Ben Bova has not been mention and I view him as Clarke's rightful heir. In particular his "Planet Series".
I had the opportunity to dine with Bova and his lovely wife some years back. He was quite gracious when I explained not being much of a Sci-Fi reader, Clarke being about it for me. He remarked that I had bet on the right author. We hade an interesting discussion about flying to Mars.
Sorry, I did not bring this up to be about me but just how down to earth Bova is, as Clarke was. He is an excellent writer and visionary. It all seems so natural and possible.