That would be two times as fast as a jet flight and four times faster than a high-speed train.

速度将是喷气式飞机的两倍，是高速列车的四倍。

Ultimately, there's no reason why space travel should be, in terms of future incomes, much more expensive than jet flight today.

最终，就未来收入而言，太空旅行没有理由比今天的喷气式飞机飞行昂贵得多。