Mars: The dynamics of orbiting satellites and gravity model development.

摘要

This thesis addressed three major questions: (1) What is the sensitivity of satellites to the Mars gravity field? (2) Can the range measurements to the Viking Orbiters be used to improve the solutions for the Mars gravity field? (3) What improvements can be made to the force models for spacecraft in orbit about Mars?; Mars orbiting satellites, including the Mariner 9 spacecraft, the two Viking Orbiters, the Mars Observer spacecraft (scheduled for launch in September 1992), and the natural Martian satellites of Phobos and Deimos, have orbits with different periods and geometries. Kaula's (1966) linear theory of orbit element perturbations was used to analyze the sensitivity of these satellites to the Mars gravity field. Numerical procedures were developed to evaluate the Kaula eccentricity functions, and to determine the RMS position and velocity sensitivity of the highly eccentric Viking and Mariner 9 orbits. The amplitude and frequency of the orbit perturbations were characterized. This information was used to optimize the processing of the Viking and Mariner 9 tracking data for the task of Mars gravity field determination.; Over the course of the Viking mission 26,000 range measurements to the two Viking Orbiters were obtained. This observable has not previously been incorporated into Mars gravity solutions. A portion of the range data was processed simultaneously with the Doppler data to develop spherical harmonic models of the Mars gravity field. Tests with orbit overlaps, orbit predictions, and with the gravity field covariances show that the range data contribute positively to the gravity field solutions. This research indicates that the range measurements to the Mars Observer spacecraft can be used to supplement the Doppler data by improving the determination of both the orbit and the gravity field.; Previous analyses have not incorporated the perturbing force due to the Martian moons, and due to the Mars radiation pressure on the trajectories of Mars orbiting satellites. The magnitude of these perturbations was calculated for Mariner 9 and the Viking Orbiters, as well as for Mars Observer. It is shown that Phobos produces measurable third-body perturbations on the orbits of both Mariner 9 and the Vikings.; The Infrared Thermal Mapper (IRTM) measurements of the Mars albedo and thermal emission (obtained by Viking Orbiters 1 and 2) were used to develop zonal spherical harmonic models of the Mars albedo, and third degree and order spherical harmonic models of the Mars thermal emission. These models were applied to the Mars Observer (MO) mapping orbit. This research shows that the Mars radiation pressure will produce perturbations on the orbit of MO that exceed the planned precision of the X-band Doppler data (0.1 mm/s). The effects of the Mars radiation pressure must be included in the trajectory force model for this spacecraft.