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Santa María la Real de Nieva, Spain

Lara M.,Real Observatorio de la Armada
Acta Astronautica

The behavior of low altitude near-circular lunar orbits is a key design issue for some missions related to the physical exploration of the Moon. Because of its masconian character, the gravity field of the Moon requires higher order truncations to give a realistic description of the long-term behavior of low-lunar orbits. We show that the required understanding of the dynamical behavior in the vicinity of the Moon can be reached through the combination of analytical techniques and periodic orbits computation. A model that consists of a high degree, zonal truncation of the Selenopotential superimposed to the Earth mass-point attraction is used to explore the existence and orbital characteristics of long-lifetime orbits close to the Moon at any inclination. The averaging provides a global view on the frozen orbit's geometry and local descriptions of the averaged flow. But it also makes available the short-period terms of the transformation from mean to osculating elements. A refinement of the osculating elements by means of differential corrections allows to compute lunar repeat ground-trace orbits in high fidelity potentials without restricting to zonal models. © 2011 Elsevier Ltd. All rights reserved. Source

Lara M.,Real Observatorio de la Armada | Palacian J.F.,Public University of Navarra | Yanguas P.,Public University of Navarra | Corral C.,GMV Aerospace and Defence S.A.
Acta Astronautica

In the framework of the elliptic restricted three-body problem we develop an analytical theory for spacecraft motion close to Mercury. Besides the perturbations due to the gravity of the Sun and Mercury and the eccentricity of Mercury's orbit around the Sun, i.e., the elliptic restricted three-body problem, the theory includes the effects of the oblateness and the possible latitudinal asymmetry of Mercury, and is valid for any eccentricity of the spacecraft's orbit. The initial Hamiltonian defines a non-autonomous but periodic dynamical system of two degrees of freedom. The mean motion of the spacecraft and the time are averaged using two successive Lie-Deprit transformations. The resulting Hamiltonian defines a one degree of freedom system and depends upon three essential parameters. When the latitudinal asymmetry coefficient vanishes the flow of this system is entirely analyzed through the discussion of the occurrence of its (relative) equilibria and bifurcations in accordance with the parameters the problem depends upon. Frozen orbits of the initial system together with their stability are obtained related to the relative equilibria. If the latitudinal asymmetry of Mercury is taken into account, the equatorial symmetry of the problem is broken and introduces important changes in the dynamics. A variety of tests show a very good agreement between averaged and non-averaged models, and the reliability of the theory is further checked by performing long-term integrations in ephemeris. © 2009 Elsevier Ltd. All rights reserved. Source

Diaz J.,CSIC - Institute of Earth Sciences Jaume Almera | Gallart J.,CSIC - Institute of Earth Sciences Jaume Almera | Villasenor A.,CSIC - Institute of Earth Sciences Jaume Almera | Mancilla F.,University of Granada | And 5 more authors.
Geophysical Research Letters

Controversial evolutionary models have been proposed for the Gibraltar Arc system, a complex interaction zone between the Eurasia and African plates. Here we derive new mantle anisotropic constraints from SKS splitting measurements on a dense network of about 90 broad-band stations deployed over South Iberia and North Morocco. The inferred fast polarization directions (FPD) clearly show a spectacular rotation along the arc following the curvature of the Rif-Betic chain, while stations located at the South and South-East edges show distinct patterns. These results support geodynamical processes invoking a fast retreating slab rather than convective-removal and delamination models. The FPD variations along the Gibraltar arc can be explained by fossil anisotropy acquired during the Western Mediterranean Eocene subduction, while changes to the South and South-East of the Rif-Betic chain could be the imprint of a flow episode around an Alboran high velocity slab during its Miocene fragmentation from the Algerian slab. © 2010 by the American Geophysical Union. Source

Lara M.,Real Observatorio de la Armada | Pelaez J.,Technical University of Madrid | Urrutxua H.,Technical University of Madrid
Acta Astronautica

For long enough tethers, the coupling of the attitude and orbital dynamics may show non-negligible effects in the orbital motion of a tethered satellite about a central body. In the case of fast rotating tethers the attitude remains constant, on average, up to second order effects. Besides, for a tether rotating in a plane parallel to the equatorial plane of the central body, the attitude-orbit coupling effect is formally equal to the perturbation of the Keplerian motion produced by the oblateness of the central body and, therefore, may have a stabilizing effect in the orbital dynamics. In the case of a tethered satellite in a low lunar orbit, it is demonstrated that feasible tether lengths can help in modifying the actual map of lunar frozen orbits. © 2012 Elsevier Ltd. Source

Ferrer S.,University of Murcia | Lara M.,Real Observatorio de la Armada
Astronomical Journal

For rigid bodies close to a sphere, we propose an analytical solution that is free from elliptic integrals and functions, and can be fundamental for application to perturbed problems. After reordering the Hamiltonian as a perturbed spherical rotor, the Lie-series solution is generated up to an arbitrary order. Using the inertia parameters of different solar system bodies, the comparison of the approximate series solution with the exact analytical one shows that the precision reached with relatively low orders is at the same level of the observational accuracy for the Earth and Mars. Thus, for instance, the periodic errors of the mathematical solution are confined to the microarcsecond level with a simple second-order truncation for the Earth. On the contrary, higher orders are required for the mathematical solution to reach a precision at the expected level of accuracy of proposed new theories for the rotational dynamics of the Moon. © 2010. The American Astronomical Society. Source

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