It's this sense of the unknown that makes the far side of the moon such an interesting place for scientific and space research.

正是这种对未知的感觉，使得月球的远侧成为科学和太空研究的一个有趣的地方。

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The soundness of the business case is unknown to outsiders. Mr. Bigelow declines to say if he has firm commitments from any countries or companies to rent space on his space stations.

对局外人来说，这种商业模式是否可靠还是未知之数，在被问及是否已经向其他国家或公司作出要出租太空站空间的承诺时，毕格罗也拒绝提供答案。

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Using Newton's formula for gravity, astronomers have detected previously unknown stars and planets, including Neptune and Pluto, from the effect of their gravity on other space objects.

l利用牛顿的引力计算公式，天文学家发现了许多过去不知道的恒星和行星，其中包括海王星和冥王星。这是根据它们对其他太空物体的引力作用测算出来的。

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Ed White would leave the protection of the spacecraft and move out into the unknown emptiness of space.

VOA: special.2009.06.24

Predicting the location of the termination shock was hard, the researchers say, because the precise conditions in interstellar space are unknown.

BBC: Voyager impression (Nasa)

The films, showing man in space, on the Moon, on Mars, and the "unknown", fascinated the boy Rutan.

BBC: The Moon

And just as some early explorers made the ultimate sacrifice while searching for unknown lands, space pioneers may also pay a steep price for bravely going where no human has gone before.

CNN: Mars on the brain? Red Planet pioneers to face cosmic mind trip