The Mars Descent Vehicle (MDV) is the vehicle which the astronauts of an Ares mission would use to descend from the Hermes (which would have been in orbit around Mars) to a landing location on Mars.
Once the crew had soft landed on mars they would ditch the MDV and begin setting up the HAB and other vital components
.jpg){kind=link}
The SpaceX Dragon could have been used as a Mars Descent Vehicle - it is powered by Hypergolic fuel which is mentioned in the book as what Mark Watney took from the MDV to make water.
It is powered by Hypergolic fuel which Mark Watney used to make water to grow his potatoes in.