When I read the book I was totally thrilled on the realism that Andy Weir packed into the story, and still wrote an absolute page-turner book!
With the formulas on the
Atomic Rockets page, I tried to draft a concept of the 'Hermes' as a nuclear-powered, ion-driven vessel.
I collected the tidbits of information from the book on maneuvers and flight duration, summarized them in a spreadsheet.
I have to say this was long before the movie. My concept was by far less cinematic.
I ended up with a 60 ton dry mass vessel, consisting of an 85 m long truss, an inflatable trans-hab on one end, and a reactor on the other,
spinning head-over-heels for artificial gravity.
The reactor had a thermal power of 10 MW, with an electrical yield of 8 MW.
Using two arrays of ion engines allowed flight times of 124 days single route, as described in the book.
Calculation data and a short description is included in the attached file 'Hermes.zip.'
The design may be outdated nowadays, but maybe the figures can help to make a proper Orbiter vessel.
