Just finished this - in one sitting. The second of Ian Sales 'Apollo Quartet' series. (I hate the way most SF has to be in a series of books these days and I am no fan of most modern SF - and certainly not 'fantasy'). However, this writer is at the the 'hard' end of SF - which is the end that I do read occasionally. I think I enjoyed the first book more. This one switches between two time periods twenty years or so apart which I is always find annoying when I am getting into one plot to have to switch to another and back again. I particularly enjoyed the earlier period strand about the first man on Mars and what happens to him there. I was not so thrilled with the later strand about faster-than-light travel (but all, I understand, within the laws of physics - backed up with copious references). I almost missed the last chapter, tucked away at the very end - and it seems to explain what happened although I had another alternative explanation which I thought was going to be the case. So I am not sure I totally understood why the 'Earth 2' settlement had disappeared. This author plays with alternative pasts and presents blended in with 'actual' past events in an interesting way and clearly knows his way around an Apollo spacecraft.