A method for modelling the surface of irregular celestial bodies

The surface function R(θ, φ) of irregular celestial bodies (small satellites like Phobos and Deimos, cometary nuclei or small asteroids) is expanded in terms of spherical harmonics. A method is given to determine the expansion coefficients by comparing the calculated contours with the contours extracted from a series of images of the body. With given expansion coefficients this method can be applied to orientation systems of the spacecraft approaching the body. Furthermore, physical quantities like volume, centre-of-mass coordinates, moments of inertia and the gravitational field of the body can be calculated analytically. Under the assumption that the gravitational potential can be determined experimentally a method is described to calculate the radial mass density profile of the body. (author)