoff surface moves subsonically with the rotor in forward flight. The finite-difference solution is interpolated onto this cylindrical surface at each time step and a Kirchhoff integration is used to carry the acoustic signal to the far field. Computed values for high-speed impulsive noise show excellent agreement with model-rotor and flight-test experimental data. Results from the new method offer high accuracy with reasonable computer resource requirements.
    Keywords: ACOUSTICS
    Type: NASA-CR-196132 , NAS 1.26:196132 , RIACS-TR-94-06 , Army Science Conference; Jun 20, 1994 - Jun 24, 1994; Orlando, FL; United States
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  • 2
    Publication Date: 2019-07-13
    Description: Free-space optical communications offers expanded data return capacity, from probes distributed throughout the solar system and beyond. Space-borne and Earth-based optical transceivers used for communicating optically, will periodically encounter near Sun pointing. This will result in an increase in the scattered background light flux, often contributing to degraded link performance. The varying duration of near Sun pointing link operations relative to the location of space-probes, is discussed in this paper. The impact of near Sun pointing on link performance for a direct detection photon-counting communications system is analyzed for both ground- and space-based Earth receivers. Finally, impact of near Sun pointing on spaceborne optical transceivers is discussed.
    Keywords: Lunar and Planetary Science and Exploration
    Type: IEEE Aerospace Conference; Mar 04, 2006 - Mar 11, 2006; Big Sky, MT; United States
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  • 3
    Publication Date: 2019-07-13
    Description: NASA is planning a series of short and long duration human and robotic missions to explore the Moon and then Mars. A key objective of the missions is to grow, through a series of launches, a system of systems communication, navigation, and timing infrastructure at minimum cost while providing a network-centric infrastructure that maximizes the exploration capabilities and science return. There is a strong need to use architecting processes in the mission pre-formulation stage to describe the systems, interfaces, and interoperability needed to implement multiple space communication systems that are deployed over time, yet support interoperability with each deployment phase and with 20 years of legacy systems. In this paper we present a process for defining the architecture of the communications, navigation, and networks needed to support future space explorers with the best adaptable and evolable network-centric space exploration infrastructure. The process steps presented are: 1) Architecture decomposition, 2) Defining mission systems and their interfaces, 3) Developing the communication, navigation, networking architecture, and 4) Integrating systems, operational and technical views and viewpoints. We demonstrate the process through the architecture development of the communication network for upcoming NASA space exploration missions.
    Keywords: Lunar and Planetary Science and Exploration
    Type: E-16232 , International Conference on System of Systems Engineering (SoSE); Apr 16, 2007 - Apr 18, 2007; San Antonio, TX; United States
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  • 4
    Publication Date: 2019-07-13
    Description: A new method is developed for modeling helicopter high-speed impulsive (HSI) noise. The aerodynamics and acoustics near the rotor blade tip are computed by solving the Euler equations on an unstructured grid. A stationary Kirchhoff surface integral is then used to propagate these acoustic signals to the far field. The near-field Euler solver uses a solution-adaptive grid scheme to improve the resolution of the acoustic signal. Grid points are locally added and/or deleted from the mesh at each adaptive step. An important part of this procedure is the choice of an appropriate error indicator. The error indicator is computed from the flow field solution and determines the regions for mesh coarsening and refinement. Computed results for HSI noise compare favorably with experimental data for three different hovering rotor cases.
    Keywords: ACOUSTICS
    Type: NASA-CR-195090 , NAS 1.26:195090 , RIACS-TR-93-10 , AIAA PAPER 93-4359 , AIAA Aeroacoustics Conference; Oct 25, 1993 - Oct 27, 1993; Long Beach, CA; United States
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