 I wrote a whole book on this subject, Leaving Earth. The only reason you build a space station at this time in human history is to learn how to build an interplanetary spaceship. If you're going to put people up in orbit for a long period of time, you're trying to figure out how to build a ship that can get them to other planets. Well, ISS was not designed with that in mind. It was designed mostly as a jobs program for the U.S. government.