Optimization adn Guidance of Very Low-Thrust Transfers to Geostatoinary Orbit

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J. Gil-Fernandez; L. Tarabini; M. Graziano; M. A. Gomez-Tierno (2008), JBIS, 61, 139-145

Refcode: 2008.61.139
Keywords: Trajectory optimization, low-thrust, optimal control, non-linear programming, guidance

A new hybrid direct-indirect optimization algorithm is presented to compute the minimum-time transfer between two orbits, including the phasing with a desired spacecraft. Very-low thrust means several hundred revolutions to perform the large change in orbital elements. The optimal control solution of the fast-evolution problem combined with a direct method for the secular trajectory avoids the numerical instability arising in very long propagations, decreases the computational time, reduces the sensitivity to the initial guess and provides a feasible transfer at every optimization step. Optimization of transfers from GTO to GEO is presented and two types of trajectories are analysed, sub-synchronous (apogee constrained below GEO altitude) and super-synchronous (free apogee altitude). The optimization of a transfer from LEO to a very high orbit (11 x 23 RE) is presented, showing the applicability of the method to different problems. A guidance algorithm is presented to compensate the deviations of the real trajectory from the optimal one due to off-nominal conditions. The results in closed-loop simulation of the guidance scheme to compensate deterministic perturbations not considered in the optimization show good performances in both analysed missions.

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