继任的系统同样是设计用来2020年重返月球的，同时作为远征火星的踏脚石。
That successor system is also designed to return humans to the moon by 2020, as a stepping stone to visiting Mars.
继任的系统同样是设计用来2020年重返月球的，同时作为远征火星的踏脚石。
That successor system is also designed to return humans to the moon by 2020, as a stepping stone to visiting Mars.
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