Manned surveillance missions are critical to obtaining useful intelligence .

载人视察一直都是获得有用信息的重要方式。

Manned spaceflight is no longer a two-horse race .

载人航天领域不再是两匹马的比赛。

Manned spacecraft are also in danger .

载人航天器也将处于危险之中。

Space shuttles are the fastest reusable manned vehicles ever built .

太空梭是人们建造的速度最快且可以重复使用的载人工具。

Since then the u.s. manned program has been stuck in low orbit .

在那之后，美国载人航天计划便一直徘徊在近地轨道。