Reported in this paper is the result of the mission analysis of the asteroid explorer mission. Following the results of HAYABUSA, the Japanese asteroid explorer, JAXA has started the study of the next asteroid exploration mission. The mission now under study gives priority on "early" achievement of the sample return from an asteroid with primitive composition. Therefore, the design of the spacecraft follows that of HAYABUSA basically as it is, and the spacecraft is planned to be launched in early 2010s. The objective of the mission analysis is to design a mission sequence, which has launch window in early 2010s, which is feasible by a HAYABUSA-type spacecraft, and whose target asteroid complies with the science objective. The result includes the selection of the target asteroid, the design of nominal mission sequence, and some back up plans.