I notice that garygibsonsf has been too shy to recommend his own excellent
Stealing Light, which is available as an ebook from waterstones for the sony if you follow the link. I'm not sure if there's a kindle edition about the place, but you can always demand one from amazon. This is hard SF, but perhaps not "hard as nails".
I would not have been so shy to mention my own book if it were hard enough for you, but I doubt it
Definitely fitting that description is Blindsight by Peter Watts, but I can only find it as a kindle edition, unfortunately. However, earlier books of his are available for free on the download section of this forum.