Abstract | There are many researches that should be done in the exosphere and magnetosphere of Mercury, but most of them require close observations that can be done only by a spacecraft around Mercury. Many of those observations benefit from long durations data collecting, which means to keep the spacecraft in orbit as long as we can. An important limitation for the duration of a space mission is its capability to make orbital maneuvers to correct orbit shifts due to the several perturbing forces acting in the spacecraft. In this way, the search for adequate orbits for these spacecraft is very important for a successful exploration of Mercury. An “adequate orbit” means an orbit where the natural forces acting in the spacecraft minimizes orbit shifts, therefore reducing the need of orbital maneuvers, so extending the lifetime of the mission.
In this way, the present research proposes the use of solar sails to control those orbits. It is an engine which propulsion is based in the solar radiation pressure to move the spacecraft. The main goal is to provide a large and flat reflective film with minimum structural support. The dynamics includes the non-sphericity of Mercury, the gravitational perturbation from the Sun and the solar radiation pressure. The approach is to make plot maps to search for frozen orbits (which are orbits with smaller variation of the orbital elements) with long durations around Mercury. In this way, sets of initial conditions that generate orbits that may contribute with the scientific missions that will visit the planet Mercury in the next years are found.
The dynamics considers the J2 and J3 zonal terms and the C22 sectorial term of the gravity field of Mercury, which is assumed to be orbiting the Sun in an elliptical and inclined orbit. To obtain the equations of motion of the spacecraft, it is used the double-averaged analytical model to reduce the degrees of freedom of the system by eliminating the short-period terms coming from the motion of the spacecraft and the third body.
The results identified frozen orbits that have smaller amplitudes in the variations of the orbital elements, in particular eccentricity, inclination and argument of the periapsis. One example of a set of initial conditions that generate an interesting orbit is: semi-major axis 2700 km, inclination 90 degrees, argument of periapsis 270 degrees, longitude of the ascending node 90 degrees and eccentricity 0.02159. Orbits like that may contribute to missions similar to the BepiColombo, because its orbital elements are less disturbed. We also make maps to identify important low-altitude regions around Mercury to place a spacecraft. It is observed the higher impact of the J3 term and the contribution of the C22 term to decrease the disturbing effect in the region. Frozen orbits in different altitudes are found, which give more flexibility to mission designers.
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