The Experts below are selected from a list of 63 Experts worldwide ranked by ideXlab platform
Dilmurat M. Azimov - One of the best experts on this subject based on the ideXlab platform.
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Integrated Targeting and Guidance for Powered Planetary Descent
The Journal of the Astronautical Sciences, 2018Co-Authors: Dilmurat M. Azimov, Robert H. BishopAbstract:This paper presents an on-board guidance and targeting design that enables explicit state and Thrust vector control and on-board targeting for planetary descent and landing. These capabilities are developed utilizing a new closed-form solution for the constant Thrust Arc of the braking phase of the powered descent trajectory. The key elements of proven targeting and guidance Architectures, including braking and approach phase quartics, are employed. It is demonstrated that implementation of the proposed solution avoids numerical simulation iterations, thereby facilitating on-board execution of targeting procedures during the descent. It is shown that the shape of the braking phase constant Thrust Arc is highly dependent on initial mass and propulsion system parameters. The analytic solution process is explicit in terms of targeting and guidance parameters, while remaining generic with respect to planetary body and descent trajectory design. These features increase the feasibility of extending the proposed integrated targeting and guidance design to future cargo and robotic landing missions.
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Extremal Control and Guidance Solutions for Orbital Transfer with Intermediate Thrust
The Journal of the Astronautical Sciences, 2015Co-Authors: Dilmurat M. Azimov, Fernando A. SanabriaAbstract:Mayer’s variational problem of determining optimal trajectories of motion with constant exhaust velocity and limited mass-flow rate in a Newtonian field is considered. Analytical solutions for extremal transfers between two coplanar elliptical orbits via one and two intermediate-Thrust Arcs are presented. It is shown that in the cases of transfers via one and two intermediate-Thrust Arcs, the orbital parameters have to satisfy respectively two constraints and one constraint imposed by the continuity conditions formed at the junctions. This means that respectively two and one of these orbital parameters must not be arbitrary. Furthermore, by utilizing the analytical solutions for the intermediate-Thrust Arcs, the corresponding extremal guidance laws for a transfer between two points with arbitrary position vectors and for a transfer between elliptical orbits are presented. The guidance commands are formulated in terms of commanded Thrust angle and commanded mass-flow rate. A numerical example illustrating the proposed trajectory and guidance solutions is discussed. The results of the computations are compared to those of similar one- and two- impulsive transfers, and a low-Thrust orbit raising maneuver. It is demonstrated that for some eccentricities of the terminal orbits, the fuel consumption for a transfer via an intermediate-Thrust Arc is comparable to that of the two-impulsive transfers. Analyses show that a maneuver with such an Arc may be fuel-efficient with longer duration and higher Thrust than that of the low-Thrust maneuver. The trajectory computations and guidance performances are illustrated by graphical relationships.
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Enhanced Apollo-Class Real-Time Targeting and Guidance for Powered Descent and Precision Landing
AIAA Guidance Navigation and Control (GNC) Conference, 2013Co-Authors: Dilmurat M. AzimovAbstract:A new class of closed-form analytic solutions for the constant Thrust Arc of the braking and approach phases of the powered lunar descent and landing trajectory is presented as an enhancement of Apollo ground-based targeting solutions. The proposed solutions enable an Apollo-class explicit, integrated, real-time, on-board targeting and guidance procedures. These solutions enhance the lunar landing vehicle flight software and onboard guidance with real-time targeting and targeting capabilities while retaining the essential elements and concepts of the proven Apollo lunar descent algorithms. It is shown that real-time targeting problem for powered descent and precision landing can be formulated entirely by closed-form analytical solutions. It is also shown that a wide range of analysis of targeting and guidance parameters can be readily performed. The enhanced Apollo targeting and guidance solutions are applied to the Apollo 11 and Apollo 12 trajectories and shown to compare favorably to the published actual descent trajectory. The proposed solutions are then applied to a precision landing problem for a new landing site at the lunar south pole.
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Extremal Analytical Solutions for Intermediate-Thrust Arcs in a Newtonian Field
Journal of Guidance Control and Dynamics, 2010Co-Authors: Dilmurat M. AzimovAbstract:The variational problem of determining optimal trajectories of motion with constant exhaust velocity and limited mass-flow rate in a central Newtonian field is considered. The first-order necessary conditions of optimality reduce the problem to a Hamiltonian canonical system of equations for intermediate- and maximum-Thrust Arcs, both of which have no complete analytical solutions to date. The approach used in this work is based on the analytical integration of the canonical system by employing its first integrals and invariant expressions. Several new classes of extremal analytical solutions for planar intermediate-Thrust Arcs with free and fixed flight times are presented. The solutions describe families of spiral trajectories around the center of attraction. The main result of the paper is that, in their current form with known integrals, the differential equations of the variational problem for intermediate-Thrust Arcs are integrable in elementary functions and quadratures, and the solution of this problem with such Arcs can be reduced to a system of algebraic continuity equations formed for each junction point. These solutions can be used as representative reference trajectories for guidance algorithms and to compute initial values of Lagrange multipliers for high-fidelity trajectory optimization software. As an illustrative example, the transfer maneuver to a given elliptical parking orbit using an intermediate-Thrust Arc is discussed. Results of simulations for three study cases containing the change of eccentricity and semiparameter of the parking orbit and specific impulses are presented.
Fernando A. Sanabria - One of the best experts on this subject based on the ideXlab platform.
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Extremal Control and Guidance Solutions for Orbital Transfer with Intermediate Thrust
The Journal of the Astronautical Sciences, 2015Co-Authors: Dilmurat M. Azimov, Fernando A. SanabriaAbstract:Mayer’s variational problem of determining optimal trajectories of motion with constant exhaust velocity and limited mass-flow rate in a Newtonian field is considered. Analytical solutions for extremal transfers between two coplanar elliptical orbits via one and two intermediate-Thrust Arcs are presented. It is shown that in the cases of transfers via one and two intermediate-Thrust Arcs, the orbital parameters have to satisfy respectively two constraints and one constraint imposed by the continuity conditions formed at the junctions. This means that respectively two and one of these orbital parameters must not be arbitrary. Furthermore, by utilizing the analytical solutions for the intermediate-Thrust Arcs, the corresponding extremal guidance laws for a transfer between two points with arbitrary position vectors and for a transfer between elliptical orbits are presented. The guidance commands are formulated in terms of commanded Thrust angle and commanded mass-flow rate. A numerical example illustrating the proposed trajectory and guidance solutions is discussed. The results of the computations are compared to those of similar one- and two- impulsive transfers, and a low-Thrust orbit raising maneuver. It is demonstrated that for some eccentricities of the terminal orbits, the fuel consumption for a transfer via an intermediate-Thrust Arc is comparable to that of the two-impulsive transfers. Analyses show that a maneuver with such an Arc may be fuel-efficient with longer duration and higher Thrust than that of the low-Thrust maneuver. The trajectory computations and guidance performances are illustrated by graphical relationships.
Fei Zhang - One of the best experts on this subject based on the ideXlab platform.
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Semi-analytical approach for computing near-optimal low-Thrust transfers to geosynchronous orbit
Aerospace Science and Technology, 2016Co-Authors: Lei Zhang, Bo Xu, Muzi Li, Fei ZhangAbstract:Abstract In this paper, a novel semi-analytical approach is developed for solving minimum-time and minimum-fuel low-Thrust transfers to geosynchronous orbit. The proposed method is mainly based on two intuitive control strategies, with one focusing on the instantaneous variation of orbit elements, and the other concerning the cumulative effect of Thrust force. By optimizing the objective functions of the two strategies, analytical Thrust-steering laws are derived for each case. With the use of a refined efficiency factor, Thrust Arc locations can also be optimized during the transfer. In addition, selection of weights and other parameters further improves the performance of the resulting trajectories. Finally, two examples of transfers are presented. The computed trajectories are very close to, or even better than the optimal results obtained from the traditional direct and indirect techniques. Due to its simplicity and good performance, the proposed method would be particularly useful for preliminary mission analysis.
Chandeok Park - One of the best experts on this subject based on the ideXlab platform.
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Necessary conditions for the optimality of singular Arcs of spacecraft trajectories subject to multiple gravitational bodies
Advances in Space Research, 2013Co-Authors: Chandeok ParkAbstract:Abstract This document analyzes the optimality of intermediate Thrust Arcs (singular Arcs) of spacecraft trajectories subject to multiple gravitational bodies. A series of necessary conditions for optimality are formally derived, including the generalized Legendre–Clebsch condition. As the order of singular optimality turns out to be two, an explicit formula for the singular optimal control is also presented. These analytical outcomes are validated by showing that they are identical to Lawden’s classical result if the equations of motion are reduced for a central gravity field. Practical utility is demonstrated by applying these analytical derivations to a candidate optimal trajectory near the Moon subject to solar and Earth perturbation. While the candidate optimal trajectory turns out to be bang-singular-bang, the intermediate Thrust Arc satisfies all the necessary conditions for optimality.
Kathleen C. Howell - One of the best experts on this subject based on the ideXlab platform.
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Optimal, Low-Thrust, Path-Constrained Transfers between Libration Point Orbits using Invariant Manifolds
AIAA AAS Astrodynamics Specialist Conference, 2010Co-Authors: Jeffrey J. Stuart, Martin T. Ozimek, Kathleen C. HowellAbstract:Low-Thrust transfers between libration point orbits can be applied in many potential mission scenarios, such as extended science missions or cargo transport. This investigation considers the inclusion of a variable speci c impulse engine into a primer vector-based, fuel optimizing transfer strategy. A multiple shooting procedure with analytical gradients yields rapid solutions and o ers an investigation into the trade space between ight time and consumption of fuel mass. Path and performance constraints can be included at node points along the Thrust Arc. Integration of invariant manifolds into the design strategy, for greater fuel savings, may also yield improved performance.