载人宇宙飞行的前景看上去充满了越来越多的变数。
The future for manned space flight is looking increasingly uncertain .
宇航局计划4年之后发射新型的宇宙飞行器，然后在2020年以前恢复载人登月飞行，最后的目标是登上火星。
NASA wants to resume manned flights to the Moon by 2020 with the eventual goal of reaching Mars.
宇航局计划4年之后发射新型的宇宙飞行器，然后在2020年以前恢复载人登月飞行，最后的目标是登上火星。
NASA wants to resume manned flights to the Moon by 2020 with the eventual goal of reaching Mars.
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