The system error of guidance instruments together with that of orbit t
racking is considered and a mathematical model for estimating both of
them is established. A thorough investigation oi:he accurate calculati
on of circumstance function and the effects of the system error model
is made. Finally, the estimator of the two kinds of errors is presente
d based on nonlinear regression model and the accuracy of the presente
d estimator is given. Theoretical analysis and simulation results conf
irm the validity and effectiveness of this method.