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  • AIRCRAFT STABILITY AND CONTROL  (3)
  • COMMUNICATIONS AND RADAR  (1)
  • Metals and Metallic Materials
  • 1990-1994  (4)
  • 1
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    A low-complexity and high performance concatenated coding scheme for high-speed satellite communications (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This report presents a low-complexity and high performance concatenated coding scheme for high-speed satellite communications. In this proposed scheme, the NASA Standard Reed-Solomon (RS) code over GF(2(exp 8) is used as the outer code and the second-order Reed-Muller (RM) code of Hamming distance 8 is used as the inner code. The RM inner code has a very simple trellis structure and is decoded with the soft-decision Viterbi decoding algorithm. It is shown that the proposed concatenated coding scheme achieves an error performance which is comparable to that of the NASA TDRS concatenated coding scheme in which the NASA Standard rate-1/2 convolutional code of constraint length 7 and d sub free = 10 is used as the inner code. However, the proposed RM inner code has much smaller decoding complexity, less decoding delay, and much higher decoding speed. Consequently, the proposed concatenated coding scheme is suitable for reliable high-speed satellite communications, and it may be considered as an alternate coding scheme for the NASA TDRS system.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-192715 , REPT-93-001 , NAS 1.26:192715
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Optimal recovery from microburst wind shear (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The flight path of a twin-jet transport aircraft is optimized in a microburst encounter during approach to landing. The objective is to execute an escape maneuver that maintains safe ground clearance and an adequate stall margin during the climb-out portion of the trajectory. A cost function penalizing rate of climb deviations from a nominal value and rate of elevator deflection produces qualitatively good results in a variety of microburst encounters. The optimal maneuver is a gradual pitch-up that ceases near the core of the microburst, followed by a slight reduction in pitch attitude in the tailwind area of the microburst. A minimum airspeed constraint in the optimization prevents excessive airspeed loss in very severe microbursts. The aircraft equations of motion include short-period dynamics, so that the optimization solves directly for the control surface deflections required to achieve the optimal flight paths.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: AIAA PAPER 92-4338 , AIAA Atmospheric Flight Mechanics Conference; Aug 10, 1992 - Aug 12, 1992; Hilton Head Island, SC; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Optimal recovery from microburst wind shear (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 16; 6; p. 1010-1017.
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Target pitch angle for the microburst escape maneuver (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: Recovery performance of a commuter-type aircraft in a microburst encounter is studied using a constant-pitch-attitude strategy and flight path optimization. Results obtained indicate that the pitch attitude which maximized climb rate in a wind shear condition is strongly dependent on whether the aircraft is subjected to a horizontal shear or a downdraft. The pitch attitude which maximizes ground clearance depends on the altitude of the encounter, the strength of the microburst, and the initial position of the aircraft with respect to the downburst core. Best results are obtained at relatively low target pitch angles, in severe wind shear encounters at very low altitudes. A technique for maximizing ground clearance involves maintaining a low pitch attitude early in the encounter, followed by a gradual pitch-up that ceases when the wind shear has been excited.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: AIAA PAPER 92-0730
    Format: text
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    NASA TECHNICAL REPORTS
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