A question I have been asked about Mars Crossing is:
is the technology used in the book to make rocket fuel on Mars is real, or is it science fiction?
Yes, making rocket propellant on Mars is, in fact, technology that really exists, although I assumed some advances in the technology for the novel. As you can guess, making return propellant on-site makes a Mars mission a lot easier. The technology is known as "In Situ Resources Utilization," or "ISRU".
The easiest resource to make propellant from on Mars is the Martian atmosphere, which has the advantage of being available everywhere on Mars (no scouting or mining missions needed!). Another possible resource is the polar ice. In the book, both of these strategies are used.
The Martian atmosphere is extremely thin, and composed mostly of carbon dioxide. There are several technologies that have been demonstrated (on Earth only, so far) to start with carbon dioxide and make rocket fuel. One likely reaction is the Sabatier reaction (which requires hydrogen as well as carbon dioxide):
4H2 + CO2 --> CH4 + 2H2O
The water (H2O) produced by the reaction is then electrolyzed to produce oxygen and hydrogen; the hydrogen is re-used to produce more methane.
Another choice is directly electrolyzing CO2 into carbon monoxide (CO) and Oxygen, using a zirconia electrolysis medium:
2 CO2 --> 2CO + O2
In the novel, both of these techniques are used.
There are some web sites discussing the technology in some detail. A detailed concept for a Mars mission using in-situ propellant manufacture was the "Mars Direct" mission originally proposed by Robert Zubrin and David Baker, and Mars propellant manufacture was incorporated into the NASA Mars Reference Mission design. In Mars Crossing, the U.S. Mars missions use many of the Mars Direct concepts for mission design. The Brazilian mission in the book instead uses the polar landing strategy.
As a footnote, I was part of a team that was designing and building the first demonstration of fuel production on Mars. The experiment was called the "Mars ISPP Precursor" (where "ISPP" stands for "In-situ propellant production"), and was designed to produce oxygen by the electrolysis process.