The Rosetta spacecraft has been successfully launched on 2nd March 2004 to its new target comet 67 P/Churyumov-Gerasimenko. The science objectives of the Rosetta Radio Science Investigations (RSI) experiment address fundamental aspects of cometary physics such as the mass and bulk density of the nucleus, its gravity field, its interplanetary orbit perturbed by nongravitational forces, its size and shape, its internal structure, the composition and roughness of the nucleus surface, the abundance of large dust grains, the plasma content in the coma and the combined dust and gas mass flux. The masses of two asteroids, Steins and Lutetia, shall be determined during flybys in 2008 and 2010, respectively. Secondary objectives are the radio sounding of the solar corona during the superior conjunctions of the spacecraft with the Sun during the cruise phase.The radio carrier links of the spacecraft Telemetry, Tracking and Command (TT&C) subsystem between the orbiter and the Earth will be used for these investigations. An Ultrastable oscillator (USO) connected to both transponders of the radio subsystem serves as a stable frequency reference source for both radio downlinks at X-band (8.4 GHz) and S-band (2.3 GHz) in the one-way mode. The simultaneous and coherent dual-frequency downlinks via the High Gain Antenna (HGA) permit separation of contributions from the classical Doppler shift and the dispersive media effects caused by the motion of the spacecraft with respect to the Earth and the propagation of the signals through the dispersive media, respectively.The investigation relies on the observation of the phase, amplitude, polarization and propagation times of radio signals transmitted from the spacecraft and received with ground station antennas on Earth. The radio signals are affected by the medium through which the signals propagate (atmospheres, ionospheres, interplanetary medium, solar corona), by the gravitational influence of the planet on the spacecraft and finally by the performance of the various systems involved both on the spacecraft and on ground.
Asteroids absorb solar radiation, which is later re-emitted. In this paper, an analytic approach for the description of the effects of this thermal emission on the rotation and orbit of an asteroid of unspecified shape is presented. The theory is connected directly to the physics of the problem, and the important results caused by a delayed thermal response of the surface are, therefore, parameterized by the fundamental surface properties of the asteroid. Overall results of previous numerical studies are recovered and an application to the elongated and irregularly-shaped asteroid Eros shows correspondence. The dependency of the derived differential equations on the dynamical variables is explicit and simple. We argue that if the transport of asteroids within the main belt is caused by thermal emission, then there is a preference for the shapes of Earth orbit crossing, regolith-covered asteroids.
It is demonstrated how globally distributed outgassing activity on a triaxial comet nucleus bridges the gap between the intuitive Sekanina model, used for comet orbit solutions, and the physics of the problem. In this activity and shape limit, it is shown how a recoil force component, which originates from a day‐side restricted sublimation process, is necessary to describe the comet's rotational evolution. Modifications of the non‐gravitational force cosines are suggested, with a fundamentally different interpretation than before. Applications to asteroid rotation yield that the ability of specular reflection, of solar photons on an asteroid's surface, to change the asteroid's rotation period and equatorial obliquity, is not dependent on the overall shape of the asteroid.
An analytical model for the diurnal YORP and Yarkovsky effects is described, which reproduces the overall results from previous numerical studies. Important shape parameters are identified and general forms of the differential equations are presented. The force cosines for comet orbit solutions are modified in order to include both thermal lag and geometrical effects.
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