人们离开地球、长期生活在外层空间的时代为期不远了。美国航天局将在九十年代中期建立永久性外层空间轨道站;计划到2005年在月球上建立基地;并旨在2035年发射飞向火星的载人飞船。尽管太空人航天史已有20余年,但无人知道在脱离了地球的保护性大气层和重力吸引后,人在外层空间终究能活多久。 It is not far off from the time when people left Earth and lived in outer space for so long. NASA will establish a permanent orbiting outer space orbital station in the mid-1990s; it plans to establish a base on the moon by 2005; and aiming to launch a 2035 manned spacecraft to Mars. Despite more than two decades of history in astronaut space, no one knows how long human life in outer space can ultimately be after it has escaped Earth’s protective atmosphere and gravity.