On 16:30, Dec. 13th, 2012, in the deep sky of about 7 Million kilometers far away from the earth, the satellite “ Chang’e 2” succeeded to pass by an asteroid named after Toutatis, an Ares of Celtic Tales in the western. It is the first time that the optic image has been taken in the world. It is also the first time for the human being to make the measurement of Touratis in such a close distance.

Wether to determine the orbit of Touratis precisely is key to the success of re-exploring experiments of “Chang’e 2”. PMO play a major role in the optic detection and precise measurements of the orbit. In order to complete such a task, the scientist of PMO and the lab of the Deep Sky Exploration made a careful analysis, predicted the image by simulations when passing by. In addition, the scientists in PMO closely collaborated with other technicians of the satellites，re-checking the results from all the aspects such as images of the moon when “Chang’e 2” in the orbit, the inertia posture of the satellite “  Chang’e 2”, and the strategies of photographs. Furthermore, with the help from the people of the controlling system, the time and the distance of the intersecting point are obtained when the satellite “Chang’e 2” met Toutatis.

Xinglong Observatory, Xuyi Observatory Station, Lijiang Observatory Station, Hawii Observatory, as well as Chilly CITO, totally five observatory, six optical telescopes has been taken to observe Toutatis by Chinese Academic Sciences (CAS), under the unified arrangements of the center of Moon Exploration and Space Engineering, and the Moon and Deep Sky Exploration lab of CAS. There are totally about 500 sets of effective data between May to Nov of 2012. All the data has been analyzed and reduced in PMO. The scientists in PMO obtained the precise orbit, within the error of 5 km. Such a result has been evaluated by the experts, and employed directly, which offers the important scientific criteria to secure the task of closely passing by the astroid for the satellite “ Chang’e 2”. The simulations are so successful, which has been confirmed after obtaining the optical image.

In a word, the scientists in PMO independently determined the orbit of Toutatis, succeeded to complete the task of re-exploring experiments of the satellite “Chang’e 2”.