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  • 1
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    Optimal trajectories for the aeroassisted flight experiment (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The optimal trajectories of the aeroassisted flight experiment (AFE) spacecraft are analyzed in a three-dimensional space using the full system of six ODEs describing the atmospheric pass. The optimal trajectories are computed for two possible transfers: indirect ascent to a 178 NM perigee via a 197 NM apogee and direct ascent to a 178 NM apogee. For each transfer, two cases are investigated: (1) the bank angle is continuously variable, and (2) the trajectory is divided into segments along which the bank angle is constant. It is shown that the optimal trajectories for both cases coalesce into a two subarc trajectory, with the bank angle constant in each subarc. It is also shown that, during the atmospheric pass, the peak values of the changes of the orbital inclination and the longitude of the ascending node are nearly zero.
    Keywords: ASTRODYNAMICS
    Type: IAF PAPER 89-361
    Format: text
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  • 2
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    Optimal trajectories for the Aeroassisted Flight Experiment. Part 2: Equations of motion in an inertial system (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The determination of optimal trajectories for the aeroassisted flight experiment (AFE) is discussed. The AFE refers to the study of the free flight of an autonomous spacecraft, shuttle-launched and shuttle-recovered. Its purpose is to gather atmospheric entry environmental data for use in designing aeroassisted orbital transfer vehicles (AOTV). It is assumed that: (1) the spacecraft is a particle of constant mass; (2) the Earth is rotating with constant angular velocity; (3) the Earth is an oblate planet, and the gravitational potential depends on both the radial distance and the latitude (harmonics of order higher than four are ignored); and (4) the atmosphere is at rest with respect to the Earth. Under these assumptions, the equations of motion for hypervelocity atmospheric flight (which can be used not only for AFE problems, but also for AOT problems and space shuttle problems) are derived in an inertial system. Transformation relations are supplied which allow one to pass from quantities computed in an inertial system to quantities computed in an Earth-fixed system and vice versa.
    Keywords: ASTRODYNAMICS
    Type: NASA-CR-186135 , NAS 1.26:186135 , AAR-239-PT-2
    Format: application/pdf
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  • 3
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    Optimal trajectories for the aeroassisted flight experiment. Part 3: Formulation, results, and analysis (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The determination of optimal trajectories for the aero-assisted flight experiment (AFE) is investigated. The intent of this experiment is to simulate a GEO-to-LEO transfer, where GEO denotes a geosynchronous Earth orbit and LEO denotes a low Earth orbit. The trajectories of an AFE spacecraft are analyzed in a 3D-space, employing the full system of 6 ODEs describing the atmospheric pass. The atmospheric entry conditions are given, and the atmospheric exit conditions are adjusted in such a way that the following conditions are satisfied: (1) the atmospheric velocity depletion is such that, after exiting, the AFE spacecraft first ascends to a specified apogee and then descends to a specified perigee; and (2) the exit orbital plane is identical with the entry orbital plane. The final maneuver, not analyzed here, includes the rendezvous with and the capture by the space shuttle.
    Keywords: ASTRODYNAMICS
    Type: NASA-CR-186165 , NAS 1.26:186165 , AAR-242-PT-3
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  • 4
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    Optimal trajectories for the Aeroassisted Flight Experiment. Part 1: Equations of motion in an Earth-fixed system (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The determination of optimal trajectories for the aeroassisted flight experiment (AFE) is discussed. The AFE refers to the study of the free flight of an autonomous spacecraft, shuttle-launched and shuttle-recovered. Its purpose is to gather atmospheric entry environmental data for use in designing aeroassisted orbital transfer vehicles (AOTV). It is assumed that: (1) the spacecraft is a particle of constant mass; (2) the Earth is rotating with constant angular velocity; (3) the Earth is an oblate planet, and the gravitational potential depends on both the radial distance and the latitude (harmonics of order higher than four are ignored); and (4) the atmosphere is at rest with respect to the Earth. Under these assumptions, the equations of motion for hypervelocity atmospheric flight (which can be used not only for AFE problems, but also for AOT problems and space shuttle problems) are derived in an Earth-fixed system. Transformation relations are supplied which allow one to pass from quantities computed in an Earth-fixed system to quantities computed in an inertial system, and vice versa.
    Keywords: ASTRODYNAMICS
    Type: NASA-CR-186134 , NAS 1.26:186134 , AAR-238-PT-1
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  • 5
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    Optimal trajectories for aeroassisted, noncoplanar orbital transfer. II - LEO-to-LEO transfer (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Both classical and minimax problems of optimal control arising in the study of noncoplanar, aeroassisted orbital transfer are considered and are illustrated with the example of LEO-to-LEO transfer. Trajectory control is achieved by modulation of the lift coefficient and the angle of bank. Problems considered include the minimization of the energy required for orbital transfer, maximization of the flight time during the atmospheric portion of the trajectory, and minimization of the peak heating rate. The near-grazing solution is found to be a good compromise between energy and heating requirements.
    Keywords: ASTRODYNAMICS
    Type: IAF PAPER 87-328
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  • 6
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    Optimal trajectories for the aeroassisted flight experiment. Part 4: Data, tables, and graphs (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The determination of optimal trajectories for the aeroassisted flight experiment (AFE) is discussed. Data, tables, and graphs relative to the following transfers are presented: (IA) indirect ascent to a 178 NM perigee via a 197 NM apogee; and (DA) direct ascent to a 178 NM apogee. For both transfers, two cases are investigated: (1) the bank angle is continuously variable; and (2) the trajectory is divided into segments along which the bank angle is constant. For case (2), the following subcases are studied: two segments, three segments, four segments, and five segments; because the time duration of each segment is optimized, the above subcases involve four, six, eight, and ten parameters, respectively. Presented here are systematic data on a total of ten optimal trajectories (OT), five for Transfer IA and five for Transfer DA. For comparison purposes and only for Transfer IA, a five-segment reference trajectory RT is also considered.
    Keywords: ASTRODYNAMICS
    Type: NASA-CR-186164 , NAS 1.26:186164 , AERO-ASTRONAUTICS-243-PT-4
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  • 7
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    Optimal trajectories for the aeroassisted flight experiment (1989)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The determination of optimal trajectories for the aeroassisted flight experiment (AFE) is discussed. The intent of this experiment is to simulate a GEO-to-LEO transfer, where GEO denotes a geosynchronous earth orbit and LEO denotes a low earth orbit. The trajectories of an AFE spacecraft are analyzed in a 3D-space, employing the full system of 6 ordinary differential equations (ODEs) describing the atmospheric pass. The atmospheric entry conditions are given, and the atmospheric exit conditions are adjusted. Two possible transfers are considered: (1) indirect ascent to a 178 NM perigee via a 197 NM apogee; and (2) direct ascent to a 178 NM apogee.
    Keywords: ASTRODYNAMICS
    Type: NASA-CR-186133 , NAS 1.26:186133 , IAF-89-361 , Congress of the International Astronautical Federation; Oct 07, 1989 - Oct 13, 1989; Malaga; Spain
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  • 8
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    Optimization and guidance of trajectories for coplanar, aeroassisted orbital transfer (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Guidance trajectories for coplanar aeroassisted orbital transfer (AOT) from high earth orbit to LEO are presently optimized under the assumption of trajectory control during its endoatmospheric phase by alpha-dependent lift coefficient. Optimal trajectories are first computed by minimizing the total velocity impulse required for AOT; attention is then given to guidance trajectories capable of approximating such key properties of the optimal trajectories as minimum altitude, exit velocity, and exit path inclination, in real time. A switch is made from target-altitude guidance to target path inclination-guidance according to the velocity depletion required for optimum flight.
    Keywords: ASTRODYNAMICS
    Type: Journal of the Astronautical Sciences (ISSN 0021-9142); 38; 311-333
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  • 9
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    Nearly-grazing optimal trajectories for noncoplanar, aeroassisted orbital transfer (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: This paper discusses aeroassisted orbital transfer maneuvers under the assumption that the terminal orbital inclinations are different. Both GEO-to-LEO and LEO-to-LEO transfers are considered in connection with a spacecraft which is controlled during the atmospheric pass via the angle of attack and the angle of bank. Within the framework of classical optimal control, the following problems are studied: the minimization of the total characteristic velocity (P1); the minimization of the time integral of the square of the path inclination (P5); and the minimization of the peak heating rate (Q1). Numerical solutions are obtained by means of the sequential gradient-restoration logarithm for optimal control problems under the conditions that, for the problem (P1), the plane change components are optimized, while for the problems (P5) and (Q1), the plane change components are kept at the levels determined for problem (P1). The engineering implications of the solutions are discussed, in order to determine the most useful solutions in the light of energy requirements and heat transfer requirements.
    Keywords: ASTRODYNAMICS
    Type: Journal of the Astronautical Sciences (ISSN 0021-9142); 36; 139-157
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  • 10
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    Optimal trajectories for aeroassisted, coplanar orbital transfer (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Classical and minimax optimal control problems arising in the study of aeroassisted coplanar orbit transfer from a high planetary orbit to a low one are considered. Attention is given to (1) the minimization of the energy required for the maneuver; (2) minimization of the time integral of the heating rate; (3) minimization of the time of flight during the atmospheric portion of the trajectory; (4) maximization of the time of flight during the atmospheric portion of the trajectory; (5) minimization of the time integral of the path inclination; and (6) minimization of the sum of the squares of the entry and exit path inclinations.
    Keywords: ASTRODYNAMICS
    Type: Journal of Optimization Theory and Applications (ISSN 0022-3239); 52; 1-24
    Format: text
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