We have learned and mastered space travel.

　　這時地球人已經學會并掌握了太空飛行。

　　Pioneer John Glenn was a pioneer in space travel.

　　約翰·格倫是太空飛行的先驅者。

　　Many companies are pursuing commercialized space travel.

　　許多公司在追求把太空旅行商業(yè)化。