| 摘 要： | In China’s asteroid mission to be launched around 2025,(7968)133 P/Elst-Pizarro(hereafter 133 P)will be the second target,after a visit to asteroid(469219)Kamo’oalewa.This paper describes a simulation of precise orbit determination for the spacecraft around comet 133 P,as well as estimation of its gravitational parameter(GM)value and the solar radiation pressure coefficient Cr for the spacecraft.Different cometocentric distances of 200,150 and 100 km orbits are considered,as well as two tracking modes:exclusive two-way range-rate mode(Earth station to spacecraft)and combinations of two-way range-rate and local spacecraft onboard ranging to the comet.Compared to exclusive two-way range-rate,the introduction of local ranging observables improves the final GM uncertainties by up to one order of magnitude.An ephemeris error in the orbit of 133 P is also considered,and we show that,to obtain a reliable estimate of the GM for 133 P,this error cannot exceed a one km range.
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