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  • Chemistry  (4)
  • MECHANICAL ENGINEERING  (4)
  • SPACECRAFT DESIGN, TESTING AND PERFORMANCE  (4)
  • Oryza sativa L.  (3)
  • 11
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    Profile modification to minimize spur gear dynamic loading (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An analytical computer simulation program for dynamic modeling of low-contact-ratio spur gear systems is presented. The procedure computes the static transmission error of the gears operating under load and uses a fast Fourier transform to generate the frequency spectrum of the static transmission error at various tooth profile modifications. The dynamic loading response of an unmodified (perfect involute) gear pair was compared with that of gears with various profile modifications. Correlations were found between various profile modifications and the resulting dynamic loads. An effective error, obtained from frequency domain analysis of the static transmission error of the gears, gave a very good indication of the optimum profile modification to reduce gear dynamic loading. Design curves generated by dynamic simulation at various profile modifications are given for gear systems operated at various loads. Optimum profile modifications can be determined from these design curves for improved gear design.
    Keywords: MECHANICAL ENGINEERING
    Type: 1989 International Power Transmission and Gearing Conference; Apr 25, 1989 - Apr 28, 1989; Chicago, IL; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 12
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    An attitude reorientation algorithm for the Galileo spacecraft (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper presents an onboard closed loop attitude reorientation algorithm for a dual-spin spacecraft, Galileo. The basic concept for the design uses the despun stator as a reference and fires a sequence of fixed duration thruster pulses to precess the angular momentum vector to its commanded orientation. The error signals used to despin the stator and to perform the turn are derived from the stator error quaternion which is computed using gyro outputs. Constraints considered in the design include gyro rate saturation, plume impingement effects, system parameter variations, as well as software reliability and flexibility. The performance of the algorithm was predicted by analysis and confirmed by computer simulation results. It was concluded that a reorientation accuracy of better than 1 milliradian with a nutation angle of less than 1 degree during the turn can be achieved.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 84-2010
    Format: text
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    NASA TECHNICAL REPORTS
  • 13
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    A scheme for tracking and pointing at small celestial bodies during high velocity encounters (1982)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A scheme has been developed and verified for closed-loop tracking and pointing space-borne science instruments at small celestial bodies, such as comets and asteroids, during high velocity encounters. To overcome ephemeris uncertainties for these bodies, the scheme involves sequential estimation of flyby model parameters. The design consists of a two-axis gimballed platform mounted on a three-axis stabilized spacecraft. A platform-mounted optical tracker provides closed-loop target measurements and precision micro-step actuators enable high-rate platform slewing. For comet missions which involve dust particle impact disturbances, a dual-mode attitude control scheme is presented for minimizing transient response time.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 82-1617 , Guidance and Control Conference; Aug 09, 1982 - Aug 11, 1982; San Diego, CA
    Format: text
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    NASA TECHNICAL REPORTS
  • 14
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    Spin-Down and Active Nutation Controller /SDANC/ for the Galileo project (1980)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The Spin-Down and Active Nutation Controller stabilizes the Galileo spacecraft during spin-down from approximately 70 to 1 rpm. Angular motion of the spacecraft is sensed through a pair of accelerometers and a sun sensor which is needed only at low spin rates. Spin and nutation information is derived by a set of 'loosely coupled' spin and transverse rate estimators. Spin rate is reduced by two spin-down thrusters. The transverse angular rate is compared with a variable threshold; exceeding the threshold activates axial thrusters which impart appropriate transverse torque to reduce the nutation. The scheme was verified by extensive computer simulations and has been demonstrated over a wide range of initial conditions.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 80-1734 , Guidance and Control Conference; Aug 11, 1980 - Aug 13, 1980; Danvers, MA
    Format: text
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    NASA TECHNICAL REPORTS
  • 15
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    Dynamic loading of spur gears with linear or parabolic tooth profile modifications (1989)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A computer simulation was conducted to investigate the effects of both linear and parabolic tooth profile modification on the dynamic response of low-contact-ratio spur gears. The effect of the total amount of modification and the length of the modification zone were studied at various loads and speeds to find the optimal profile modification for minimal dynamic loading. Design charts consisting of normalized maximum dynamic load curves were generated for gear systems operated at various loads and with different tooth profile modification. An optimum profile modification can be determined from these design charts to minimize the dynamic loads of spur gear systems.
    Keywords: MECHANICAL ENGINEERING
    Type: 1989 International Power Transmission and Gearing Conference; Apr 25, 1989 - Apr 28, 1989; Chicago, IL; United States
    Format: text
    Location Call Number Expected Availability
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    NASA TECHNICAL REPORTS
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