The woderful novella The Wandering Earth by Liu Cixin (not to be confused with the short story collection of the same title) is a free download again at Amazon:
http://www.amazon.com/The-Wandering-.../dp/B007JL6IYU
I cannot recommend this novella (and everything by Liu Cixin, in fact) highly enough. This is my review of The Wandering Earth, in case you're curious:
http://sentidodelamaravilla.blogspot...liu-cixin.html