□□经过2万多人近30个月的不懈努力,对航天飞机进行了约50项、300多处改进;经过几百万次计算机模拟试验,并在风洞试验中检测了冰片以不同方式撞击航天飞机造成的效果;经过反复研究和不断创新,且为确保发射安全而多次推迟发射日期;在投入几百万个工时和约15亿美元,美国发现号航 After nearly 30 months of unrelenting efforts of more than 20,000 people, it carried out about 50 or more improvements to the space shuttle. After several million computer simulation tests and testing of ice flakes in wind tunnel tests, Impact on the space shuttle; after repeated research and constant innovation, and in order to ensure launching security and repeatedly postponed the launch date; in millions of man-hours and about 1.5 billion US dollars, the United States found that the number of flights