1　美国1 .1　航天飞机□□美航宇局 ( NASA)将航天飞机作为第一代可重复使用运载器。目前仍在服役的航天飞机有哥伦比亚号、奋进号、阿特兰蒂斯号和发现号 4架。自从 1 981年航天飞机首次发射之后 ,美国的航天飞机已完成了 1 0 0余次发射任务。2 0 0 1年 ,航天飞机共执行了6次 1 US 1.1 Space Shuttle □ NASA uses the space shuttle as the first generation reusable carrier. Space shuttles currently in service include Columbia, Endeavor, Atlantis and Discovery. Since the first space shuttle was launched in 1981, the U.S. space shuttle has completed more than 100 missions. In 2001, the space shuttle performed a total of 6 times