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Asteroid Perturbations and Mass Determination for the ASTROD Space Mission

Due to the high-precision nature of the ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) mission concept, the asteroid perturbations on the ASTROD spacecraft is crucial. These perturbations need to be modelled and determined together with relativistic effects and other solar-system parameters. In a previous investigation (Su et al., Planetary and Space Science, 47, 339-43[1999]), we used the mass estimation of Ceres, Pallas and Vesta in the literature to calculate their perturbations on the ASTROD spacecraft. Recently, we established an ephemeris framework (CGC 1) including the 3 big asteroids and used this ephemeris framework to simulate the determination of their masses together with other solar-system parameters and relativistic-gravity parameters. In this paper, we extend the CGC 1 to CGC 2 ephemeris framework to include 492 asteroids (with diameter > 65 km) . We then use CGC 2 to simulate the determination of ten parameters -- the masses of Ceres, Pallas and Vesta, the six average densities for the other 489 asteroids, classified into C, S,M,E,G and U types, and the rate of change of the gravitational constant G. The fractional mass uncertainties for Ceres, Pallas and Vesta are about 10**(-3)-10**(-4); the fractional density uncertainties for six types of asteroids are about 10**(-2)-10**(-3); that for G-dot/G is about 10**(-14)-10**(-15)/yr. This mass and density determination will be useful for the determination and understanding of the structure and origin of asteroids.