The Effects of Outgassing Jets on the Rotation of a Comet Nucleus and on theTrajectory of an Orbiting Spacecraft.

[摘要] An outgassing jet model is presented in support of spacecraft navigation for future missions to comets. The outgassing jet is modelled as an emission cone while the comet nucleus is modelled as a uniform density triaxial ellipsoid. The heliocentric orbit motion as well as in the strength of the outgassing jet are accounted for in the equations of motion. This model can predict the rotational evolution of a comet nucleus as a result the outgassing jets;; reactive torques as well as for simulation of an orbiting spacecraft;;s trajectory through jet passages and the estimation of the physical outgassing properties of jets from perturbations to the spacecraft;;s motion.A rotational evolution model of a comet nucleus is presented and predictspossible levels of rotational excitation for a comet nucleus under torques producedby multiple discrete outgassing jets located on the surface. An analytical theory forthe secular solution to the rotational motion of comets with an axis of symmetry is derived and used to predict rotational state changes over multiple perihelion passages.A method of characterizing the comet nucleus dynamics to predict the end state ofthe rotation is found from the averaged equations. Applications of these analyticalresults to predict the stochastic evolution of a comet nucleus rotation are outlined.This thesis also identifies and analyzes stable Sun synchronous orbits in a Hillrotating frame which can be applied to any small body in the solar system. Thestability of these orbits is due to the inclusion of solar radiation pressure effects. Thestability of the orbits in terms of escaping the comet is analyzed though construction of zero-velocity curves and the use of spectral analysis. The effect of orbital perturbations from outgassing jets on the stability criterion are also considered in the stability analysis of a spacecraft in orbit about a comet. Once these orbits have been identified, the effects of a non-spherical body are explored. Impulsive and finite burn control schemes to restrict a stable orbit;;s motion are determined, showing that it is feasible to implement a form of orbital hovering in the terminator plane of a comet.

[发布机构] University of Michigan

[效力级别] Aerospace Engineering

[关键词] Comet Outgassing Jets;Aerospace Engineering;Engineering;Aerospace Engineering