  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.
