The Hermes from The Martian is a very big ship, this is a Kerbal stock parts only build of it, some in-space assembly required.

Kermes 2 in Kerbin orbit

The Kermes 2 is assembled from seven modules, each includes a lifter to get it to assembly orbit (~150Km):

Command & Lab Module
Comms & Sensor Array
Ring
Hub & Docking
Aft Panels
Propellent Tanks
Propulsion

The propulsion segment has 18 Ion engines which are sufficient to move the craft in Kerbal orbit, have not attempted a Duna transfer yet but there should be sufficient Xenon Gas on board to make the trip.

For Historical purposes here is the original Kermes which had some issues:

Kermes - Assembeled

Included are several craft files, each with a launcher setup for assembly at about 150Km above Kerbin.

Lift and assembly in roughly this order:

- Command & Lab Module

- Forward Panels

- Docking Ports

- Hub

- Propulsion

- Spoke x 4

- Ring Braces

Some assembly required ;)