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Astron. Astrophys. 347, 1009-1028 (1999)


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Numerical simulation of the dust flux on a spacecraft in orbit around an aspherical cometary nucleus - I

M. Fulle 1, J.F. Crifo 2 and A.V. Rodionov 3

1 Osservatorio Astronomico di Trieste, Via Tiepolo 11, I-34131 Trieste, Italy (fulle@ebe.oat.ts.astro.it)
2 CNRS, Service d'Aéronomie, B.P.3, F-91371 Verrières-le-Buisson Cedex, France (crifo@aerov.jussieu.fr)
3 Central Research Institute on Machine Building (TsNIIMASch), Pyonierskaya 4, Korolev, Moscow Region 141070, Russia

Received 26 November 1998 / Accepted 25 March 1999

Abstract

This study is the first investigation of the dust collection by a spacecraft orbiting a cometary nucleus, which is based on a physically consistent ab-initio model of the dust distribution in the vicinity of an aspherical comet nucleus. The homogeneous bean-shaped nucleus of Crifo & Rodionov (1997a) is used, with updated parameter values adapted to comet 46P/Wirtanen, target of the Rosetta mission, but the conclusions of the study have a general significance. The near-nucleus dust distribution is computed from the dusty gasdynamic model of the above reference, except that a power-law size distribution with differential exponent [FORMULA] is used here. The more distant distribution is computed from a Keplerian fountain model. Dust flux and fluences are evaluated for surfaces with various orientations, taking or not into account flux collimation, so that both the signal from dust analysers and the spacecraft contamination can be assessed. The results are compared to previous evaluations based either on the unphysical, spherically symmetric coma assumption, or on the highly asymmetric "effective nucleus dust source" derived from the Giotto Halley flyby in-situ dust measurements by Fulle et al. (1995), scaled appropriately to the present problem. The main results are the following: (1) The results based on the spherical assumption can at best be used for a global (benchmark) test of the correctness of a more realistic models, but otherwise do not represent the fluxes or fluences undergone by any spacecraft surface during any realistic sequence of spacecraft orbits; (2) there is a strong difference between the results from the present model, and those based on Fulle et al. (1995), due in part to the fact that the present dust source is less anisotropic that the "effective" source derived there; the two evaluations thus provide for the first time an estimate of the prediction uncertainties associated with the absence of a precise knowledge of the nucleus shape; (3) other differences between the present and previous results are due to the non-radiality of the near-nucleus motion, and to the total absence of a biunivocal mass-terminal velocity relation in the present model; (4) the "reflected" component of grains returned towards the nucleus by radiation pressure appears particularly sensitive to the dust ejection model, and is therefore a potentially important quantity to measure, to constrain such models; (5) the strongest dust irradiation is generally obtained for orbits located in the dawn-dusk meridian; (6) proper allowance for the non-radial near-nucleus dust motion is extremely critical to the strategy of dust fluence reduction on critical spacecraft systems.

Key words: comets: general – comets: individual: 46P/Wirtanen

Send offprint requests to: M. Fulle

© European Southern Observatory (ESO) 1999

Online publication: June 6, 1999

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