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  • Other Sources  (17)
  • 2000-2004  (17)
  • 1985-1989
  • 2001  (17)
  • 11
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    Intrinsic near-24-h pacemaker period determines limits of circadian entrainment to a weak synchronizer in humans (2001)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Endogenous circadian clocks are robust regulators of physiology and behavior. Synchronization or entrainment of biological clocks to environmental time is adaptive and important for physiological homeostasis and for the proper timing of species-specific behaviors. We studied subjects in the laboratory for up to 55 days each to determine the ability to entrain the human clock to a weak circadian synchronizing stimulus [scheduled activity-rest cycle in very dim (approximately 1.5 lux in the angle of gaze) light-dark cycle] at three approximately 24-h periods: 23.5, 24.0, and 24.6 h. These studies allowed us to test two competing hypotheses as to whether the period of the human circadian pacemaker is near to or much longer than 24 h. We report here that imposition of a sleep-wake schedule with exposure to the equivalent of candle light during wakefulness and darkness during sleep is usually sufficient to maintain circadian entrainment to the 24-h day but not to a 23.5- or 24.6-h day. Our results demonstrate functionally that, in normally entrained sighted adults, the average intrinsic circadian period of the human biological clock is very close to 24 h. Either exposure to very dim light and/or the scheduled sleep-wake cycle itself can entrain this near-24-h intrinsic period of the human circadian pacemaker to the 24-h day.
    Keywords: Life Sciences (General)
    Type: Proceedings of the National Academy of Sciences of the United States of America (ISSN 0027-8424); 98; 24; 14027-32
    Format: text
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  • 12
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    A model driven architecture for cross-discipline data access (2001)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The PDS is exploring object-oriented data technology to support cross-discipline data access using a software component framework and a metadata driven implementation.
    Type: Raytheon Scientific Data Center Symposium; Jan 01, 2001; Pasadena, CA; United States
    Format: text
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  • 13
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    Aerodynamic Performance of Scale-Model Turbofan Outlet Guide Vanes Designed for Low Noise (2001)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The design of effective new technologies to reduce aircraft propulsion noise is dependent on an understanding of the noise sources and noise generation mechanisms in the modern turbofan engine. In order to more fully understand the physics of noise in a turbofan engine, a comprehensive aeroacoustic wind tunnel test programs was conducted called the 'Source Diagnostic Test.' The text was cooperative effort between NASA and General Electric Aircraft Engines, as part of the NASA Advanced Subsonic Technology Noise Reduction Program. A 1/5-scale model simulator representing the bypass stage of a current technology high bypass ratio turbofan engine was used in the test. The test article consisted of the bypass fan and outlet guide vanes in a flight-type nacelle. The fan used was a medium pressure ratio design with 22 individual, wide chord blades. Three outlet guide vane design configurations were investigated, representing a 54-vane radial Baseline configuration, a 26-vane radial, wide chord Low Count configuration and a 26-vane, wide chord Low Noise configuration with 30 deg of aft sweep. The test was conducted in the NASA Glenn Research Center 9 by 15-Foot Low Speed Wind Tunnel at velocities simulating the takeoff and approach phases of the aircraft flight envelope. The Source Diagnostic Test had several acoustic and aerodynamic technical objectives: (1) establish the performance of a scale model fan selected to represent the current technology turbofan product; (2) assess the performance of the fan stage with each of the three distinct outlet guide vane designs; (3) determine the effect of the outlet guide vane configuration on the fan baseline performance; and (4) conduct detailed flowfield diagnostic surveys, both acoustic and aerodynamic, to characterize and understand the noise generation mechanisms in a turbofan engine. This paper addresses the fan and stage aerodynamic performance results from the Source Diagnostic Test.
    Keywords: Aerodynamics
    Type: NASA/TM-2001-211352 , NAS 1.15:211352 , E-13168 , AIAA Paper 2002-0374 , 40th Aerospace Sciences Meeting and Exhibit; Jan 14, 2002 - Jan 17, 2002; Reno, NV; United States
    Format: application/pdf
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  • 14
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    Relative Navigation for Formation Flying of Spacecraft (2001)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: This paper presents a robust and efficient approach for relative navigation and attitude estimation of spacecraft flying in formation. This approach uses measurements from a new optical sensor that provides a line of sight vector from the master spacecraft to the secondary satellite. The overall system provides a novel, reliable, and autonomous relative navigation and attitude determination system, employing relatively simple electronic circuits with modest digital signal processing requirements and is fully independent of any external systems. Experimental calibration results are presented, which are used to achieve accurate line of sight measurements. State estimation for formation flying is achieved through an optimal observer design. Also, because the rotational and translational motions are coupled through the observation vectors, three approaches are suggested to separate both signals just for stability analysis. Simulation and experimental results indicate that the combined sensor/estimator approach provides accurate relative position and attitude estimates.
    Keywords: Astrodynamics
    Type: 2001 Flight Mechanics Symposium; 115-129; NASA/CP-2001-209986
    Format: application/pdf
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  • 15
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    An Earth Entry Vehicle For Returning Samples From Mars (2001)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The driving requirement for design of a Mars Sample return mission is assuring containment of the returned samples. The impact of this requirement on developmental costs, mass allocation, and design approach of the Earth Entry Vehicle is significant. A simple Earth entry vehicle is described which can meet these requirements and safely transport the Mars Sample Return mission's sample through the Earth's atmosphere to a recoverable location on the surface. Detailed analysis and test are combined with probabilistic risk assessment to design this entirely passive concept that circumvents the potential failure modes of a parachute terminal descent system. The design also possesses features that mitigate other risks during the entry, descent, landing and recovery phases. The results of a full-scale drop test are summarized.
    Keywords: Aircraft Design, Testing and Performance
    Type: AAAF Paper ARVS-102 , 2nd International Symposium on Atmospheric Reentry Vehicles and Systems; Mar 26, 2001 - Mar 29, 2001; Arcachon; France
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  • 16
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    Design and Integration of a Rotor Alone Nacelle for Acoustic Fan Testing (2001)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A brief summary of the design, integration and testing of a rotor alone nacelle (RAN) in NASA Glenn's 9'x 15' Low Speed Wind Tunnel (LSWT) is presented. The purpose of the RAN system was to provide an "acoustically clean" flow path within the nacelle to isolate that portion of the total engine system acoustic signature attributed to fan noise. The RAN design accomplished this by removing the stators that provided internal support to the nacelle. In its place, two external struts mounted to a two-axis positioning table located behind the tunnel wall provided the support. Nacelle-mounted lasers and a closed-loop control system provided the input to the table to maintain nacelle to fan concentricity as thermal and thrust loads displaced the strut-mounted fan. This unique design required extensive analysis and verification testing to ensure the safety of the fan model, propulsion simulator drive rig, and facility, along with experimental consistency of acoustic data obtained while using the RAN system. Initial testing was used to optimize the positioning system and resulted in concentricity errors of +/- 0.0031 in. in the horizontal direction and +0.0035/-0.0013 in, in the vertical direction. As a result of successful testing, the RAN system will be transitioned into other acoustic research programs at NASA Glenn Research Center.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2001-210820 , NAS 1.15:210820 , E-12738 , AIAA Paper 2001-1058 , 39th Aerospace Sciences Meeting and Exhibit; Jan 08, 2001 - Jan 11, 2001; Reno, NV; United States
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  • 17
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    A Preliminary Formation Flying Orbit Dynamics Analysis for Leonardo-BRDF (2001)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Leonardo-BRDF is a new NASA mission concept proposed to allow the investigation of radiative transfer and its effect on the Earth's climate and atmospheric phenomenon. Enabled by the recent developments in small-satellite and formation flying technology, the mission is envisioned to be composed of an array of spacecraft in carefully designed orbits. The different perspectives provided by a distributed array of spacecraft offer a unique advantage to study the Earth's albedo. This paper presents the flight dynamics analysis performed in the context of the Leonardo-BRDF science requirements. First, the albedo integral is investigated and the effect of viewing geometry on science return is studied. The method used in this paper, based on Gauss quadrature, provides the optimal formation geometry to ensure that the value of the integral is accurately approximated. An orbit design approach is presented to achieve specific relative orbit geometries while simultaneously satisfying orbit dynamics constraints to reduce formation-keeping fuel expenditure. The relative geometry afforded by the design is discussed in terms of mission requirements. An optimal Lambert initialization scheme is presented with the required DeltaV to distribute all spacecraft from a common parking orbit into their appropriate orbits in the formation. Finally, formation-keeping strategies are developed and the associated DeltaV's are calculated to maintain the formation in the presence of perturbations.
    Keywords: Spacecraft Design, Testing and Performance
    Type: 2001 IEEE Aerospace Conference; Mar 10, 2001 - Mar 17, 2001; Big Sky, MT; United States
    Format: application/pdf
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