航天飞机的主发动机现在是免费的。

As for the space shuttle main engines, those are now free.

youdao

尽管离子发动机不能使航天飞机很好地摆脱地球引力。

Though an ion engine could never lift a spacecraft out of Earth's gravity well.

youdao

尽管离子发动机不能使航天飞机很好地摆脱地球引力。

Though an ion engine could never lift a spacecraft out of Earth's gravity well.

youdao