On the dynamical stability of the Rosetta orbiter. I.

Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway e-mail: [eirik.mysen;kaare.aksnes]@astro.uio.no

Received: 5 October 2005
Accepted: 11 May 2006

Abstract

The Rosetta probe is to monitor, from a bound orbit, its primary target comet 67P/Churyumov-Gerasimenko for extended periods of time. As a preliminary assessment of the challenges involved, the strengths of the effects which perturb the spacecraft's cometocentric Keplerian trajectory are evaluated. It is found that in our adopted nominal scenario, where the CO outgassing rate is set to one tenth of its upper limit, motion could be considered regular a long time after rendezvous. Furthermore, in this weak limit, gravity perturbations have a negligible destabilizing effect on the shape of the orbit, while the secular impact risk under the effect of radiation pressure is minimized by placing the orbit in the plane normal to the cometocentric direction of the Sun, with a low initial eccentricity. The comet's heliocentric distance for probe escape for an orbit started in the solar plane-of-sky, however, is seen to be dependent on the initial semi-major axis only, and linearly so. In order to calculate the dynamical effects of outgassing, a radially directed, asymmetric and periodically time-varying pressure field is adopted. Accordingly, it is shown that specific field asymmetries, related to the tendency of the outgassing field to “remember” the direction of comet motion, represent the extreme scenarios as far as orbital stability for the full problem is concerned.