Computer Science
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..364l&link_type=abstract
European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a
Computer Science
Scientific paper
Introduction We developed an orbit simulation tool for BepiColombo scheduled for arrival at Mercury in 2019. The mission will consist of two spacecraft, the MPO (Mercury Planetary Orbiter, ESA) and the MMO (Mercury Magnetospheric Orbiter, JAXA). We simulate the orbit evolutions of the two considering perturbing forces for a time of 2 years from arrival. This study was undertaken for mission planning purposes and estimates of surface coverage for the onboard mapping instruments. Orbit Perturbations Perturbing forces acting on the Keplerian MPO and MMO orbits include Mercury's non-spherical mass distribution parameters, the gravitational force of the sun, and solar radiation pressure (faintest). Because of the perturbing accelerations, semi-major axis, eccentricity, inclination, ascending node, argument of pericenter, show complex variations. The program simulates the evolution of all these elements over a period of 2 years. The software was programmed in FORTRAN, using SPICE subroutines. Numerical Integration Several of the Runge-Kutta methods are implemented in the software for a numerical integration of the equations of motion. Starting from initial values for the state vector (i.e., position and velocity) at time t0 given in [2], we obtain the spacecraft trajectory with an accuracy of the order of 1 m by choosing a stepsize of 50 s [1]. The results of the numerical calculation were checked with the results of a similar Bepi Colombo orbit simulation by ESOC [2] and showed very good agreement. Gravity Field Coefficients The MARINER 10 spacecraft executed 3 flybys of Mercury (1974/75). From spacecraft tracking, a first estimate of the gravity parameter GM and crude limits for J2 could be obtained. Higher-order gravitational coefficients, e.g., C30 and C22 are practically unknown. Results (Examples) Fig. 1 shows the evolution of the pericenter height for the MPO during the 2 mission years using the typical error bounds (6.0 ± 2.0)E-5 [4] for J2 = -C20. In addition, the Sun is included as a perturbing body. The orbiter will impact the surface after 200 days or after 800 days, if no orbit corrections are made. The variation in pericenter height is about -50 km/year, or 75 km/year, in good agreement with [2]. Fig. 2 shows the evolution of the pericenter height for the MPO for the assumption that only the Sun's gravity and C20 are perturbing the orbit. The change of the pericenter height is about -15 km/year and decreases linearly. Fig. 3 shows that the inclination of the orbit oscillates between +0.045° and -0.015°. Outlook Following MESSENGER's Mercury flyby on January 14, 2008, Smith et al. [3] have reported new values for the gravitational coefficients including error bounds based on analysis of MESSENGER tracking data. When publicly available, these new parameters will be included in our software to greatly improve our confidence in the BepiColombo orbit predictions. References [1] Montenbruck O. and Gill, E. (2000) Satellite Orbits. [2] Gracia, D. et al .(2007) BepiColombo Mercury Cornerstone Consolidated Report on Mission Analysis, 32-40. [3] Smith, David E. et al. (2008) Mercury Gravity Observations during the MESSENGER Flyby of January 2008. [4] J. D. Anderson et al. (1986) The Mass, Gravityfield and Ephemeris of Mercury
Hussmann Hauke
Lüdicke F.
Oberst Jürgen
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