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PHOBOS CLOSE ENCOUNTERS BY MARS EXPRESS AND ITS INTERNAL STRUCTURE

PHOBOS CLOSE ENCOUNTERS BY MARS EXPRESS AND ITS INTERNAL STRUCTURE V. Lainey , T.Andert, P. Rosenblatt, V. Dehant, J.P. Barriot, M. Pätzold. MAGE network. RST 2004. The two Martian satellites. Discovered in 1877 but no mutual perturbations. Phobos. Deimos.

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PHOBOS CLOSE ENCOUNTERS BY MARS EXPRESS AND ITS INTERNAL STRUCTURE

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  1. PHOBOS CLOSE ENCOUNTERS BY MARS EXPRESS AND ITS INTERNAL STRUCTURE V. Lainey, T.Andert, P. Rosenblatt, V. Dehant, J.P. Barriot, M. Pätzold MAGE network RST 2004

  2. The two Martian satellites Discovered in 1877 but no mutual perturbations Phobos Deimos no mass value untill Viking (1977) F.Colas, Pic du Midi GM of Phobos • E. J. Christensen et al., 1977, GM = 0.66  0.08x10-3 km3 s-2 • R. H. Tolson et al., 1977, GM = 0.73  0.07x10-3 km3 s-2 • B. G. Williams et al., 1988, GM = 0.85  0.07x10-3 km3 s-2 • Y. Kolyuka et al., 1991, GM = 0.722  0.005x10-3 km3 s-2 • D. E. Smith et al., 1995, GM = 0.587  0.055x10-3 km3 s-2 Systematic errors in the processing!

  3. MaRS: Mars Radio Science Experiment Close flybys between MEX/Phobos (2005-?)  first direct determination of the dynamical oblateness of Phobos! (mass, J2, C22, …, centre of figure/centre of mass)  Important constraint on the internal structure (density, composition)

  4. Fit of Phobos gravity field Method in 2 steps: GINS: orbit of MEX without Phobos perturbation 1st step Mars Initial conditions x Phobos NOE:  Fit of Phobos GM and first oblateness coefficients 2nd step

  5. *Numerical Orbit Elaboration *Géodésie par Intégrations Numériques Simultanées (primary developed at CNES) GINS/NOE: Why two softwares? GINS* (developed for artificial satellites) NOE* (developed for natural satellites) Spacecraft integration: -gravity field of the planet -non-gravitational accelerations (atmosphere, radiation pressure, albedo) -DE406 planetary perturbation -relativistic corrections -attitude of the satellite N body system: -mutual perturbations -gravity field of all bodies -spin of satellites (resonances...?) -DE406 planetary perturbations -tides (planet satellites) High efficiency and save a lot of time

  6. Schedule December 2004: -New ephemeris of Phobos will be released (decreasing the residuals, fit of COF/COM) Beginning of 2005: -GINS and NOE will be operational for simulation (use of Viking data...?) -T.Andert's software will explore the link between Phobos' gravity field and its internal structure

  7. Next flyby on January 2005 Next flyby on January 2005 Conclusion We do hope to have the observation

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