Drive

This is a free short story, marketed as a “prequel” to the Expanse. It is available here: http://www.syfy.com/theexpanse/drive/

As a prequel, I don't really find this very useful. It gives a bit of background on the Earth and Mars division and the creation Epstein drive. If this is meant for people unfamiliar with the series, this won't really give them much of a background.

However for fans of the series already, this offers some nice little tidbits of world building.

Overall this is well written like the rest, and is a super fast read. With it being available for free, if you're a fan of the series, no reason not to give it a quick read.