美航宇局(NASA)决定把空间站上运行开始时的宇航员一次驻留时间,从过去计划的3个月改为4个月,第2年开始延长至6个月,这是为适应“挑战者”号航天飞机事故后,减少依赖航天飞机所作的努力。倘若轮换时间加长,和空间站联络的航天飞机发射次数就可相应减少。因空间站上宇航员每次替换一半,按原先计划光轮换宇航员每年需航天飞机提供8次飞行。假如驻留4 NASA decided to change the dwell time of astronauts at the beginning of the operation of the space station from 3 months planned in the past to 4 months and extended to 6 months in the second year, Challenger "after the space shuttle accident, reducing the efforts to rely on the space shuttle. In the event of a longer rotation, the number of shuttle launches associated with the station may be reduced accordingly. Due to the replacement of astronauts on the space station by half at a time, the astronauts will be required to provide 8 rounds of space shuttle per year as originally planned. If you stay 4