  ASTROD (Astrodynamical Space Test of Relativity using Optical Devices)
mission concept is to conduct high-precision measurement of relativistic
effects,solar-system parameters and gravitational waves. In this paper, we
first extend the stochastic model to simulate the determination of the masses
of three big asteroids (Ceres, Vesta and Pallas). With one range observation
per day for each spacecraft from 25 days to 800 days of the mission and ten
range observations per day for each spacecraft from 800 days to 1050 days of
the mission (when the apparent positions of the two spacecraft are close to the
Sun), the accuracies of determining these parameters are 4.6*10**(-7) for
gamma, 4.0*10**(-7) for beta, 1.2*10**(-8) for J2, and 6.4*10**(-5) M_Ceres,
7.6*10**(-4) M_Pallas, 8.1*10**(-5) M_Vesta for the mass determination of
Ceres, Pallas and Vesta respectively. We then include in the simulation and
determination the rate of change of the gravitational constant (G-dot), and an
anomalous constant acceleration (aa) directed towards the Sun (Pioneer
Anomaly). At the end of 1050 days of simulation, the accuracies of determining
these two parameters are 9.5*10**(-15)/yr for G-dot/G and 2.0*10**(-16) m/s2
for a_a. The mass loss rate of the inner solar system is at the level of
1*10**(-13) M_Sun/yr. The accurate determinat-ion of &#288;/G will mean a need
to simultaneously determine the mass loss rate. In other words, the mission
gives a way to monitor the mass loss rate of the Sun if &#288;/G can be
determined independently.
